Inhibitory motor innervation of the gall bladder musculature by intrinsic neurones containing nitric oxide in the Australian Brush-tailed possum (Trichosurus vulpecula)

Background-Gall bladder functions are modulated by neurones intrinsic to th e organ. Data are available on the neurochemical composition of intrinsic a nd extrinsic nerves innervating the gall bladder but are lacking on specifi c functional classes of gall bladder, neurones. Aims-To characterise the intrinsic motor neurones of the gall bladder and i dentify their roles using pharmacological techniques. Methods-Retrograde tracing from the possum gall bladder muscle in vitro all owed identification of intrinsic motor neurones., Subsequently, their conte nt of choline acetyltransferase and nitric oxide synthase, markers of acety lcholine and nitric oxide containing neurones, was established using immuno histochemical. techniques. Organ bath pharmacology was used to evaluate neu rotransmission by acetylcholine and nitric oxide in gall bladder muscle str ips. Results-Innervation of the gall bladder musculature by neurones, of both th e muscular and serosal plexuses was demonstrated. A large proportion (62%) of these motor neurones were immunoreactive for nitric oxide synthase. All gall bladder neurones, showed immunoreactivity for choline acetyltransferas e. Organ bath pharmacology confirmed the neuroanatomical data, showing acet ylcholine and nitric oxide mediating neurotransmission to the gall bladder musculature. Conclusions-Neurones containing acetylcholine and nitric oxide, located wit hin the muscular and serosal plexuses, provide excitatory and inhibitory mo tor innervation of the gall bladder, respectively. The large inhibitory inn ervation suggests active relaxation of the gallbladder during filling, medi ated by intrinsic nerves.