Electrophysiological effects of cocaine and procaine on dorsal raphe serotonin neurons.
The effects of cocaine and procaine on the spontaneous activity of serotonin (5-hydroxytryptamine, 5-HT) neurons in the dorsal raphe nucleus of the chloral hydrate anesthetized male rat were characterized using extracellular single-unit and microiontophoretic recording techniques. Intravenous cocaine elicited a potent, dose-dependent inhibition of 5-HT cell firing with a cumulative dose to 50% inhibition of cell firing of 0.66 +/- 0.11 mg/kg (means +/- S.E.M.; N = 17). In contrast, systemic administration of the local anesthetic procaine did not significantly alter cell firing in cumulative doses up to 16 mg/kg (N = 10). Microiontophoretic application of cocaine, but not procaine, also depressed spontaneous cell firing of 5-HT-containing neurons and potentiated the inhibitory effects of 5-HT in the dorsal raphe nucleus. The depressant effects on 5-HT neurons following systemic or microiontophoretic application of cocaine may result from autoinhibition of 5-HT neurons, presumably as a consequence of cocaine-induced 5-HT reuptake inhibition.
Cunningham
K A
KA
Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston 77550.
Lakoski
J M
JM
D000818:Animals; D003042:Cocaine / Q000008:administration & dosage / Q000494:pharmacology*; D007478:Iontophoresis; D008297:Male; D011343:Procaine / Q000008:administration & dosage / Q000494:pharmacology*; D011903:Raphe Nuclei / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000032:analysis*
D012701:Serotonin; D011343:Procaine; D003042:Cocaine