Neuropeptide Y inhibits axonal transport of particles in neurites of cultured adult mouse dorsal root ganglion cells

Neuropeptide Y (NPY) plays a modulatory role in processing nociceptive information. The present study investigated the effects of NPY on axonal transport of particles in neurites of cultured adult dorsal root ganglion (DRG) cells using video-enhanced microscopy. Application of NPY decreased the number of particles transported in both the anterograde and retrograde directions. This effect was persistently observed during NPY application and was reversed after washout. The inhibitory effect of NPY was concentration dependent between 10(-9) M and 10(-6) M. The instantaneous velocity of individual particles moving in anterograde and retrograde directions was also reduced by NPY. Both the NPY Y1 receptor agonist [Leu31,Pro34]-NPY and NPY Y2 receptor agonist NPY(13-36) mimicked the effect of NPY on the number of transported particles. An immunocytochemical study using an antiserum against the NPY Y1 receptor protein revealed that the Y1 receptor was expressed in the majority (85.9 %) of cultured adult mouse DRG cells. Pre-treatment of cells with pertussis toxin, a GTP-binding protein (G protein) inhibitor, completely blocked the inhibitory effect of NPY. Each application of SQ-22536, an adenylate cyclase inhibitor, and H-89, a protein kinase A inhibitor, mimicked and occluded the effect of NPY. In contrast, dibutyryl cAMP (dbcAMP), a membrane permeable cAMP analogue, and forskolin, an activator of adenylate cyclase, produced a transient increase in axonal transport. The application of dbcAMP and forskolin in combination with NPY negated the effect of NPY alone. These results suggest that NPY, acting at Y1 and Y2 receptors, inhibits axonal transport of particles in sensory neurones. The effect seems to be mediated by a pertussis toxin-sensitive G protein, adenylate cyclase, and protein kinase A pathway. Therefore, NPY may be a modulatory factor for axonal transport in sensory neurones.

GABAergic modulation of primary gustatory afferent synaptic efficacy

Modulation of synaptic transmission at the primary sensory afferent synapse is well documented for the somatosensory and olfactory systems. The present study was undertaken to test whether GABA impacts on transmission of gustatory information at the primary afferent synapse. In goldfish, the vagal gustatory input terminates in a laminated structure, the vagal lobes, whose sensory layers are homologous to the mammalian nucleus of the solitary tract. We relied on immunoreactivity for the GABA-transporter, GAT-1, to determine the distribution of GABAergic synapses in the vagal lobe. Immunocytochemistry showed dense, punctate GAT-1 immunoreactivity coincident with the layers of termination of primary afferent fibers. The laminar nature and polarized dendritic structure of the vagal lobe make it amenable to an in vitro slice preparation to study early synaptic events in the transmission of gustatory input. Electrical stimulation of the gustatory nerves in vitro produces synaptic field potentials (fEPSPs) predominantly mediated by ionotropic glutamate receptors. Bath application of either the GABA(A) receptor agonist muscimol or the GABA(B) receptor agonist baclofen caused a nearly complete suppression of the primary fEPSP. Coapplication of the appropriate GABA(A) or GABA(B) receptor antagonist bicuculline or CGP-55845 significantly reversed the effects of the agonists. These data indicate that GABAergic terminals situated in proximity to primary gustatory afferent terminals can modulate primary afferent input via both GABA(A) and GABA(B) receptors. The mechanism of action of GABA(B) receptors suggests a presynaptic locus of action for that receptor.

Activin and bone morphogenetic proteins are present in perinatal sensory neuron target tissues that induce neuropeptides

Previous studies have shown that sensory target tissues induce neuropeptides in naïve sensory neurons, and that activin and bone morphogenetic proteins (BMPs) are capable of inducing neuropeptides associated with nociception in embryonic sensory neurons in vitro. The goal of the present study was to learn if these ligands were available in native sensory neuron target tissues at correct developmental periods to play this inductive role in vivo. Sensory neurons initially contact their peripheral target tissues and begin to express neuropeptides during late embryogenesis, and we demonstrate that activin and BMPs are present in the embryo and neonate to regulate sensory neuron differentiation. Native embryonic and neonatal target tissues were analyzed by immunoblot and immunohistochemical studies using ligand-specific antibodies. Although activin was easily solubilized, BMPs were detected only after high salt extraction, suggesting that BMPs were bound to extracellular moieties and were capable of acting only locally in native tissues. One inhibitor, noggin, was present in both embryonic skin and muscle. In combination, these data suggest that neuronal differentiation is unlikely to be regulated by simple expression of ligand, but that the functional availability of ligand is a critical component confering biological activity.

GABAergic pretectal terminals contact GABAergic interneurons in the cat dorsal lateral geniculate nucleus

Anterograde tracing techniques combined with postembedding immunocytochemical staining were used to determine the gamma amino butyric acid (GABA) content of pretectogeniculate (PT-LGN) terminals and their postsynaptic targets. The results provide evidence that PT-LGN terminals are GABAergic and that they contact GABAergic interneurons. These results corroborate previous anatomical studies and support the idea that the PT-LGN projection functions to disinhibit thalamocortical cells in the dorsal lateral geniculate nucleus.

Neuropeptide Y inhibits the hyperexcitability of type A neurons in chronically compressed dorsal root ganglion of the rat

Our recent data revealed adrenergic sensitivity in chronically compressed dorsal root ganglion (DRG) of rats. As neuropeptide Y (NPY) is a common sympathetic co-transmitter, we investigated the effect of NPY on injured DRG neurons. The expression of NPY Y1 and Y2 receptors and the effect of NPY on chronically compressed DRG neurons were studied using in situ hybridization and extracellular single fiber recording in vitro, respectively. After DRG compression, the expression of Y1 receptor was distinctly increased in large and medium-sized DRG neurons, while Y2 receptor was increased in small DRG neurons. NPY inhibited both the spontaneous activity and the excitatory effect of norepinephrine in injured DRG A-neurons. The results suggest a possibility that NPY may inhibit the hyperexcitability of injured DRG A-neurons via increased Y1 receptor following chronic compression.

Expression of tachykinins in nonnociceptive vagal afferent neurons during respiratory viral infection in guinea pigs

Immunohistochemistry was combined with retrograde labeling to characterize the effect of respiratory infection with Sendai virus on the number of Substance P/Neurokinin A-containing vagal afferent neurons whose cell bodies resided in the nodose ganglia and whose receptive fields were located in guinea pig trachea. Of the neurons labeled from the trachea of vehicle-inoculated guinea pigs, few stained positively for Substance P/Neurokinin A (approximately 3% of total labeled neurons). These neurons had small diameter cell bodies (mode = 16-20 microm), a feature of nociceptive-like C-fibers. Viral infection (Day 4 after inoculation) was associated with a significantly greater number of labeled neurons containing Substance P/Neurokinin A (approximately 20% of total labeled neurons). The majority of these had a relatively large cell body diameter (mode = 36- 40 microm), a feature of nonnociceptive afferent neurons. This induction appeared to be reversible as there were significantly fewer Substance P/Neurokinin A positive neurons in nodose ganglia from virus-inoculated guinea pigs at Day 28 after inoculation, a time point when virus-induced airway inflammation had all but resolved. These findings support the hypothesis that viral infection leads to a qualitative change in the vagal afferent innervation of guinea pig airways such that both small diameter nociceptive-like neurons and large diameter nonnociceptive neurons express tachykinins.

Allergic inflammation-induced neuropeptide production in rapidly adapting afferent nerves in guinea pig airways

In the vagal-sensory system, neuropeptides such as substance P and calcitonin gene-related peptide (CGRP) are synthesized nearly exclusively in small-diameter nociceptive type C-fiber neurons. By definition, these neurons are designed to respond to noxious or tissue-damaging stimuli. A common feature of visceral inflammation is the elevation in production of sensory neuropeptides. Little is known, however, about the physiological characteristics of vagal sensory neurons induced by inflammation to produce substance P. In the present study, we show that allergic inflammation of guinea pig airways leads to the induction of substance P and CGRP production in large-diameter vagal sensory neurons. Electrophysiological and anatomical evidence reveals that the peripheral terminals of these neurons are low-threshold Adelta mechanosensors that are insensitive to nociceptive stimuli such as capsaicin and bradykinin. Thus inflammation causes a qualitative change in chemical coding of vagal primary afferent neurons. The results support the hypothesis that during an inflammatory reaction, sensory neuropeptide release from primary afferent nerve endings in the periphery and central nervous system does not require noxious or nociceptive stimuli but may also occur simply as a result of stimulation of low-threshold mechanosensors. This may contribute to the heightened reflex physiology and pain that often accompany inflammatory diseases.

Temporal regulation of neuropilin-1 expression and sensitivity to semaphorin 3A in NGF- and NT3-responsive chick sensory neurons

The extracellular molecule semaphorin 3A (Sema3A) is proposed to be a negative guidance cue that participates in patterning DRG sensory axons in the developing chick spinal cord. During development Sema3A is first expressed throughout the spinal cord gray matter, but Sema3A expression later disappears from the dorsal horn, where small-caliber cutaneous afferents terminate. Sema3A expression remains in the ventral horn, where large-muscle proprioceptive afferents terminate. It has been proposed that temporal changes in the sensitivity of different classes of sensory afferents to Sema3A contribute to the different pathfinding of these sensory afferents. This study compared the expression of the semaphorin 3A receptor subunit, neuropilin-1, and the collapse response of growth cones to semaphorin 3A for NGF (cutaneous)- and NT3 (proprioceptive)-dependent sensory axons extended from E6-E10 chick embryos. Growth cones extended from E6 DRGs in NT3-containing medium expressed neuropilin-1 and collapsed in response to Sema3A. From E7 until E10 NT3-responsive growth cones expressed progressively lower levels of neuropilin-1, and were less sensitive to Sema3A. On the other hand, growth cones extended from DRGs in NGF-containing medium expressed progressively higher levels of neuropilin-1 and higher levels of collapse response to Sema3A over the period from E6-E10. Thus, developmental patterning of sensory terminals in the chick spinal cord may arise from changes in both Sema3A expression in the developing spinal cord and accompanying changes in neuronal expression of the Sema3A receptor subunit, neuropilin-1.

Comparing the efficacy of two fluorescent retrograde tracers in labeling the motor and sensory neuron populations of the rat sciatic nerve

We compared the efficacy with which the fluorescent tracers Fast Blue (FB) and Diamidino Yellow (DY) retrogradely label neutrons. Trace crystals were applied to the sciatic nerve exclusively (single label) or serially (double label). Unbiased cell counts showed that FB and DY label similar numbers of motoneurons (P=1.00, df 5) or DRG neurons (P=0.95, df 5) when applied exclusively. Plotting of motoneurons revealed a similar pattern of distribution of FB and DY labeled neurons. When the tracers were applied serially, 79% of labeled motoneurons and 77% of labeled DRG neurons were double-labeled irrespective of which tracer was applied first. Equal proportions of the remaining labeled neurons were single-labeled with FB or DY. These data show that FB and DY label equal numbers of motor and sensory neurons of the sciatic nerve following exclusive or serial application of tracers. These findings support the use of FB and DY together in serial fluorescent labeling experiments.

The expression of bradykinin B(1) receptors on primary sensory neurones that give rise to small caliber sciatic nerve fibres in rats

The bradykinin B(1) receptor has been considered as an important mediator for inflammatory pain. In the present study, we have investigated the fibre types of sciatic nerve primary sensory neurones that express B(1) receptors by retrograde tracing in combination with immunohistochemical staining, or double-immunohistochemical staining. Approximately 12% of the A-fibre dorsal root ganglion neurones, retrogradely labelled from an intra-sciatic nerve injection of fluorescein isothiocyanate-conjugated cholera toxin B subunit, were B(1) receptor-immunoreactive. Over 70% of the small diameter dorsal root ganglion neurones, retrogradely labelled from an intra-sciatic nerve injection of tetramethylrhodamine isothiocyanate-conjugated wheat germ agglutinin, were B(1) receptor-immunoreactive. Over 50% of the (predominantly non-peptidergic) C-fibre dorsal root ganglion neurones, retrogradely labelled from an intra-sciatic nerve injection of fluorescein isothiocyanate-conjugated Bandeiraea simplicifolia isolectin B4, were B(1) receptor-immunoreactive. When calcitonin gene-related peptide, which is contained mainly in small caliber C- and A(delta)-fibre primary afferents, and B(1) receptors were stained with a double-immunofluorescent method, over 80% of the calcitonin gene-related peptide-positive dorsal root ganglion neurones were B(1) receptor-immunoreactive. From these results we suggest that B(1) receptors are predominantly expressed by small diameter primary afferent neurones that give rise to sciatic nerve fibres, which include both peptidergic and non-peptidergic C-fibres and A(delta)-fibres. Since peripheral nociceptive information is primarily transmitted by C- and A(delta)-fibres, B(1) receptors may be involved in the modulation of nociceptive transduction or transmission.

Noxious somatic inputs to hypothalamic-midbrain projection neurones: a comparison of the columnar organisation of somatic and visceral inputs to the periaqueductal grey in the rat

The induction of Fos protein was used to localise hypothalamic neurones activated by noxious somatic stimulation. This was combined with retrograde transport of fluorescent latex microspheres from identified 'pressor' and 'depressor' sites in the dorsolateral/lateral or ventrolateral columns of the periaqueductal grey (PAG). Fos-positive neurones were found throughout the rostral hypothalamus. Of those neurones activated by noxious somatic stimuli that projected to the PAG all but one was retrogradely labelled from sites that included the lateral column. Only one neurone was double labelled following injection of tracer at a depressor site in the ventrolateral PAG. This is in marked contrast to visceroresponsive hypothalamic neurones, a larger proportion of which project to the PAG and which, as reported previously, preferentially target depressor sites in the ventrolateral sector. These results are discussed in relation to the roles of the anterior hypothalamus and the different functional columns of the PAG in co-ordinating autonomic and sensory functions in response to nociceptive inputs originating in different peripheral domains.

Expression of a kinase anchoring protein 79 and synaptophysin in the developing human red nucleus

Our previous study showed that in the human fetal and neonatal brain, the magnocellular and parvocellular parts of the red nucleus can be well delineated by calcium-binding proteins. To study the development of rubral afferents, the expression of A kinase anchoring protein 79 (AKAP79) and synaptophysin (SYN) was examined in the human fetal red nucleus. It was found that during prenatal development both AKAP79 and SYN expression increased gradually although a major alteration in the distribution of the proteins within the two compartments of the red nucleus was not observed. In AKAP79 immunopreparations, the magnocellular part became well demarcated from 23 weeks of gestation onwards and both parts showed punctate immunolabelling with moderate to high packing densities of immunoreactive cells. SYN immunoreactivity with a punctate appearance was, however, mainly located in the parvocellular part. It was evenly distributed throughout the compartment at 14-22 weeks of gestation, and then from 23 weeks to the time of birth, there was a pericellular arrangement of SYN. Our observations are mainly in line with connectivity data regarding the red nucleus.

Expression and localization of insulin receptor in rat dorsal root ganglion and spinal cord

The expression and localization of the insulin receptor (IR) was examined in rat dorsal root ganglia (DRG) and spinal cord using Western blotting, in situ hybridization and immunocytochemistry. Western blotting showed that the molecular weight of the IR beta subunit was higher in PNS than that found in CNS. Both IR mRNA and protein expressions were highest in small-sized sensory DRG neurons and myelinated sensory root fibers expressed higher levels of IR protein than myelinated anterior root fibers. In the spinal cord, IR immunoreactive neurons were present in lateral lamina V and in lamina X, suggesting the presence of IR in nociceptive pathways. Electronmicroscopy of DRGs revealed a polarized localization of the IR in abaxonal Schwann cell membranes, outer mesaxons in close vicinity to tight junctions of both myelinating and non-myelinating Schwann cells and to plasma membranes of sensory neurons. From these findings, we speculate that insulin may play a role in sensory fibers involved in nociceptive function often perturbed in diabetic neuropathy. The high expression of IR localizing to tight junctions of dorsal root mesaxons of DRGs may suggest a regulatory role on barrier functions compensating for the lack of a blood-nerve barrier in dorsal root ganglia. This is consistent with the colocalization of IR with tight junctions of the paranodal barrier and endoneurial endothelial cells in peripheral nerve.

Differential distribution of afferents containing serotonin and neuropeptide Y within the marmoset suprachiasmatic nucleus

Neuropeptide Y-containing fibers/terminals were immunohistochemically detected in the ventral portion of the marmoset suprachiasmatic nucleus, approximately matching the distribution of its retinal afferents. On the other hand, serotonergic fibers/terminals were found mostly in central and dorsal areas of the suprachiasmatic nucleus, almost completely sparing its ventral portion. These data may represent a morphological substrate for differential actions of serotonin and neuropeptide Y in the control of circadian rhythmicity in marmosets.

SSeCKS immunolabeling in rat primary sensory neurons

SSeCKS (src suppressed C kinase substrate) is a protein kinase C substrate that may play a role in tumor suppression. Recently described in fibroblasts, testes and mesangial cells, SSeCKS may have a function in the control of cell signaling and cytoskeletal arrangement. To investigate the distribution of SSeCKS throughout the nervous system, representative sections of brain, spinal cord and dorsal root ganglia were processed using immunofluorescence. Labeling of central axonal collaterals of primary sensory neurons was observed in the dorsal horn at all spinal levels. SSeCKS-immunoreactivity was also observed in the cerebellum, medulla and sensory ganglia (including trigeminal ganglia). The pattern and distribution of anti-SSeCKS labeling in dorsal root ganglia and the dorsal horn of the spinal cord was similar to that observed for other markers of small primary sensory neurons. Therefore, the coexistence of SSeCKS with substance P, CGRP and acid phosphatase was examined in sections of sensory ganglia, spinal cord and medulla using double immunofluorescent labeling for SSeCKS and substance P/CGRP or sequential SSeCKS immunofluorescence and acid phosphatase/fluoride-resistant acid phosphatase enzyme histochemistry. A small portion of the SSeCKS-labeled cell bodies appeared to represent a subpopulation of substance P (4.8%) and CGRP (4.7%) containing neurons, while 45.0% contained fluoride-resistant acid phosphatase reactivity. These results indicate that SSeCKS has a restricted distribution within the nervous system and that expression of this protein may reflect the specific signaling requirements of a distinct population of nociceptive sensory neurons.

Medullary pathways involved in cardiac sympathoexcitatory reflexes in the cat

Stimulation of cardiac sympathetic afferents evokes excitatory cardiovascular reflexes. However, the exact regions in the brain that integrate these reflexes have not been identified. Expression of c-Fos in the neurons provides a useful marker of the activated neurons. In the present study, we examined the response of c-Fos within the medulla of the cat to chemical stimulation of cardiac sympathetic afferents. After bilateral sinoaortic denervation and cervical vagotomy, we applied bradykinin (BK, 1-10 microg, n=7) six times to the anterior ventricular surface every 20 min. We observed consistent increases in blood pressure and heart rate while the vehicle for BK (0.9% saline, n=6) produced no responses. Ninety minutes after the end of the sixth treatment, transcardial perfusion was performed with 4% paraformaldehyde and the brainstem was harvested for immunohistochemical staining. Compared to the control animals, we noted Fos immunoreactive neurons in the nucleus of the solitary tract, lateral tegmental field, caudal and rostral ventrolateral medulla (VLM), and vestibular nucleus in the BK-treated cats (all P<0.05). Fos immunoreactivity was found in catecholaminergic neurons of the VLM. These findings indicate that the activated neurons in the medulla, especially in the VLM, are involved in integration of cardiac-cardiovascular sympathoexcitatory reflexes.

Nerve fibers in lumbar spine structures and injured spinal roots express the sensory neuron-specific sodium channels SNS/PN3 and NaN/SNS2

STUDY DESIGN

This prospective study examined the innervation of lumbar spine in tissues from patients with lower back pain and spine nerve roots from patients with traumatic brachial plexus injuries.

OBJECTIVES

To demonstrate the presence of nerve fibers in lumbar spine structures and spine nerve roots, and to determine whether they express the sensory neuron-specific sodium channels SNS/PN3 and NaN/SNS2.

SUMMARY OF BACKGROUND DATA

The anatomic and molecular basis of low back pain and sciatica is poorly understood. Previous studies have demonstrated sensory nerves in the facet joint capsule and prolapsed intervertebral disc, but not in the ligamentum flavum. The voltage-gated sodium channels SNS/PN3 and NaN/SNS2 are expressed by sensory neurone that mediate pain, but their presence in the lumbar spine is unknown.

METHODS

Tissue samples of ligamentum flavum (n = 32), facet joint capsule (n = 20), intervertebral disc (n = 15), and spine roots (n = 8) were immunostained with specific antibodies to protein gene product 9.5 (a panneuronal marker), SNS/PN3, and NaN/SNS2.

RESULTS

Protein gene product 9.5 immunoreactive nerve fibers were detected in 72% of the ligamentum flavum specimens and 70% of the facet joint capsule specimens, but in only 20% of the intervertebral disc specimens. The study detected SNS/PN3- and NaN/SNS2-positive fibers, respectively, in 28% and 3% of the ligamentum flavum specimens and 25% and 15% of the facet joint capsule specimens. Numerous SNS/PN3- and NaN/SNS2-positive fibers were found in the acutely injured spine roots, and some were still present in the dorsal roots in the chronic state.

CONCLUSIONS

As the findings showed, SNS/PN3- and NaN/SNS2-immunoreactivity is present in a subset of nerve fibers in lumbar spine structures, including ligamentum flavum, and in injured spine roots. Selective SNS/PN3- and NaN/SNS2-blocking agents may provide new therapy for back pain and sciatica.

Right atrial stretch induces renal nerve inhibition and c-fos expression in parvocellular neurones of the paraventricular nucleus in rats

The paraventricular nucleus of the hypothalamus plays a pivotal role in the regulation of plasma volume. Part of the response to an increase in volume load is an inhibition of renal sympathetic nerve activity. The present experiments were designed to determine which subnuclei of the paraventricular nucleus are involved in this sympatho-inhibitory response. Experiments were performed on anaesthetised rats. Activated neurones were recognised by the expression of the early gene c-fos, identified by immunohistochemical labelling of its protein product Fos. Plasma volume loading with 4 % Ficoll 70, using an infusion-withdrawal procedure (2 ml over 1 min) repeated 15 times over 1 h revealed a total of 775 +/- 101 (n = 6) Fos-positive neurones scattered throughout both the magnocellular and parvocellular subnuclei. In comparison, sustained hypertension resulted in 452 +/- 56 (n = 3) Fos-positive neurones similarly distributed, whereas a normotensive control group (n = 3) displayed 115 +/- 18 Fos-positive neurones. Because of this lack of a specific effect we used a more selective stimulation of right atrial receptors via a balloon placed at the junction of the superior vena cava and the right atrium so it did not impede venous return. Inflation of the balloon inhibited renal sympathetic nerve activity (36 +/- 5 %, n = 7) and repetitive inflation over 1 h resulted in c-fos activation of a small number of neurones (54 +/- 14) located only in the parvocellular subnuclei. Whether these are inhibitory interneurones acting within the paraventricular nucleus, or spinally projecting neurones which inhibit or excite renal sympathetic activity by an action in the spinal cord remains to be determined.

Mast cells differentially express and release active high molecular weight neurotrophins

Nerve growth factor (NGF), a target-derived factor for survival and maintenance of peripheral and central neurons, has been implicated in inflammatory processes. Mast cells are the principal effector cells in IgE-dependent hypersensitivity reactions, and also play a role in diseases characterised by inflammation, including those of the nervous system like multiple sclerosis. Mast cells are capable of synthesising and responding to NGF, although the occurrence of other members of the NGF family of neurotrophins and their protein forms have not been described. Immunoblot analysis with highly selective neurotrophin antibodies has now been used to show that rat peritoneal mast cells express a higher molecular weight form (73 kDa) of NGF, but not the monomeric (13 kDa) NGF polypeptide. Mast cells also expressed 73 kDa forms of neurotrophin-4 and neurotrophin-3; brain-derived neurotrophic factor was not detected. Medium conditioned by degranulating peritoneal mast cells contained similar high molecular weight forms of NGF and neurotrophin-4 on Western blots, but no neurotrophin-3. Mast cell-derived neurotrophin immunoreactivities were inhibited by the respective peptide antigen, further demonstrating the specificity of the mast cell-derived neurotrophic protein. Mast cell-released proteins supported the survival of cultured chicken embryonic neural crest- and placode-derived sensory neurons; neurotrophic activities were inhibited by neutralising antibodies for NGF and neurotrophin-4, respectively. High molecular isoforms of neurotrophins have been reported to occur in experimental colitis and in the inflamed gut of patients with Crohn's disease and ulcerative colitis, tissue sites rich in mast cells. The data suggest an important role for neurotrophins in the pathophysiology of inflammatory disease.

Change in excitability and phenotype of substance P and its receptor in cat Abeta sensory neurons following peripheral inflammation

The effect of peripheral inflammation on spontaneous firing and level of substance P (SP) and its receptor in electrophysiologically identified cat Abeta neurons of dorsal root ganglion (DRG) was studied in vivo using a combination of intracellular recording, dye injection and immunohistochemical techniques. Following injection of carrageenan (Carg) into cat hindpaw, the number of Abeta neurons with spontaneous firing was enhanced significantly (42.9%, n=182) in comparison with control (16.8%, n=149, P<0.01). DRG Abeta neurons became less depolarized 2-4 h following Carg injection. After identifying the cell properties, Lucifer Yellow was injected and SP-like immunoreactivity (SP-LI) was then detected. A total of 17% of Abeta sensory neurons exhibited SP-LI in inflammatory cat. We also found in rat DRGs that the number of SP-LI positive large cells (>35 microm) was also significantly increased in Carg-treated DRG (11.8+/-1.2, n=8) compared with untreated DRG (1.8+/-0.8, n=8, P<0.01). In control cat, the topical use of SP in DRG did not induce any response of Abeta neurons. However, in Carg-treated cat, SP depolarized the membrane potential in most Abeta neurons (68.2%, n=22). L668,169, an antagonist of SP receptor, completely blocked the SP-induced responses. Furthermore, repeated application of SP did not induce obvious desensitization of Abeta neurons. These data suggest that peripheral inflammation increased the excitability, SP level and sensitivity of SP receptor of Abeta neurons. Therefore, we concluded that Abeta sensory neurons appear to contribute to inflammatory allodynia.

Vesicular glutamate transporter 2 in the brain-gut axis

Previous reports have indicated that vesicular glutamate transporters (VGLUTs) are found only in central neurons. We show that neurons in the gut, which also contain glutamate and markers of intrinsic primary afferent neurons, display VGLUT2 immunoreactivity in several species, including humans. Glutamatergic (VGLUT2-immunoreactive) varicosities, which often co-stored choline acetyltransferase and the vesicular acetylcholine transporter, were apposed to a subset of nerve cell bodies in the submucosal and myenteric plexus. Retrograde tracing with FluoroGold demonstrated that VGLUT2 is found in nodose and dorsal root ganglia neurons innervating the stomach. Thus, VGLUT2 is found in intrinsic and extrinsic primary afferent neurons, which suggests that glutamate is as primary afferent neurotransmitter that transfers information from the mucosa to the enteric plexuses and brain.

Small primary sensory neurons innervating epidermis and viscera display differential phenotype in the adult rat

Target tissues contribute to the phenotype and function of sensory neurons. Due to lack of appropriate markers for trkA expressing sensory axons and terminals, the detailed peripheral projection of these neurons is unclear. In this study, the peripheral projections of trkA immunoreactive neurons are characterized using the combined techniques of immunohistochemistry and retrograde tracing. We found approximately 65% of all neurons projecting to the adrenal gland and kidney are trkA immunoreactive, whereas 6, 14 and 37% of neurons innervating whisker follicle, epidermis and footpad, respectively, are immunoreactive for trkA. A low proportion of trkA immunoreactive neurons innervating epidermis indicates that the majority of sensory neurons innervating epidermis are independent of trkA signalling for their normal function. We further investigated whether these epidermal projecting neurons can bind isolectin IB4. We found approximately 70% of all neurons innervating epidermis are IB4 binding neurons, but they did not express trkA. Thus, NGF sensitive neurons primarily project to viscera but not epidermis or other skin structures, whereas IB-4 positive neurons primarily project to epidermis in the adult rat.

GABA(B)R expressed on vagal afferent neurones inhibit gastric mechanosensitivity in ferret proximal stomach

GABA(B)-receptor (GABA(B)R) agonists reduce transient lower esophageal sphincter relaxation (TLESR) and reflux episodes through an action on vagal pathways. In this study, we determined whether GABA(B)R are expressed on vagal afferent neurones and whether they modulate distension-evoked discharge of vagal afferents in the isolated stomach. Vagal mehanoreceptor activity was recorded following distensions of the isolated ferret proximal stomach before and after perfusion with the GABA(B)R-selective agonists baclofen and 3-aminopropylphosphinic acid (3-APPiA). Retrograde labeling and immunohistochemistry were used to identify GABA(B)R located on vagal afferent neurones in the nodose ganglia. Vagal afferent fibers responded to isovolumetric gastric distension with an increase in discharge. The GABA(B)-receptor agonists baclofen (5 x 10(-5) M) and 3-APPiA (10(-6) to 10(-5) M) but not muscimol (GABA(A)-selective agonist: 1.3 x 10(-5) M) significantly decreased afferent distension-response curves. The effect of baclofen (5 x 10(-5) M) was reversed by the GABA(B)-receptor antagonist CGP 62349 (10(-5) M). Over 93% of retrogradely labeled gastric vagal afferents in the nodose ganglia expressed immunoreactivity for the GABA(B)R. GABA(B)R expressed on vagal afferent fibers directly inhibit gastric mechanosensory activity. This is likely a contributing mechanism to the efficacy of GABA(B)-receptor agonists in reducing TLESR and reflux episodes in vivo.

Osteopontin-immunoreactivity in the rat trigeminal ganglion and trigeminal sensory nuclei

Osteopontin-immunoreactivity (OPN-ir) was examined in the oro-facial tissues and trigeminal sensory nuclei (principal sensory nucleus and spinal trigeminal nucleus) to ascertain the peripheral ending and central projection of OPN-containing primary sensory neurons in the trigeminal ganglion (TG). No staining was observed using mouse monoclonal anti-OPN antibody preabsorbed with recombinant mature OPN. OPN-immunoreactive (ir) peripheral endings were classified into two types: encapsulated and unencapsulated types. Unencapsulated endings were subdivided into two types: simple and complex types. Simple endings were characterized by the thin neurite that was usually devoid of ramification. These endings were seen in the hard plate and gingiva. The complex type was characterized by the thick ramified neurite, and observed in the vibrissa, hard palate, and molar periodontal ligament. Encapsulated endings were found only in the hard palate. The trigeminal sensory nuclei contained OPN-ir cell bodies and neuropil. The neuropil was devoid of ir in laminae I and II of the medullary dorsal horn (MDH), and had various staining intensities in other regions of the trigeminal sensory nuclei. Transection of the infraorbital and inferior alveolar nerves caused an increase of OPN-ir intensity in ipsilateral TG neurons. The staining intensity of the neuropil also increased in the trigeminal sensory nuclei ipsilateral to the neurotomy excepting laminae I and II of the MDH. The present study indicates that OPN-ir primary sensory neurons in the TG innervate encapsulated and unencapsulated corpuscular endings. Such neurons probably project their central terminals to the trigeminal sensory nuclei except for the superficial laminae of the MDH.

Axo-axonic GABA-immunopositive synapses on the primary afferent fibers in frogs

In three frog species Rana esculenta, Rana temporaria and Xenopus laevis, the contacts established by gamma-aminobutyric acid and glutamate decarboxylase immunoreactive (-ir) terminals upon primary afferent fibers were studied using confocal and electron microscopy. For confocal microscopy, the primary afferent fibers were labeled through the dorsal root with Dextran-Texas Red, whereas gamma-aminobutyric acid and glutamate decarboxylase immunoreactivity were revealed with fluorescein isothiocyanate. Appositions of gamma-aminobutyric acid and glutamate decarboxylase immunoreactive profiles onto primary afferent fibers were observed and were considered as putative axo-axonic contacts of GABAergic terminals upon primary afferents. The latter was confirmed by the ultrastructural finding of axo-axonic synapses from gamma-aminobutyric acid immunopositive boutons upon the HRP-labeled primary afferent fibers in postembedding immunoelectron microscopic study. Such synapses may represent the morphological basis of GABAergic presynaptic inhibition of primary afferent fibers.

Presynaptic effects of biogenic amines modulating synaptic transmission between identified sensory neurons and giant interneurons in the first instar cockroach

Intracellular recording was used to investigate the modulatory effects of serotonin and octopamine on the identified synapses between filiform hair sensory afferents and giant interneurons in the first instar cockroach, Periplaneta americana. Serotonin at 10(-4) mol l(-1) to 10(-3) mol l(-1) reduced the amplitude of the lateral axon-to-ipsilateral giant interneuron 3 excitatory postsynaptic potentials. and octopamine at 10(-4) mol l(-1) increased their amplitude. Similar effects were seen on excitatory postsynaptic potentials in dorsal giant interneuron 6. Several lines of evidence suggest that both substances modulate the amplitude of excitatory postsynaptic potentials by acting presynaptically, rather than on the postsynaptic neuron. The fitting of simple binomial distributions to the postsynaptic potential amplitude histograms suggested that, for both serotonin and octopamine, the number of synaptic release sites was being modulated. Secondly, the amplitudes of miniature excitatory postsynaptic potentials recorded in the presence of tetrodotoxin were unaffected by either modulator. Finally, recordings from contralateral giant interneuron 3, which has two identifiable populations of synaptic inputs, showed that each modulator had a more pronounced effect on excitatory postsynaptic potentials evoked by the lateral axon than on those evoked by the medial axon. Immunocytochemistry confirmed that neuropilar processes containing serotonin are present in close proximity to these synapses.

5-HT(3)-receptor subunits A and B are co-expressed in neurons of the dorsal root ganglion

The type 3 serotonin (5-HT(3)) receptor is the only ligand-gated ion channel receptor for serotonin (5-HT). Many pharmacological, behavioral, and electrophysiological studies indicate heterogeneous properties for this receptor. Although the basis for this heterogeneity is unknown, one possible explanation for these findings resides in the subunit composition of the receptor. Two 5-HT(3)-receptor subunits have been cloned: the 5-HT(3)-receptor subunit A (5-HT(3A)) and the 5-HT(3)-receptor subunit B (5-HT(3B)). Recombinant co-expression of 5-HT(3A) and 5-HT(3B) subunits produces a functional heteromeric 5-HT(3A/3B) receptor with pharmacological and electrophysiological properties different from those displayed by the 5-HT(3A) homomeric receptor. In the present report, we used in situ hybridization histochemistry to demonstrate that the 5-HT(3B) subunit is expressed in rat dorsal root ganglion (DRG) neurons. We determined with cellular resolution that 5-HT(3B) subunit mRNA was expressed in 43.2 +/- 2.8% of the total population of DRG neurons. By comparison, the 5-HT(3A) subunit was more widely expressed, with 70.0 +/- 2.8% of the total population of DRG neurons expressing this subunit. Further analyses showed that most of the neurons containing mRNA for the 5-HT(3B) subunit (91.5 +/- 3.4%) also expressed the 5-HT(3A) subunit. In contrast, nearly half the population of neurons expressing 5-HT(3A) subunit lacked (52.8 +/- 5.9%) transcripts for the 5-HT(3B) subunit. These results provide the first evidence indicating that the 5-HT(3B) subunit of the 5-HT(3) receptor is expressed in DRG and suggest that sensory neurons have the capacity to synthesize at least two structurally different 5-HT(3) receptors: a heteromeric 5-HT(3A/3B) receptor and a homomeric 5-HT(3A) receptor. Consequently, 5-HT(3) receptors with different properties might be present in peripheral and central axons of the DRG. These findings open the possibility that distinct types of 5-HT(3) receptors may be involved in perception and/or processing of sensory information. J. Comp. Neurol. 438:163-172, 2001. Published 2001 Wiley-Liss, Inc.

Calbindin immunoreactivity of enteric neurons in the guinea-pig ileum

Previous studies have identified Dogiel type II neurons with cell bodies in the myenteric plexus of guinea-pig ileum to be intrinsic primary afferent neurons. These neurons also have distinctive electrophysiological characteristics (they are AH neurons) and 82-84% are immunoreactive for calbindin. They are the only calbindin-immunoreactive neurons in the plexus. Neurons with analogous shape and electrophysiology are found in submucosal ganglia, but, with antibodies used in previous studies, they lack calbindin immunoreactivity. An antiserum that is more effective in revealing calbindin in the guinea-pig enteric nervous system has been reported recently. In the present work, we found that this antiserum reveals the same population that was previously identified in myenteric ganglia, and does not reveal any further population of myenteric nerve cells. In submucosal ganglia, 9-10% of nerve cells were calbindin immunoreactive with this antiserum. The submucosal neurons with calbindin immunoreactivity were also immunoreactive for choline acetyltransferase, but not for neuropeptide Y (NPY) or vasoactive intestinal peptide (VIP). Small calbindin-immunoreactive neurons (average profile 130 microm2) were calretinin immunoreactive, whereas the large calbindin-immunoreactive neurons (average profile 330 microm2) had tachykinin (substance P) immunoreactivity. Calbindin immunoreactivity was seen in about 50% of the calretinin neurons and 40% of the tachykinin-immunoreactive submucosal neurons. It is concluded that, in the guinea-pig ileum, only one class of myenteric neuron, the AH/Dogiel type II neuron, is calbindin immunoreactive, but, in the submucosal ganglia, calbindin immunoreactivity occurs in cholinergic, calretinin-immunoreactive, secretomotor/vasodilator neurons and AH/Dogiel type II neurons.

Mitochondrial DNA deletions parallel age-linked decline in rat sensory nerve function

In rats, the function of sensory nerves in the hind limb declines significantly with age. Normally aging rats and rats treated neonatally with capsaicin were studied here. Quantification of vascular response and substance P in young (3 months) and old (24 months) rats showed additive effects of age and capsaicin treatment. The levels in dorsal root ganglion of a particular deletion in mitochondrial DNA (mtDNA(4834)) were about 300-fold higher in old compared to young rats. Capsaicin treatment had no significant effect on mtDNA(4834) abundance. Dorsal root ganglia of old (but not young) rats were found to contain a spectrum of multiple deletions. The abundance of mtDNA(4834) in dorsal root ganglia from individual rats correlated strongly with their decline in vascular function, even where vascular responses were systematically depressed due to prior capsaicin treatment. One possibility is that mitochondrial DNA mutations directly lead to functional decline at mitochondrial and tissue levels. Alternatively, loss of mitochondrial DNA integrity and physiological decline may be consequences of the same factor, such as oxidative stress.

Nitric oxide modulates renal sensory nerve fibers by mechanisms related to substance P receptor activation

Nerve terminals containing neuronal nitric oxide synthase (nNOS) are localized in the renal pelvic wall where the sensory nerves containing substance P and calcitonin gene-related peptide (CGRP) are found. We examined whether nNOS is colocalized with substance P and CGRP. All renal pelvic nerve fibers that contained nNOS-like immunoreactivity (-LI) also contained substance P-LI and CGRP-LI. In anesthetized rats, renal pelvic perfusion with the nNOS inhibitor S-methyl-L-thiocitrulline (L-SMTC, 20 microM) prolonged the afferent renal nerve activity (ARNA) response to a 3-min period of increased renal pelvic pressure from 5 +/- 0.4 to 21 +/- 2 min (P < 0.01, n = 14). The magnitude of the ARNA response was unaffected by L-SMTC. Similar effects were produced by N(omega)-nitro-L-arginine methyl ester (L-NAME) but not D-NAME. Increasing renal pelvic pressure produced similar increases in renal pelvic release of substance P before and during L-SMTC, from 5.9 +/- 1.4 to 13.6 +/- 4.2 pg/min before and from 4.9 +/- to 12.6 +/- 2.7 pg/min during L-SMTC. L-SMTC also prolonged the ARNA response to renal pelvic perfusion with substance P (3 microM) from 1.2 +/- 0.2 to 5.6 +/- 1.1 min (P < 0.01, n = 9) without affecting the magnitude of the ARNA response.

IN CONCLUSION

activation of NO may function as an inhibitory neurotransmitter regulating the activation of renal mechanosensory nerve fibers by mechanisms related to activation of substance P receptors.

Attenuation of the afferent limb of the baroreceptor reflex in streptozotocin-induced diabetic rats

Diabetic autonomic neuropathy is a common complication following prolonged diabetes. Alterations of cardiovascular reflexes contribute to the increased cardiovascular morbidity and mortality seen in diabetic patients. This study sought to better characterize these complications by investigating the afferent limb of the baroreceptor reflex in an experimental rat model of diabetes. Streptozotocin (STZ)-induced diabetic and euglycemic control rats were studied at 8- and 16-week time points after initiation of the experiment. Activation of the afferent limb of the baroreceptor reflex was assessed by measuring the numbers of c-Fos-immunoreactive (ir) neurons in the CNS site of termination of the baroreceptor afferent neurons, the nucleus of the solitary tract (NTS). Initial experiments established that baseline cardiovascular parameters and NTS expression of c-Fos-ir neurons were not different between diabetic and control rats at either time point. Phenylephrine (PE)-induced activation of baroreceptors resulted in a significant elevation in the numbers of c-Fos-ir neurons in the NTS of control rats. Although diabetic rats showed similar pressor responses to PE, the activation of c-Fos-ir neurons in the NTS of diabetic rats was significantly attenuated. At both 8 and 16 weeks, STZ-induced diabetic rats had significantly fewer c-Fos-ir neurons in the commissural NTS and in the caudal subpostrernal NTS when compared to the non-diabetic control animals receiving PE. These data suggest that STZ-induced diabetes, for a period of 8 and 16 weeks, results in reduced activity in the afferent baroreceptor input to the NTS, and are consistent with diabetes-induced damage to baroreceptor afferent nerves.

Topological relationship between corticotropin-releasing factor-immunoreactive cerebellar afferents and tyrosine hydroxylase-immunoreactive Purkinje cells in a hereditary ataxic mutant, rolling mouse Nagoya

Using immunohistochemistry we examined the distribution of corticotropin-releasing factor-positive cerebellar afferents and the topological relationship between their projections and the distribution of tyrosine hydroxylase-positive Purkinje cells in an ataxic mutant, rolling mouse Nagoya. In the mutants, some climbing fibers were more intensely stained for corticotropin-releasing factor, but their zonal distribution remained the same as in non-ataxic littermates (control mice). These climbing fibers arose from the dorsal accessory nucleus, the ventral lamella of principal nucleus, the dorsomedial cell group, the subnucleus A, the beta subnucleus and the ventrolateral protrusion of the inferior olive, since perikarya in these olivary subdivisions were more intensely stained for corticotropin-releasing factor than in controls. Some mossy fiber rosettes in the vermal lobules, the simple lobule, the crus I of ansiform lobule, the copula pyramidis and the flocculus also exhibited corticotropin-releasing factor immunoreactivity and were more densely stained in the mutants than in controls. Double immunostaining for corticotropin-releasing factor and tyrosine hydroxylase in the mutant cerebellum revealed that the distribution of tyrosine hydroxylase-positive Purkinje cells corresponded to terminal fields of corticotropin-releasing factor-positive climbing fibers but not corticotropin-releasing factor-positive mossy fibers. This study indicated an increased corticotropin-releasing factor immunoreactivity in some climbing or mossy fibers in the cerebellum of rolling mouse Nagoya. We also found that the distribution of tyrosine hydroxylase-positive Purkinje cells corresponded to terminal fields of corticotropin-releasing factor-positive climbing fibers in the mutant cerebellum. As the transcription of the tyrosine hydroxylase gene is facilitated by Ca2+, abnormal tyrosine hydroxylase expression in the mutant Purkinje cells may indicate functional abnormality by alterations in intracellular Ca2+ concentrations. Therefore, we suggest that an increased level of corticotropin-releasing factor in a specific population of climbing fibers may alter the function of their target Purkinje cells.

Retrograde tracing of zinc-enriched (ZEN) neuronal somata in rat spinal cord

The zinc selenide autometallographic (ZnSeAMG) technique for tracing the retrograde axonal transport of zinc ions in zinc-enriched (ZEN) neurons was used to map the distribution of ZEN neuronal somata in rat spinal cord. After a local injection of sodium selenide into the dorsal or ventral horn, ZnSeAMG-labeled ZEN neurons appeared in Rexed's laminae V, VII and X while laminae I and II were void. A few scattered ZEN somata were observed in the remaining laminae. The labeled neurons differed in shape and size, and the relatively high level of labeled somata around the injection site suggests that many ZEN neurons have relatively short axons or boutons en passage close to the neuronal origin. Ultrastructurally, the retrogradely transported zinc selenide clusters were found in the lysosomes of ZEN somata and proximal dendrites. Electron microscopic studies also revealed two different kinds of ZEN terminals: (1) terminals with flat synaptic vesicles making symmetric synaptic contacts; and (2) terminals with round vesicles making asymmetric synaptic contacts. The present study suggests the existence of propriospinal systems of ZEN neurons comprising both segmental and intersegmental ZEN connections and having either inhibitory or excitatory ZEN terminals. The ZEN neurons seem to form a vast network of terminals located primarily in the gray matter, but also contacting dendrites radiating into the white matter. Important functions of this rather massive system of ZEN terminals can not be deduced from our present knowledge, but the systems appear to be involved in both motor and sensory functions.

Primary structure and developmental expression of zebrafish sodium channel Na(v)1.6 during neurogenesis

A zebrafish sodium channel cDNA encoding a 1949-amino acid polypeptide, Na(v)1.6, was isolated. Two transcripts were detected in zebrafish adult brain but not in cardiac or skeletal muscle. The RNase protection analysis confirmed the neural specificity of zebrafish Na(v)1.6 24 hours postfertilization (hpf) Na(v)1.6 was expressed in the trigeminal ganglion, anterior and posterior lateral line ganglia, rhombomeres, and Rohon-Beard neurons. This preferential localization suggests that Na(v)1.6 plays an important role in tactile sensitivity. The abundance of zebrafish Na(v) 1.6 mRNA in the central and peripheral nervous systems increased markedly between 48 and 72 hpf, during the maturation of the nervous system.

Roles of fibroblast growth factor 2 during innervation of the avian inner ear

The importance of individual members of the fibroblast growth factor gene family during innervation of the vertebrate inner ear is not clearly defined. Here we address the role of fibroblast growth factor 2 (FGF-2 or basic FGF) during development of the chicken inner ear. We found that FGF-2 stimulated survival of isolated cochlear and vestibular neurons during distinct phases of inner ear innervation. The potential neurotrophic role of FGF-2 was confirmed by its expression in the corresponding sensory epithelia and the detection of one of its high-affinity receptors in inner ear neurons. Finally, we have analysed the potential of the amplicon system based on defective herpes simplex virus type 1 (HSV-1) vectors to express FGF-2 in cochlear neurons. Overexpression of FGF-2 in cochlear neurons resulted in neuronal differentiation demonstrating the presence of biologically active growth factor. This study underlines the potential of FGF-2 to control innervation and development of sensory epithelia in the avian inner ear. Furthermore, amplicon vectors may provide a useful tool to analyse gene function in isolated neurons of the vertebrate inner ear.

Nerve growth factor induces P2X(3) expression in sensory neurons

Glial cell line-derived neurotrophic factor (GDNF) and nerve growth factor (NGF) are neuroprotective for subpopulations of sensory neurons and thus are candidates for pain treatment. However, delivering these factors to damaged neurons will invariably result in undamaged systems also being treated, with possible consequences for sensory processing. In sensory neurons the purinergic receptor P2X(3) is found predominantly in GDNF-sensitive nociceptors. ATP signalling via the P2X(3) receptor may contribute to pathological pain, suggesting an important role for this receptor in regulating nociceptive function. We therefore investigated the effects of intrathecal GDNF or NGF on P2X(3) expression in adult rat spinal cord and dorsal root ganglia (DRG). In control spinal cords, P2X(3) expression was restricted to a narrow band of primary afferent terminals within inner lamina II (II(i)). Glial cell line-derived neurotrophic factor treatment increased P2X(3) immunoreactivity within lamina II(i) but not elsewhere in the cord. Nerve growth factor treatment, however, induced novel P2X(3) expression, with intense immunoreactivity in axons projecting to lamina I and outer lamina II and to the ventro-medial afferent bundle beneath the central canal. In the normal DRG, we found a greater proportion of P2X(3)-positive neurons at cervical levels, many of which were large-diameter and calcitonin gene-related peptide-positive. In both cervical and lumbar DRG, the number of P2X(3)-positive cells increased following GDNF or NGF treatment. De novo expression of P2X(3) in NGF-sensitive nociceptors may contribute to chronic inflammatory pain.

Selective distribution of mu-opioid receptors in C1 adrenergic neurons and their afferents

Agonists of the mu-opioid receptor (MOR) have profound effects on blood pressure, heart rate, and respiration that may be mediated by C1 adrenergic neurons in the rostral ventrolateral medulla (RVL). C1 neurons are sympathoexcitatory and are involved in both tonic and reflex regulation of sympathetic outflow. This study was designed to determine whether C1 neurons, or their afferents, contain MOR. C1 neurons were identified by using an antibody against the epinephrine synthesizing enzyme phenylethanolamine-N-methyl transferase (PNMT), whereas MOR was localized by using an antipeptide antibody that recognizes the cloned MOR, MOR1. Combined immunoperoxidase and immunogold methods were used to examine the cellular distribution of MOR1 relative to PNMT-containing neurons in the RVL. MOR1 was found in 22% of PNMT-containing dendrites (n = 392), whereas MOR1-containing axons or axon terminals contacted 14% of PNMT-containing dendrites. This distribution was heterogenous with regard to dendritic size: PNMT-labeled dendrites containing MOR1 were usually large (60% were >1.2 microm), whereas PNMT-containing dendrites that received MOR1-labeled afferents were usually small (79% were <1.2 microm). Individual dendrites rarely contained MOR1 at both pre- and postsynaptic sites. Together these results suggest that MOR agonists may directly influence the activity of C1 neurons, as well as the activity of select afferents to these cells. Plasmalemmal membrane labeling for MOR1 was more frequent in smaller PNMT-containing dendrites, suggesting that postsynaptic receptors are more readily available for ligand binding in small dendrites, although the receptor was more frequently detected in larger PNMT dendrites. The selective distribution of MORs to specific pre- and postsynaptic sites suggests the receptor may be selectively trafficked to positions where it may regulate afferent activity that is heterogeneously distributed along the dendritic tree of C1 neurons.

Voltage-gated K+ channels in chemoreceptor sensory neurons of rat petrosal ganglion

A subpopulation of sensory neurons in the petrosal ganglion transmits information between peripheral chemoreceptors (glomus cells) in the carotid body and relay neurons in the nucleus of the solitary tract. Expression of voltage-gated K+ channels in these neurons was characterized by immunohistochemical localization. Five members of the Kv1 family, Kv1.1, Kv1.2, Kv1.4, Kv1.5 and Kv1.6 and members of two other families, Kv2.1 and Kv4.3, were identified in over 90% of the chemoreceptor neurons. Although the presence of these channel proteins was consistent throughout the population, individual neurons showed considerable variation in K+ current profiles.

Differential regulation of P2X(3) mRNA expression by peripheral nerve injury in intact and injured neurons in the rat sensory ganglia

The P2X(3) receptor is a ligand-gated cation channel activated by the binding of extracellular adenosine 5'-triphosphate (ATP), an agent that has been suggested to have a role in the nociceptive pathway after tissue and nerve injury. After peripheral nerve injury, both down regulation and up regulation of the P2X(3) receptor in sensory ganglion neurons have been observed. The purpose of this study was to examine the precise regulation of P2X(3) mRNA expression in primary sensory neurons after nerve injury. We used two nerve injury models in the rat, the transection of the tibial and common peroneal nerves and the transection of the infraorbital nerve, and observed dorsal root ganglion (DRG) and trigeminal ganglion neurons, respectively. P2X(3) mRNA in both neuron populations was detected by in situ hybridization with an oligonucleotide probe that was confirmed by Northern blot analysis. To identify axotomized neurons, we examined the expression of activating transcription factor 3 (ATF3), which is regarded as a neuronal-injury marker, using immunohistochemistry. In the DRG, the mean percentage of P2X(3) mRNA-labeled neurons relative to the total number of neurons increased from 32.7% in the naive rats to 42.7% at 3 days after injury. The mean percentage of P2X(3) mRNA-labeled neurons in ATF3 immunoreactive (ir) neurons was 29.5% at 3 postoperative days, which gradually decreased to 11.2% at 28 days after injury. In the trigeminal ganglion, the mean percentage of P2X(3) mRNA-labeled neurons was 36.9% at 3 days after injury, versus 26.0% in the naive rats. In the ATF3-ir neurons, the mean percentage of P2X(3) mRNA-labeled neurons was 25.3% at 1 postoperative day and was reduced to 6.1% at 28 postoperative days. The finding that P2X(3) mRNA in ATF3-ir neurons decreased significantly after injury indicates that axotomized neurons decreased the expression of P2X(3) mRNA, despite the increase in P2X(3) mRNA relative to the total number of sensory ganglion neurons. These data strongly suggest that P2X(3) mRNA expression increases in intact neurons and that P2X(3) mRNA in intact neurons may play a role in the pathomechanism of post-nerve injury in primary sensory neurons.

Jun, Fos and Krox in the hippocampus after noxious stimulation: simultaneous-input-dependent expression and nuclear speckling

Stimulation of sensory C-fibres produces extensive expression of the Fos, Jun and Krox families of inducible transcription factors (ITFs) in many nociceptive CNS areas [28]. In the hippocampus, however, c-Fos is only weakly induced by such stimulation, and expression of the other ITFs has not been studied. Here we examine the effects of single, repeated and simultaneous C-fibre inputs on ITF expressions in the rat hippocampus. A brief, strong electrical stimulation of sciatic nerve C-fibres induced little or no expression of c-Fos or Krox-20. In contrast, FosB was induced and continued to rise in all areas, whereas the basal expressions of c-Jun and Krox-24 were initially reduced but then returned during the subsequent 36 h. A weak noxious cutaneous stimulus applied to one hindpaw induced only weak expressions of the ITFs. However, if the sciatic stimulation was applied contralaterally and 6 h beforehand, this weak stimulus strongly induced Krox-24, but not other ITFs, i.e. there was a potentiation of Krox-24 expression. When these two stimuli were applied simultaneously a few c-Fos labelled cells did appear, and there was and an increased Krox-24 expression. There was also a strong potentiation of FosB and a strong reduction in c-Jun expression. This simultaneous stimulation was the only type of stimulation to induce expression of Krox-20. Also after simultaneous stimulation the majority of the nuclear labelling for FosB, but not of the other ITFs, had a speckled appearance. MK-801 blocked these changes in ITF expressions, but it could also cause the C-fibre stimulations to induce c-Fos and c-Jun in specific areas of the hippocampus. Thus C-fibre stimulation does affect transcription factor activity in the hippocampus; and the strong responses of some ITFs to simultaneous inputs points to their having a role as 'genetic coincidence detectors' in the hippocampus.

Distribution of serotonin 5-HT(2A) receptors in afferents of the rat striatum

Treatment with conventional antipsychotic drugs (APDs) is accompanied by extrapyramidal side effects (EPS), which are thought to be due to striatal dopamine D(2) receptor blockade. In contrast, treatment with atypical APDs is marked by a low incidence or absence of EPS. The reduced motor side effect liability of atypical APDs has been attributed to a high serotonin 5-HT(2A) receptor affinity coupled with a relatively low D(2) affinity. Despite the high density of 5-HT(2A) binding sites in the striatum, there are few detectable 5-HT(2A) mRNA-expressing neurons in the striatum. This suggests that most striatal 5-HT(2A) receptors are heteroceptors located on afferent axons. A combined retrograde tracer-immunohistochemistry method was used to determine the sites of origin of striatal 5-HT(2A)-like immunoreactive axons. 5-HT(2A)-like immunoreactive neurons in both the cortex and globus pallidus were retrogradely labeled from the striatum; very few nigrostriatal or thalamostriatal neurons expressed 5-HT(2A)-like immunoreactivity. Within the striatum, parvalbumin-containing interneurons displayed 5-HT(2A) immunolabeling; these neurons are the targets of cortical and pallidal projections. Our data indicate that cortico- and pallido-striatal neurons are the major source of 5-HT(2A) receptor binding in the striatum, and suggest that cortico- and pallido-striatal neurons are strategically positioned to reduce the motor side effects that accompany striatal D(2) receptor blockade or are seen in parkinsonism.

Sodium channel beta1 and beta2 subunits parallel SNS/PN3 alpha-subunit changes in injured human sensory neurons

Voltage-gated sodium channels consist of a pore-containing alpha-subunit and one or more auxiliary beta-subunits, which may modulate channel function. We previously demonstrated that sodium channel SNS/PN3 alpha-subunits were decreased in human sensory cell bodies after spinal root avulsion injury, and accumulated at injured nerve terminals in pain states. Using specific antibodies for immunohistochemistry, we have now detected sodium channel beta1 and beta2 subunits in sensory cell bodies within control human postmortem sensory ganglia (78% of small/medium (< or = 50 microm) and 68% of large (> or = 50 microm) cells); their changes in cervical sensory ganglia after avulsion injury paralleled those described for SNS/PN3 alpha-subunits. Our results suggest that alpha- and beta-subunits share common regulatory mechanisms, but present distinct targets for novel analgesics.

Plasticity of TTX-sensitive sodium channels PN1 and brain III in injured human nerves

Sensory neurones co-express voltage-gated sodium channels that mediate TTX-sensitive (TTX-S) and TTX-resistant (TTX-R) currents, which may contribute to chronic pain after nerve injury. We previously demonstrated that TTX-R channels were decreased acutely in human sensory cell bodies after central axotomy, but accumulated in nerve terminals after peripheral axotomy. We have now studied the TTX-S channels PN1 and Brain III, using specific antibodies for immunohistochemistry, in dorsal root ganglia (DRG) from 10 patients with traumatic central axotomy, nerves from 16 patients with peripheral axotomy, and controls. PN1 showed temporal changes similar to the TTX-R channels in sensory cell bodies of injured DRG. In contrast, Brain III was found only in injured nerves (not control nerves, or control/central axotomy DRG). PNI and Brain III are distinct targets for novel analgesics.

Responsiveness of sympathetic and sensory iridial nerves to NGF treatment in young and aged rats

Altered neuronal responses to trophic factors may play a role in neuronal maintenance in adulthood and may also be involved in neuronal atrophy in old age. We have investigated this issue in the rat iris, studying responsiveness of sympathetic and sensory iridial nerves to a range of NGF concentrations in mature and aged rats. We show here that growth responses of sensory nerves to NGF, as measured by quantitative immunohistochemistry and image analysis, were unchanged in old rats. In contrast, there was a small but significant reduction in responsiveness of aged sympathetic neurons. The shapes of the dose-response curves for sensory and sympathetic neurons were different, with a larger response over a narrower range of concentrations in sensory neurons. Lower levels of p75 immunoreactivity were observed in iridial nerves from old compared to young rats. NGF treatment had no effect on receptor staining in young rats but restored 'young' levels of p75 staining in old rats. Our results do not support the hypothesis of a primary role for NGF in maintenance or atrophy of nerves in ageing.

Correlation between putative inhibitory molecules at the dorsal root entry zone and failure of dorsal root axonal regeneration

The molecular mechanisms involved in preventing regenerating dorsal root axons from entering the spinal cord at the dorsal root entry zone (DREZ) are obscure. We used immunohistochemistry, in situ hybridization, and electron microscopy to study axonal regeneration after dorsal rhizotomy in adult rats and its relationship to cellular changes and the distribution of putative growth inhibitory molecules in this region. Astrocyte processes, ending as bulb-shaped expansions, grew up to 700 microm into the basal lamina tubes of injured roots, where regenerating axons were also present. Some of these axons approached or reached the DREZ but grew no further; others turned back toward the ganglion, suggesting the presence of repulsive cues in or near the DREZ. Tenascin-C mRNA and protein and CSPG stub immunoreactivity were strongly upregulated in the roots after rhizotomy, but were only weakly expressed in the DREZ. Tenascin-R immunoreactivity was confined to CNS tissue, and unaffected by rhizotomy. Large, rounded GFAP-negative, NG2-immunoreactive cells, a few of which were OX42 positive, were found in the DREZ following rhizotomy. Astrocyte processes projecting into the roots were tenascin-R and NG2 negative. Hence, only NG2-expressing cells and tenascin-R were appropriately situated to inhibit regeneration through the DREZ.

P2X(2) receptor immunoreactivity in the dorsal vagal complex and area postrema of the rat

Adenosine 5'-triphosphate (ATP) can function as a fast synaptic transmitter through its actions on ionotropic (P2X) and metabotropic (P2Y) receptors in neuronal tissue. The ionotropic receptors have been classified into seven subtypes (P2X(1)-P2X(7)) by molecular cloning. However, they are difficult to distinguish pharmacologically owing to an absence of specific agonists and antagonists. In this study we used neuroanatomical methods to determine the origin and neurochemical phenotype of the P2X(2) subtype of purinoceptor in the dorsal medulla of the rat. Using immunohistochemistry we observed dense networks of P2X(2) receptor immunoreactive labelled fibres and terminals in the dorsal vagal complex and area postrema, as well as labelled cell bodies in the dorsal vagal nucleus and the area postrema. The P2X(2) receptor was localized presynaptically in vagal afferent fibres and terminals in the nucleus tractus solitarius at the ultrastructural level by combining injections of an anterograde tracer (biotin dextran amine) into the nodose ganglion with pre-embedding immunogold visualization of P2X(2) immunoreactivity. Terminals immunoreactive for the P2X(2) receptor in the nucleus tractus solitarius were found to contain glutamate, but not GABA immunoreactivity by post-embedding immunogold-labelling techniques. In cell bodies in the area postrema, dual immunofluorescence also indicated that P2X(2) receptor immunoreactive cells are glutamatergic but not GABAergic. The P2X(2) receptor was localized to vagal preganglionic neurons in the dorsal vagal nucleus that were identified by prior intraperitoneal injections of the retrograde tracer FluoroGold. No cells immunoreactive for the P2X(2) receptor were observed in the nucleus tractus solitarius. The localization of P2X(2) receptor immunoreactivity presynaptically in vagal afferent terminals indicates that the receptor may be involved in modulating transmitter release from vagal afferent fibres. Furthermore, the presence of the P2X(2) receptor in vagal preganglionic cells and in glutamatergic cells of the area postrema implies that it may, respectively, play a role in regulation of vagal efferent cell activity and modulation of excitatory outputs from the area postrema to other brain regions.

Transport of endosomal early antigen 1 in the rat sciatic nerve and location in cultured neurons

Early endosomal antigen 1 (EEA1) is known to be a marker of early endosomes and in cultured hippocampal neurons it preferentially localizes to the dendritic but not the axonal compartment. We show in cultured dorsal root ganglia and superior cervical ganglia neurons that EEA1 localizes to the cell bodies and the neurites of both sensory and sympathetic neurons. We then show in vivo using a ligated rat sciatic nerve that EEA1 significantly accumulates on the proximal side and not on the distal side of the ligation. This suggests that EEA1 is transported in the anterograde direction in axons either as part of the homeostatic process or to the nerve ligation site in response to nerve injury.

Coexistence of kappa- and delta-opioid receptors in rat spinal cord axons

It has been found that heterodimers of kappa- and delta-opioid receptors can occur in vitro, but it has been unclear whether they also occur in intact animals. In the present study we examined whether kappa-delta heterodimers might occur in vivo by staining for these receptors with two-color fluorescence immunocytochemistry. Sections of rat spinal cord were double-stained using rabbit anti-kappa opioid receptor combined with rat anti-delta-opioid receptor. It was found that axons in the superficial dorsal horn of the spinal cord were double-labeled. In addition, structures within axonal varicosities were sometimes double-labeled. We conclude that single axons, and single structures within axons, express both kappa- and delta-opioid receptors. These observations are consistent with heterodimers of these receptors existing in vivo.

Immunocytochemical identification and analysis of the diffuse bipolar cell type DB6 in macaque monkey retina

The distribution and morphology of CD15-immunoreactive bipolar cells were studied in the retina of macaque monkey. Labelled cells have a large dendritic tree contacting several cones and a narrowly stratified axon terminal that ends deep in the inner plexiform layer, close to the ganglion cell layer. The morphology of the labelled cells corresponds to that of the diffuse bipolar cell type named DB6 by Boycott & Wässle (1991; Eur. J. Neurosci., 3,1069). We conclude that CD15 is a marker for DB6 bipolar cells, enabling the quantitative analysis of the distribution and connectivity of this diffuse bipolar cell type.

nompA encodes a PNS-specific, ZP domain protein required to connect mechanosensory dendrites to sensory structures

Mutations in the no-mechanoreceptor-potential A (nompA) gene, which eliminate transduction in Drosophila mechanosensory organs, disrupt contacts between neuronal sensory endings and cuticular structures. nompA encodes a transmembrane protein with a large, modular extracellular segment that includes a zona pellucida (ZP) domain and several plasminogen N-terminal (PAN) modules. It is specifically expressed in type I sense organs of the peripheral nervous system by the support cells that ensheath the neuronal sensory process. A green fluorescent protein (GFP)-NompA fusion protein is localized to the dendritic cap, an extracellular matrix that covers the ciliary outer segment of the sensory process and that shows organizational defects in nompA mutants. The structure and location of NompA suggest that it forms part of a mechanical linkage required to transmit mechanical stimuli to the transduction apparatus.