Effects of glutamate on the serotonin-induced responses of vestibular neurons.
The aim of this work was to verify whether and how spontaneous or glutamate(GLU)-induced enhancements of the neuronal firing rate modified the responsiveness of the vestibular neurons to microiontophoretic application of serotonin (5-HT). During experiments performed on anaesthetized Wistar rats the responses to 5-HT applications were studied in neurons of the lateral vestibular nucleus identified by the antidromic activation upon stimulation of the vestibulospinal tract. The magnitude (in percent) of the 5-HT induced excitatory responses decreased (hyperbolic correlation, r = 0.91) when the background mean firing rate was enhanced spontaneously or by long-lasting application of GLU. Even in high-discharging units, the response never changed its sign. The trend to a depression of the response to 5-HT in function of the background discharge was observed when either the enhancement of firing occurred spontaneously and it was induced by an application of GLU, no significant difference (F-test) being found between the two cases. It is concluded that serotoninergic afferents can exert a strong control upon the vestibular neurons when the background activity is depressed, and only a weak influence when the neuronal firing is enhanced by other excitatory afferents. It remains to verify whether the type of interference observed between GLU and 5-HT is specific or can be also detected between 5-HT and other excitatory neuromediators.
Licata
F
F
Istituto di Fisiologia umana, Università di Catania.
Li Volsi
G
G
Maugeri
G
G
Ciranna
L
L
Santangelo
F
F
D000818:Animals; D004347:Drug Interactions; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000494:pharmacology*; D009435:Synaptic Transmission / Q000187:drug effects*; D014726:Vestibular Nuclei / Q000187:drug effects*
D005971:Glutamates; D012701:Serotonin; D018698:Glutamic Acid