Manipulation of central nervous system histamine or histaminergic receptors (H1) affects food intake in rats

The reported studies were designed to examine relationships between central nervous system histamine, histaminergic receptors (H1) and food intake in rats. The hypothesis being tested was as follows: "One component of the neuroregulation of food intake involves histaminergic activity in the hypothalamus as influenced by variation of histamine levels and/or H1 receptor concentrations." We performed combinations of dietary, surgical and pharmacological treatments on male or female rats. We fed groups of male or female rats diets containing either 4 g casein/100 g diet (low protein diet) or 25 q casein/100 g diet (normal protein). Rats with surgical ablation of the paraventricular nucleus did not decrease food intake when fed the low protein diet, whereas adrenalectomized rats did. Increasing central histamine levels decreased food intake, whereas decreasing central histamine increased food intake. Rats injected with histaminergic (H1) antagonists lost the ability to detect low protein diet in short-term experiments and had improved efficiency of weight gain. Rats that were fed the low protein diet or pair-fed the normal protein diet had greater H1 receptor concentrations in whole brain preparations when compared with rats fed the normal protein diet. No differences were noted due to gender. Thus, manipulation of histamine levels affected food intake as hypothesized, i.e., increasing central histamine decreased food in rats fed the normal protein diet, whereas decreasing central histamine or blockade of H1 receptors increased food intake in rats fed the low protein diet.