Dual roles in feeding for AMPA/kainate receptors: receptor activation or inactivation within distinct hypothalamic regions elicits feeding behavior.

We have previously shown that hypothalamic injections of glutamate, or agonists of its ionotropic receptors (iGluRs), elicit intense feeding responses in satiated rats [Brain Res. 613 (1993) 88, Brain Res. 630 (1993) 41]. While attempting to clarify the role of the AMPA and kainate (KA) receptor subtypes in glutamatergic feeding systems, we discovered that lateral hypothalamic (LH) injection of high doses of the competitive AMPA/KA receptor antagonist, NBQX (10 and 30 nmol), elicited a pronounced feeding response. We questioned whether this effect was due to inactivation of AMPA or possibly KA receptors. To determine whether other AMPA/KA antagonists can also elicit feeding, we tested whether injection of CNQX, another AMPA/KA receptor antagonist, also stimulates eating and whether these feeding stimulatory effects were due to antagonists' actions in the LH or in other hypothalamic sites. Here we report that NBQX and CNQX elicit feeding in a dose dependent manner and are most effective when injected into the perifornical hypothalamus (PFH), or into the paraventricular nucleus (PVN) and, to a lesser extent, into the LH of satiated rats. In contrast, AMPA was most effective in stimulating feeding when injected into the LH, confirming previous reports. These data suggest that either activation or inactivation of AMPA/KA receptors in distinct but overlapping hypothalamic sites may be sufficient to induce feeding behavior, indicating a broadened role for glutamate in hypothalamic feeding mechanisms.