Histamine in brain may have no role for histaminergic control of food-related drinking in the rat.

Adult male Sprague-Dawley rats surgically fitted with a cannula positioned in the third cerebral ventricle were tested for drinking after exogenous histamine or after eating with or without antagonism of H1 and/or H2 receptors for histamine using intracerebroventricular (ICV) dexbrompheniramine (DXB; 12.5-50 micrograms) or cimetidine (C; 25-100 micrograms). Histamine (0.06-16 micrograms) given ICV failed to elicit drinking. For rats drinking in response to subcutaneous (SC) histamine, ICV DXB alone did not affect drinking, whereas ICV DXB plus C, and ICV C given alone inhibited drinking. Such inhibition appeared to be relatively selective for drinking elicited by SC histamine, because ICV 50 micrograms DXB plus 100 micrograms C abolished drinking elicited by SC histamine, but failed to inhibit drinking after 12-hr water deprivation. When rats ate and drank after food deprivation, ICV DXB alone and ICV DXB plus C did not significantly inhibit food-related water intake. The inhibition of food-related drinking by ICV 100 micrograms C given alone was accompanied by inhibition of eating. In summary, histamine had unimpressive dipsogenic effects when given ICV, ICV DXB and C inhibited drinking elicited by SC histamine, but ICV DXB and C failed to inhibit food-related drinking in a manner parallel to the selective effects of intraperitoneal injection of these drugs on drinking elicited by eating. This suggests that it is histamine and histamine receptors in the periphery rather than in brain that have the predominant role for a histaminergic mechanism for drinking elicited by eating in the rat, but our findings do not rule out a role(s) for histamine in brain in the control of ingestive behavior.