Developmental expression of proenkephalin mRNA and peptides in rat striatum.

The development of proenkephalin (PE) gene expression in the rat striatum was examined at the mRNA and peptide levels. Immunocytochemistry was performed with antisera generated to the PE-specific peptide product Met-enkephalin-Arg-Gly-Leu (MERGL). The distribution of immunostaining was compared with the distribution of PE mRNA, determined by in situ hybridization with an oligonucleotide probe. PE mRNA first appeared at E16 in the caudal ventrolateral striatum, followed at E17-18 by the appearance of MERGL immunoreactivity in a similar distribution. The anatomical gradients of PE gene expression were similar to the pattern of histogenesis of striatal neurons, suggesting that the timing of PE gene expression is related to the time of neuronal withdrawal from the mitotic cycle. The relation of the development of PE gene expression to the known patterns of striatal histogenesis, neurochemical compartmentalization and dopaminergic innervation is discussed.