Oxytocin excites gastric-related neurones in rat dorsal vagal complex

1. Dorsal medullary injections of oxytocin (OT) influence gastric motor and secretory function via a vagally mediated mechanism. Thus, it was hypothesized that OT altered the firing rate of brain stem vagal neurones that were specifically related to gastric function. 2. To study this, glass microelectrode/injection pipette arrays were used to record the activity of gastric-related neurones in the dorsal vagal complex (DVC), which includes vagal sensory neurones in the nucleus tractus solitarius (NTS) and motor neurones in the dorsal motor nucleus (DMN). After identifying such a neurone, spontaneous activity was monitored before and after micropressure injection of OT and vehicle solutions from the pipettes. 3. Two methods were used to identify neurones that were related to gastric function. One method employed a gastric balloon to identify DVC neurones that were responsive to gastric inflation. The second method employed a gastric vagal stimulating electrode, which permitted the identification of gastric-related NTS and DMN cells via orthodromic or antidromic activation, respectively. 4. Twenty-four of forty-two gastric-inflation-related neurones responded to administration of OT (100-400 fmol in 100-400 pl). The majority of those responding to OT were activated by this peptide (21/24). All the cells tested (n = 13) remained sensitive to gastric inflation after administration of OT. Also, OT was found to excite the majority of cells that were identified as gastric-related NTS (nine excited; one no effect) or DMN cells (eleven excited; two no effect). 5. These studies support the hypothesis that central oxytocinergic neurones influence gastric motility and secretion by increasing the excitability of central vagal neurones in the NTS and DMN that are related to gastric function.