Abstract
Neurons of male rat major pelvic ganglia (MPG) can be classified into sympathetic and parasympathetic neurons according to the electrophysiological properties; membrane capacitance, expression of T-type Ca2+ channels and GABAA receptors, and the firing patterns during depolarization. Serotonin (5-hydroxytryptamine, 5-HT), a synaptic transmitter, localized immunohistochemically within the pelvic ganglia; but its functional role remains unclear in autonomic transmissions. In the present study, we investigated the function and molecular expression of 5-HT3 receptor in MPG neurons using electrophysiological, calcium imaging and RT-PCR techniques. Focal application of 5-HT elicited fast inward currents and depolarized membrane potential in parasympathetic neurons showing phasic firing patterns (n=32). MDL7222 (1 μM) and Y25130 (10 μM), selective 5-HT3 receptor antagonists, completely abolished the 5-HT-induced inward current and depolarization (n=10). In the fluo-3-loaded cells, 5-HT also induced a rapid increase in intracelluar [Ca2+]. Conversely, sympathetic neurons expressing GABAA receptor did not respond to 5-HT application at all (n=22). RT-PCR analysis revealed that MPG neurons contain mRNAs for 5-HT3A and 5-HT3B subunits. Taken together, our data suggest that parasympathetic MPG neurons express 5-HT3 receptors whose activation can mediate fast synaptic transmission. This study was supported by KOSEF Grant (R05-2003-000-11448-0). [Jpn J Physiol 54 Suppl:S138 (2004)]
