Modulation of neuronal choline acetyltransferase activity by factors derived from cultures of non-neuronal cells from the CNS

Septal neuron cholinergic and GABAergic functions: differential regulation by basic fibroblast growth factor and epidermal growth factor

Numerous studies suggest that growth and trophic factors play roles in the development and mature function of brain neurons. Recently, growth factors whose actions were previously characterized on non-neuronal cells have been localized to the brain. We sought to determine whether these factors influence septal cholinergic function. Initially, we defined the effects of basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF) on septal cholinergic cells in dissociated neuronal culture. Both factors elevated activity of the acetylcholine synthetic enzyme, choline acetyltransferase (CAT). To determine whether the factors acted directly on neurons or whether glia mediated the effects, a mitotic inhibitor, 5-fluorodeoxyuridine (FDUR), was added to the cultures to eliminate dividing glia. The action of EGF was completely blocked by the addition of FDUR. However, bFGF elevated CAT activity even in the presence of FDUR. Consequently, bFGF may regulate septal cholinergic function directly, whereas EGF may affect cholinergic cells indirectly through glia. To determine whether increases in CAT activity reflect increased enzyme activity per neuron or an increase in the number of cholinergic cells, bFGF-treated cultures were stained for acetylcholinesterase (AChE) to determine numbers of cholinergic cells. No differences in AChE-positive cells were noted, suggesting that bFGF increased CAT activity per cholinergic neuron. To determine whether bFGF regulates other populations in the septum, we examined GABAergic neurons by monitoring the activity of glutamic acid decarboxylase (GAD), a GABA synthetic enzyme. Basic FGF significantly increased GAD activity; however, the effect was completely abolished by addition of FDUR. Thus, bFGF may act directly on cholinergic neurons and indirectly on GABA cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Muscle-derived factors reverse the cholinotoxic effects of ethanol during early neuroembryogenesis in the chick embryo

The interaction between muscle-derived factors and ethanol on cholinergic neuronal expression was studied in the chick embryo during early neuroembryogenesis using choline acetyltransferase (ChAT) as cholinergic neuronal marker. Ethanol (10 mg/50 microliters) and limb muscle extract (130 micrograms protein/50 microliters) (LME) were administered in ovo either alone or concomitantly at embryonic days 1-3 (E1-E3); or ethanol was given E1-E3 and followed by LME at E4-E7. All groups were sacrificed at embryonic day 8 (E8) and ChAT activity was assayed in homogenates of whole brain and of spinal cord. As previously reported, ethanol at E1-3 produced a 30% decrease in brain ChAT activity and 35% in spinal cord. Concomitant administration of ethanol and LME at embryonic days E1-E3 eliminated the decrease in choline acetyltransferase activity produced by ethanol in the brain, but not in the spinal cord. On the other hand, administration of LME at embryonic days E4-E7 to embryos pretreated with ethanol at embryonic days E1-E3, raised ChAT activity to control level in the spinal cord, but only partially restored ChAT activity in the brain. In view of the alleged neurotrophic effects of muscle-derived factors on neuronal survival and neuronal growth, we interpret these findings to suggest that LME in addition to its ability to decrease natural neuronal death, may prevent death resulting from neurotoxicity.

Muscle-derived factors enhance cholinergic neuronal expression in the chick embryo--II. In culture studies

The effects of muscle-derived factors on the cholinergic and GABAergic neuronal phenotypes were studied in cultures derived from 3-day-old whole chick embryo (E3WE) consisting of proliferating neuroblasts and 8-day-old chick embryo cerebral hemispheres (E8CH) consisting of differentiated neurons. The effects of limb muscle extract (LME) were examined either when added to the culture medium or to the polylysine coating substratum cultures. We also compared the effects of LME derived from 8- to 15-day-old chick embryos. We found that LME added to the medium not only increased choline acetyltransferase activity, a marker for cholinergic neurons throughout the development of neurons in E3WE or E8CH culture, but also delayed the decline in the activity observed in untreated cultures. The marked increase in choline acetyltransferase activity in E8CH cultures grown on substratum-bound LME as compared to those grown in medium-containing LME, suggests that LME factors may be adhesion-promoting substances stimulating neuronal growth. These findings provide evidence that muscle-derived factors may be important in early cholinergic phenotypic expression and support our previous in ovo studies indicating that target-derived factors in limb muscle extract have general cholinotrophic effect.

Muscle-derived factors enhance cholinergic neuronal expression in the chick embryo--I. In ovo studies

The effects of muscle-derived factors were studied in the chick embryo in ovo, during early neuroembryogenesis. Limb muscle extract (LME) administration during embryonic period E1-E7 produced a significant increase in choline acetyltransferase activity of both spinal cord and brain in 8-day-old chick embryos. Similar treatment failed to induce significant change in the GABAergic phenotypes as assessed by the activity of the enzyme glutamic acid decarboxylase. Administration of limb muscle extract at either embryonic days 1-3 or 4-7 produced a significant increase in choline acetyltransferase activity in the brain, indicating that the critical period of limb muscle extract in the brain to be between embryonic days E1 and E7, a period of neuronal proliferation and differentiation in the brain. On the other hand, LME administration produced no effect on spinal cord choline acetyltransferase activity when given at embryonic days 1-3, whereas it produced a marked increase when given at embryonic days 4-7. Thus, the critical period of limb muscle extract effect in the spinal cord appears to be confined to embryonic days E4-E7, a period of neuronal differentiation and cell death in the spinal cord. These findings indicate that the cholinotrophic activity of muscle-derived factors is not limited to the muscle target tissues but have a general effect on cholinergic neurons in the CNS. Whether these cholinotrophic effects are mediated by a common factor or by different factors is still under investigation.