Changes in motor activities induced by microinjections of the selective dopamine agonists LY 171555, quinpirole hydrochloride, and SK&F 38393 into the habenula nucleus

The effects on behaviour of microinjections into the habenula complex of selective agonists for dopamine D-1 (SK&F 38393) and D-2 (LY 171555) receptors were documented in a holeboard, open-field test. The D-2 agonist reduced grooming responses, locomotor activity and rearing behaviour. In contrast, the D-1 agonist increased rearing and locomotor activity but was without effect on grooming responses. Neither drug produced significant effects on inspective hole exploration. The data extend findings of behavioural consequences of central D-1 receptor activation and provide direct evidence in support of the functional and behavioural importance of intrahabenular dopamine receptor sites. The findings are consistent with suggestions for feedback regulation of habenular efferents to midbrain dopaminergic neurons. Effects of both receptor agonists on some responses but not others indicates potential complex interactions between D-1 and D-2 receptors within the habenula.