Ectopic substance P and calcitonin gene-related peptide immunoreactive fibres in the spinal cord of transgenic mice over-expressing nerve growth factor

The aim of this study was to investigate the in vivo effects of CNS over-expression of nerve growth factor (NGF) on primary sensory neurons. To achieve this objective a transgenic mouse model was generated which bore a chick NGF gene driven by the myelin basic protein promoter. Northern blot analysis demonstrated that high levels of NGF mRNA were detected in the spinal cord of adult transgenic mice. Using immunocytochemistry NGF-immunoreactive (IR) oligodendrocytes were observed throughout the white matter. Furthermore, numerous ectopic substance P (SP)- and calcitonin gene-related peptide (CGRP)-IR fibres were detected in the white matter of the spinal cord of transgenic mice. NGF-IR oligodendrocytes and ectopic SP- and CGRP- fibres were entirely absent from control mice. In the cervical and lumbar dorsal root ganglia, the percentages of SP-IR neurons were significantly higher in transgenic mice when compared with controls. At the electron microscope level, ectopic SP- and CGRP-IR fibres were characterized as unmyelinated axons and axonal boutons. SP colocalized with CGRP in some of those axonal boutons and fibres. Capsaicin treatment of adult mice completely abolished the ectopic SP-IR fibres, confirming their primary sensory origin. Our results indicate that primary sensory neurons are responsive to NGF over-expression in the CNS. Ectopic SP- and CGRP-IR fibres in the white matter are likely to represent collateral sprouts of the central processes of the dorsal root ganglion cells which were triggered by NGF over-expressed in the myelinating oligodendrocytes in the spinal cord of transgenic mice.

Acidic FGF induces NGF and its mRNA in the injured neocortex of adult animals

Recently we reported that human recombinant acidic fibroblast growth factor (aFGF) is capable of preventing degeneration of nucleus basalis magnocellularis neurons in vivo and inducing growth of astrocytes in vitro. In the present study, the effects of aFGF on the concentration of nerve growth factor (NGF) and its messenger RNA were investigated in the rat cerebral cortex following unilateral cortical infarction. Lesioned animals exhibited a significant increase of NGF in the remaining cortex ipsilateral to the lesion. After combining cortical lesion with intracerebroventricular application of aFGF (12 micrograms/day for 7 days), we observed an 8-fold increase in the NGF concentration and a marked increase in the level of steady state NGF mRNA relative to controls ipsilaterally, and a less pronounced aFGF effect in the contralateral cerebral cortex. These results support the hypothesis that the neurotrophic effects previously shown for aFGF and basic FGF (bFGF) in neurotrophin-sensitive neurons is mediated by inducing increased production of NGF within the injured central nervous system (CNS) of adult animals.

NGF-mediated synaptic sprouting in the cerebral cortex of lesioned primate brain

In the present study, coronal brain sections of cortically devascularized non-human primates (Cercopithecus aethiops) were used to assess the lesion-associated synaptic loss, and the effect of exogenous nerve growth factor (NGF) in preventing or reversing this neurodegeneration. The sections were immunolabeled with antibodies against the synaptic marker protein synaptophysin (SYN), as well as choline acetyltransferase (ChAT) and parvalbumin (PV) markers that identify cholinergic neurons and interneurons, respectively. We found that, compared to sham-operated animals, in the lesioned vehicle treated animals SYN immunoreactivity near the lesioned site in the frontoparietal cortex was decreased by 31%. Similarly, corrected optical density values of immunostained sections specific for ChAT in the nucleus basalis of Meynert (ipsilateral to the lesion) decreased by 20% and PV-immunoreactive neurons near the lesion decreased by 47%. In contrast, NGF-treated lesioned animals showed levels of SYN, ChAT, and PV immunoreactivity similar to sham controls. These results are consistent with previous studies and support the view that NGF may not only prevent neurodegenerative changes after neocortical infarction by protecting vulnerable neurons, but also is capable of inducing sprouting and synaptogenesis.

Differential expression of p140trk, p75NGFR and growth-associated phosphoprotein-43 genes in nucleus basalis magnocellularis, thalamus and adjacent cortex following neocortical infarction and nerve growth factor treatment

A loss of target-derived neurotrophic factors is hypothesized to be one of the major determinants of central nervous system neuronal degeneration. In order to obtain further insight into early neuronal responses to injury, lesion-induced alterations in the expression of high- and low-affinity nerve growth factor receptors, as well as growth-associated phosphoprotein-43 genes in nucleus basalis magnocellularis, thalamic and neocortical neurons were studied. For this purpose, unilateral cortical devascularization operations were conducted on adult rats. Animals received i.c.v. infusions of vehicle or nerve growth factor (12 micrograms/day) and were killed at one, three, seven and 15 days post-lesion. In situ hybridization studies using 35S-labelled oligonucleotide probes for p75NGFR, p140trk and growth-associated phosphoprotein-43 messenger RNAs reveals that these genes were differentially regulated following the lesion. In the nucleus basalis magnocellularis ipsilateral to the lesion, p140trk gene expression significantly decreased on days 3 and 7, while p75NGFR messenger RNA initially increased on day 3 and decreased on days 7 and 15 after lesion. GAP-43 messenger RNA levels were significantly increased in the nucleus basalis magnocellularis on post-lesion days 3 and 7. Moreover, in contrast to p75NGFR or 140trk, growth-associated phosphoprotein-43 messenger RNA levels were significantly increased in pyramidal neurons located in the remaining cortex adjacent to the cortical lesion at all time points. In the lateral and ventroposterior nuclei of the thalamus, growth-associated phosphoprotein-43 messenger RNA level was slightly increased on days 1 and 3 and was dramatically decreased, significantly below the levels in sham-operated controls, on post-lesion days 7 and 15. During nerve growth factor application, the level of p140trk messenger RNA in the lesioned nucleus basalis magnocellularis returned to values observed in the contralateral nucleus basalis magnocellularis while p75NGFR messenger RNA was increased above values noted in all animals not treated with nerve growth factor. Nerve growth factor treatment did not affect the expression of growth-associated phosphoprotein-43 messenger RNA in any of the areas studied. p140trk messenger RNA was not up-regulated during the time that nerve growth factor was applied, as observed for p75NGFR, but only eight days after interrupting nerve growth factor treatment. Three cell types, nucleus basalis magnocellularis, cortical pyramidal and thalamic neurons, were probably affected in different ways by the devascularization with respect to lesion extent. Consequently, the remaining number of synaptic contacts in each of these brain areas is most likely different which may lead to a differential regulation of growth-associated phosphoprotein-43 messenger RNA.(ABSTRACT TRUNCATED AT 400 WORDS)

Alz-50 recognizes epitopes in primary sensory fibres and in neurons of the substantia gelatinosa of the spinal cord. An ultrastructural study in the rat

The monoclonal antibody Alz-50 has been proposed as a marker for cellular pathological changes in Alzheimer's disease. However, it has been reported that this antibody also reacts with specific epitopes in normal individuals. Furthermore, intense Alz-50 immunoreactivity has been recently described in the hypothalamus and spinal cord of rat and monkey. In the present study, we analysed the distribution pattern of Alz-50 immunostaining in the spinal cord of the adult rat. Using light microscopy, immunostained fibres and varicosities were detected mainly in laminae I-II, although some immunostaining lamina I and the outer two thirds of lamina II. The varicosities appeared either scalloped or dome-shaped and contained numerous agranular synaptic vesicles and a few dense-core vesicles. Most varicosities were presynaptic to dendrites. A few immunostained cell bodies and dendrites were also observed, but glial cells were never immunostained. Some ultrathin sections were processed for postembedding immunogold detection of calcitonin gene-related peptide and GABA immunoreactivities. Most of the varicosities which were immunoreactive for Alz-50 also showed calcitonin gene-related peptide immunoreactivity. In contrast, GABA immunoreactivity was never co-localized with Alz-50 immunoreactivity. These results indicate that, in the superficial dorsal horn, the epitope recognized by the Alz-50 antibody is located mainly, but not exclusively, in primary sensory fibres.

Nerve growth factor treatment restores [3H]QNB binding site density in adult rat subjected to cortical infarction

The effects of unilateral cortical devascularization and nerve growth factor treatment on muscarinic cholinoceptors labelled with [3H]QNB were investigated in rat cerebral cortex. The lesion induced a significant ipsilateral decrease in the density (Bmax) but not in the affinity (kD) of [3H]QNB binding sites. Intraventricular infusion of 2.5 S mouse nerve growth factor (NGF) increased the density of binding sites such that Bmax values of lesioned animals treated with NGF were not different from control subjects.

Pharmacological characterization of nerve growth factor and/or monosialoganglioside GM1 effects on cholinergic markers in the adult lesioned brain

The regulation of cholinergic markers by exogenous nerve growth factor (NGF) and/or monosialoganglioside GM1 (GM1) treatment was examined in various brain areas of unilaterally decorticated rats, with particular emphasis on the basal forebrain system. Treatment of decorticated rats, i.c.v. via a minipump, with various doses of NGF or GM1 for a period of 7 days prevented the lesion-induced decline in nucleus basalis magnocellularis choline acetyltransferase (ChAT) activity in a dose-dependent manner. These treatments also stimulated cortical ChAT activity as well as high-affinity choline uptake. Cholinergic markers in other brain areas studied were unaffected by the lesion or these treatments, except in the striatum in which exogenous NGF but not GM1 caused dose-dependent increases in ChAT activity and high-affinity choline uptake. Glutamic acid decarboxylase activity was unaffected by the lesion or treatments in all brain areas studied. Cotreatment of lesioned rats with GM1 did not affect NGF potency but did increase its maximal efficacy in the nucleus basalis magnocellularis and cortex, but not in the striatum. Treatment of cortically lesioned rats with maximal doses of GM1 and/or NGF did not differentially alter "soluble" or "membrane bound" forms of ChAT. In addition, choline uptake kinetic parameters also were affected similarly by these agents as evidenced by augmented Vmax and unaltered Km values. Distinct effects of NGF and GM1 were observed, however, in regard to the delay possible in treatment time onset. No significant alteration in NGF receptor density or affinity were noted in the remaining cortex of GM1-treated decorticated rats, suggesting that GM1 interacts with an alternative facet of NGF signal transduction to potentiate NGF effects on cholinergic markers.

Microencapsulation and the grafting of genetically transformed cells as therapeutic strategies to rescue degenerating neurons of the CNS

A number of approaches have been developed to deliver growth factors within the central nervous system of adult mammals. Initially a variety of neurotrophic factors were administered either by single intracerebroventricular or local injections directly into brain tissues or via permanently installed cannulae for chronic administrations. More recently delivery systems including conjugates, biodegradable and non-biodegradable implants and microspheres as well as genetically engineered cells have been introduced in order to provide a prolonged supply of neurotrophic factors and to prevent their enzymatic degradation. In this review we examine a variety of means of delivering neurotrophic factors (mainly nerve growth factor) with the primary focus upon the use of microencapsulated neurotrophins and cells genetically modified to produce them. In addition, this review highlights some difficulties and future trends in the development of novel delivery systems hopefully more suitable for investigations in different areas of neuroscience.

Primate models of cholinergic dysfunction

Neuropathological studies are currently providing extensive information upon which to base experimental models of neurodegenerative diseases. While it seems unlikely that a single model encompassing all aspects of degenerative dementia will be developed in the near future, models that are more restricted in their scope can provide useful data about processes which range from cellular to behavioral disturbances. In this article we present recent primate studies revealing that mature basal forebrain cholinergic neurons degenerate as a consequence of the removal of their target. Both fimbria fornix transection and cortical devascularization seem to be useful tools in the assessment of potential neurotrophic and neuroprotective properties of pharmacological agents.

Enkephalin-, thyrotropin-releasing hormone- and substance P-immunoreactive axonal innervation of the ventrolateral dendritic bundle in the cat sacral spinal cord: an ultrastructural study

The distribution and synaptic arrangement of thyrotropin-releasing hormone-, substance P- and enkephalin-immunoreactive axonal boutons have been studied in the ventrolateral nucleus (Onuf's nucleus) of the upper sacral spinal cord segments in the cat. For this purpose, the peroxidase-antiperoxidase immunohistochemical technique was used. Immunoreactive axonal boutons were traced in complete series of sections in order to reveal synaptic contacts with the bundled dendrites of the ventrolateral nucleus. As judged from the cross-sectional diameter of the postsynaptic dendrites, the distribution of immunoreactive boutons was non-random. Enkephalin-immunoreactive axonal boutons, presumed to be mostly of segmental origin, displayed a rather restricted distribution to mainly (> 80%) medium-to-large dendrites. Thyrotropin-releasing hormone-immunoreactive boutons, that derive from supraspinal levels, were also found to impinge on medium-to-large dendrites (> 80%), indicating a proximal location within the dendritic trees. The skewness toward large postsynaptic dendrites was even more marked for thyrotropin-releasing hormone- than for enkephalin-immunoreactive boutons. Substance P-immunoreactive boutons, that are of either supraspinal or spinal origin, showed a more even distribution throughout the dendritic trees, including both thin distal branches and thick proximal dendrites. In view of the well-known fact that virtually all thyrotropin-releasing hormone-immunoreactive boutons in the ventral horn co-contain substance P (and serotonin) it was assumed that substance P-immunoreactive boutons in synaptic contact with the finest-calibre dendrites as well as most of those with a very proximal juxtasomatic location on the dendritic trees were of segmental origin, while those impinging on medium-to-large dendrites could be of either spinal or supraspinal origin. Fine-calibre dendrites (< 1 micron) represent about 25% of the dendritic branches in the ventrolateral nucleus, but receive, with the exception of substance P (8%), very little (< 3%) peptidergic or GABAergic (Ramírez-León and Ulfhake, 1993) input, although the degree of dendritic membrane covering by bouton profiles in the ventrolateral nucleus does not seem to vary much with the calibre of the postsynaptic dendrite (Ramírez-León and Ulfhake, 1993). Both substance P- and enkephalin-immunoreactive axonal boutons established synaptic contact with more than one dendrite. Furthermore, one and the same bouton could be found in contact with two dendrites that were coupled to each other by a dendro-dendritic contact of desmosomal or puncta adherentia type.(ABSTRACT TRUNCATED AT 400 WORDS)

Neocortical infarction in subhuman primates leads to restricted morphological damage of the cholinergic neurons in the nucleus basalis of Meynert

The aim of the present study was to investigate the long-term effect of cortical infarction on the subhuman primate (Cercopithecus aethiops) basal forebrain. The lesion, carried out by cauterizing the pial blood vessels supplying the left fronto-parieto-temporal neocortex, induced retrograde degenerative processes within the ipsilateral nucleus basalis of Meynert. The morphometrical analysis revealed that significant shrinkage of cholinergic neurons and loss of neuritic processes were localized within the intermediate regions of the nucleus basalis. The average cross-sectional areas of choline acetyltransferase-immunoreactive neurons in the intermedio-ventral (Ch4iv) and intermedio-dorsal (Ch4id) nucleus basalis were decreased to 62.5 +/- 9.5 and 58.0 +/- 8.6%, respectively, of the sham-operated values. Although an apparent loss of Nissl-stained magnocellular neurons in Ch4iv and Ch4id was found by applying a quantitative analysis based on a perikaryal-size criterion, data obtained by the quantification of immunostained material failed to reveal any significant decrease of cholinergic cell density. Results are discussed in view of future application of this ischemic model to study processes of retrograde degeneration following cortical target removal and to assess potential neurotrophic and neuroprotective properties of pharmacologic agents.

Intraventricular application of BDNF and NT-3 failed to protect nucleus basalis magnocellularis cholinergic neurones

Quantitative analysis of ChAT immunoreactive neurones was used to evaluate the protective potential of BDNF or NT-3 against retrograde changes in nucleus basalis magnocellularis (nbm) cholinergic neurones after unilateral partial devascularization of the rat neocortex. A daily intracerebroventricular dose of 12 micrograms, proven to be effective for NGF and aFGF in the same experimental paradigm, was administered by minipump infusion for a 1-week period. Thirty days after lesioning, neuronal shrinkage and loss of neuritic processes were not prevented by treatment. The results indicate that intracerebroventricularly delivered BDNF and NT-3 are not as effective as NGF and aFGF in protection of nbm cholinergic neurones against lesion-induced changes in adult rat brain.

Nerve growth factor and the monosialoganglioside GM1: analogous and different in vivo effects on biochemical, morphological, and behavioral parameters of adult cortically lesioned rats

This study examined the behavioral effects of maximal doses of exogenous NGF and/or GM1 when given intracerebroventricularly to adult rats with unilateral cortical lesions. In addition, the long-term effects of these agents on choline acetyltransferase (ChAT), glutamic acid decarboxylase (GAD) activity, and choline uptake, as well as on ChAT and NGF receptor (p75NGFR) immunoreactivity in various brain regions, were also investigated. When retested in passive avoidance and Morris water maze tasks, 30 days postlesion (i.e., 2 weeks after termination of treatment), decorticated vehicle-treated rats showed retention and reacquisition deficits which were equally attenuated by NGF (6 micrograms/day, 14 days) or NGF + GM1 (750 micrograms/day, 14 days) treatment. By contrast, lesioned animals which received GM1 alone only showed improved reacquisition of the two tasks. After behavioral testing (52 days postlesion) lesioned vehicle-treated animals had decreased ChAT activity in the ipsilateral nucleus basalis magnocellularis (NBM) but not in other subcortical brain areas examined. Neuronal loss was observed only in the ventrolateral nucleus of the ipsilateral dorsal thalamus. However, using quantitative image analysis a significant shrinkage of ChAT immunoreactive (IR) and p75NGFR-IR NBM neurons as well as a decrease in their neuritic network was noted, particularly in the mid portion of the NBM. GM1 and NGF equally prevented these deficits in the NBM and, furthermore, enhanced ChAT activity and choline uptake in the remaining cortex ipsilateral to the lesion site. These alterations in NBM and cortical cholinergic markers were even more augmented in rats which received both NGF and GM1 treatment. By contrast, the noted NGF-induced increase in striatal ChAT activity was not further increased by concomitant GM1 treatment. GAD activity in all brain areas examined was unaltered by the lesion or any of the treatments and the apparent thalamic neuronal retrograde degeneration was not prevented by any of the treatments. It is concluded that GM1 or NGF treatment can distinctly affect performance of cortically lesioned rats in passive avoidance and Morris water maze tasks despite their equal ability to serve as long-term neuroprotective agents for the basalo-cortical cholinergic pathway.

Differential regulation of c-fos expression after cortical brain injury during development

Unilateral cortical brain injury is accompanied by widespread expression of c-fos protein(s) throughout the wounded cortex, including areas far from the lesion site. Here we report that this phenomenon is differentially regulated during development. At postnatal day (PD) 10 or 15, when rats were sacrificed 1.5 h after a mechanical cortical injury, they did not show an increase in c-fos immunoreactivity far from the wound, despite the fact that some of these animals (PD 15) displayed a positive response close to the lesion. At PD 22, the same injury induced an increase in c-fos-immunoreactive nuclei in the piriform cortex ipsilateral, but not contralateral, to the lesion. This pattern was maintained up to at least PD 360. Similarly, the presence of c-fos-immunoreactive cells was observed in the ipsilateral cingulate cortex in animals 22 days old and older. The pattern of c-fos expression in adult animals after mechanical damage was compared with other models of focal brain injury: application of potassium to the cortical surface and devascularization. Though all models generated c-fos expression far from the lesion site, potassium application resulted in higher numbers of c-fos-positive cells, particularly in the cingulate cortex. This study shows that c-fos expression after cortical brain injury is regulated differently during development, and that dissimilar models of cortical injury induce qualitatively similar responses although c-fos-like protein expression differs quantitatively.

Potentiation of nerve growth factor-induced alterations in cholinergic fibre length and presynaptic terminal size in cortex of lesioned rats by the monosialoganglioside GM1

The effect of monosialoganglioside GM1 and/or nerve growth factor treatment on the cholinergic innervation of the rat cortex was studied using both light- and electron-microscopic techniques assisted by image analysis. Adult male Wistar rats were unilaterally decorticated and received continuous infusions, via minipump, of vehicle, GM1 (1.5 mg/day) and/or nerve growth factor (12 micrograms/day) into the cerebroventricular space. Treatments were initiated immediately post-lesion and ended after seven days. Thirty days post-lesion (i.e. 23 days after the end of drug administration) brains were processed for choline acetyltransferase immunocytochemistry for either light- or electron-microscopic analysis. At this time-point choline acetyltransferase-immunoreactive neurons in the ipsilateral nucleus basalis magnocellularis were significantly reduced in size especially in the mid portion of this nucleus, in lesion vehicle-treated rats. Moreover, decreases in choline acetyltransferase immunoreactive fibre length (ranging from 31 to 50%) and varicosity number (ranging from 26 to 39%) occurred in all cortical layers within a portion of the remaining cortex of these animals. Monosialoganglioside GM1 or nerve growth factor treatment equally attenuated deficits in nucleus basalis magnocellularis cell size and cortical choline acetyltransferase immunoreactive fibre length. However, nerve growth factor, but not monosialoganglioside GM1 treatment also increased choline acetyltransferase-immunoreactive varicosity number above control levels. In lesioned rats which received both nerve growth factor and the monosialoganglioside GM1, the mean cross-sectional area of nucleus basalis magnocellularis cholinergic neurons did not differ significantly from control values. By contrast, cortical choline acetyltransferase-immunoreactive fibre length and varicosity number were significantly increased above control values and that induced by nerve growth factor treatment alone. Quantitative electron-microscopic analysis showed that cholinergic boutons in cortical layer V were considerably shrunken in lesioned vehicle-treated rats and that GM1 treatment failed to significantly attenuate this deficit. However, exogenous nerve growth factor provoked a significant increase (35% above control values) in cortical cholinergic presynaptic terminal size which was even further augmented by concurrent GM1 treatment (69% above control values). This trophic factor-induced increase in bouton size was confirmed using serial electron microscopy and computer-assisted three-dimensional reconstruction of the cholinergic varicosities. The number of synaptic contacts in cortical layer V was also found to be significantly reduced (45% of control values) in lesioned vehicle-treated rats but was maintained at control levels by exogenous GM1 treatment. In addition, a significant increase (95% above control levels) in the number of choline acetyltransferase-immunoreactive boutons with synaptic differentiations was noted in lesioned nerve growth factor-treated rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of acidic fibroblast growth factor on cholinergic neurons of nucleus basalis magnocellularis and in a spatial memory task following cortical devascularization

The ability of acidic fibroblast growth factor to elicit a trophic response in the nervous system of the rat was tested in vitro and in vivo. Treatment of cultured septal cells with acidic fibroblast growth factor resulted in an elongation of glial processes as assessed by immunostaining for glial fibrillary acidic protein. Increased choline acetyltransferase was also observed. The responses to acidic fibroblast growth factor in vivo were studied in rats trained in a spatial memory task, using the Morris water maze. Randomly selected animals were subjected to unilateral cortical devascularization. This lesion results in partial unilateral infarction of the neocortex, and in retrograde degeneration of the nucleus basalis magnocellularis. Animals were tested post-lesion for memory retention and were then killed for morphological studies. Intracerebroventricular administration of acidic fibroblast growth factor (0.6 microgram/h for seven days starting at surgery) prevented the lesion-induced impairment in this test, and reduced the nucleus basalis magnocellularis cholinergic degeneration, as assessed by morphometric choline acetyltransferase-like immunoreactivity and radioenzymatic assay for choline acetyltransferase activity. The preservation of the phenotype of injured cholinergic neurons of the nucleus basalis magnocellularis by acidic fibroblast growth factor was indicated by the maintenance of the cross-sectional area of cell bodies and mean length of neuritic processes one month after surgery. The effect of acidic fibroblast growth factor in non-cholinergic cells remains to be investigated. It is suggested that acidic fibroblast growth factor may alleviate the lesion-induced deficit in the memory retention task by preventing disruption of functional connections between nucleus basalis magnocellularis and intact cortical areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Microencapsulation of genetically engineered fibroblasts secreting nerve growth factor

We demonstrated that genetically modified fibroblasts can be encapsulated into biocompatible, biodegradable spheres retaining their viability and capacity to continuously secrete nerve growth factor (NGF) for at least two months. Genetically engineered rat fibroblasts producing NGF were encapsulated in an alginate-polylysine gel with the ultimate objective of improving transplantation methodologies. Cultures were suspended in a sodium alginate solution and the suspension was extruded drop-wise into a solution of calcium chloride. Morphological properties of the spheres were assessed by light and electron microscopy. The spheres had a homogenous external membrane, without fibroblasts, protruding from the surface of the capsular membrane. The NGF determinations in culture media showed that encapsulated fibroblasts continued to synthesize NGF for at least 60 days. We also confirmed that secreted NGF was biologically active, by assessing the induction of choline acetyltransferase (ChAT) activity in dissociated embryonic rat septal cultures. These results encourage further studies using in vivo models to determine the value of applying microencapsulated genetically modified cells secreting trophic factors as a therapeutic strategy for central nervous system (CNS) injuries.