The Neuroendocrine System in the Intestinal Tract and Pancreas of Antarctic Fish
253
in nonadrenergic, noncholinergic nervous control of pancreatic and
intestinal secretion, motility and blood flow; they appear to stimulate the
release of islet hormones and the flow of pancreatic juice [31].
Surprisingly, in our Antarctic specimens, many sub P-IR fibers were
seen, especially in the outer portion of the large islet, near glucagon- and
PP-IR cells (Figs. 11,12). No sub P-IR fibers were until now seen in the
pancreatic endocrine portion of S. cabrilla, D. annularis and of other
teleosts [26,29], and only few sub P-IR fibers seem to be present in the
endocrine pancreas of mammals [32].
Sub P enhances the blood flow but does not seem to have any influence
on the release of mammalian pancreatic hormones. No data are available
about the role of this peptide on fish pancreatic function. Nevertheless the
finding of sub P-IR nerve fibers surrounding the endocrine cells of the
Antarctic fish pancreatic islet suggests that this peptide might play some
role in the release of pancreatic hormones.
Conclusions
A general conclusion can be drawn from the data reviewed here: a great
variability is present in the NES of teleosts, and, furthermore, a peculiar
pattern of peptide immunoreactivity is present in the digestive system of
Antarctic notothenioid teleosts. This probably means that peptides
different from those usually found in temperate teleosts are involved in
the regulation of intestinal motility, blood flow and pancreatic hormone
release.
The channichthyids, which are the most phyletic ally derived among
notothenioids, are those presenting the great differences concerning in
particular the innervation of the blood vessel wall, the muscular layers,
and the endocrine islets.
The enteric nervous system seems to be less developed than that of
nonAntarctic teleosts. VIP- and PACAP-IR nerve fibers were less
frequently seen and they are reduced in the Brockmann body where
numerous sub P-IR nerve fibers were instead found. On the contrary a
greater frequency of CCKlgastrin-, serotonin- and somatostatin-IR cells
and nerve elements was found throughout the intestinal wall. The finding
of insulin immunoreactivity in the gut endocrine cells and nerve elements
of C. antarcticus deserves further investigation.
At present it is difficult to explain the meaning of these results;
nevertheless, we should remember that the NES may play an important
role in the control of digestive functions, and the NES itself is under the
control of many factors. One of these could be the environmental
conditions, such as the low sea water temperature. This can affect the
blood flow and the digestive functions, and these problems can be
253
in nonadrenergic, noncholinergic nervous control of pancreatic and
intestinal secretion, motility and blood flow; they appear to stimulate the
release of islet hormones and the flow of pancreatic juice [31].
Surprisingly, in our Antarctic specimens, many sub P-IR fibers were
seen, especially in the outer portion of the large islet, near glucagon- and
PP-IR cells (Figs. 11,12). No sub P-IR fibers were until now seen in the
pancreatic endocrine portion of S. cabrilla, D. annularis and of other
teleosts [26,29], and only few sub P-IR fibers seem to be present in the
endocrine pancreas of mammals [32].
Sub P enhances the blood flow but does not seem to have any influence
on the release of mammalian pancreatic hormones. No data are available
about the role of this peptide on fish pancreatic function. Nevertheless the
finding of sub P-IR nerve fibers surrounding the endocrine cells of the
Antarctic fish pancreatic islet suggests that this peptide might play some
role in the release of pancreatic hormones.
Conclusions
A general conclusion can be drawn from the data reviewed here: a great
variability is present in the NES of teleosts, and, furthermore, a peculiar
pattern of peptide immunoreactivity is present in the digestive system of
Antarctic notothenioid teleosts. This probably means that peptides
different from those usually found in temperate teleosts are involved in
the regulation of intestinal motility, blood flow and pancreatic hormone
release.
The channichthyids, which are the most phyletic ally derived among
notothenioids, are those presenting the great differences concerning in
particular the innervation of the blood vessel wall, the muscular layers,
and the endocrine islets.
The enteric nervous system seems to be less developed than that of
nonAntarctic teleosts. VIP- and PACAP-IR nerve fibers were less
frequently seen and they are reduced in the Brockmann body where
numerous sub P-IR nerve fibers were instead found. On the contrary a
greater frequency of CCKlgastrin-, serotonin- and somatostatin-IR cells
and nerve elements was found throughout the intestinal wall. The finding
of insulin immunoreactivity in the gut endocrine cells and nerve elements
of C. antarcticus deserves further investigation.
At present it is difficult to explain the meaning of these results;
nevertheless, we should remember that the NES may play an important
role in the control of digestive functions, and the NES itself is under the
control of many factors. One of these could be the environmental
conditions, such as the low sea water temperature. This can affect the
blood flow and the digestive functions, and these problems can be