Localization of dopamine D1A and D1B receptor mRNAs in the forebrain and midbrain of the domestic chick.

The distribution and cellular localization of dopamine D1A and D1B receptor mRNAs in the forebrain and midbrain of the domestic chick were examined using in situ hybridization histochemistry with 35[S]-dATP labeled oligonucleotide probes, visualized with film and emulsion autoradiography. Labeling for D1A receptor mRNA was intense in the medial and lateral striatum, and moderately abundant in the pallial regions termed the archistriatum and the neostriatum, in the hypothalamic paraventricular nucleus region, and in the superficial gray layer of optic tectum of the midbrain. D1B receptor mRNA was abundant in the medial and lateral striatum, and in the pallial region termed the hyperstriatum ventrale, and moderately abundant in the intralaminar dorsal and posterior thalamus and in the superficial gray of the optic tectum. At the cellular level, about 75% of neurons in the medial striatum and 59% of neurons in the lateral striatum were labeled for D1A receptor mRNA, whereas about 39% of the neurons in the medial striatum and 21% in the lateral striatum were labeled for D1B receptor mRNA. Large striatal neurons were not labeled for D1A or D1B receptor mRNA. The data suggest that while both D1A and D1B receptors mediate dopaminergic responses in many neurons of the avian striatum, primarily D1A receptors mediate dopaminergic responses in the archistriatum and the neostriatum, while primarily D1B receptors mediate dopaminergic responses in the hyperstriatum ventrale and the thalamus.