Characteristics of the vagally driven non‐adrenergic, non‐cholinergic inhibitory innervation of ferret gastric corpus.

Abstract

This paper reports a quantitative in vivo study on the vagal activation of the intramural non-adrenergic, non-cholinergic inhibitory nerves in the ferret gastric corpus. The nature of the inhibitory neurotransmitter was also investigated. In the atropinized, guanethidine-treated, urethane-anasthetized ferret, electrical stimulation (10 s at 20 V, 1-20 Hz, 0.5 ms pulses) of the cervical vagi produced a prompt fall in intracorpus pressures that was related to the stimulus frequency. The maximal response was achieved at 10 Hz. The time taken for the intracorpus pressure to return to pre-stimulus levels after 10 s period of stimulation was related to the stimulus frequency; at 10 Hz the pressure took approximately 11 min to recover. In contrast to studies in the cat (Martinson and Muren, 1963), there was no detectable difference in the electrical threshold for activation of the vagal excitatory and vagal inhibitory fibers. The nature of the vagal non-adrenergic, non-cholinergic inhibitory neurotransmitter was investigated using a variety of antagonists and agonists. ATP, adenosine, .alpha..beta.-methylene ATP and .beta..gamma.-methylene ATP all contracted the corpus in the presence of vagotomy, atropine, guanethidine and indomethacin. The vagally induced all in corpus pressure was not blocked by high doses of .alpha..beta.-methylene ATP. A variety of peptides were investigated for their effects on corpus pressure in the presence of atropine, guanethidine and vagotomy. Bombesin, pentagastrin, substance P, cholecystokinin octapeptide (CCK-8) and bradykinin all produced an increase in intracorpus pressure. Neurotensin and vasoactive intestinal polypeptide (VIP) both decreased intracorpus pressure, and of the 2 VIP most closely mimicked the response to vagal activation of the non-cholinergic, non-adrenergic inhibitory neurones. The results provide support for the involvement of a peptide (possibly VIP) rather than a purine in the vagally driven decrease in intracorpus pressure in the ferret.