Excitation of lateral horn neurons of the neonatal rat spinal cord by 5-hydroxytryptamine.
The effects of 5-hydroxytryptamine (5-HT) on lateral horn cells contained in thin in vitro slices of neonatal rat spinal cord were investigated by means of intracellular recording techniques. Superfusion of 5-HT (1-100 microM) to lateral horn cells caused a concentration-dependent membrane depolarization leading to, in some instances, repetitive cell discharges. A number of lateral horn cells could be activated antidromically by stimulating the ventral rootlets. The conduction velocity of the antidromic spikes was estimated to be 0.3-2 m/s which corresponds to that of the axons of rat sympathetic preganglionic neurons reported by others. The 5-HT depolarization evoked in neurons that could be activated antidromically was similar to that elicited from unidentified lateral horn cells. The depolarization induced by 5-HT could be partially eliminated by low Ca/high Mg solution or tetrodotoxin in a portion of lateral horn cells and was accompanied by an increase in membrane resistance. The response was nullified near the membrane potential at which the spike after hyperpolarization was abolished; a clear reversal of polarity was not observed at a more negative potential level. The 5-HT depolarization was reversibly blocked by methysergide and cyproheptadine and enhanced by fluoxetine, a 5-HT-uptake inhibitor. The results indicate that the indoleamine primarily exerted an excitatory action on lateral horn cells, including those tentatively identified as sympathetic preganglionic neurons, by a direct depolarization which appears to be mediated by decrease of a voltage-sensitive K conductance and partly by an indirect effect via the release of an excitatory substance(s).
D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D001339:Autonomic Fibers, Preganglionic / Q000502:physiology; D002118:Calcium / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000494:pharmacology*; D013116:Spinal Cord / Q000166:cytology* / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology
D012701:Serotonin; D013779:Tetrodotoxin; D008274:Magnesium; D002118:Calcium