In peripheral nerves, large caliber axons are ensheathed by myelin-elaborating Schwann cells. Multiple lines of evidence demonstrate that expression of the genes encoding myelin structural proteins occurs in Schwann cells in response to axonal instructions. To gain further insight into the mechanisms controlling myelin gene expression, we used reporter constructs in transgenic mice to search for the DNA elements that regulate the myelin basic protein (MBP) gene. Through this in vivo investigation, we provide evidence for the participation of multiple, widely distributed, positive and negative elements in the overall control of MBP expression. Notably, all constructs bearing a 0.6 kb far-upstream sequence, designated Schwann cell enhancer 1 (SCE1), expressed at high levels in myelin-forming Schwann cells. In addition, robust targeting activity conferred by SCE1 was shown to be independent of other MBP 5' flanking sequence. These observations suggest that SCE1 will make available a powerful tool to drive transgene expression in myelinating Schwann cells and that a focused analysis of the SCE1 sequence will lead to the identification of transcription factor binding sites that positively regulate MBP expression.

The effects of nerve growth factor (3(-NGF) and ganglioside GM1 on forebrain cholinergic neurons were examined in vivo and in vitro. Following unilateral decortication of rats, GM1 (5 mg/kg per day) administered intracerebroventricularly could protect forebrain cholinergic neurons of the nucleus basalis magnocellularis from retrograde degeneration in a manner comparable to P-NGF. Administered in combination with (-NGF, GM1 produced a significant increase in choline acetyltransferase activity in the nucleus basalis magnocellularis and remaining cortex ipsilateral to the lesion. Concentrations of GM1 that were ineffective when administered alone in this lesion model, when given with .3-NGF, potentiated (i-NGF effects in both of the above brain areas. In dissociated septal cells in vitro, an increase in choline acetyltransferase activity was noted at fi-NGF concentrations as low as 0

In this study light and EM quantitative analysis were used to examine whether exogenous nerve growth factor (NGF) could affect terminal fields and synaptic connections in the adult rat brain in vivo. Adult rats received, immediately after unilateral decortication, 2.5S NGF (12 lag/day) or vehicle intracerebroventricularly for 7 days.Thirty days after the lesion cholinergic fiber length was quantified, using image analysis, in the remaining cortical area adjacent to the lesion site in each animal. Rats that had received vehicle showed a significantly reduced cortical choline acetyltransferase-immunoreactive fiber network in the remaining cortex when compared with control animals. By contrast, the network in lesioned rats that had received 2.5S NGF was not different from control animals. Furthermore, the number of cortical choline acetyltransferase-immunoreactive varicosities, which decreased in vehicle-treated lesioned rats, significantly increased above control in lesioned rats that had received 2.5S NGF. At the ultrastructural level, 30 days after the lesion, animals that had received vehicle showed shrunken cholinergic boutons in cortical layer V and fewer synapses compared with control animals. Exogenous NGF, administered to lesioned rats, increased to supernormal levels both size of cholinergic boutons and number of synaptic contacts. These parameters were unaltered in unlesioned rats treated with NGF. This study demonstrates that exogenous NGF can cause significant compensatory changes in terminal fields and synaptic connections in the adult fully differentiated central nervous system.Repairing and restoring function to injured neural pathways is the ultimate goal of regeneration studies in the central nervous system (CNS). Achieving this goal, though, requires that some degree of reorganization in neural circuitry and connections should occur, but presently little is known about agents that can regulate such events in the fully differentiated CNS. Potential candidates to mediate these phenomena are growth factors, of which nerve growth factor (NGF) is a prototype (1). Numerous studies have now demonstrated the neurotrophic effects of NGF on adult basal forebrain cholinergic neurons in vivo (2-5). However, despite these studies there is no direct morphological evidence to indicate that NGF actions can be extended to CNS synaptic remodeling. For the most part, studies involving exogenous NGF and brain injury have examined effects of NGF on cholinergic neurochemical markers, cell survival, and morphology and have provided only indirect evidence for sprouting (6). Although NGF can facilitate axonal growth when a bridge of peripheral nervous tissue is provided (7), the full extent of trophic factor-induced effects in the mature CNS remains to be established. In particular, whether these substances can modify synapses in the adult animal is unknown. We have, therefore, investigated whether exogenous NGF can affect these elements in the central cholinergic system.The nucleus basalis magnocellularis (NBM) ...

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