Serotonin-evoked modifications of the neuronal firing rate in the superior vestibular nucleus: a microiontophoretic study in the rat.
Microiontophoretic ejection (10-100 nA) of serotonin (5-hydroxytryptamine) into the superior vestibular nucleus induced modifications of the mean firing rate in 87% of the neurons examined. The responses to 5-hydroxytryptamine application were excitatory in 48% of the cells, inhibitory in 29%, and biphasic (inhibitory/excitatory) in the remaining 10%. The excited neurons were scattered throughout the nucleus; the units inhibited or characterized by biphasic responses were distinctly more numerous in the ventrolateral sector of the nucleus. The magnitude of both excitatory and inhibitory effects was dose-dependent. The excitatory responses to 5-hydroxytryptamine were blocked or greatly reduced by two 5-hydroxytryptamine antagonists, methysergide and ketanserin, or even reversed in many cases. Inhibitory responses were enhanced by simultaneous application of 5-hydroxytryptamine antagonists in half of the units studied. In the remaining units, ketanserin left the response unmodified, whereas methysergide reduced but never quite blocked it. The application of 5-methoxy-N,N- dimethyltryptamine, a 5-hydroxytryptamine agonist more effective on 5-hydroxytryptamine1 than on 5-hydroxytryptamine2 receptors, and of 8-hydroxy-2(di-n-propyl-amino) tetralin, a 5-hydroxytryptamine1A-specific agonist, induced a decrease in the firing rate which was unaffected by methysergide. These results support the hypothesis that 5-hydroxytryptamine exerts various functions throughout the superior vestibular nucleus by various receptors and that the inhibitory action is limited to an area of it.(ABSTRACT TRUNCATED AT 250 WORDS)
Licata
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Istituto di Fisiologia umana-Viale Andrea Doria 6, Catania, Italy.
Li Volsi
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Maugeri
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Ciranna
L
L
Santangelo
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F
D017371:8-Hydroxy-2-(di-n-propylamino)tetralin / Q000494:pharmacology; D000818:Animals; D005071:Evoked Potentials / Q000187:drug effects; D007478:Iontophoresis; D008297:Male; D008784:Methysergide / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D011985:Receptors, Serotonin / Q000187:drug effects / Q000502:physiology; D012701:Serotonin / Q000008:administration & dosage / Q000494:pharmacology*; D013238:Stereotaxic Techniques; D013997:Time Factors; D014726:Vestibular Nuclei / Q000187:drug effects / Q000502:physiology*
D011985:Receptors, Serotonin; D012701:Serotonin; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; D008784:Methysergide