The central nervous regulation of ruminant gastric activity

An extensive survey of the literature relating to the central nervous control of ruminant forestomach motility reveals that the present state of knowledge is very unsatisfactory. Although there is convincing evidence that the fundamental mechanism concerned is situated in the medulla oblongata, and that the efferent pathway from this involves the dorsal vagal nucleus, little else can be deduced.

The experiments described in this thesis, therefore, have been designed to provide more information on the location and activity of the reticulo-ruminal motor centre in sheep. Since a study of this type necessarily involves recording gastric motility, it is important that the technical and theoretical problems con- :cerned are realised. Section 1 of this thesis, therefore, is devoted to a critical survey of the methods which have been used for recording gastric motility, and of the limitations of each.

The second section of the thesis describes a series of experiments carried out in an attempt to determine the extent to which the centre is responsible for regulating motility of the forestomach - particularly of the rumen. The innervation of the rumen is described in some detail, and evidence is presented which suggests that the ventral vagal trunk does not send significant numbers of motor nerve fibres to the rumen sacs. This finding is considered in relation to the fact that after transection of the dorsal vagal trunk, motility of the rumen sacs is abolished for several days, but subsequently returns before reinnervation by the transected nerve.

The linal section describes experiments carried out to demonstrate the location of the reticulo-ruminal motor centre in sheep, by determining the positions of degenerating neurons in the medulla and sensory vagal ganglia following transection of the vagal trunks. Point electrical stimulation of the dorsal vagal nucleus caused an inhibition of gastric motility - the precise area from which effects could be elicited is then described. Other responses some¬ times seen on point electrical stimulation are also described. Finally, patterns of unit neuronal discharge, recorded from the dorsal vagal nucleus, are described and classified in relation to rumino-reticvlar motility. 'The findings are discussed in relation to one another, and their significance in relation to the regulation of gastric motility is considered.