Increased investigative activity after presynaptic dopaminergic stimulation measured by a fixed-interval recording...

A fixed-interval recording procedure was used to study the effects of catecholaminergic agonists and antagonists on the exploratory behaviour pattern in male rats. One particular element of this pattern, the investigative behaviour, was found to be sensitive to drugs acting on both noradrenaline and dopamine receptors. An increase in investigative activity (IA) and a slight decrease in the other exploratory (OE) activity was caused by alpha-methyl-p-tyrosine. The alpha 2-receptor agonists clonidine and B-HT 933 decreased both the IA and the OE activity. These effects were counteracted by yohimbine. Activation of presynaptic dopamine receptors by low doses of apomorphine (less than or equal to 0.2 mg/kg) and B-HT 920 resulted in significant increase in IA and a decrease in OE activity. Higher doses of apomorphine (0.7 and 1.0 mg/kg) decreased or abolished IA but increased OE activity. We assume this effect to be due to postsynaptic receptor stimulation. Pretreatment with haloperidol counteracted the effects of apomorphine and B-HT 920. An increase in IA is probably due to a decrease in dopaminergic activity, which can be induced by presynaptic receptor activation. The decrease in IA after presynaptic noradrenergic stimulation cannot at present, however, be related to a specific influence, since the possibility of general effects on locomotion cannot be ruled out. The increase in IA observed after presynaptic dopaminergic activation and the fixed-interval recording procedure may be valuable instruments in the search for selectively acting compounds with dopaminergic activity.