Lateral parabrachial subnucleus lesions abolish feeding induced by mercaptoacetate but not by 2-deoxy-D-glucose

Lesions of the area postrema/nucleus of the solitary tract (AP/NTS) region abolish feeding induced by mercaptoacetate (MA) and 2-deoxy-D-glucose (2DG), metabolic inhibitors that selectively impair fatty acid and glucose utilization, respectively. Because the AP/NTS region is important for both MA- and 2DG-induced feeding, the present experiment investigated the involvement of the lateral parabrachial nucleus (1PBN), which is innervated by AP/NTS neurons, in these feeding responses. Electrolytic and ibotenic acid lesions were directed at the entire parabrachial nucleus or at specific lateral parabrachial subnuclei. Rats with electrolytic lesions were tested for feeding in response to 0.9% NaCl (subcutaneous or intraperitoneal), MA (400, 600, and 800 mumol/kg ip), and 2DG (100 and 200 mg/kg sc). Ibotenate-lesioned rats were tested with NaCl and MA only. Lesions were verified either by cresyl violet staining or by glial fibrillary acidic protein immunohistochemistry. Bilateral destruction of the 1PBN severely impaired or abolished MA-induced feeding. Cell bodies important for MA-induced feeding appear to be localized in the dorsal-central 1PBN subnuclear area, because both electrolytic and cytotoxin microlesions centered in this area abolished feeding in response to MA. Fibers of passage important for MA-induced feeding appear to pass through the external and superior 1PBN because electrolytic but not cytotoxin lesions of these subnuclei disrupted the feeding response. In contrast, 2DG-induced feeding did not differ significantly from sham-lesioned controls in any of the 1PBN lesion groups. These results indicate that 2DG and MA stimulate feeding by activating separate central neural pathways and, perhaps, distinct metabolic controls of food intake.