CONSIDERATIONS OF THE EFFERENT NERVOUS MECHANISM OF THE VAGO-VAGAL REFLEX RELAXATION OF THE STOMACH IN THE DOG

Abstract

Harper et al. (1) and Cragg and Evans (2) showed reflex relaxation of the stomach of cats and rabbits by electrical stimulation of the central cut end of the abdominal vagus nerve. One of the present authors reported that a single shock stimulation of the central end of the abdominal vagal trunk evoked a reflex discharge which was conveyed to the abdominal vicera via the other trunk (3). The transmedullary pathways involved in this reflex may exist in the immediate superficial caudal region of the obex (4). These evidences indicate that the vagus nerve provides afferent and efferent pathways for the reflex influence on the stomach. There is a considerable amount of literature which suggests that the efferent vagus nerve to the stomach contains both excitatory and inhibitory nerve fibres (See review of McSwiney (5)). Recently, the existence of the non-adrenergic inhibitory nerve fibres in the vagus was shown by Martinson (6, 7) in cats, and by Campbell (8) in guinea-pigs. Bülbring and Gershon (9) confirmed the presence of such inhibitory fibres in the vagal pathway to the stomach in guinea-pigs and mice, and suggested that 5-HT, with acetylcholine, may be a neurotransmitter at the ganglionic synapse in the inhibitory pathway. The aim of the present investigation is to obtain information concerning the nature of the efferent pathways participating in the vago-vagal gastric relaxation of the dog. Some of the results have already been described briefly (10-12).