Age-related changes in the effects of 5-hydroxytryptamine on substantia gelatinosa neurons of the trigeminal subnucleus caudalis

► Hyperpolarization was the major response in SG neurons in response to 5-HT application. ► Percentage of SG neurons showing hyperpolarization to 5-HT was higher in immature. ► Amplitude of 5-HT-induced hyperpolarization decreased with increasing postnatal age. ► Postnatal age of 3weeks is a critical period for 5-HT-induced hyperpolarizing effects. The trigeminal subnucleus caudalis (Vc) is the critical brainstem relay site of orofacial nociceptive processing to higher brain centers. The descending serotonergic pathway from the brainstem exerts inhibitory or facilitatory effects on nociceptive transmission in the spinal dorsal horn and the Vc, and SG neurons of the Vc exhibit hyperpolarization, no response or depolarization in response to 5-hydroxytryptamine (5-HT) application. In this study, we examined age-related changes in the effects of 5-HT on SG neurons of the Vc using immature, peripubertal and adult male mice and gramicidin-perforated patch recordings under the current-clamp mode. In the three age groups, hyperpolarization was the major response in SG neurons exhibiting membrane potential changes in response to 5-HT application. The proportion of the SG neurons responding to 5-HT by hyperpolarization was significantly higher in the immature (20/27) than in the adult mice (10/26; P