VAGAL EFFERENT FIBER RESPONSES TO GASTRIC AND ESOPHAGEAL MECHANICAL AND CHEMICAL STIMULI IN THE FERRET

Gastric and oesophageal afferent inputs to vagal efferent fibres were investigated in Urethane anaesthetized ferrets. Mechanical, chemical, and pharmacological stimuli were tested and efferent activity recorded from single cervical vagal fibres. Fibres showed either no basal disc harge or low frequency, irregular patterns of resting discharge; only those which showed > 50% excitation or inhibition of basal activity wi th both gastric distension and oesophageal balloon distension were stu died further. These responses were rapid and maintained only for the d uration of the stimuli. 18/32 efferent fibres tested also showed chang es in discharge in response to acid infused slowly into the distal oes ophagus. These responses were larger after repeated acid infusions. Su bsequent intra-oesophageal capsaicin elicited a similar response in 7/ 8 fibres. These responses were reproducible with repeated capsaicin in fusions in 2/4 fibres and desensitized in 2/4 fibres. 2 capsaicin-resp onsive fibres were unresponsive to oesophageal acidification. 4/12 fib res tested responded to close intraarterial injections of capsaicin an d 9/12 to close intraarterial bradykinin. These responses were brief a nd of shea latency. Vagal efferent responses to mechanical and chemica l stimuli above were unchanged after the NK-1 receptor antagonist CP96 ,345 (4 mg/kg i.v.). Subsequently, bilateral vagotomy caudal to the re cording site abolished the basal activity in 4/7 fibres. In the 3 fibr es where spontaneous activity remained, none of these responded to oes ophageal distension or intra-oesophageal acid (2/2 fibres tested) afte r vagotomy, whereas 2/2 fibres tested still responded to gastric diste nsion. The response of 1 fibre to intraarterial bradykinin and capsaic in was unchanged by vagotomy. We conclude that vagal efferent neurones respond to gastro-oesophageal mechanical inputs and also receive conv ergent input from oesophageal acid-sensitive and gastrointestinal brad ykinin-and capsaicin-sensitive afferents. These afferent inputs are no t mediated via NK-1 receptors. There also exists a nonvagal afferent i nput onto vagal efferent neurones which is probably spinal and likewis e non NK-1 receptor mediated. (C) 1997 Elsevier Science B.V.