DARPP-32 development in the caudate nucleus is independent of afferent input from the substantia nigra

DARPP-32, a dopamine- and adenosine 3′:5′-monophosphate regulated neuronal phosphoprotein, M_r 32 kDa, is a phenotypic marker of the medium-size spiny neurons of the mammalian caudate-putamen. In the present study, we examined the ontogeny of DARPP-32 protein and mRNA, and compared it to the ontogeny of tyrosine hydroxylase and synapsin I, a synaptic-vesicle phosphoprotein. In vivo, the amount of DARPP-32 protein per mg total protein increased throughout the first three postnatal weeks, and then declined to plateau at adult levels. The mRNA level closely paralleled the protein, except that its rise preceded that of the protein. Tyrosine hydroxylase levels rose throughout the first 4 postnatal weeks, and synapsin I levels rose steadily during the same period. Primary reaggregate cultures containing cells from the caudate-putamen expressed DARPP-32 with a time course similar to that seen in vivo. The level of expression was not altered by coculturing with dopaminergic neurons from the rostral mesencephalic tegmentum. Thus, the postnatal increase in DARPP-32 levels in the caudate-putamen appears to be independent of transsynaptic or end-organ influences from the substantia nigra.