Methamphetamine is an addictive drug of abuse that can produce neurotoxic effects in dopamine ner... more Methamphetamine is an addictive drug of abuse that can produce neurotoxic effects in dopamine nerve endings of the striatum. The purpose of this study was to identify new genes that may play a role in the highly complex cascade of events associated with methamphetamine intoxication. Using Affymetrix oligonucleotide arrays, 12 488 genes were simultaneously interrogated and there were 152 whose expression levels were changed following methamphetamine treatment. The genes are grouped into broad functional categories with inflammatory/immune response elements, receptor/signal transduction components and ion channel/transport proteins among the most populated. Many genes within these categories can be linked to ion regulation and apoptosis, both of which have been implicated in methamphetamine toxicity, and numerous factors associated with microglial activation emerged with significant changes in expression. For example, brain-derived neurotrophic factor (BDNF) 2
A long-standing goal of substance abuse research has been to link drug-induced behavioral outcome... more A long-standing goal of substance abuse research has been to link drug-induced behavioral outcomes with the activity of specific brain regions to understand the neurobiology of addiction behaviors and to search for drug-able targets. Here, we tested the hypothesis that cocaine produces locomotor (behavioral) sensitization that correlates with increased calcium channel-mediated neuroactivity in brain regions linked with drug addiction, such as the nucleus accumbens (NAC), anterior striatum (AST) and hippocampus, as measured using manganese-enhanced MRI (MEMRI). Rats were treated with cocaine for 5 days, followed by a 2-day drug-free period. The following day, locomotor sensitization was quantified as a metric of cocaine-induced neuroplasticity in the presence of manganese. Immediately following behavioral testing, rats were examined for changes in calcium channel-mediated neuronal activity in the NAC, AST, hippocampus and temporalis muscle, which was associated with behavioral sensit...
Tryptophan hydroxylase, the initial and rate-limiting enzyme in the biosynthesis of the neurotran... more Tryptophan hydroxylase, the initial and rate-limiting enzyme in the biosynthesis of the neurotransmitter serotonin, is activated by protein kinase A and calcium/calmodulin-dependent protein kinase. One important aspect of the regulation of any enzyme by a phosphorylation-dephosphorylation cascade, and one that is lacking for tryptophan hydroxylase, lies in the identification of its site of phosphorylation by protein kinases. Recombinant forms of brain tryptophan hydroxylase were expressed as glutathione S-transferase fusion proteins and exposed to protein kinase A. This protein kinase phosphorylates and activates full-length tryptophan hydroxylase. The inactive regulatory domain of the enzyme (corresponding to amino acids 1-98) was also phosphorylated by protein kinase A. The catalytic core of the hydroxylase (amino acids 99-444), which expresses high levels of enzyme activity, was neither phosphorylated nor activated by protein kinase A. Conversion of serine-58 to arginine resulted...
Traumatic brain injury (TBI) results from a blow to the head and can range in severity from mild ... more Traumatic brain injury (TBI) results from a blow to the head and can range in severity from mild to severe. Mild TBI is the most common form of head injury and constitutes about 80–90 % of all cases. Repetitive mild TBI (rmTBI) has emerged as a significant public health concern as the number of individuals experiencing this type of injury in military combat operations and in athletic endeavors continues to increase at a very high rate. The medical and scientific communities have only just started to grapple with its complexity and are struggling to understanding the underlying pathotrajectory and to develop and implement tests to detect and assess rmTBI. For the most part, routine imaging approaches and standard neuropsychological tests contribute little to the evaluation and management of rmTBI. A better understanding of the pathological consequences of rmTBI, including elucidating the role of hypoperfusion, could be achieved with a validated animal model, but most existing models ...
Much of the social behavior in which rodents engage is related to reproduction, such as maintaini... more Much of the social behavior in which rodents engage is related to reproduction, such as maintaining a breeding territory, seeking mates, mating, and caring for their young. Rodents belong to the internally fertilizing species that require sexual behavior for reproduction. The dyadic, heterosexual patterns of most mammalian species are sexually dimorphic, but they also share mutual components in both sexes: sexual attraction is reciprocal, sexual initiative is assumed, appetitive behavior is engaged in, and mating involves consummatory and postconsummatory phases in females as well as in males. Serotonin, a phylogenetically ancient molecule, is the most widely distributed neurotransmitter in the brain and its signaling pathways are essential for numerous functions including sexual behavior. Since the late 1960s, brain serotonergic neurotransmission has been considered to exert an inhibitory influence on the neural mechanisms mediating sexual behavior. This contention was based mainly on the observations that a decrease in central serotonergic activity facilitated the elicitation of sexual behavior, whereas an increase in central serotonergic activity attenuated it. However, the discovery of over 14 types of serotonin receptors has added numerous layers of complexity to the study of serotonin and sexual behavior. Evidence shows that, upon activation, certain receptor subtypes facilitate, whereas some others suppress, sexual behavior, as well as sexual arousal and motivation. Furthermore, the role of these receptors has been shown to be different in the male and female sexes. The use of serotonergic pharmacological interventions, mouse strains with genetic polymorphisms causing alterations in the levels of brain serotonin, and animal models with genetic manipulations of various serotonin effectors has helped delineate the fundamental role of this neurotransmitter in the regulation of sexual behavior. This review aims to examine the basics of the components of female and male sexual behavior and the participation of the serotonin system in the modulation of these behaviors, with emphasis on rodents. Behavioural Pharmacology 00:000-000
Maternal care is an indispensable component of offspring survival and development in all mammals ... more Maternal care is an indispensable component of offspring survival and development in all mammals and necessary for reproductive success. Although brain areas regulating maternal behaviors are innervated by serotonergic afferents, very little is known about the role of this neurotransmitter in these behaviors. To evaluate the contribution of serotonin to maternal care, we used mice with a null mutation in the gene for tryptophan hydroxylase-2 (TPH2), which results in a genetic depletion of brain serotonin, and tested them in a wide range of maternal behavior paradigms. We found that litters born to and reared by TPH2(-/-) mothers showed decreased survival, lower weaning weights and increased cannibalization. In addition, TPH2(-/-) mothers performed poorly in pup retrieval, huddling, nest construction and high-arched back nursing. Aggression in TPH2(-/-) dams was not triggered by lactation and was steadily high. Survival and weaning weight deficits of TPH2(-/-) pups were rescued by cr...
Pharmacological studies have suggested that nerve-released catecholamines may play an important r... more Pharmacological studies have suggested that nerve-released catecholamines may play an important role in the regulation of vascular tone and in the modulation of sensory nerve activity in animal teeth. We have used tyrosine hydroxylase-immunohistochemistry to detect catecholamine-producing cells in human dental pulp and high performance liquid chromatography to identify and quantitate catecholamines in this tissue. Tyrosine hydroxylase-immunoreactivity was confined to a sub-population of nerve fibres that were mainly localized around blood vessels. Considerable concentrations of norepinephrine (17.8 +/- 3.75 pg/mg tissue) and much lower concentrations of dopamine and epinephrine (0.27 +/- 0.10 and 0.19 +/- 0.11 pg/mg, respectively) were measured in all samples examined. It is suggested that catecholamines in human dental pulp are exclusively contained in nervous structures that are mainly associated with blood vessels and that norepinephrine is the candidate neurotransmitter of these...
AJP: Regulatory, Integrative and Comparative Physiology, 2014
The sleep-wake cycle and motor activity, but not temperature, are disrupted over the light-dark c... more The sleep-wake cycle and motor activity, but not temperature, are disrupted over the light-dark cycle in mice genetically depleted.
The effects of retinal location, serial letter position, and order of approximation to English on... more The effects of retinal location, serial letter position, and order of approximation to English on the accuracy of report of tachistoscopically presented letter arrays were examined. Processing time was controlled by a visual mask. The results show the following: (1) Overall accuracy is higher for arrays which appeared symmetrically around a central fixation point than for arrays which appeared either in the right or left visual field. (2) The first and last letters of an array are identified with the greatest accuracy except with symmetrical arrays.
Reductions in function within the serotonin (5HT) neuronal system have long been proposed as etio... more Reductions in function within the serotonin (5HT) neuronal system have long been proposed as etiological factors in depression. Selective serotonin reuptake inhibitors (SSRIs) are the most common treatment for depression, and their therapeutic effect is generally attributed to their ability to increase the synaptic levels of 5HT. Tryptophan hydroxylase 2 (TPH2) is the initial and rate-limiting enzyme in the biosynthetic pathway of 5HT in the CNS, and losses in its catalytic activity lead to reductions in 5HT production and release. The time differential between the onset of 5HT reuptake inhibition by SSRIs (minutes) and onset of their antidepressant efficacy (weeks to months), when considered with their overall poor therapeutic effectiveness, has cast some doubt on the role of 5HT in depression. Mice lacking the gene for TPH2 are genetically depleted of brain 5HT and were tested for a depression-like behavioral phenotype using a battery of valid tests for affective-like disorders in animals. The behavior of TPH2 −/− mice on the sucrose preference test, tail suspension test, and forced swim test and their responses in the unpredictable chronic mild stress and learned helplessness paradigms was the same as wild-type controls. While TPH2 −/− mice as a group were not responsive to SSRIs, a subset responded to treatment with SSRIs in the same manner as wild-type controls with significant reductions in immobility time on the tail suspension test, indicative of antidepressant drug effects. The behavioral phenotype of the TPH2 −/− mouse questions the role of 5HT in depression. Furthermore, the TPH2 −/− mouse may serve as a useful model in the search for new medications that have therapeutic targets for depression that are outside of the 5HT neuronal system.
Vasoactive intestinal peptide plays an important role in the trans-synaptic activation of tyrosin... more Vasoactive intestinal peptide plays an important role in the trans-synaptic activation of tyrosine hydroxylase in sympathoadrenal tissues in response to physiological stress. Since tyrosine hydroxylase is thought to be subsaturated with its cofactor, tetrahydrobiopterin, we tested the hypothesis that up-regulation of tyrosine hydroxylase gene expression following vasoactive intestinal peptide treatment is accompanied by a concomitant elevation of intracellular tetrahydrobiopterin biosynthesis. We also investigated the second messenger systems involved in vasoactive intestinal peptide's effects on tetrahydrobiopterin metabolism. Our results demonstrate that treatment of PC12 cells for 24 h with vasoactive intestinal peptide induced intracellular tetrahydrobiopterin levels 3.5-fold. This increase was due to increased expression of the gene encoding GTP cyclohydrolase, the initial and rate-limiting enzyme in tetrahydrobiopterin biosynthesis, which was blocked by the transcriptional inhibitor, actinomycin D. Activation of tyrosine hydroxylase and GTP cyclohydrolase by vasoactive intestinal peptide was mediated by cyclic-AMP. Furthermore, stimulation of cyclic-AMP-mediated responses or protein kinase C activity induced the maximal in vitro activities of both tyrosine hydroxylase and GTP cyclohydrolase; the responses were additive when both treatments were combined. Induction of sphingolipid metabolism had no effect on the activation of tyrosine hydroxylase, while it induced GTP cyclohydrolase in a protein kinase C-independent manner.
Methamphetamine is an addictive drug of abuse that can produce neurotoxic effects in dopamine ner... more Methamphetamine is an addictive drug of abuse that can produce neurotoxic effects in dopamine nerve endings of the striatum. The purpose of this study was to identify new genes that may play a role in the highly complex cascade of events associated with methamphetamine intoxication. Using Affymetrix oligonucleotide arrays, 12 488 genes were simultaneously interrogated and there were 152 whose expression levels were changed following methamphetamine treatment. The genes are grouped into broad functional categories with inflammatory/immune response elements, receptor/signal transduction components and ion channel/transport proteins among the most populated. Many genes within these categories can be linked to ion regulation and apoptosis, both of which have been implicated in methamphetamine toxicity, and numerous factors associated with microglial activation emerged with significant changes in expression. For example, brain-derived neurotrophic factor (BDNF) 2
A long-standing goal of substance abuse research has been to link drug-induced behavioral outcome... more A long-standing goal of substance abuse research has been to link drug-induced behavioral outcomes with the activity of specific brain regions to understand the neurobiology of addiction behaviors and to search for drug-able targets. Here, we tested the hypothesis that cocaine produces locomotor (behavioral) sensitization that correlates with increased calcium channel-mediated neuroactivity in brain regions linked with drug addiction, such as the nucleus accumbens (NAC), anterior striatum (AST) and hippocampus, as measured using manganese-enhanced MRI (MEMRI). Rats were treated with cocaine for 5 days, followed by a 2-day drug-free period. The following day, locomotor sensitization was quantified as a metric of cocaine-induced neuroplasticity in the presence of manganese. Immediately following behavioral testing, rats were examined for changes in calcium channel-mediated neuronal activity in the NAC, AST, hippocampus and temporalis muscle, which was associated with behavioral sensit...
Tryptophan hydroxylase, the initial and rate-limiting enzyme in the biosynthesis of the neurotran... more Tryptophan hydroxylase, the initial and rate-limiting enzyme in the biosynthesis of the neurotransmitter serotonin, is activated by protein kinase A and calcium/calmodulin-dependent protein kinase. One important aspect of the regulation of any enzyme by a phosphorylation-dephosphorylation cascade, and one that is lacking for tryptophan hydroxylase, lies in the identification of its site of phosphorylation by protein kinases. Recombinant forms of brain tryptophan hydroxylase were expressed as glutathione S-transferase fusion proteins and exposed to protein kinase A. This protein kinase phosphorylates and activates full-length tryptophan hydroxylase. The inactive regulatory domain of the enzyme (corresponding to amino acids 1-98) was also phosphorylated by protein kinase A. The catalytic core of the hydroxylase (amino acids 99-444), which expresses high levels of enzyme activity, was neither phosphorylated nor activated by protein kinase A. Conversion of serine-58 to arginine resulted...
Traumatic brain injury (TBI) results from a blow to the head and can range in severity from mild ... more Traumatic brain injury (TBI) results from a blow to the head and can range in severity from mild to severe. Mild TBI is the most common form of head injury and constitutes about 80–90 % of all cases. Repetitive mild TBI (rmTBI) has emerged as a significant public health concern as the number of individuals experiencing this type of injury in military combat operations and in athletic endeavors continues to increase at a very high rate. The medical and scientific communities have only just started to grapple with its complexity and are struggling to understanding the underlying pathotrajectory and to develop and implement tests to detect and assess rmTBI. For the most part, routine imaging approaches and standard neuropsychological tests contribute little to the evaluation and management of rmTBI. A better understanding of the pathological consequences of rmTBI, including elucidating the role of hypoperfusion, could be achieved with a validated animal model, but most existing models ...
Much of the social behavior in which rodents engage is related to reproduction, such as maintaini... more Much of the social behavior in which rodents engage is related to reproduction, such as maintaining a breeding territory, seeking mates, mating, and caring for their young. Rodents belong to the internally fertilizing species that require sexual behavior for reproduction. The dyadic, heterosexual patterns of most mammalian species are sexually dimorphic, but they also share mutual components in both sexes: sexual attraction is reciprocal, sexual initiative is assumed, appetitive behavior is engaged in, and mating involves consummatory and postconsummatory phases in females as well as in males. Serotonin, a phylogenetically ancient molecule, is the most widely distributed neurotransmitter in the brain and its signaling pathways are essential for numerous functions including sexual behavior. Since the late 1960s, brain serotonergic neurotransmission has been considered to exert an inhibitory influence on the neural mechanisms mediating sexual behavior. This contention was based mainly on the observations that a decrease in central serotonergic activity facilitated the elicitation of sexual behavior, whereas an increase in central serotonergic activity attenuated it. However, the discovery of over 14 types of serotonin receptors has added numerous layers of complexity to the study of serotonin and sexual behavior. Evidence shows that, upon activation, certain receptor subtypes facilitate, whereas some others suppress, sexual behavior, as well as sexual arousal and motivation. Furthermore, the role of these receptors has been shown to be different in the male and female sexes. The use of serotonergic pharmacological interventions, mouse strains with genetic polymorphisms causing alterations in the levels of brain serotonin, and animal models with genetic manipulations of various serotonin effectors has helped delineate the fundamental role of this neurotransmitter in the regulation of sexual behavior. This review aims to examine the basics of the components of female and male sexual behavior and the participation of the serotonin system in the modulation of these behaviors, with emphasis on rodents. Behavioural Pharmacology 00:000-000
Maternal care is an indispensable component of offspring survival and development in all mammals ... more Maternal care is an indispensable component of offspring survival and development in all mammals and necessary for reproductive success. Although brain areas regulating maternal behaviors are innervated by serotonergic afferents, very little is known about the role of this neurotransmitter in these behaviors. To evaluate the contribution of serotonin to maternal care, we used mice with a null mutation in the gene for tryptophan hydroxylase-2 (TPH2), which results in a genetic depletion of brain serotonin, and tested them in a wide range of maternal behavior paradigms. We found that litters born to and reared by TPH2(-/-) mothers showed decreased survival, lower weaning weights and increased cannibalization. In addition, TPH2(-/-) mothers performed poorly in pup retrieval, huddling, nest construction and high-arched back nursing. Aggression in TPH2(-/-) dams was not triggered by lactation and was steadily high. Survival and weaning weight deficits of TPH2(-/-) pups were rescued by cr...
Pharmacological studies have suggested that nerve-released catecholamines may play an important r... more Pharmacological studies have suggested that nerve-released catecholamines may play an important role in the regulation of vascular tone and in the modulation of sensory nerve activity in animal teeth. We have used tyrosine hydroxylase-immunohistochemistry to detect catecholamine-producing cells in human dental pulp and high performance liquid chromatography to identify and quantitate catecholamines in this tissue. Tyrosine hydroxylase-immunoreactivity was confined to a sub-population of nerve fibres that were mainly localized around blood vessels. Considerable concentrations of norepinephrine (17.8 +/- 3.75 pg/mg tissue) and much lower concentrations of dopamine and epinephrine (0.27 +/- 0.10 and 0.19 +/- 0.11 pg/mg, respectively) were measured in all samples examined. It is suggested that catecholamines in human dental pulp are exclusively contained in nervous structures that are mainly associated with blood vessels and that norepinephrine is the candidate neurotransmitter of these...
AJP: Regulatory, Integrative and Comparative Physiology, 2014
The sleep-wake cycle and motor activity, but not temperature, are disrupted over the light-dark c... more The sleep-wake cycle and motor activity, but not temperature, are disrupted over the light-dark cycle in mice genetically depleted.
The effects of retinal location, serial letter position, and order of approximation to English on... more The effects of retinal location, serial letter position, and order of approximation to English on the accuracy of report of tachistoscopically presented letter arrays were examined. Processing time was controlled by a visual mask. The results show the following: (1) Overall accuracy is higher for arrays which appeared symmetrically around a central fixation point than for arrays which appeared either in the right or left visual field. (2) The first and last letters of an array are identified with the greatest accuracy except with symmetrical arrays.
Reductions in function within the serotonin (5HT) neuronal system have long been proposed as etio... more Reductions in function within the serotonin (5HT) neuronal system have long been proposed as etiological factors in depression. Selective serotonin reuptake inhibitors (SSRIs) are the most common treatment for depression, and their therapeutic effect is generally attributed to their ability to increase the synaptic levels of 5HT. Tryptophan hydroxylase 2 (TPH2) is the initial and rate-limiting enzyme in the biosynthetic pathway of 5HT in the CNS, and losses in its catalytic activity lead to reductions in 5HT production and release. The time differential between the onset of 5HT reuptake inhibition by SSRIs (minutes) and onset of their antidepressant efficacy (weeks to months), when considered with their overall poor therapeutic effectiveness, has cast some doubt on the role of 5HT in depression. Mice lacking the gene for TPH2 are genetically depleted of brain 5HT and were tested for a depression-like behavioral phenotype using a battery of valid tests for affective-like disorders in animals. The behavior of TPH2 −/− mice on the sucrose preference test, tail suspension test, and forced swim test and their responses in the unpredictable chronic mild stress and learned helplessness paradigms was the same as wild-type controls. While TPH2 −/− mice as a group were not responsive to SSRIs, a subset responded to treatment with SSRIs in the same manner as wild-type controls with significant reductions in immobility time on the tail suspension test, indicative of antidepressant drug effects. The behavioral phenotype of the TPH2 −/− mouse questions the role of 5HT in depression. Furthermore, the TPH2 −/− mouse may serve as a useful model in the search for new medications that have therapeutic targets for depression that are outside of the 5HT neuronal system.
Vasoactive intestinal peptide plays an important role in the trans-synaptic activation of tyrosin... more Vasoactive intestinal peptide plays an important role in the trans-synaptic activation of tyrosine hydroxylase in sympathoadrenal tissues in response to physiological stress. Since tyrosine hydroxylase is thought to be subsaturated with its cofactor, tetrahydrobiopterin, we tested the hypothesis that up-regulation of tyrosine hydroxylase gene expression following vasoactive intestinal peptide treatment is accompanied by a concomitant elevation of intracellular tetrahydrobiopterin biosynthesis. We also investigated the second messenger systems involved in vasoactive intestinal peptide's effects on tetrahydrobiopterin metabolism. Our results demonstrate that treatment of PC12 cells for 24 h with vasoactive intestinal peptide induced intracellular tetrahydrobiopterin levels 3.5-fold. This increase was due to increased expression of the gene encoding GTP cyclohydrolase, the initial and rate-limiting enzyme in tetrahydrobiopterin biosynthesis, which was blocked by the transcriptional inhibitor, actinomycin D. Activation of tyrosine hydroxylase and GTP cyclohydrolase by vasoactive intestinal peptide was mediated by cyclic-AMP. Furthermore, stimulation of cyclic-AMP-mediated responses or protein kinase C activity induced the maximal in vitro activities of both tyrosine hydroxylase and GTP cyclohydrolase; the responses were additive when both treatments were combined. Induction of sphingolipid metabolism had no effect on the activation of tyrosine hydroxylase, while it induced GTP cyclohydrolase in a protein kinase C-independent manner.
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Papers by Donald Kuhn