Upregulation Of Neurotrophic Factor Research Articles

Time Course of Neurotrophic Factor Upregulation and Retinal Protection against Light-Induced Damage after Optic Nerve Section

To assess neurotrophic factor upregulation in the retina after damage to the optic nerve and relate that regulation to changes in photoreceptor stability and function. Retinas of adult pigmented (Long-Evans) rats were examined at successive times (1-60 days) after unilateral optic nerve section. The distribution and expression of ciliary neurotrophic factor (CNTF) and basic fibroblast growth factor (FGF-2) and their receptor elements FGFR1 and CNTFRalpha were studied with immunohistochemistry and Western blot analysis. FGF-2 and CNTF mRNA levels were also assessed, with semiquantitative reverse transcription-PCR. Levels and localization of the intracellular signaling molecule ERK and its activated, phosphorylated form pERK, were examined by immunohistochemistry. To assess the correlation between neurotrophic factor levels and their protective effect against light damage, albino (Sprague-Dawley) rats were exposed to bright continuous light (1000 lux) for 24 or 48 hours at successive times after nerve section. The TUNEL technique was used to visualize neuronal cell death in the retina. CNTF upregulation was detected 1 week after optic nerve section, peaked at 2 weeks, and fell to control levels at 4 weeks. CNTF appeared first in the inner retina in the ganglion cells, then in the Muller cells in which it became prominent at the outer limiting membrane (OLM) and in the outer segment (OS) region of photoreceptors. FGF-2 upregulation became prominent, particularly in photoreceptors, 21 to 28 days after surgery, continued to 2 months, and slowly declined thereafter. Double labeling with antibodies to ligand and the receptor showed colocalization of CNTF to its receptor at the OS region, whereas FGF-2-to-FGFR1 binding was found in the outer nuclear (ONL) and outer plexiform (OPL) layers. Optic nerve section provided a significant protective effect against light-induced damage in the first 2 weeks. There was no protection when animals were exposed to damaging light 1 month after nerve section. The upregulation of CNTF 7 to 14 days after nerve section correlates with a reduction in the a-wave described previously. Colocalization of CNTF and CNTFRalpha on the outer segments suggests that CNTF acts at the photoreceptor membrane. The slower upregulation of FGF-2 correlates with a reduction of the b-wave. FGF-2/FGFR1 colocalization in the OPL suggests that this factor acts at the synaptic terminals of photoreceptors, modulating the release of neurotransmitters. The time course of pERK upregulation suggests that the successive upregulation of CNTF and FGF-2 activates the ERK pathway. Based on the time course of protection against bright continuous light, it seems that CNTF plays a major role in this effect, and FGF-2 has a less important role in the protection against light-induced damage.

A combined treatment with 1α,25-dihydroxy-vitamin D 3 and 17β-estradiol reduces the expression of heat shock protein-32 (HSP-32) following cerebral cortical ischemia

1α,25-(OH) 2-vitamin D 3 (1,25-D 3) and 17β-estradiol are both known to act neuroprotectively in certain experimental in vitro and in vivo settings and it has been noted that both steroids lead to an upregulation of certain neurotrophic factors. Here, we studied the effects of 1α,25-(OH) 2-vitamin D 3 or 17β-estradiol or their combined application on heat shock protein-32 (HSP-32) distribution after focal cortical ischemia using the well established photothrombosis model. Heat shock protein-32 is a well-established marker of the cerebral oxidative stress response and contributes to neuroprotection by metabolising cytotoxic free heme to carbon monoxide, iron and biliverdin. Photothrombotically lesioned rats were injected i.p. 1 h after injury with either 1 μg 1α,25-(OH) 2-vitamin D 3/kg or 7 μg 17β-estradiol/kg or a combination of both steroids. Groups of non-lesioned steroid-treated rats and lesioned, solvent-treated rats served as controls. In contrast to non-lesioned rats, in lesioned animals a significant increase in heat shock protein-32 expression occurred which was slightly, but non-significantly altered in the groups treated either with 1α,25-(OH) 2-vitamin D 3 or 17β-estradiol alone when compared to the solvent-treated control group. Only the combined treatment with 1α,25-(OH) 2-vitamin D 3 and 17β-estradiol resulted in a significant reduction of glial heat shock protein-32 immunoreactivity within the lesion-remote cortical areas supplied by the affected middle cerebral artery (MCA), indicating that both steroids act synergistically in a protective manner.

Voluntary exercise following traumatic brain injury: brain-derived neurotrophic factor upregulation and recovery of function

Voluntary exercise leads to an upregulation of brain-derived neurotrophic factor (BDNF) and associated proteins involved in synaptic function. Activity-induced enhancement of neuroplasticity may be considered for the treatment of traumatic brain injury (TBI). Given that during the first postinjury week the brain is undergoing dynamic restorative processes and energetic changes that may influence the outcome of exercise, we evaluated the effects of acute and delayed exercise following experimental TBI. Male Sprague–Dawley rats underwent either sham or lateral fluid-percussion injury (FPI) and were housed with or without access to a running wheel (RW) from postinjury days 0–6 (acute) or 14–20 (delayed). FPI alone resulted in significantly elevated levels of hippocampal phosphorylated synapsin I and phosphorylated cyclic AMP response element-binding-protein (CREB) at postinjury day 7, of which phosphorylated CREB remained elevated at postinjury day 21. Sham and delayed FPI-RW rats showed increased levels of BDNF, following exercise. Exercise also increased phosphorylated synapsin I and CREB in sham rats. In contrast to shams, the acutely exercised FPI rats failed to show activity-dependent BDNF upregulation and had significant decreases of phosphorylated synapsin I and total CREB. Additional rats were cognitively assessed (learning acquisition and memory) by utilizing the Morris water maze after acute or delayed RW exposure. Shams and delayed FPI-RW animals benefited from exercise, as indicated by a significant decrease in the number of trials to criterion (ability to locate the platform in 7 s or less for four consecutive trials), compared with the delayed FPI-sedentary rats. In contrast, cognitive performance in the acute FPI-RW rats was significantly impaired compared with all the other groups. These results suggest that voluntary exercise can endogenously upregulate BDNF and enhance recovery when it is delayed after TBI. However, when exercise is administered to soon after TBI, the molecular response to exercise is disrupted and recovery may be delayed.

Neuroprotective role of phosphodiesterase inhibitor ibudilast on neuronal cell death induced by activated microglia

The phosphodiesterase inhibitor, ibudilast, has many effects on lymphocytes, endothelial cells, and glial cells. We examined the neuroprotective role of ibudilast in neuron and microglia co-cultures. Ibudilast significantly suppressed neuronal cell death induced by the activation of microglia with lipopolysaccharide (LPS) and interferon (IFN)-γ. To examine the mechanisms by which ibudilast exerts a neuroprotective role against the activation of microglia, we examined the production of inflammatory and anti-inflammatory mediators and trophic factors following ibudilast treatment. In a dose-dependent manner, ibudilast suppressed the production of nitric oxide (NO), reactive oxygen species, interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α and enhanced the production of the inhibitory cytokine, IL-10, and additional neurotrophic factors, including nerve growth factor (NGF), glia-derived neurotrophic factor (GDNF), and neurotrophin (NT)-4 in activated microglia. Thus, ibudilast-mediated neuroprotection was primarily due to the inhibition of inflammatory mediators and the upregulation of neurotrophic factor. In the CA1 region of hippocampal slices, long-term potentiation (LTP) induced by high frequency stimulation (HFS) could be inhibited with LPS and interferon-γ stimulation. Ibudilast returned this LTP inhibition to the levels observed in controls. These results suggest that ibudilast may be a useful neuroprotective and anti-dementia agent counteracting neurotoxicity in activated microglia.

Glial cell line-derived neurotrophic factor and brain-derived neurotrophic factor sustain the axonal regeneration of chronically axotomized motoneurons in vivo

In contrast to injuries in the central nervous system, injured peripheral neurons will regenerate their axons. However, axotomized motoneurons progressively lose their ability to regenerate their axons, following peripheral nerve injury often resulting in very poor recovery of motor function. A decline in neurotrophic support may be partially responsible for this effect. The initial upregulation of glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) by Schwann cells of the distal nerve stump after nerve injury has led to the speculation that they are important for motor axonal regeneration. However, few experiments directly measure the effects of exogenous BDNF or GDNF on motor axonal regeneration. This study provided the first direct and quantitative evidence that long-term continuous treatment with exogenous GDNF significantly increased the number of motoneurons which regenerate their axons, completely reversing the negative effects of chronic axotomy. The beneficial effect of GDNF was not dose-dependent. A combination of exogenous GDNF and BDNF on motor axonal regeneration was significantly greater than either factor alone, and this effect was most pronounced following long-term continuous treatment. The ability of GDNF, either alone or in combination with BDNF, to increase the number of motoneurons that regenerated their axons correlated well with an increase in axon sprouting within the distal nerve stump. Thus long-term continuous treatment with neurotrophic factors, such as GDNF and BDNF, can be used as a viable treatment to sustain motor axon regeneration.

Factors influencing nerve regeneration

This paper describes the most important cellular and molecular factors that influence nerve regeneration. The first prerequisite for axonal regeneration is survival of the neuron. This depends on neuron type, age, and the degree and proximity of the injury to the cell body. Spinal motoneurons are less susceptible to injury-induced death than cranial motoneurons and sensory neurons. The surviving neurons undergo changes characteristic of a switch from a transmitting mode to a growing mode. They produce various neurotrophic factors and their receptors influencing the neuron and the non-neuronal cells such as Schwann cells. The distal nerve stump undergoes degenerative processes including removal of axons and phagocytosis of myelin debris, the so-called Wallerian degeneration. Until the second day phagocytosis is done by Schwann cells, hematogenous macrophages invade the distal stump at the second day and phagocyte the whole debris within two weeks. Devoid of axonal contact, the myelinating Schwann cells switch their function from myelination to growth support for the regenerating axons, including cell proliferation, downregulation of myelin components and upregulation of neurotrophic factors. Additionally, the Schwann cells form the so-called Bands of Büngner, cell columns serving as pathway for the growing axon. Trophic factors, cell adhesion molecules and extracellular matrix influence the neuron, the growing axon and the endorgan as well as the non-neuronal cells such as Schwann cells, fibroblasts and macrophages. Application of drugs or trophic substances to enhance nerve regeneration after trauma and reconstruction is in the very beginning, and thus requires further experimental and clinical studies. Experimentally, FK 506 was found to support axonal regeneration after crush lesions and nerve grafting. Growth factors are currently administered clinically in other neurological diseases.

Bimodal upregulation of glial cell line-derived neurotrophic factor (GDNF) in the neonatal rat brain following ischemic/hypoxic injury

In order to delineate the spatial and temporal patterns of glial cell line-derived neurotrophic factor (GDNF) expression following ischemic/hypoxic injury in immature and neonatal brain, GDNF protein levels and immunocytochemistry were studied in rats subjected to a modified Levine procedure. Significant upregulation of GDNF protein occurred in a bimodal fashion in the damaged left cerebral cortex and hippocampus, while the levels in the right cerebral hemisphere of both control and ischemic groups remained relatively unchanged. Immunocytochemical studies indicated that the early rise in GDNF levels was most likely to be related to enhanced neuronal release of GDNF. The second rise was probably related to progressive astrogliosis that occurred in response to injury. In contrast to the lack of GDNF expression among astrocytes in normal mature brains, reactive astrocytes in the neonate appear to possess a ready capacity to express GDNF. Spatial and temporal changes in the pattern of GDNF expression following injury, as determined in this study may provide insight into the functions of GDNF in vivo and into possible therapeutic approaches toward prevention of damage or rescue of neurons following brain injury.

Neurotrophic Signaling in Normal and Degenerating Rodent Retinas

Several types of insult cause up-regulation of neurotrophic factors and their receptors in the retina resulting in decreased photoreceptor cell death from subsequent injury. This phenomenon is more prominent in rats than in mice and neurotrophic factors are more efficacious in rats than mice. If up-regulation of neurotrophic factor receptors on photoreceptor cells early in the course of degenerations contributes to neurotrophic factor survival-promoting activity, it may also increase the ability to detect neurotrophic factor-induced signaling in photoreceptors, particularly in rats. In this study, these hypotheses were investigated by performing immunohistochemical staining for the phosphorylated form of extracellular receptor kinase (pERK) or c-fos after intravitreous injection of neurotrophic factors in wild type rats or mice, or those with inherited retinal degenerations. In both rats and mice either early or late in the course of degeneration, or in wild type animals, intravitreous injection of brain-derived neurotrophic factor, ciliary neurotrophic factor, or fibroblast growth factor-2 caused immunostaining for pERK and c-fos in cells of the inner retina, particularly Müller cells, but not in photoreceptors. These data add to the mounting evidence suggesting that neurotrophic factors act indirectly through Müller cells to promote photoreceptor survival.

Resistance of the dentate gyrus to induced apoptosis during ageing is associated with increases in transforming growth factor-β1 messenger RNA

Up-regulation of endogenous neurotrophic factors may protect against apoptosis during ageing. Recent studies showed that the expression of several neurotrophic factors increased with age in specific regions of the rat brain. Previously, we showed that removal of trophic adrenal steroids by adrenalectomy induced apoptosis in the dentate gyrus of adult rats, which was accompanied by increased expression of transforming growth factor-β1 (TGF-β1) messenger RNA. In this study, we compared the relative densities of apoptotic cells in the dentate gyrus with TGF-β1 messenger RNA expression in virgin male Fischer 344 rats ranging from 2 to 26 months of age across three treatment groups: adrenalectomy, adrenalectomy with corticosterone replacement, or sham operation. Seven days after adrenalectomy an increase in the density of apoptotic cells was observed in rats of all age groups compared with sham-operated and corticosterone-treated groups. By in situ hybridisation, the glial messenger RNAs, TGF-β1 and glial fibrillary acidic protein as a marker of ageing, increased following adrenalectomy in the dentate gyrus in rats of all ages compared with control groups. Interestingly, within adrenalectomy groups, both the number and density of apoptotic cells decreased significantly by 6–8 months with a further decrease at 24–26 months of age. Furthermore, the amount of apoptosis corresponded to changes in TGF-β1 expression, notably in: (i) adrenalectomised rats showing a significant inverse correlation and (ii) 24–26-month-old rats with the lowest induced apoptosis showing increased expression at the time of adrenalectomy. These studies show that resistance to adrenalectomy-induced apoptosis in the dentate gyrus is associated with increases in TGF-β1 messenger RNA expression. Furthermore, the endogenous up-regulation of neurotrophic factors, such as the increase in TGF-β1 expression in the oldest rats, suggests that the aged brain may have compensatory mechanisms, which protect against apoptosis.

Neurotrophic Factors and Receptors in the Immature and Adult Spinal Cord after Mechanical Injury or Kainic Acid

Delivery of neurotrophic factors to the injured spinal cord has been shown to stimulate neuronal survival and regeneration. This indicates that a lack of sufficient trophic support is one factor contributing to the absence of spontaneous regeneration in the mammalian spinal cord. Regulation of the expression of neurotrophic factors and receptors after spinal cord injury has not been studied in detail. We investigated levels of mRNA-encoding neurotrophins, glial cell line-derived neurotrophic factor (GDNF) family members and related receptors, ciliary neurotrophic factor (CNTF), and c-fos in normal and injured spinal cord. Injuries in adult rats included weight-drop, transection, and excitotoxic kainic acid delivery; in newborn rats, partial transection was performed. The regulation of expression patterns in the adult spinal cord was compared with that in the PNS and the neonate spinal cord. After mechanical injury of the adult rat spinal cord, upregulations of NGF and GDNF mRNA occurred in meningeal cells adjacent to the lesion. BDNF and p75 mRNA increased in neurons, GDNF mRNA increased in astrocytes close to the lesion, and GFRalpha-1 and truncated TrkB mRNA increased in astrocytes of degenerating white matter. The relatively limited upregulation of neurotrophic factors in the spinal cord contrasted with the response of affected nerve roots, in which marked increases of NGF and GDNF mRNA levels were observed in Schwann cells. The difference between the ability of the PNS and CNS to provide trophic support correlates with their different abilities to regenerate. Kainic acid delivery led to only weak upregulations of BDNF and CNTF mRNA. Compared with several brain regions, the overall response of the spinal cord tissue to kainic acid was weak. The relative sparseness of upregulations of endogenous neurotrophic factors after injury strengthens the hypothesis that lack of regeneration in the spinal cord is attributable at least partly to lack of trophic support.

Upregulation of ciliary neurotrophic factor (CNTF) and CNTF receptor alpha in rat kidney with ischemia-reperfusion injury.

Ciliary neurotrophic factor (CNTF) is presumed to play a role as a survival factor in neuronal cells, but little is known about its role in the kidney. To investigate this, the expression of CNTF and CNTF receptor alpha (CNTFR alpha) was analyzed in the ischemic rat kidney. An ischemia/reperfusion (I/R) injury was induced by clamping both renal arteries for 45 min. Animals were killed at 1, 2, 3, 5, 7, 14, and 28 d after ischemia. The expression of CNTF and CNTFR alpha was monitored by reverse transcription-PCR, in situ hybridization, immunoblotting, immunohistochemistry, and electron microscopy. In sham-operated rat kidneys, CNTF expression was weak and limited to the descending thin limb of the loop of Henle. With I/R injury, CNTF mRNA and protein expressions were strikingly increased as compared with the sham-operated rat kidney, and the immunoreactivity of CNTF was mainly observed in the regenerating proximal tubules. The expression of CNTFR alpha mRNA was also increased after I/R injury, and its location and expression patterns were similar to the expression of CNTF. These findings suggest a possible role of CNTF as a growth factor during renal tubular repair processes after I/R injury and an autocrine or paracrine function of CNTF acting against CNTFR alpha.

Amelioration of neurotoxic effects of HIV envelope protein gp120 by fibroblast growth factor: a strategy for neuroprotection.

Approximately two thirds of patients with human immunodeficiency virus encephalitis (HIVE) show cognitive impairment and neurodegeneration, while one third are cognitively unimpaired and their neuronal populations are preserved. Thus, it is possible that these individuals might have the capacity to produce neurotrophic factors capable of protecting neurons against the deleterious effects of HIV. In this context, the main objective of this study was to determine whether fibroblast growth factor 1 (FGF1) is protective against HIV. For this purpose levels of FGF1 immunoreactivity were determined in the frontal cortex of 35 AIDS cases subdivided into 4 groups according to the presence or absence of HIVE and neurodegeneration. In cases without both HIVE and neurodegeneration, mild to moderate levels of FGFI immunoreactivity were observed in pyramidal neurons, while in cases with HIVE but without neurodegeneration, levels were significiantly elevated. In contrast, individuals with both HIVE and neurodegeneration showed low levels of neuronal FGF1 immunoreactivity. Furthermore, studies in primary human neuronal cultures treated with the HIV envelope protein-gp120 in the presence or absence of FGF1 showed that FGF1 was protective against gpl20 neurotoxicity in a dose-dependent manner. Taken together, these results support the notion that upregulation of certain neurotrophic factors, such as FGF1, might protect the central nervous system from the neurotoxic effects of HIV.

Up-regulation of glial cell line-derived neurotrophic factor (GDNF) following traumatic spinal cord injury.

We investigated the temporal and spatial expression patterns of the GDNF gene after subjecting rats to an acute contusion injury of the spinal cord using the weight drop technique. Reverse transcriptase-polymerase chain reaction (RT-PCR) revealed that GDNF transcription in the spinal cord began to increase within 30 min after injury and peaked within 3 h. Immunohistochemical analysis showed GDNF immunoreactivity to be present mainly in microglia and macrophages 1 day after injury, but not in neurons or astrocytes. This immediate upregulation of GDNF gene expression may be a component of an inflammatory process and probably exerts a protective effect on neurons following spinal cord injury (SCI).

Upregulation of glial cell line-derived neurotrophic factor (GDNF) in the rat cochlea following noise

There are endogenous intracellular mechanisms that provide cells with protection from stress, as well as repair from damage. These pathways often involve stress proteins and neurotrophic factors. The present study used Western blot analysis to examine changes in glial cell line-derived neurotrophic factor (GDNF) following noise overstimulation. A noise exposure was utilized which causes a temporary threshold shift and has been previously shown to upregulate heat shock protein 72 in the rat cochlea. This noise exposure also provides protection from a second noise exposure that would otherwise cause a permanent threshold shift. Experimental animals were assessed 2, 4, 8 and 12 h after cessation of noise exposure. Control animals received the same treatment except for the noise exposure and were assessed at the 8 h time point. A moderate expression of GDNF was observed in the normal cochlea. No significant change in GDNF levels was observed at 2 or 4 h following noise overstimulation. However, a significant increase was found at 8 h. At 12 h following noise overstimulation, GDNF levels were no longer significantly elevated from normal. These results suggest that GDNF is involved in the endogenous stress response in the cochlea and are consistent with the protection that exogenously applied GDNF has been shown to provide.

Upregulation of ciliary neurotrophic factor in reactive Müller cells in the rat retina following optic nerve transection

We have investigated the expression and cellular localization of ciliary neurotrophic factor (CNTF) in the rat retina following optic nerve transection. In the normal retina, CNTF immunoreactivity was restricted to profiles in the ganglion cell layer. Following optic nerve transection, immunoreactivity appeared in Müller cell somata and processes and its intensity increased between three and seven days post-lesion. Quantitative evaluation by immunoblotting confirmed that CNTF expression increased continuously up to 7 days after optic nerve transection (to 430% of control levels), but decreased again to 250% of controls at 4 weeks post-lesion. Our findings suggest that CNTF supplied by Müller cells may play a protective role for axotomized ganglion cells in the rat retina.

Up-regulation of glial cell line-derived neurotrophic factor (GDNF) following traumatic spinal cord injury

Up-regulation of glial cell line-derived neurotrophic factor (GDNF) following traumatic spinal cord injury

Neuronal–Glial Differential Expression of TGF-α and Its Receptor in the Dorsal Root Ganglia in Response to Sciatic Nerve Lesion

Injury to peripheral nerves often results in structural and functional changes in the dorsal root ganglia (DRG). Although the mechanisms underlying these changes remain largely unknown, satellite cell activation and up-regulation of several neurotrophic factors in the DRG occur in response to the nerve lesion, modulating the plasticity of affected neurons. To investigate potential roles of transforming growth factor α (TGF-α) in these plastic changes in the DRG following a sciatic nerve transection, here we examined the expression in DRGs of TGF-α and its receptor (EGF receptor), molecules known to be mitogenic to glia and Schwann cells and to be neurotrophic for some differentiated neurons. In the normal DRGs, TGF-α and its receptor are expressed mainly in small neurons and satellite cells surrounding some large or medium-sized neurons as determined by immunohistochemistry and in situ hybridization. In response to sciatic nerve lesion, there was a marked and differential up-regulation of TGF-α and EGF receptor expression within DRG, evident as early as 24 h after lesion and lasting for at least 14 days. While the up-regulated TGF-α was localized mainly on satellite cells in the ipsilateral and contralateral DRGs, EGF receptor up-regulation was mainly neuronal (with the expression expanding to include all neurons) in the ipsilateral DRGs, but mainly glial in the contralateral DRGs. These changes in TGF-α and its receptor expression suggest that TGF-α may play a role in the satellite cell proliferation and/or activation as well as in neuronal survival after nerve lesion.

Neuroprotective effects of brain-derived neurotrophic factor in seizures during development

Although the immature brain is highly susceptible to seizures, it is more resistant to seizure-induced neuronal loss than the adult brain. The developing brain contains high levels of neurotrophins which are involved in growth, differentiation and survival of neurons. To test the hypothesis that neurotrophins may protect the developing brain from seizure-induced neuronal loss, brain-derived neurotrophic factor up-regulation was blocked by intracerebroventricular infusion of an 18mer antisense oligodeoxynucleotide sequence to brain-derived neurotrophic factor in 19-day-old rats using micro-osmotic pumps. Control rats were infused with sense or missense oligodeoxynucleotide. Status epilepticus was induced by intraperitoneal administration of kainic acid 24 h after the start of oligodeoxynucleotide infusion. Seizure duration was significantly increased in the antisense oligodeoxynucleotide plus kainic acid group compared to groups that received kainic acid alone or kainic acid plus sense or missense oligodeoxynucleotide. There was no difference between groups in the latency to forelimb clonus. A twofold increase in brain-derived neurotrophic factor levels was observed in the hippocampus 20 h following kainic acid-induced seizures. This kainic acid-induced increase was absent in animals receiving infusion of antisense oligodeoxynucleotide to brain-derived neurotrophic factor at time of seizure induction. Hippocampi of rats in this group (antisense oligodeoxynucleotide plus kainic acid) showed a loss of CA1 and CA3 pyramidal cells and hilar interneurons. This neuronal loss was not dependent upon seizure duration since animals injected with diazepam to control seizure activity in the antisense plus kainic acid group also showed similar neuronal loss. Administration of kainic acid or infusion of antisense alone did not produce any cell loss in these regions. Induction of seizures at postnatal day 20, in the presence or absence of antisense oligonucleotide, did not produce an impairment in learning and memory when tested 15 days later in the Morris water maze. The hippocampi of these animals did not show any synaptic reorganization as assessed by growth-associated protein-43 immunostaining and Timm staining. Our findings confirm prior studies demonstrating that seizures in the immature brain are associated with little, if any, cell loss. However, when seizure-induced increase in brain-derived neurotrophic factor is blocked, seizures do result in neuronal loss in the developing brain. Thus, brain-derived neurotrophic factor appears to provide protection against kainic acid seizure-induced neuronal damage in the developing brain.

Up-regulation of glial cell line-derived neurotrophic factor (GDNF) expression in regenerating muscle fibers in neuromuscular diseases

Glial cell line-derived neurotrophic factor (GDNF) has been shown to exert a target-derived trophic factor for motor neurons. Immunohistochemical analyses revealed that expression of GDNF in regeneration muscle fibers was up-regulated in polymyositis (PM) and Duchenne type muscular dystrophy (DMD). Reverse transcriptase polymerase chain reaction (RT-PCR) analyses showed that the full length GDNF was up-regulated in PM and DMD muscle; normal muscle exhibited mostly truncated GDNF. The results indicate that the GDNF expression is regulated in regeneration of human skeletal muscle.

Cellular hybridization for BDNF, trkB, and NGF mRNAs and BDNF-immunoreactivity in rat forebrain after pilocarpine-induced status epilepticus.

The messenger RNAs (mRNAs) for the neurotrophins, brain-derived neurotrophic factor (BDNF), and nerve growth factor (NGF), are upregulated during epileptic seizure activity, as visualized by in situ hybridization techniques. Neurotrophins might be protective against excitotoxic cell stress, and the upregulation during seizures might provide such cell protection. In this study, a high dose of pilocarpine (300 mg/kg) was used to induce long-lasting, limbic motor status epilepticus and a selective pattern of brain damage. The regulation of BDNF, trkB, and NGF mRNA was studied by in situ hybridization at 1, 3, 6, and 24 h after induction of limbic motor status epilepticus. BDNF immunoreactivity was examined with an anti-peptide antibody and the neuropathological process studied in parallel. BDNF mRNA increased in hippocampus, neocortex, piriform cortex, striatum, and thalamus with a maximum at 3-6 h. Hybridization levels increased earlier in the resistant granule and CA1 cells as compared to the vulnerable CA3 neurons. BDNF immunoreactivity was elevated in dentate gyrus at 3-6 h. trkB mRNA increased in the entire hippocampus. NGF mRNA in hippocampus appeared in dentate gyrus at 3-6 h and declined in hilar neurons at 6-24 h. Cell damage was found in the CA3 area, entire basal cortex, and layers II/III of neocortex. Endogenous neurotrophins are upregulated during status epilepticus caused by pilocarpine, which is related to the coupling between neuronal excitation and trophic factor expression. This upregulation of neurotrophic factors may serve endogenous protective effects; however, the excessive levels of neuronal hyperexcitation resulting from pilocarpine seizures lead to cell damage which cannot be prevented by endogenous neurotrophins.