ONTOGENY OF THE D1 DOPAMINE-RECEPTOR IN THE RAT STRIATONIGRAL SYSTEM - AN IMMUNOHISTOCHEMICAL STUDY

Antibodies were raised against a recombinant protein to analyse the pre- and postnatal ontogeny of the neurons expressing the D1 dopamine receptor in the striatum by immunohistochemistry. We report that D1 immunoreactivity is detectable from gestational day (G) 15 and is distributed homogeneously throughout the striatum from G15 to G18. From G19-20 to postnatal day (P) 3, D1 immunoreactivity becomes heterogeneous and predominates in cell bodies of the patch compartment while very limited immunoreactivity is detectable in the matricial compartment. The differential intensity between patches and matrix reaches its peak around PO, From P2, the pattern of D1 immunoreactivity progressively assumes the homogeneous distribution characteristic of the adult striatum. The expression of D1 mRNA in striatal neurons, as investigated by in situ hybridization, displays a similar pattern during this period, Substance P mRNA is also preferentially expressed in the patch compartment during the same period. D1 immunoreactivity appears at G17 in the substantia nigra as clusters of fibres and increases subsequently until reaching its adult form during the first postnatal week. These results demonstrate that the two compartments of the developing striatum display differential transcriptional and translational activity for the D1 gene and consequently two different and successive patterns of expression of D1 protein: patch neurons first express D1 receptor intensely while matrix neurons express it later and in smaller amounts so that D1 receptor appears transiently during the perinatal period as a marker of the patch compartment.