Basic Research for the role and mechanism of histamine in visual procession

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We investigated the changes of histamine receptors in the brains of rats after unilateral enucleation and monocular deprivation using quantitative autoradiography. The H3 receptor binding in the visually deprived superior colliculus (SO. Contralateral to the enucleated eye, was significantly increased 5, 15, 30 and 45 days after unilateral cnuclcation. Continuous injection of (S)-alpha-fluoronielhylhistidine. A specific inhibitor of l.-hislidine decarboxylase, and local injection of quinolinic acid attenuated the effect of unilateral enucleation in the SC. In infant rats, the H3 receptor binding in the visually deprived superior colliculus was significant!} increased after unilateral enucleation. Hut there were no effects of monocular deprivation on the receptor bindings. No significant changes in H1 and H2 receptor bindings were observed in the SC after unilateral enucleation and monocular deprivation. The [^<35>S]GTPγS-binding response was significantly increased in the contralateral SC in which H3 receptor binding response was enhanced. The increased [^<35>S]GTPγS signal was reversed with H_3-selective antagonists, whereas specific H_1 and H_2 antagonists were proved ineffective.These results suggest that retinal differentiation induced an increase in histamine H3 receptor binding sites, probably by selective adjustment of hislamine neurons in response to unilateral enucleation, and the tip-regulated H3 receptors caused by denervation were coupled with G proteins.