title: Influence of serotonin on the glutamate-induced excitations of secondary vestibular neurons in the rat.
abstract: The excitatory responses evoked by glutamate and its agonists in secondary vestibular neurons of the rat were studied during microiontophoretic application of 5-hydroxytryptamine (5-HT). Ejection of 5-HT modified neuronal responsiveness to glutamate in 86% of the studied units, the effect being a depression of the excitatory responses in two-thirds of cases and an enhancement in the remaining third. 5-HT was also effective in modifying 94% of the responses evoked by N-methyl-d-aspartate (NMDA), inducing a depressive effect in 76% of cases and an enhancement in the remaining ones. Quisqualate-evoked effects were depressed and enhanced by 5-HT in about the same number of cases; in contrast, kainate-evoked responses were enhanced. The depressive action of 5-HT was mimicked by application of alpha-methyl-5-hydroxytryptamine (alpha-Me-5-HT), a 5-HT(2) receptor agonist, whereas the enhancing effect could be evoked by application of 8-hydroxy-2(di-n-propylamino)tetralin (8-OH-DPAT), a selective 5-HT(1A) receptor agonist. The 5-HT(2) receptor antagonist ketanserin was able to reduce, but not to block totally, the depressive action of 5-HT on glutamate- or NMDA-evoked responses. No significant difference was detected between neuronal responses in the lateral and the superior vestibular nucleus. These results indicate that 5-HT is able to modulate the responsiveness of secondary vestibular neurons to excitatory amino acids. Its action is mostly depressive, involves 5-HT(2) receptors, and is exerted on NMDA receptors. A minor involvement of other 5-HT receptors (at least 5-HT(1A)) and other glutamate receptors (for quisqualate and kainate) in the modulatory action of 5-HT is plausible.
authors.affiliation: Department of Physiological Sciences, University of Catania, Catania, Italy. glivolsi@mbox.unict.it
authors.forename: G
authors.initials: G
authors.lastname: Li Volsi
authors.forename: F
authors.initials: F
authors.lastname: Licata
authors.forename: G
authors.initials: G
authors.lastname: Fretto
authors.forename: M D
authors.initials: MD
authors.lastname: Mauro
authors.forename: F
authors.initials: F
authors.lastname: Santangelo
mesh_terms: D000818:Animals; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000494:pharmacology*; D007608:Kainic Acid / Q000494:pharmacology; D016202:N-Methylaspartate / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects* / Q000502:physiology*; D016318:Quisqualic Acid / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D017459:Receptors, Amino Acid / Q000502:physiology; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology; D012701:Serotonin / Q000494:pharmacology*; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D014726:Vestibular Nuclei / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*
chemical_list: D018690:Excitatory Amino Acid Agonists; D017459:Receptors, Amino Acid; D016194:Receptors, N-Methyl-D-Aspartate; D017366:Serotonin Receptor Agonists; D012701:Serotonin; D018698:Glutamic Acid; D016202:N-Methylaspartate; D016318:Quisqualic Acid; D007608:Kainic Acid