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.