Comparison of c-jun, junB, and junD mRNA expression and protein in the rat dorsal root ganglia following sciatic nerve transection.

The present study was designed to compare the expression of the Jun family of protooncogenes following nerve injury. Adult rats were anesthetized and the sciatic nerve transected. Dorsal root ganglia (DRG) at 1, 2, 3, and 7 days after nerve transection were collected, their total RNA extracted, and Northern blots performed using 32P-labeled oligonucleotide probes. The constitutive expression of c-jun mRNA was very low in DRG. Induction of c-jun mRNA was observed by day 1 after nerve transection, with a sixfold peak at 3 days and a twofold induction still present by day 7. The constitutive expression of junB mRNA was also low in the DRG, and sciatic nerve transection produced only a modest induction (1.7-fold by day 3) in the DRG ipsilateral to the nerve cut. junD mRNA was constitutively expressed at high levels in the DRG, and its level of expression did not in the DRG, and its level of expression did not change after sciatic nerve transection. Immunocytochemistry studies demonstrated a pattern of c-Jun, JunB, and JunD immunoreactivity (IR) associated with the cell nuclei of DRG neurons. c-Jun IR was found at very low levels in the undamaged contralateral DRG neurons, but sciatic nerve transection dramatically increased the number of c-Jun-immunoreactive neurons. Dot blot immunoblotting assay confirmed that the DRG ipsilateral to the sciatic nerve cut contained a higher level of c-Jun protein than the contralateral control DRG. Similar to c-Jun IR, JunB IR was minimal in the undamaged contralateral DRG. However, the DRG ipsilateral to the nerve transection did not show an increase in the number of immunoreactive neurons. JunD protein was expressed at high levels in the contralateral DRG, and this level of expression persisted after sciatic nerve transection in the ipsilateral DRG. DNA gel retardation assay experiments with an AP-1 consensus sequence showed a single DNA-protein complex. This complex was increased in ipsilateral as compared with contralateral DRG extracts. The amount of DNA-protein complex was reduced by c-Jun protein antiserum but was not altered when treated with a Fos antibody. We conclude that c-jun, junB and junD mRNAs and proteins are differentially regulated in the DRG after sciatic nerve transection.

Adjuvant-induced inflammation of rat paw is associated with altered calcitonin gene-related peptide immunoreactivity within cell bodies and peripheral endings of primary afferent neurons.

Local inflammation is associated with profound changes in the biochemistry and physiology of primary afferent nerve fibers and the central neurons responding to their signals. In some tissues, the neural changes accompanying inflammation include sprouting and cytochemical changes that are delayed several days after the initial injury. In the present study, we have analyzed the effect of complete Freund's adjuvant (CFA)-induced inflammation in the rat paw on calcitonin gene-related peptide (CGRP) immunoreactivity (IR) in dorsal root ganglia and within tissue of the inflamed paw. We quantified the CGRP-IR within the L1, L4, and L6 ganglia, and in ankle, midpaw, joint and toe tissues. Analysis of the processed tissue revealed a significant increase in the percentage of CGRP-positive cells within L4 dorsal root ganglia ipsilateral to an inflamed hindpaw six days after administration of CFA. There was a parallel increase in the number and staining density of detectable CGRP-immunoreactive fibers in periarticular and perivascular tissues of the inflamed digits and inflamed ankle. The other tissues of the paw, including epidermis and the regions surrounding the abcesses, did not have detectable changes in CGRP-immunoreactive fibers, despite tissue swelling and dystrophic changes in the foot that included loss of mast cell staining. These data demonstrate that local inflammation of the rat paw has delayed influences on the peripheral nervous system, in addition to a number of previously characterized acute effects. The alterations of CGRP-IR were focused around specific tissue types, such as joints and subdermal blood vessels, and absent from others, such as epidermis or in the areas surrounding abscesses. This suggests production of local factors within reactive tissues that selectively interact with nerve fibers to induce changes in CGRP-IR within the fibers.

SR13/PMP-22 expression in rat nervous system, in PC12 cells, and C6 glial cell lines.

SR13/PMP-22 is a protein that was identified after screening a sciatic nerve cDNA library. Our study focused on comparing the level and pattern of expression of SR13/PMP-22 protein and RNA. Northern blot analysis revealed that although SR13/PMP-22 mRNA was present in all nervous tissues and cells studied, levels were at least seven fold higher in the sciatic nerve and the spinal cord. During sciatic nerve postnatal development and maturation, the SR13/PMP-22 mRNA was detected at 2 days after birth, reached a maximal level at day 24, and decreased to 1/3 of the maximum in adult animals. Nerve transection reduced the level of SR13/PMP-22 mRNA to less than 5% in the segment distal to the nerve injury. Experiments using in situ hybridization localized the SR13/PMP-22 mRNA in Schwann cells. Schwann cells present in the vicinity or distal to the nerve cut repressed the signal for the message. In situ hybridization experiments also demonstrated that dorsal root ganglia satellite cells contained the message for SR13/PMP-22. The SR13/PMP-22 antisera used in our study showed a complex pattern of staining. As expected, the SR13/PMP-22 antibody peptide 1 immunoreacted with the sciatic nerve sheath. However, immunocytochemistry of the dorsal root ganglia revealed that the staining was contained in the neuron's cell body and processes and also in satellite cells. We also identified immunoreactive cell bodies and fibers in the spinal cord dorsal horn. Tissue culture studies demonstrated that SR13/PMP-22 mRNA is induced in NGF treated PC12 but not in C6 glioma cell lines grown under experimental conditions that stimulated cell growth arrest. Our experiments suggest that SR13/PMP-22 may have some other function(s) in addition to its hypothesized role in peripheral myelination.

Quantification of axotomy-induced alteration of neuropeptide mRNAs in dorsal root ganglion neurons with special reference to neuropeptide Y mRNA and the effects of neonatal capsaicin treatment.

Alteration in mRNA expression in dorsal root ganglia (DRG) neurons encoding 5 neuropeptides was quantitatively compared in normal rats and in those neonatally treated with capsaicin, a selective neurotoxin which destroys a subpopulation of DRG neurons with unmyelinated axons. Adult rats received a unilateral transection of the sciatic nerve and were killed 7 days later. Oligonucleotide probes specific for the genes encoding neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), galanin (GAL), somatostatin (SOM), and calcitonin gene-related peptide (CGRP) were used for in situ hybridization and RNA blot analysis. Following the nerve cut, RNA blot analysis demonstrated a dramatic induction of NPY, VIP, and GAL mRNA levels from the undetectable constitutive level of expression. Conversely, CGRP and SOM mRNAs, which are constitutively expressed, were reduced 55% and 70%, respectively, following the nerve cut. A unimodal size distribution for neurons expressing NPY mRNA was determined, with a mean cross-sectional area of 1700 microns2 representing 24.4% of DRG neurons ipsilateral to the nerve cut. Neurons expressing VIP mRNA were mainly small sized, with a cross-sectional area of approximately 700 microns2, while those expressing GAL mRNA were both small (approximately 700 microns2) and medium (approximately 1,300 microns2) sized. The percentages of neurons expressing VIP or GAL mRNA were 19.9% and 33.7%, respectively. In neonatal capsaicin-treated rats, there was a 10% reduction in neurons expressing NPY mRNA, a 37% reduction for VIP, and a 27% for GAL mRNA compared to vehicle-treated rats after nerve cut. Capsaicin-sensitive neurons comprised 37% of CGRP neurons and 83% of SOM neurons. These observations suggest that NPY is primarily induced in myelinated primary afferent neurons, while VIP and GAL mRNA induction occurs in a mixed population, a sizeable percentage of which has unmyelinated axons. Additionally, SOM mRNA expression is associated mainly with unmyelinated primary afferents.

Diencephalic projections from the superficial and deep laminae of the medullary dorsal horn in the rat.

An important function of the medullary dorsal horn (MDH) is the relay of nociceptive information from the face and mouth to higher centers of the central nervous system. We studied the central projection pattern of axons arising from the MDH by examining the axonal transport of Phaseolus vulgaris-leucoagglutinin (PHA-L). Labeled axon and axon terminal distributions arising from the MDH were analyzed at the light microscopic level. After large injections of PHA-L into both superficial and deep laminae of the MDH in the rat, labeled axons were observed in the nucleus submedius of the thalamus (SUB), ventroposterior thalamic nucleus medialis (VPM), ventroposterior thalamic nucleus parvicellularis (VPPC), posterior thalamic nuclei (PO), zona incerta (ZI), lateral hypothalamic nucleus (LH), and posterior hypothalamic nucleus (PH). Restriction of PHA-L into only the superficial laminae resulted in heavy axon and varicosity labeling in the SUB, VPM, PO, and VPPC and light labeling in LH. In contrast, after injections into deep laminae, labeled axons were mainly distributed in ZI and PH; some were also in VPM and LH, and fewer still in PO and SUB. Varicosities in VPM, SUB, and PO were significantly larger than those in VPPC, ZI, LH, and PH. Varicosity density was highest in SUB and lowest in the VPPC. We concluded that there are two distinct nociceptive pathways, one originating from the superficial MDH and terminating primarily in the dorsal diencephalon and the second originating from deep laminae of the MDH and terminating primarily in the ventral diencephalon. We propose that in the rat, input from the deeper laminae is primarily involved in the motivational-affective component of pain, whereas input from the superficial MDH is related to both the sensory-discriminative and motivational-affective component of pain.

Peripheral inflammation is associated with increased glutamic acid decarboxylase immunoreactivity in the rat spinal cord.

We have examined the frequency and distribution of neuron profiles immunoreactive for glutamic acid decarboxylase, a biosynthetic enzyme for the putative inhibitory neurotransmitter, gamma aminobutyric acid, in the lumbar spinal cord of colchicine-treated rats with unilateral inflammation of a hindpaw. Ipsilateral to the inflamed hindpaw, there was an apparent increase in the levels of glutamic acid decarboxylase, as indicated by significant increases in the number of visible glutamic acid decarboxylase-like immunoreactive profiles within the superficial dorsal horn, neck of the dorsal horn and the deep gray matter at L4. An increase limited to the deep gray matter at L6 was also seen. No alteration was identified at L2. These results are the first to demonstrate that peripheral inflammation is associated with altered levels of glutamic acid decarboxylase-like immunoreactivity.

Spinal opioid analgesic effects are enhanced in a model of unilateral inflammation/hyperalgesia: possible involvement of noradrenergic mechanisms.

We have examined the spinal analgesic activity of opioid agonists and antagonists in a model of short term, unilateral, carrageenan-induced inflammation/hyperalgesia. Rats received a single s.c. injection of carrageenan (2-6 mg in saline) 3-24 h prior to testing hindpaw withdrawal latencies to noxious thermal stimuli. Dose-response curves for intrathecally administered agonists with mu- and/or delta-opioid activity were shifted to the left for inflamed hindpaws when compared to contralateral non-inflamed paws. The selective kappa-receptor agonist U-50,488H had no activity in this analgesic assay on either inflamed or non-inflamed paws when administered intrathecally. However, systemic administration of U-50,488H did produce significant elevations of paw withdrawal latencies in inflamed paws. The alpha 2-adrenoceptor agonist clonidine also produced dose-dependent antinociception in the paw withdrawal assay after systemic or intrathecal administration. Inflamed hindpaws were significantly more sensitive to the antinociceptive effect of morphine on inflamed hindpaws was blocked by the opioid antagonist naloxone or the alpha 2-adrenoceptor antagonist idazoxan. The effect of clonidine was only blocked by idazoxan. Antagonists alone had no significant effect on withdrawal latencies. The data indicate that the analgesic action of opioids during conditions of inflammation may depend on an interaction with spinal noradrenergic pathways.

Evidence for calcitonin gene-related peptide contacts on a population of lamina I projection neurons.

Using double-labeling techniques, we evaluated small diameter primary afferent input, as indicated by calcitonin gene-related peptide-immunoreactive varicosities, to a population of lamina I projection neurons in the rat lumbar spinal cord. About one third of the lamina I neurons labeled after injections of a retrograde tracer into the region surrounding the brachium conjunctivum received contacts from immunoreactive varicosities. Significantly fewer immunoreactive varicosities were in apposition to fusiform neurons than pyramidal or flattened neurons. A positive correlation was found between the size of the retrogradely labeled neuron and the number of contacts received. This study demonstrates that a known population of nociceptive lamina I neurons received direct input from presumed nociceptive primary afferents.

Distribution and size of GABAergic neurons in area 7b and the retroinsular cortex of the monkey.

The distribution of gamma-aminobutyric acid (GABA) neurons was examined in the retroinsular cortex (Ri) and area 7b of the monkey. GABA-immunoreactive somata and puncta were observed in all layers of Ri and area 7b. The densest concentration of these neurons was located in layers I and II. The vast majority (98.9%) of GABA-immunoreactive somata were less than 15 microns in major diameter. These data demonstrate that high concentrations of GABAergic neurons are located in those cortical layers that have been shown to receive afferent projections from corticocortical fibers.

Peripheral inflammation is associated with increased dynorphin immunoreactivity in both projection and local circuit neurons in the superficial dorsal horn of the rat lumbar spinal cord.

The present study combined the retrograde transport of fluorescent tracers with the immunocytochemical identification of dynorphin A(1-8) in superficial dorsal horn neurons to examine whether peripheral inflammation-induced dynorphin increases are found in local circuit neurons only or also in neurons projecting at least to the caudal mesencephalon. Evidence is presented that complete Freund's adjuvant-induced inflammation produces a large increase in the number of lamina I dynorphin-containing projection and non-projection neurons, and in the number of lamina II dynorphin local circuit neurons.

Spinal lamina I projection neurons in the rat: collateral innervation of parabrachial area and thalamus.

A major ascending nociceptive pathway from spinal lamina I to the mesencephalon has previously been reported in the cat, rat and monkey. In the present paper, we have used single and double retrograde labeling techniques to describe this projection system and its collateralization to the thalamus in the rat. Injections of wheat germ agglutinin-horseradish peroxidase into the pontomesencephalic parabrachial area labeled cell bodies bilaterally in lamina I and deeper laminae of the spinal cord. Bilateral lesions of the dorsolateral funiculi at thoracic levels reduced labeling of lamina I neurons caudal to the lesions. Combined injections of fluorescent retrograde tracers into the lateral thalamus and parabrachial area resulted in double labeling of projection neurons in lamina I, lamina IV VIII and the lateral spinal nucleus of the cervical and lumbar enlargements. Double-labeled neurons were especially abundant in lamina I. Thus, we have demonstrated a major lamina I projection through the dorsolateral funiculi to the parabrachial area with significant collateralization to the thalamus. Moreover, since more than 80% of retrogradely labeled lamina I spinothalamic tract cells had collaterals to the parabrachial area we have indirectly demonstrated the presence of a dorsolateral funicular pathway for lamina I spinothalamic neurons in the rat. More lamina I neurons were retrogradely labeled from midbrain injections as compared to thalamic injections. The significance of these findings rest on previous work in this and other laboratories and concerns the understanding of spinal nociceptive mechanisms. Lamina I projection neurons are primarily nociceptive-specific in their response properties and have been shown to project to both the midbrain and thalamus via the dorsolateral funiculus in a number of species. The role of this projection system in nociceptive transmission may lie in its ability to distribute precise information to multiple brain stem sites which in turn activate autonomic or affective responses or descending pain modulatory mechanisms.

Immunocytochemical identification of long ascending, peptidergic lumbar spinal neurons terminating in either the medial or lateral thalamus in the rat.

The peptidergic content of rat spinothalamic tract neurons was investigated by combining the retrograde transport of the fluorescent dye Fluoro-gold with immunocytochemistry for enkephalin, dynorphin or vasoactive intestinal polypeptide. Evidence is presented for the existence of enkephalin and dynorphin in a subpopulation of spinothalamic neurons terminating in the medial thalamus and vasoactive intestinal polypeptide in a subpopulation terminating primarily in the lateral thalamus.

Immunocytochemical identification of long ascending peptidergic neurons contributing to the spinoreticular tract in the rat.

In the present study, we examined the peptidergic content of lumbar spinoreticular tract neurons in the colchicine-treated rat. This was accomplished by combining the retrograde transport of the fluorescent dye True Blue with the immunocytochemical labeling of neurons containing cholecystokinin-8, dynorphin A1-8, somatostatin, substance P or vasoactive intestinal polypeptide. After True Blue injections into the caudal bulbar reticular formation, separate populations of retrogradely labeled cells were identified as containing cholecystokinin-like, dynorphin-like, substance P-like or vasoactive intestinal polypeptide-like immunoreactivity. Retrogradely labeled somatostatin-like neurons were not identified in any of the animals examined. Each population of double-labeled cells showed a different distribution in the lumbar spinal cord. The highest yield of double-labeling occurred for cholecystokinin, with 16% of all intrinsic cholecystokinin-like neurons containing True Blue. These double labeled neurons were found predominantly at the border between lamina VII and the central canal region. About 11% of intrinsic vasoactive intestinal polypeptide-like neurons in the lumbar spinal cord were retrogradely labeled from the bulbar reticular formation. These neurons were found mostly in the lateral spinal nucleus, with only a few double-labeled cells located deep in the gray matter. Dynorphin-like double-labeled neurons were localized predominantly near the central canal; a smaller population was also seen in the lateral spinal nucleus. It was found that double-labeled dynorphin-like neurons made up 8% of all intrinsic dynorphin-like neurons. Retrogradely-labeled substance P-like neurons were rare; the few double-labeled neurons were found in the lateral spinal nucleus and lateral lamina V. These findings suggest a significant role for spinal cord peptides in long ascending systems beyond their involvement in local circuit physiology.

Altered responses of nociceptive cat lamina I spinal dorsal horn neurons after chronic sciatic neuroma formation.

The activity of lumbar spinal dorsal horn lamina I neurons with afferent drive from the sciatic nerve was studied in intact cats and in cats with acute sciatic nerve transection or chronic sciatic nerve transection with neuroma formation. The majority (51 of 75) of neurons recorded in lamina I ipsilateral to a neuroma had no receptive field and could only be identified by their responses to electrical stimulation of the sciatic nerve. The remainder could be activated by the sciatic nerve, but their responses to mechanical stimulation were irregular in comparison to the stable responses of cells recorded in control animals and to the responses of cells contralateral to chronic nerve lesions. Animals with acute nerve transections demonstrated a loss of sciatic nerve-innervated cells with receptive fields except for those cells located on the lateral edge of the dorsal horn, which had normal, proximal receptive fields and response characteristics. In addition, the characteristic somatotopy of lamina I cells was not observed in some cats with chronic neuromata. The mediolateral distribution of cell types indicated that some cells had altered receptive fields following chronic nerve transection. The data presented for lamina I neurons agrees with the observation of spinal cord plasticity first presented for cat dorsal horn cells. Since there is no evidence for a redistribution of intact afferent fibers following chronic nerve transection in adult mammals, the mechanism of altered somatotopy may involve alterations in synaptic efficacy at existing synapses.

Neurochemical identification of afferents onto spinomedullary neurons in the rat spinal cord central gray matter.

The synaptic relationship between spinal cord central gray projection neurons and immunocytochemically identified afferents in the rat were examined at the light microscopic level using the combined techniques of retrogradely transported True blue and serotonin (5-HT), enkephalin (ENK), and substance P (SP) immunocytochemistry. At L4-L6, numerous retrogradely labeled neurons could be identified around the central canal after large bulbar injections of True blue. Of these projection neurons, 75% were apposted by 5-HT varicosities, 57% by ENK varicosities and 58% by SP varicosities. Hemisection of the spinal cord produced a marked reduction in the amount of 5-HT immunoreactivity and the number of putative 5-HT contacts observed on neurons of the spinal cord central gray. A small decrease in SP immunoreactivity and putative contacts was seen after dorsal rhizotomy. Neither rhizotomy nor hemisection produced discernable changes in ENK immunofluorescence. Based on the distributions of 5-HT, ENK and SP in the spinal cord, we suggest that a more precise delineation of lamina X in the rat can be made according to immunocytochemical rather than strictly morphological criteria.

Funicular location of the ascending axons of neurons adjacent to the spinal cord central canal in the rat.

Neurons adjacent to the central canal in the rat spinal cord were retrogradely labeled bilaterally after injection of horseradish peroxidase into the bulbar reticular formation. Lesions restricted to parts of the ventral lateral funiculus in thoracic or high lumbar segments on the side ipsilateral to the injections produced significant bilateral reductions in labeling. Lesions that included the entire ipsilateral ventral lateral funiculus greatly reduced the number of labeled neurons surrounding the central canal caudal to the lesion. Lesions of either the dorsal lateral funiculus, or midline lesions encompassing both the dorsal and ventral columns had no significant effect on labeling. Spinoreticular tract neurons on both sides of the central canal issue axons that ascend in the ventral lateral funiculus of the side ipsilateral to their termination.

A long ascending pathway of enkephalin-like immunoreactive spinoreticular neurons in the rat.

In the present study, we examined whether some long ascending spinal cord neurons contain enkephalin by combining the retrograde transport of the fluorescent dye True Blue with enkephalin immunocytochemistry. Evidence is presented for the existence of enkephalin in a subpopulation of spinoreticular neurons in the rat located in the central canal region and adjacent gray matter.

Postsynaptic dorsal column pathway of the rat. I. Anatomical studies.

As one of a series of studies of the ascending spinal cord pathways that might be involved in nociception in the rat, we have examined the projection to the dorsal column nuclei that originates in the spinal cord dorsal horn using the retrograde transport of horseradish peroxidase (HRP). This projection in other animals has been called the postsynaptic dorsal column (PSDC) pathway. Small iontophoretic injections of HRP into the cuneate nucleus (CN) labeled more than 350 neurons in alternate sections within the ipsilateral gray matter of segments C6-8. Fewer than 25 neurons were labeled in L4-6 by injections into CN. Injections of HRP confined to the gracile nucleus (GN) labeled more than 200 neurons within a narrow band extending across the ipsilateral dorsal horn subjacent to substantia gelatinosa of L4-6. Fewer than 10 cells were labeled in C6-8 by such injections. Labeling in lumbar neurons following injections into GN was prevented by transection of the dorsal columns at T10, T8, or C2. Thus, neurons labeled by such injections ascend entirely within the dorsal columns. Lesions of the dorsal columns in C2 reduced the number of labeled neurons in the cervical cord following CN injections by approximately 90%. Combined lesions of the dorsal columns and ipsilateral dorsal lateral funiculus (DLF) reduced the number of cells labeled in C6-8 by approximately 98%. Thus, the majority of labeled neurons in the cervical enlargement project to CN via the dorsal columns; a small secondary component of the cervical projection to CN appears to ascend within the DLF. To compare the relative sizes of the projections to the dorsal column nuclei from PSDC neurons and dorsal root ganglion cells (DRG), labeled neurons were counted in the gray matter of the cervical and lumbar enlargements and the corresponding DRG. In the four animals so examined, PSDC neurons constituted over 38% of the neurons that projected to CN and approximately 30% of the cells that projected to GN. These findings indicate that the PSDC projection of the rat is capable of providing a large somatotopically organized input to the dorsal column nuclei.