L4 Dorsal Root Ganglion Neurons Research Articles

Increase of preprotachykinin mRNA and substance P immunoreactivity in spared dorsal root ganglion neurons following partial sciatic nerve injury.

Complete sciatic nerve injury reduces substance P (SP) expression in primary sensory neurons of the L4 and L5 dorsal root ganglia (DRG), due to loss of target-derived nerve growth factor (NGF). Partial nerve injury spares a proportion of DRG neurons, whose axons lie in the partially degenerating nerve, and are exposed to elevated NGF levels from Schwann and other endoneurial cells involved in Wallerian degeneration. To test the hypothesis that SP is elevated in spared DRG neurons following partial nerve injury, we compared the effects of complete sciatic nerve transection (CSNT) with those of two types of partial injury, partial sciatic nerve transection (PSNT) and chronic constriction injury (CCI). As expected, a CSNT profoundly decreased SP expression at 4 and 14 days postinjury, but after PSNT and CCI the levels of preprotachykinin (PPT) mRNA, assessed by in situ hybridization, and the SP immunoreactivity (SP-IR) of the L4 and L5 DRGs did not decrease, nor did dorsal horn SP-IR decrease. Using retrograde labelling with fluorogold to identify spared DRG neurons, we found that the proportion of these neurons expressing SP-IR 14 days after injury was much higher than in neurons of normal DRGs. Further, the highest levels of SP-IR in individual neurons were detected in ipsilateral L4 and L5 DRG neurons after PSNT and CCI. We conclude that partial sciatic nerve injury elevates SP levels in spared DRG neurons. This phenomenon might be involved in the development of neuropathic pain, which commonly follows partial nerve injury.

Up-regulation of preprotachykinin and calcitonin gene-related peptide messenger RNA in L4 dorsal root ganglion neurons following L5 spinal nerve ligation; a rat neuropathic pain model

The anti-emetic mechanism of action of fentanyl to inhibit nicotine (5 mg/kg, s.c.)-induced emesis was investigated in Suncus murinus. The anti-emetic action of fentanyl (40 μg/kg, s.c.) was antagonised by the opioid receptor antagonists naltrexone (1 mg/kg, s.c.), naloxone (1 mg/kg, s.c.), M8008 (16S-methylcyprenorphine; 1 mg/kg, s.c.) and MR 2266 (5,9-diethyl-2-(3-furylmethyl)2′-hydroxy-7,7-benzomorphan; 1 mg/kg) but not by naloxone methylbromide (1 mg/kg, s.c.), naloxone methyliodide (1 mg/kg, s.c.), naltrindole (1 mg/kg, s.c.), DIPPA (2-(3,4-dichlorophenyl)-N-methyl-N-[1S)-1-(3-isothiocyanatophenyl)-2-(1-pyrrolidinyl)ethyl]acetamide; 3 mg/kg, i.p.) or naloxonazine (35 mg/kg, i.p.). This indicates an involvement of μ2-opioid receptors within the brain to mediate the anti-emetic effect of fentanyl. In other studies, naloxone 10–60 mg/kg, s.c. induced dose-related emesis but naltrexone was only emetic at 60 mg/kg, s.c. and naloxone methylbromide failed to induce emesis at doses up to 60 mg/kg, s.c. The emesis induced by a high dose of naloxone 60 mg/kg, s.c. was antagonized by CP-99,994 ((+)-(2S,3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine; 3–30 mg/kg, i.p.), 8-OH-DPAT, ((±)-8-hydroxy-dipropylaminotetralin; 0.003–0.3 mg/kg, s.c.), buspirone (3 mg/kg, s.c.) and fluphenazine (1–3 mg/kg, i.p.) but not by naltrexone (1–30 mg/kg, s.c.), metoclopramide (0.3–3 mg/kg, i.p.), sulpiride (0.3–3 mg/kg, i.p.), domperidone (0.1–3 mg/kg, i.p.), ondansetron (0.3–3 mg/kg, i.p.), granisetron (0.3–3 mg/kg, i.p.), scopolamine (0.3–3 mg/kg, i.p.) or promethazine (0.3–3 mg/kg, i.p.). The data is discussed in relation to opioid receptor mechanisms moderating emesis and the identification of potential sites of drug action available to inhibit the emetic reflex.

Local anaesthesia prevents acute inflammatory changes in neuropeptide messenger RNA expression in rat dorsal root ganglia neurons

Sensory neuropeptides, synthesised in dorsal root ganglia (DRG), are implicated in neurogenic inflammation and nociception in arthritis. Adjuvant monoarthritis increases primary afferent activity and alters expression of neuropeptide genes in DRG We investigated the role of neural discharge in the early changes in neuropeptide gene expression. Adjuvant injection increased preprotachykinin (PPT) and calcitonin gene-related peptide (CGRP) messenger RNA (mRNA) after 8 h, whereas somatostatin mRNA expression remained unchanged, in innervating L5 DRG neurons. The changes in PPT mRNA expression were prevented by concurrent local anaesthesia of the sciatic nerve. Our results suggest that electrical activity mediates, in part, the changes in DRG gene expression in response to acute inflammation.

Some sensory neurons express neuropeptide Y receptors: potential paracrine inhibition of primary afferent nociceptors following peripheral nerve injury

Neuropeptide Y (NPY) has been suggested to exert antinociceptive actions by inhibiting the release of neurotransmitters from trigeminal and dorsal root ganglia (DRG) neurons, but the site of direct NPY action in vivo and the NPY receptor subtype mediating these effects are unknown. 125I-peptide YY (PYY) was used to localize and characterize NPY receptor binding sites in trigeminal ganglia, DRG, and spinal cord of the rat, rabbit, and monkey. In the rat, rabbit, and monkey, 5-20% of trigeminal ganglia and DRG neurons express NPY binding sites. Unilateral cuff-induced neuropathy or transection of the rat sciatic nerve did not significantly alter the density or number of DRG neurons expressing NPY receptors. A unimodal size distribution for L4 and L5 DRG neurons expressing NPY binding sites in the rat was determined, with a mean cross-sectional area of 947 microns 2. In the spinal cord the highest concentration of NPY receptors is found in laminae I, II, V, X, and Onuf's nucleus. Pharmacological experiments using selective Y1 and Y2 receptor antagonists suggest that Y2 is the prominent NPY receptor subtype expressed in trigeminal ganglia neurons, DRG neurons, and spinal cord. Previous studies have demonstrated that a population of large-diameter, presumably myelinated primary afferents express NPY after peripheral nerve injury. NPY released from these injured large-diameter DRG neurons may act in a paracrine fashion to block the transmission of nociceptive information from the small- and medium-diameter DRG neurons that constitutively express NPY receptors. NPY receptors are therefore uniquely positioned to inhibit primary afferent nociceptors directly, especially after peripheral nerve injury.

Cholecystokinin in mammalian primary sensory neurons and spinal cord: in situ hybridization studies in rat and monkey.

The peptide cholecystokinin (CCK) has been suggested to be involved in nociception, but its exact localization at the level of the spinal cord and in spinal ganglia has been a controversial issue. Therefore the distribution of messenger RNA (mRNA) for CCK was studied by in situ hybridization using oligonucleotide probes on sections of adult rat lumbar dorsal root ganglia following unilateral section of the sciatic nerve and on sections of untreated monkey trigeminal ganglia, spinal cord and spinal ganglia from all levels. For comparison, calcitonin gene-related peptide (CGRP) mRNA was also studied in the monkey tissue using the same techniques. Peripheral sectioning of the sciatic nerve in the rat resulted in the appearance of detectable CCK mRNA in up to 30% of remaining ipsilateral L4 and L5 dorsal root ganglion neurons 3 weeks after surgery, with a distinct but more limited appearance also in the contralateral ganglia. No cells, or only single cells, could be seen in normal control rat ganglia. In contrast, in the normal monkey, approximately 20% of dorsal root ganglion neurons, regardless of spinal level, and 10% of trigeminal ganglia neurons expressed mRNA for CCK. CGRP mRNA was expressed at detectable levels in approximately 80% of these monkey dorsal root ganglion neurons. In the monkey spinal cord, CCK mRNA was detected in the dorsal horn and in motoneurons, whereas CGRP mRNA was only seen in motoneurons. The present results suggest that CCK peptides can be involved in sensory processing in the dorsal horn of the spinal cord in normal monkeys and in rats after peripheral nerve injury, adding one more possible excitatory peptide to the group of mediators in the dorsal horn.

Role of gastric acid suppression in the treatment of gastro-oesophageal reflux disease.

Gastro-oesophageal reflux disease is a common condition with a complex pathophysiology. Despite the spectrum of abnormalities, gastric acid has a central role in mucosal damage, and the mainstay of medical treatment is suppression of gastric acid secretion. The results of antisecretory treatment as assessed by endoscopic healing are reviewed. H2 receptor antagonists give more rapid symptom relief than placebo and can produce endoscopic improvement in 31-88% of cases depending on the severity of oesophagitis. Complete healing, however, is seen only in 27-45% of patients and these have mainly grades I-II disease. Improved healing rates can be obtained by increasing the degree of acid suppression or the length of treatment. The addition of a prokinetic agent may be beneficial. Omeprazole heals 67-92% of patients overall and although most successful in the lower grades of oesophagitis, can also heal 48-62% of patients with grade IV disease. The degree and rate of healing seem to be related to the reduction in oesophageal acid exposure and thus may correlate with the degree and duration of acid suppression over 24 hours obtained by the various treatments. The underlying pathophysiology is unchanged, however, and long term treatment may be needed to maintain remission.

Populations of rat spinal primary afferent neurons with choleragenoid binding compared with those labelled by markers for neurofilament and carbohydrate groups: a quantitative immunocytochemical study

A quantitative comparison was made of the population of L5 dorsal root ganglion neurons that bind choleragenoid and the population of neurons labelled by RT97, an anti-neurofilament antibody, SSEA3, an antibody to a globoseries carbohydrate group and 1B2, an antibody to a lactoseries carbohydrate group. Neurons with choleragenoid binding formed a population of 37% of all the cells and 94% of these were also immunoreactive to RT97. The choleragenoid-and RT97-positive groups of cells showed the same size distribution. Two small populations of cells existed which were choleragenoid negative/RT97 positive and choleragenoid positive/RT97 negative. SSEA3 immunoreactivity was found in 8% of the dorsal root ganglion neurons which were of all sizes. The 1B2 immunoreactivity was found in 32% of the dorsal root ganglion cells, the majority of which were in the small size range. More than half of the SSEA3-positive cells but only a few of the 1B2-positive neurons were labelled for choleragenoid. These results demonstrate that choleragenoid labels the majority of the light (RT97-positive) cell population and that light cells unlabelled by choleragenoid are small in number and spread across a wide size range.

Glutamate-immunoreactivity in the trigeminal and dorsal root ganglia, and intraspinal neurons and fibres in the dorsal horn of the rat

Putative aspartergic and glutamatergic sensory neurons in the rat were identified by autoradiography and immunocytochemistry respectively. Approximately 3% of large L4 dorsal root ganglion neurons (diameter 18-52 microns) accumulated radiolabelled aspartate, whereas all satellite glia had high affinity for the amino acid. Glutamate-immunofluorescent (Glu-FITC) dorsal root ganglia neurons comprised 38.3% at S1, 35.6% at L2, 33.9% at C5 and 28.8% at T6. Numbers of immunoreactive neurons were higher with the more sensitive peroxidase-anti-peroxidase (Glu-PAP) method; and the cell counts totalled 42% (S1), 41.2% (L4), 35% (C5) and 34.6% (T6). The trigeminal ganglion (TG) contained 24% Glu-FITC and 32.3% Glu-PAP positive cells. The majority of glutamate-immunoreactive sensory neurons were small, ranging from 10-35 microns with median diameters of 17.5 microns (C5), 21 microns (S1), 24.2 microns (TG) and 28.5 microns (L2). It is evident therefore, that a subgroup of class B cells are glutamatergic. Glutamate immunoreactivity in the spinal cord was similar in all segments and was localized in the superficial lamina and substantia gelatinosa of the dorsal horn. Stained interneurons were located among the immunoreactive fibres. The dorsolateral funiculus contained dense plexus of immunoreactive fibres which increased in prominence after intraperitoneal injection of L-gluatamate, but penetration of exogenous glutamate into the grey matter was limited. Instead, the meninges and basal layers of the spinal blood vessels were intensely immunoreactive. The studies describe the subtypes of acidic amino acidergic neurons and relates the immunohistochemistry to a functional subclass.

Anatomical studies of dorsal column axons and dorsal root ganglion cells after spinal cord injury in the newborn rat

The response of dorsal column axons was studied after neonatal spinal overhemisection injury (right hemicord and left doral funiculus). Rat pups (N = 11) received this spinal lesion at the C2 level within 30 hours after birth. The cauda equina was exposed 3 months later in one group of chronic operates (N = 5) and in a group of normal adults (N = 2), and all spinal roots from L5 caudally were cut bilaterally; 4 days later the spinal cord and medulla were processed for Fink-Heimer impregnation of degenerating axons and terminals. In a second group of chronic operates (N = 6) and normal adult controls (N = 4) the left sciatic nerve was injected with a cholera toxin-HRP conjugate (C-HRP), followed by a 2-3 day transganglionic transport period, and then the spinal cord and medulla were processed with tetramethylbenzidine histochemistry. Both control groups have a consistent dense projection in topographically adjacent regions of the dorsal funiculus and gracile nucleus. However, there is no sign of axonal growth around the lesion in either group of chronic experimental operates. Instead, there is a decreased density of projection within the dorsal funiculus near the lesion site. Many remaining C-HRP labeled axons in the experimental operates have abnormal, thick varicosities and swollen axonal endings (5-10 microns x 10-30 microns) within the dorsal funiculus through several spinal segments caudal to the lesion. Ultrastructural analysis of the dorsal funiculus in three other chronic experimental operates reveals the presence of numerous vesicle filled axonal profiles and reactive endings which appear similar to the C-HRP labeled structures. Transganglionic labeling after C-HRP sciatic nerve injections (N = 4) and retrograde labeling of L4, L5 dorsal root ganglion neurons after fast blue injections of the gracile nucleus (N = 6) both suggest that all dorsal column axons project to the gracile nucleus in the newborn rat. Dorsal root ganglion (DRG) cell survival following the neonatal overhemisection injury was also examined in the L4 and L5 DRG. DRG neurons that project to the gracile nucleus were prelabeled by injecting fast blue into this nucleus at birth two days prior to the cervical overhemisection spinal injury. Both normal littermates (N = 9) and spinally injured animals (N = 12) were examined after postinjection survival periods of 10 or 22 days.(ABSTRACT TRUNCATED AT 400 WORDS)

Death of some dorsal root ganglion neurons and plasticity of others following sciatic nerve section in adult and neonatal rats

Newborn animals recover from neurological injury to a greater extent than adults in spite of the greater vulnerability of developing neurons to retrograde or transneuronal degeneration (Kennard, '42; Goldman, '74; Prendergast and Stelzner, '76; Bregman and Goldberger, '82, '83). The cellular mechanisms underlying this "infant lesion effect" are incompletely understood (Bregman and Goldberger, '82). The dorsal root ganglion (DRG) is an excellent model in which to compare the developing and adult nervous system with respect to the effects of axotomy on cell survival and cellular function. We studied the survival of L5 DRG neurons after section-ligation of the sciatic nerve of adult and neonatal rats and used qualitative and quantitative immunocytochemical methods to examine changes in intraspinal substance P immunoreactivity (SPIR). Retrograde transport of wheatgerm agglutinin-horseradish (WGA-HRP) peroxidase applied to the sciatic nerve of adult or neonatal rats demonstrated that 70% of the neurons in the normal L5 DRG project into the sciatic nerve at the site of transection. In adults 20% of all L5 DRG neurons died between 10 and 60 days postoperative; in newborns 50% of the neurons died between 5 and 10 days. These results indicate that 30% of axotomized neurons in adults and 75% in neonates die after sciatic nerve section and that neuron loss is both more rapid and more extensive in neonates. No cell death was observed in the L5 DRG of neonates after dorsal rhizotomy, thus suggesting that at this stage of development the survival of DRG neurons depends on the peripheral but not the central process. SPIR in laminae I and II of both adult and newborn operates decreased and then recovered, but the time course and extent of the recovery differ. In adults SPIR was depleted in the medial portion of the L5 segment ipsilateral to surgery by 10 days postoperative and remained depleted for at least 2 months. By 1 year partial recovery occurred, but remained incomplete even at the longest survival time studied (15 months). SPIR, which is present in the dorsal horn at birth, was diminished in ipsilateral laminae I and II by 4 days after nerve section on the day of birth. Between 30 days and 60 days, the density of SPIR in the dorsal horn ipsilateral to surgery became virtually indistinguishable from that on the contralateral, intact side, suggesting a more rapid and complete recovery than in adults.(ABSTRACT TRUNCATED AT 400 WORDS)

Conduction velocity changes along the processes of rat primary sensory neurons

Conduction velocities of rat L4, L5 and L6 dorsal root ganglion neurons were measured in vitro, from several points on the peripheral nerve and dorsal root. Conduction velocities calculated from a single stimulation point (12–26 mm from the ganglion) proved accurate for fibres conducting up to 17 m/s in the peripheral nerve and up to 14 m/s in the dorsal root, but tended to underestimate the value for faster fibres. C-fibre neurons of the L4 and L5 ganglia had a unimodal distribution of conduction velocities below 1.3 m/s.These were discontinuous with A-fibre conduction velocities, which also had a unimodal distribution and had no clear Aδ peak. In contrast, conduction velocities of L6 ganglion neurons showed no discontinuity between C- and A-fibres, but had a clear Aδ peak.In A-fibre neurons, dorsal root conduction velocities were on average about 14% slower than, and linearly related to, those in the peripheral nerve. However, in individual neurons the dorsal root conduction velocity could be slower or faster than that in the peripheral nerve. In C-fibre neurons dorsal root conduction velocities were almost always slower (average 28%) but not correlated with those of the peripheral nerve. Slowing of conduction velocity along the sciatic nerve was seen in most fibres conducting at less than 2 m/s, but not in faster fibres. The slowing was substantial (up to 60%), sometimes from the Aδ to the C-fibre range, and sudden, occurring at a distance of between 15 and 29mm from the ganglion.

Cell death in the adult rat dorsal root ganglion after hind limb amputation, spinal cord transection, or both operations

Cell death of embryonic neurons which are unable to attain a proper target is well established. A delayed cell death of adult neurons permanently separated from their target tissue has been demonstrated for several cell groups. Cells of the dorsal root ganglia (DRG) are unique in that a single T-shape neurite has a peripheral branch which extends (for root L5) to the hind limb and a central branch extending into the spinal cord. We found a significant loss of L5 DRG neurons 25 weeks after hind limb amputation. This finding is consistent with the hypothesis that neuron survival is dependent on connection with a suitable target. We were unable to detect cell death in the DRG of L5 after complete spinal cord transection at T9. Separation of DRG cells from their central target is unimportant to neuronal survival.