IN-VIVO ELECTROPHYSIOLOGICAL MATURATION OF NEURONS DERIVED FROM A MULTIPOTENT PRECURSOR (EMBRYONAL CARCINOMA) CELL-LINE

The multipotent embryonal carcinoma (EC) P19 cell line differentiates into neurons, glia and smooth muscle following exposure to retinoic ac id (RA). RA-induced differentiation is irreversible and the neurons th at develop are abundant, post-mitotic, and survive for prolonged perio ds in culture or when grafted into the CNS of adult rats. Striatal sli ces containing grafted P19 cells were studied with intracellular recor ding and labelling techniques to examine the development of electrophy siological and morphological properties of P19-derived neurons over a period of 6 to 120 days after grafting into ibotenic acid lesioned str iatum. Cells from 1-week-old grafts had a range of immature electrophy siological characteristics including unstable resting membrane potenti als (RMP's) and very high membrane input resistances (Rin's). Many wer e not able to produce action potentials (AP's). In contrast, the major ity of cells recorded from 2- and 3-week-old grafts had stable RMP's, moderate Rin's, and were able to produce regenerative AP's. In grafts over 4 weeks of age, the majority of P19-derived neurons had mature ne uronal electrophysiological characteristics including RMP's of -60 mV, Rin's of 100-300 M Omega, and overshooting AP's. Morphologically, P19 derived neurons increase in soma size from 12-15 mu in diameter in 7- 14-day-old grafts, to 25-35 mu in diameter in grafts 50-120 days old. Developing neurons exhibited a variety of morphotypes with increasingl y complex processes and lengths of process extension. Our results demo nstrate a developmental progression of the electrophysiology of P19-de rived neurons, culminating in mature characteristics closely resemblin g those of adult rodent hippocampal or cortical pyramidal neurons. The ability to easily alter these cells genetically provides a powerful m odel for addressing issues specific to neuronal development.