Decreased locomotor and investigatory exploration after denervation of catecholamine terminal fields in the forebrain of rats.

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Abstract
Exploratory behaviors were examined after bilateral microinjections of 6-hydroxydopamine into 2 hypothalamic sites that produced different patterns of denervation of forebrain catecholamine terminal fields. After anterolateral injections rats locomoted and reared less in a novel open field, responded abnormally to changes in the degree of novelty of the open field, and investigated a novel object less. These were deficits in exploratory behavior because they were not secondary to the inhibition of open-field behavior by hyperemotionality, by general motor disability, or by the failure to detect novel spaces or objects. Such anterolateral injections produced loss of catecholamine fibers, determined histochemically, in neocortical, hippocampal, anterolateral hypothalamic, mesolimbic, mesocortical and anteromedioventral striatal terminal fields and loss of dopaminergic perikarya in the A10 and anteromedial A9 cell groups. No deficits in exploratory behaviors occurred after bilateral anteromedial 6-hydroxydopamine injections that denervated neocortical, hippocampal and anteromedial hypothalamic catecholamine terminal fields. A critical forebrain catecholaminergic innervation for exploratory responses to novel stimuli may be within areas that were denervated by anterolateral but not by anteromedial hypothalamic 6-hydroxydopamine injections. These areas were mesolimbic, mesocortical, anteromedioventral and anterolateral hypothalamic terminal fields.