Abstract
Expression of a D1 dopamine receptor was examined in the rat brain by using a combination of in situ hybridization and in vitro receptor autoradiography. Cells expressing D1 receptor mRNA were localized to many, but not all, brain regions receiving dopaminergic innervation. The highest levels of hybridization were detected in the caudate-putamen, nucleus accumbens, and olfactory tubercle. Cells expressing D1 receptor mRNA were also detected throughout the cerebral cortex, limbic system, hypothalamus, and thalamus. D1 receptor mRNA was differentially expressed in distinct regions of the hippocampal formation. Dentate granule cells were labeled in dorsal but not ventral regions, whereas the subicular complex was prominently labeled in ventral but not dorsal regions. Intermediate to high levels of D1 binding sites, but no hybridizing D1 receptor mRNA, were detected in the substantia nigra pars reticulata, globus pallidus, entopeduncular nucleus, and subthalamic nucleus. In these brain regions, which are involved in the efferent flow of information from the basal ganglia, D1 receptors may be localized on afferent nerve terminals originating in other brain regions. These results indicate that in addition to a role in control of motor function, the D1 receptor may also participate in the cognitive, affective, and neuroendocrine effects of dopaminergic neurotransmission.