Differential expression of mRNAs for neurotrophins and their receptors after axotomy of the sciatic nerve

The neurotrophin family includes NGF, brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4). Previous studies have demonstrated that expression of NGF and its low-affinity receptor is induced in nonneuronal cells of the distal segment of the transected sciatic nerve suggesting a role for NGF during axonal regeneration (Johnson, E. M., M. Taniuchi, and P. S. DeStefano. 1988. Trends Neurosci. 11:299-304). To assess the role of the other neurotrophins and the members of the family of Trk signaling neurotrophin receptors, we have here quantified the levels of mRNAs for BDNF, NT-3, and NT-4 as well as mRNAs for trkA, trkB, and trkC at different times after transection of the sciatic nerve in adult rats. A marked increase of BDNF and NT-4 mRNAs in the distal segment of the sciatic nerve was seen 2 wk after the lesion. The increase in BDNF mRNA was mediated by a selective activation of the BDNF exon IV promoter and adrenalectomy attenuated this increase by 50%. NT-3 mRNA, on the other hand, decreased shortly after the transection but returned to control levels 2 wk later. In Schwann cells ensheathing the sciatic nerve, only trkB mRNA encoding truncated TrkB receptors was detected with reduced levels in the distal part of the lesioned nerve. Similar results were seen using a probe that detects all forms of trkC mRNA. In the denervated gastrocnemius muscle, the level of BDNF mRNA increased, NT-3 mRNA did not change, while NT-4 mRNA decreased. In the spinal cord, only small changes were seen in the levels of neutrophin and trk mRNAs. These results show that expression of mRNAs for neurotrophins and their Trk receptors is differentially regulated after a peripheral nerve injury. Based on these results a model is presented for how the different neurotrophins could cooperate to promote regeneration of injured peripheral nerves.     

Glial cell line-derived neurotrophic factor (GDNF) is a neurotrophic factor for sensory neurons: Comparison with the effects of the neurotrophins

We compared the effects of glial cell line-derived neurotrophic factor (GDNF) on dorsal root ganglion (DRG) sensory neurons to that of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin 3 (NT-3). All of these factors were retrogradely transported to sub-populations of sensory neuron cell bodies in the L4/L5 DRG of neonatal rats. The size distribution of ¹²⁵I-GDNF-labeled neurons was variable and consisted of both small and large DRG neurons (mean of 506.60 μm²). ¹²⁵I-NGF was preferentially taken up by small neurons with a mean cross-sectional area of 383.03 μm². Iodinated BDNF and NT-3 were transported by medium to large neurons with mean sizes of 501.48 and 529.27 μm², respectively. A neonatal, sciatic nerve axotomy-induced cell death model was used to determine whether any of these factors could influence DRG neuron survival in vivo. GDNF and NGF rescued nearly 100% of the sensory neurons. BDNF and NT-3 did not promote any detectable level of neuronal survival despite the fact that they underwent retrograde transport. We examined the in vitro survival-promoting ability of these factors on neonatal DRG neuronal cultures derived from neonatal rats. GDNF, NGF, and NT-3 were effective in vitro, while BDNF was not. The range of effects seen in the models described here underscores the importance of testing neuronal responsiveness in more than one model. The biological responsiveness of DRG neurons to GDNF in multiple models suggests that this factor may play a role in the development and maintenance of sensory neurons. © 1997 John Wiley & Sons, Inc. J Neurobiol 32: 22–32, 1997.     

Effect of Electroacupuncture on Neurotrophin Expression in Cat Spinal Cord after Partial Dorsal Rhizotomy

Neuroplasticity of the spinal cord following electroacupuncture (EA) has been demonstrated although little is known about the possible underlying mechanism. This study evaluated the effect of EA on expression of neurotrophins in the lamina II of the spinal cord, in cats subjected to dorsal rhizotomy. Cats received bilateral removal of L1–L5 and L7–S2 dorsal root ganglia (DRG, L6 DRG spared) and unilateral EA. They were sacrificed 7 days after surgery, and the L6 spinal segment removed and processed by immunohistochemistry and in situ hybridization histochemistry, to demonstrate the expression of neurotrophins. Significantly greater numbers of nerve growth factor (NGF) and neurotrophin-3 (NT-3) positive neurons, brain-derived neurotrophic factor (BDNF) immunoreactive varicosities and NT-3 positive neurons and glial cells were observed in lamina II on the acupunctured (left) side, compared to the non-acupunctured, contralateral side. Greater number of neurons expressing NGF mRNA was also observed on the acupunctured side. No signal for mRNA to BDNF and NT-3 was detected. The above findings demonstrate that EA can increase the expression of endogenous NGF at both the mRNA and protein level, and BDNF and NT-3 at the protein level. It is postulated that EA may promote the plasticity of the spinal cord by inducing increased expression of neurotrophins.     

Fibroblast-like cells from rat plantar skin and neurotrophin-transfected 3T3 fibroblasts influence neurite growth from rat sensory neurons in vitro

Our previous finding that skin-derived and muscle-derived molecules can be used to sort regenerating rat sciatic nerve axons evoked questions concerning neuron-target interactions at the level of single cells, which prompted the present study. The results show that dorsal root ganglion (DRG) neurons co-cultured with fibroblast-like skin-derived cells emit many neurites. These have a proximal linear segment and a distal network of beaded branches in direct relation to skin-derived cells. Electron microscopic examination of such co-cultures showed bundles of neurites at some distance from the target cells and single profiles closely apposed to subjacent cells. RNase protection assay revealed that cultivated skin-derived cells express nerve growth factor (NGF), brain derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and neurotrophin-4 (NT-4). In co-cultures of DRG neurons and 3T3 fibroblasts overexpressing either of the neurotrophins produced by skin-derived cells the picture varied. NT-3 transfected 3T3 fibroblasts gave a growth pattern similar to that seen with skin-derived cells. Neurons co-cultured with mock-transfected 3T3 fibroblasts were small and showed weak neurite growth. In co-cultures with a membrane insert between skin-derived cells or 3T3 fibroblasts and DRG neurons few neurons survived and neurite growth was very sparse. We conclude that skin-derived cells stimulate neurite growth from sensory neurons in vitro, that these cells produce NGF, BDNF, NT-3 and NT-4 and that 3T3 fibroblasts producing NT-3 mimic the effect of skin-derived cells on sensory neurons in co-culture. Finally the results suggest that cell surface molecules are important for neuritogenesis.     

Characterization of the Responses of Purkinje Cells to Neurotrophin Treatment

Abstract: The ability of the neurotrophins nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4/5 (NT-4/5) to promote neuronal survival and phenotypic differentiation was examined in dissociated cultures from embryonic day 16 rat cerebellum. BDNF treatment increased the survival of neuron-specific enolase-immunopositive cells by 250 and 400% after 8 and 10 days in culture, respectively. A subpopulation of these neurons, the Purkinje cells, identified by calbindin staining, was increased to an equivalent extent, ∼200%, following BDNF, NT-4/5, or NT-3 treatment. The number of GABAergic neurons, identified by GABA immunoreactivity, was greatly increased by treatment with BDNF (470%) and moderately by NT-4/5 (46%), whereas NT-3 was without effect. NGF failed to increase the number of either Purkinje cells or GABAergic neurons. Addition of BDNF within 48 h of cell plating was required to obtain a maximal increase in Purkinje cell number after 8 days. In contrast, the NT-3 responses were nearly equivalent even if treatment was delayed for 96 h after plating. BDNF, NT-4/5, and NT-3, but not NGF, induced the rapid expression of the immediate early gene c- fos . Immunocytochemical double-labeling with antibodies to c-fos and calbindin was used to identify Purkinje cells that responded to neurotrophin treatment by induction of c-fos. After 4 days in vitro, both BDNF and NT-3 induced the formation of c-fos protein in calbindin-immunopositive neurons, whereas NT-4/5 did not. The latter results suggest that although BDNF and NT-4/5 have been shown to act through a common receptor, TrkB, it appears that the effects of BDNF and NT-4/5 are not identical.     

Selective dependence of mammalian dorsal root ganglion neurons on nerve growth factor during embryonic development.

We have investigated the NGF dependence of dorsal root ganglion (DRG) neurons in mammals using a paradigm of multiple in utero injections of a high titer anti-NGF antiserum. We have determined the specificity of our antiserum in relation to other members of the NGF neurotrophin family and found no cross-reactivity with brain-derived neurotrophic factor (BDNF) or neurotrophin-3 (NT-3). To identify various classes of DRG neurons, we have stained their characteristic central projections with Dil. We show here that the NGF dependence of DRG neurons is strikingly selective. Although a majority of DRG neurons are lost after NGF deprivation during embryonic life, these are almost exclusively small diameter neurons that project to laminae I and II of the dorsal horn and presumably subserve nociception and thermoreception. Larger neurons that project to more ventral spinal laminae and subserve other sensory modalities do not require NGF for survival. These NGF-independent DRG neurons likely require one of the more recently identified neurotrophins, BDNF or NT-3.     

Expression of neurotrophin receptors trkB and trkC and their ligands in rat adrenal gland and the intermediolateral column of the spinal cord

Neurotrophins and their trk receptors constitute major classes of signaling molecules with important actions in the developing and adult nervous system. With regard to the sympathoadrenal cell lineage, which gives rise to sympathetic neurons and chromaffin cells, neurotrophin-3 (NT-3) and nerve growth factor (NGF) are thought to influence developing sympathetic neurons. Neurotrophin requirements of chromaffin cells of the adrenal medulla are less well understood than those for NGF. In order to provide the bases for understanding of putative functions of neurotrophins for the development and maintenance of chromaffin cells and their preganglionic innervation, in situ hybridization has been used to study the expression of brain-derived neurotrophic factor (BDNF) and NT-3, together with their cognate receptors trkB and trkC, in the adrenal gland and in the intermediolateral column (IML) of the spinal cord. BDNF is highly expressed in the embryonic adrenal cortex and later in cells of the cortical reticularis zone. Adrenal medullary chromaffin cells fail to express detectable levels of mRNAs for BDNF, NT-3, and their cognate receptors trkB and trkC. Neurons in the IML express BDNF and trkB, and low levels of NT-3 and trkC. Our data make it unlikely that BDNF and NT-3 serve as retrograde trophic factors for IML neurons but suggest roles of BDNF and NT-3 locally within the spinal cord and possibly for sensory nerves of the adrenal cortex.     

Enhanced synthesis of brain-derived neurotrophic factor in the lesioned peripheral nerve: different mechanisms are responsible for the regulation of BDNF and NGF mRNA

Nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are molecules which regulate the development and maintenance of specific functions in different populations of peripheral and central neurons, amongst them sensory neurons of neural crest and placode origin. Under physiological conditions NGF is synthesized by peripheral target tissues, whereas BDNF synthesis is highest in the CNS. This situation changes dramatically after lesion of peripheral nerves. As previously shown, there is a marked rapid increase in NGF mRNA in the nonneuronal cells of the damaged nerve. The prolonged elevation of NGF mRNA levels is related to the immigration of activated macrophages, interleukin-1 being the most essential mediator of this effect. Here we show that transsection of the rat sciatic nerve also leads to a very marked increase in BDNF mRNA, the final levels being even ten times higher than those of NGF mRNA. However, the time-course and spatial pattern of BDNF mRNA expression are distinctly different. There is a continuous slow increase of BDNF mRNA starting after day 3 post-lesion and reaching maximal levels 3-4 wk later. These distinct differences suggest different mechanisms of regulation of NGF and BDNF synthesis in non-neuronal cells of the nerve. This was substantiated by the demonstration of differential regulation of these mRNAs in organ culture of rat sciatic nerve and Schwann cell culture. Furthermore, using bioassays and specific antibodies we showed that cultured Schwann cells are a rich source of BDNF- and ciliary neurotrophic factor (CNTF)-like neurotrophic activity in addition to NGF. Antisera raised against a BDNF-peptide demonstrated BDNF-immunoreactivity in pure cultured Schwann cells, but not in fibroblasts derived from sciatic nerve.     

Distinct modulatory actions of TGF-β and LIF on neurotrophin-mediated survival of developing sensory neurons

The neurotrophins nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) are important for the regulation of survival and differentiation of distinct, largely non-overlapping populations of embryonic sensory neurons. We show here that the multifunctional cytokine transforming growth factor-β (TGF-β) fails to maintain sensory neurons cultured from embryonic day (E) 8 chick dorsal root ganglia (DRG), although DRG neurons are immunoreactive for the TGF-β receptor type II, which is essential for TGF-β signaling. However, in combination with various concentrations of NT-3 and NT-4, but not NGF, TGF-β3 causes a further significant increase in neuron survival. In DRG cell cultures treated with NGF, NT-3, and NT-4, a neutralizing antibody to TGF-β decreases neuron survival suggesting that endogenous TGF-β in these cultures affects the efficacies of neurotrophins. Consistent with this notion and a modulatory role of TGF-β in neurotrophin functions is the observation that TGF-β2 and-β3 immunoreactivities and TGF-β3 mRNA are located in embryonic chick DRG in close association with neurons from E5 onwards. We also show that leukemia inhibitory factor (LIF) significantly decreases NGF-mediated DRG neuron survival. Together, these data indicate that actions and efficacies of neurotrophins are under distinct control by TGF-β and LIF in vitro, and possibly also in vivo. Special issue dedicated to Dr. Hans Thoenen.     

Expression of mRNAs for PPT, CGRP, NF-200, and MAP-2 in cocultures of dissociated DRG neurons and skeletal muscle cells in administration of NGF or NT-3

Both neurotrophins (NTs) and target skeletal muscle (SKM) cells are essential for the maintenance of the function of neurons and nerve-muscle communication. However, much less is known about the association of target SKM cells with distinct NTs on the expression of mRNAs for preprotachykinin (PPT), calcitonin-gene related peptide (CGRP), neurofilament 200 (NF-200), and microtubule associated protein 2 (MAP-2) in dorsal root ganglion (DRG) sensory neurons. In the present study, a neuromuscular coculture model of dissociated dorsal root ganglion (DRG) neurons and SKM cells was established. The morphology of DRG neurons and SKM cells in coculture was observed with an inverted phase contrast microscope. The effects of nerve growth factor (NGF) or neurotrophin-3 (NT-3) on the expression of mRNAs for PPT, CGRP, NF-200, and MAP-2 was analyzed by real time-PCR assay. The morphology of DRG neuronal cell bodies and SKM cells in neuromuscular coculture at different conditions was similar. The neurons presented evidence of dense neurite outgrowth in the presence of distinct NTs in neuromuscular cocultures. NGF and NT-3 increased mRNA levels of PPT, CGRP, and NF-200, but not MAP-2, in neuromuscular cocultures. These results offer new clues towards a better understanding of the association of target SKM cells with distinct NTs on the expression of mRNAs for PPT, CGRP, NF-200 and MAP-2, and implicate the association of target SKM cells and NTs with DRG sensory neuronal phenotypes.     

Opposite regulation of calbindin and calretinin expression by brain-derived neurotrophic factor in cortical neurons

Regulation of calbindin and calretinin expression by brain-derived neurotrophic factor (BDNF) was examined in primary cultures of cortical neurons using immunocytochemistry and northern blot analysis. Here we report that regulation of calretinin expression by BDNF is in marked contrast to that of calbindin. Indeed, chronic exposure of cultured cortical neurons for 5 days to increasing concentrations of BDNF (0.1-10 ng/ml) resulted in a concentration-dependent decrease in the number of calretinin-positive neurons and a concentration-dependent increase in the number of calbindin-immunoreactive neurons. Consistent with the immunocytochemical analysis, BDNF reduced calretinin mRNA levels and up-regulated calbindin mRNA expression, providing evidence that modifications in gene expression accounted for the changes in the number of calretinin- and calbindin-containing neurons. Among other members of the neurotrophin family, neurotrophin-4 (NT-4), which also acts by activating tyrosine kinase TrkB receptors, exerted effects comparable to those of BDNF, whereas nerve growth factor (NGF) was ineffective. As for BDNF and NT-4, incubation of cortical neurons with neurotrophin-3 (NT-3) also led to a decrease in calretinin expression. However, in contrast to BDNF and NT-4, NT-3 did not affect calbindin expression. Double-labeling experiments evidenced that calretinin- and calbindin-containing neurons belong to distinct neuronal subpopulations, suggesting that BDNF and NT-4 exert opposite effects according to the neurochemical phenotype of the target cell.     

In Vivo Regulation of Brain-Derived Neurotrophic Factor in Dorsal Root Ganglia Is Mediated by Nerve Growth Factor-Triggered Akt Activation during Cystitis

The role of brain-derived neurotrophic factor (BDNF) in sensory hypersensitivity has been suggested; however the molecular mechanisms and signal transduction that regulate BDNF expression in primary afferent neurons during visceral inflammation are not clear. Here we used a rat model of cystitis and found that the mRNA and protein levels of BDNF were increased in the L6 dorsal root ganglia (DRG) in response to bladder inflammation. BDNF up-regulation in the L6 DRG was triggered by endogenous nerve growth factor (NGF) because neutralization of NGF with a specific NGF antibody reduced BDNF levels during cystitis. The neutralizing NGF antibody also subsequently reduced cystitis-induced up-regulation of the serine/threonine kinase Akt activity in L6 DRG. To examine whether the NGF-induced Akt activation led to BDNF up-regulation in DRG in cystitis, we found that in cystitis the phospho-Akt immunoreactivity was co-localized with BDNF in L6 DRG, and prevention of the endogenous Akt activity in the L6 DRG by inhibition of phosphoinositide 3-kinase (PI3K) with a potent inhibitor LY294002 reversed cystitis-induced BDNF up-regulation. Further study showed that application of NGF to the nerve terminals of the ganglion-nerve two-compartmented preparation enhanced BDNF expression in the DRG neuronal soma; which was reduced by pre-treatment of the ganglia with the PI3K inhibitor LY294002 and wortmannin. These in vivo and in vitro experiments indicated that NGF played an important role in the activation of Akt and subsequent up-regulation of BDNF in the sensory neurons in visceral inflammation such as cystitis.     

Semaphorin 3A and neurotrophins: a balance between apoptosis and survival signaling in embryonic DRG neurons

Large numbers of neurons are eliminated by apoptosis during nervous system development. For instance, in the mouse dorsal root ganglion (DRG), the highest incidence of cell death occurs between embryonic days 12 and 14 (E12-E14). While the cause of cell death and its biological significance in the nervous system is not entirely understood, it is generally believed that limiting quantities of neurotrophins are responsible for neuronal death. Between E12 and E14, developing DRG neurons pass through tissues expressing high levels of axonal guidance molecules such as Semaphorin 3A (Sema3A) while navigating to their targets. Here, we demonstrate that Sema3A acts as a death-inducing molecule in neurotrophin-3 (NT-3)-, brain-derived neurotrophic factor (BDNF)- and nerve growth factor (NGF)-dependent E12 and E13 cultured DRG neurons. We show that Sema3A most probably induces cell death through activation of the c-Jun N-terminal kinase (JNK)/c-Jun signaling pathway, and that this cell death is blocked by a moderate increase in NGF concentration. Interestingly, increasing concentrations of other neurotrophic factors, such as NT-3 or BDNF, do not elicit similar effects. Our data suggest that the number of DRG neurons is determined by a fine balance between neurotrophins and Semaphorin 3A, and not only by neurotrophin levels.     

Neurotrophins and their receptors in rat peripheral trigeminal system during maxillary nerve growth

We examined the expression of the neurotrophins (NTFs) and their receptor mRNAs in the rat trigeminal ganglion and the first branchial arch before and at the time of maxillary nerve growth. The maxillary nerve appears first at embryonic day (E)10 and reaches the epithelium of the first branchial arch at E12, as revealed by anti-L1 immunohistochemistry. In situ hybridization demonstrates, that at E10- E11, neurotrophin-3 (NT-3) mRNA is expressed mainly in the mesenchyme, but neurotrophin-4 (NT-4) mRNA in the epithelium of the first branchial arch. NGF and brain-derived neurotrophic factor (BDNF) mRNAs start to be expressed in the distal part of the first brachial arch shortly before its innervation by the maxillary nerve. Trigeminal ganglia strongly express the mRNA of trkA at E10 and thereafter. The expression of mRNAs for low-affinity neurotrophin receptor (LANR), trkB, and trkC in trigeminal ganglia is weak at E10, but increases by E11-E12. NT-3, NT-4, and more prominently BDNF, induce neurite outgrowth from explant cultures of the E10 trigeminal ganglia but no neurites are induced by NGF, despite the expression of trkA. By E12, the neuritogenic potency of NGF also appears. The expression of NT-3 and NT-4 and their receptors in the trigeminal system prior to target field innervation suggests that these NTFs have also other functions than being the target-derived trophic factors.     

NT-3, BDNF, and NGF in the developing rat nervous system: parallel as well as reciprocal patterns of expression.

To obtain insight into the site and stage specificity of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) action in vivo, we compared the expression patterns of the genes for these three related neurotrophic factors as well as for the NGF receptor in developing and adult rats. Initial embryonic expression of these related neurotrophic factors approximately coincides with the onset of neurogenesis. However, the levels at which the three factors are expressed at this time and throughout the developing nervous system are dramatically different. NT-3 is by far the most highly expressed in immature regions of the CNS in which proliferation, migration, and differentiation of neuronal precursors is ongoing. NT-3 expression dramatically decreases with maturation of these regions. By contrast, BDNF expression is low in developing regions of the CNS and increases as these regions mature. NGF expression varies during the development of discrete CNS regions, but not in any consistent manner compared with NT-3 and BDNF. Despite the dramatic variations, NT-3, BDNF, and NGF do share one striking similarity--high level expression in the adult hippocampus. Our observations are consistent with the idea that NT-3, BDNF, and NGF have paralleled as well as reciprocal roles in vivo.     

Differential Regulation of Hippocampal Neurotrophins During Aging in Rats

Abstract: Neurotrophins are a family of neurotrophic factors with considerable structural homology. We used sensitive and specific two-site enzyme immunoassays to assess age-associated changes in levels of three neurotrophins—nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3)—in the hippocampus of Fischer 344 rats. Expressions of these proteins and their mRNAs were compared in the same animals. More than 200 ng of BDNF per gram of tissue was detected in the hippocampus of 2-month-old rats. This amount was two and 100 times greater than that of NT-3 and NGF, respectively. The levels of BDNF and NT-3 increased further 2–6 months after birth, whereas NGF content declined during this period, and the altered protein levels of all three neurotrophins were maintained 6–18 months postnatally. In contrast to the patterns of protein expression, BDNF mRNA levels increased during both of these periods, and the NT-3 mRNA levels appeared to decline. Changes in the expression of BDNF mRNA and NGF protein were opposite to those reported to occur in Alzheimer's disease. These results suggest that, during normal aging in rats, neurotrophin expression is regulated independently at both the mRNA and posttranslational levels. Any deficiency in their regulation might contribute to neurodegenerative disorders.     

Neurotrophin-4: a survival factor for adult sensory neurons

The nerve growth factor (NGF) family of neurotrophins provides a substantial part of the normal trophic support for sensory neurons during development. Although these neurotrophins, which include Brain-Derived Neurotrophic Factor (BDNF), Neurotrophin-3 (NT-3), and Neurotrophin-4 (NT-4), continue to be expressed into adulthood, there is little evidence that they are survival factors for adult neurons. Here we have examined the age-dependent neurotrophic requirements of a specialized type of mechanoreceptive neuron, called a D-hair receptor, in the dorsal root ganglion (DRG). Studies using knockout mice have demonstrated that the survival of D-hair receptors is dependent upon both NT-3 and NT-4. Here, we show that the time period when D-hair receptors require these two neurotrophins is different. Survival of D-hair receptors depends on NT-3 early in postnatal development and NT-4 later in the mature animal. The age-dependent loss of D-hair neurons in older NT-4 knockout mice was accompanied by a large reduction (78%) in neurons positive for the NT-4 receptor (trkB) together with neuronal apoptosis in the DRG. This is the first evidence that sensory neurons have a physiological requirement for a single neurotrophin for their continued survival in the adult.     

Expression profiles of BDNF splice variants in cultured DRG neurons stimulated with NGF

Expression of brain-derived neurotrophic factor (BDNF) mRNA is increased in the dorsal root ganglion (DRG) in response to peripheral inflammation. Nerve growth factor (NGF) from inflammatory tissue is thought to induce expression of BDNF. Recently, it was reported that the BDNF gene has eight non-coding exons that are transcribed independently into several splice variants. Expression of these splice variants in DRG neurons stimulated with NGF has not been studied. We examined changes in expression of BDNF splice variants in a rat model of peripheral inflammation and in cultured DRG neurons exposed to NGF. Total BDNF mRNA was increased by inflammation in vivo and by NGF in vitro. Among all splice variants, exon 1-9 showed the greatest increase in expression in both experiments. Our results indicate that exon 1-9 contributes to changes in total BDNF levels and may play an important role in the acute response of DRG to NGF.