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Neurobiology of Nutrition Laboratory, Pennington Biomedical Research Center, Louisiana State University, Baton Rouge, Louisiana 70808
To test the possible role of
N-methyl-D-aspartate
(NMDA) glutamate receptors in the transmission of gastrointestinal
satiety signals at the level of the nucleus of the solitary tract
(NTS), we assessed the effect of fourth ventricular infusion of the
noncompetitive NMDA receptor antagonist MK-801 on short-term sucrose
intake and on gastric distension-induced Fos expression in the dorsal
vagal complex of unanesthetized rats. MK-801, although not affecting initial rate of intake, significantly increased sucrose intake during
the later phase of the meal (10-30 min, 8.9 ± 1.0 vs. 2.9 ± 0.8 ml, P < 0.01). In the
medial subnucleus of the NTS, the area postrema, and the dorsal motor
nucleus, MK-801 did not reduce gastric distension-induced Fos
expression and itself did not significantly induce Fos expression. In
the dorsomedial, commissural, and gelatinosus subnuclei, MK-801 in
itself produced significant Fos expression and significantly reduced
(
75%, P < 0.05)
the ability of gastric distension to induce Fos expression, assuming an
additive model with two separate populations of neurons activated by
distension and the blocker. Although these results are consistent with
NMDA receptor-mediated glutamatergic transmission of vagal satiety signals in general, they lend limited support for such a role in the
transmission of specific gastric distension signals.
vagal afferents; nucleus of the solitary tract; medulla oblongata; glutamate receptor
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