A PHYSIOLOGICAL-ROLE OF BRAIN HISTAMINE DURING ENERGY DEFICIENCY

Histaminergic activation in the rat hypothalamus was investigated unde r a deficit in energy supply. Easting of rats for 24 h increased hypot halamic histamine (HA) content. Intraperitoneal (IF) injection of insu lin (2 U/kg) increased pargyline-induced accumulation of tele-methylhi stamine (t-MH) leaving steady-state HA and t-MH levels unaffected, whi ch implies enhancement of HA turnover rate. The insulin infusion induc ed hypoglycemia both in rats with and without pargyline pretreatment. Infusion of 2-deoxy-D-glucose (2-DG) into the third cerebroventricle a lso produced an increase in pargyline-induced accumulation of t-MH and no change in steady-state HA and t-MH levels. The 2-DG infusion induc ed hyperglycemia. Hypothalamic glycogen content decreased after 24 h s tarvation, but this decrease was prevented by depletion of HA by alpha -fluoromethylhistidine. Absolute glycogen contents in the cortex were lower than those in the hypothalamus, and were not affected by fasting or depletion of HA. The results indicate that activation of hypothala mic HA in response to glucoprivation may modulate homeostatic control of energy supply in the brain.