Chronic bombesin treatment increased the [³H]spiperone binding, glutamate decarboxylase and choline acetyltransferase activity in the rat brain

The effects of chronic bombesin (BBS) on [³H]spiperone (SPD) binding activity, choline acetyltransferase (ChAT), acetylcholinesterase (AChE) and glutamate decarboxylase (GAD) were investigated in the rat brain corpus striatum (CS). The chronic i.p. administration of BBS to rats increased: (1) the specific [³H]SPD binding to the striatal P_m (plasma membrane) 16%, P < 0.03 and 34%, P < 0.008 at 5 μg/kg and 10 μg/kg respectively), (2) the specific GAD activity in the CS by 52% (5 μg/kg, n.s.) and 46% (10 μg/kg, P<0.05) respectively, (3) the specific ChAT activity in the CS by 54% (10 μg/kg, P < 0.002) and (4) the specific AChE activity by 23% (10 μg/kg, P < 0.02) after 14 days. It increased only: (1) the specific [³H]SPD binding by 29% (P < 0.001, at 10μg/kg) and (2) the specific GAD activity by 23% (P < 0.015, 10 μg/kg), after 7 days. Neither ChAT nor AChE activity was affected after 7 days treatment of BBS at 10 μg/kg. In vitro study showed that BBS at 0.2μM did not affect any of the neurochemical parameters examined in the CS. Thus, the changes in brain chemistry caused by chronic BBS were not due to direct effects of BBS but may be mediated through its metabolites or CCK release. Data indicate that the central effects of peripherally administered BBS are dependent on both the duration and the dosage of the drug treatment and that the dopaminergic and GABAergic systems seem to be more vulnerable to chronic BBS than the cholinergic system in the rat brain CS. Results suggest that BBS may play a role in regulating the dopaminergic, GABAergic and cholinergic systems in the brain.