Regulation of GFRalpha-1 and GFRalpha-2 mRNAs in rat brain by electroconvulsive seizure

The influence of both acute and chronic electroconvulsive seizure (ECS) or antidepressant drug treatments on expression of mRNAs encoding glial cell line-derived neurotrophic factor (GDNF) and its receptors, GFRalpha-1, GFRalpha-2, and c-Ret proto-oncogene (RET) in the rat hippocampus was examined by in situ hybridization. Two hours after acute ECS, levels of GFRalpha-1 mRNA in the dentate gyrus were significantly increased. This increase peaked to nearly 3-fold at 6 h after acute ECS and returned to basal levels 24 h after treatment. Chronic (once daily for 10 days) ECS significantly increased the expression of GFRalpha-1 mRNA nearly 5-fold after the last treatment. Levels of GFRalpha-2 mRNA in the dentate gyrus were also significantly increased by acute and chronic ECS, although this effect was less than that observed for GFRalpha-1. Maximum induction of GFRalpha-2 was 30% and 70% compared to sham in response to acute or chronic ECS, respectively. Levels of GDNF and RET mRNAs were not significantly changed following either acute or chronic ECS treatment at the time points examined. Chronic (14 days) administration of different classes of antidepressant drugs, including tranylcypromine, desipramine, or fluoxetine, did not significantly affect the GDNF, GFRalpha-1, GFRalpha-2, or RET mRNA levels in CA1, CA3, and dentate gyrus areas of hippocampus. The results demonstrate that acute ECS increases the expression of GFRalpha-1 and GFRalpha-2 and that these effects are enhanced by chronic ECS. The results also imply that regulation of the binding components of GDNF receptor complex may mediate the adaptive responses of the GDNF system to acute and chronic stimulation.     

Localization of GDNF/neurturin receptor (c-ret, GFRalpha-1 and alpha-2) mRNAs in postnatal rat brain: differential regional and temporal expression in hippocampus, cortex and cerebellum

Recent studies have identified a multi-component receptor system for the neurotrophic factor, glial cell line-derived neurotrophic factor (GDNF) and its homolog, neurturin (NTN), comprising the signaling tyrosine kinase, Ret and multiple GPI-linked binding proteins, GDNF family receptor alpha-1 and alpha-2 (GFRalpha-1 and GFRalpha-2). In the present study the localization of c-ret and GFRalpha-1 and GFRalpha-2 mRNAs was assessed in the developing rat brain from postnatal day 4 to 70 by in situ hybridization histochemistry, using specific [35S]-labeled oligonucleotides. GFRalpha-1 and GFRalpha-2 mRNAs were differentially distributed throughout the brain at all ages studied, particularly in cerebral cortex, hippocampus, substantia nigra and regions of the thalamus and hypothalamus - both distributions overlapping but different to that of c-ret mRNA. C-ret mRNA was abundant in areas such as the lateral habenula, reticular thalamic nucleus, substantia nigra pars compacta, cranial motor nuclei, and the Purkinje cell layer of the cerebellum. GFRalpha-1 mRNA was abundant in dorsal endopiriform nucleus, medial habenula, reticular thalamic nucleus, pyramidal and granule cell layers of the hippocampus, substantia nigra pars compacta and in cranial motor nuclei. GFRalpha-2 mRNA was highly expressed in many regions including olfactory bulb, lateral olfactory tract nucleus, neocortical layers IV and VI, septum, zona incerta, and arcuate and interpeduncular nuclei. GFRalpha-2 mRNA was detected in the pyramidal cell layers (CA3) of hippocampus at P4 and P7, but was no longer detectable at P14 and beyond, including P70 (adult). GFRalpha-2 mRNA was also detected in Purkinje cells throughout the cerebellum in young postnatal rats, but was enriched in the posterior lobes at P28 and P70. These localization studies support evidence of GDNF/NTN as target-derived and autocrine/paracrine trophic factors in developing brain pathways and earlier suggestions of unique and complex signaling mechanisms for these factors via a family of receptors. Strong expression of GFRalpha-1 and GFRalpha-2 mRNAs in adult brain suggests possible non-trophic functions of GDNF/NTN, as described for other neurotrophins, such as brain-derived neurotrophic factor.     

Evidence for a ligand-specific signaling through GFRalpha-1, but not GFRalpha-2, in the absence of Ret.

Glial cell line-derived neurotrophic factor (GDNF) and neurturin (NTN) are two homologeous proteins that have been recognized as potent survival factors for distinct neuronal populations. GDNF and NTN act through a two-component receptor system consisting of the ligand-specific binding subunits GDNF family receptor (GFR)alpha-1 and GFRalpha-2 and the common transducing subunit c-Ret. In addition, it has been demonstrated that GDNF can signal through GFRalpha-1 in the absence of c-Ret. In the present study, we sought to determine whether a similar c-Ret-independent signaling applies for GFRalpha-2. In addition, we have characterized the ligand specificity of the c-Ret-independent action of GFRalphas. To establish an assay system for these studies, several neural cell lines were screened for the presence of GDNF and NTN receptor subunits by RT-PCR and immunoblot analysis. c-Ret expression was detectable only in Neuro2A cells, which did not express GFRalpha-1 or GFRalpha-2. The neuronal cell line LS expressed GFRalpha-2, and the glial cell line Mes42 expressed GFRalpha-1, whereas the neuronal cell line B104 expressed both GFRalpha-1 and GFRalpha-2. Stimulation of B104 and Mes42 cells with GDNF, but not with NTN, for 10 min resulted in CREB phosphorylation. In apparent contrast, neither NTN nor GDNF promoted CREB activation in LS and Neuro2A cells. Moreover, exposure of LS cells to NTN or GDNF also failed to activate AKT and ERK. Together these findings provide evidence that, in contrast to GFRalpha-1, GFRalpha-2 fails to signal in the absence of c-Ret. In addition, these observations reveal that c-Ret-independent signaling of GFRalpha-1 is ligand- specific and occurs only with GDNF.     

Discordant expression of c-Ret and glial cell line-derived neurotrophic factor receptor alpha-1 mRNAs in response to motor nerve injury in neonate rats.

Adult motoneurons can survive following axotomy, whereas neonate motoneurons result in cell death. Following hypoglossal nerve axotomy in neonate rat, Glial cell line-Derived Neurotrophic Factor (GDNF) receptor alpha-1 (GFRalpha-1) mRNA expression was dramatically suppressed in the injured motoneurons, while a slight increase of c-Ret mRNA expression was observed. In adult, both GFRalpha-1 and c-Ret mRNAs increased substantially after axotomy. The present result suggests that the difference of motoneuron fate after axotomy may be partly due to the coordinate or discordant responses of GFRalpha-1 and c-Ret expression to nerve injury.     

Immunocytochemical mapping of Fos protein following seizures in gerbils indicates the activation of hippocampal neurons

The expression of the proto-oncogene, c-fos, and its protein, Fos, has been shown to be a useful marker for elevated levels of neuronal activity generated in the brain following different stimuli, including seizures. Since previous studies indicated hippocampal involvement in seizure activity in gerbils, Fos immunocytochemistry was used to determine whether hippocampal neurons become activated following environmentally induced seizures in this animal. Gerbils with maximal seizures showed many Fos-immunolabeled neurons in the granule cell layer and hilus of the dentate gyrus, as well as in CA3 and CA1 of the hippocampus. These gerbils had significantly greater numbers of Fos-immunolabeled dentate granule cells than gerbils with less severe seizures or no seizures. The number of dentate granule cells and CA3 pyramidal cells with Fos immunolabeling increased in an exponential manner with increased seizure severity. Many Fos-immunolabeled neurons were found in several regions of the neo- and paleocortex and in other limbic structures including the piriform cortex, cortical amygdaloid nucleus, and arcuate nucleus of the hypothalamus. These results indicate that hippocampal neurons are activated following seizures in a genetic model, and provide further proof that the hippocampal formation is involved in the circuitry for seizures in gerbils.     

Changes in cholecystokinin mRNA expression after amygdala kindled seizures: an in situ hybridization study

Cholecystokinin (CCK) can be a potent anticonvulsant neuropeptide in certain seizure models. Therefore, we examined whether seizures produced by electrical kindling of the amygdala or electroconvulsive seizures (ECS) would affect the expression of CCK mRNA in rat brain. Following a single kindled seizure, CCK mRNA expression was decreased about 20–58% in the amygdala. In contrast, after multiple consecutive kindled seizures, CCK mRNA expression was increased in the amygdala, cerebral cortex, CA1 pyramidal cell layer of the hippocampus and dentate hilus. A single ECS produced no effect on CCK mRNA expression, but multiple ECS increased expression in the interneurons of the hippocampus 24 h after the last seizure. Since seizures produced by ECS can be anticonvulsant to further ECS or kindled seizures, the CCK increases in the hippocampus may represent a compensatory anticonvulsant adaptation observed in both models. Overall, the kindling-induced alterations in CCK expression appear to be more complex involving multiple brain regions and distinct temporal properties.     

Brain Insults in Rats Induce Increased Expression of the BDNF Gene through Differential Use of Multiple Promoters

The rat brain-derived neurotrophic factor (BDNF) gene consists of four short 5-exons linked to separate promoters and one 3'-exon encoding the mature BDNF protein. Using in situ hybridization we demonstrate here that kindling-induced seizures, cerebral ischaemia and insulin-induced hypoglycaemic coma increase BDNF mRNA levels through insult- and region-specific usage of three promoters within the BDNF gene. Both brief (2 min) and longer (10 min) periods of forebrain ischaemia induced significant and major increases only of exon III mRNA in the dentate gyrus. Following hypoglycaemic coma (1 and 30 min), exon III mRNA was markedly elevated in the dentate gyrus and, in addition, exon I mRNA showed a moderate increase. Single and recurrent (n = 40) hippocampal seizures significantly increased expression of exon I, II and III mRNAs in the dentate gyrus granule cells. After recurrent seizures, including generalized convulsions, there were also major increases of both exon I and III mRNAs in the CA3 region, amygdala, piriform cortex and neocortex, whereas in the hippocampal CA1 sector marked elevations were detected only for exon III mRNA. The insults had no effect on the level of exon IV mRNA in the brain. The region- and insult-specific pattern of promoter activation might be of importance for the effectiveness of protective responses as well as for the regulation of plastic changes following brain insults.     

Quantitative analyses of GFRalpha-1 and GFRalpha-2 mRNAs and tyrosine hydroxylase protein in the nigrostriatal system reveal bilateral compensatory changes following unilateral 6-OHDA lesions in the rat

Copy numbers of mRNAs for GFRalpha-1 and GFRalpha-2, the preferred receptors for glial cell line-derived neurotrophic factor (GDNF) and neurturin (NTN) were determined by real-time quantitative RT-PCR (QRT-PCR). Receptor expression was assessed in striatum (ST) and substantia nigra (SN) of normal rats and rats acutely or progressively lesioned by 6-OHDA injected into the medial forebrain bundle or ST, respectively. GFRalpha-1 mRNA was clearly detected in normal ST. In normal SN, significantly higher expression of both receptors was observed. At 4 weeks after acute lesion, GFRalpha-2 mRNA was markedly decreased in SN bilaterally, whereas GFRalpha-1 mRNA in SN and ST was not affected. A progressive lesion resulted in a progressive decrease of GFRalpha1 mRNA in ST bilaterally. In SN, levels of GFRalpha-1 mRNA were not significantly affected by a progressive lesion, whereas GFRalpha-2 mRNA was markedly decreased bilaterally. Quantitative western blotting standardized against tyrosine hydroxylase (TH) protein from PC12 cells revealed the expected decrease in TH protein in lesioned SN, but also significant increases in TH protein in contralateral, unlesioned SNs at 4 weeks after both acute and progressive lesions. These data suggest that previously unrecognized compensatory changes in the nigrostriatal system occur in response to unilateral dopamine depletion. Since the changes observed in receptor expression did not always parallel loss of dopamine neurons, cells in addition to the nigral dopamine neurons appear to be affected by a 6-OHDA insult and are potential targets for the neurotrophic factors, GDNF and NTN.     

Behavioral changes and expression of heat shock protein hsp-70 mRNA, brain-derived neurotrophic factor mRNA, and cyclooxygenase-2 mRNA in rat brain following seizures induced by systemic administration of kainic acid

Kainic acid-induced seizures in rats represent an established animal model for human temporal lobe epilepsy. However, it is well-known that behavioral responses to the systemic administration of kainic acid are inconsistent between animals. In this study, we examined the relationship between expression of genes, neuropathological damage, and behavioral changes (seizure intensity and body temperature) in rats after systemic administration of kainic acid. The considerable differences in the response to kainic acid-induced seizures were observed in rats after a single administration of kainic acid (12 mg/kg i.p.). There was no detection of the expression of heat shock protein hsp-70 mRNA and HSP-70 protein in brain of vehicle-treated controls and in animals exhibiting weak behavioral changes (stage 1–2). A moderate expression of hsp-70 mRNA was detected throughout all regions (the pyramidal cell layers of CA1–3 and dentate gyrus) of the hippocampus, the basolateral, lateral, central and medial amygdala, the piriform cortex, and the central medial thalamic nucleus of rats that developed moderate seizures (stage 3–4). Marked expression of hsp-70 mRNA was detected in the all regions (cingulate, parietal, somatosensory, insular, entorhinal, piriform cortices) of cerebral cortex and all regions of hippocampus, and the central medial thalamic nucleus of the rats that developed severe seizures (stage 4–5). In addition, marked HSP-70 immunoreactivity was detected in the pyramidal cell layers of CA1 and CA3 regions of hippocampus, all regions (cingulate, parietal, somatosensory, insular, piriform cortices) of cerebral cortex, and the striatum of rats that developed severe seizures (stage 4–5). Furthermore, a marked expression of cyclooxygenase-2 (COX-2) mRNA and brain-derived neurotrophic factor (BDNF) mRNA levels by kainic acid-induced behavioral seizures (stage 3–4 or stage 4–5) was detected in all hippocampal pyramidal cell layers, granule layers of dentate gyrus, piriform cortex, neocortex, and amygdala. The present study suggest that the behavioral changes (seizure intensity and body temperature) and neuropathological damage after systemic administration of kainic acid are inconsistent between animals, and that these behavioral changes (severity of kainic acid-induced limbic seizures) might be correlated with gene expression of hsp-70 mRNA, COX-2 mRNA, and BDNF mRNA in rat brain.     

Differential regulation of mRNAs for neuropeptide Y and its receptor subtypes in widespread areas of the rat limbic system during kindling epileptogenesis.

Expression of mRNAs for neuropeptide Y (NPY) and its receptor subtypes Y1 (Y1-R), Y2 (Y2-R) and Y5 (Y5-R) was studied in adult rat brain using in situ hybridization after 40 rapidly recurring seizures induced with 5-min interval by hippocampal kindling stimulations. At 2-4 h post-seizure, NPY mRNA levels were markedly elevated in dentate granule cells, CA1 and CA3 pyramidal layers, amygdala and piriform and entorhinal cortices. Gene expression had returned to control level in the dentate granule cell layer at 48 h but remained high in the other areas, reaching baseline at 1 week. Transient decreases of Y1-R mRNA levels were detected at 2-4 h in hippocampal subregions, amygdala, piriform, entorhinal and somatosensory cortices. The Y2-R mRNA levels were reduced at 2-4 h in the CA3 region and piriform cortex, but exhibited marked increases at 48 h and 1 week post-seizure in the dentate gyrus, amygdala and piriform and entorhinal cortices. At 3 weeks, Y2-R mRNA expression had virtually returned to baseline. Elevated Y5-R mRNA levels were only detected at 2-4 h and confined to dentate granule cell layer and piriform and entorhinal cortices. These results demonstrate a cell- and region-specific, differential regulation of mRNA expression for NPY and Y1-R, Y2-R, and Y5-R in the limbic system following recurring seizures. Because the gene changes were transient, it seems unlikely that the presumed alterations of the corresponding proteins are involved in the maintenance of the epileptic syndrome, which develops up to 4 weeks post-seizure in the present model and is stable thereafter. Our data provide further support for the hypothesis that the changes of NPY and its receptors act to dampen seizure susceptibility, and suggest that the cascade of gene changes is orchestrated to optimize this anticonvulsant effect.     

Protein kinase C subspecies distinguish major cell types in rat hippocampus: an immunocytochemical and in situ hybridization histochemical study.

This study compares the distribution of protein kinase C (PKC) alpha and beta with the distribution of PKC epsilon in the hippocampal formation of rats by immunocytochemistry and in situ hybridization histochemistry. Alpha and PKC beta are members of the group A PKC genes that were first described; PKC epsilon is a member of the group B PKC genes that were more recently identified by molecular cloning. A combination of all three gene products and their mRNAs overlapped in their distributions in dentate granule cells and pyramidal and nonpyramidal neurons. However, each subspecies predominated in one of the major cell types. PKC alpha-immunoreactivity and mRNA were most intense in CA2-3 pyramidal cells and dendrites, whereas PKC beta-immunoreactivity and mRNA were most intense in CA1 pyramidal cells and dendrites. PKC epsilon-immunoreactivity and mRNA were concentrated in dentate granule cells and CA3 pyramidal cells. Furthermore, PKC epsilon-immunoreactivity was detectable in mossy fibers. Each subspecies labeled different kinds of interneurons that were particularly numerous in, but not restricted to, the hilus. These data support the contention that different subtypes of hippocampal neurons are distinguished by the expression of different combinations of PKC subspecies under resting conditions.     

Expression of N-Methyl-D-Aspartate receptor subunit mRNAs in the human brain: Hippocampus and cortex

N-methyl-D-aspartate receptor (NR) activation in the hippocampus and neocortex plays a central role in memory and cognitive function. We analyzed the cellular expression of the five NR subunit (NR1 and NR2A-D) mRNAs in these regions with in situ hybridization and human ribonucleotide probes. Film autoradiograms demonstrated a distinct pattern of hybridization signal in the hippocampal complex and the neocortex with probes for NR1, NR2A, and NR2B mRNA. NR2C and NR2D probes yielded scattered signals without a distinct organization. At the emulsion level, the NR1 probe produced high-density hybridization signals across the hippocampal complex. NR2A mRNA was higher in dentate granule cells and pyramidal cells in CA1 and subiculum compared to hilus neurons. NR2B mRNA expression was moderate throughout, with higher expression in dentate granule cells, CA1 and CA3 pyramidal cells than in hilus neurons. In the hippocampal complex, the NR2C probe signal was not different from background in any region, whereas the NR2D probe signal resulted in low to moderate grain densities. We analyzed NR subunit mRNA expression in the prefrontal, parietal, primary visual, and motor cortices. All areas displayed strong NR1 hybridization signals. NR2A and NR2B mRNAs were expressed in cortical areas and layers. NR2C mRNA was expressed at low levels in distinct layers that differed by region and the NR2D signal was equally moderate throughout all regions. Pyramidal cells in both hippocampus and neocortex express NR1, NR2A, NR2B, and, to a lesser extent, NR2D mRNA. Interneurons or granular layer neurons and some glial cells express NR2C mRNA. J. Comp. Neurol. 390:75–90, 1998. © 1998 Wiley-Liss, Inc.     

GDNF, RET and GFRalpha-1-3 mRNA expression in the developing human spinal cord and ganglia.

The identification of endogenous neurotrophic factors and their receptors in human spinal cord is important not only to understand development, but also in the consideration of possible future therapies for neurodegenerative disorders and trauma. Using in situ hybridization, the expression of glial cell line-derived neurotrophic factor (GDNF), neurturin (NTN), persephin (PSP), GFRalpha-1, GFRalpha-2, GFRalpha-3 and RET mRNA in human fetal spinal cord was studied. Strong GDNF mRNA hybridization signal, presumably restricted to Clarke's nucleus, was detected in the thoracic spinal cord. mRNA encoding GFRalpha-1 was expressed in the entire spinal cord gray matter with particularly high expression in the ventral horn. GFRbeta-1 was also expressed more weakly in dorsal root ganglia. NTN and persephin mRNA were not detected in either the fetal spinal cord or the dorsal root ganglia. mRNA coding for GFRalpha-2, however, was found in most cells of the spinal cord gray matter. A strong expression of GFRalpha-3 mRNA was detected in dorsal root ganglia cells and Schwann cells. The transducing receptor RET was expressed strongly in motorneurons and dorsal root ganglion neurons. We conclude that basic features concerning the role of the GDNF family of ligands and their receptors revealed in rodents applies to humans.     

Differential NPY mRNA expression in granule cells and interneurons of the rat dentate gyrus after kainic acid injection

Using in situ hybridization histochemistry neuropeptide Y (NPY) mRNA expression was investigated after intraperitoneal injection of kainic acid (KA) and after local application of KA or quinolinic acid into the dentate gyrus of the rat. Enhanced concentrations of NPY mRNA were observed in interneurons of the hilus, including presumptive fusiform neurons and pyramidal-shaped basket cells already 4 hours after initiation of limbic seizures by KA (10 mg/kg, i.p.). IncreaseD NPY expression persisted in neurons resistant to seizure-induced cell death (6–48 h after i.p. KA). Exceptionally high hybridization signals were found in interneurons of the hilus and the CA1 and CA3 sectors 8 months after KA-induced limbic seizures. In the granule cell layer only a transient but pronounced increase in NPY mRNA was observed 12–24 h after injection. Only moderate changes were observed in this cell layer at later intervals. Anticonvulsant treatment with thiopental, after a brief period of generalized seizures, prevented the increase in NPY mRNA in granule cells but not in interneurons. No change in NPY message was found also in granule cells of rats which responded with mild “wet dog shake” behvior but not with motor seizures to KA injection. Local injections of low doses of KA (0.05–0.2 nmol) or quinolinic acid (6.5–100 nmol) into the dentate gyrus of the hippocampus under deep thiopental anesthesia, after 24 h, resulted in increased concentrations of NPY message in interneurons of the ipsilateral, but not of the contralateral hilus and not in granule cells. Higher doses of the excitatory amino acid analogs caused partial neurodegeneration at the injection site, but enhanced NPY expression in interneurons of the contralateral dentate. Only the highest dose of quinolinic acid (100 nmol), resulting in general neuronal cell loss at the injection area, induced enhanced NPY mRNA expression also in granule cells of the contralateral dentate gyrus. The experiments suggest different mechanisms for NPY mRNA expression in interneurons and in granule cells of the dentate gyrus. Whereas in the stratum granulosum NPY mRNA expression was only observed after generalized limbic seizures, in hilar interneurons it was augmented by only moderate neuronal stimulation or directly by KA. © 1994 Wiley-Liss, Inc.     

Fibroblast growth factor-2 requires glial-cell-line-derived neurotrophic factor for exerting its neuroprotective actions on glutamate-lesioned hippocampal neurons

FGF-2 is a potent neurotrophic factor for several populations of CNS neurons and has been shown to protect hippocampal neurons from glutamate-induced cell death in vitro and in vivo. Mechanisms underlying the neurotrophic and protective actions of FGF-2 have been resolved only in part. Using glutamate-treated cultured hippocampal neurons we show that FGF-2 shares its neuroprotective capacity with GDNF. Hippocampal neurons express glial-cell-line-derived neurotrophic factor (GDNF), its receptors c-Ret and the lipid-anchored GDNF family receptor-alpha1 (GFRalpha-1), and the FGF receptor 1 (FGFR I). Neutralizing antibodies to GDNF abolish the neuroprotective effect of FGF-2. In support of the notion that GDNF is required to permit the protective effects of FGF-2 we find that FGF-2 up-regulates GDNF and GFRalpha-1 in hippocampal neurons. Furthermore, FGF-2-induced GDNF causes enhanced phosphorylation of c-Ret and the signaling components Akt and Erk. A putative downstream target of FGF-2 and GDNF are bcl-2 gene family members, whose mRNAs are differentially up-regulated by the two factors. Together, these data suggest that GDNF is an important protective factor for glutamate-lesioned hippocampal neurons and an essential mediator of the neuroprotective actions of FGF-2.     

Limbic seizures induce a differential regulation of the expression of nerve growth factor, brain-derived neurotrophic factor and neurotrophin-3, in the rat hippocampus.

Small unilateral electrolytic lesions placed in the hilus of the dentate gyrus produce limbic seizures. We have investigated the effects of these hilar lesions on the levels of the mRNAs encoding for 3 neurotrophic factors (NTF): nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT3). 'In situ' hybridization histochemistry with synthetic oligonucleotides was used to analyze their mRNA distribution and levels. In agreement with previously published data (Science, 245 (1989) 758-761), NGF mRNA was found bilaterally, quickly and transiently increased in granule cells of the dentate gyrus. Only 2 h after the onset of limbic seizures, mRNA levels for BDNF were also found to be dramatically elevated in both sides of the hippocampus, reaching a maximum 30-fold increase in the granule cell layer of the dentate gyrus 5 h after the lesion. Moreover, increased levels of this mRNA were also been found in the pyramidal layer of the CA3 (5-fold) and CA1 (15-fold) hippocampal fields. In contrast, NT3 mRNA was found to be clearly and bilaterally decreased in dentate gyrus granule cells, reaching 5- to 6-fold decreased levels at 12 h after lesion. Taken together, these results clearly show a different regulation of neurotrophic factors genes (NGF, BDNF and NT3) expression in the different hippocampal fields, as a consequence of seizure-producing hilar lesions.