Histamine in the insect nervous system: distribution, synthesis and metabolism.

The distribution of histamine in the nervous systems of the locust, the cockroach, and the sphinx moth was mapped and the capacity of locust nervous tissue to synthesise and metabolise histamine was assessed. In all three species the highest levels of histamine were present in the retina and in the lamina neuropil of the optic lobe. Lower levels of histamine were detectable throughout the nervous system. In the locust the retina was shown to synthesise considerable quantities of histamine. The optic lobe and metathoracic ganglion synthesised smaller, though significant, amounts of histamine. Metabolic inactivation of histamine in locust nervous tissue was shown to occur primarily via oxidation to imidazole-4-acetic acid and via N-acetylation to N-acetyl histamine. Whereas the retina and the optic lobe formed the two metabolic products in approximately equal proportions, the metathoracic ganglion produced almost three times as much N-acetyl histamine as imidazole-4-acetic acid.