Serotonin excites arcuate neurons directly but inhibits them through intercalated GABAergic neurons.
Effects of serotonin (5-HT) on spontaneous discharges of single hypothalamic arcuate neurons were observed in rat brain slices by extracellular recordings. The results showed that (1) of 149 neurons selected randomly and tested for 5-HT application, 33 (22.2%) were excited, 82 (55.0%) were inhibited, and 34 (22.8%) showed biphasic responses or failed to respond; (2) substitution of low Ca(2+)-high Mg(2+) artificial cerebrospinal fluid (aCSF) for normal aCSF abolished the 5-HT-induced inhibitory effect but failed to affect the 5-HT-induced excitatory effect; (3) cyproheptadine, a non-selective 5-HT receptor antagonist, could block either the 5-HT-induced excitatory or inhibitory effects in all neurons tested; and (4) bicuculline, a GABA(A)-receptor antagonist, blocked the 5-HT-induced inhibitory effect. These results imply (1) 5-HT excites arcuate neurons through a mechanism that is insensitive to the decreased extracellular Ca(2+), suggesting a direct postsynaptic action of 5-HT on the 5-HT-receptors located in the membrane of the neurons recorded; and (2) 5-HT might elicit the inhibitory effect through a Ca(2+)-sensitive release of GABA from intercalated GABAergic local neurons that are excited first by 5-HT.
Kang
Yu-Ming
YM
Department of Neurobiology, Shanxi Medical University, Taiyuan, 030001, China. qiaojt@public.ty.sx.cn
Chen
Jian-Yong
JY
Ouyang
Wei
W
Qiao
Jian-Tian
JT
D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000187:drug effects* / Q000502:physiology; D003533:Cyproheptadine / Q000494:pharmacology; D066298:In Vitro Techniques; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012701:Serotonin / Q000494:pharmacology*; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
D003533:Cyproheptadine; D012701:Serotonin; D005680:gamma-Aminobutyric Acid