Several pharmacological and physiological studies have suggested that GABAA receptors (GABAA Rs) may exist in the rat major pelvic ganglion (MPG), a large coalescent pelvic ganglion that contains both sympathetic and parasympathetic components which innervates pelvic organs. However, the presence of GABAA R in the MPG has never been demonstrated directly by morphological studies. In the present study, we used immunohistochemistry to demonstrate the existence of GABAA R β2/3 subunits for the first time in the rat MPG. We also analyzed the neurochemical properties of MPG neurons expressing GABAA R β2/3 subunits. GABAA R β2/3-immunoreactive (-IR) neurons occupied 27.4 ± 7.0% of the whole neuronal population, and many of these (77.6%) were co-localized with tyrosine hydroxylase (TH). Likewise, most (86.5%) of TH-IR neurons were GABAA R β2/3-positive. GABAA R β2/3 subunits were also expressed in a few VIP- or NOS-IR neurons, the cholinergic or non-adrenergic, non-cholinergic (NANC) neurons. These results suggest that GABAA Rs are involved in the modulation of most sympathetic, noradrenergic neurons and also a subset of VIP and NOS neurons of the rat MPG.
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