The firing rate of single cerebellar nuclear neurons was studied during microiontophoretic applic... more The firing rate of single cerebellar nuclear neurons was studied during microiontophoretic application of noradrenaline (NA), 5hydroxytryptamine (5-HT) and their agonists in deeply anesthetized rats. NA application depressed the neuronal firing rate more in the medial nucleus (MN) than in the interpositus (IN) and in the lateral nucleus (LN). These responses were mimicked by a 2 and, to a lesser extent, b receptor agonists. 5-HT evoked inhibition in MN and various effects (inhibitory, excitatory, biphasic) in IN and LN. Excitatory responses were more numerous in the posterior than in the anterior zone of IN. Agonists at 5-HT 1A and 5-HT 2 receptors mimicked inhibition only. In conclusion, NA and 5-HT exerted a similar action on MN neurons; in contrast, the effects of 5-HT on IN and LN were more differentiated than those exerted by NA.
Excitatory responses evoked by N-methyl-Daspartate (NMDA) in the vestibular nuclei (VN) of the ra... more Excitatory responses evoked by N-methyl-Daspartate (NMDA) in the vestibular nuclei (VN) of the rat were studied in vivo during microiontophoretic application of noradrenaline (NA) and/or its agonists and antagonists. Ejection of NA-modified excitatory responses mediated by NMDA receptors (NMDAR) in all neurons tested; the effect was enhancement in 59% of cases and depression in the remaining 41%. Enhancements prevailed in all VN with the exception of the lateral vestibular nucleus, where both effects were recorded in an equal number of cases. The enhancing action of NA on NMDAR-mediated responses was mimicked by the noradrenergic beta-receptor agonist isoproterenol, the beta 1 specific agonist denopamine and the alpha 2 agonist clonidine. These effects were blocked respectively by the generic beta-receptor antagonist timolol, the beta 1 antagonist atenolol and the alpha 2 antagonist yohimbine. In contrast, application of the alpha 1 receptor agonist cirazoline and the specific alpha 1 antagonist prazosin respectively mimicked and partially antagonized the depression of NMDAR-mediated excitations induced by NA. Double-labeling immunohistochemical techniques demonstrated broad colocalization of NMDAR (specifically NR1 and NR2 subunits) with noradrenergic receptors (alpha 1 , alpha 2 and beta 1) in many VN neurons; only minor differences were found between nuclei. These results indicate that NA can produce generalized modulation of NMDAR-mediated excitatory neurotransmission in VN, which may in turn modify synaptic plasticity within the nuclei.
The firing rate of single cerebellar nuclear neurons was studied during microiontophoretic applic... more The firing rate of single cerebellar nuclear neurons was studied during microiontophoretic application of noradrenaline (NA), 5hydroxytryptamine (5-HT) and their agonists in deeply anesthetized rats. NA application depressed the neuronal firing rate more in the medial nucleus (MN) than in the interpositus (IN) and in the lateral nucleus (LN). These responses were mimicked by a 2 and, to a lesser extent, b receptor agonists. 5-HT evoked inhibition in MN and various effects (inhibitory, excitatory, biphasic) in IN and LN. Excitatory responses were more numerous in the posterior than in the anterior zone of IN. Agonists at 5-HT 1A and 5-HT 2 receptors mimicked inhibition only. In conclusion, NA and 5-HT exerted a similar action on MN neurons; in contrast, the effects of 5-HT on IN and LN were more differentiated than those exerted by NA.
Excitatory responses evoked by N-methyl-Daspartate (NMDA) in the vestibular nuclei (VN) of the ra... more Excitatory responses evoked by N-methyl-Daspartate (NMDA) in the vestibular nuclei (VN) of the rat were studied in vivo during microiontophoretic application of noradrenaline (NA) and/or its agonists and antagonists. Ejection of NA-modified excitatory responses mediated by NMDA receptors (NMDAR) in all neurons tested; the effect was enhancement in 59% of cases and depression in the remaining 41%. Enhancements prevailed in all VN with the exception of the lateral vestibular nucleus, where both effects were recorded in an equal number of cases. The enhancing action of NA on NMDAR-mediated responses was mimicked by the noradrenergic beta-receptor agonist isoproterenol, the beta 1 specific agonist denopamine and the alpha 2 agonist clonidine. These effects were blocked respectively by the generic beta-receptor antagonist timolol, the beta 1 antagonist atenolol and the alpha 2 antagonist yohimbine. In contrast, application of the alpha 1 receptor agonist cirazoline and the specific alpha 1 antagonist prazosin respectively mimicked and partially antagonized the depression of NMDAR-mediated excitations induced by NA. Double-labeling immunohistochemical techniques demonstrated broad colocalization of NMDAR (specifically NR1 and NR2 subunits) with noradrenergic receptors (alpha 1 , alpha 2 and beta 1) in many VN neurons; only minor differences were found between nuclei. These results indicate that NA can produce generalized modulation of NMDAR-mediated excitatory neurotransmission in VN, which may in turn modify synaptic plasticity within the nuclei.
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