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Evidence suggesting the neurotransmitter glutamate acts at selective receptor subtypes to elicit feeding during sensory specific satiety, an animal model of overeating.

Many behavioral and physiological factors regulating overeating and obesity have not been elucidated. A leading contributor in the epidemic rise in obesity in the U.S. is thought to be the availability of a large variety of highly palatable foods. An animal model of overeating, sensory specific satiety (SSS), demonstrates that a rat fed to satiety on one food will eat more when offered a second meal consisting of a different, more palatable food. Although numerous brain areas are known to regulate feeding behavior, the lateral hypothalamus (LH) may play a key role in regulating overeating during SSS (Rolls et al, Brain Research, 1986). Studies from our lab suggest that the neurotransmitter glutamate acts at LH NMDA receptors to initiate overeating. Here, we questioned whether glutamate acts selectively at NMDA receptors to elicit feeding or whether it also acts at the AMPA receptor subtype. We hypothesized that overeating will be suppressed with an LH injection of GYKI 52466, an AMPA receptor antagonist. Cannulas were implanted into the rats' LH via stereotaxic surgery (N=10). Once fed to satiety on chow, 0.3[micro]L of GYKI 52466 [doses = 0 (control) & 10 nmol, counterbalanced] were injected into the LH, and the rats were offered chow or Kellogg's Froot Loops[R]. Cumulative food intake (g) was recorded and analyzed. Under control conditions, rats exhibited SSS and ate significantly more Froot Loops[R] (3.3 +/- 0.4 g) than chow (0.7 +/-0.4 g) during the second meal (p<0.001, by ANOVA and Student Newman Keuls). Injection of GYKI 52466 did not decrease intake of Froot Loops[R]. Thus, SSS was observed again in the experimental condition with Froot Loops[R] and chow intakes of 2.8 +/- 0.44 g &. 0.41 +/-0.44 g, respectively (p=0.002). Although GYKI 52466 did not inhibit SSS as expected, these data support our previously mentioned studies on NMDA receptors and suggest that glutamate may be acting selectively at this receptor subtype to regulate overeating.
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Author:Henry, J.M.; Davis, G.R.; Hettes, S.R.
Publication:Bulletin of the South Carolina Academy of Science
Date:Jan 1, 2005
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