The postnatal development of large light and small dark neurons in mouse dorsal root ganglia: a statistical analysis of cell numbers and size

Neuropeptide Y-expressing dorsal horn inhibitory interneurons gate spinal pain and itch signalling

Somatosensory information is processed by a complex network of interneurons in the spinal dorsal horn. It has been reported that inhibitory interneurons that express neuropeptide Y (NPY), either permanently or during development, suppress mechanical itch, with no effect on pain. Here, we investigate the role of interneurons that continue to express NPY (NPY-INs) in the adult mouse spinal cord. We find that chemogenetic activation of NPY-INs reduces behaviours associated with acute pain and pruritogen-evoked itch, whereas silencing them causes exaggerated itch responses that depend on cells expressing the gastrin-releasing peptide receptor. As predicted by our previous studies, silencing of another population of inhibitory interneurons (those expressing dynorphin) also increases itch, but to a lesser extent. Importantly, NPY-IN activation also reduces behavioural signs of inflammatory and neuropathic pain. These results demonstrate that NPY-INs gate pain and itch transmission at the spinal level, and therefore represent a potential treatment target for pathological pain and itch.

RAGE activation in macrophages and development of experimental diabetic polyneuropathy

It is suggested that activation of receptor for advanced glycation end products (RAGE) induces proinflammatory response in diabetic nerve tissues. Macrophage infiltration is invoked in the pathogenesis of diabetic polyneuropathy (DPN), while the association between macrophage and RAGE activation and the downstream effects of macrophages remain to be fully clarified in DPN. This study explored the role of RAGE in the pathogenesis of DPN through the modified macrophages. Infiltrating proinflammatory macrophages impaired insulin sensitivity, atrophied the neurons in dorsal root ganglion, and slowed retrograde axonal transport (RAT) in the sciatic nerve of type 1 diabetic mice. RAGE-null mice showed an increase in the population of antiinflammatory macrophages, accompanied by intact insulin sensitivity, normalized ganglion cells, and RAT. BM transplantation from RAGE-null mice to diabetic mice protected the peripheral nerve deficits, suggesting that RAGE is a major determinant for the polarity of macrophages in DPN. In vitro coculture analyses revealed proinflammatory macrophage-elicited insulin resistance in the primary neuronal cells isolated from dorsal root ganglia. Applying time-lapse recording disclosed a direct impact of proinflammatory macrophage and insulin resistance on the RAT deficits in primary neuronal cultures. These results provide a potentially novel insight into the development of RAGE-related DPN.

Distribution of Large and Small Dorsal Root Ganglion Neurons in Common Marmosets

The aim of this study was to elucidate the size and distribution of dorsal root ganglion (DRG) neurons in non-human primates and to compare them with those of rodent DRG neurons. By measuring the size of NeuN-, NF200-, and peripherin-positive DRG neurons in the lumbar spinal cord of rats and marmosets, we found that the cell size distribution pattern was comparable in both species, although DRG neurons in marmosets were larger than those of rodents. This is the first demonstration that DRG neurons in marmosets have a bimodal size distribution, which has been well established in rodents and humans.

Sensory neuronopathies: A case series and literature review

Sensory neuronopathies are heterogeneous disorders of dorsal root ganglia. The clinical and laboratory features in a single-centre series, including response to treatment and outcome have been described. They retrospectively included 54 patients meeting Camdessanché et al (2009) criteria for sensory neuronopathy. The patients were classified according to their likely aetiology and analysed their demographic, clinical, neurophysiological, histological and spinal MRI features. The outcome with the modified Rankin Scale (mRS) was evaluated, and the response to treatment was assessed. About 54 patients were included (18 male; median age 54.5 years). The most common initial symptoms were hypoaesthesia, paraesthesia, ataxia and pain. Half of patients had a slow onset, greater than 12 months before seeing a neurologist. The aetiology as possibly inflammatory (meaning nonspecific laboratory evidence of immune abnormality) in 18 patients (33%), paraneoplastic 8 (15%), autoimmune 7 (13%) and idiopathic 6 (11%) was classified. About 31 patients received immune therapy of which 11 (35%) improved or stabilised. Corticosteroids were the most used treatment (24 patients) and cyclophosphamide had the highest response rate (3/6, 50%). At the final follow up (median 24 months) 67% had mRS ≥3 and 46% mRS ≥4, including 15% who died. Worse outcome was associated with generalised areflexia and pseudoathetosis by logistic regression, and with motor involvement and raised CSF protein by univariate analysis. Sensory neuronopathies caused severe disability, especially in patients with generalised areflexia and pseudoathetosis. Of those without an obvious cause, most had some evidence of dysimmunity. Some patients had a positive response to immunotherapy, but rarely enough to improve disability much.

HDAC1 Expression, Histone Deacetylation, and Protective Role of Sodium Valproate in the Rat Dorsal Root Ganglia After Sciatic Nerve Transection

Nerve injury is an important reason of human disability and death. We studied the role of histone deacetylation in the response of the dorsal root ganglion (DRG) cells to sciatic nerve transection. Sciatic nerve transection in the rat thigh induced overexpression of histone deacetylase 1 (HDAC1) in the ipsilateral DRG at 1-4 h after axotomy. In the DRG neurons, HDAC1 initially upregulated at 1 h but then redistributed from the nuclei to the cytoplasm at 4 h after axotomy. Histone H3 was deacetylated at 24 h after axotomy. Deacetylation of histone H4, accumulation of amyloid precursor protein, a nerve injury marker, and GAP-43, an axon regeneration marker, were observed in the axotomized DRG on day 7. Neuronal injury occurred on day 7 after axotomy along with apoptosis of DRG cells, which were mostly the satellite glial cells remote from the site of sciatic nerve transection. Administration of sodium valproate significantly reduced apoptosis not only in the injured ipsilateral DRG but also in the contralateral ganglion. It also reduced the deacetylation of histones H3 and H4, prevented axotomy-induced accumulation of amyloid precursor protein, which indicated nerve injury, and overexpressed GAP-43, a nerve regeneration marker, in the axotomized DRG. Therefore, HDAC1 was involved in the axotomy-induced injury of DRG neurons and glial cells. HDAC inhibitor sodium valproate demonstrated the neuroprotective activity in the axotomized DRG.

Age-related molecular changes in the lumbar dorsal root ganglia of mice: Signs of sensitization, and inflammatory response

Aging is a major risk factor for numerous painful, inflammatory, and degenerative diseases including disc degeneration. A better understanding of how the somatosensory nervous system adapts to the changing physiology of the aging body will be of great significance for our expanding aging population. Previously, we reported that chronological aging of mouse lumbar discs is pathological and associated with behavioral changes related to pain. It is established that with age and degeneration the lumbar discs become inflammatory and innervated. Here we analyze the aging lumbar dorsal root ganglia (DRGs) and spinal cord dorsal horn (SCDH) in mice between 3 and 24 months of age for age-related somatosensory adaptations. We observe that as mice age there are signs of peripheral sensitization, and response to inflammation at the molecular and cellular level in the DRGs. From 12 months onwards the mRNA expression of vasodilator and neurotransmitter, Calca (CGRP); stress (and survival) marker, Atf3; and neurotrophic factor, Bdnf, increases linearly with age in the DRGs. Further, while the mRNA expression of neuropeptide, Tac1, precursor of Substance P, did not change at the transcriptional level, TAC1 protein expression increased in 24-month-old DRGs. Additionally, elevated expression of NFκB subunits, Nfkb1 and Rela, but not inflammatory mediators, Tnf, Il6, Il1b, or Cox2, in the DRGs suggest peripheral nerves are responding to inflammation, but do not increase the expression of inflammatory mediators at the transcriptional level. These results identify a progressive, age-related shift in the molecular profile of the mouse somatosensory nervous system and implicates nociceptive sensitization and inflammatory response.

The Expression of E2F1, p53, and Caspase 3 in the Rat Dorsal Root Ganglia After Sciatic Nerve Transection

Neurotrauma is among the main causes of human disability and mortality. Nerve injury impairs not only neurons but also causes death of satellite glial cells remote from the injury site. We studied the dynamics of expression of different proapoptotic proteins (E2F1, p53, caspase 3) in the dorsal root ganglia (DRG) of a rat after sciatic nerve transection. TUNEL staining and immunoblotting were used for analysis of cell apoptosis and axotomy-induced biochemical changes. Apoptosis of glial cells was observed at 24 h after sciatic nerve transection and increased on day 7, when apoptosis of some neurons only started. The earliest proapoptotic event in the injured DRG was overexpression of transcription factor E2F1 at 4 h after sciatic nerve transection. This preceded the induction of p53 and cleavage of caspase 3 at 24-h post-axotomy. The nerve injury marker amyloid precursor protein and the nerve regeneration marker GAP-43 were overexpressed in DRG on day 7 after sciatic nerve transection. We also developed a novel fluorescence method for differential visualization of the rat DRG and nerves by means of double staining with propidium iodide and Hoechst 33342 that impart red and blue-green fluorescence, respectively. The present experiments showed that glial cells remote from the nerve transection site were more vulnerable to axotomy than DRG neurons. E2F1 and p53 may be considered promising molecular targets for development of potential neuroprotective agents.

Repressor element 1-silencing transcription factor drives the development of chronic pain states

Chronic pain is an unmet clinical problem with vast individual, societal, and economic impact. Pathologic activity of the peripheral somatosensory afferents is one of the major drivers of chronic pain. This overexcitable state of somatosensory neurons is, in part, produced by the dysregulation of genes controlling neuronal excitability. Despite intense research, a unifying theory behind neuropathic remodelling is lacking. Here, we show that transcriptional suppressor, repressor element 1-silencing transcription factor (REST; neuron-restrictive silencing factor, NRSF), is necessary and sufficient for the development of hyperalgesic state after chronic nerve injury or inflammation. Viral overexpression of REST in mouse dorsal root ganglion (DRG) induced prominent mechanical and thermal hyperalgesia in vivo. Sensory neuron-specific, inducible Rest knockout prevented the development of such hyperalgesic state in 3 different chronic pain models. Genetic deletion of Rest reverted injury-induced hyperalgesia. Moreover, viral overexpression of REST in the same neurons in which its gene has been genetically deleted restored neuropathic hyperalgesia. Finally, sensory neuron specific Rest knockout prevented injury-induced downregulation of REST target genes in DRG neurons. This work identified REST as a major regulator of peripheral somatosensory neuron remodelling leading to chronic pain. The findings might help to develop a novel therapeutic approache to combat chronic pain.

Nociceptor subtypes and their incidence in rat lumbar dorsal root ganglia (DRGs): focussing on C-polymodal nociceptors, Aβ-nociceptors, moderate pressure receptors and their receptive field depths

A recent study with Ca++-sensitive-dyes in neurons in whole DRGs (Table 5) found that much lower percentages of nociceptors were polymodal-nociceptors (PMNs) (Emery et al., 2016), than the 50-80% values in many electrophysiological fiber studies. This conflict highlighted the lack of knowledge about percentages of nociceptor-subtypes in the DRG. This was analysed from intracellularly-recorded neurons in rat lumbar DRGs stimulated from outside the skin. Polymodal nociceptors (PMNs) were 11% of all neurons and 19% of all nociceptors. Most PMNs had C-fibers (CPMNs). Percentages of C-nociceptors that were CPMNs varied with receptive field (RF) depths, whether superficial (∼80%), dermal (25%), deep (0%) or cutaneous (superficial + dermal) (40%). This explains CPMN percentages 40-90%, being highest, in electrophysiological studies using cutaneous nerves, and lowest in studies that also include deep RFs, including ours, and the recent Ca++-imaging studies in whole DRGs. Despite having been originally described in 1967 (Burgess and Perl), both Aβ-nociceptors and Aβ-moderate pressure receptors (MPRs) remain overlooked. Most A-fiber nociceptors in rodents have Aβ-fibers. Of rat lumbar Aβ-nociceptors with superficial RFs, 50% were MPRs with variable medium-low trkA-expression. Despite having conduction velocities at the two extremes for nociceptors, both CPMNs and MPRs have relatively low thresholds, superficial/epidermal RFs and low trkA-expression. For abbreviations used see Table 5.

Reactive Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Imaging Using an Intrinsically Photoreactive Paternò-Büchi Matrix for Double-Bond Localization in Isomeric Phospholipids

The location and identity of phospholipids (PLs) within tissues can serve as diagnostic markers for tissue types or diseases. Whereas mass spectrometry imaging (MSI) has emerged as a powerful bioanalytical tool to visualize PL distributions, inferring PL identities from MSI experiments is challenging. Especially, C═C double-bond (DB) positions are not identifiable in most MSI experiments. Herein, we introduce benzophenone (BPh) as a novel reactive matrix for matrix-assisted laser desorption/ionization (MALDI). BPh promotes desorption/ionization and simultaneously serves as derivatization reagent that allows functionalization of unsaturated PLs during the MALDI process via a laser-light driven Paternò-Büchi (PB) reaction without the need for additional equipment. Using BPh, PB product ions of numerous PL classes are readily generated to pinpoint the location of DBs. High lateral resolution MSI results of DB-position isomers are presented, highlighting the capabilities of BPh as a PB-reactive MALDI matrix to potentially unveil the impact of DB-position isomers in PL metabolism.

Development of Intrathecal AAV9 Gene Therapy for Giant Axonal Neuropathy

An NIH-sponsored phase I clinical trial is underway to test a potential treatment for giant axonal neuropathy (GAN) using viral-mediated GAN gene replacement (https://clinicaltrials.gov/ct2/show/NCT02362438). This trial marks the first instance of intrathecal (IT) adeno-associated viral (AAV) gene transfer in humans. GAN is a rare pediatric neurodegenerative disorder caused by autosomal recessive loss-of-function mutations in the GAN gene, which encodes the gigaxonin protein. Gigaxonin is involved in the regulation, turnover, and degradation of intermediate filaments (IFs). The pathologic signature of GAN is giant axonal swellings filled with disorganized accumulations of IFs. Herein, we describe the development and characterization of the AAV vector carrying a normal copy of the human GAN transgene (AAV9/JeT-GAN) currently employed in the clinical trial. Treatment with AAV/JeT-GAN restored the normal configuration of IFs in patient fibroblasts within days in cell culture and by 4 weeks in GAN KO mice. IT delivery of AAV9/JeT-GAN in aged GAN KO mice preserved sciatic nerve ultrastructure, reduced neuronal IF accumulations and attenuated rotarod dysfunction. This strategy conferred sustained wild-type gigaxonin expression across the PNS and CNS for at least 1 year in mice. These results support the clinical evaluation of AAV9/JeT-GAN for potential therapeutic outcomes and treatment for GAN patients.

Dual effects of brain sparing opioid in newborn rats: Analgesia and hyperalgesia

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The peripherally acting opioid loperamide produces sustained antinociception in the newborn rat.

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Loperamide minimally crosses the blood brain barrier in the newborn rat.

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Daily systemic administration of loperamide produces opioid induced hyperalgesia in the newborn rat.

Effective pain management in neonates without the unwanted central nervous system (CNS) side effects remains an unmet need. To circumvent these central effects we tested the peripherally acting (brain sparing) opioid agonist loperamide in neonate rats. Our results show that: 1) loperamide (1 mg/kg, s.c.) does not affect the thermal withdrawal latency in the normal hind paw while producing antinociception in all pups with an inflamed hind paw. 2) A dose of loperamide 5 times higher resulted in only 6.9 ng/mL of loperamide in the cerebrospinal fluid (CSF), confirming that loperamide minimally crosses the blood–brain barrier (BBB). 3) Unexpectedly, sustained administration of loperamide for 5 days resulted in a hyperalgesic behavior, as well as increased excitability (sensitization) of dorsal root ganglia (DRGs) and spinal nociceptive neurons. This indicates that opioid induced hyperalgesia (OIH) can be induced through the peripheral nervous system. Unless prevented, OIH could in itself be a limiting factor in the use of brain sparing opioids in the neonate.

Substance P in Dorsal Root Ganglion Neurons in Young and Adult Rats, after Nociceptive Stimulation during the Neonatal Period

The nervous system is highly plastic during the neonatal period, being sensitive to noxious stimuli, which may cause short- and long-term pain responsivity changes. Understanding plasticity in peripheral pain pathways is crucial, particularly when the nervous system is still under development and remodeling process. Substance P (SP) is widely used as a marker for peripheral neurons with unmyelinated and small myelinated fibers. We investigated the number of SP immunoreactive neurons in the dorsal root ganglion (DRG) of male and female Wistar rats, 15 and 180 days after nociceptive stimulation during the neonatal period. Right and left 5th lumbar (L5) DRG were incubated in rabbit polyclonal anti-substance P primary followed by biotinylated donkey anti-rabbit secondary antibodies. Reaction was revealed with a nickel-diaminobenzidine solution. Labeled neurons were counted and compared between ages, genders and groups. Gender differences were present in both ages, with the number of SP-positive DRG neurons being larger in 15-days-old males on both sides. After 180 days, males showed a larger number of SP-positive neurons than females only on the nociceptive stimulated side. An increased number of SP-positive neurons in the DRG on the stimulated side was present in females, immediately after nociceptive stimulation, but not after 180 days. In conclusion, neonatal noxious stimulation caused a permanent increase in SP-positive DRG neurons in males that was not observed in females, suggesting that differences in pain processing/responsivity between genders could be related to morphological alterations of the nervous system. Anat Rec, 301:849-861, 2018. © 2017 Wiley Periodicals, Inc.

Morphological and functional diversity of first-order somatosensory neurons

First-order somatosensory neurons transduce and convey information about the external or internal environment of the body to the central nervous system. They are pseudo unipolar neurons with cell bodies residing in one of several ganglia located near the central nervous system, with the short branch of the axon connecting to the spinal cord or the brain stem and the long branch extending towards the peripheral organ they innervate. Besides their sensory transducer and conductive role, somatosensory neurons also have trophic functions in the tissue they innervate and participate in local reflexes in the periphery. The cell bodies of these neurons are remarkably diverse in terms of size, molecular constitution, and electrophysiological properties. These parameters have provided criteria for classification that have proved useful to establish and study their functions. In this review, we discuss ways to measure and classify populations of neurons based on their size and action potential firing pattern. We also discuss attempts to relate the different populations to specific sensory modalities.

Local GABAergic signaling within sensory ganglia controls peripheral nociceptive transmission

The integration of somatosensory information is generally assumed to be a function of the central nervous system (CNS). Here we describe fully functional GABAergic communication within rodent peripheral sensory ganglia and show that it can modulate transmission of pain-related signals from the peripheral sensory nerves to the CNS. We found that sensory neurons express major proteins necessary for GABA synthesis and release and that sensory neurons released GABA in response to depolarization. In vivo focal infusion of GABA or GABA reuptake inhibitor to sensory ganglia dramatically reduced acute peripherally induced nociception and alleviated neuropathic and inflammatory pain. In addition, focal application of GABA receptor antagonists to sensory ganglia triggered or exacerbated peripherally induced nociception. We also demonstrated that chemogenetic or optogenetic depolarization of GABAergic dorsal root ganglion neurons in vivo reduced acute and chronic peripherally induced nociception. Mechanistically, GABA depolarized the majority of sensory neuron somata, yet produced a net inhibitory effect on the nociceptive transmission due to the filtering effect at nociceptive fiber T-junctions. Our findings indicate that peripheral somatosensory ganglia represent a hitherto underappreciated site of somatosensory signal integration and offer a potential target for therapeutic intervention.

Degeneration of proprioceptive sensory nerve endings in mice harboring amyotrophic lateral sclerosis-causing mutations

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that primarily targets the motor system. Although much is known about the effects of ALS on motor neurons and glial cells, little is known about its effect on proprioceptive sensory neurons. This study examines proprioceptive sensory neurons in mice harboring mutations associated with ALS, in SOD1(G93A) and TDP43(A315T) transgenic mice. In both transgenic lines, we found fewer proprioceptive sensory neurons containing fluorescently tagged cholera toxin in their soma five days after injecting this retrograde tracer into the tibialis anterior muscle. We asked whether this is due to neuronal loss or selective degeneration of peripheral nerve endings. We found no difference in the total number and size of proprioceptive sensory neuron soma between symptomatic SOD1(G93A) and control mice. However, analysis of proprioceptive nerve endings in muscles revealed early and significant alterations at Ia/II proprioceptive nerve endings in muscle spindles before the symptomatic phase of the disease. Although these changes occur alongside those at α-motor axons in SOD1(G93A) mice, Ia/II sensory nerve endings degenerate in the absence of obvious alterations in α-motor axons in TDP43(A315T) transgenic mice. We next asked whether proprioceptive nerve endings are similarly affected in the spinal cord and found that nerve endings terminating on α-motor neurons are affected during the symptomatic phase and after peripheral nerve endings begin to degenerate. Overall, we show that Ia/II proprioceptive sensory neurons are affected by ALS-causing mutations, with pathological changes starting at their peripheral nerve endings.

Size Distribution Imaging by Non-Uniform Oscillating-Gradient Spin Echo (NOGSE) MRI

Objects making up complex porous systems in Nature usually span a range of sizes. These size distributions play fundamental roles in defining the physicochemical, biophysical and physiological properties of a wide variety of systems - ranging from advanced catalytic materials to Central Nervous System diseases. Accurate and noninvasive measurements of size distributions in opaque, three-dimensional objects, have thus remained long-standing and important challenges. Herein we describe how a recently introduced diffusion-based magnetic resonance methodology, Non-Uniform-Oscillating-Gradient-Spin-Echo (NOGSE), can determine such distributions noninvasively. The method relies on its ability to probe confining lengths with a (length)6 parametric sensitivity, in a constant-time, constant-number-of-gradients fashion; combined, these attributes provide sufficient sensitivity for characterizing the underlying distributions in μm-scaled cellular systems. Theoretical derivations and simulations are presented to verify NOGSE's ability to faithfully reconstruct size distributions through suitable modeling of their distribution parameters. Experiments in yeast cell suspensions - where the ground truth can be determined from ancillary microscopy - corroborate these trends experimentally. Finally, by appending to the NOGSE protocol an imaging acquisition, novel MRI maps of cellular size distributions were collected from a mouse brain. The ensuing micro-architectural contrasts successfully delineated distinctive hallmark anatomical sub-structures, in both white matter and gray matter tissues, in a non-invasive manner. Such findings highlight NOGSE's potential for characterizing aberrations in cellular size distributions upon disease, or during normal processes such as development.

Nerve stretch injury induced pain pattern and changes in sensory ganglia in a clinically relevant model of limb-lengthening in rabbits

We used a model of tibial lengthening in rabbits to study the postoperative pain pattern during limb-lengthening and morphological changes in the dorsal root ganglia (DRG), including alteration of substance P (SP) expression. Four groups of animals (naive; OG: osteotomized only group; SDG/FDG: slow/fast distraction groups, with 1 mm/3 mm lengthening a day, respectively) were used. Signs of increasing postoperative pain were detected until the 10(th) postoperative day in OG/SDG/FDG, then they decreased in OG but remained higher in SDG/FDG until the distraction finished, suggesting that the pain response is based mainly on surgical trauma until the 10(th) day, while the lengthening extended its duration and increased its intensity. The only morphological change observed in the DRGs was the presence of large vacuoles in some large neurons of OG/SDG/FDG. Cell size analysis of the S1 DRGs showed no cell loss in any of the three groups; a significant increase in the number of SP-positive large DRG cells in the OG; and a significant decrease in the number of SP-immunoreactive small DRG neurons in the SDG/FDG. Faster and larger distraction resulted in more severe signs of pain sensation, and further reduced the number of SP-positive small cells, compared to slow distraction.

Control of somatic membrane potential in nociceptive neurons and its implications for peripheral nociceptive transmission

Peripheral sensory ganglia contain somata of afferent fibres conveying somatosensory inputs to the central nervous system. Growing evidence suggests that the somatic/perisomatic region of sensory neurons can influence peripheral sensory transmission. Control of resting membrane potential (E_rest) is an important mechanism regulating excitability, but surprisingly little is known about how E_rest is regulated in sensory neuron somata or how changes in somatic/perisomatic E_rest affect peripheral sensory transmission. We first evaluated the influence of several major ion channels on E_rest in cultured small-diameter, mostly capsaicin-sensitive (presumed nociceptive) dorsal root ganglion (DRG) neurons. The strongest and most prevalent effect on E_rest was achieved by modulating M channels, K2P and 4-aminopiridine-sensitive K_V channels, while hyperpolarization-activated cyclic nucleotide-gated, voltage-gated Na⁺, and T-type Ca²⁺ channels to a lesser extent also contributed to E_rest. Second, we investigated how varying somatic/perisomatic membrane potential, by manipulating ion channels of sensory neurons within the DRG, affected peripheral nociceptive transmission in vivo. Acute focal application of M or K_ATP channel enhancers or a hyperpolarization-activated cyclic nucleotide-gated channel blocker to L5 DRG in vivo significantly alleviated pain induced by hind paw injection of bradykinin. Finally, we show with computational modelling how somatic/perisomatic hyperpolarization, in concert with the low-pass filtering properties of the t-junction within the DRG, can interfere with action potential propagation. Our study deciphers a complement of ion channels that sets the somatic E_rest of nociceptive neurons and provides strong evidence for a robust filtering role of the somatic and perisomatic compartments of peripheral nociceptive neuron.

Peripheral nerve injury modulates neurotrophin signaling in the peripheral and central nervous system

Peripheral nerve injury disrupts the normal functions of sensory and motor neurons by damaging the integrity of axons and Schwann cells. In contrast to the central nervous system, the peripheral nervous system possesses a considerable capacity for regrowth, but regeneration is far from complete and functional recovery rarely returns to pre-injury levels. During development, the peripheral nervous system strongly depends upon trophic stimulation for neuronal differentiation, growth and maturation. The perhaps most important group of trophic substances in this context is the neurotrophins (NGF, BDNF, NT-3 and NT-4/5), which signal in a complex spatial and timely manner via the two structurally unrelated p75(NTR) and tropomyosin receptor kinase (TrkA, Trk-B and Trk-C) receptors. Damage to the adult peripheral nerves induces cellular mechanisms resembling those active during development, resulting in a rapid and robust increase in the synthesis of neurotrophins in neurons and Schwann cells, guiding and supporting regeneration. Furthermore, the injury induces neurotrophin-mediated changes in the dorsal root ganglia and in the spinal cord, which affect the modulation of afferent sensory signaling and eventually may contribute to the development of neuropathic pain. The focus of this review is on the expression patterns of neurotrophins and their receptors in neurons and glial cells of the peripheral nervous system and the spinal cord. Furthermore, injury-induced changes of expression patterns and the functional consequences in relation to axonal growth and remyelination as well as to neuropathic pain development will be reviewed.

Immunohistological demonstration of CaV3.2 T-type voltage-gated calcium channel expression in soma of dorsal root ganglion neurons and peripheral axons of rat and mouse

Previous behavioral studies have revealed that CaV3.2 T-type calcium channels support peripheral nociceptive transmission and electrophysiological studies have established the presence of T-currents in putative nociceptive sensory neurons of dorsal root ganglion (DRG). To date, however, the localization pattern of this key nociceptive channel in the soma and peripheral axons of these cells has not been demonstrated due to lack of isoform-selective anti-CaV3.2 antibodies. In the present study a new polyclonal CaV3.2 antibody is used to localize CaV3.2 expression in rodent DRG neurons using different staining techniques including confocal and electron microscopy (EM). Confocal microscopy of both acutely dissociated cells and short-term cultures demonstrated strong immunofluorescence of anti-CaV3.2 antibody that was largely confined to smaller diameter DRG neurons where it co-localized with established immuno-markers of unmyelinated nociceptors, such as, CGRP, IB4 and peripherin. In contrast, a smaller proportion of these CaV3.2-labeled DRG cells also co-expressed neurofilament 200 (NF200), a marker of myelinated sensory neurons. In the rat sciatic nerve preparation, confocal microscopy demonstrated anti-CaV3.2 immunofluorescence which was co-localized with both peripherin and NF200. Further, EM revealed immuno-gold labeling of CaV3.2 preferentially in association with unmyelinated sensory fibers from mouse sciatic nerve. Finally, we demonstrated the expression of CaV3.2 channels in peripheral nerve endings of mouse hindpaw skin as shown by co-localization with Mrgpd-GFP-positive fibers. The CaV3.2 expression within the soma and peripheral axons of nociceptive sensory neurons further demonstrates the importance of this channel in peripheral pain transmission.

The effects of L-NAME on neuronal NOS and SOD1 expression in the DRG-spinal cord network of axotomised Thy 1.2 eGFP mice

Nitric oxide (NO) plays an important role in pathophysiology of the nervous system. Copper/zinc superoxide dismutase (SOD1) reacts with superoxide, which is also a substrate for NO, to provide antioxidative protection. NO production is greatly altered following nerve injury, therefore we hypothesised that SOD1 and NO may be involved in modulating axotomy responses in dorsal root ganglion (DRG)-spinal network. To investigate this interaction, adult Thy1.2 enhanced membrane-bound green fluorescent protein (eGFP) mice underwent sciatic nerve axotomy and received NG-nitro- <l-arginine methylester (L-NAME) or vehicle 7-9 days later. L4-L6 spinal cord and DRG were harvested for immunohistochemical analyses. Effect of injury was confirmed by axotomy markers; small proline-rich repeat protein 1A (SPRR1A) was restricted to ipsilateral neuropathology, while Thy1.2 eGFP revealed also contralateral crossover effects. L-NAME, but not axotomy, increased neuronal NO synthase (nNOS) and SOD1 immunoreactive neurons, with no colocalisation, in a lamina-dependent manner in the dorsal horn of the spinal cord. Axotomy and/or L-NAME had no effect on total nNOS+ and SOD1+ neurons in DRG. However, L-NAME altered SOD1 expression in subsets of axotomised DRG neurons. These findings provide evidence for differential distribution of SOD1 and its modulation by NO, which may interact to regulate axotomy-induced changes in DRG-spinal network.

Morphological and morphometric study of the opossum's dorsal root ganglia neurons

The ultrastructural characteristics and the morphometric evaluation of the different types of neurons present in the dorsal root ganglia (DRG) of the South American opossum (Didelphis albiventris) were studied. Four adult male animals were used and the neurons from cervical and lumbar DRG were removed and processed for histological and transmission electron microscopy observations. The morphometric data were obtained from serial sections stained by H/E and Masson's trichrome. The number of neurons in cervical and lumbar DRG was 22 300 and 31 000, respectively. About 68% of the cervical neurons and 62.5% of the lumbar neurons presented areas up to 1300 µm(2) and were considered as the small neurons of the DRG. The ultrastructural observations revealed two morphological types of neurons: clear large neurons and dark small neurons. The nuclei of both cell types are spherical and the chromatin is disperse and rarefected. The cytoplasm of the dark small neuron is more electron dense and shows a regular distribution of small mitochondria and many rough reticulum cisterns in the periphery. A small Golgi apparatus was close to the nucleus and many disperse neurofilaments occupy most parts of the cytoplasm. Smooth reticulum cisterns are rare and lipofucsin-like inclusions are present at some points. In the clear large neurons, the organelles are homogenously scattered through the cytoplasm. The neurofilaments are close packed forming bundles and small mitochondria and rough reticulum cisterns are disperse. Lipofucsin-like inclusions are more frequent in these cells.

B-Afferents: A fundamental division of the nervous system mediating homeostasis?

The peripheral nervous system (PNS) has classically been separated into a somatic division composed of both afferent and efferent pathways and an autonomic division containing only efferents. J. N. Langley, who codified this asymmetrical plan at the beginning of the twentieth century, considered different afferents, including visceral ones, as candidates for inclusion in his concept of the “autonomic nervous system” (ANS), but he finally excluded all candidates for lack of any distinguishing histological markers. Langley's classification has been enormously influential in shaping modern ideas about both the structure and the function of the PNS. We survey recent information about the PNS and argue that many of the sensory neurons designated as “visceral” and “somatic” are in fact part of a histologically distinct group of afferents concerned primarily autonomic function. These afferents have traditionally been known as “small dark” neurons or B-neurons. In this target article we outline an association between autonomic and B-neurons based on ontogeny, cell phenotype, and functional relations, grouping them together as part of a common reflex system involved in homeostasis. This more parsimonious classification of the PNS, made possible by the identification of a group of afferents associated primarily with the ANS, avoids a number of confusions produced by the classical orientation. It may also have practical implications for an understanding of nociception, homeostatic reflexes, and the evolution of the nervous system.

Immunohistochemical characterization of TH13-L2 spinal ganglia neurons in sheep (Ovis aries)

Spinal ganglia (SG) neurons are commonly classified according to various specific features. The most widespread classification based on morphological and ultrastructural features subdivides SG neurons into light and small dark neurons. Using immunohistochemical, histochemical and lectin methods, it is possible to further subdivide the small dark neurons into two subpopulations: peptidergic and nonpeptidergic neurons. The majority of studies on SG neurons were carried out on mice and rats; there are few or no studies on large mammals. In this study, some of the widely used neuronal markers, neurofilament 200 kDa (NF200), substance P (SP), calcitonin gene-related peptide (CGRP) and isolectin B4 (IB4), were employed to characterize neuronal nitric oxide synthase (nNOS)-immunoreactivity (-IR) in sheep (Ovis aries) SG (Th13-L2) neurons. The majority of the SG neurons were IB4-labeled (79 +/- 10%), followed by NF200- (45 +/- 4%), NOS- (44 +/- 10%), SP- (42 +/- 5%) and CGRP-IR (35 +/- 7%) neurons. The triple staining experiments showed that a higher percentage (75 +/- 16%) of NOS-IR neurons bound both IB4 and CGRP, or both IB4 and SP (49 +/- 6%). The IB4 marker showed an unexpected staining pattern; in fact, IB4-labeled neurons largely colocalized with NF200, usually considered a marker of light SG neurons, and with CGRP and SP. For this reason, IB4 cannot be employed in sheep to differentiate between light and dark neurons, or between peptidergic and nonpeptidergic neurons. These results suggest the importance of being cautious when comparing data among different species.

Early postnatal loss of heat sensitivity among cutaneous myelinated nociceptors in Swiss-Webster mice

Cutaneous myelinated nociceptors are known to exhibit considerable heterogeneity in their response to noxious heat. In the present experiments, we studied heat sensitivity among myelinated nociceptors during early postnatal life to determine whether this heterogeneity is correlated with other physiological and anatomical properties. A total of 129 cutaneous myelinated nociceptors were recorded intracellularly and characterized using mechanical and thermal skin stimuli in ex vivo preparations from neonatal Swiss-Webster (SW) mice across postnatal ages P2-P10; physiologically identified cells were iontophoretically labeled with neurobiotin for analyses of dorsal horn terminations from heat-sensitive and heat-insensitive cells. Our results show that heat sensitivity is not strictly correlated with other physiological or anatomical properties, most notably mechanical threshold or laminar termination patterns, of myelinated nociceptors at these ages. Further, we found a marked decline in the number of heat-sensitive myelinated mechanonociceptors (A-mechanoheat nociceptors [AMHs]) during this early postnatal period. Indeed, 68% of myelinated nociceptors were AMHs between P2 and P5, whereas this percentage dropped to 36% between P6 and P10. Multiple independent lines of evidence suggest that this decrease reflects a change in phenotype in a subset of myelinated nociceptors that lose sensitivity to noxious heat in early postnatal life. Interestingly, evidence was also obtained for a significant strain difference since the early transient excess in the number of AMHs in P2-P5 SW neonates was not present in similarly aged neonates from the C57Bl/6 strain. Potential mechanisms underlying these postnatal changes in AMH number are discussed.

Nestin expression in glial and neuronal progenitors of the developing human spinal ganglia

Expression of the neural crest marker nestin was studied in glial and neuronal progenitors of developing human spinal ganglia using immunohistochemistry in 10 conceptuses, 5-10 weeks old. Quantification was performed by counting the ratio of positive cells in the total cell number, expressed as mean + or - SD and by the Mann-Whitney test. Strong expression of nestin in the 5th-6th developmental week (56%) decreased to 49% in the foetal period. During the same period, number of PGP9.5-positive cells increased from 38% to 42%. At earliest stages, the number of cells expressing GFAP was two folds higher (21%) than S100 (11%). During further development, their number nearly levelled (23% and 28%, respectively), and finally reached level of 25% for GFAP and 40% for S100. While expression of nestin was constantly higher in the dorsal parts of spinal ganglia, number of PGP9.5-, GFAP- and S100-positive cells was higher in their ventral parts, thus indicating ventral to dorsal direction of spinal ganglia differentiation. Co-localization of nestin and GFAP or nestin and S100 was observed during the whole investigate period, while PGP9.5 did not co-localize with nestin. Some ganglion cells simultaneously co-expressing GFAP and S100 might be satellite cells and immature Schwann cells. We suggest that some nestin-positive cells might be capable to differentiate into neurons during the earliest stages of development. Gangliogenesis seems to be important process during the whole ganglion development. Continuous presence of neural crest cells during development might be important in regenerative processes following damage of the spinal ganglia.

Dynamic expression of the TRPM subgroup of ion channels in developing mouse sensory neurons

Despite the significance of transient receptor potential (TRP) channels in sensory physiology, little is known of the expression and developmental regulation of the TRPM (melastatin) subgroup in sensory neurons. In order to find out if the eight TRPM subgroup members (TRPM1-TRPM8) have a possible role in the sensory nervous system, we characterized the developmental regulation of their expression in mouse dorsal root ganglion (DRG) from embryonic (E) day 12 to adulthood. Transcripts for all channels except for TRPM1 were detected in lumbar and thoracic DRG and in nodose ganglion (NG) with distinguishable expression patterns from E12 until adult. For most channels, the expression increased from E14 to adult with the exception of TRPM5, which displayed transient high levels during embryonic and early postnatal stages. Cellular localization of TRPM8 mRNA was found only in a limited subset of very small diameter neurons distinct in size from other populations. These neurons did not bind isolectin B4 (IB4) and expressed neither the neuropeptide calcitonin gene-related peptide (CGRP) nor neurofilament (NF)200. This suggests that TRPM8(+) thermoreceptive sensory neurons fall into a separate group of very small sized neurons distinct from peptidergic and IB4(+) subtypes of sensory neurons. Our results, showing the expression and dynamic regulation of TRPM channels during development, indicate that many TRPM subfamily members could participate during nervous system development and in the adult by determining distinct physiological properties of sensory neurons.

Proliferation and differentiation of glial and neuronal progenitors in the development of human spinal ganglia

Development and differentiation of the spinal ganglia were investigated in 10 human embryos and foetuses, ranging in age between 5th and 10th developmental weeks. The aim of the study was to estimate the spatial and temporal appearance, percentage and duration of proliferation process among neural crest cells and differentiating glial cells and neurons. The process of proliferation and differentiation of cell lineages from neural crest to neurons or glial cell was analysed using immunohistochemical and immunofluorescence methods in paraffin sections. Quantification of reacting cells was performed by counting the ratio of cells stained or double-stained to specific antibodies in the number of total cell population. Data were expressed as mean+/-SD, while the difference between dorsal and ventral parts of the spinal ganglia were analysed by the Mann-Whitney test. The Ki-67 proliferation marker had the strongest expression in the 5th and 6th developmental weeks (42% of positive cells), showing also significantly higher proliferation rate in the dorsal parts of the spinal ganglia than in the ventral parts (Mann-Whitney, p=0.003). During further development, the number of proliferating cells subsequently decreased to 32% in the foetal period. A majority of the proliferating cells expressed neural crest marker nestin (71.5%) or glial cell marker S100 protein (17%). Neurons (stained with PGP9.5 marker) showed no signs of proliferation. Some cells co-expressed both neural crest cells and glial cell markers. Our results indicate the highest proliferation activity of the progenitor neural crest cells, which slightly decreased with progression of spinal ganglia differentiation. On the contrary, glial cells displayed increasing proliferation activity at later developmental stages, thus conforming significance of gliogenesis during human spinal ganglia development. Although neurogenesis was not found during the investigated period, we could not exclude the possibility of neuronal differentiation from neural crest cells, or even immature glial cells.

Characterization of a thy1.2 GFP transgenic mouse reveals a tissue-specific organization of the spinal dorsal horn

In this study, transgenic mice in which membrane-linked enhanced green fluorescent protein (mGFP) is expressed from the Thy1.2 promoter were used. In these mice, a subpopulation of small to medium sized DRG neurons double stained for IB4 but not for CGRP. Most of the peripheral terminals traversed the dermis and ramify within the epidermis and form superficial terminals. Within the spinal cord, these afferents terminated exclusively within the substantia gelatinosa (SG). A second fibre type in the skin also expressed mGFP, and formed club-shaped endings towards the bases of hairs. Injury to the sciatic nerve resulted in mGFP loss from the SG ipsilateral to the nerve injury, but also in the corresponding region contralaterally. Together, these findings reveal the specificity of connectivity of a defined subpopulation of DRG sensory neurons innervating the epidermis and this will facilitate analysis of their physiological functions.

Developmental patterns of caspase-3, bax and bcl-2 proteins expression in the human spinal ganglia

The distribution of the bcl-2, bax and caspase-3 proteins was investigated in the cells of developing human spinal ganglia. Paraffin sections of 10 human conceptuses between 5th and 9th gestational weeks were analysed morphologically, immunohistochemically and by TUNEL-method. Cells positive to caspase-3 had brown stained nuclei or nuclear fragmentations. At earliest stages, 6% of ganglion population were caspase-3 positive cells. Later on, a significant increase in number of caspase-3 positive cells appeared, particularly in the ventral part of ganglia (12%), and subsequently decreased to 6%. TUNEL-positive cells had the same distribution pattern as caspase-3 positive cells. Bax-positive cells followed the developmental pattern similar to caspase-3 cells, changing in range between 20% and 32%. There were 8% of bcl-2 positive cells at earliest stages. They increased significantly in dorsal part of the ganglion during the 7th week (28%), and than dropped to 15% by the end of the 8th week. These findings suggest a ventro-dorsal course of development in human spinal ganglia. Number of bcl-2, bax and caspase-3 positive cells changed in a temporally and spatially restricted manner, coincidently with ganglion differentiation. While apoptosis might control cell number, bcl-2 could act in suppression of apoptosis and enhancement of cell differentiation.

The giant fibrillar center: a nucleolar structure enriched in upstream binding factor (UBF) that appears in transcriptionally more active sensory ganglia neurons

This paper studies the molecular organization, neuronal distribution and cellular differentiation dynamics of the giant fibrillar centers (GFCs) of nucleoli in rat sensory ganglia neurons. The GFC appeared as a round nucleolar domain (1-2 microm in diameter) partially surrounded by the dense fibrillar component and accompanied by numerous small FCs. By immunocytochemistry, the GFC concentrated the upstream binding factor, which may serve as a marker of this structure, and also contain RNA polymerase I, DNA topoisomerase I, SUMO-1 and Ubc9. However, they lack ubiquitin-proteasome conjugates and 20S proteasome. Transcription assay with 5'-fluorouridine incorporation revealed the presence of nascent RNA on the dense fibrillar component of the neuronal nucleolus, but not within the low electron-density area of the GFC. The formation of GFCs is neuronal size dependent: they were found in 58%, 30% and 0% of the large, medium and small neurons, respectively. GFCs first appeared during the postnatal period, concomitantly with a stage of neuronal growth, myelination and bioelectrical maturation. GFCs were not observed in segregated nucleoli induced by severe inhibition of RNA synthesis. We suggest that the formation of GFCs is associated with a high rate of ribosome biogenesis of the transcriptionally more active large-size neurons.

Hyperglycemia alters enzyme activity and cell number in spinal sensory ganglia

Peripheral sensory diabetic neuropathy is characterized by morphological, electrophysiological and neurochemical changes to a subpopulation of primary afferent neurons. Here, we utilized a transgenic mouse model of diabetes (OVE26) and age-matched controls to histologically examine the effect of chronic hyperglycemia on the activity or abundance of the enzymes acid phosphatase, cytochrome oxidase and NADPH-diaphorase in primary sensory neuron perikarya and the dorsal horn of the spinal cord. Quantitative densitometric characterization of enzyme reaction product revealed significant differences between diabetic, compared to control, animals for all three enzymes. Levels of acid phosphatase reaction product were found to be significantly reduced in both small diameter primary sensory somata and the dorsal horn. Cytochrome oxidase activity was found to be significantly lower in small primary sensory somata while NADPH-diaphorase labeling was found to be significantly higher in small primary sensory somata and significantly lower in the dorsal horn. In addition to these observed biochemical changes, ratiometric analysis of the number of small versus large diameter primary sensory perikarya in diabetic and control animals demonstrated a quantifiable decrease in the number of small diameter cells in the spinal ganglia of diabetic mice. These results suggest that the OVE26 model of diabetes mellitus produces an identifiable disturbance in specific metabolic pathways of select cells in the sensory nervous system and that this dysfunction may reflect the progression of a demonstrated cell loss.

Sympathetic sprouting near sensory neurons after nerve injury occurs preferentially on spontaneously active cells and is reduced by early nerve block

Some chronic pain conditions are maintained or enhanced by sympathetic activity. In animal models of pathological pain, abnormal sprouting of sympathetic fibers around large- and medium-sized sensory neurons is observed in dorsal root ganglia (DRGs). Large- and medium-sized cells are also more likely to be spontaneously active, suggesting that sprouting may be related to neuron activity. We previously showed that sprouting could be reduced by systemic or locally applied lidocaine. In the complete sciatic nerve transection model in rats, spontaneous activity initially originates in the injury site; later, the DRGs become the major source of spontaneous activity. In this study, spontaneous activity reaching the DRG soma was reduced by early nerve blockade (local perfusion of the transected nerve with TTX for the 1st 7 days after injury). This significantly reduced sympathetic sprouting. Conversely, increasing spontaneous activity by local nerve perfusion with K(+) channel blockers increased sprouting. The hyperexcitability and spontaneous activity of DRG neurons observed in this model were also significantly reduced by early nerve blockade. These effects of early nerve blockade on sprouting, excitability, and spontaneous activity were all observed 4-5 wk after the end of early nerve blockade, indicating that the early period of spontaneous activity in the injured nerve is critical for establishing the more long-lasting pathologies observed in the DRG. Individual spontaneously active neurons, labeled with fluorescent dye, were five to six times more likely than quiescent cells to be co-localized with sympathetic fibers, suggesting a highly localized correlation of activity and sprouting.

Time course of substance P expression in dorsal root ganglia following complete spinal nerve transection

Recent evidence suggests that substance P (SP) is up-regulated in primary sensory neurons following axotomy and that this change occurs in larger neurons that do not usually produce SP. If this is so, then the up-regulation may allow normally neighboring, uninjured, and nonnociceptive dorsal root ganglion (DRG) neurons to become effective in activating pain pathways. By using immunohistochemistry, we performed a unilateral L5 spinal nerve transection on male Wistar rats and measured SP expression in ipsilateral L4 and L5 DRGs and contralateral L5 DRGs at 1-14 days postoperatively (dpo) and in control and sham-operated rats. In normal and sham-operated DRGs, SP was detectable almost exclusively in small neurons (< or =800 microm2). After surgery, the mean size of SP-positive neurons from the axotomized L5 ganglia was greater at 2, 4, 7, and 14 dpo. Among large neurons (>800 microm2) from the axotomized L5, the percentage of SP-positive neurons increased at 2, 4, 7, and 14 dpo. Among small neurons from the axotomized L5, the percentage of SP-positive neurons was increased at 1 and 3 dpo but was decreased at 7 and 14 dpo. Thus, SP expression is affected by axonal damage, and the time course of the expression is different between large and small DRG neurons. These data support a role for SP-producing, large DRG neurons in persistent sensory changes resulting from nerve injury.

Immunohistochemical, Histochemical and Radioassay Analysis of Nitric Oxide Synthase Immunoreactivity in the Lumbar and Sacral Dorsal Root Ganglia of the Dog

In this study, immunohistochemistry for neuronal nitric oxide synthase (bNOS-IR), nicotinamide adenine dinucleotide phosphate diaphorase histochemistry (NADPHd) and nitric oxide synthase radioassay were used to study the occurrence, number and distribution pattern of nitric oxide synthesizing neurons in the lumbar (L1-L7) and sacral (S1-S3) dorsal root ganglia of the dog. Nitric oxide synthase immunolabelling was present in a large number of small- (area <1,000 microm(2)) and medium-sized (area 1,000-2,000 microm(2)) as well as in a limited number of large-sized (area >2000 microm(2)) neurons. Although neuronal nitric oxide synthase immunolabelling and histochemical staining provided intense staining of multiple small- and medium-sized neurons in all lumbar and sacral dorsal root ganglia, immuno-labelled or histochemically stained somata exhibited little topographic distribution in individual dorsal root ganglia. Great heterogeneity was noticed in the immunolabelling of medium-sized nitric oxide synthase immunopositive neurons ranging from lightly immuno-labelled somata to heavily immunoreactive ones with completely obscured nuclei. Both staining procedures proved to be highly effective in visualizing intraganglionic fibers of various diameters. In general, the largest fibers revealed at the peripheral end of lumbar and sacral dorsal root ganglia were larger, 6.49-9.35 mum in diameter, while those running centrally and proceeding into the dorsal roots were about 30% reduced, ranging between 5.32 and 8.67 microm in diameter. Peripherally, the occurrence of nitric oxide synthase detected in axonal profiles, and confirmed histochemically, in the specimens of the femoral and sciatic nerves, is the first indication of the presence of nitric oxide synthase in the peripheral processes of somata located in L4-S2 dorsal root ganglia. Large and thin central nitric oxide synthase immunoreactive processes of L1-S3 dorsal root ganglion neurons segregate shortly before entering the spinal cord, the former making a massive medial bundle in the dorsal root accompanied by a slim lateral bundle penetrating Lissauer's tract. Quantitative assessment of the distribution of bNOS-IR and/or NADPHd-stained neurons showed a peculiar pattern in relation to spinal levels. Apparent incongruity was found in the total number of NADPHd-stained versus bNOS-IR neurons, demonstrating a clear prevalence of small bNOS-IR somata in all lumbar ganglia, while medium-sized NADPHd-stained somata clearly prevailed all along the rostrocaudal axis with a peak in L5 ganglion. While the number of small bNOS-IR neurons clearly outnumbered NADPHd-stained and NADPHd-unstained somata in S1-S3 ganglia, an inverse relation appeared comparing the total number of medium-sized NADPHd-stained and NADPHd-unstained somata compared with the number of moderate and intense bNOS-IR neurons. Densitometry of bNOS-IR and NADPHd-stained neurons in lumbar and sacral ganglia revealed two distinct subsets of densitometric profiles, one relating to more often found medium-sized bNOS immuno-labelled and the other, characteristic for moderately bNOS immunoreactive somata of the same cell size. Considerable differences in catalytic nitric oxide synthase activity, determined by conversion of [(3)H]arginine to [(3)H]citrulline were obtained in lumbosacral dorsal root ganglia all along the lumbosacral intumescence, the lowest (0.898+/- 0.2 dpm/min/microg protein) being in the L4 dorsal root ganglion and the highest (4.194+/-0.2 dpm/min/microg protein) in the S2 dorsal root ganglion.

P2X receptors in the rat uterine cervix, lumbosacral dorsal root ganglia, and spinal cord during pregnancy

ATP, an intracellular energy source, is released from cells during tissue stress, damage, or inflammation. The P2X subtype of the ATP receptor is expressed in rat dorsal root ganglion (DRG) cells, spinal cord dorsal horn, and axons in peripheral tissues. ATP binding to P2X receptors on nociceptors generates signals that can be interpreted as pain from damaged tissue. We have hypothesized that tissue stress or damage in the uterine cervix during late pregnancy and parturition can lead to ATP release and sensory signaling via P2X receptors. Consequently, we have examined sensory pathways from the cervix in nonpregnant and pregnant rats for the presence of purinoceptors. Antiserum against the P2X3-receptor subtype showed P2X3- receptor immunoreactivity in axon-like structures of the cervix, in small and medium-sized neurons in the L6/S1 DRG, and in lamina II of the L6/S1 spinal cord segments. Retrograde tracing confirmed the projections of axons of P2X3-receptor-immunoreactive DRG neurons to the cervix. Some P2X3-receptor-positive DRG neurons also expressed estrogen receptor-alpha immunoreactivity and expressed the phosphorylated form of cyclic AMP response-element-binding protein at parturition. Western blots showed a trend toward increases of P2X3-receptor protein between pregnancy (day 10) and parturition (day 22-23) in the cervix, but no significant changes in the DRG or spinal cord. Since serum estrogen rises over pregnancy, estrogen may influence purinoceptors in these DRG neurons. We suggest that receptors responsive to ATP are expressed in uterine cervical afferent nerves that transmit sensory information to the spinal cord at parturition.

Fate of transient catecholaminergic cell types revealed by site-specific recombination in transgenic mice

Catecholamine-producing cell types are generated from specified neuronal lineages during vertebrate development. The catecholaminergic phenotype is also expressed transiently in some cell types in non-catecholaminergic tissues, including the sensory ganglia, enteric ganglia, and ventral portions of the neural tube during embryonic development. The fate of the transient catecholaminergic cell types at later developmental stages, however, has not been elucidated. We developed a Cre-loxP-mediated recombination system under the control of the dopamine beta-hydroxylase (DBH) promoter, which drives gene expression in typical noradrenergic and adrenergic cell groups as well as in transient catecholaminergic cell types. Expression of Cre recombinase in transgenic mice resulted in an efficient recombination in noradrenergic and adrenergic cell groups at the adult stage. The recombination was also induced in the cranial nerve/spinal cord motor neurons and sensory/enteric ganglion neurons. Analysis of recombination patterns in transgenic mouse embryos showed the occurrence of recombination during prenatal development in both cell types exhibiting the typical and transient catecholaminergic phenotypes. Because the DBH gene promoter is expressed transiently in the ventral neural tube and sensory ganglion during embryonic development, our results provide evidence that the cell types showing a transient catecholaminergic phenotype in these tissues are destined to become mature motor neurons or sensory ganglion neurons during subsequent differentiation.

Target-determined expression of ?3 isoform of the Na+,K+-ATPase in the somatic nervous system of rat

Factors that determine the differential expression of isoforms of Na(+),K(+)-ATPase in the nervous system of vertebrates are not understood. To address this question we studied the expression of alpha(3) Na(+),K(+)-ATPase in the L5 dorsal root ganglia (DRG) of developing rat, the normal adult rat, and the adult rat after peripheral axotomy. During development, the first alpha(3) Na(+),K(+)-ATPase-positive DRG neurons appear by embryonic day 21. At birth, the L5 DRG have a full complement (14 +/- 2%) of these neurons. By 15 days after sciatic nerve transection in adult rat, the number of alpha(3) Na(+),K(+)-ATPase-positive DRG neurons and small myelinated L5 ventral root axons decreases to about 35% of control counts. These results combined with data from the literature suggest that the expression of alpha(3) Na(+),K(+)-ATPase by rat somatic neurons is determined by target-muscle spindle-derived factors.