Expression of phenylethanolamine N-methyltransferase (PNMT) and neuropeptide Y (NPY) in embryonic rat medulla oblongata grown in Oculo

Expression and development of specific markers of the adrenergic phenotype were studied in central neurons grown in transplant system. Medulla oblongata from embryonic day 12.5 (E12.5) or E18 rat was grafted into the anterior chamber of the eye of adult rat hosts. After two months, grafts were examined for the presence of immunoreactivity (IR) and catalytic activity to the epinephrine-synthesizing enzyme, phenylethanolamine N-methyltransferase (PNMT, E.C. 2.1.1.28), a specific adrenergic marker. In addition, grafts were examined for immunoreactivity to neuropeptide Y (NPY) and tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine synthesis. In E12.5 grafts, PNMT was expressed de novo, enzyme activity developed to levels similar to those in adult rat brainstem and PNMT-IR neurons were observed. TH-IR and NPY-IR neurons were also observed. In contrast, PNMT-IR was not observed in E18 grafts even though these already contained PNMT-IR neurons at the time of grafting. This was not due to poor growth of E18 grafts, in general, since TH-IR neurons were present and the protein content of the grafts was similar to that of E12.5 grafts. These studies suggest that adrenergic neurons survive well in oculo if they are transplanted prior to the age when neuroblasts have initially expressed the adrenergic phenotype, migrated to their final positions and elaborated processes. In addition, these studies establish a transplant system in which factors required for the development of central adrenergic neurons can be more easily studied than in situ.