Effects of histamine H-3-ligands on the levodopa-induced turning behavior of hemiparkinsonian rats

Histamine H-3-receptors act as heteroreceptors on many neurons. The effects of H-3-ligands (an agonist, R-alpha-methylhistamine and an antagonist, thi operamide) on levodopa-induced turning behavior in a rat model of Parkinson 's disease were quite similar to those seen with alpha(2)-adrenoceptor liga nds (dexmedetomidine and atipamezole). R-alpha-methylhistamine clearly redu ced contralateral turning behavior but the increase of turning behavior aft er thioperamide was less clear. The lack of effect of H-3-ligands, in contr ast to alpha(2)-ligands, on the amphetamine induced ipsilateral turning beh avior points to different roles or neuronal distribution of these two presy naptic receptors. We propose that in this lesion model, H-3-receptors modif y those pathways participating striatal outflow. (C) 2000 Elsevier Science Ltd. All rights reserved.