Achyranthes bidentata polypeptide k enhances the survival, growth and axonal regeneration of spinal cord motor neurons in vitro.

Achyranthes bidentata polypeptide k (ABPPk), a powerful active component from a traditional Chinese medicinal herb-Achyranthes bidentata Bl., has exhibited promising neuroprotective activity due to its multiple-targeting capability. However, the effect of ABPPk on the survival, growth and axonal regeneration of spinal cord motor neurons remains unclear. Here, a modified method, which is more optimized for embryonic cells in ambient carbon dioxide levels, was used for acquisition of rat embryonic spinal cord motor neurons with high survival and purity. ABPPk concentration-dependently enhanced the neuronal viability and promoted the neurite outgrowth. Co-culture of motor neurons and skeletal myocytes model indicated that ABPPk enhanced the neuromuscular junction development and maturation. A microfluidic axotomy model was further established for the axonal disconnection, and ABPPk significantly accelerated the axonal regeneration of motor neurons. Furthermore, we demonstrated that the upregulation of three neurofilament protein subunits in motor neurons might be relevant to the mechanisms of the growth-promoting effect of ABPPk. Our findings provide an experimental and theoretical basis for the development of ABPPk as a potential application in the development of treatment strategy for nerve injury diseases.

Levetiracetam Protects Against Cognitive Impairment of Subthreshold Convulsant Discharge Model Rats by Activating Protein Kinase C (PKC)-Growth-Associated Protein 43 (GAP-43)-Calmodulin-Dependent Protein Kinase (CaMK) Signal Transduction Pathway.

BACKGROUND Subclinical epileptiform discharges (SEDs) are defined as epileptiform electroencephalographic (EEG) discharges without clinical signs of seizure in patients. The subthreshold convulsant discharge (SCD) is a frequently used model for SEDs. This study aimed to investigate the effect of levetiracetam (LEV), an anti-convulsant drug, on cognitive impairment of SCD model rats and to assess the associated mechanisms. MATERIAL AND METHODS A SCD rat model was established. Rats were divided into an SCD group, an SCD+ sodium valproate (VPA) group, and an SCD+ levetiracetam (LEV) group. The Morris water maze was used to evaluate the capacity of positioning navigation and space exploration. The field excitatory post-synaptic potentials (fEPSPs) were evaluated using a bipolar stimulation electrode. NCAM, GAP43, PS95, and CaMK II levels were detected using Western blot and RT-PCR, respectively. PKC activity was examined by a non-radioactive method. RESULTS LEV shortens the latency of platform seeking in SCD rats in positioning navigation. fEPSP slopes were significantly lower in the SCD group, and LEV treatment significantly enhanced the fEPSP slopes compared to the SCD group (P<0.05). The NCAM and GAP-43 levels were increased and PSD-95 levels were increased in SCD rats (P<0.05), which were improved by LEV treatment. The PKC activity and CaMK II levels were decreased in SCD rats and LEV treatment significantly enhanced PKC activity and increased CaMK II levels. CONCLUSIONS Cognitive impairment in of SCD model rats may be caused by decreased PKC activity, low expression of CaMK II, and inhibition of LTP formation. LEV can improve cognitive function by activating the PKC-GAP-43-CaMK signal transduction pathway.

AMPA receptors are involved in prefrontal direct current stimulation effects on long-term working memory and GAP-43 expression.

Anodal Direct Current Stimulation (DC) over prefrontal cortex improves working memory. This study investigated the influence of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) on prefrontal anodal DC-induced effects on spatial working memory and GAP-43 expression. Male Wistar rats well-trained in radial maze procedures received five sessions of anodal epidural DC stimulation (eDCS: 400 µA, 13 min, one daily session) over the left mPFC, or a respective sham procedure, and afterwards they received a single dose (1 mg/kg) of perampanel (PRP), an AMPARs antagonist, or vehicle 30 min before the performance of 4-h delayed task. The prefrontal cortex (PFC) and hippocampus (HPC) were removed 24-h later and GAP-43 (growth-associated protein) expression was measured by Western blot analysis. Repetitive eDCS decreased the number of errors in the 4-h post-delay performance (p < 0.05) and increased the expression of GAP-43 (p < 0.01) in the PFC when compared to sham stimulation. These behavioral and prefrontal molecular changes induced by the repetitive eDCS seem to involve AMPAR activity, because they were abolished when AMPARs were blocked by PRP (p < 0.01 and 0.05, respectively). Besides, in the HPC, changes of GAP-43 expression induced by eDCS was only seen when AMPARs were blocked by PRP. Therefore, the neuronal plasticity involving AMPARs may underlie, at least in part, the improving of spatial working memory and GAP-43 expression induced by the repetitive anodal prefrontal DC stimulation.

Luteolin Ameliorates Cognitive Impairments by Suppressing the Expression of Inflammatory Cytokines and Enhancing Synapse-Associated Proteins GAP-43 and SYN Levels in Streptozotocin-Induced Diabetic Rats.

Luteolin, a flavonoid isolated from Cirsium japonicum, has antioxidant, anti-inflammatory and neuroprotective activities. Our previous studies brought a prospect that luteolin benefited diabetic rats with cognitive impairments. In this study, we examined whether luteolin could suppress the inflammatory cytokines, thus increasing synapse-associated proteins in streptozotocin (STZ)-induced diabetes in rat models. The model rats underwent luteolin treatment for 8 consecutive weeks, followed by assessment of cognitive performances with MWM test. Nissl staining was employed to assess the neuropathological changes in the hippocampus and the effects of luteolin on diabetic rats. With animals sacrificed, expressions of inflammatory cytokines including interleukin-1ß (IL-1ß) and tumor necrosis factor-α (TNF-α) and synapse-associated proteins including growth-associated protein-43 (GAP-43) and synaptophysin (SYN) were determined. The results affirmed improvement of behavioral performances in the MWM test, downexpression of glycation end products (AGEs) in the plasma and the receptor for advanced glycation end products in the hippocampus, inhibition of IL-1ß and TNF-α in both the hippocampus and plasma in diabetic rats. Furthermore, luteolin treatment upregulated the expressions of GAP-43 and SYN in the hippocampus. Thus, luteolin could ameliorate the cognitive dysfunctions in STZ-induced diabetic rat model.

[The influence of dipole modifiers on the channel-forming activity of amyloid and amyloid-like peptides in lipid bilayers].

We have studied the steady-state transmembrane current induced by amyloid and amyloid-like peptides in lipid bilayers in the presence of dipole modifiers. It has been shown that the addition of dipole modifier, phloretin, to the membrane bathing solutions leads to an increase in the multichannel activity of amyloid beta-peptide fragment 25-35, [Gly35]-amyloid beta-peptide fragment 25--35, prion protein fragment 106-126 and amyloid-like peptides myr-BASP1 (1--13), myr-BASP1(1--19) and GAP-43(1--40). We have found that the effect of phloretin is not the result of dipole potential changes due to adsorption of this modifier on the membrane. Using the various fragments of amyloid beta-peptide, presenilin, prion protein and neuronal proteins BASP1 and GAP-43 allowes to conclude that the steady-state peptide-induced transmembrane current in the case of addition of phloretin is due to the electrostatic interaction between the positively charged channel-forming agents and negatively charged dipole modifier. The results obtained by electron microscopy have demonstrated that this interaction increases degree of peptide oligomerization.

Intrathecal administration of botulinum toxin type A improves urinary bladder function and reduces pain in rats with cystitis.

BACKGROUND: Botulinum toxin A (Onabot/A) has been shown to have an antinociceptive effect. This might be due to an impairment of sensory nerves not only in the peripheral but also in the central nervous system. In this work, we analysed both systems by studying the effect of intrathecal (i.t.) administration of botulinum toxin A in an animal model of bladder pain and hyperactivity induced by cyclophosphamide (CYP). METHODS: Rats were implanted with an i.t. catheter at the L6 segment. Bladder pain was induced by intraperitoneal (i.p.) injection of CYP. Five experimental groups were created: (1) Saline i.p. + i.t.; (2) Onabot/A i.t.; (3) CYP i.p. + saline i.t.; (4) CYP i.p. + Onabot/A i.t. 48 h after CYP; and (5) Onabot/A i.t. 30 days. Mechanical sensitivity was assessed in the abdomen and hindpaws. Motor activity was observed in an open-field arena. Bladder reflex activity was evaluated by cystometry. At the end, bladders and spinal cord were immunoreacted (IR) against cleaved SNAP-25 (cSNAP-25), c-Fos, p-ERK, calcitonin gene-related peptide (CGRP) and GAP43. RESULTS: The toxin reduced pain symptoms, bladder hyperactivity, expression of neuronal activation markers and CGRP, typically up-regulated in this inflammatory model. The presence of cSNAP-25 was detected in the spinal cord and bladder fibres from animals treated with Onabot/A. No somatic or visceral motor impairments were observed. CONCLUSIONS: Our findings suggest that i.t. Onabot/A has a strong analgesic effect in a model of severe bladder pain. This route of administration can be further explored to treat intractable forms of pain.

Growth-associated protein-43 expression in cocultures of dorsal root ganglion neurons and skeletal muscle cells with different neurotrophins.

INTRODUCTION: Both target skeletal muscle (SKM) cells and neurotrophins (NTs) are essential for the maintenance of neuronal function and nerve-muscle communication. The effects of different NTs and SKM cells on growth-associated protein-43 (GAP-43) expression in dorsal root ganglion (DRG) neurons have not been clarified. METHODS: The morphological relationship between DRG neurons and SKM cells in neuromuscular cocultures was observed by scanning electron microscopy. The levels of GAP-43 and its mRNA were determined after administration of different NTs. RESULTS: DRG neurons demonstrated dense neurite outgrowth in the presence of NTs. Distinct NTs promoted GAP-43 and its mRNA expression in neuromuscular cocultures of DRG neurons and SKM cells. CONCLUSIONS: These results offer new clues for a better understanding of the effects of distinct NTs on GAP-43 expression in DRG sensory neurons in the presence of target SKM cells and implicate NTs and target SKM cells in DRG neuronal regeneration.

Melatonin attenuates methamphetamine-induced reduction of tyrosine hydroxylase, synaptophysin and growth-associated protein-43 levels in the neonatal rat brain.

Methamphetamine (METH) is a most commonly abused drug which damages nerve terminals by causing formation of reactive oxygen species (ROS), apoptosis, and finally neuronal damage. Fetal exposure to neurotoxic METH causes significant behavioral effects. The developing fetus is substantially deficient in most antioxidative enzymes, and may therefore be at high risk from both endogenous and drug-enhanced oxidative stress. Little is known about the effects of METH on vesicular proteins such as synaptophysin and growth-associated protein 43 (GAP-43) in the immature brain. The present study attempted to investigate the effects of METH-induced neurotoxicity in the dopaminergic system of the neonatal rat brain. Neonatal rats were subcutaneously exposed to 5-10mg/kg METH daily from postnatal day 4-10 for 7 consecutive days. The results showed that tyrosine hydroxylase enzyme levels were significantly decreased in the dorsal striatum, prefrontal cortex, nucleus accumbens and substantia nigra, synaptophysin levels decreased in the striatum and prefrontal cortex and growth-associated protein-43 (GAP-43) levels significantly decreased in the nucleus accumbens of neonatal rats. Pretreatment with 2mg/kg melatonin 30 min prior to METH administration prevented METH-induced reduction in tyrosine hydroxylase, synaptophysin and growth-associated protein-43 protein levels in different brain regions. These results suggest that melatonin provides a protective effect against METH-induced nerve terminal degeneration in the immature rat brain probably via its antioxidant properties.

Diazinon oxon affects the differentiation of mouse N2a neuroblastoma cells.

The aim of this study was to assess the neurotoxicity of diazinon oxon (DZO), a major in vivo metabolite of the phosphorothionate insecticide diazinon (DZ), on differentiating mouse N2a neuroblastoma cells. When used at concentrations of 1, 5 and 10 microM, DZO did not cause cell death but it impaired the outgrowth of axon-like processes after 24 h. Densitometric scanning of Western blots of lysates of N2a cells revealed that exposure to 5 or 10 microM DZO for 24 h increased the expression of phosphorylated neurofilament heavy chain (NFH) compared to controls, while there was no significant change in total NFH. By contrast, treatment of N2a cells with 1-10 microM DZO resulted in marked reductions in the expression of the axon growth-associated protein GAP-43. DZO-treated cells also showed an increased expression of the heat shock protein HSP-70 compared to controls. The above biochemical changes were not temporally related to inhibition of acetylcholinesterase (AChE). These data suggest that biologically relevant, subcytotoxic levels of DZO may exert neurotoxic effects on differentiating cells and that the mechanisms involved are different from those attributed to its parent compound.

Peroxisome proliferator-activated receptor-alpha is required for the neurotrophic effect of oleic acid in neurons.

Oleic acid synthesized by astrocytes behaves as a neurotrophic factor for neurons, up-regulating the molecular markers of axonal and dendritic outgrowth, growth-associated protein 43 and microtubule-associated protein 2. In this work, the nature of the receptor involved in this neurotrophic effect was investigated. As oleic acid has been reported to be a ligand and activator of the peroxisome proliferator-activated receptor (PPAR), we focus on this family of receptors. Our results show that PPARalpha, beta/delta, and gamma are expressed in neurons in culture. However, only the agonists of PPARalpha, Wy14643, GW7647 and oleoylethanolamide, promoted neuronal differentiation, while PPAR beta/delta and gamma agonists did not modify neuronal differentiation. Consequently, we investigated the involvement of PPARalpha (Nr1c1) in oleic acid-induced neuronal differentiation. Our results indicate that oleic acid activates PPARalpha in neurons. In addition, the effect of oleic acid on neuronal morphology, growth-associated protein 43 and microtubule-associated protein 2 expression decreases in neurons after PPARalpha has been silenced by small interfering RNA. Taken together, our results suggest that PPARalpha could be the receptor for oleic acid in neurons, further broadening the range of functions attributed to this family of transcription factors. Although several works have reported that PPARalpha could be involved in neuroprotection, the present work provides the first evidence suggesting a role of PPARalpha in neuronal differentiation.

Chronic brain cytochrome oxidase inhibition selectively alters hippocampal cholinergic innervation and impairs memory: prevention by ladostigil.

A 25-35% reduction of brain cytochrome oxidase (COx) activity found in Alzheimer's disease (AD) could contribute to neuronal dysfunction and cognitive impairment. The present study replicated the reduction in brain COx activity in rats by administering sodium azide (NaN(3)) for 4 weeks via Alzet minipumps at the rate of 1 mg/kg/h, and determined its effect on hippocampal cholinergic transmission, spatial and episodic memory. NaN(3) caused a selective reduction in choline acetyltransferase (ChAT) immunoreactivity in the diagonal band, a major source of cholinergic input to the hippocampus and cingulate cortex, without altering the number of cholinergic neurons. NaN(3) also induced a significant increase in vesicular acetylcholine transporter (VAChT)-immunoreactive varicosities, GAP-43 in the subgranular layer and of transferrin receptors (TfR) in the hilus of the dentate gyrus. These neurochemical changes were associated with impairment in spatial learning in the Morris water maze and in episodic memory in the object recognition test. Chronic treatment with ladostigil, a novel cholinesterase and monoamine oxidase inhibitor, prevented the decrease in ChAT in the diagonal band, the compensatory increase in synaptic plasticity and TfR and the memory deficits without restoring COx activity. Ladostigil had no significant effect on ChAT activity, synaptic plasticity or TfR in control rats. Ladostigil may have a beneficial effect on cognitive deficits in AD patients that have a reduction in cortical COx activity and cholinergic hypofunction.

Cyclosporin-A enhances non-functional axonal growing after complete spinal cord transection.

Therapeutic approaches that promote both neuroprotection and neuroregeneration would be valuable for spinal cord (SC) injury therapies. Cyclosporin-A (CsA) is an immunosuppressant that, due to its mechanism of action, could both protect and regenerate the neural tissue after injury. Previous studies have already demonstrated that intraperitoneal administration of CsA at a dose of 2.5 mg/kg/12 h during the first 2 days after SC contusion, followed by 5 mg/kg/12 h orally, diminishes tissue damage and improves motor recovery. In order to evaluate the effect of this CsA dosing regimen on axonal growth, we assessed motor recovery, presence of axons establishing functional connections and expression of GAP-43 in rats subjected to a complete SC transection. The Basso-Beattie-Bresnahan rating scale did not show difference in motor recovery of CsA or vehicle-treated rats. Moreover, somato-sensorial evoked potentials demonstrated no functional connections in the SC of these animals. Nevertheless, histological studies showed that: i) a significant number of CsA-treated rats presented growing axons, although they deviated perpendicularly at the edge of the stumps, surrounding them, ii) the expression of GAP-43 in animals treated with CsA was higher than that observed in the control group. Finally, anterograde tracing of the corticospinal tract of rats subjected to an incomplete SC transection showed no axonal fibers reaching the caudal stump. In summary, CsA administered at the dosing-regimen that promotes neuroprotection in SC contused rats induces both GAP-43 expression and axonal growth; however, it failed to generate functional connections in SC transected animals.

Catalpol increases hippocampal neuroplasticity and up-regulates PKC and BDNF in the aged rats.

Rehmannia, a traditional Chinese medical herb, has a long history in age-related disease therapy. Previous work has indicated that catalpol is a main active ingredient performing neuroprotective effect in rehmannia, while the mechanism underlying the effect remains poorly understood. In this study, we attempt to investigate the effect of catalpol on presynaptic proteins and explore a potential mechanism. The hippocampal levels of GAP-43 and synaptophysin in 3 groups of 4 months (young group), 22-24 months (aged group) and catalpol-treated 22-24 months (catalpol-treated group) rats were evaluated by western blotting. Results clearly showed a significant decrease in synaptophysin (46.6%) and GAP-43 (61.4%) levels in the aged group against the young animals and an increase (45.0% and 31.8% respectively) in the catalpol-treated aged rats in comparison with the untreated aged group. In particular, synaptophysin immunoreactivity (OD) in the dentate granule layer of the hippocampus was increased 0.0251 in the catalpol-treated group as compared with the aged group. The study also revealed a catalpol-associated increase of PKC and BDNF in the hippocampus of the catalpol-treated group in comparison with the aged rats and highly correlated with synaptophysin and GAP-43. Such positive correlations between presynaptic proteins and signaling molecules also existed in the young group. These results suggested that catalpol could increase presynaptic proteins and up-regulate relative signaling molecules in the hippocampus of the aged rats. Consequently, it seemed to indicate that catalpol might ameliorate age-related neuroplasticity loss by "normalizing" presynaptic proteins and their relative signaling pathways in the aged rats.

Chronic vitamin D3 treatment protects against neurotoxicity by glutamate in association with upregulation of vitamin D receptor mRNA expression in cultured rat cortical neurons.

The vitamin D receptor (VDR) is believed to mediate different biologic actions of vitamin D3, an active metabolite of vitamin D, through regulation of gene expression after binding to specific DNA-response element (VDRE) on target genes. To further understand roles of both vitamin D3 and VDR in the central nervous system, we examined VDRE binding in nuclear extracts prepared from discrete rat brain regions and cultured rat cortical neurons by electrophoretic mobility shift assay. The highest activity of VDRE binding was found in the cerebellum among other brain regions examined, but sequence specific by taking into consideration the efficient competition with excess unlabeled VDRE but not with mutated VDRE. On in situ hybridization analysis, cells stained for VDR mRNA were abundant in neuron-enriched areas of cerebral cortex, hippocampus and cerebellar cortex in the mouse brain. Chronic treatment of vitamin D3 increased the expression of microtubule-associated protein-2, growth-associated protein-43 and synapsin-1 in cultured rat cortical neurons, suggesting a trophic role of vitamin D3 in differentiation and maturation of neurons. Neuronal cell death by brief glutamate exposure was significantly protected in cultured cortical neurons chronically treated with vitamin D3. Parallel studies showed that VDR mRNA was significantly upregulated 12-24 hr after brief glutamate exposure in cultured neurons chronically treated with vitamin D3, but not in those with vehicle alone. Our results suggest that vitamin D3 may play a role in mechanisms relevant to protective properties against the neurotoxicity of glutamate through upregulation of VDR expression in cultured rat cortical neurons.

Effects of docosahexaenoic acid on the survival and neurite outgrowth of rat cortical neurons in primary cultures.

Effects of docosahexaenoic acid (DHA) on survival and neurite outgrowth were investigated in primary cultures of rat cortical neurons. Cell cultures were prepared from cortex on embryonic day 18 (E-18) for treatment with a series of DHA concentrations (12.5, 25, 50, 75, 100 and 200 microM). Docosahexaenoic acid (25-50 microM) significantly enhanced neuronal viability, but lower concentration of DHA (12.5 microM) did not show an obvious effect. In contrast, higher concentrations of DHA (100-200 microM) exerted the significant opposite effects by decreasing neuronal viability. Furthermore, treatment with 25 microM DHA significantly prevented the neurons from death after different culture days in vitro (DIV). Moreover, measurements from the cultures exposed to 25 microM DHA immediately after plating showed significant increases in the percentage of cells with neurites, the mean number of neurite branches, the total neuritic length per cell and the length of the longest neurite in each cell after 24 and 48 h in vitro (HIV). The DHA-treated neurons had greater growth-associated protein-43 (GAP-43) immunoactivity and higher phosphatidylserine (PS) and phosphatidylethanolamine (PE) contents, but lower phosphatidylcholine (PC) content than control neurons. The significant increased DHA contents were also observed in both PE and PS in the treated neurons. These findings suggest that optimal DHA (25 microM) may have positive effects on the survival and the neurite outgrowth of the cultured fetal rat cortical neurons, and the effects probably are related to DHA-stimulating neuron-specific protein synthesis and its enhancing the discrete phospholipid (PL) content through enrichment of DHA in the PL species.

Regulation of GAP-43 expression by chronic desipramine treatment in rat cultured hippocampal cells.

BACKGROUND: The importance of molecular and cellular changes in hippocampus in major depression and in the mechanism of action of antidepressants has become increasingly clear. Identification of novel targets for antidepressants in hippocampus is important to understanding their therapeutic effects. METHODS: We used cDNA microarray to measure the expression patterns of multiple genes in primary cultured rat hippocampal cells. In situ hybridization and Northern and immunoblotting analysis were used to determine brain regional distribution and mRNA and protein levels of target genes. RESULTS: After comparing hybridized signals between control and desipramine treated groups, we found that chronic treatment with desipramine increased the expression of six genes and decreased the expression of two genes. One of the upregulated genes is growth associated protein GAP-43. In situ hybridization revealed that desipramine increased GAP-43 gene expression in dentate gyrus but not other brain regions. Northern and immunoblotting analysis revealed that desipramine increased GAP-43 mRNA and protein levels. GAP-43 expression is also increased by another antidepressant, tranylcypromine, but not by lithium or haloperidol. CONCLUSIONS: Because GAP-43 regulates growth of axons and modulates the formation of new connections, our findings suggest that desipramine may have an effect on neuronal plasticity in the central nervous system.

Distribution of GAP-43, beta-III tubulin and F-actin in developing and regenerating axons and their growth cones in vitro, following neurotrophin treatment.

Brain derived neurotrophic factor (BDNF) when added to explant cultures of both embryonic and adult retinal ganglion cell (RGC) axons exerted a marked effect on their growth cone size and complexity and also on the intensity of GAP-43, beta-III tubulin and F-actin immunoreaction product in their axons. GAP-43 was distributed in axons, lamellipodia, and filopodia whereas beta-III tubulin was distributed along the length of developing and adult regenerating axons and also in the C-domain of their growth cones. BDNF-treated developing RGC growth cones were larger and displayed increased numbers of GAP-43 and microtubule-containing branches. Although filopodia and lamellipodia were lost from both developing and adult RGC growth cones following trkB-IgG treatment, the intensity of the immunoreaction product of all these molecules was reduced and trkB-IgGs had no effect on the axonal distribution of betas-III tubulin and GAP-43. BDNF-treated growth cones also displayed increased numbers of F-actin containing filopodia and axonal protrusions. This study demonstrates, for the first time, that trkB-IgG treatment causes the loss of F-actin in the P-domain of growth cone tips in developing and regenerating RGC axons. Although microtubules and F-actin domains normally remained distinct in cultured growth cones, beta-III tubulin and F-actin overlapped within the growth cone C-domain, and within axonal protrusions of adult RGC axons, under higher concentrations of BDNF. The collapse of RGC growth cones appeared to correlate with the loss of F-actin. In vitro, trkB signalling may therefore be involved in the maintenance and stabilisation of RGC axons, by influencing F-actin polymerisation, stabilisation and distribution.

Physiological and morphological plasticity induced by chronic treatment with NT-3 or NT-4/5 in hippocampal slice cultures.

Expression of neurotrophins (NTs) and their receptors is elevated in the adult CNS under several neuropathological conditions. We have investigated the anatomical and electrophysiological consequences of chronic NT-3 or NT-4/5 treatment on established organotypic hippocampal slice cultures maintained in vitro for > 14 days. Both NT-3 and NT-4/5 increased spontaneous, action potential-dependent excitatory synaptic activity (sEPSCs), but only NT-3 increased inhibitory synaptic activity (sIPSCs) in CA3 pyramidal cells. Both NTs strongly promoted spontaneous synaptic bursting activity. Spontaneous bursts of EPSCs were observed after either NT treatment but only NT-3-treated cultures exhibited an increase in spontaneous bursts of IPSCs. In addition, sIPSC bursts were eliminated by blocking glutamatergic excitation. The frequency of miniature inhibitory postsynaptic currents, but not miniature excitatory postsynaptic currents, was also increased by both NT-3 and NT-4/5. Furthermore, NT-3 and NT-4/5 induced an up-regulation of the growth-associated protein GAP-43, suggesting that neurotrophins may be able to induce axonal reorganization in established neuronal networks. CA1 pyramidal cells exhibited slight alterations in dendritic branching after NT-4/5, but not NT-3 treatment. We conclude that chronic treatment with NT-3 or NT-4/5 can affect an established hippocampal network by elevating spontaneous inhibitory and excitatory synaptic activity and inducing coordinated pre- and postsynaptic structural changes.

The Ginkgo biloba extract modulates the balance between proliferation and differentiation in the olfactory epithelium of adult mice following bulbectomy.

Abstract - The adult olfactory receptor neurons (ORNs), located in the olfactory epithelium (OE) are permanently renewed thanks to neuronal progenitors present in the deep part of the OE, the globose basal cells (GBCs). Following the ablation of their synaptic target, the olfactory bulb (OB), ORNs degenerate by apoptosis and a wave of neurogenesis, including proliferation of GBCs and neuronal differentiation of their progeny, restores the olfactory function. The Ginkgo biloba extract (EGb 761) (Beaufour Ipsen, France) was administered to adult mice at the doses of 50 or 100 mg/kg, following bilateral bulbectomy and its effects on the expression of PCNA, reflecting the number of proliferating GBCs and on growth associated protein 43 (GAP-43), expressed by differentiating neurons were measured by Western blotting. PCNA expression peaked 9 days post-bulbectomy in untreated animals, but 7 days post-lesion in EGb 761-treated animals. A simultaneous reduction in GAP-43 expression suggested that EGb 761 may temporarily favor the proliferation of GBCs rather than their entry into the differentiation pathway. Probably as a consequence of the earlier onset of the neurogenetic response to bulbectomy, neuronal differentiation was enhanced in the OE, 3 weeks post-bulbectomy. These data suggest that EGb 761 may have beneficial effects upon neurogenesis in the OE through changing the balance between proliferation and differentiation.