MANIPULATION OF CENTRAL-NERVOUS-SYSTEM HISTAMINE OR HISTAMINERGIC RECEPTORS (H-1) AFFECTS FOOD-INTAKE IN RATS

The reported studies were designed to examine relationships between ce ntral nervous system histamine, histaminergic receptors (H-1) and food intake in rats. The hypothesis being tested was as follows: ''One com ponent of the neuroregulation of food intake involves histaminergic ac tivity in the hypothalamus as influenced by variation of histamine lev els and/or H-1 receptor concentrations.'' We performed combinations of dietary, surgical and pharmacological treatments on male or female ra ts. We fed groups of male or female rats diets containing either 4 g c asein/100 g diet (low protein diet) or 25 g casein/100 g diet (normal protein). Rats with surgical ablation of the paraventricular nucleus d id not decrease food intake when fed the low protein diet, whereas adr enalectomized rats did. Increasing central histamine levels decreased food intake, whereas decreasing central histamine increased food intak e. Rats injected with histaminergic (H-1) 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 H-1 receptor concentrati ons in whole brain preparations when compared with rats fed the normal protein diet. No differences were noted due to gender. Thus, manipula tion of histamine levels affected food intake as hypothesized, i.e., i ncreasing central histamine decreased food in rats fed the normal prot ein diet, whereas decreasing central histamine or blockade of H-1 rece ptors increased food intake in rats fed the low protein diet.