Effects of 5-hydroxytryptamine on the firing rates of neurons of the lateral vestibular nucleus in the rat.
5-hydroxytryptamine (5-HT) was delivered microiontophoretically (20-80 nA) to cells of the lateral vestibular nucleus of anaesthetized rats to test its influence on the spontaneous activity of single neurons. 5-HT increased the rate of firing of 94% of the units tested. The enhancement persisted for up to 700 s after the end of the 5-HT ejection and the maximum magnitude of the excitation (10-3400%) showed a hyperbolic correlation (rho = 0.86) with background firing. In 43% of units the enhancement was preceded by a short-lasting (less than 105 s) depression of the neuronal firing rate, the magnitude of which was unrelated to the background mean firing rate. Both components of the 5-HT response were dose-dependent. Only the excitatory responses were antagonized by metergoline, methysergide and ketanserin. The putative 5-HT agonist, 5-methoxy-N,N-dimethyltryptamine, applied microiontophoretically, depressed the background firing rate and was not antagonized by methysergide. These results demonstrate that 5-HT modifies the responsiveness of vestibular neurons and suggest that at least two mechanisms and maybe two types of receptors are activated by 5-HT in this nucleus.
Licata
F
F
Institute of Human Physiology, Catania, Italy.
Li Volsi
G
G
Maugeri
G
G
Santangelo
F
F
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D007650:Ketanserin / Q000494:pharmacology; D008297:Male; D008711:Metergoline / Q000494:pharmacology; D008784:Methysergide / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000494:pharmacology*; D014726:Vestibular Nuclei / Q000187:drug effects / Q000502:physiology*
D008711:Metergoline; D012701:Serotonin; D007650:Ketanserin; D008784:Methysergide