Effect of motilin on the discharge of rat hippocampal neurons responding to gastric distension and its potential mechanism

The study aims to find the effect of motilin on neuronal activity of gastric distension-responsive neurons in rat hippocampus and its possible mechanism. Single unit discharges in the hippocampal CA1 region were recorded extracellularly by means of four-barrel glass micropipettes in anesthetized rats and the expression of nNOS in hippocampus was observed by fluo-immunohistochemistry staining. Of the 171 recorded neurons, 76.0% were GD-excitatory (GD-E) neurons and 24.0% were GD-inhibited (GD-I) neurons. The 57.6% of GD-E neurons showed an excitatory response to motilin and the same effect was observed in 51.7% GD-I neurons. However, when NOS inhibitor nitro-l-arginine methyl ester (l-NAME) was administrated previously, the followed motilin-induced excitatory responsiveness of GD-responsive neurons was reduced. In contrast, discharge activity of GD-responsive neurons with motilin was enhanced by pretreatment of NO precursor l-arginine. The expression of nNOS-IR positive neurons was significantly increased in CA1 after administration of motilin. Our findings suggested that motilin excited the GD-responsive neurons in the hippocampal CA1 region and the excitatory effect of motilin may be mediated by the endogenous NO.