Peripherally and centrally administered bombesin induce Fos-like immunoreactivity in different brain regions in rats

Bombesin (BBS) suppresses food intake when administered either peripherally or centrally to rats, but the brain systems involved in the anorectic action remain unclear. We addressed this question by examining Fos-like immunoreactivity (Fos-IR), a marker of neuronal activation, in rat brain following either intraperitoneal (i.p.) or 4th cerebroventricular (4V) administration of BBS. It was found that the hypothalamic paraventricular nucleus showed strong Fos-IR following either i.p. BBS in the dose range 20-80 micrograms/kg, or 4V BBS at a dose of 60 ng/rat. Additionally, different effects of i.p. and 4V BBS were observed in the following regions: (1) a strong Fos-IR was seen in the area postrema (caudal part) only following i.p. but not 4V BBS; (2) while i.p. BBS-induced Fos-IR was almost evenly distributed throughout the medial subdivision of the nucleus of the solitary tract, 4V BBS-induced Fos-IR was much stronger in the rostral part than in the caudal part of this region; (3) although the lateral parabrachial nucleus, the central nucleus of the amygdala and the bed nucleus of the stria terminalis showed strong Fos-IR following both i.p. and 4V BBS, subregional distribution of the Fos-IR was not the same. These sites were previously found to show strong Fos-IR after administration of either cholecystokinin (CCK) or dexfenfluramine (DF), but with different subregional distribution. The Fos-IR pattern induced by i.p. BBS was similar to that induced by CCK, and the Fos-IR pattern induced by 4V BBS was similar to that induced by DF.