Transient cyclic AMP accumulation mediated by dopamine D1 receptors in the chick embryo optic lobe

Late developmental expression of DARPP-32 in the chick optic tectum

Immunohistochemical techniques reveal that the dopamine- and cAMP-regulated phosphoprotein DARPP-32 is detectable in neurons of the chick optic tectum starting on embryonic day 13. The expression levels then increase steadily from embryonic day 15 through the first posthatching day. After 15 days posthatching, expression of DARPP-32 reaches the adult pattern, with many labeled cells in tectal layers 11 and 12. These cells exhibit a bipolar shape, with long processes directed both to the deep and superficial layers. These results suggest that DARPP-32 is present in specific neuronal populations of the chick tectum and that this protein may not have a function in early ontogenetic processes.

Development of dopamine receptors in the forebrain of the domestic chick in relation to auditory imprinting. An autoradiographic study

The rostro-medial neostriatum/hyperstriatum ventrale (MNH) and the neostriatum dorsocaudale (Ndc) are forebrain regions which play a role in auditory filial imprinting. Both regions receive a distinct dopaminergic input from the mesencephalon and we were interested to investigate if the dopaminergic system, which is known to play a role in associative learning processes and neuronal plasticity is involved in auditory imprinting. Using ligand autoradiography we studied the distribution and density of dopamine receptors (D1 and D2 type) in the forebrain of socially isolated chicks during the first postnatal week and compared these data with the values of age-matched imprinted chicks. D1- and D2-receptors were present in the chick forebrain on the day of hatching and they showed in general, the same distribution until postnatal day 7. Between days 0 and 2 the D2-receptor density increased significantly in the lobus parolfactorius and paleostriatum augmentatum while for D1-receptor density no significant changes were detectable. The receptor densities in the investigated forebrain regions did not differ significantly between imprinted and control chicks. These results suggest that auditory imprinting does not induce alterations of dopamine receptor density, however, more subtle changes can not be excluded. The presented detailed data about the developmental profile of dopamine receptors within distinct brain regions is a further step towards a more specific interpretation of behavioral effects of dopamine receptor agonists or antagonists at different postnatal ages.

The dopamine D1D receptor. Cloning and characterization of three pharmacologically distinct D1-like receptors from Gallus domesticus

Three genomic clones encoding dopamine D1-like receptors were isolated from the avian species Gallus domesticus. Two of these genes encode proteins of 451 and 488 amino acids, which, based on deduced amino acid sequence identity and homology of exhibited pharmacological profiles, appear to be species homologs of mammalian and vertebrate D1/D1A and D5/D1B receptors, respectively. The third genomic clone, termed D1D, encodes a protein of 445 amino acids displaying a deduced amino acid sequence identity within putative transmembrane domains of 75% to mammalian D1/D1A and 77% to D5/D1B receptors with overall sequence homologies of only 49% and 46%, respectively. Membranes from COS-7 cells transfected with D1D DNA bound [3H]SCH-23390 in a saturable manner with high affinity (approximately 300 pM) and with a pharmacological profile clearly indicative of a dopamine D1-like receptor. The D1D receptor exhibited affinities for 6,7-dihydroxy-2-aminotetralin and dopamine 10-fold higher than D1/D1A receptors, characteristic of the D5/D1B receptor subfamily. In contrast, the D1D receptor bound dopaminergic agents, such as SKF-38393, apomorphine, pergolide, and lisuride, with affinities 10-fold higher than other cloned mammalian or vertebrate D1A/D1B receptor subtypes, while both clozapine and haloperidol displayed considerably lower affinity for the D1D receptor. Based on the low overall amino acid sequence identity (54%) and unique pharmacological profile, the avian dopamine D1D receptor does not appear to be a species homolog of the recently cloned vertebrate D1C receptor (Sugamori, K.S., Demchyshyn, L. L., Chung, M., and Niznik, H. B. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 10536-10540). As with all cloned mammalian and vertebrate D1-like receptors, the D1D receptor stimulates adenylate cyclase activity in the presence of dopamine or SKF-82526. Northern blot analysis reveals the selective expression of both avian D1D and D1A receptor mRNAs only in brain with the D1B receptor more widely distributed and localized in tissues such as brain, kidney, and spleen. The isolation of four distinct vertebrate dopamine D1 receptor subtypes suggests the existence of additional mammalian D1 like receptor genes that may account for the observed pharmacological and biochemical multiplicity of dopamine D1-like receptor mediated events.