Abstract The adaptive changes produced by repeated exposure to nicotine play a crucial role in th... more Abstract The adaptive changes produced by repeated exposure to nicotine play a crucial role in the establishment of dependence. While many brain areas are enriched in nicotinic acetylcholine receptors (nAChRs) and participate in the addictive effects of nicotine, recently, the habenular circuit, which is highly enriched in α3β4α5 nAChRs, has emerged as a critical node for acquisition of nicotine intake and difficulties in smoking cessation. This book chapter will review the anatomical and functional connections of the medial habenula-interpeduncular nucleus (MHb-IPN) circuit and the unique molecular and electrophysiological properties of habenular synapses that underlie the neuroadaptive changes that occur in response to chronic nicotine.
Proceedings of the National Academy of Sciences of the United States of America, Feb 25, 2020
The habenula, an ancient small brain area in the epithalamus, densely expresses nicotinic acetylc... more The habenula, an ancient small brain area in the epithalamus, densely expresses nicotinic acetylcholine receptors and is critical for nicotine intake and aversion. As such, identification of strategies to manipulate habenular activity may yield approaches to treat nicotine addiction. Here we show that GPR151, an orphan G-protein–coupled receptor (GPCR) highly enriched in the habenula of humans and rodents, is expressed at presynaptic membranes and synaptic vesicles and associates with synaptic components controlling vesicle release and ion transport. Deletion of Gpr151 inhibits evoked neurotransmission but enhances spontaneous miniature synaptic currents and eliminates short-term plasticity induced by nicotine. We find that GPR151 couples to the G-alpha inhibitory protein Gα o1 to reduce cyclic adenosine monophosphate (cAMP) levels in mice and in GPR151-expressing cell lines that are amenable to ligand screens. Gpr151– knockout (KO) mice show diminished behavioral responses to nicotine and self-administer greater quantities of the drug, phenotypes rescued by viral reexpression of Gpr151 in the habenula. These data identify GPR151 as a critical modulator of habenular function that controls nicotine addiction vulnerability.
Journal of Biochemistry and Molecular Biology, May 31, 2009
The process by which adult neural stem cells generate new and functionally integrated neurons in ... more The process by which adult neural stem cells generate new and functionally integrated neurons in the adult mammalian brain has been intensely studied, but much more remains to be discovered. It is known that neural progenitors progress through distinct stages to become mature neurons, and this progression is tightly controlled by cell-cell interactions and signals in the neurogenic niche. However, less is known about the cell-intrinsic signaling required for proper progression through stages of adult neurogenesis. Techniques have recently been developed to manipulate genes specifically in adult neural stem cells and progenitors in vivo, such as the use of inducible transgenic mice and viral-mediated gene transduction. A critical mass of publications utilizing these techniques has been reached, making it timely to review which molecules are now known to play a cell-intrinsic role in regulating adult neurogenesis in vivo. By drawing attention to these isolated molecules (e.g. Notch), we hope to stimulate a broad effort to understand the complex and compelling cascades of intrinsic signaling molecules important to adult neurogenesis. Understanding this process opens the possibility of understanding brain functions subserved by neurogenesis, such as memory, and also of harnessing neural stem cells for repair of the diseased and injured brain. [BMB reports 2009; 42(5): 245-259]
Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature, Jan 11, 2014
Background-Chronic exposure to nicotine elicits physical dependence in smokers, yet the mechanism... more Background-Chronic exposure to nicotine elicits physical dependence in smokers, yet the mechanism and neuroanatomical bases for withdrawal symptoms are unclear. As in humans, rodents undergo physical withdrawal symptoms after cessation from chronic nicotine characterized by increased scratching, head nods, and body shakes. Results-Here we show that induction of physical nicotine withdrawal symptoms activates GABAergic neurons within the interpeduncular nucleus (IPN). Optical activation of IPN GABAergic neurons via light stimulation of channel rhodopsin elicited physical withdrawal symptoms in both nicotine-naïve and chronic nicotine-exposed mice. Dampening excitability of GABAergic neurons during nicotine withdrawal through IPN-selective infusion of an NMDA receptor antagonist or through blocking IPN neurotransmission from the medial habenula reduced IPN neuronal activation and alleviated withdrawal symptoms. During chronic nicotine exposure, nicotinic acetylcholine receptors containing the β4 subunit were upregulated in somatostatin interneurons clustered in the dorsal region of the IPN. Blockade of these receptors induced withdrawal signs more dramatically in nicotine-dependent compared to nicotine-naïve mice and activated non-somatostatin neurons in the IPN. Conclusions-Together, our data indicate that therapeutic strategies to reduce IPN GABAergic neuron excitability during nicotine withdrawal, for example, by activating nicotinic receptors on somatostatin interneurons, may be beneficial for alleviating withdrawal symptoms and facilitating smoking cessation.
Neuronal nicotinic acetylcholine receptors (nAChRs) regulate the rewarding actions of nicotine co... more Neuronal nicotinic acetylcholine receptors (nAChRs) regulate the rewarding actions of nicotine contained in tobacco that establish and maintain the smoking habit. nAChRs also regulate the aversive properties of nicotine, sensitivity to which decreases tobacco use and protects against tobacco use disorder. These opposing behavioral actions of nicotine reflect nAChR expression in brain reward and aversion circuits. nAChRs containing a4 and b2 subunits are responsible for the high-affinity nicotine binding sites in the brain and are densely expressed by reward-relevant neurons, most notably dopaminergic, GABAergic, and glutamatergic neurons in the ventral tegmental area. High-affinity nAChRs can incorporate additional subunits, including b3, a6, or a5 subunits, with the resulting nAChR subtypes playing discrete and dissociable roles in the stimulatory actions of nicotine on brain dopamine transmission. nAChRs in brain dopamine circuits also participate in aversive reactions to nicotine and the negative affective state experienced during nicotine withdrawal. nAChRs containing a3 and b4 subunits are responsible for the low-affinity nicotine binding sites in the brain and are enriched in brain sites involved in aversion, including the medial habenula, interpeduncular nucleus, and nucleus of the solitary tract, brain sites in which a5 nAChR subunits are also expressed. These aversion-related brain sites regulate nicotine avoidance behaviors, and genetic variation that modifies the function of nAChRs in these sites increases vulnerability to tobacco dependence and smoking-related diseases. Here, we review the molecular, cellular, and circuit-level mechanisms through which nicotine elicits reward and aversion and the adaptations in these processes that drive the development of nicotine dependence. Significance Statement-Tobacco use disorder in the form of habitual cigarette smoking or regular use of other tobacco-related products is a major cause of death and disease worldwide. This article reviews the actions of nicotine in the brain that contribute to tobacco use disorder.
The CHRNA5-CHRNA3-CHRNB4 gene cluster, encoding the α5, α3, and β4 nicotinic acetylcholine recept... more The CHRNA5-CHRNA3-CHRNB4 gene cluster, encoding the α5, α3, and β4 nicotinic acetylcholine receptor (nAChR) subunits, has been linked to nicotine dependence. The habenulo-interpeduncular (Hb-IPN) tract is particularly enriched in α3β4 nAChRs. We recently showed that modulation of these receptors in the medial habenula (MHb) in mice altered nicotine consumption. Given that β4 is rate-limiting for receptor activity and that single nucleotide polymorphisms (SNPs) in CHRNB4 have been linked to altered risk of nicotine dependence in humans, we were interested in determining the contribution of allelic variants of β4 to nicotine receptor activity in the MHb. We screened for missense SNPs that had allele frequencies >0.0005 and introduced the corresponding substitutions in Chrnb4. Fourteen variants were analyzed by co-expression with α3. We found that β4A90I and β4T374I variants, previously shown to associate with reduced risk of smoking, and an additional variant β4D447Y, significantly increased nicotine-evoked current amplitudes, while β4R348C, the mutation most frequently encountered in sporadic amyotrophic lateral sclerosis (sALS), showed reduced nicotine currents. We employed lentiviruses to express β4 or β4 variants in the MHb. Immunoprecipitation studies confirmed that β4 lentiviral-mediated expression leads to specific upregulation of α3β4 but not β2 nAChRs in the Mhb. Mice injected with the β4-containing virus showed pronounced aversion to nicotine as previously observed in transgenic Tabac mice overexpressing Chrnb4 at endogenous sites including the MHb. Habenular expression of the β4 gain-of-function allele T374I also resulted in strong aversion, while transduction with the β4 loss-of function allele R348C failed to induce nicotine aversion. Altogether, these data confirm the critical role of habenular β4 in nicotine consumption, and identify specific SNPs in CHRNB4 that modify nicotine-elicited currents and alter nicotine consumption in mice.
Ascl1 (Mash1) is a bHLH transcription factor essential for neural differentiation during embryoge... more Ascl1 (Mash1) is a bHLH transcription factor essential for neural differentiation during embryogenesis but its role in adult neurogenesis is less clear. Here we show that in the adult brain Ascl1 is dynamically expressed during neurogenesis in the dentate gyrus subgranular zone (SGZ) and more rostral subventricular zone (SVZ). Specifically, we find Ascl1 levels low in SGZ Type-1 cells and SVZ B cells but increasing as the cells transition to intermediate progenitor stages. In vivo genetic lineage tracing with a tamoxifen (TAM) inducible Ascl1 CreERT2 knock-in mouse strain shows that Ascl1 lineage cells continuously generate new neurons over extended periods of time. There is a regionally-specific difference in neuron generation, with mice given TAM at postnatal day 50 showing new dentate gyrus neurons through 30 days post-TAM, but showing new olfactory bulb neurons even 180 days post-TAM. These results show that Ascl1 is not restricted to transit amplifying populations but is also found in a subset of neural stem cells with long-term neurogenic potential in the adult brain.
Drugs of abuse produce widespread effects on the structure and function of neurons throughout the... more Drugs of abuse produce widespread effects on the structure and function of neurons throughout the brain's reward circuitry, and these changes are believed to underlie the long-lasting behavioral phenotypes that characterize addiction. Although the intracellular mechanisms regulating the structural plasticity of neurons are not fully understood, accumulating evidence suggests an essential role for neurotrophic factor signaling in the neuronal remodeling which occurs after chronic drug administration. Brain-derived neurotrophic factor (BDNF), a growth factor enriched in brain and highly regulated by several drugs of abuse, regulates the phosphatidylinositol 3′-kinase (PI3K), mitogen-activated protein kinase (MAPK), phospholipase Cγ (PLCγ) and nuclear factor kappa B (NFκB) signaling pathways, which influence a range of cellular functions including neuronal survival, growth, differentiation, and structure. This review discusses recent advances in our understanding of how BDNF and its signaling pathways regulate structural and behavioral plasticity in the context of drug addiction.
The transcriptional program that controls adult neurogenesis is unknown. We generated mice with a... more The transcriptional program that controls adult neurogenesis is unknown. We generated mice with an inducible stem cell-specific deletion of Neurod1, resulting in substantially fewer newborn neurons in the hippocampus and olfactory bulb. Thus, Neurod1 is cell-intrinsically required for the survival and maturation of adult-born neurons. The ability to generate new neurons provides the brain with an important level of plasticity for maintaining cellular homeostasis and potentially underlies a response to injury. Studies of adult neurogenesis have revealed extrinsic signals controlling the fate of resident neural stem cells 1. However, the cell-intrinsic transcription factors required to generate and promote the survival of newborn neurons have not been fully elucidated. During development, the proneural basic helix-loop-helix (bHLH) transcription factors are essential for embryonic neurogenesis 2. To identify genes required for adult neurogenesis, we focused on the bHLH transcription factor Neurod1 (also known as NeuroD or Beta2) 3,4. Neurod1 is predominantly expressed in the nervous system late in development and is therefore more likely to be involved in terminal differentiation, neuronal maturation and survival 3,5,6. Because Neurod1-null mice die perinatally from neonatal diabetes as a result of the loss of Ins gene expression 7 , we used an inducible gene ablation approach and found that Neurod1 is necessary for newborn granule cells to survive and fully mature in the adult mammalian brain. To define the cells in the hippocampus subgranular zone (SGZ) that express Neurod1, we stained for NeuroD1 and a variety of cell type-specific markers in nestin promoter-driven GFP transgenic reporter mice 8 (Fig. 1 and Supplementary Fig. 1). NeuroD1 was not expressed in the type 1 (nestin-GFP and GFAP double positive) radial stem-like cell (Fig.
bioRxiv (Cold Spring Harbor Laboratory), Jul 31, 2019
Highlights • Habenula neurons are enriched in nicotinic, opioid, cannabinoid and GPR151 receptors... more Highlights • Habenula neurons are enriched in nicotinic, opioid, cannabinoid and GPR151 receptors • GPR151 modulates synaptic fidelity and release probability at habenular terminals. • Habenular GPR151 plays a role in drug abuse and food intake/weight control • GPR151 couples to the G-alpha inhibitory protein Gα o1 to reduce cAMP levels. eTOC Blurb Antolin-Fontes at al. identify a G protein-coupled receptor, GPR151, which is highly enriched in human habenular neurons. These neurons are primarily enriched with nicotinic, opioid and cannabinoid receptors. We find that GPR151 modulates habenular synaptic vesicle release probability and behavioral responses to these drugs of abuse. compulsive disorder (Proulx et al., 2014) and drug addiction (Antolin-Fontes et al., 2015; McLaughlin et al., 2017). The global impact of substance abuse and addiction disorders on health and economy is well documented. Currently, about 1.3 billion people consume tobacco and 185 million people use psychoactive drugs (WHO), while the Department of Health and Human services estimates that 2.1 million people in the US have an opioid use disorder, while another 11.2 million misuse opioids. Irrespective of the type of drug, addiction is a chronic relapsing disorder characterized by compulsive drug seeking, escalation of intake, and development of affective and physical symptoms of withdrawal upon abrupt discontinuation or decrease in intake (Koob and Volkow, 2016). Animal studies and human imaging analyses have revealed that many psychoactive drugs act on the mesocorticolimbic dopamine system, a circuit that appears to be common to the rewarding effects of some drugs of abuse, as well as other reinforcing natural behaviors such as eating, thirst, gambling and sexual drive (Lammel et al., 2014; Lammel et al., 2012; Nutt et al., 2015).However recent findings challenge the view that DA release has an exclusive role in reward processing and that stress, and aversive stimuli activate and remodel partially overlapping networks within the mesocorticolimbic dopamine (DA) system (Ostroumov and Dani, 2018). More recently, other structures have been implicated in reward and aversion, including the habenula (Antolin-Fontes et al., 2015; Boulos et al., 2019; Mathis and Kenny, 2018). Increasing evidence suggests that the degree of sensitivity to both the rewarding and aversive aspects of an addictive drug and the severity of the withdrawal after discontinuing its use contribute to the addiction process (Koob and Volkow, 2016). Understanding the mechanisms of these processes may reveal novel insights into the mechanics of the disorder and identify new targets for medications development.
As the leading preventable cause of cancer and death, nicotine use and dependence have been the s... more As the leading preventable cause of cancer and death, nicotine use and dependence have been the subject of a multitude of genetic studies in the past decade, ranging from candidate gene studies to genome-wide association studies (GWAS) to prospective studies. The genetics of nicotine addiction, smoking, and cancer are multifactorial, as would be expected from a complex behavior such as cigarette smoking. The combined heritability based on twin studies is estimated at 50–75 % (Li, Am J Med Sci 326(4): 168–73, 2003; Hall et al. Tob Control 11(2): 119–24, 2002; Lessov et al. Psychol Med 34(5): 865–79, 2004.; Lessov-Schlaggar et al. Int J Epidemiol 35(5): 1278–85, 2006; Maes et al. Psychol Med 34(7): 1251–61, 2004), with a large number of genes contributing to a small amount of risk individually. Some genes contribute to the quantity of nicotine used, while another set is associated with the duration of nicotine use, and yet another set is linked with severity of nicotine dependence. Associated “risky” genes comprise genes encoding for nicotinic acetylcholine receptor (nAChR) subunits, but also include genes like the bitter taste receptor. Still others have been associated with initiation and with success, or lack thereof, in cessation. In this chapter we review the current findings in the genetics of smoking, focusing on those studies that have linked nicotinic acetylcholine receptors (nAChR) to nicotine addiction, and further discuss how mutations in these receptors alter their function.
Progress has been made over the last decade in our understanding of the brain areas and circuits ... more Progress has been made over the last decade in our understanding of the brain areas and circuits involved in nicotine reward and withdrawal, leading to models of addiction that assign different addictive behaviors to distinct, yet overlapping, neural circuits (Koob and Volkow, 2010; Lobo and Nestler, 2011; Tuesta et al., 2011; Volkow et al., 2011). Recently the habenulointerpeduncular (Hb-IPN) midbrain pathway has re-emerged as a new critical crossroad that influences the brain response to nicotine. This brain area is particularly enriched in nicotinic acetylcholine receptor (nAChR) subunits α5, α3 and β4 encoded by the CHRNA5-A3-B4 gene cluster, which has been associated with vulnerability to tobacco dependence in human genetics studies. This finding, together with studies in mice involving deletion and replacement of nAChR subunits, and investigations of the circuitry, cell types and electrophysiological properties, have begun to identify the molecular mechanisms that take place in the MHb-IPN and underlie critical aspects of nicotine dependence. In the current review we describe the anatomical and functional connections of the MHb-IPN system, as well as the contribution of specific nAChRs subtypes in nicotine-mediated behaviors. Finally, we discuss the specific electrophysiological properties of MHb-IPN neuronal populations and how nicotine exposure alters their cellular physiology, highlighting the unique role of the MHb-IPN in the context of nicotine aversion and withdrawal.
The discovery of genetic variants in the CHRNA5-CHRNA3-CHRNB4 gene cluster associated with heavy ... more The discovery of genetic variants in the CHRNA5-CHRNA3-CHRNB4 gene cluster associated with heavy smoking and higher relapse risk has led to the identification of the midbrain habenulainterpeduncular axis as a critical relay circuit in the control of nicotine dependence. Although clear roles for a3, b4 and a5
Abstract The adaptive changes produced by repeated exposure to nicotine play a crucial role in th... more Abstract The adaptive changes produced by repeated exposure to nicotine play a crucial role in the establishment of dependence. While many brain areas are enriched in nicotinic acetylcholine receptors (nAChRs) and participate in the addictive effects of nicotine, recently, the habenular circuit, which is highly enriched in α3β4α5 nAChRs, has emerged as a critical node for acquisition of nicotine intake and difficulties in smoking cessation. This book chapter will review the anatomical and functional connections of the medial habenula-interpeduncular nucleus (MHb-IPN) circuit and the unique molecular and electrophysiological properties of habenular synapses that underlie the neuroadaptive changes that occur in response to chronic nicotine.
Proceedings of the National Academy of Sciences of the United States of America, Feb 25, 2020
The habenula, an ancient small brain area in the epithalamus, densely expresses nicotinic acetylc... more The habenula, an ancient small brain area in the epithalamus, densely expresses nicotinic acetylcholine receptors and is critical for nicotine intake and aversion. As such, identification of strategies to manipulate habenular activity may yield approaches to treat nicotine addiction. Here we show that GPR151, an orphan G-protein–coupled receptor (GPCR) highly enriched in the habenula of humans and rodents, is expressed at presynaptic membranes and synaptic vesicles and associates with synaptic components controlling vesicle release and ion transport. Deletion of Gpr151 inhibits evoked neurotransmission but enhances spontaneous miniature synaptic currents and eliminates short-term plasticity induced by nicotine. We find that GPR151 couples to the G-alpha inhibitory protein Gα o1 to reduce cyclic adenosine monophosphate (cAMP) levels in mice and in GPR151-expressing cell lines that are amenable to ligand screens. Gpr151– knockout (KO) mice show diminished behavioral responses to nicotine and self-administer greater quantities of the drug, phenotypes rescued by viral reexpression of Gpr151 in the habenula. These data identify GPR151 as a critical modulator of habenular function that controls nicotine addiction vulnerability.
Journal of Biochemistry and Molecular Biology, May 31, 2009
The process by which adult neural stem cells generate new and functionally integrated neurons in ... more The process by which adult neural stem cells generate new and functionally integrated neurons in the adult mammalian brain has been intensely studied, but much more remains to be discovered. It is known that neural progenitors progress through distinct stages to become mature neurons, and this progression is tightly controlled by cell-cell interactions and signals in the neurogenic niche. However, less is known about the cell-intrinsic signaling required for proper progression through stages of adult neurogenesis. Techniques have recently been developed to manipulate genes specifically in adult neural stem cells and progenitors in vivo, such as the use of inducible transgenic mice and viral-mediated gene transduction. A critical mass of publications utilizing these techniques has been reached, making it timely to review which molecules are now known to play a cell-intrinsic role in regulating adult neurogenesis in vivo. By drawing attention to these isolated molecules (e.g. Notch), we hope to stimulate a broad effort to understand the complex and compelling cascades of intrinsic signaling molecules important to adult neurogenesis. Understanding this process opens the possibility of understanding brain functions subserved by neurogenesis, such as memory, and also of harnessing neural stem cells for repair of the diseased and injured brain. [BMB reports 2009; 42(5): 245-259]
Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature, Jan 11, 2014
Background-Chronic exposure to nicotine elicits physical dependence in smokers, yet the mechanism... more Background-Chronic exposure to nicotine elicits physical dependence in smokers, yet the mechanism and neuroanatomical bases for withdrawal symptoms are unclear. As in humans, rodents undergo physical withdrawal symptoms after cessation from chronic nicotine characterized by increased scratching, head nods, and body shakes. Results-Here we show that induction of physical nicotine withdrawal symptoms activates GABAergic neurons within the interpeduncular nucleus (IPN). Optical activation of IPN GABAergic neurons via light stimulation of channel rhodopsin elicited physical withdrawal symptoms in both nicotine-naïve and chronic nicotine-exposed mice. Dampening excitability of GABAergic neurons during nicotine withdrawal through IPN-selective infusion of an NMDA receptor antagonist or through blocking IPN neurotransmission from the medial habenula reduced IPN neuronal activation and alleviated withdrawal symptoms. During chronic nicotine exposure, nicotinic acetylcholine receptors containing the β4 subunit were upregulated in somatostatin interneurons clustered in the dorsal region of the IPN. Blockade of these receptors induced withdrawal signs more dramatically in nicotine-dependent compared to nicotine-naïve mice and activated non-somatostatin neurons in the IPN. Conclusions-Together, our data indicate that therapeutic strategies to reduce IPN GABAergic neuron excitability during nicotine withdrawal, for example, by activating nicotinic receptors on somatostatin interneurons, may be beneficial for alleviating withdrawal symptoms and facilitating smoking cessation.
Neuronal nicotinic acetylcholine receptors (nAChRs) regulate the rewarding actions of nicotine co... more Neuronal nicotinic acetylcholine receptors (nAChRs) regulate the rewarding actions of nicotine contained in tobacco that establish and maintain the smoking habit. nAChRs also regulate the aversive properties of nicotine, sensitivity to which decreases tobacco use and protects against tobacco use disorder. These opposing behavioral actions of nicotine reflect nAChR expression in brain reward and aversion circuits. nAChRs containing a4 and b2 subunits are responsible for the high-affinity nicotine binding sites in the brain and are densely expressed by reward-relevant neurons, most notably dopaminergic, GABAergic, and glutamatergic neurons in the ventral tegmental area. High-affinity nAChRs can incorporate additional subunits, including b3, a6, or a5 subunits, with the resulting nAChR subtypes playing discrete and dissociable roles in the stimulatory actions of nicotine on brain dopamine transmission. nAChRs in brain dopamine circuits also participate in aversive reactions to nicotine and the negative affective state experienced during nicotine withdrawal. nAChRs containing a3 and b4 subunits are responsible for the low-affinity nicotine binding sites in the brain and are enriched in brain sites involved in aversion, including the medial habenula, interpeduncular nucleus, and nucleus of the solitary tract, brain sites in which a5 nAChR subunits are also expressed. These aversion-related brain sites regulate nicotine avoidance behaviors, and genetic variation that modifies the function of nAChRs in these sites increases vulnerability to tobacco dependence and smoking-related diseases. Here, we review the molecular, cellular, and circuit-level mechanisms through which nicotine elicits reward and aversion and the adaptations in these processes that drive the development of nicotine dependence. Significance Statement-Tobacco use disorder in the form of habitual cigarette smoking or regular use of other tobacco-related products is a major cause of death and disease worldwide. This article reviews the actions of nicotine in the brain that contribute to tobacco use disorder.
The CHRNA5-CHRNA3-CHRNB4 gene cluster, encoding the α5, α3, and β4 nicotinic acetylcholine recept... more The CHRNA5-CHRNA3-CHRNB4 gene cluster, encoding the α5, α3, and β4 nicotinic acetylcholine receptor (nAChR) subunits, has been linked to nicotine dependence. The habenulo-interpeduncular (Hb-IPN) tract is particularly enriched in α3β4 nAChRs. We recently showed that modulation of these receptors in the medial habenula (MHb) in mice altered nicotine consumption. Given that β4 is rate-limiting for receptor activity and that single nucleotide polymorphisms (SNPs) in CHRNB4 have been linked to altered risk of nicotine dependence in humans, we were interested in determining the contribution of allelic variants of β4 to nicotine receptor activity in the MHb. We screened for missense SNPs that had allele frequencies >0.0005 and introduced the corresponding substitutions in Chrnb4. Fourteen variants were analyzed by co-expression with α3. We found that β4A90I and β4T374I variants, previously shown to associate with reduced risk of smoking, and an additional variant β4D447Y, significantly increased nicotine-evoked current amplitudes, while β4R348C, the mutation most frequently encountered in sporadic amyotrophic lateral sclerosis (sALS), showed reduced nicotine currents. We employed lentiviruses to express β4 or β4 variants in the MHb. Immunoprecipitation studies confirmed that β4 lentiviral-mediated expression leads to specific upregulation of α3β4 but not β2 nAChRs in the Mhb. Mice injected with the β4-containing virus showed pronounced aversion to nicotine as previously observed in transgenic Tabac mice overexpressing Chrnb4 at endogenous sites including the MHb. Habenular expression of the β4 gain-of-function allele T374I also resulted in strong aversion, while transduction with the β4 loss-of function allele R348C failed to induce nicotine aversion. Altogether, these data confirm the critical role of habenular β4 in nicotine consumption, and identify specific SNPs in CHRNB4 that modify nicotine-elicited currents and alter nicotine consumption in mice.
Ascl1 (Mash1) is a bHLH transcription factor essential for neural differentiation during embryoge... more Ascl1 (Mash1) is a bHLH transcription factor essential for neural differentiation during embryogenesis but its role in adult neurogenesis is less clear. Here we show that in the adult brain Ascl1 is dynamically expressed during neurogenesis in the dentate gyrus subgranular zone (SGZ) and more rostral subventricular zone (SVZ). Specifically, we find Ascl1 levels low in SGZ Type-1 cells and SVZ B cells but increasing as the cells transition to intermediate progenitor stages. In vivo genetic lineage tracing with a tamoxifen (TAM) inducible Ascl1 CreERT2 knock-in mouse strain shows that Ascl1 lineage cells continuously generate new neurons over extended periods of time. There is a regionally-specific difference in neuron generation, with mice given TAM at postnatal day 50 showing new dentate gyrus neurons through 30 days post-TAM, but showing new olfactory bulb neurons even 180 days post-TAM. These results show that Ascl1 is not restricted to transit amplifying populations but is also found in a subset of neural stem cells with long-term neurogenic potential in the adult brain.
Drugs of abuse produce widespread effects on the structure and function of neurons throughout the... more Drugs of abuse produce widespread effects on the structure and function of neurons throughout the brain's reward circuitry, and these changes are believed to underlie the long-lasting behavioral phenotypes that characterize addiction. Although the intracellular mechanisms regulating the structural plasticity of neurons are not fully understood, accumulating evidence suggests an essential role for neurotrophic factor signaling in the neuronal remodeling which occurs after chronic drug administration. Brain-derived neurotrophic factor (BDNF), a growth factor enriched in brain and highly regulated by several drugs of abuse, regulates the phosphatidylinositol 3′-kinase (PI3K), mitogen-activated protein kinase (MAPK), phospholipase Cγ (PLCγ) and nuclear factor kappa B (NFκB) signaling pathways, which influence a range of cellular functions including neuronal survival, growth, differentiation, and structure. This review discusses recent advances in our understanding of how BDNF and its signaling pathways regulate structural and behavioral plasticity in the context of drug addiction.
The transcriptional program that controls adult neurogenesis is unknown. We generated mice with a... more The transcriptional program that controls adult neurogenesis is unknown. We generated mice with an inducible stem cell-specific deletion of Neurod1, resulting in substantially fewer newborn neurons in the hippocampus and olfactory bulb. Thus, Neurod1 is cell-intrinsically required for the survival and maturation of adult-born neurons. The ability to generate new neurons provides the brain with an important level of plasticity for maintaining cellular homeostasis and potentially underlies a response to injury. Studies of adult neurogenesis have revealed extrinsic signals controlling the fate of resident neural stem cells 1. However, the cell-intrinsic transcription factors required to generate and promote the survival of newborn neurons have not been fully elucidated. During development, the proneural basic helix-loop-helix (bHLH) transcription factors are essential for embryonic neurogenesis 2. To identify genes required for adult neurogenesis, we focused on the bHLH transcription factor Neurod1 (also known as NeuroD or Beta2) 3,4. Neurod1 is predominantly expressed in the nervous system late in development and is therefore more likely to be involved in terminal differentiation, neuronal maturation and survival 3,5,6. Because Neurod1-null mice die perinatally from neonatal diabetes as a result of the loss of Ins gene expression 7 , we used an inducible gene ablation approach and found that Neurod1 is necessary for newborn granule cells to survive and fully mature in the adult mammalian brain. To define the cells in the hippocampus subgranular zone (SGZ) that express Neurod1, we stained for NeuroD1 and a variety of cell type-specific markers in nestin promoter-driven GFP transgenic reporter mice 8 (Fig. 1 and Supplementary Fig. 1). NeuroD1 was not expressed in the type 1 (nestin-GFP and GFAP double positive) radial stem-like cell (Fig.
bioRxiv (Cold Spring Harbor Laboratory), Jul 31, 2019
Highlights • Habenula neurons are enriched in nicotinic, opioid, cannabinoid and GPR151 receptors... more Highlights • Habenula neurons are enriched in nicotinic, opioid, cannabinoid and GPR151 receptors • GPR151 modulates synaptic fidelity and release probability at habenular terminals. • Habenular GPR151 plays a role in drug abuse and food intake/weight control • GPR151 couples to the G-alpha inhibitory protein Gα o1 to reduce cAMP levels. eTOC Blurb Antolin-Fontes at al. identify a G protein-coupled receptor, GPR151, which is highly enriched in human habenular neurons. These neurons are primarily enriched with nicotinic, opioid and cannabinoid receptors. We find that GPR151 modulates habenular synaptic vesicle release probability and behavioral responses to these drugs of abuse. compulsive disorder (Proulx et al., 2014) and drug addiction (Antolin-Fontes et al., 2015; McLaughlin et al., 2017). The global impact of substance abuse and addiction disorders on health and economy is well documented. Currently, about 1.3 billion people consume tobacco and 185 million people use psychoactive drugs (WHO), while the Department of Health and Human services estimates that 2.1 million people in the US have an opioid use disorder, while another 11.2 million misuse opioids. Irrespective of the type of drug, addiction is a chronic relapsing disorder characterized by compulsive drug seeking, escalation of intake, and development of affective and physical symptoms of withdrawal upon abrupt discontinuation or decrease in intake (Koob and Volkow, 2016). Animal studies and human imaging analyses have revealed that many psychoactive drugs act on the mesocorticolimbic dopamine system, a circuit that appears to be common to the rewarding effects of some drugs of abuse, as well as other reinforcing natural behaviors such as eating, thirst, gambling and sexual drive (Lammel et al., 2014; Lammel et al., 2012; Nutt et al., 2015).However recent findings challenge the view that DA release has an exclusive role in reward processing and that stress, and aversive stimuli activate and remodel partially overlapping networks within the mesocorticolimbic dopamine (DA) system (Ostroumov and Dani, 2018). More recently, other structures have been implicated in reward and aversion, including the habenula (Antolin-Fontes et al., 2015; Boulos et al., 2019; Mathis and Kenny, 2018). Increasing evidence suggests that the degree of sensitivity to both the rewarding and aversive aspects of an addictive drug and the severity of the withdrawal after discontinuing its use contribute to the addiction process (Koob and Volkow, 2016). Understanding the mechanisms of these processes may reveal novel insights into the mechanics of the disorder and identify new targets for medications development.
As the leading preventable cause of cancer and death, nicotine use and dependence have been the s... more As the leading preventable cause of cancer and death, nicotine use and dependence have been the subject of a multitude of genetic studies in the past decade, ranging from candidate gene studies to genome-wide association studies (GWAS) to prospective studies. The genetics of nicotine addiction, smoking, and cancer are multifactorial, as would be expected from a complex behavior such as cigarette smoking. The combined heritability based on twin studies is estimated at 50–75 % (Li, Am J Med Sci 326(4): 168–73, 2003; Hall et al. Tob Control 11(2): 119–24, 2002; Lessov et al. Psychol Med 34(5): 865–79, 2004.; Lessov-Schlaggar et al. Int J Epidemiol 35(5): 1278–85, 2006; Maes et al. Psychol Med 34(7): 1251–61, 2004), with a large number of genes contributing to a small amount of risk individually. Some genes contribute to the quantity of nicotine used, while another set is associated with the duration of nicotine use, and yet another set is linked with severity of nicotine dependence. Associated “risky” genes comprise genes encoding for nicotinic acetylcholine receptor (nAChR) subunits, but also include genes like the bitter taste receptor. Still others have been associated with initiation and with success, or lack thereof, in cessation. In this chapter we review the current findings in the genetics of smoking, focusing on those studies that have linked nicotinic acetylcholine receptors (nAChR) to nicotine addiction, and further discuss how mutations in these receptors alter their function.
Progress has been made over the last decade in our understanding of the brain areas and circuits ... more Progress has been made over the last decade in our understanding of the brain areas and circuits involved in nicotine reward and withdrawal, leading to models of addiction that assign different addictive behaviors to distinct, yet overlapping, neural circuits (Koob and Volkow, 2010; Lobo and Nestler, 2011; Tuesta et al., 2011; Volkow et al., 2011). Recently the habenulointerpeduncular (Hb-IPN) midbrain pathway has re-emerged as a new critical crossroad that influences the brain response to nicotine. This brain area is particularly enriched in nicotinic acetylcholine receptor (nAChR) subunits α5, α3 and β4 encoded by the CHRNA5-A3-B4 gene cluster, which has been associated with vulnerability to tobacco dependence in human genetics studies. This finding, together with studies in mice involving deletion and replacement of nAChR subunits, and investigations of the circuitry, cell types and electrophysiological properties, have begun to identify the molecular mechanisms that take place in the MHb-IPN and underlie critical aspects of nicotine dependence. In the current review we describe the anatomical and functional connections of the MHb-IPN system, as well as the contribution of specific nAChRs subtypes in nicotine-mediated behaviors. Finally, we discuss the specific electrophysiological properties of MHb-IPN neuronal populations and how nicotine exposure alters their cellular physiology, highlighting the unique role of the MHb-IPN in the context of nicotine aversion and withdrawal.
The discovery of genetic variants in the CHRNA5-CHRNA3-CHRNB4 gene cluster associated with heavy ... more The discovery of genetic variants in the CHRNA5-CHRNA3-CHRNB4 gene cluster associated with heavy smoking and higher relapse risk has led to the identification of the midbrain habenulainterpeduncular axis as a critical relay circuit in the control of nicotine dependence. Although clear roles for a3, b4 and a5
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Papers by Jessica Ables