Regional distribution of histamine and tele-methylhistamine in the rat, mouse and guinea-pig brain.

Regional histamine (HA) and tele-methylhistamine (t-MH) contents were determined in the rat, mouse and guinea-pig brain. The highest HA and t-MH levels were found in the hypothalamus of all species. Fairly high t-MH levels were observed in the amygdala of all species and in the guinea-pig hippocampus. The t-MH/HA ratio was higher in the regions of the telencephalon than in the diencephalon and brainstem. The cerebellum and spinal cord showed extremely low t-MH/HA ratios. These results suggest higher histaminergic neuronal activities in the hypothalamus and some regions of the telencephalon than in other parts of the brain.