Biology Reference
In-Depth Information
50 neurons) were located in the MP and small ganglia (two to four neurons) or
isolated neurons were observed intermingled with the longitudinal muscular
fascicles of the lips. No neurons were found in the SMP. Both in the floor and in
the lips, many NOS-IR fibers were observed along the entire length of the RG,
parallel to the longitudinal axis of the muscle fascicles. Only a few NOS-IR fibers
were located in the external longitudinal muscle layer of the floor and in the
submucosa. NOS-IR neurons were located in the MP; they were more abundant
in the floor than in the lips, and we rarely observed neurons located singly or
grouped into small clusters of two to three cells among the muscle fascicles of the
lips. NOS-IR neurons showed great variability in both size and morphology; they
exhibited an irregular outline with either short, well-stained processes or an ovoid
shape. In these neurons, a long process arising from the side opposite the nucleus
could sometimes be seen without showing a given polarity. The neurons were more
abundant in the floor than in the lips, and their number increased proceeding
distally; however, their percentages were similar in the proximal and distal parts.
Almost all ganglia in the floor contained NOS-IR neurons that were often arranged
around the periphery of the ganglia, and some ganglia showed only NOS-IR
neurons. Approximately 80% of the NOS-IR neurons in the floor coexpressed
GAL; this percentage decreased in the lips (approximately 40%). Many neurons
coexpressed DBH (from 32% to 58%) but rarely (less than 0.5%) TH and SP. We
never observed NOS-IR neurons expressing CGRP, CALB, IB4, and NF; however,
we never found neurons stained with neurochemical markers used to identify
primary sensory neurons.
3.4 Discussion
This study shows a rich innervation in the RG of lambs, having a peculiar aspect
with respect to the other districts of the same species and probably related to its
particular function in suckling and adult animals. Contrary to what has been
observed in the intestinal plexuses of both small and large mammals, including
sheep (Lalatta-Costerbosa et al.
2007
), no neurons were detected in the SMP.
Similarly, SMP neurons, which are generally involved in secretion and vasodila-
tion, are very few or absent in the esophagus and stomach of many mammals,
including the sheep FSs (Yamamoto et al.
1995
). Therefore, it is plausible to think
that the myenteric ganglia in the lamb RG control mucosal functions. In the present
study, many NOS-IR neurons coexpressed GAL. This neuropeptide is widely
expressed in the CNS as well as in the ENS. In the GIT, the best-known effect of
GAL is its ability to regulate GIT motility, either acting as a neurotransmitter
by binding to three different G-protein-coupled receptors, all expressed in the
GIT smooth muscle cells, or acting as a neuromodulator by both increasing and
decreasing the release of neurohumoral substances (Gross and Pothoulakis
2007
).
