A MULTIDISCIPLINARY STUDY INTO CHANGES IN THE VAGUS NERVE FOLLOWING PARTIAL CHRONIC VAGOTOMY
A MULTIDISCIPLINARY STUDY INTO CHANGES IN THE VAGUS NERVE FOLLOWING PARTIAL CHRONIC VAGOTOMY
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Date
1984-02
Authors
ASALA, SAMUEL ABAYOMI
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Abstract
The ferret was used as a model for studying the effect
of chronic abdominal partial vagotomy on gastric motility
and innervation of the gastric wall by the surviving
abdominal vagal trunk. The fibre composition of the vagus
nerve trunks was also determined and correlated as much as
possible with the results of the two series of experiments
above. Gastric motility was measured indirectly by
measuring the intragastric pressure that was associated
with it in response to stimulation of the cervical vagus
nerves.
Acute ventral trunk vagotomy did not significantly
reduce the intragastric pressure response to cervical vagal
stimulation. Similarly, following chronic ventral trunk
vagotomy, intragastric pressure response to cervical vagal
stimulation did not differ significantly from the acute and
control values until after three months when it increased
significantly above acute values probably as a result of
re-innervation of the gastric wall by regenerative sprouts
from the proximal nerve segment. Acute dorsal trunk
vagotomy resulted in a significant reduction of intragastric
pressure response to cervical vagal stimulation below control
values. Following chronic dorsal trunk vagotomy,
intragastric pressure response to cervical vagal stimulation
significantly increased above the acute value and reached
the control value five days after vagotomy. The intragastric
pressure maintained a plateau at this normal value
throughout the three months period of the experiments.
Regenerative sprouts were not seen after chronic dorsal
trunk vagotomy.
Light microscope autoradiographic study of the normal
distribution of each of the abdominal vagal trunks in the
gastric wall showed that the ventral trunk was distributed
exclusively to the ventral surface of the stomach. The
dorsal trunk was distributed to the dorsal surface of the
stomach as well as the ventral surface of the pyloric
antrum and the pylorus. Three weeks after ventral trunk
vagotomy or dorsal trunk vagotomy, there was no change in
the pattern of distribution of both abdominal vagal trunks.
There was no tendency for compensatory spread of the surviving
vagal trunk to the denervated areas of the stomach.
Pre-ganglionic vagal efferent fibres reach the submucosal
plexus but not the mucosa.
Electron microscope analysis of vagus nerve fibre composition
showed that the left and right cervical vagus
nerves contain equal numbers of fibres whereas the ventral
trunk contains only about 50 percent of the number of fibres
in the dorsal trunk. The total number of fibres in both
abdominal vagus nerve trunks is only 5 0 percent of all
fibres in the cervical trunks. Thirteen percent of all
fibres in the cervical vagus nerves and less than 1 percent
of those in the abdominal trunks are myelinated. The vagus
nerve is essentially composed of afferent fibres with only
12 percent of cervical and 7 percent of abdominal vagaltrunks being efferent. The size-frequency distribution
of the myelinated fibres is unimodal with a distinct peak
at 2 to 3 µm diameter. Less than 1 percent of the
myelinated fibres have diameters above 8 µm. Myelinated
fibres less than 1 urn diameter were seen but they form a
very small percentage of all myelinated fibres. Because
the myelinated fibres of the vagus nerve in the ferret
have generally small diameters, and because the nerve is
composed mostly of non-myelinated C-fibres, the vagus nerve
in this animal is a slowly conducting nerve.
Description
A thesis submitted for the degree of Doctor of Philosophy
in the University of Sheffield, U.K.
DEPARTMENT OF ANATOMY AND CELL BIOLOGY
Keywords
MULTIDISCIPLINARY,, VAGUS,, NERVE,, CHRONIC,, VAGOTOMY