Lesions of the dorsal vagal complex abolish increases in meal size induced by NMDA receptor blockade

Rats increase meal size and duration after intraperitoneal injection of MK-801, a non-competitive N-methyl- d-aspartate (NMDA) receptor antagonist. This effect depends upon intact vagal fibers, since the antagonist does not increase intake when visceral afferent and efferent pathways have been interrupted by bilateral subdiaphragmatic vagotomy. NMDA receptors have been demonstrated on vagal afferent fibers and on second-order neurons in the medial subnucleus of the solitary tract (NTS), the area postrema (AP), and the dorsal motor nucleus of the vagus. To determine whether neurons in these structures are crucial for NMDA receptor effects on feeding, we examined the effect of MK-801 on intake of 15% sucrose in rats with aspiration lesions of the AP and adjacent NTS. MK-801 (100 μg/kg, i.p.) significantly increased sucrose intake in these lesioned rats compared to sham-lesioned rats (32.3±0.1 ml versus 23.3±0.1 ml, P