Excitatory GABA_A receptor in autonomic pelvic ganglion neurons innervating bladder

Major pelvic ganglia (MPG) are relay centers for autonomic reflexes such as micturition and penile erection. MPG innervate the urogenital system, including bladder. γ-Aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the mammalian central nervous system, and may also play an important role in some peripheral autonomic ganglia, including MPG. However, the electrophysiological properties and function of GABA_A receptor in MPG neurons innervating bladder remain unknown. This study examined the electrophysiological properties and functional roles of GABA_A receptors in bladder-innervating neurons identified by retrograde Dil tracing. Neurons innervating bladder showed previously established parasympathetic properties, including small membrane capacitance, lack of T-type Ca²⁺ channel expression, and tyrosine-hydroxylase immunoreactivity. GABA_A receptors were functionally expressed in bladder innervating neurons, but GABA_C receptors were not. GABA elicited strong depolarization followed by increase of intracellular Ca²⁺ in neurons innervating bladder, supporting the hypothesis GABA may play an important role in bladder function. These results provide useful information about the autonomic function of bladder in physiological and pathological conditions.