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S Varon

Publications and source records attributed to S Varon.

At least 37 records · Page 2Linked to original sources
PubMed1995

Characterization of neurotrophic activity in the silicone-chamber model for nerve regeneration.

In the present study, the authors reevaluated the temporal course and properties of neurotrophic activities present in the fluid accumulating in the silicone-chamber model for nerve regeneration. The fluid collected from silicone chambers was tested in four different dissociated neuronal cell cultures. Furthermore, the activity of the chamber fluid was examined, using a cell blot technique. There was one major peak of neurotrophic activity and this activity peaked early, about 3 to 6 hr after nerve injury. Results also indicate that the chamber fluid contains at least two types of neurotrophic activities, namely nerve growth factor and ciliary neurotrophic factor.

Animals↗
PubMed1994

Distribution of corticospinal motor neurons in the postnatal rat: quantitative evidence for massive collateral elimination and modest cell death.

The postnatal development of rat corticospinal motor neurons (CSMN) was studied by retrograde tracing with cholera toxin B subunit (CTB) injected into the upper cervical dorsal spinal cord on the first postnatal day (P0), P3, P10, P20, and at adulthood. CTB-labeled neurons were visualized by immunocytochemistry and extensively quantified throughout the cortex. At P0, CSMN were found to an extent similar to that reported in P3 animals with other neuronal tracers, now permitting in vitro studies of neonatal CSMN. Between P0 and P3, the number of labeled neurons increased by 30% to a total maximum of approximately 185,000 in both cortices. The increase occurred throughout the cortex. At P10, the number of labeled CSMN had decreased to 60% of the number at P3. Fewer CSMN were evident particularly in the perirhinal cortex. Between P10 and P20, the number of CSMN decreased further to 52% of the maximal number at P3. This decrease occurred predominantly in the cingulate and parietal cortex. The number of labeled CSMN in rats injected at P0 and analyzed at P20 was 10% lower than the number in P0-injected littermates that were analyzed at P3, which suggests that only a small portion of the "disappearing" CSMN undergoes developmental neuronal death. Thus, the spinal projection of the remaining 38% is apparently eliminated between P3 and P20. Detailed quantitative analysis of the CSMN distribution demonstrated that neuronal death occurs predominantly in the perirhinal cortex. In contrast, axonal elimination of corticospinal projections occurred throughout the CSMN field, i.e., primarily in the frontal, occipital, and perirhinal cortex between P3-P10 and in the cingulate and parietal cortex between P10-P20.

Animals↗
PubMed1994

Changes in nerve growth factor immunoreactivity following entorhinal cortex lesions: possible molecular mechanism regulating cholinergic sprouting.

To assess the possible role of trophic factors in lesion-induced plasticity, we have used a sensitive immunohistochemical technique to evaluate changes in nerve growth factor (NGF) staining in the hippocampal formation 3, 8, 16, and 30 days following entorhinal cortex lesions. Our results indicate that a band of NGF immunoreactivity appears in the outer molecular layer of the ipsilateral dentate gyrus following entorhinal ablation. The distribution of the NGF-immunoreactive band exactly coincides with the distribution of sprouting cholinergic terminals revealed by acetylcholinesterase histochemistry or NGF-receptor immunostaining. Increased NGF-immunoreactivity is detectable at 3 days postlesion, is most intense at 8 days, and decreases to near control levels by 30 days. Lesion-induced increases in NGF immunostaining also occur in animals in which septohippocampal fibers had been removed by prior destruction of the fimbria-fornix. Increases in NGF-immunoreactivity, however, are substantially reduced in animals receiving intraventricular injections of colchicine, which presumably blocks NGF release. These results indicate that 1) increases in NGF immunostaining, which occur following entorhinal lesions, precede any changes in cholinergic sprouting parameters and are greatest during the period of maximal cholinergic sprouting; 2) increased NGF-immunoreactivity is not due to NGF binding by septohippocampal fibers; and 3) increased NGF-immunoreactivity appears to depend on the release of NGF by neurons that produce it. We hypothesize that, following entorhinal lesions, NGF immunostaining within the hippocampal formation may represent NGF "anchored" within the tissue and that NGF accumulation by such a mechanism may direct the sprouting response of NGF-sensitive cholinergic neurons.

Acetylcholinesterase↗
PubMed1994

Nerve growth factor-like immunoreactive profiles in the primate basal forebrain and hippocampal formation.

The distribution of nerve growth factor (NGF), the prototypic neurotropin, within the basal forebrain and hippocampal formation of young adult monkeys and aged humans was characterized with an affinity purified polyclonal beta-NGF antibody raised against mouse beta-NGF. In the basal forebrain of both primates, a granular NGF-like immunoreactive (ir) reaction product was observed within neurons of the medial septum, nucleus of the diagonal band, and nucleus basalis of Meynert. NGF-like immunoreactivity exclusively colocalized within p75 NGF receptor (NGFR) containing basal forebrain neurons. The intensity of NGF immunolabeling varied between cell bodies. Many NGF-ir perikarya were highly immunoreactive. In other basal forebrain neurons, NGF-like immunoreactivity was either undetectable or minimally expressed. In the hippocampus of both species, NGF-like immunoreactivity was mainly localized within the hilus of the dentate gyrus and within CA3 and CA2 hippocampal subfields. A marked diminution in NGF-like staining was seen in CA1. Within the hippocampal formation, NGF-like immunoreactivity was heaviest within the neuropil of stratum radiatum, intermediate in stratum oriens, and lightest in stratum pyramidal. NGF-like immunoreactivity was not found within the granule or pyramidal cells of the dentate gyrus and hippocampal formation, respectively. These findings demonstrate the presence of an NGF-like antigen in association with monkey and human magnocellular basal forebrain neurons and within their hippocampal target sites. This lends support to the hypothesis that NGF is internalized from sources located within target regions of the primate cholinergic basal forebrain neurons and is retrogradely transported to these cell bodies where the NGF trophic effect likely occurs.

Animals↗
PubMed1994

Neurite outgrowth from cultured CNS neurons is promoted by inhibitors of protein and RNA synthesis.

We examined the effects of changes caused by the blocking of protein and RNA synthesis on neurite outgrowth from neurons of the central nervous system (CNS) in primary culture. Exposure to cycloheximide and actinomycin-D led to dramatic increases in the length of neurites in cultures of neurons from various rat or chick CNS regions. Inhibitor-induced neurite outgrowth was observed (1) from dopaminergic neurons in mixed cultures of the rat substantia nigra or (2) in pure cultures of rat and chick neurons grown on a polyornithine/laminin substratum. These results suggest that neurite outgrowth from CNS neurons is kept restricted, at least in culture, by the continuous production of a labile neurite-inhibiting protein intrinsic to the neurons, which rapidly decays following inhibition of protein or RNA synthesis.

Animals↗
PubMed1994

Effects of ciliary neurotrophic factor on the survival and response to nerve growth factor of cultured rat sympathetic neurons.

The development and maturation of cells depends not only on their genetic history, but also on sequences and combinations of environmental signals appropriate to their developmental age. Early postnatal rat sympathetic neurons are dependent on nerve growth factor (NGF) for survival in vivo and in vitro, but earlier sympathetic neuroblasts may not require NGF. Ciliary neurotrophic factor (CNTF) provides short-term in vitro trophic support to embryonic and neonatal sympathetic neurons, but its role in vivo is not understood. In this study we examined further the capability of CNTF to support neonatal rat superior cervical ganglion (SCG) sympathetic neurons in vitro and the effect of CNTF on the trophic activities of NGF. SCG neurons cultured with either CNTF or NGF survived for 24 hr in low-density cultures depleted of nonneuronal cells, in contrast to neurons with neither factor. However, with CNTF only a fraction of the NGF-maintained number of neurons survived for 6 days. CNTF given in combination with NGF in these nonneuron-depleted cultures produced a significant decrease in the number of neurons surviving for 6 days, compared to the number supported by NGF alone. If such cultures were supplemented with Schwann cells, very different results were obtained: CNTF alone supported the 6-day survival of 80% as many neurons as did NGF, and the combination of CNTF with NGF produced no decrease in neuronal survival. Antibody to NGF did not block the support provided by CNTF and Schwann cells. Immunostaining for the low-affinity NGF receptor (LNGFR), intense in the NGF-supported neurons, was absent in the CNTF-supported neurons and reduced in the neurons exposed to the combination of NGF and CNTF. These results show that CNTF can act synergistically with a Schwann cell-derived agent to provide trophic support to neonatal sympathetic neurons, and that it can down-regulate the responsiveness of those neurons to NGF.

Animals↗
PubMed1994

Regeneration of adult rat sensory axons into intraspinal nerve grafts: promoting effects of conditioning lesion and graft predegeneration.

The effect of intraspinally implanted predegenerated peripheral nerve grafts and/or conditioning lesions on the regenerative capacity of central ascending sensory axons was investigated in the adult rat. Regenerating sensory fibers were analyzed after their transganglionic labeling with cholera toxin B subunit, usually 1 month after implantation. A conditioning lesion (transection of the tibial and peroneal nerve) caused a fivefold increase in the number of sensory fibers within the fresh graft when applied on the day of grafting and a sevenfold increase when applied 1 week before. In the latter case, a small portion of the fibers (10%) had reached the rostral end of the nerve graft. In the absence of a conditioning lesion, the number of fibers regenerating into a predegenerated nerve graft (collected from the distal part of the peroneal nerve that had been axotomized 1 week earlier) was similar to that found in a fresh graft. However, predegenerated grafts received three and five times more fibers than a fresh graft when conditioning lesions were applied on or 1 week before the day of grafting. With the combination of a predegenerated graft and a 1-week conditioning, most (> 90%) of the regenerating fibers had reached the rostral graft-host border. In animals with a fresh graft, a portion of the axotomized fibers formed terminal club-like structures. Much fewer fibers displayed such clubs in animals with a predegenerated graft or a conditioning lesion, suggesting a preventive action of either treatment. A time-course study with the combined treatments showed that regenerating sensory fibers had already entered the graft after 3 days. Between 1 and 2 weeks, a maximum number of fibers had reached the rostral end of the nerve graft. However, after 2 months, the number of fibers was decreased, i.e., the initial advantage of predegeneration had diminished. The current results demonstrate the necessity of a conditioning lesion for successful regeneration of central sensory fibers, possibly resulting from an earlier induction of the neuronal growth response which allows the axon to enter the graft before the formation of a graft-host barrier. The predegeneration of the nerve graft augments the growth response of the axotomized central sensory fibers, probably by providing a more supportive terrain and/or enhancement of the neuronal response. The presence of a large number of fibers at the rostral graft-host border now provides the opportunity to investigate the effects of neurotrophic factors on the regenerative capacity of the ascending rat sensory fibers into the denervated spinal cord in vivo.

Animals↗
PubMed1994

Nerve growth factor influences the distribution of sympathetic sprouting into the hippocampal formation by implanted superior cervical ganglia.

Following cholinergic denervation of the hippocampal formation, peripheral sympathetic fibers from the superior cervical ganglion (SCG) sprout into hippocampal tissue. The molecular mechanism controlling this process is unknown, although a role by trophic factors seems likely. In the present study, neonatal SCG were used as biological probes to investigate the association between NGF-immunoreactive regions in the hippocampal formation and areas innervated by regrowing sympathetic fibers. Cholinergic deafferentation of the hippocampal formation was achieved by a fimbria-fornix transection and neonatal SCG were placed into the lesion cavity, abutting the rostral pole of the hippocampus. At 16 days following ganglia transplantation, NGF immunoreactivity within the hippocampal formation appeared indistinguishable from unlesioned controls and was localized within the mossy fiber region of the dentate gyrus and CA3 and CA2 hippocampal subfields. Sympathetic innervation, revealed in adjacent sections by dopamine beta-hydroxylase or p75LNGFR immunoreactivity, was also restricted primarily to the mossy fiber region. Ablation of the entorhinal cortex at the time of transplantation resulted in the appearance of an additional discrete band of NGF immunoreactivity within the outer molecular layer of the dentate gyrus. In animals receiving an entorhinal lesion concurrent with the SCG transplant, sympathetic fibers were observed not only within the mossy fiber region but also within the outer molecular layer of the dentate gyrus where the lesion-induced NGF immunoreactivity appeared. These results support the hypothesis that topographic distributions of NGF may be used in the hippocampal formation to define terminal fields for sprouting NGF-sensitive neuronal populations.

Animals↗
PubMed1994

Nerve growth factor in CNS repair.

The hypothesis that neurotrophic factors play important roles in the adult central nervous system (CNS) has been successfully investigated in the past decade with regard to experimental and pathologic situations. Trophic roles in adult CNS axonal regeneration, on the other hand, have received much less attention. We review three groups of recent studies that demonstrate the relevance of nerve growth factor (NGF) for the regeneration of selected axons into adult central nervous tissue. The first group concerns a septohippocampal model where transected septal cholinergic axons are allowed to regrow into the hippocampal formation through a peripheral nerve bridge implanted into the transection lesion gap. NGF is required in the bridge, enhances penetration of the hippocampal tissue when infused there, and both attracts and promotes sprouting within the septum when infused in the lateral ventricle or the septal tissue itself. The second group of studies concerns the development of a spinal cord sensory regeneration model, where dorsal root ganglionic axons regrow into a nerve bridge placed within the dorsal spinal cord. Preliminary data indicate that NGF infusion rostral to the bridge once again promotes substantial penetration of the adult cord tissue by the regenerating NGF-sensitive fibers. In the third group of studies, attention has been shifted to the location of endogenous NGF in the adult rat hippocampal formation and the normal or lesion-induced occurrence of extrasomal NGF immunoreactivity. These regions of anchored NGF have the ability to attract NGF-sensitive growing axons and may provide opportunities to investigate local cues for final definition of terminal fields.

Animals↗
PubMed1993

Ciliary neurotrophic factor prevents degeneration of adult rat substantia nigra dopaminergic neurons in vivo.

We have investigated the neuroprotective effects of recombinant human ciliary neurotrophic factor (CNTF) for injured dopaminergic neurons of the adult rat substantia nigra compacta. Fourteen days after a unilateral transection of the nigrostriatal pathway two-thirds of the neurons (identified by retrograde labeling) had degenerated. In sharp contrast, 73% (a few cases, > 90%) of this cell loss was prevented by continuous infusion of CNTF close to the injured neurons. However, CNTF did not prevent the disappearance of the transmitter-synthesizing enzyme tyrosine hydroxylase. Thus, CNTF has potent neurotrophic effects for injured adult rat dopaminergic substantia nigra neurons, whose degeneration plays a major causative role in Parkinson disease.

Animals↗
PubMed1993

CNTF protection of oligodendrocytes against natural and tumor necrosis factor-induced death.

A proportion of developing oligodendrocytes undergo natural cell death by apoptosis, and mature oligodendrocytes die, either by apoptosis or necrosis, in response to injurious signals such as cytotoxic cytokines and complement. Ciliary neurotrophic factor (CNTF), a trophic factor found in astrocytes in the central nervous system (CNS), promoted the survival and maturation of cultured oligodendrocytes. This trophic factor also protected oligodendrocytes from death induced by tumor necrosis factors (apoptosis) but not against complement (necrosis). These results suggest that CNTF functions in the survival of oligodendrocytes during development and may lead to therapeutic approaches for degenerative diseases of the CNS that involve oligodendrocyte destruction.

Animals↗
PubMed1993

Cooperative effects of ciliary neurotrophic factor and norepinephrine on tyrosine hydroxylase expression in cultured rat locus coeruleus neurons.

Ciliary neurotrophic factor (CNTF) was found to promote the expression of tyrosine hydroxylase (TH) immunoreactivity by cultured noradrenergic neurons from the locus coeruleus (LC) of E18 rat fetuses, but only in the concomitant presence of norepinephrine (NE), their own neurotransmitter. The number of TH-positive cells in LC cultures was shown to decrease by 65% within 3 days and by 75% after 6 days. Treatment with 10 TU/ml human recombinant CNTF together with 1 microM NE was able to fully maintain the initial number of TH-positive neurons for 3 days. This effect, however, was no longer seen after 6 days of continuous exposure. A 24-hr treatment with CNTF/NE was capable of completely restoring the initial number of TH-positive cells, even if its addition was delayed for 2 days. Moreover, when its addition was delayed for 5 days, CNTF/NE restored approximately 80% of the TH-positive neurons that were initially present. These results suggest that the disappearance of TH-positive neurons in LC cultures is not due to their death, but rather to the reduced expression of TH and that the simultaneous exposure to CNTF and NE upregulates TH. Effects on TH-positive cell number were not evoked by CNTF or NE alone. The CNTF/NE effect was dependent on protein synthesis, but was only partially inhibited by RNA synthesis inhibitors, suggesting that both transcription from preexisting mRNA and synthesis of new RNA were stimulated. The effect of CNTF/NE was mediated by alpha 2-adrenoceptors, since it was blocked by alpha 2-antagonists and since alpha 2-agonists were able to substitute for NE. Our results suggest a novel mechanism of regulation of the phenotype of the noradrenergic LC neuron, involving the collaborative influences of CNTF and norepinephrine, their own neurotransmitter.

Adrenergic Fibers↗
PubMed1993

Neurotropism of nerve growth factor for adult rat septal cholinergic axons in vivo.

Nerve growth factor (NGF) can induce sprouting of axotomized adult rat medial septum cholinergic neurons and promote their regeneration into septohippocampal nerve grafts and hippocampal formation. This study investigated the potential neurotropic (chemotactic/attracting) action of NGF in the adult rat cholinergic septohippocampal regeneration model. (i) Some animals received sciatic nerve grafts between the disconnected septum and hippocampal formations on each side. A 4-week infusion with NGF into the rostral portion of the lateral ventricle induced sprouting of cholinergic fibers in the dorsolateral septum with a gradient toward the lateral ventricle. However, the number of cholinergic axons entering the nerve bridge was only one-third that observed in vehicle-infused animals, suggesting that NGF had diverted many of the regrowing axons away from the nerve toward the ventricle. (ii) In animals implanted with nerves for 2 weeks and concurrently infused with NGF into the fornix, proximal to the lesion and grafts, cholinergic sprouting occurred in the mediodorsal septum, i.e., was oriented toward the infused fornix. Essentially no fibers had entered the nerve bridge, suggesting that all regrowing fibers had remained near the NGF source. (iii) When animals with a unilateral fimbria-fornix transection (but no nerve graft) were infused with NGF into the lateral ventricle on the opposite side, cholinergic sprouting was oriented toward the midline of the septum. (iv) Infusion of low doses of NGF directly into the (lesioned) septum induced a sprouting response localized around the infusion site. (v) No sprouting occurred when intraventricular NGF infusion was applied to normal (nonlesioned) animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1993

Convergent regulation by ciliary neurotrophic factor and dopamine of tyrosine hydroxylase expression in cultures of rat substantia nigra.

Ciliary neurotrophic factor and dopamine were found to enhance the expression of tyrosine hydroxylase immunoreactivity in cultured neurons from the substantia nigra of 16-day-old rat fetuses. The number of tyrosine hydroxylase-positive cells decreased progressively to approximately 30% by 96 h. Treatment with 5 microM dopamine maintained the tyrosine hydroxylase-positive neurons at 60% for 48 h, but not for longer. Concurrent treatment with 5 microM dopamine and 20 trophic units/ml ciliary neurotrophic factor had a greater impact on tyrosine hydroxylase-positive cells, resulting in the maintenance of 70% of the initial number for up to 72 h, but not beyond that time. When dopamine or dopamine/ciliary neurotrophic factor treatments were applied for 24 h after a 48-h delay, the number of tyrosine hydroxylase-positive cells was restored to 60 and 80%, respectively, but not restoration was observed with 96-h delayed treatments. These results suggest that dopamine and ciliary neurotrophic factor, alone or in combination, are not able to support the survival of tyrosine hydroxylase-positive neurons, but reduce their apparent numerical loss by enhancing the expression of tyrosine hydroxylase. The effects of dopamine, alone or in combination with ciliary neurotrophic factor, were predominantly mediated by D2 receptors, since they were blocked by selective D2 receptor antagonists and since the D2 receptor agonist quinpirole was able to substitute for dopamine. The effects of dopamine and ciliary neurotrophic factor were similar in astroblast-rich and in astroblast-depleted cultures, suggesting that they were not mediated through glial cells. These results extend our previous observations on locus coeruleus cultures, in which the concurrent treatment with ciliary neurotrophic factor and norepinephrine was shown to enhance tyrosine hydroxylase expression (but not survival) of noradrenergic neurons. They also consolidate the view that ciliary neurotrophic factor and the neuron's own transmitter act in convergence and in an autocrine/paracrine mode as regulators of the corresponding neurotransmitter phenotype.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1993

Potential regulation by trophic factors of low-affinity NGF receptors in spinal motor neurons.

Developing spinal motor neurons (SMN) express low-affinity nerve growth factor receptors (LNGFR) but not high-affinity transducing NGF receptors. Moreover, SMN are not supported by NGF in vitro. In the normal adult rat most SMN are not LNGFR immunoreactive (LNGFR-IR), but they transiently reexpress LNGFR (though not the high-affinity receptor) after peripheral nerve injury. With a cut lesion of the sciatic nerve (when only a neuroma forms), the number of LNGFR-IR SMN at L4-L6 rapidly increases to a maximum between day 1 and 7 and returns to baseline levels by day 30. After a crush lesion (accompanied by regeneration to the muscle), LNGFR-IR SMN appear in about the same numbers, but they start to disappear 1 week later. We speculate that the similar appearance and differential decline of LNGFR-IR seen after the two types of lesions are regulated by the availability of a common signal such as ciliary neurotrophic factor. The adult SMN model provides a good opportunity to investigate the reexpression of LNGFR after peripheral nerve injury, and more generally, the unknown role and regulation of LNGFR.

Animals↗
PubMed1993

Nerve growth factor immunoreactivity in the anterior pituitary of the rat.

Nerve growth factor (NGF) has long been recognized for its neurotrophic actions upon sensory and sympathetic neurons of the PNS and upon cholinergic neurons of the CNS basal forebrain. Much evidence, however, suggests that potential reciprocal interactions between NGF and various endocrine systems may also occur. In the present investigation we used immunohistochemical techniques to investigate whether NGF is found within the adult rat pituitary, thereby suggesting a possible interaction within this critical neuroendocrine gland. Our results indicate that NGF immunoreactivity is present only within the anterior lobe of the male and female rat pituitary and is exclusively localized within cells immunoreactive for thyroid stimulating hormone (TSH).

Animals↗
PubMed1993

CNTF promotes the survival of neonatal rat corticospinal neurons in vitro.

Corticospinal neurons were identified in cell cultures of neonatal rat cortex by immunostaining of cholera toxin B subunit (CTB), retrogradely transported from the cervical part of the spinal cord. The CTB-immunoreactive neurons were larger than the neurons in the overall (unstained) neuronal population and represented a small fraction of it (average of 0.3%) after 6 hours in vitro. The number of both total and CTB-labeled neurons declined progressively with time in culture. The neuronal death was, however, markedly faster in the CTB-labeled neuronal population than in the overall neuronal population. Ciliary neurotrophic factor (CNTF) promoted the survival of CTB-positive corticospinal neurons in a dose-dependent manner; with CNTF, the death rate of the CTB-labeled neurons became identical to that of the overall population.

Animals↗