248
O. Tagliafierro et al.
mammals; however in recent years, increasing data are also available for
fish, particularly teleosts whose NES appears no simpler than that of
mammals.
Teleosts are characterized by great variability in the number,
distribution and localization of neuroendocrine elements. This variability
could be related to that of some morphological gut characters such as
presence or absence of the stomach, the number of pyloric ceca, or the
kind of nutrients, and environmental conditions [4-6].
Immunohistochemistry has shown the presence of a number of peptides
and of serotonin in nerves and endocrine cells of the fish gut and pancreas.
Most of the peptides have been grouped into a few families on the basis of
their similarity in amino acid sequence, shown by biochemical methods
[7-10]; for example, vasoactive intestinal peptide (VIP), peptide histidine
isoleucine (PHI), pituitary adenyl ate cyclase activating peptide (P ACAP) ,
glucagon and secretin are grouped into the glucagon/VIP family. The
distribution and localization of these bioactive substances in the gastroenteropancreatic (GEP) tract of fish are currently detected by means of
immunohistochemical methods although recently more resolution has
been gained through the in situ hybridisation technique [11]. In both cases
a major problem is that of specificity, because the first method utilizes
antibodies raised against mammalian peptides, and the second one utilizes
mammalian cDNA probes to detect mRNAs encoding a particular peptide
or its precursor. For this reason the immunodetected substances in fishes
can be only partly similar to those used to produce the antisera or the
cDNA probes. The utilization of a panel of different specificity controls
can overcome this problem [12].
The physiological interpretation of these substances in fish is in
progress, and numerous experiments are in favor of their role in the
control of gastrointestinal absorption, secretion, motility, blood flow,
growth and differentiation, and furthermore in the regulation of the
mucosal immune and inflammatory response [13-17]. Some of these
functions are greatly influenced by temperature, thus the enteropancreatic
neuroendocrine system of Antarctic fish could show significant deviations
from that of other teleosts [18,19].
The Enteropancreatic Tract of Antarctic Notothenioid Teleosts
There are only few papers concerning the morphology and histology of
the digestive system in Antarctic teleosts. In these fish there is a
simplification of intestinal loops and a reduction of the number of pyloric
ceca. The intestinal wall is generally similar to that of other teleosts [2022] but the enteric submucous plexus seems to be reduced and is lacking
neuron cell bodies [23]. The pancreas is diffuse, as in most
O. Tagliafierro et al.
mammals; however in recent years, increasing data are also available for
fish, particularly teleosts whose NES appears no simpler than that of
mammals.
Teleosts are characterized by great variability in the number,
distribution and localization of neuroendocrine elements. This variability
could be related to that of some morphological gut characters such as
presence or absence of the stomach, the number of pyloric ceca, or the
kind of nutrients, and environmental conditions [4-6].
Immunohistochemistry has shown the presence of a number of peptides
and of serotonin in nerves and endocrine cells of the fish gut and pancreas.
Most of the peptides have been grouped into a few families on the basis of
their similarity in amino acid sequence, shown by biochemical methods
[7-10]; for example, vasoactive intestinal peptide (VIP), peptide histidine
isoleucine (PHI), pituitary adenyl ate cyclase activating peptide (P ACAP) ,
glucagon and secretin are grouped into the glucagon/VIP family. The
distribution and localization of these bioactive substances in the gastroenteropancreatic (GEP) tract of fish are currently detected by means of
immunohistochemical methods although recently more resolution has
been gained through the in situ hybridisation technique [11]. In both cases
a major problem is that of specificity, because the first method utilizes
antibodies raised against mammalian peptides, and the second one utilizes
mammalian cDNA probes to detect mRNAs encoding a particular peptide
or its precursor. For this reason the immunodetected substances in fishes
can be only partly similar to those used to produce the antisera or the
cDNA probes. The utilization of a panel of different specificity controls
can overcome this problem [12].
The physiological interpretation of these substances in fish is in
progress, and numerous experiments are in favor of their role in the
control of gastrointestinal absorption, secretion, motility, blood flow,
growth and differentiation, and furthermore in the regulation of the
mucosal immune and inflammatory response [13-17]. Some of these
functions are greatly influenced by temperature, thus the enteropancreatic
neuroendocrine system of Antarctic fish could show significant deviations
from that of other teleosts [18,19].
The Enteropancreatic Tract of Antarctic Notothenioid Teleosts
There are only few papers concerning the morphology and histology of
the digestive system in Antarctic teleosts. In these fish there is a
simplification of intestinal loops and a reduction of the number of pyloric
ceca. The intestinal wall is generally similar to that of other teleosts [2022] but the enteric submucous plexus seems to be reduced and is lacking
neuron cell bodies [23]. The pancreas is diffuse, as in most