1063-0740/04/3003- © 2004
Russian Journal of Marine Biology, Vol. 30, No. 3, 2004, pp. 209–213.
Original Russian Text Copyright © 2004 by Biologiya Morya, Chusovitina.
To date, it is generally accepted that nitric oxide,
produced continuously by speciﬁc enzymes, is a uni-
versal regulator of cellular and tissue metabolism . It
is reported to regulate the feeding function in mam-
mals, including humans, whose enteric nervous system
contains numerous nitroxidergic cells and ﬁbers .
The data available on the nitroxidergic innervation of
the ﬁsh digestive tract are scarce.
The present study deals with the distribution and
morphological peculiarities of nitroxidergic cells in the
digestive tract of the shishamo smelt
MATERIALS AND METHODS
Fish were caught in Amurskii Bay (Sea of Japan) in
August–October 2002 and were kept in aerated seawa-
ter aquaria for several days. When in the aquaria, the
ﬁsh were not fed. In all, 20 11- to 14.6-cm mature spec-
imens of either sex were used. The nitroxidergic ele-
ments were revealed in cryostat sections and whole
mounts as described by Hope and Vincent .
Portions of the esophagus, stomach, and upper and
rectal portions of the intestine 0.5 cm long were
obtained from 10 animals and were ﬁxed in 4%
paraformaldehyde solution on a 0.1-M phosphate
buffer (pH 7.2) at 4
C for 2 h. They were then washed
in 3–4 portions of 15% sucrose solution at the same
temperature for 20 h, frozen in cryostat. Then, longitu-
dinal and transverse sections 25 and 40
m thick were
prepared. The sections were thermostated in 0.5 mM
NADPH (Sigma), 0.5 mM nitro blue tetrazolium
(Sigma), and 0.3% Triton X-100 in 0.15 M tris-HCl
buffer (pH 8.0) at 37
C for 1 h. Nitro blue tetrazolium
is reduced by NADPH-diaphorase to diformazan pre-
cipitate, a topographical marker of NADPH-d–contain-
ing nerve cells. Ten digestive tract whole mounts were
prepared as follows: a portion of the digestive tract
from the esophagus to the anus was dissected, and the
esophagus, stomach, and intestine were separated and
stretched using glass sticks. They were then ﬁxed and
otherwise processed as above and were spread on
slides. All preparations were rapidly washed in distilled
water, dehydrated in ethanol series, and embedded in
dammar resin. The preparations were observed and
photographed using an Olympus BH-RFCA BHS
microscope. The spatial density of nitroxidergic cells
was measured in 1-cm
RESULTS AND DISCUSSION
Nitroxidergic nerve cells and ﬁbers were revealed in
all studied parts of the digestive tract (see table).
In the esophagus, a nitroxidergic plexus formed by
nerve ﬁber bundles, ganglia, and separate neurons was
revealed in the periphery of the circular muscle layer.
Nitroxidergic Innervation of the Digestive Tract of the Shishamo
S. V. Chusovitina
Institute of Marine Biology, Far East Division, Russian Academy of Sciences,
Vladivostok, 690041 Russia
Received October 20, 2003
—The distribution and morphology of nitroxidergic elements in the esophagus, stomach, and intestine
of the shishamo smelt
(Teleostei: Salmoniformes) were studied. Nitroxidergic cells and
ﬁbers were found in all examined parts of the digestive tract, occurring most frequently in the stomach and rec-
tal portion of the intestine. The spatial density of the nerve cells and ﬁbers was maximum in the myenteric
plexus and circular muscle layer and decreased in the longitudinal muscle layer and in the submucous plexus.
teleost ﬁsh, digestive tract, nitric oxide, enteric nervous system.
Spatial density of nitroxidergic nerve cells in the myenteric
plexus of the digestive tract of the shishamo smelt
Region of the digestive tract Number of cells per cm
Regions of the intestine: