Inhibiton of neurons in the amygdala by dorsal raphe stimulation: mediation through a direct serotonergic pathway.
This study presents data showing that the dorsal raphe nucleus (DRN) has a marked inhibitory influence upon neurons in the amygdala and that this inhibitory effect is mediated by a direct DRN-amygdala serotonergic pathway. The evidence may be briefly summarized as follows:(1) on the same amygdaloid cells, both iontophoresis of serotonin (5-HT) and electrical stimulation of the DRN markedly inhibited spontaneous single unit activities; (2) the latency of DRN-induced inhibition was relatively short and is compatible with the conduction velocities (which were determined by antidromic activation of the 5-HT pathway) of unmyelinated 5-HT fibers; (3) destruction of 5-HT projections by 5,7-dihydroxytryptamine (5,7-DHT) or pharmacological depletion of 5-HT by parachlorophenylalanine (PCPA) prevented the inhibitory responsed to DRN stimulation in the great majority of cells studied; (4) in PCPA-pretreated animals, injection of 5-hydroxytryptophan (5-HTP) reversed the PCPA effect, restoring the responses of amygdaloid cells to DRN stimulation. In the amygdala, the presumptive 5-HT antagonists which we tested did not block the inhibitory effects of 5-HT except that intravenously administered LSD blocked the inhibitory responses produced by submaximal DRN stimulation. The implications of these results for the possible functions of 5-HT in the amygdala is discussed.
D006916:5-Hydroxytryptophan / Q000494:pharmacology; D000200:Action Potentials; D000679:Amygdala / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D001933:Brain Stem / Q000502:physiology*; D003533:Cyproheptadine / Q000494:pharmacology; D003655:Decerebrate State; D004558:Electric Stimulation; D010134:Fenclonine / Q000494:pharmacology; D006801:Humans; D008238:Lysergic Acid Diethylamide / Q000494:pharmacology; D008297:Male; D008784:Methysergide / Q000494:pharmacology; D009431:Neural Conduction; D009433:Neural Inhibition; D009434:Neural Pathways; D051381:Rats; D012701:Serotonin / Q000494:pharmacology*; D013268:Stimulation, Chemical; D014363:Tryptamines / Q000494:pharmacology
D014363:Tryptamines; D003533:Cyproheptadine; D012701:Serotonin; D008238:Lysergic Acid Diethylamide; D006916:5-Hydroxytryptophan; D010134:Fenclonine; D008784:Methysergide