Neuronal responses to 5-hydroxytryptamine in the red nucleus of rats.
The effects of microiontophoretic 5-hydroxytryptamine (5-HT) on the firing rate of red nucleus (RN) neurons were studied in urethane-anesthetized rats. The background discharge rate of almost all the neurons tested (97%) was modified by 5-HT, and generally increased (89%). Responses were dose dependent. Twenty-three percent of the excitatory responses were preceded by a short inhibitory phase. No significant difference in the effect of 5-HT was found between those RN neurons that project to the spinal cord and those that do not The excitatory responses to 5-HT were blocked or greatly reduced by the 5-HT antagonists methysergide and ketanserin, and were even reversed in some cases. The 5-HT2/5-HT1A antagonist spiperone, in small doses, also blocked the transient inhibitory phases in addition to the excitatory effects. In RN neurons exhibiting a short-lasting inhibition in the response to 5-HT, the 5-HT1A agonist 8-hydroxy-2(di-n-propyl-amino)tetralin (8-OH-DPAT) induced inhibitory effects. These results support the hypothesis that 5-HT exerts control throughout the RN, mostly by acting on 5-HT2 receptors. Furthermore, an influence of this amine on the electrical activity of small groups of RN neurons by 5-HT1A receptors, and eventually by different mechanisms, appears probable. The functional significance of serotoninergic control of RN neuronal activity is discussed.
Licata
F
F
Università di Catania, Istituto di Fisiologia umana, Italy.
Li Volsi
G
G
Maugeri
G
G
Santangelo
F
F
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D004558:Electric Stimulation; D004594:Electrophysiology; D007478:Iontophoresis; D008297:Male; D009434:Neural Pathways / Q000166:cytology / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012012:Red Nucleus / Q000166:cytology / Q000187:drug effects*; D012701:Serotonin / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D013116:Spinal Cord / Q000166:cytology / Q000502:physiology
D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D012701:Serotonin