Neuron-enriched cultures derived from spinal cord of 10-day-old chick embryos: Influence of neuropeptides on neuronal survival, proliferation and cholinergic expression

Abstract

The developmental regulation of cell proliferation, survival and cholinergic expression by growth hormone-releasing hormone (GHRH) and somatostatin (SRIF) was investigated in neuronenriched cultures derived from 10-day-old embryonic chick spinal cord. In this study, 3H-thymidine incorporation into DNA was assessed, using two different applications, in order to determine both cellular proliferation and survival. The rate of neuroblast proliferation in both control and neuropeptide-treated cultures increased or remained the same up to day 6. However, in neuropeptide-treated cultures the magnitude of cell proliferation remained at levels higher than those observed in controls through day 6 and was most significant in SRIF-treated cultures at C4. In all groups, proliferation markedly declined by day 8. Survival of neuronal cells labelled at C4 remained high up to day 12 in all three groups, then drastically declined by day 17. Neuronal survival in the neuropeptide-treated cultures was also higher than in controls. Cholinergic expression, as assessed by activity of choline acetyltransferase (ChAT), responded differentially to neuropeptide treatment. Cultures treated with GHRH (100 nM) exhibited a long term significant enhancement in ChAT activity throughout the culture period, whereas those treated with SRIF (50 nM) expressed a transient decline in ChAT activity. Videometric analysis showed that both neuropeptides enhanced neuronal aggregation, neuritic arborization and neuritic length. These findings lead us to suggest that GHRH and SRIF may provide neurotrophic signals important not only for neuronal proliferation and survival but also for cholinergic neuronal expression. Furthermore, we propose that GHRH possesses specific cholinotrophic properties, whereas SRIF may act as a general neurotrophic factor.