Influence of Serotonin on the Glutamate-Induced Excitations of Secondary Vestibular Neurons in the Rat

• Published in: Experimental neurology 2001-12, Vol.172 (2), p.446-459
• Main Authors: Li Volsi, Guido, Licata, Flora, Fretto, Giovanna, Mauro, Michela Di, Santangelo, Francesca
• Format: Article
• Language: English
• Subjects: 5-hydroxytryptamine; Animals; Biological and medical sciences; Evoked Potentials - drug effects; Evoked Potentials - physiology; Excitatory Amino Acid Agonists - pharmacology; glutamate; Glutamic Acid - pharmacology; Headache. Facial pains. Syncopes. Epilepsia. Intracranial hypertension. Brain oedema. Cerebral palsy; Kainic Acid - pharmacology; Medical sciences; microiontophoresis; N-methyl-[formula omitted]-aspartate; N-Methylaspartate - pharmacology; Nervous system (semeiology, syndromes); neurochemistry; Neurology; Neurons - drug effects; Neurons - physiology; Quisqualic Acid - pharmacology; Rats; Rats, Wistar; receptors; Receptors, Amino Acid - physiology; Receptors, N-Methyl-D-Aspartate - physiology; Serotonin - pharmacology; Serotonin Receptor Agonists - pharmacology; unitary activities; vestibular nuclei; Vestibular Nuclei - cytology; Vestibular Nuclei - drug effects; Vestibular Nuclei - physiology
• ISSN: 0014-4886; 1090-2430
• DOI: 10.1006/exnr.2001.7804

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 α-methyl-5-hydroxytryptamine (α-Me-5-HT), a 5-HT2 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-HT1A receptor agonist. The 5-HT2 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-HT2 receptors, and is exerted on NMDA receptors. A minor involvement of other 5-HT receptors (at least 5-HT1A) and other glutamate receptors (for quisqualate and kainate) in the modulatory action of 5-HT is plausible.