DMV extrasynaptic NMDA receptors regulate caloric intake in rats
Courtney Clyburn, R. Alberto Travagli, Amy C. Arnold, Kirsteen N. Browning
Courtney Clyburn, R. Alberto Travagli, Amy C. Arnold, Kirsteen N. Browning
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Research Article Gastroenterology Neuroscience

DMV extrasynaptic NMDA receptors regulate caloric intake in rats

Abstract

Acute high-fat diet (aHFD) exposure induces a brief period of hyperphagia before caloric balance is restored. Previous studies have demonstrated that this period of regulation is associated with activation of synaptic N-methyl-D-aspartate (NMDA) receptors on dorsal motor nucleus of the vagus (DMV) neurons, which increases vagal control of gastric functions. Our aim was to test the hypothesis that activation of DMV synaptic NMDA receptors occurs subsequent to activation of extrasynaptic NMDA receptors. Sprague-Dawley rats were fed a control or high-fat diet for 3–5 days prior to experimentation. Whole-cell patch-clamp recordings from gastric-projecting DMV neurons; in vivo recordings of gastric motility, tone, compliance, and emptying; and food intake studies were used to assess the effects of NMDA receptor antagonism on caloric regulation. After aHFD exposure, inhibition of extrasynaptic NMDA receptors prevented the synaptic NMDA receptor–mediated increase in glutamatergic transmission to DMV neurons, as well as the increase in gastric tone and motility, while chronic extrasynaptic NMDA receptor inhibition attenuated the regulation of caloric intake. After aHFD exposure, the regulation of food intake involved synaptic NMDA receptor–mediated currents, which occurred in response to extrasynaptic NMDA receptor activation. Understanding these events may provide a mechanistic basis for hyperphagia and may identify novel therapeutic targets for the treatment of obesity.

Authors

Courtney Clyburn, R. Alberto Travagli, Amy C. Arnold, Kirsteen N. Browning

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Figure 4

siRNA-mediated knockdown of GRIN2B prevents the activation of synaptic NMDARs.

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siRNA-mediated knockdown of GRIN2B prevents the activation of synaptic N...
(A) Representative traces from gastric-projecting aHFD DMV neurons after microinjection of siRNA targeted against GRIN2B (red, upper) or scrambled RNA controls (black, lower). Neurons were current-clamped at a potential that allowed action potential firing of approximately 1 Hz. Perfusion with AP5 (25 μM) had no effect on action potential firing rate in siRNA rats, but decreased action potential firing rate in scrambled RNA rats. (B) Graphical summary of the effects of AP5 on action potential firing GRIN2B siRNA rats (red; n = 7 cells, 3 rats) and scrambled RNA rats (black; n = 6 cells, 3 rats) after aHFD exposure. Neurons were current-clamped at a potential that allowed for action potential firing of approximately 1 Hz. AP5 had no effect on action potential firing rate in siRNA rats (red; left), but decreased action potential firing rate in scrambled RNA rats. *P < 0.05 versus baseline (Student’s paired t test). (C) Six overlapping consecutive traces from gastric-projecting aHFD DMV neurons voltage-clamped at –50mV illustrating mEPSCs in siRNA (red, upper) or scrambled RNA (black, lower) microinjected rats. Perfusion with AP5 (25 μM) decreased mEPSC frequency in scrambled but not siRNA rats. (D) Graphical summary of the effects of AP5 on mEPSC frequency in siRNA and scrambled RNA rats. AP5 had no effect on mEPSC frequency in siRNA rats (red, left), even after perfusion with DHK (red open, middle). Conversely, AP5 decreased mEPSC frequency in scrambled RNA rats (black, right). *P < 0.05 versus baseline (1-way ANOVA followed by post hoc Dunnett’s multiple-comparison test). (E) Graphical summary of GRIN2B gene expression measured by qPCR in the DMV (left) and hypoglossus (right; control region) in aHFD rats microinjected with siRNA (n = 4 rats) or scrambled RNA (n = 5 rats). Each experiment had 2 replicates. The siRNA injection reduced GRIN2B mRNA by approximately 60% in the DMV with no effect in hypoglossus. Data were normalized to β-actin and expressed as fold change using the 2–ΔΔCT method. *P < 0.05 versus scrambled RNA (Student’s unpaired t test).