Cell Bodies Of Dorsal Root Ganglion Neurons Research Articles

Role of bradykinin and prostaglandin EP4 receptors in regulating TRPV1 channel sensitization in rat dorsal root ganglion neurons.

Transient receptor potential vanilloid type-1 (TRPV1) channels play key roles in chronic pain conditions and are modulated by different inflammatory mediators to elicit heat sensitisation. Bradykinin is a 9-amino acid peptide chain that promotes inflammation. The aim of present study is to investigate how bradykinin and prostaglandin receptors (EP3 and EP4 ) modulate the sensitisation of TRPV1-mediated responses. Calcium imaging studies of rat dorsal root ganglion (DRG) neurons were employed to investigate the desensitizing responses of TRPV1 ion channels by capsaicin, and the re-sensitization of TRPV1 by bradykinin, then to explore the role EP3 and EP4 receptors in mediating these bradykinin-dependent effects. Immunocytochemistry was used to study the co-expression and distribution of EP4, TRPV1, COX-1 and B2 in rat DRG neurons. Desensitization was seen upon repeated capsaicin application, we show that bradykinin-mediated sensitization of capsaicin-evoked calcium responses in rat DRG neurons occurs is dependent on COX-1 activity and utilizes a pathway that involves EP4 but not EP3 receptors. Immunocytochemical techniques revealed that EP4, TRPV1, COX-1 and B2 proteins are expressed mainly in small diameter (<1000 μm2 ) cell bodies of rat DRG neurons which are typically nociceptors. The present study provides suggestive evidence for a potential signalling pathway through which bradykinin may regulate TRPV1 ion channel function via EP4 receptors. In addition to confirming existing knowledge, the anatomical distribution and colocalization of these proteins in DRG neurons as revealed by this study offer valuable insight.

IGF-1 Via PI3K/Akt/S6K Signaling Pathway Protects DRG Neurons with High Glucose-induced Toxicity.

Hyperglycemia-induced toxicity of neurons contributes to the pathogenesis and progression of diabetic neuropathy (DNP). High concentration glucose triggered reactive oxygen species (ROS) overproduction and induced cell apoptosis of neurons from dorsal root ganglion (DRG) in vitro. Currently, there is no effective therapeutic method to retard this devastating complication or neurotoxicity induced by high glucose. Insulin-like growth factor-1 (IGF-1) has multi-neurotrophic actions which need to be explored regarding its actions and mechanisms on relieving high glucose induced neurotoxicity. Herein, high concentration glucose was exposed to the DRG neurons in vitro. The effects of IGF-1 on relieving high glucose-induced neurotoxicity were evaluated. We illustrated that IGF-1 enhanced regeneration of neurites sent from DRG neuronal cell bodies and increased neuronal viability which inhibited by high glucose challenge. IGF-1 alleviated neuronal apoptosis caused by high glucose exposure. IGF-1 also suppressed the intracellular ROS overproduction and ATF3 expression upregulation which was induced by high glucose insult. The anti-neurotoxic effects of IGF-1 might be through restoration of prosurvival PI3K/Akt/S6K signaling. These data shed some light on the treatment of intractable DNP and suggested that IGF-1 might be a potential effective agent on relieving high glucose induced neurotoxicity.

Toxicological effect of inhaled mosquito coil smoke on male fertility: Oxidative stress and antioxidant response

Evidence is emerging for a role of rough endoplasmic reticulum (RER) in the form of stress granules, the unfolded protein response and protein bodies in the response of neurons to injury and in neurodegenerative diseases. Here, we have studied the role of the peripheral target in regulating the RER and polyribosomes of Nissl bodies in axotomised adult cat dorsal root ganglion (DRG) neurons where axonal regeneration and peripheral target reinnervation was either allowed or denied. Retrograde labelling with horseradish peroxidise was used as an independent marker to enable selection of only those DRG neuronal cell bodies with axons in the injured intercostal nerves. Indications of polyribosomal dispersal were seen by 6 h following axotomy, and by 24 h the normal orderly arrangement of lamellae of RER in Nissl bodies had become disorganised. These ultrastructural changes preceded light microscopical chromatolysis by 1–3 d. The retrograde response was maximal 8–32 d after axotomy. Clusters of debris-laden satellite cells/macrophages were present at this time but no ultrastructural evidence of neuronal apoptosis or necrosis was seen and there were no differences in the initial retrograde response according to the type of injury. By 64 d following axotomy with reinnervation, approximately half the labelled DRG neurons showed restoration of the orderly arrangement of RER and polyribosomes in their Nissl bodies. This was not seen after axotomy with reinnervation denied. We propose that the target-dependent changes in Nissl body ultrastructure described here are part of a continuum that can modify neuronal protein synthesis directed towards growth, maintenance or death of the neuron. This represents a possible structural basis for mediating the varied effects of neurotrophic interactions.

Target-dependence of sensory neurons: An ultrastructural comparison of axotomised dorsal root ganglion neurons with allowed or denied reinnervation of peripheral targets

Evidence is emerging for a role of rough endoplasmic reticulum (RER) in the form of stress granules, the unfolded protein response and protein bodies in the response of neurons to injury and in neurodegenerative diseases. Here, we have studied the role of the peripheral target in regulating the RER and polyribosomes of Nissl bodies in axotomised adult cat dorsal root ganglion (DRG) neurons where axonal regeneration and peripheral target reinnervation was either allowed or denied. Retrograde labelling with horseradish peroxidise was used as an independent marker to enable selection of only those DRG neuronal cell bodies with axons in the injured intercostal nerves. Indications of polyribosomal dispersal were seen by 6h following axotomy, and by 24h the normal orderly arrangement of lamellae of RER in Nissl bodies had become disorganised. These ultrastructural changes preceded light microscopical chromatolysis by 1–3d. The retrograde response was maximal 8–32d after axotomy. Clusters of debris-laden satellite cells/macrophages were present at this time but no ultrastructural evidence of neuronal apoptosis or necrosis was seen and there were no differences in the initial retrograde response according to the type of injury. By 64d following axotomy with reinnervation, approximately half the labelled DRG neurons showed restoration of the orderly arrangement of RER and polyribosomes in their Nissl bodies. This was not seen after axotomy with reinnervation denied. We propose that the target-dependent changes in Nissl body ultrastructure described here are part of a continuum that can modify neuronal protein synthesis directed towards growth, maintenance or death of the neuron. This represents a possible structural basis for mediating the varied effects of neurotrophic interactions.

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.

Endosome-mediated retrograde axonal transport of P2X3 receptor signals in primary sensory neurons

Neurotrophins and their receptors adopt signaling endosomes to transmit retrograde signals. However, the mechanisms of retrograde signaling for other ligand/receptor systems are poorly understood. Here, we report that the signals of the purinergic (P)2X(3) receptor, an ATP-gated ion channel, are retrogradely transported in dorsal root ganglion (DRG) neuron axons. We found that Rab5, a small GTPase, controls the early sorting of P2X(3) receptors into endosomes, while Rab7 mediates the fast retrograde transport of P2X(3) receptors. Intraplantar injection and axonal application into the microfluidic chamber of α, β-methylene-ATP (α, β-MeATP), a P2X selective agonist, enhanced the endocytosis and retrograde transport of P2X(3) receptors. The α, β-MeATP-induced Ca(2+) influx activated a pathway comprised of protein kinase C, rat sarcoma viral oncogene and extracellular signal-regulated protein kinase (ERK), which associated with endocytic P2X(3) receptors to form signaling endosomes. Disruption of the lipid rafts abolished the α, β-MeATP-induced ERK phosphorylation, endocytosis and retrograde transport of P2X(3) receptors. Furthermore, treatment of peripheral axons with α, β-MeATP increased the activation level of ERK and cAMP response element-binding protein in the cell bodies of DRG neurons and enhanced neuronal excitability. Impairment of either microtubule-based axonal transport in vivo or dynein function in vitro blocked α, β-MeATP-induced retrograde signals. These results indicate that P2X(3) receptor-activated signals are transmitted via retrogradely transported endosomes in primary sensory neurons and provide a novel signaling mechanism for ligand-gated channels.

CLP36 interacts with palladin in dorsal root ganglion neurons

CLP36, a member of the alpha-actinin-associated LIM protein (ALP)/enigma protein family, plays a role in neurite outgrowth in the peripheral nervous system. However, the underlying molecular mechanisms are not known. In this study, we performed yeast two-hybrid screening of an E18 mouse whole-body cDNA library with CLP36 as the bait and isolated palladin as a CLP36-binding protein. Palladin is an actin-binding protein and it was shown to have a role in the extension of cortical neurons. A coimmunoprecipitation study showed that CLP36 and palladin formed a complex in the dorsal root ganglion (DRG). In addition, CLP36 and palladin were colocalized in the neurites and cell bodies of primary DRG neurons. Furthermore, sciatic nerve transection increased the expression of both CLP36 and palladin mRNAs in DRG neurons, with the increase in CLP36 mRNA being more prominent. This implies that CLP36 has a more specific role in nerve regeneration than palladin. Our results suggest that CLP36 may interact with palladin to influence neurite outgrowth during sciatic nerve regeneration.

Differential expression of ATP7A, ATP7B and CTR1 in adult rat dorsal root ganglion tissue.

BackgroundATP7A, ATP7B and CTR1 are metal transporting proteins that control the cellular disposition of copper and platinum drugs, but their expression in dorsal root ganglion (DRG) tissue and their role in platinum-induced neurotoxicity are unknown. To investigate the DRG expression of ATP7A, ATP7B and CTR1, lumbar DRG and reference tissues were collected for real time quantitative PCR, RT-PCR, immunohistochemistry and Western blot analysis from healthy control adult rats or from animals treated with intraperitoneal oxaliplatin (1.85 mg/kg) or drug vehicle twice weekly for 8 weeks.ResultsIn DRG tissue from healthy control animals, ATP7A mRNA was clearly detectable at levels similar to those found in the brain and spinal cord, and intense ATP7A immunoreactivity was localised to the cytoplasm of cell bodies of smaller DRG neurons without staining of satellite cells, nerve fibres or co-localisation with phosphorylated heavy neurofilament subunit (pNF-H). High levels of CTR1 mRNA were detected in all tissues from healthy control animals, and strong CTR1 immunoreactivity was associated with plasma membranes and vesicular cytoplasmic structures of the cell bodies of larger-sized DRG neurons without co-localization with ATP7A. DRG neurons with strong expression of ATP7A or CTR1 had distinct cell body size profiles with minimal overlap between them. Oxaliplatin treatment did not alter the size profile of strongly ATP7A-immunoreactive neurons but significantly reduced the size profile of strongly CTR1-immunoreactive neurons. ATP7B mRNA was barely detectable, and no specific immunoreactivity for ATP7B was found, in DRG tissue from healthy control animals.ConclusionsIn conclusion, adult rat DRG tissue exhibits a specific pattern of expression of copper transporters with distinct subsets of peripheral sensory neurons intensely expressing either ATP7A or CTR1, but not both or ATP7B. The neuron subtype-specific and largely non-overlapping distribution of ATP7A and CTR1 within rat DRG tissue may be required to support the potentially differing cuproenzyme requirements of distinct subsets of sensory neurons, and could influence the transport and neurotoxicity of oxaliplatin.

Modulation of Transient Receptor Potential Vanilloid 4-Mediated Membrane Currents and Synaptic Transmission by Protein Kinase C

BackgroundTransient receptor potential Vanilloid (TRPV) receptors are involved in nociception and are expressed predominantly in sensory neurons. TRPV1, a non-selective cation channel has been extensively studied and is responsible for inflammatory thermal hypersensitivity. In this study, the expression and function of TRPV4 have been characterized and compared with those of TRPV1.ResultsImmunohistochemical studies revealed that both TRPV1 and TRPV4 were co-expressed in dorsal root ganglion (DRG) neuronal cell bodies and in the central terminals of laminae I and II of the spinal dorsal horn (DH). In Ca2+ fluorescence imaging and whole-cell patch-clamp experiments, TRPV1- and TRPV4-mediated responses were observed in a population of the same DRG neurons. Sensitization of TRPV1 has been shown to be involved in inflammatory pain conditions. Incubation with phorbol 12, 13-dibutyrate (PDBu), a PKC activator, resulted in a significant potentiation of TRPV4 currents in DRG neurons. In TRPV4 expressing HEK 293T cells, PDBu increased 4α-phorbol 12, 13-didecanoate (4α-PDD)-induced single-channel activity in cell-attached patches, which was abrogated by bisindolylmaleimide (BIM), a selective PKC inhibitor. TRPV4 is also expressed at the central terminals of sensory neurons. Activation of TRPV4 by 4α-PDD increased the frequency of miniature excitatory post synaptic currents (mEPSCs) in DRG-DH neuronal co-cultures. 4α-PDD-induced increase in the frequency of mEPSCs was further enhanced by PDBu. The expression of TRP channels has been shown in other areas of the CNS; application of 4α-PDD significantly increased the mEPSC frequency in cultured hippocampal neurons, which was further potentiated by PDBu, whereas, TRPV1 agonist capsaicin did not modulate synaptic transmission.ConclusionThese results indicate that TRPV4 and TRPV1 are co-expressed in certain DRG neurons and TRPV4 can be sensitized by PKC not only in DRG neuronal cell bodies, but also in the central sensory and non-sensory nerve terminals. Co-expression of TRPV1 and TRPV4 ion channels, their modulation of synaptic transmission and their sensitization by PKC may synergistically play a role in nociception.

TREK-2 (K2P10.1) and TRESK (K2P18.1) are major background K+ channels in dorsal root ganglion neurons

Dorsal root ganglion (DRG) neurons express mRNAs for many two-pore domain K(+) (K(2P)) channels that behave as background K(+) channels. To identify functional background K(+) channels in DRG neurons, we examined the properties of single-channel openings from cell-attached and inside-out patches from the cell bodies of DRG neurons. We found seven types of K(+) channels, with single-channel conductance ranging from 14 to 120 pS in 150 mM KCl bath solution. Four of these K(+) channels showed biophysical and pharmacological properties similar to TRESK (14 pS), TREK-1 (112 pS), TREK-2 (50 pS), and TRAAK (73 pS), which are members of the K(2P) channel family. The molecular identity of the three other K(+) channels could not be determined, as they showed low channel activity and were observed infrequently. Of the four K(2P) channels, the TRESK-like (14 pS) K(+) channel was most active at 24 degrees C. At 37 degrees C, the 50-pS (TREK-2 like) channel was the most active and contributed the most (69%) to the resting K(+) current, followed by the TRESK-like 14-pS (16%), TREK-1-like 112-pS (12%), and TRAAK-like 73-pS (3%) channels. In DRG neurons, mRNAs of all four K(2P) channels, as well as those of TASK-1 and TASK-3, were expressed, as judged by RT-PCR analysis. Our results show that TREKs and TRESK together contribute >95% of the background K(+) conductance of DRG neurons at 37 degrees C. As TREKs and TRESK are targets of modulation by receptor agonists, they are likely to play an active role in the regulation of excitability in DRG neurons.

902. Modulation of Voltage-Gated Potassium Channels in Dorsal Root Ganglion Neurons by an Inducible Adenoviral Vector In Vivo

Injury to the nerve or dorsal root ganglion (DRG) reduces voltage-gated potassium (Kv) channel expression and increases neuronal excitability in DRG neurons. Kv channels are therefore potential targets of gene therapy for chronic pain. An adenoviral vector, containing a reporter gene encoding the enhanced green fluorescent protein (GFP) and a Kv gene, was delivered to the fourth lumbar (L4) DRG of adult rat by microinjection via a small catheter inserted under the epineurium of the spinal nerve 3 to 5 mm from the DRG. The in vivo expression of the transferred gene was controlled by an ecdysone analog via an ecdysone-inducible promoter in the viral vector. Three types of vectors were used. A control vector (AdEGI) contained only the GFP gene. A vector intended to reduce votage gated potassium channels (AdKv1.xDN) had a dominant-negative Kv1.3 gene that disrupted Kv1 channels. A vector to increase inwardly rectifying K current (AdKir2.1) had the human Kir2.1 gene. Sharp-electrode intracellular recordings were obtained in vivo from the ipsilateral L4 DRG neurons. As early as one day, and lasting longer than 2 weeks, injection of the control vector AdEGI produced a slight but significant decrease in force of a Von-Frey filament required to elicit withdrawal of the ipsilateral hindpaw. There was no decrease in withdrawal latency to heating the same paw. Compared with the effects of AdEGI, induction of the AdKv1.xDN produced (1) a further decrease of mechanical withdrawal threshold, and (2) increased neuronal excitability as indicated by a decreased rheobase, higher input resistance, and a wider action potential with a smaller afterhyperpolarization in GFP-labeled medium and large cell bodies of DRG neurons. Whereas induction of the AdKir2.1 produced no significant change in paw withdrawal, it did decrease neuronal excitability in GFP-labeled DRG neurons as indicated by a hyperpolarized resting potential, a higher rheobase and a lower input resistance. By applying adenoviral vectors carrying different types of potassium channel genes, we could either increase or decrease the excitability of DRG neurons, and modulate the pain-related behaviors of the animal. In order for gene therapy to treat neuropathic pain we will need to develop viral vectors that reach a greater number of hyperexcitable neurons.

Inhibition of a hyperpolarization-activated current by clonidine in rat dorsal root ganglion neurons.

Whole cell voltage- and current-clamp recordings were carried out to investigate the effects of clonidine, an alpha 2-adrenoceptor agonist, in L4 and L5 dorsal root ganglion (DRG) neurons of the rat. In voltage-clamp mode, application of 20 microM clonidine reversibly reduced the inward current evoked by hyperpolarizing voltage steps. The "clonidine-sensitive current" was obtained by subtracting the current during clonidine application from the control current, and its properties were as follows. 1) It was a slowly activating inward current evoked by hyperpolarization. 2) The reversal potential in the standard extracellular solution ([K+]o = 5 mM, [Na+]o = 151 mM) was -38.3 mV, and reduction of [Na+]o shifted it to a more negative potential, whereas an increase of [K+]o shifted it to a more positive potential, indicating that the current was carried by Na+ and K+ (PNa/PK = 0.22). 3) The relationship between the chord conductance underlying the clonidine-sensitive current and voltage could be fitted by a Boltzmann equation. These results indicate that the clonidine-sensitive current corresponds to a hyperpolarization-activated current (Ih), i.e., clonidine inhibits Ih in rat DRG neurons. DRG neurons were classified as small (15.9-32.9 microns diam), medium-sized (33-42.9 microns), and large (43-63.6 microns), and 7 of 19, 24 of 25, and 22 of 22 of these types exhibited Ih with mean +/- SE clonidine-induced inhibition values of 36.1 +/- 3.5% (n = 7), 43.1 +/- 3.7% (n = 24), and 35.1 +/- 2.7% (n = 22), respectively. Clonidine application to L4 and L5 DRG neurons excised from rats the sciatic nerves of which had been transected 14-35 days previously (transected DRG neurons) also reduced Ih. In current-clamp mode, 9 of 13 intact and 4 of 6 transected medium-sized DRG neurons that exhibited Ih responded to clonidine with hyperpolarization (> 2 mV). Some medium-sized DRG neurons exhibited repetitive action potentials in response to a depolarizing current pulse, and clonidine reduced the firing discharge frequencies in 8 of 11 intact and 3 of 4 transected neurons tested. Injection of a hyperpolarizing current pulse produced time-dependent rectification in DRG neurons that exhibited Ih, and clonidine blocked this rectification in all intact and transected neurons tested. These results suggest that inhibition of Ih due to alpha 2-adrenoceptor activation contributes to modulation of DRG neuronal activity in rats. On the basis of our findings, we discuss the possible mechanisms whereby sympathetically released norepinephrine modulates the abnormal activity of DRG neuronal cell bodies after nerve injury.

Effects of peripheral nerve ligation on expression of μ-opioid receptor in sensory ganglion neurons: an immunohistochemical study in dorsal root and nodose ganglion neurons of the rat

The present study was attempted to examine if μ-opioid receptor (MOR) might be transported by axonal flow peripherally through peripheral axons of somatic sensory ganglion neurons. After unilateral ligation of the sciatic nerve or the vagus nerve distal to the dorsal root ganglion (DRG) or nodose ganglion (NG), MOR-like immunoreactivity (MOR-LI) of neuronal cell bodies in the DRG of the fourth and fifth lumbar nerves, NG, ambiguus nucleus (Amb) and dorsal motor nucleus of the vagus nerve (DMV) on the side of the ligation was apparently reduced within 1 week after the nerve ligation. However, within 24 h after the nerve ligation, a transient enhancement of MOR-LI was observed in cell bodies of DRG neurons, sciatic nerve stump proximal to the ligature, and cell bodies of NG neurons on the side of the ligation; such a transient enhancement of MOR-LI was not detected in the Amb and DMV. The results suggest that MOR undergoes centrifugal axonal flow in peripheral axons of somatic and visceral sensory ganglion neurons, and that MOR synthesis in sensory ganglion neurons is vulnerable to damage of the peripheral axons.

Multiple signals underlie the axotomy-induced up-regulation of c-JUN in adult sensory neurons

We examined the axotomy-induced expression of the immediate-early gene (proto-oncogene) c- jun in the Ola mouse mutant (which exhibits a dramatic delay in Wallerian degeneration) using immunocytochemistry to c-JUN (the protein product of the protooncogene c- jun). c-JUN-like protein immunoreactivity was present in a similar proportion (ca. 60%) of L4 dorsal root ganglion (DRG) neuronal cell bodies from normal (C57/6J/BL) and Ola mice at 1 week following a sciatic nerve crush (axotomy). In normal mice, the intensity and extent of staining declined at 3 weeks, correlating with regeneration. In contrast, Ola mice exhibited a marked reduction (by 77%) in the extent of staining at 2 weeks. At 3 weeks (coinciding to the onset of extensive axonal degeneration in this mutant), staining levels were increased to 1 week levels. Taken together, these findings suggest that multiple signals (both independent and dependent on axonal degeneration) regulate c- jun expression in DRG neuronal cell bodies.

Regulation of aberrant neurofilament phosphorylation in neuronal perikarya. IV. Evidence for the involvement of two signals

Axonal regeneration over long distances is dependent upon events occurring both in the distal stump and in the neuronal cell body. Little is known concerning how events in the distal stump influence the cell body response to injury, or the axon reaction. In the present study, we examined this relationship for one component of the axon reaction (i.e. aberrant neurofilament (NF) phosphorylation) in the C57BL/Ola (Ola) mouse mutant, a model which exhibits delayed Wallerian degeneration (up to 3 weeks) and retarded regeneration of sensory neurons. Non-axotomized normal (C57/6J/BL) and Ola mice demonstrated modest immunostaining to phosphorylated NF (pNF) epitopes (using monoclonal antibody 06–17) in some (11%) L4 dorsal root ganglion (DRG) neuronal cell bodies. In normal mice, modest to intense immunoreactivity was present in 43% of DRG neurons at 1 week following a sciatic nerve crush (axotomy). The intensity and extent of staining declined with reinnervation, being reduced slightly at 2 weeks and more notably by 3 weeks following axotomy. In Ola mice, the intensity and extent (43%) of staining were not different from normal axotomized mice at 1 week following axotomy. However, the intensity was less and the extent of staining reduced by 28% at 2 weeks following axotomy. By 3 weeks, staining levels were again increased, being similar to that observed in Ola and normal mice at 1 week following axotomy. Taken together, the results suggest that aberrant expression of pNF epitopes in DRG neuronal cell bodies is regulated by at least two signals. The first signal is not dependent upon processes associated with Wallerian degeneration since pNF expression is fully developed in Ola mice when the vast majority of fibers remain intact. This suggests that induction arises from the loss of a target tissue-derived retrogradely transported trophic signal. The presence of a second signal is suggested by the failure of Ola mice to maintain (at 2 weeks) the level of pNF expression. This indicates that events in the distal stump may influence both the magnitude and duration of the axon reaction.