Synthesis, and central and peripheral axonal transport of substance P in a dorsal root ganglion-nerve preparation in vitro

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.

Substance P Regulation in Epilepsy

Background:

Epilepsy is a common neurological disease characterized by abnormal temporary discharge of neurons in the central nervous system. In recent years, studies have revealed the localization and changes in the density of neuropeptides, such as substance P (SP) in the pathogenesis of epilepsy. This review is a concise overview of SP and their physiologic and pathologic functions on regulating epilepsy, and the underline mechanisms.

Methods:

We research and collect relative online content for reviewing the effects of SP in Epilepsy.

Results:

The SP/NK-1 receptor system may induce seizures and play an important role in status epilepticus and in experimental animal models of epilepsy. Newest studies show that several mechanisms may explain the excitatory effects of the SP/NK-1 receptor signaling pathway in epilepsy. By binding to the NK-1 receptor, NK-1 receptor antagonists may block the pathophysiological effects of SP, and further studies are needed to confirm the possible anti-epileptic activity of NK-1 receptor antagonists.

Conclusion:

SP plays crucial roles on through binding with NK-1 receptor during epilepsy pathologic processing, and the NK-1 receptor is receiving a great attention as a therapeutic target for treating epilepsy. Thus, the use of NK-1 receptor antagonists for the treatment of epilepsy should be investigated in further studies.

Increase of transcription factor EB (TFEB) and lysosomes in rat DRG neurons and their transportation to the central nerve terminal in dorsal horn after nerve injury

In the spinal dorsal horn (DH), nerve injury activates microglia and induces neuropathic pain. Several studies clarified an involvement of adenosine triphosphate (ATP) in the microglial activation. However, the origin of ATP together with the release mechanism is unclear. Recent in vitro study revealed that an ATP marker, quinacrine, in lysosomes was released from neurite terminal of dorsal root ganglion (DRG) neurons to extracellular space via lysosomal exocytosis. Here, we demonstrate a possibility that the lysosomal ingredient including ATP released from DRG neurons by lysosomal-exocytosis is an additional source of the glial activation in DH after nerve injury. After rat L5 spinal nerve ligation (SNL), mRNA for transcription factor EB (TFEB), a transcription factor controlling lysosomal activation and exocytosis, was induced in the DRG. Simultaneously both lysosomal protein, LAMP1- and vesicular nuclear transporter (VNUT)-positive vesicles were increased in L5 DRG neurons and ipsilateral DH. The quinacrine staining in DH was increased and co-localized with LAMP1 immunoreactivity after nerve injury. In DH, LAMP1-positive vesicles were also co-localized with a peripheral nerve marker, Isolectin B4 (IB4) lectin. Injection of the adenovirus encoding mCherry-LAMP1 into DRG showed that mCherry-positive lysosomes are transported to the central nerve terminal in DH. These findings suggest that activation of lysosome synthesis including ATP packaging in DRG, the central transportation of the lysosome, and subsequent its exocytosis from the central nerve terminal of DRG neurons in response to nerve injury could be a partial mechanism for activation of microglia in DH. This lysosome-mediated microglia activation mechanism may provide another clue to control nociception and pain.

Changes in the disposition of substance P in the rostral ventromedial medulla after inflammatory injury in the rat

This study examined whether peripheral inflammatory injury increases the levels or changes the disposition of substance P (SubP) in the rostral ventromedial medulla (RVM), which serves as a central relay in bulbospinal pathways of pain modulation. Enzyme immunoassay and reverse transcriptase quantitative polymerase chain reaction were used to measure SubP protein and transcript, respectively, in tissue homogenates prepared from the RVM and the periaqueductal gray (PAG) and cuneiform nuclei of rats that had received an intraplantar injection of saline or complete Freund's adjuvant (CFA). Matrix-Assisted Laser Desorption/Ionization Time of Flight analysis confirmed that the RVM does not contain hemokinin-1 (HK-1), which can confound measurements of SubP because it is recognized equally well by commercial antibodies for SubP. Levels of SubP protein in the RVM were unchanged four hours, four days and two weeks after injection of CFA. Tac1 transcripts were similarly unchanged in the RVM four days or two weeks after CFA. In contrast, the density of SubP immunoreactive processes in the RVM increased 2-fold within four hours and 2.7-fold four days after CFA injection; it was unchanged at two weeks. SubP-immunoreactive processes in the RVM include axon terminals of neurons located in the PAG and cuneiform nucleus. SubP content in homogenates of the PAG and cuneiform nucleus was significantly increased four days after CFA, but not at four hours or two weeks. Tac1 transcripts in homogenates of these nuclei were unchanged four days and two weeks after CFA. These findings suggest that there is an increased mobilization of SubP within processes in the RVM shortly after injury accompanied by an increased synthesis of SubP in neurons that project to the RVM. These findings are consonant with the hypothesis that an increase in SubP release in the RVM contributes to the hyperalgesia that develops after peripheral inflammatory injury.

PET-scan shows peripherally increased neurokinin 1 receptor availability in chronic tennis elbow: visualizing neurogenic inflammation?

In response to pain, neurokinin 1 (NK1) receptor availability is altered in the central nervous system. The NK1 receptor and its primary agonist, substance P, also play a crucial role in peripheral tissue in response to pain, as part of neurogenic inflammation. However, little is known about alterations in NK1 receptor availability in peripheral tissue in chronic pain conditions and very few studies have been performed on human beings. Ten subjects with chronic tennis elbow were therefore examined by positron emission tomography (PET) with the NK1 specific radioligand [(11)C]GR205171 before and after treatment with graded exercise. The radioligand signal intensity was higher in the affected arm as compared with the unaffected arm, measured as differences between the arms in volume of voxels and signal intensity of this volume above a reference threshold set as 2.5 SD above mean signal intensity of the unaffected arm before treatment. In the eight subjects examined after treatment, pain ratings decreased in all subjects but signal intensity decreased in five and increased in three. In conclusion, NK1 receptors may be activated, or up-regulated in the peripheral, painful tissue of a chronic pain condition. This up-regulation does, however, have moderate correlation to pain ratings. The increased NK1 receptor availability is interpreted as part of ongoing neurogenic inflammation and may have correlation to the pathogenesis of chronic tennis elbow.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00888225 http://clinicaltrials.gov/

Substance P signaling mediates BMP-dependent heterotopic ossification

Heterotopic ossification (HO) is a disabling condition associated with neurologic injury, inflammation, and overactive bone morphogenetic protein (BMP) signaling. The inductive factors involved in lesion formation are unknown. We found that the expression of the neuro-inflammatory factor Substance P (SP) is dramatically increased in early lesional tissue in patients who have either fibrodysplasia ossificans progressiva (FOP) or acquired HO, and in three independent mouse models of HO. In Nse-BMP4, a mouse model of HO, robust HO forms in response to tissue injury; however, null mutations of the preprotachykinin (PPT) gene encoding SP prevent HO. Importantly, ablation of SP(+) sensory neurons, treatment with an antagonist of SP receptor NK1r, deletion of NK1r gene, or genetic down-regulation of NK1r-expressing mast cells also profoundly inhibit injury-induced HO. These observations establish a potent neuro-inflammatory induction and amplification circuit for BMP-dependent HO lesion formation, and identify novel molecular targets for prevention of HO.

Biosynthesis, axonal transport and turnover of neuronal substance P

In dorsal root ganglia substance P is synthesized ribosomally, probably via a precursor. A second peptide, apparently a modified form of substance P (8-11), is cosynthesized with substance P and transported with it down both dorsal roots and peripheral branches. Four times as much substance P-like immunoreactivity is transported peripherally as centrally. Only 30% of axonal substance P-like immunoreactivity is available for rapid axonal transport and this is transported at a rate of 4.9 mm h-1. Axonal transport is not necessary for substance P synthesis. Doses of anisomycin which inhibit CNS protein synthesis by more than 95% do not cause any fall in substance P levels over an eight-hour period in ganglia, spinal cord or brain, suggesting that turnover is slower than that of conventional transmitters. However, stimulation of the hindlimbs of these animals reduces substance P levels in the dorsal horn. The turnover rate of spinal cord substance P, estimated either by relating the amount transported down dorsal roots to that in terminals or by measuring the decline of substance P levels after intrathecal colchicine, is four to five days. The functional organization of the substance P neuron is discussed with particular reference to the maintenance of peptide levels in terminals.

Neurokinin-1 receptor enhances TRPV1 activity in primary sensory neurons via PKCepsilon: a novel pathway for heat hyperalgesia

The neuropeptide substance P (SP) is expressed in unmyelinated primary sensory neurons and represents the best known "pain" neurotransmitter. It is generally believed that SP regulates pain transmission and sensitization by acting on neurokinin-1 receptor (NK-1), which is expressed in postsynaptic dorsal horn neurons. However, the expression and role of NK-1 in primary sensory neurons are not clearly characterized. Our data showed that NK-1 was expressed in both intact and dissociated dorsal root ganglion (DRG) neurons. In particular, NK-1 was mainly coexpressed with the capsaicin receptor TRPV1 (transient receptor potential vanilloid subtype 1), a critical receptor for the generation of heat hyperalgesia. NK-1 agonist [Sar(9), Met(O2)(11)]-substance P (Sar-SP) significantly potentiated capsaicin-induced currents and increase of [Ca2+]i in dissociated DRG neurons. NK-1 antagonist blocked not only the potentiation of TRPV1 currents but also heat hyperalgesia induced by intraplantar Sar-SP. NK-1 antagonist also inhibited capsaicin-induced spontaneous pain, and this inhibition was enhanced after inflammation. To analyze intracellular cross talking of NK-1 and TRPV1, we examined downstream signal pathways of G-protein-coupled NK-1 activation. Sar-SP-induced potentiation of TRPV1 was blocked by inhibition of G-protein, PLCbeta (phospholipase C-beta), or PKC but not by inhibition of PKA (protein kinase A). In particular, PKCepsilon inhibitor completely blocked both Sar-SP-induced TRPV1 potentiation and heat hyperalgesia. Sar-SP also induced membrane translocation of PKCepsilon in a portion of small DRG neurons. These results reveal a novel mechanism of NK-1 in primary sensory neurons via a possible autocrine and paracrine action of SP. Activation of NK-1 in these neurons induces heat hyperalgesia via PKCepsilon-mediated potentiation of TRPV1.

Magnetic resonance imaging and magnetic resonance myelography in the presurgical diagnosis of lumbar foraminal stenosis

STUDY DESIGN

Retrospective case series with a control group.

OBJECTIVE

To measure the diagnostic performance of magnetic resonance imaging (MRI) and MR myelography (MRM) for symptomatic foraminal stenosis in patients who need surgery.

SUMMARY OF BACKGROUND DATA

MR images are extensively used in the evaluation of foraminal stenosis and are often used to evaluate nerves exiting from the foramen. There has been no published report of the diagnostic performance of these imaging methods (MRI and MRM).

METHODS

Diagnostic performances were studied in 90 patients in whom the site of the stenosis was confirmed by means of selective decompression surgeries. The disease prevalence among patients was 26% (23 of 90 patients). The disease prevalence among foramens was 3% (25 of 936 foramens). The prevalence of abnormal findings in 27 asymptomatic volunteers was also studied. Two blinded observers interpreted foraminal narrowing on combinations of sagittal and axial MR images, abnormalities of the course of the nerve root in the foramen, and spinal nerve swelling on MRM.

RESULTS

The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of MRI for the diagnosis of symptomatic foraminal stenosis were 96%, 67%, 4%, and 100%, respectively. The corresponding values for abnormal nerve root course on MRM were 96%, 83%, 7%, and 100%, respectively, and for spinal nerve swelling on MRM were 60%, 99%, 35%, and 99%, respectively.

CONCLUSIONS

Compared with conventional MRI, MRM affords more specific information for the presurgical diagnosis of symptomatic foraminal stenosis.

Sensory neuropeptide mRNA up-regulation is bilateral in periodontitis in the rat: a possible neurogenic component to symmetrical periodontal disease

Periodontal disease is a common multifactorial chronic inflammatory disease in humans. In inflammatory conditions that are known to be associated with changes in nociception, such as arthritis, the neuronal expression of the proinflammatory neuropeptides, substance P and calcitonin gene-related peptide is altered. In this study the expression of these neuropeptides' mRNAs has been studied in an inflammatory model that shows no behavioural evidence of altered nociception. Periodontitis was induced in male rats by intragingival injection of lipopolysaccharide adjacent to the second right mandibular molar. The animals were killed at various times after lipopolysaccharide injection and right and left trigeminal ganglia and brain were processed for in situ hybridization for beta-preprotachykinin and alpha-calcitonin gene-related peptide mRNAs. Expression of both neuropeptide mRNAs was significantly increased only in small neurons in the mandibular division of the trigeminal ganglion ipsilateral to the LPS injection from 3 to 10 days postinjection. Neuropeptide mRNA expression was also significantly increased in the contralateral trigeminal ganglion at day 10. No significant changes in neuropeptide mRNA levels were seen in the maxillary and ophthalmic divisions of the trigeminal ganglia or in the trigeminal mesencephalic nucleus. The up-regulation of substance P and CGRP mRNAs in periodontal disease suggests that this is associated with the inflammatory process rather than nociception, as this disease does not appear to result in altered nociception in either rats or humans. The contralateral alteration in neuropeptide mRNA expression suggests a role for neurogenic mechanisms in the development of periodontal disease.

Subcutaneous administration of botulinum toxin A reduces formalin-induced pain

Botulinum toxin type A (BoNT-A) produced by the bacterium Clostridium botulinum is a potent inhibitor of acetylcholine release in the neuromuscular junction and has been used to treat many disorders related to excessive muscle contraction. However, BoNT-A has recently been used in pain therapy to treat myofascial pain, low back pain and various types of headaches, including migraine. The purpose of this study is to investigate the antinociceptive effect of BoNT-A and its underlying mechanism in the rat formalin inflammatory pain model. BoNT-A (3.5, 7, 15 and 30 U/kg) or vehicle was administered to the plantar surface of the right hindpaw of male Sprague-Dawley rats. BoNT-A dose-dependently (P<0.05) inhibited formalin-induced nociceptive behavior during phase 2 but not during phase 1 when administered 5 h to 12 days before formalin challenge. The onset of the antinociceptive effect started at 5 h after pre-treatment and this effect lasted for at least 12 days. BoNT-A (7 U/kg) also reduced edema. Consistent with the lack of effect in the formalin phase 1, BoNT-A, at 15 U/kg, had no effect on acute thermal nociception; no local muscle weakness was observed at this dose. Pre-treatment of rats with BoNT-A (3.5, 7 or 15 U/kg) all significantly reduced formalin-evoked glutamate (Glu) release. These results demonstrate that local peripheral injection of BoNT-A significantly reduces formalin-induced nociceptive behaviors with the absence of obvious muscle weakness. Such an antinociceptive effect of BoNT-A is associated with the inhibition of formalin-induced release of Glu (and/or neuropeptides) from primary afferent terminals.

NEUROPEPTIDES AND NEUROGENIC MECHANISMS IN ORAL AND PERIODONTAL INFLAMMATION

It is generally accepted that the nervous system contributes to the pathophysiology of peripheral inflammation, and a neurogenic component has been implicated in many inflammatory diseases, including periodontitis. Neurogenic inflammation should be regarded as a protective mechanism, which forms the first line of defense and protects tissue integrity. However, severe or prolonged noxious stimulation may result in the inflammatory response mediating injury rather than facilitating repair. This review focuses on the accumulating evidence suggesting that neuropeptides have a pivotal role in the complex cascade of chemical activity associated with periodontal inflammation. An overview of neuropeptide synthesis and release introduces the role of neuropeptides and their interactions with other inflammatory factors, which ultimately lead to neurogenic inflammation. The biological effects of the neuropeptides substance P (SP), calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), and neuropeptide Y (NPY) are summarized, and evidence for their involvement in the localized inflammatory lesions which characterize periodontitis is presented. In this context, the role of CGRP in bone metabolism is described in more detail. Recent research highlighting the role of the nervous system in suppressing pain and inflammation is also discussed.

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.

Peptide immunoreactivity and ultrastructure of rat urinary bladder nerve fibers after topical desensitization by capsaicin or resiniferatoxin

In the present study the decrease of neuropeptide containing nerve fibers and the increase in the volume threshold to reflex micturition occurring in the rat bladder after intravesical application of capsaicin or resiniferatoxin were compared. The ultrastructure of bladder terminal axons was evaluated at the moment of maximal peptide depletion and compared to that of nerve fibers after systemic capsaicin application. Adult Wistar rats were treated intravesically for 30 min with 0.5 ml of 100 nM RTX, 1 mM capsaicin or 30% ethanol in saline, the vehicle solution. Twenty-four hours and 1, 2, 3, 4 and 8 weeks later the bladders were immunostained for CGRP, SP, VIP and NPY. Cystomanometric studies were performed 24 h and 1, 8, and 12 weeks after vanilloid instillation. Twenty-four hours after systemic capsaicin or intravesical capsaicin or RTX, bladders were prepared for electron microscopic (EM) observation. Intravesical capsaicin or RTX decreased, in a similar way, the number of CGRP and SP-IR (immunoreactive) fibers coursing in the muscular layer and the mucosa. IR fibers amounted to less than 20% of controls at 24 h and returned to normal levels in the eighth week. At the EM level, bladders treated with topical vanilloids did not show morphological changes in terminal axons coursing in the mucosa. In contrast, bladders from animals treated systemically with capsaicin contained numerous grossly degenerated nerve fibers. VIP and NPY-IR fibers were not affected by the treatment. Cystometrograms showed an increase of the volume threshold to reflex micturition that started at 24 h and disappeared at 12 weeks. We conclude that intravesical capsaicin or RTX were equally effective in terms of reducing the number of SP and CGRP-IR fibers and increasing the volume threshold for reflex micturition. Both changes were transient and were not associated with ultrastructural changes of the bladder nerve fibers, excluding terminal axon degeneration as the main mechanism of action of intravesical vanilloids.

Effects of substance P and calcitonin gene-related peptide on axonal transport in isolated and cultured adult mouse dorsal root ganglion neurons

Substance P and calcitonin gene-related peptide (CGRP) released from primary sensory neurons are known to play important roles in nociception and nociceptive transmission. In the present study, we attempted to clarify the roles of these neuropeptides in the regulation of axonal transport in sensory neurons. Cells were isolated from adult mouse dorsal root ganglia and cultured in F-12 medium containing fetal bovine serum for 48 h until their neurites were grown. These isolated and cultured DRG cells were mostly (>98%) small (diameter <25 microm) and medium (diameter, 25-40 microm) in size, and were immunoreactive for substance P and CGRP (85.9 and 66. 0% of total cells, respectively). Video-enhanced microscopy was applied to observe particles transported within neurites. Application of substance P (100 nM) decreased the number of particles transported in both anterograde and retrograde directions in each of DRG neurons tested (n=5). The instantaneous velocities of individual particles transported in anterograde and retrograde directions were also reduced by substance P. In contrast, alpha-CGRP (100 nM) increased the number of particles transported in both directions in each of DRG neurons tested (n=5), and also increased the instantaneous velocities of particles transported bidirectionally. Application of beta-CGRP (100-1000 nM) did not elicit any effect on axonal transport. Therefore, axonal transport in sensory neurons seems to be modulated by substance P and alpha-CGRP, both of which can be derived from its own and adjacent sensory neurons.

Capsaicin-sensitive afferents are involved in signalling transneuronal effects between cutaneous sensory nerves

The aim of the present study was to investigate changes in contralateral nerves associated with peripheral nerve injuries. Transection and subsequent regeneration of the saphenous nerve on one side caused a suppression of the ability of the contralateral saphenous nerve to produce a neurogenic plasma extravasation response. This effect was transient, and was first evident two weeks after injury, reaching its maximum at four weeks, but was no longer detectable at eight weeks. This change was paralleled by a decrease in the content of substance P, a neuropeptide involved in neurogenic plasma extravasation, in the contralateral nerve. The neurotoxin capsaicin was used to deplete the nerve of a subclass of C-fibres, namely the polymodal nociceptor afferents. Pretreatment of the nerve to be lesioned with capsaicin was sufficient to significantly attenuate the changes in the plasma extravasation response and substance P content observed on the contralateral side. The effectiveness of the capsaicin treatment was confirmed by histological examination. These results strongly suggest that changes observed at a site distant from the location of the nerve injury are dependent on the integrity of capsaicin-sensitive C-fibre afferents within the injured nerve. Furthermore, given that the contralateral nerve has commonly been used as the control for an injury conducted on the homologous nerve or muscle on the opposite side of the body, the underlying assumption being that the contralateral nerve remained unchanged, the present findings emphasize the need for separate groups of control animals which have undergone no surgical procedures.

Elevated substance-P-like immunoreactivity levels in spinal dialysates during the formalin test in normal and diabetic rats

Pharmacologic studies implicate the involvement of substance P in spinal nociceptive processing during the formalin test. However, no direct measurement of the temporal changes in substance P levels within the spinal cord of conscious animals has been reported. Further, dissociation between substance P levels and formalin-evoked nocifensive behavior may exist in diabetic rats, as exaggerated hyperalgesic behavior coexists with reduced peripheral nerve substance P levels. The present study was performed to directly measure the appearance of substance-P-like immunoreactivity (SP-LI) in spinal CSF of conscious, unrestrained rats using microdialysis techniques following injection of formalin into the hindpaw. The effect of diabetes upon formalin-evoked SP-LI levels in spinal CSF dialysates was also determined. In control rats, SP-LI increased in spinal dialysates following formalin injection and levels were maximal 20-30 min after injection, rising to 325% of basal values (p<0.02). Diabetic rats exhibited reduced (p<0.05) SP-LI in their spinal roots, while basal levels in spinal CSF were not different from controls. Formalin-evoked nocifensive behavior was increased in diabetic rats but SP-LI levels in spinal CSF dialysates after paw formalin injection were significantly (p<0.05) attenuated, reaching a maximum of only 161% of basal levels. This was accompanied by attenuated swelling at the formalin injection site and increased thermal response latencies. While increased SP-LI in spinal CSF coincides with phase 2 behavior in the formalin test and may contribute to spinal nociceptive processing during this period, exaggerated spinal substance P release is unlikely to underlie the increased nocifensive behavior seen in diabetic rats.

Central and peripheral expression of neurokinin-1 and neurokinin-3 receptor and substance P-encoding messenger RNAs: peripheral regulation during formalin-induced inflammation and lack of neurokinin receptor expression in primary afferent sensory neurons

The neurokinin-1 receptor and its tachykinin neuropeptide ligand substance P are associated with the mediation of nociception. Substance P released from primary afferent sensory neurons activates neurokinin receptors on both central and peripheral targets that mediate specific aspects of central sensitization and inflammatory function; however, an autoreceptor function for the neurokinin-1 receptor remains highly controversial. Activation of the neurokinin-1 receptor by substance P during chronic nociception increases neurokinin-1 receptor gene expression in the spinal cord. Similarly, neurokinin-3 receptors on peripheral or target tissues or neurons could play an important role in the sensitization of sensory neurons. Therefore, this study (i) mapped the steady-state levels of substance P-encoding preprotachykinin, neurokinin-1 and neurokinin-3 receptor messenger RNAs in central and peripheral tissues including sensory ganglia, and (ii) investigated whether formalin-evoked nociception altered the quantity or location of neurokinin-1 or neurokinin-3 receptor messenger RNAs in the sensory ganglia or inflamed peripheral targets for substance P. Solution hybridization-nuclease protection assays quantified neurokinin receptor messenger RNA levels in central and peripheral tissues from normal and formalin-inflamed rats. High concentrations of the neurokinin-1 receptor were found in whole brain, spinal cord, and peripheral target organs innervated by substance P-containing neurons. Measurable levels of neurokinin-3 receptor messenger RNA were found only in brain, spinal cord and urinary bladder. Results also show that neither neurokinin-1 nor neurokinin-3 receptor messenger RNAs were detectable in primary afferent sensory neurons in the dorsal root ganglia of normal or formalin-inflamed rats. Neurokinin-1 receptor messenger RNA levels were, however, significantly increased in hindpaw tissues inflamed by formalin for 6 h. These results indicate that the plasticity of neurokinin-1 receptor gene expression in non-neuronal peripheral cells could regulate sensitivity to substance P in a manner similar to that in the spinal cord dorsal horn. Altered neurokinin-1 receptor gene expression provides a useful marker of long-term nociceptive activation and may mediate peripheral mechanisms of hyperalgesia and cellular sensitization during inflammation. Importantly, inflammation does not induce a phenotypic change in afferent sensory neurons providing neurokinin receptor targets for the direct sensitization of these neurons by substance P.

Dental innervation: functions and plasticity after peripheral injury

Oral tissues including the periodontal ligament, gingiva, and tooth pulp have a relatively dense sensory innervation and a rich vascular supply. Teeth and supporting tissues are susceptible to tissue injury and inflammation, partly due to lack of collateral blood and nerve supply and to their low compliance. This review focuses on dental nerve functions and adaptive changes in the trigeminal ganglion and tooth pulp after peripheral injuries. An overview of the peptidergic innervation of oral tissues is presented, followed by a discussion of plasticity in neuropeptide expression in trigeminal peripheral neurons after local insults to teeth and peripheral nerve injuries. The functional implications of these adaptive changes are considered, with special reference to nerve regeneration, inflammation, and hemodynamic regulation.

Mechanisms of chronic pain

Chronic pain differs from acute pain in that it serves no useful function, causes suffering, limits activities of daily living, and increases costs of healthcare payments, disability, and litigation fees. Pain perception begins with activation of peripheral nociceptors and conduction through myelinated A delta and unmyelinated C fibers to the dorsal root ganglion. From here, signals travel via the spinothalamic tract to the thalamus and the somatosensory cortex. Modulation of sensory input (i.e., pain) occurs at many levels. Nociceptors are also neuroeffectors, and transmission can be modulated by their cell bodies, which secrete inflammatory mediators, neuropeptides, or other pain-producing substances. Descending pathways from the hypothalamus, which has opioid-sensitive receptors and is stimulated by arousal and emotional stress, can transmit signals to the dorsal horn that modulate ascending nociceptive transmissions. Modulation to alter the perception of pain also can occur at higher centers (e.g., frontal cortex, midbrain, medulla) by opioids, anti-inflammatory agents, as well as antagonists and agonists of neurotransmitters. This article will review our current knowledge of the mechanisms involved in (1) the transduction of tissue injury or disease signals (nociception and nociceptive receptors); (2) the transmission of signals rostrally to the thalamus and higher nervous system centers (involving perception of the quality, location, and intensity of noxious signals); and (3) the modulation of ascending sensory messages at all levels (periphery, spinal cord, and higher centers).

The extraction and assay of substance P in the rat sciatic nerve

Published data for substance P (SP) content of sciatic nerves in control rats vary greatly. This study sought possible reasons for this variability by examining the influence of homogenisation procedures, freezing and selection of left/right nerve or proximal/distal segments. Substance P-like immunoreactivity (SP-LI) content (pg/mg nerve protein +/- SD) was significantly greater in sciatic nerves which had been homogenised using motor-powered equipment (615.4 +/- 146.3) as opposed to a hand-held pestle (445.4 +/- 111.8). Our second investigation revealed that freshly homogenised nerve tissue yielded greater SP-LI (508.8 +/- 88.7) than either tissue snap frozen in liquid nitrogen (307.6 +/- 77.9), snap-frozen and stored at -70 degrees C for 7 days (331.8 +/- 53.5), or tissue allowed to remain in the cadaver for 1 h and subsequently dissected and homogenised immediately (412.6 +/- 105.8). These data also show that storage at -70 degrees C imposes no further losses on those caused by freezing and extraction of frozen tissue. Two further studies indicated no variation between left and right sciatic nerves nor any proximal-distal gradients. Hence, this study illuminated the need for samples to be homogenised using motor-powered equipment immediately upon dissection, followed by SP extraction, for complete avoidance of losses of SP-LI.

Development of an antiserum to the midportion of substance P: applications for biochemical and anatomical studies of substance P-related peptide species in CNS tissues

This report describes the generation and biochemical characterization of a high-affinity antiserum that recognizes an epitope contained in the midportion sequence of substance P, i.e., substance P4-10. Designated A47, this reagent bound a variety of related peptide species containing the substance P4-10 sequence with apparent equipotency. A double radioimmunoassay procedure was developed that utilized A47, in combination with a traditional high-affinity COOH-terminally directed anti-substance P serum, to provide quantification of mature and immature forms of substance P in CNS tissues. Across most rat CNS areas, levels of substance P-like immunoreactivity were consistently 15% higher when monitored by analyses using A47 versus anti-substance P serum. In the dorsal root ganglia, an apparent enhancement in levels of substance P-like immunoreactivity of approximately 40%, when quantified by analyses using A47 versus anti-substance P serum, was observed; this most likely reflected the presence of an active biosynthetic pool of intermediate processing forms of substance P in this tissue. Coordinated HPLC/radioimmunoassay analyses of extracted dorsal root ganglia tissues demonstrated multiple peaks of immunoreactivity corresponding to mature substance P and to several of its precursor forms found in the normal biosynthetic pathway. Of the total recovered HPLC-fractionated immunoreactivities, that corresponding to the putative immediate precursor to substance P, i.e., substance P-glycine, was the predominant peak. In an additional series of HPLC/radioimmunoassay analyses, selective decreases in immunoreactive peaks corresponding to precursor forms of substance P were observed in dorsal root ganglia tissues from rats treated with the neurotoxic agent capsaicin. These results indicated decreased turnover of substance P as a consequence of drug treatment. Finally, initial immunohistochemical analyses employing affinity-purified A47 produced an unusual pattern of labeling characterized by well defined punctate terminal elements within the superficial aspects of the dorsal horn of the spinal cord.

Biochemical characterization and anatomical distribution of a major form of unamidated precursor of substance P in rat brain

Previous work from this laboratory has provided biochemical characterization of several posttranslational processing intermediates of the neuropeptide substance P (SP) in central nervous system (CNS) tissues, including the COOH-terminal glycine-extended dodecapeptide Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-Gly (SP-G). SP-G is a major species of unprocessed SP found in rodent CNS tissues, and is the likely immediate precursor form of SP in the biosynthetic scheme. Here we present extensive characterization of the normal regional distribution of SP-G, as compared to SP, throughout the rat CNS via coordinated biochemical and morphological analyses. By radioimmunoassay (RIA), an approximate 10-fold variation in regional levels of SP-G-like immunoreactivity (SP-G-LI) was observed, ranging from 0.30 pmol/g in the amygdala, to 6.49 pmol/g in the medulla. On a normalized basis, the regional variation of unamidated precursor relative to mature peptide (SP-G-LI/SP-LI molar ratio) ranged from 0.30% in the amygdala to 5.15% in the dorsal root ganglia (DRG). Overall, the highest SP-G-LI/SP-LI ratios were found in DRG, medulla, and spinal cord, i.e. CNS areas associated with primary sensory afferent innervation via capsaicin-sensitive unmyelinated small diameter fibers. In addition, chromatographic and RIA analyses of extracted brain tissues indicated that the quantified immunoreactivities corresponding to SP, SP-G, as well as an additional COOH-terminal Gly-Lys-extended precursor, i.e., SP-G-K, displayed very similar chromatographic behavior as demonstrated for chemically authentic standards. These biochemical data were complemented by immunohistochemical analyses demonstrating a pattern of immunohistochemical staining for the presence of SP-G-LI as a defined subset of SP-LI-containing neural elements. Here, reaction product was localized to dendritic, axonal, and terminal neuronal elements in representative CNS regions of the rat, with relatively high levels of SP-G-LI found within anatomical areas containing a high density of sensory terminal structures. In an attempt to provide correlative functional anatomy, a group of rats was treated with colchicine, in order to differentially localize SP-LI- and SP-G-LI-containing somata after inhibition of axoplasmic transport. Most prominently, colchicine administration engendered immunohistochemical visualization of both SP-LI- and SP-G-LI-positive cells in mesencephalic and brainstem regions associated with stress, pain responses, and central control of autonomic function. Within this context, the coordinate expression of both SP-LI- and of SP-G-LI-positive somata in discrete brain areas is probably indicative of high ongoing rates of tachykinin synthesis coupled to utilization.

Biosynthesis and release of tachykinins from rat sensory neurons in culture

A long-term culture system of dissociated rat dorsal root (DRG) and trigeminal ganglion cells with high cell density has been developed. Two to 3 weeks after plating, the cultures consist of a nearly pure population of sensory neurons, which can be kept for more than 2 months in culture. Cultured neurons synthesize and release the tachykinins substance P (SP) and substance K (SK, neurokinin A) with a time course similar to that observed in vivo. High-pressure liquid chromatography (HPLC) analysis of peptides extracted from neuronal cultures and synthetic tachykinins revealed identical retention characteristics. Northern blot analysis of mRNAs from cultured cells with a specific tachykinin-probe demonstrated that the preprotachykinin-gene is expressed in preparations of both DRG and trigeminal ganglia cells. Depolarizing stimuli such as high potassium (47 mM) evoked a peptide release from cultured neurons in a strictly Ca(++)-dependent manner. Capsaicin, a compound known to stimulate nociceptive sensory neurons, dose-dependently released tachykinins in concentrations as low as 10(-9) M. Only total absence of Ca++ ions from the incubation medium abolished the capsaicin-induced peptide release. Nifedipine, a blocker of voltage-dependent L-type Ca++ channels, completely blocked the potassium-induced release of SP but did not reduce the capsaicin-evoked release. Mediator substances of pain and inflammation, such as bradykinin, serotonin, and histamine, triggered the release of tachykinins from sensory neurons in vitro. These results clearly demonstrate that the neurons characterized express properties similar to those of sensory neurons in vivo and provide model systems for detailed studies of the biosynthesis and release of neuropeptides as well as the participation of sensory neurons in pain and inflammatory reactions.

Localization of substance P-like immunoreactivity in guinea pig vestibular endorgans and the vestibular ganglion

The immunocytochemical distribution of substance P (SP) in guinea pig vestibular endorgans and the vestibular ganglion was investigated. Two kinds of SP-immunoreactive fibers were distinguished. Most were thick, and found around or beneath sensory hair cells. These SP-immunoreactive fibers were distributed predominantly on the slope of the crista and the peripheral region of the macula. By electron microscopy, we confirmed this type of SP-like immunoreactivity to be restricted within primary afferent neurons. Some vestibular ganglion cells also showed SP-like immunoreactivity, suggesting that SP is present in some primary afferent neurons, and is involved in afferent neurotransmission. The characteristic distribution of SP may indicate functional differences within each endorgan. The other group of immunoreactive nerve fibers, varicous thin fibers, could be found in the stroma of vestibular endorgans, nerve trunk, vestibular ganglion, and along blood vessels of the vestibular ganglion. These fibers may have a different origin, and have an influence on blood flow and certain other functions.

GABAB receptor modulation of the release of substance P from capsaicin-sensitive neurones in the rat trachea in vitro

1. The role of gamma-aminobutyric acid (GABA) as an inhibitory transmitter in the central nervous system is well documented. Recently, GABAA and GABAB receptors have been identified in the peripheral nervous system, notably on primary afferent neurones (PAN). We have utilised a multi-superfusion system to investigate the effect of selective GABA receptor agonists and antagonists on the release of substance P (SP) from the rat trachea in vitro. 2. GABA (1-100 microM) did not affect spontaneous release of SP-like immunoreactivity (LI) but caused dose-related inhibition of calcium-dependent potassium (60 mM)-stimulated SP-LI release. The greatest inhibition of 77.7 +/- 18.8% was observed at 100 microM. 3. The inhibitory effect of GABA was mimicked by the GABAB receptor agonist, (+/-)-baclofen (1-100 microM), but not the GABAA receptor agonist, 3-amino-1-propane-sulphonic acid (3-APS, 1-100 microM). Baclofen (100 microM) had no effect on SP-LI release stimulated by capsaicin (1 microM). 4. The inhibitory effect of baclofen (30 microM) was significantly reduced by prior and concomitant exposure to the GABAB receptor antagonist, phacolofen (100 microM) but not the GABAA receptor antagonist, bicuculline (10 microM). Neither antagonist, alone, affected spontaneous or potassium-stimulated SP-LI release. 5. We conclude that activation of pre-synaptic GABAB receptors on the peripheral termini of PANs in the rat trachea inhibits SP-LI release and suggest that GABAB receptor agonists may be of value in the therapeutic treatment of asthma.

Substance P-like immunoreactivity in human prenatal hippocampal formation

Presence and localization of substance P-like immunoreactive neuronal structures in human hippocampal formation during prenatal stages of ontogenesis are reported. In fetuses at 16 and 17 weeks of gestation immunoreactivity is very scarce and represented only by sporadic fibres in Ammon's horn and the entorhinal area. In specimens at 25 and 26 weeks of gestation, more or less intensely labelled perikarya of different morphology are easily detectable in deep layers of Ammon's horn and the hilus of fascia dentata. Immunoreactive beaded fibres are also present at this stage. The possibility of the existence of a substance P-containing extrinsic projection to Ammon's horn is pointed out.

Expression of beta-preprotachykinin mRNA and tachykinins in rat dorsal root ganglion cells following peripheral or central axotomy

The changes in gene expression and protein synthesis induced in neurons by axotomy usually lead to increased production of axon constituents and decreased production of molecules related to neurotransmission. Exceptions to this generalization occur, however, and it is unclear whether the injury itself changes the pattern of synthesis or whether individual mechanisms regulate the synthesis of the various axonal components. We used in situ hybridization histochemistry and immunocytochemistry to compare the changes in L4 and L5 rat dorsal root ganglion neuron levels of preprotachykinin mRNA and tachykinin peptides caused by sciatic nerve injury with those caused by dorsal root injury. Both lesions elicit regeneration, although only the axotomized peripheral processes re-establish functional contact with their targets. In the contralateral, intact dorsal root ganglia approximately 17% of neurons contained detectable levels of both mRNAs and peptides. Sciatic nerve section decreased by 70% the number of neurons labeled for preprotachykinin mRNA at three days post-operatively. Not all cells in the ganglion are axotomized by the sciatic nerve lesion; grain counts over the cells spared by the lesion showed an increased level of labeling, possibly a result of collateral sprouting by these spared cells. By two weeks, the number of cells labeled for preprotachykinin mRNA had decreased to 80% of control levels. The numbers of neurons labeled for tachykinin peptides decreased more slowly and reached approximately 50% of control numbers at two weeks. By six months post-operatively, when regeneration is largely complete, the number of neurons containing both mRNAs and peptides returned to normal. In contrast, dorsal root section did not elicit a decrease in the number of neurons labeled either for the mRNAs or the peptides at any of the post-operative intervals examined. These results indicate that axotomy is not the stimulus that elicits changes in the expression of genes coding for tachykinins. Evidence is considered indicating that interruption of the supply of peripherally derived nerve growth factor may be responsible for the changes in gene expression for tachykinins after axotomy.

High levels of mRNA coding for substance P, somatostatin and alpha-tubulin are expressed by rat and rabbit dorsal root ganglia neurons

Oligonucleotide probes complementary to alpha-tubulin, preprotachykinin A (PPT A), preprosomatostatin (PPSOM), and preproarginine-vasopressin (PPAVP) mRNA were hybridized to sections of rat and rabbit brain and dorsal root ganglia (DRG) at all spinal levels. Approximately 100% of the DRG neurons in the rat and rabbit express alpha-tubulin mRNA, 20-30% express PPT A mRNA and 5-17% express PPSOM mRNA. Whereas neurons which express PPSOM mRNA are of relative uniform size, the neurons which express PPT A mRNA segregate into two broad groups. One group is composed of smaller neurons (200-2,000 microns 2) which contain an extremely dense concentration of PPT A mRNA. The second group is composed of larger neurons (2,000-3,500 microns 2) which contain a moderate concentration of PPT A mRNA. PPAVP mRNA is present in very high concentrations in the paraventricular and supraoptic nucleus of the rat hypothalamus but is not detected in any DRG neurons. In both the rat and the rabbit the density of PPT A and PPSOM mRNA is high in individual DRG neurons in comparison to PPT A and PPSOM mRNA levels contained in most forebrain neurons. These results suggest that although the level of neuropeptide present in DRG neurons is relatively low in comparison to other brain areas, the rate of sensory neuropeptide synthesis and turnover, as reflected by mRNA content, is extremely high.

Acupuncture and sensory neuropeptides increase cutaneous blood flow in rats

The effect on blood flow of electro-acupuncture (EA) injection of substance P (SP) and calcitonin gene-related peptide (CGRP) was studied in musculocutaneous flaps in the rat, using laser Doppler flowmetry. The circulatory border was estimated before and after treatment. It was shown that treatment with EA increased the blood flow moving the circulatory border distally 66% after a treatment. Injection of NaCl into the dorsal central vein of the flap resulted in no increase in blood flow whereas SP 10(-9) M and CGRP 10(-9) M increased the blood flow so that the circulatory border moved distally 31% and 49%, respectively. It is suggested that the effect of EA on blood flow is similar to the effect achieved by injecting CGRP and SP.

Cell type and conduction velocity of rat primary sensory neurons with substance P-like immunoreactivity

A double labelling immunohistochemical study of rat L4 dorsal root ganglia was made with an anti-substance P antibody and with an antibody, RT97, which specifically labels the light cell population. Substance P-like immunoreactivity was found in 30% of the small dark neurons and 10% of the light neurons. Of the neurons with substance P-like immunoreactivity, 30% were light neurons and 70% were small dark neurons. A study of electrophysiologically characterized neurons in lumbar dorsal root ganglia with dye injection revealed substance P-like immunoreactivity in neurons with conduction velocities ranging from 0.5 to 9.5 m/s. It was seen in 50% of C-fibre neurons, in 20% of A delta-fibre neurons, and in no A alpha/beta neurons. Overall, substance-P-like immunoreactivity was found in 10% of A-fibre neurons sampled.

Dipeptidylpeptidase IV activity in Meissner corpuscles of rhesus monkey and its possible function

Histochemical investigation by means of light and electron microscopy revealed the presence of dipeptidylpeptidase IV activity in Meissner corpuscles of macaque glabrous skin. The enzyme activity was found in fibroblast-like cells forming an incomplete capsule around the Meissner corpuscle. Distinct electron-dense reaction product due to dipeptidylpeptidase IV activity was consistently localized in the plasma membrane of specialized Schwann cells enveloping the unmyelinated portion of sensory axons. Their axolemma was devoid of dipeptidylpeptidase IV reaction product. The membrane-bound dipeptidylpeptidase IV activity presented here and the occurrence of substance P-containing nerve fibers in primate Meissner corpuscles referred to elsewhere, suggest the possible functional involvement of the enzyme in the production of substance P fragments, influenced in different ways by the axon proper and its surrounding Schwann cells.

Substance P release from knee joint afferent terminals: modulation by opioids

Perfusate obtained from the intra-articular space of the knee (100 microliters/min) in the halothane-anesthetized cat under resting conditions shows no detectable substance P-like immunoreactivity (SP-LI: less than 2 pg/20 min). Antidromic activation by electrical stimulation of the sciatic nerve at stimulus intensities which evoke activity in A beta/A delta/C but not A beta fibers or the local administration of capsaicin (10(-4) M) into the intra-articular perfusate results in a stimulus-dependent increase in the levels of SP-LI in the perfusate. This release is diminished in a naloxone-(1 mg/kg, i.v.) reversible fashion by sufentanil, D-Ala2-D-Leu5-enkephalin, and D-Pen2-D-Pen5-enkephalin, but not by U50488H (10(-4) M) added to the intra-articular perfusate. These observations thus suggest that the peripheral stores of SP-LI in small primary afferents are subject to release by antidromic activity and this release is subject to modulation by mu/delta receptors on these peripheral terminals.

Substance P and somatostatin content and transport in the vagus and sciatic nerves of the aging Fischer 344 rat

The two widely distributed neuropeptides, substance P (SP) and somatostatin (SS), are synthesized in cell bodies of the sensory ganglia of the vagus and sciatic nerves and transported bidirectionally toward the central nervous system and sites of sensory innervation. In this study, the content of both peptides was measured in the vagus and sciatic nerves of Fischer 344 rats aged 4, 12 and 25 months. In addition, as an indicator of biosynthesis within the sensory ganglia, the quantity of neuropeptide transported during 22 hours in a peripheral orthograde direction was measured using the ligation technique in animals age 12, 18 and 25 months. The content and transported quantity of SP was unchanged or slightly increased in both nerves as a function of age. Somatostatin content was unchanged and transport increased in the vagus of older rats. In contrast, in the sciatic nerve, SS content was reduced by more than 30% in older rats (p less than 0.01); transported somatostatin was proportionately reduced (p less than 0.05). These findings demonstrate that neuropeptide levels in the sensory vagus are not reduced as a function of age. Somatostatinergic dorsal root ganglion neurons may be selectively vulnerable in the aging Fischer rat.

Axonal transport and tissue contents of substance P in rats with long-term streptozotocin-diabetes. Effects of the aldose reductase inhibitor 'statil'

This study examined the axonal transport of substance P-like immunoreactivity (SPLI) and its content in dorsal root ganglion, trigeminal ganglion, stomach and ileum of non-diabetic rats and two groups of rats with streptozotocin-induced diabetes of 9 months duration. One diabetic group received the aldose reductase inhibitor 'Statil' throughout the period of study. To reduce morbidity all diabetic animals were given twice-weekly injections of a long-acting insulin which restricted weight loss but did not prevent regular and severe hyperglycaemia. Axonal transport of SPLI was studied by measurement of accumulation at 12 h ligatures on the left sciatic nerve. There were no differences between the 3 groups either in the calculated anterograde and retrograde mean rates of accumulation (ranges 6.0 to 7.6 and 0.38 to 0.72 mm/h respectively) or mobile fractions of SPLI (means from 0.54 to 0.58). There were, however, marked reductions in anterograde and retrograde accumulations of SPLI in the constricted nerves of the 'untreated' diabetics (respectively 57 and 33% of controls; P less than 0.01 for both). In the 'Statil'-treated rats these deficits were attenuated (80 and 75% of controls). Diabetes also reduced the SPLI content of unligated sciatic nerve and trigeminal ganglion (65 and 75% of controls). 'Statil' prevented the deficit in the ganglion, but not in the nerve. 'Statil' treatment prevented the myo-inositol depletion and attenuated the sorbitol and fructose accumulation seen in the sciatic nerves of the untreated diabetic animals suggesting effective inhibition of aldose reductase in this tissue. The total SPLI content of the stomach and 1-cm segments of ileum were unaltered in the diabetic animals but due to the increased weights of these tissues the SPLI content per unit weight was reduced. These changes were unaffected by 'Statil'.

Effect of cutting or crushing the rat sciatic nerve on synthesis of substance P by isolated L5 dorsal root ganglia

Following cutting or crushing the rat sciatic nerve, synthesis of substance P by L5 dorsal root ganglia in vitro was reduced respectively to 20 and 40 per cent of control values. By day 64 the ability to synthesise substance P had been fully restored in crushed neurones but in cut neurones remained at a low level. We conclude that substance P synthesis is a more sensitive index of the effect of nerve injury than is substance P content and further that regenerating axons are able to support substance P synthesis before they reach their target tissue.

The contribution of capsaicin-sensitive innervation to activation of the spinal vesico-vesical reflex in rats: relationship between substance P levels in the urinary bladder and the sensory-efferent function of capsaicin-sensitive sensory neurons

In acute spinal rats (C2-C3) the transvesical infusion of saline activates a vesico-vesical excitatory reflex (Brain Res., 380 (1986) 83-93). In bladders containing a subthreshold amount of fluid the topical application of capsaicin on the outer surface of the bladder dome activated this spinal reflex and also produced a transient rise in blood pressure and heart rate. The effects of systemic capsaicin desensitization (50 mg/kg s.c. 5 min, 60 days before) on the sensory (activation of the spinal vesico-vesical reflex) and 'efferent' (tetrodotoxin-insensitive capsaicin-induced contraction) functions mediated by the capsaicin-sensitive sensory fibers were correlated to changes in substance P-like immunoreactivity (SP-LI) content of the urinary bladder in adult rats. Blockade of both sensory and efferent functions was observed at a time (60 min from capsaicin administration) when the SP-LI content of the urinary bladder was unaffected. Four days after capsaicin desensitization the SP-LI levels of the bladder are almost depleted indicating that the neuropeptide(s) are entirely stored in sensory structures. At this time the sensory-efferent functions mediated by these fibers are still blocked. At 15-60 days from systemic capsaicin desensitization there was a progressive, time-related recovery of SP-LI levels in the bladder as well as of the sensory-efferent functions. These findings indicate a role of the capsaicin-sensitive innervation of the urinary bladder in activating the spinal vesico-vesical reflex. The present findings suggest that measurement of SP-LI levels in the rat bladder may be a useful biochemical index for monitoring the function(s) of the capsaicin-sensitive, peptidergic sensory neurons.

Substance P synthesis and transport in explants of nodose ganglion/vagus nerve: effects of double ligation, 2-deoxyglucose, veratridine, and ouabain

Substance P (SP), the widely distributed undecapeptide, is synthesized in cell bodies of vagal sensory ganglia and transported bidirectionally toward the CNS and thoracic and abdominal viscera. In explants of the guinea pig inferior (nodose) vagal sensory ganglion and attached 2 cm of distal vagus nerve, SP is synthesized within the ganglion and transported predominantly distally. The quantity of distal transport is similar to that observed in vivo and provides an index of ongoing synthesis within the ganglion. In this report, the model is further characterized. Double ligation of the explant distal to the ganglion demonstrates that all the transported peptide is derived from the ganglion; there is no evidence of intraaxonal processing of peptide precursor. Approximately 50% of the peptide is in a rapid transport vs. an apparent stationary compartment. Not only transport, but also synthesis, of SP was blocked by 20 mM colchicine. Ongoing SP biosynthesis is dependent on a nutrient medium [medium 199 (M-199)] and is partially inhibited with added fetal bovine serum (FBS; 10%): total explant content in M-199/FBS vs. M-199, 1,785 +/- 101 (n = 8) vs. 2,254 +/- 123 pg (n = 9); p less than 0.02. Addition of 2-deoxyglucose (2-DG) decreased both total SP synthesis and transport (total explant content for 2-DG vs. control, 986 +/- 94 vs. 1,391 +/- 111; p less than 0.05). Medium supplemented with glucose to a final concentration of 600 mg/100 ml or with glucose (300 mg/100 ml) with or without insulin (50 ng/ml) did not alter explant SP content or transport. Veratridine (5 X 10(-6) M) inhibited both SP synthesis and transport; ouabain (10(-4) M) also inhibited synthesis, but less so transport. Tetrodotoxin reversed the effects of veratridine. These studies demonstrate the usefulness of this model, which can examine factors regulating both synthesis and transport of sensory neuropeptides in vitro. The results suggest that SP synthesis/transport may be under tonic inhibition, perhaps by both neural and humoral mechanisms.

Pathway-specific patterns of the co-existence of substance P, calcitonin gene-related peptide, cholecystokinin and dynorphin in neurons of the dorsal root ganglia of the guinea-pig

The co-existence of immunoreactivities to substance P (SP), calcitonin gene-related peptide (CGRP), cholecystokinin (CCK) and dynorphin (DYN) in neurons of the dorsal root ganglion (DRG) of guinea-pigs has been investigated with a double-labeling immunofluorescence procedure. Four main populations of neurons could be identified that contained different combinations of these peptides and had distinctive peripheral projections: (Neurons that contained immunoreactivity to SP, CGRP, CCK and DYN were distributed mainly to the skin. Neurons with immunoreactivity to SP, CGRP and CCK, but not DYN, were distributed mainly to the small blood vessels of skeletal muscles. Neurons with immunoreactivity to SP, CGRP and DYN, but not CCK, were distributed mainly to pelvic viscera and airways. Neurons containing immunoreactivity to SP and CGRP, but not CCK and DYN, were distributed mainly to the heart, systemic blood vessels, blood vessels of the abdominal viscera, airways and sympathetic ganglia. Other small populations of DRG neurons containing SP, CGRP or CCK alone also were detected. Perikarya containing these combinations of neuropeptides were not found in autonomic ganglia. The peripheral axons of neurons containing immunoreactivity to at least SP and CGRP were damaged by chronic treatment with capsaicin. However, some sensory neurons containing CCK alone were not affected morphologically by capsaicin. These results clearly show that individual DRG neurons can contain many different neuropeptides. Furthermore, the combination of neuropeptides found in any particular neuron is related to its peripheral projection.

Neurochemical characteristics of a novel dorsal root ganglion X neuroblastoma hybrid cell line, F-11

We investigated the properties of the novel dorsal root ganglion (DRG) hybrid cell line F-11 to see how closely these cells resembled normal DRG cells. Under normal growth conditions, F-11 cells appeared to contain several short neurite-like processes. However, these cells could also be grown under conditions in which they showed a much more extensive neuronal morphology, exhibiting many long neurites. Several differentiated features of DRG cells were present on F-11 cells. These included the presence of delta-opioid receptors, receptors for prostaglandins and bradykinin, and dihydropyridine-sensitive calcium channels. F-11 cells also synthesized and released a substance P-like compound, as determined by immunoreactivity. Both the number of bradykinin receptors and the voltage-sensitive calcium influx increased on cell differentiation. Opioid agonists (delta-specificity) were found to decrease cyclic AMP levels in F-11 cells in a naloxone- and pertussis toxin-reversible fashion. Bradykinin stimulated the synthesis of inositol-1,4-bisphosphate and inositol-1,4,5-trisphosphate. Ca2+ channel agonists stimulated voltage-sensitive Ca2+ influx in a dose-dependent, stereospecific manner, whereas Ca2+ channel antagonists inhibited Ca2+ influx. F-11 cells should, therefore, prove useful as models for authentic DRG neurons.

A semiautomated analysis method for catecholamines, indoleamines, and some prominent metabolites in microdissected regions of the nervous system: an isocratic HPLC technique employing coulometric detection and minimal sample preparation

The application of a commercially available coulometric electrochemical detector to the automated HPLC analysis of some monoamines and their metabolites in microdissected areas of the rat nervous system is described. Apart from the stability and high sensitivity of the system, other appealing features of the technique are the facile sample preparation and long-term sample storage characteristics which show minimal analyte degradation. Basal values of some regional monoamine and metabolite concentration are listed together with a brief appendix that serves as a user's guide to the operation and maintenance of the detection system.

A quantitative analysis of the interrelationships between subpopulations of rat sensory neurons containing arginine vasopressin or oxytocin and those containing substance P, fluoride-resistant acid phosphatase or neurofilament protein

In rat L5 dorsal root ganglia 50% of neurons contained arginine vasopressin-like immunoreactivity and 38% oxytocin-like immunoreactivity, the oxytocin entirely coexisting with the arginine vasopressin. Staining of alternate mirror-image sections with RT97 (an antibody to neurofilament protein, and a marker for large light neurons) and with arginine vasopressin antiserum showed that the two were entirely complementary, thus establishing arginine vasopressin as a marker for all small dark neurons. Mirror-image staining also showed that neurons containing substance P-like immunoreactivity and those containing fluoride-resistant acid phosphatase activity were each contained within the arginine vasopressin-positive population. Arginine vasopressin-like immunoreactivity was axonally transported in the dorsal root and (in greater quantity) in sciatic nerve. Arginine vasopressin-like immunoreactivity was present also in laminae I and II of the dorsal horn of the spinal cord and this reactivity was absent in animals which had been treated neonatally with capsaicin, suggesting that it was contained in primary afferent terminals. These results are discussed in terms of their implications for the classification of primary afferent neurons and of a possible physiological role for arginine vasopressin in these neurons.

Innervation of guinea pig heart by neurons sensitive to capsaicin

To determine the origin of non-vagal afferent fibers innervating the heart of guinea pigs, capsaicin was injected into the ventricular myocardium to induce depletion of substance P (SP). The lower cervical, upper thoracic and lumbar spinal ganglia, as well as the left atrium and base of ventricles, were assayed for SP depletion by using the enzyme-linked immunosorbent assay (ELISA) and immunohistochemical procedures. Capsaicin affected spinal ganglia from the 3 regions differently. The substance P level in lumbar spinal ganglia remained fairly constant, while the level of SP from cervical and thoracic regions declined significantly. At the maximal depletion dosage (173 micrograms of capsaicin/kg), SP concentration decreased 72.3% in cervical spinal ganglia, 45.5% in thoracic ganglia and 56.1% in the atrium. The lack of SP depletion in lumbar ganglia indicates that capsaicin acted locally on cardiac afferents rather than systemically. Data from this study suggest that capsaicin-sensitive neurons of the heart have cell bodies in the lower cervical spinal ganglia as well as in the upper thoracic spinal ganglia.