1. The motor profile of the exteriorized abomasal body and
antrum of chloralose-anaesthetized adult sheep, recorded
using balloon catheters and e.m.g. electrodes, consisted of
tonic muscular activity upon which contractile muscular
activity could be superimposed. The different motility
patterns of the body and antrum suggest that they are
separate functional entities.
2. Transection of the exteriorized abomasum into separate
body and antral pouches significantly increased antral
contraction amplitude and significantly decreased body
tone. This suggests that in the intact preparation the body
exerts an intrinsic inhibitory drive to antral contraction
amplitude, and that either the antrum exerts an intrinsic
excitatory drive to body tone or increased antral
contraction amplitude results in an extrinsic inhibitory
drive to body tone.
3. Repetitive electrical stimulation of the cut peripheral
end of the cervical vagus ( 1-10 Hz, 1-50 V, 1 ms pulse
duration for 10 s) caused body relaxation in 5 out of 7
preparations. Higher frequency electrical stimulation (10—
50 Hz) caused body contraction. In 4 preparations
electrical stimulation (1-50 Hz, 1-50 V, 1 ms pulse
duration for 10 s) of the cut peripheral end of the
cervical vagus caused antral contraction. In 3 ostensibly
identical preparations similar electrical stimulation
reduced antral contraction amplitude. Thus evidence was found for vagal excitatory and inhibitory innervation of
the abomasal body and antrum, and for an integrative
mechanism at the intramural level.
4. Body pouch inflation increased antral contraction
amplitude by a vagally-dependent mechanism, and decreased
the discharge rate of 10 out of 33 efferent units isolated
from abdominal branches of the vagus within 2 cm of the
antrum. If the decrease in unitary discharge is
instrumental in increasing antral contraction amplitude it
is likely that the units have inhibitory function.
5. The slight body pouch relaxation produced by body pouch
inflation was not altered by extrinsic denervation.
Inflation of an intra-reticular balloon produced similar
effects on the abomasal body motor profile as inflation to
the same volume of an intra-abdominal balloon placed beside
the reticulum. Thus no evidence was found for a functional
reflex corresponding to receptive relaxation found in the
6. The response of 33 efferent units, dissected from the
abdominal continuations of the dorsal and ventral vagi
within 2 cm of the antrum, to inflation of the abomasal
body pouch, and to systemic injection of 100 ug of
adrenaline was investigated. All units responding to body
pouch inflation also responded to adrenaline injection.
Unitary discharge was analysed for temporal relationships
with antral e.m.g. activity and the e.c.g. using a post
stimulus time histogram technique. Units showing discharge association with the antral e.m.g. also showed discharge
association with the e.c.g. Thus in the sheep neither
discharge response to discrete stimulation of specific
receptor populations nor the presence of system-related
rhythms in efferent discharge is necessarily indicative of
efferent destination or function.