Serotonin preferentially hyperpolarizes capsaicin-sensitive C type sensory neurons by activating 5-HT1A receptors.
The effects of serotonin (5-HT) were investigated by intracellular recording from 179 dorsal root ganglion (DRG) cells classified by conduction velocity. Bath applied 5-HT depolarized 82% and hyperpolarized 4% of the A-type cells. In C-type cells, 5-HT depolarized only 41%, but hyperpolarized 39% of the cells. The depolarizing responses were of two types; an increase or decrease in R(in), mediated by 5-HT2or3 receptors, respectively. These receptors were observed in both A- and C-type cells. Hyperpolarizing responses were largely confined to A(delta)- and C-type cells. Carboxamidotryptamine and 8-OH-dipropylamino-tetralin were full agonists in eliciting hyperpolarization, and metitepin, spiperone and spiroxitrine behaved as competitive antagonists. This indicated that hyperpolarization was mediated by a 5-HT1A receptor. A 5-HT1A&3 receptor were found co-localized on some C-type cells. A strong depolarizing response to capsaicin was observed in the subgroup of C-type neurons that were also hyperpolarized by 5-HT. Thus a co-localization of capsaicin and 5-HT1A receptors was also observed.
Todorovic
S
S
Department of Pharmacology, University of Illinois, Chicago 60612.
Anderson
E G
EG
D000818:Animals; D002211:Capsaicin / Q000494:pharmacology*; D004594:Electrophysiology; D005727:Ganglia, Spinal / Q000187:drug effects / Q000502:physiology; D009475:Neurons, Afferent / Q000187:drug effects* / Q000502:physiology; D011985:Receptors, Serotonin / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology*
D011985:Receptors, Serotonin; D012701:Serotonin; D002211:Capsaicin