Substance P- and calcitonin gene-related peptide immunoreactivity in primary afferent neurons of the cat's knee joint

Chemical Coding of Sensory Neurons Supplying the Hip Joint Capsule in the Sheep

Immunohistochemical properties of nerve fibres supplying the joint capsule were previously described in many mammalian species, but the localization of sensory neurons supplying this structure was studied only in laboratory animals, the rat and rabbit. However, there is no comprehensive data on the chemical coding of sensory neurons projecting to the hip joint capsule (HJC). The aim of this study was to establish immunohistochemical properties of sensory neurons supplying HJC in the sheep. The study was carried out on 10 sheep, weighing about 30-40 kg. The animals were injected with a retrograde neural tracer Fast Blue (FB) into HJC. Sections of the spinal ganglia (SpG) with FB-positive (FB+) neurons were stained using antibodies against calcitonin gene-related peptide (CGRP) substance P (SP), pituitary adenylate cyclase-activating peptide (PACAP), nitric oxide synthase (n-NOS), neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), Leu-5-enkephalin (Leu-Enk), galanin (GAL) and vesicular acetylcholine transporter (VACHT). The vast majority of FB+ neurons supplying HJC was found in the ganglia from the 5th lumbar to the 2nd sacral. Immunohistochemistry revealed that most of these neurons were immunoreactive to CGRP or SP (80.7 ± 8.0% or 56.4 ± 4.8%, respectively) and many of them stained for PACAP or GAL (52.9 ± 2.9% or 50.6 ± 19.7%, respectively). Other populations of FB+ neurons were those immunoreactive to n-NOS (37.8 ± 9.7%), NPY (34.6 ± 6.7%), VIP (28.7 ± 4.8%), Leu-Enk (27.1 ± 14.6) and VACHT (16.7 ± 9.6).

A preclinical physiological assay to test modulation of knee joint pain in the spinal cord: effects of oxycodone and naproxen

Sensory processing in the spinal cord during disease states can reveal mechanisms for novel treatments, yet very little is known about pain processing at this level in the most commonly used animal models of articular pain. Here we report a test of the prediction that two clinically effective compounds, naproxen (an NSAID) and oxycodone (an opiate), are efficacious in reducing the response of spinal dorsal horn neurons to noxious knee joint rotation in the monosodium iodoacetate (MIA) sensitized rat. The overall objective for these experiments was to develop a high quality in vivo electrophysiology assay to confidently test novel compounds for efficacy against pain. Given the recent calls for improved preclinical experimental quality we also developed and implemented an Assay Capability Tool to determine the quality of our assay and ensure the quality of our results. Spinal dorsal horn neurons receiving input from the hind limb knee joint were recorded in anesthetized rats 14 days after they were sensitized with 1 mg of MIA. Intravenous administered oxycodone and naproxen were each tested separately for their effects on phasic, tonic, ongoing and afterdischarge action potential counts in response to innocuous and noxious knee joint rotation. Oxycodone reduced tonic spike counts more than the other measures, doing so by up to 85%. Tonic counts were therefore designated the primary endpoint when testing naproxen which reduced counts by up to 81%. Both reductions occurred at doses consistent with clinically effective doses for osteoarthritis. These results demonstrate that clinically effective doses of standard treatments for osteoarthritis reduce pain processing measured at the level of the spinal cord for two different mechanisms. The Assay Capability Tool helped to guide experimental design leading to a high quality and robust preclinical assay to use in discovering novel treatments for pain.

The innervation of synovium of human osteoarthritic joints in comparison with normal rat and sheep synovium

OBJECTIVE

To study whether osteoarthritis (OA) in the knee is associated with a change of the innervation pattern in the synovial layer.

DESIGN

In synovial tissue from the normal knee joint of rat and sheep we studied the presence of vessels and of nerve fibres using transmission electron microscopy and immunohistochemistry. Synovial material was also obtained from patients who underwent total knee replacement surgery. This material was examined for inflammatory changes, and the presence of vessels and nerve fibres was assessed.

RESULTS

The synovium in the parapatellar region of the normal knee joint of rat and sheep exhibited a dense capillary and neuronal network. It was entered by calcitonin gene-related peptide containing sensory fibres and tyrosine hydroxylase-positive sympathetic nerve fibres. Synovial material from patients with knee OA exhibited different degrees of inflammation. Synovial material without inflammation exhibited a similar vascular and neuronal network as the normal knee joint from rat and sheep. However, in synovium with inflammatory changes we found a significant decrease of nerve fibres in depth ranges close to the synovial lining layer depending on the degree of inflammation whereas deeper regions were less affected.

CONCLUSIONS

Inflammatory changes in the synovium of OA joints are associated with a massive destruction of the capillary and neuronal network which is present in normal synovium. Due to the disappearance of the sensory fibres it is unlikely that OA pain is initiated directly in the synovium. The loss of normally innervated vascularisation may have multiple consequences for the physiological functions of the synovium.

A comparison of the short-term effects of a botulinum toxin type a and triamcinolone acetate injection on adhesive capsulitis of the shoulder

OBJECTIVE

To evaluate the short-term clinical effects of the intra-articular injection of botulinum toxin type A (BoNT-A) for the treatment of adhesive capsulitis.

METHODS

A prospective, controlled trial compared the effects of intra-articular BoNT-A (Dysport; 200 IU, n=15) with the steroid triamcinolone acetate (TA; 20 mg, n=13) in patients suffering from adhesive capsulitis of the shoulder. All patients were evaluated using a Numeric Rating Scale (NRS) of the pain intensity and a measurement of the range of motion (ROM) at baseline (before treatment) and at 2, 4, and 8 weeks post-treatment.

RESULTS

The NRS at 2 weeks (BoNT-A vs. TA; 5.0 vs. 5.2), 4 weeks (4.1 vs. 4.9) and 8 weeks (3.8 vs. 4.6) of both treatment groups were significantly lower than that measured at baseline (7.4 vs. 7.6). The ROM of patients' shoulders increased significantly from baseline in both treatment groups. There was no significant difference in the NRS of pain intensity or the ROM between the two groups. Reduction in the pain intensity score was maintained for 8 weeks post-injection in both groups. There were no significant adverse events in either treatment group.

CONCLUSION

The results suggest that there are no significant short-term differences between the intra-articular injections of BoNT-A and TA. Although BoNT-A has a high cost, it may be used as a safe alternative of TA to avoid the steroid-induced side effects or as a second-line agent, for patients who have failed to respond to the current treatments.

Influence of capsaicin on visceral hyperalgesia and its mechanism

Capsaicin (CAP) has multiple pharmacological actions, and researches have been centered on its effect on visceral hyperalgesia (VHL). Relevant studies have shown that low doses of CAP may cause VHL, while high doses can inhibit VHL. This kind of mechanism may be associated with vanilloid receptor subtype 1 (VR1) phosphorylation and dephosphorylation, substance P (SP), calcitonin-gene-related peptide (CGRP) and protease-activated receptor 2 (PAR2). CAP may be promising as a new drug for VHL treatment.

Substance P and its receptors in bone metabolism

Accumulating evidence on bone physiopathology has indicated that the skeleton contains numerous nerve fibers and its metabolism is regulated by the nervous system. Until now, more than 10 neuropeptides have been identified in bone. Substance P (SP) is a neuropeptide released from axons of sensory neurons, belongs to the tachykinin family and plays important roles in many physiological and pathological processes by acting as a neurotransmitter, neuromodulator, or trophic factor. It activates signal transduction cascades by acting on the neurokinin-1 receptor (NK(1)-R). Previous studies have confirmed that the SP-immunoreactive (IR) axons innervate bone and adjacent tissues, and that their density varies depending on the regions and physiological or pathological conditions. Over the past few decades, it has been found that SP takes part in the stimulation of bone resorption, and its receptors have been demonstrated to be located in osteoclasts. Notably, in studies of skeletal ontogeny, SP-IR axons have been shown to appear at an early stage, mostly coinciding with the sequence of long bone mineralization. These findings, together with data obtained from chemically or surgically targeted nerve deletions, strongly suggest that SP is a potent regulator of skeletal physiology. The specific distribution of SP-IR nerve fibers, the different amount of SP within regions, and the various levels of expression of NK(1)-R in targeted cells presumably related to and participate in bone metabolism. It can be predicted that the indirect roles of SP through other cytokines are as important as its direct roles in bone metabolism. This new regulating pathway of bone metabolism would have enormous implications in skeletal physiology and the relevant research might present curative potentials to a spectrum of bone diseases.

Polyethylene particle-induced bone resorption in substance P-deficient mice

Aseptic loosening is the major cause of total joint replacement failure. Substance P (SP) is a neurotransmitter richly distributed in sensory nerve fibers, bone, and bone-related tissue. The purpose of this study was to investigate the potential impact of SP on bone metabolism in polyethylene particle-induced osteolysis. We utilized the murine calvarial osteolysis model based on ultrahigh molecular weight polyethylene (UHMWPE) particles in 14 wild-type mice (C57BL/J6) and 14 SP-deficient mice. Group 1 (C57BL/J 6) and group 3 (SP-knockout) received sham surgery, and group 2 (C57BL/J6) and group 4 (SP-knockout) were treated with polyethylene particles. Analytical methods included three-dimensional micro-computed tomographic (micro-CT) analysis and histomorphometry. Bone resorption was measured within the midline suture. The number of osteoclasts was determined by counting the tartrate-resistant acid phosphatase-positive cells. UHMWPE-particle treated SP-deficient mice showed significantly reduced osteolysis compared to wild-type mice, as confirmed by histomorphometry (P < 0.001) and micro-CT (P = 0.035). Osteoclast numbers were significantly reduced in groups 3 and 4 compared to groups 1 and 2 (P < 0.001). Unexpectedly, SP-deficient mice (group 3) showed a significantly increased absolute bone mass compared to wild-type mice (group 1) (P = 0.02). The findings of our murine calvaria model lead to the assumption that SP is a promoter in particle-induced osteolysis. The pathophysiology of aseptic loosening is complex, and neuropeptides are not solely responsible for the progress of implant loosening; however, we conclude that there could be coherence between neurotransmitters and particle-induced osteolysis in patients with aseptic loosening.

Arthritis and pain. Neurogenic origin of joint pain

Arthritis pain affects millions of people worldwide yet we still have only a limited understanding of what makes our joints ache. This review examines the sensory innervation of diarthroidal joints and discusses the neurophysiological processes that lead to the generation of painful sensation. During inflammation, joint nerves become sensitized to mechanical stimuli through the actions of neuropeptides, eicosanoids, proteinase-activated receptors and ion channel ligands. The contribution of immunocytes to arthritis pain is also reviewed. Finally, the existence of an endogenous analgesic system in joints is considered and the reasons for its inability to control pain are postulated.

Involvement of DRG11 in the development of the primary afferent nociceptive system

During development, dorsal root ganglia (DRG) neurons differentiate in various subpopulations, nociceptive neurons belonging in the small-diameter class. This study addresses the role played by DRG11, a transcription factor expressed in the spinal area of projection of small-diameter DRG neurons, in the development of the primary afferent system. The various subclasses of DRG neurons were compared between wild-type and Drg11(-/-) mice at embryonic and postnatal life. In Drg11(-/-) mice, numbers of small peptidergic and non-peptidergic DRG neurons were decreased at P7 concomitant with abnormal cell death. Innervation by small DRG neurons was impaired in cutaneous, visceral and deep tissues. Large DRG neurons were not affected. The data point to a role for DRG11 in early postnatal survival of normally generated small primary afferent neurons innervating various kinds of peripheral tissues, which would explain the nociceptive deficits observed in Drg11-null mutant mice.

Localization of SP- and CGRP-immunopositive nerve fibers in the hip joint of patients with painful osteoarthritis and of patients with painless failed total hip arthroplasties

Using immunohistochemical methods we determined the presence of SP- and CGRP-immunopositive nerve fibers in the hip joint of patients with femoral neck fracture (controls, group 1), painful osteoarthritis (group 2), and painless failed total hip arthroplasties (group 3). Immunoreactive nerve fibers were found in the soft tissue of the fossa acetabuli as well as in the subintimal part of the synovial layer in the hip joint capsule of groups 1 and 2. In the capsule of controls the innervation density had a median of 5.7fibers/cm(2) for CGRP-ir and 3.2fibers/cm(2) for SP-ir afferents. In the osteoarthritic group, the density significantly increased to a median of 15.6fibers/cm(2) for CGRP-ir and 8.2fibers/cm(2) for SP-ir neurons (p=0.05). Patients with failed hip arthroplasties completely lacked these neuropeptide containing afferents. Innervation density in the fossa acetabuli of osteoarthritc patients showed a median of 14.1fibers/cm(2) for CGRP-ir and 5.9fibers/cm(2) for SP-ir afferents. From these data we assume that the hip joint capsule and the soft tissue of the fossa acetabuli are important triggers of nociception. This is supported by the fact, that patients with loosened total hip arthroplasties, where we failed to detect SP- and CGRP-immunoreactive fibers, did not feel pain. The upregulation of SP- and CGRP-positive neurons in response to arthritic stages suggests a mechanism involving neuropeptides in the maintenance of a painful degenerative joint disease and in mediating noxious stimuli from the periphery. Furthermore, these findings help to explain clinical observations, such as effectiveness of local therapy to control hip pain with intraarticular injection, synovectomy and denervation procedures.

Changes of the neuropeptides content and gene expression in spinal cord and dorsal root ganglion after noxious colorectal distension

Visceral pain/hypersensitivity is a cardinal symptom of functional gastrointestinal disorders. With their peripheral and central (spinal) projections, sensory neurons in the dorsal root ganglia (DRG) are the "gateway" for painful signals emanating from both somatic and visceral structures. In contrast to somatic pain, the neurochemical pathways involved in visceral pain/hypersensitivity have not been well studied. We hypothesized the neuropeptide changes in spinal cord and DRG during visceral pain would mirror similar changes in somatic nociception. Noxious (painful) colorectal distension (CRD) was done by distending a rectal balloon up to 60 mm Hg phasically for 1 h in Sprague-Dawley rats. The spinal content of calcitonin gene-related peptide (CGRP), substance P (SP), galanin and vasoactive intestinal peptide (VIP) as well as their mRNAs in DRG were measured at 0, 4 and 24 h after the CRD. Visceromotor reflex (VMR) was measured by recording the electromyogram at the abdominal muscle in response to CRD. Distal colorectum was removed for evaluating the presence of inflammation. No significant evidence of histological inflammation was seen in the colonic mucosa/submucosa after repeated CRD, which is confirmed by myeloperoxidase assay. The spinal content of CGRP and SP decreased significantly 4 h after CRD, while galanin and VIP levels increased gradually and reached highest level at 24 h (p<0.05). The mRNAs in DRG of the neuropeptides were significantly upregulated after CRD (p<0.05). VMR recording showed the rat's colon became hypersensitive 4 h after CRD, a sequence parallel to the spinal changes of CGRP and SP in timeframe. Noxious mechanical distension of the colorectum causes an acute change in the spinal levels of excitatory neurotransmitters (CGRP and SP), probably reflecting central release of these peptides from sensory neurons and contributing to the hypersensitivity following the noxious CRD. This is followed by a slower change in the levels of the inhibitory neurotransmitter galanin and VIP. Such stimulation results in significant alternation of the gene expression in DRG, reflecting the plasticity of the neuronal response. In the absence of visceral inflammation, the aforementioned neuropeptides are important mediators in the processing of visceral pain/hypersensitivity.

Neurogenic Aspects of Inflammation

The relationship between the inflammatory process and the nervous system is twofold. The nervous system is activated by inflammation which causes inflammatory pain and impaired motor function. Conversely, the nervous system acts back on the peripheral process. This is achieved by output systems at different levels, including primary afferent fibers (neurogenic inflammation), spinal cord (reflexes), and the brain (eg, neuroendocrine functions). This article first addresses the activation of the nociceptive system by inflammation; the second part describes the effects of the nervous system on inflamed tissue.

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.

Tachykinins and tachykinin receptors in bone

Tachykinins are neuropeptides that are widely distributed in the body and function as neurotransmitters and neuromodulators. Five tachykinin subtypes: substance P (SP), neurokinin A, neurokinin B, neuropeptide K, and neuropeptide gamma; and three receptor subtypes: neurokinin-1, -2, and -3 receptors, have been identified. SP was the first peptide of the tachykinin family to be identified. It is considered to be an important neuropeptide, and to function in the nervous system and intestine. However, recent advances in the analysis of SP receptors, particularly neurokinin-1 receptors (NK(1)-Rs) that have high affinity for SP, have demonstrated that NK(1)-Rs are distributed not only in neurons and immune cells, but also in other peripheral cells, including bone cells. This article reviews the current understanding of the distribution of SP and other tachykinins in bone, and the function of tachykinins, through neurokinin receptors. The distribution of tachykinin-immunoreactive axons and neurokinin receptors suggests that tachykinins may directly modulate bone metabolism through neurokinin receptors.

Arthritic calcitonin/alpha calcitonin gene-related peptide knockout mice have reduced nociceptive hypersensitivity

Peripheral inflammation induced with a knee joint injection of a mixture of kaolin/carrageenan (k/c) produces primary and secondary hyperalgesia. Inflammatory pain is thought to involve a variety of transmitters released from nerve terminals, including amino acids, substance P (SP) and calcitonin gene-related peptide (CGRP). In the present study, mice deficient in the calcitonin/alpha CGRP gene (CGRP(-/-)) displayed normal responses to noxious stimuli. However, the CGRP knockout mice failed to demonstrate development of secondary hyperalgesia after induction of knee joint inflammation in two tests that assess central sensitization, through testing at sites remote from the primary insult. Nociceptive behavioral responses were assessed using the hot-plate test and paw withdrawal latency (PWL) to radiant heat applied to the hindpaw. The CGRP(-/-) mice showed no signs of secondary hyperalgesia after development of knee joint inflammation, while the expected significant decrease in the PWL was observed in the CGRP(+/+) mice as control. The CGRP(-/-) mice also had a prolonged rather than a shortened response latency in the hot-plate test 4 h after knee joint injection of k/c. Immunohistological study showed that CGRP-like immunoreactivity (CGRP-LI) was absent in the spinal cord and dorsal root ganglia taken from the CGRP(-/-) mice. These results indicate that endogenous CGRP plays an important role in the plastic neurogenic changes occurring in response to peripheral inflammatory events including the development of nociceptive behaviors.

Neurovascular plasticity in the knee joint of an arthritic mouse model

Lower numbers of neuropeptide-containing fibers in arthritic joints have been found as compared to control joints. This may be the result of fiber depletion, necrosis of fibers, or proliferation of soft tissues without neural sprouting. To discriminate between these possibilities, we studied the relationships between soft tissue proliferation, changes in vascularity of synovial tissues, and changes in joint innervation during arthritis. Arthritis was induced in the knee joint of mice by a single subpatellar injection of methylated bovine serum albumin after previous immunization. Antibodies to protein gene product 9.5, S-100, and growth-associated protein-43 (GAP-43) were used to study the general innervation pattern. Antibodies to calcitonin gene-related peptide (CGRP), vasointestinal polypeptide (VIP), substance P (SP), and tyrosine hydroxylase (TH) were used to localize sensory (SP, CGRP, VIP) and sympathetic (TH) fibers. Blood vessels of the joint were studied with ink perfusion, GAP-43, and a vascular marker (LF1). Directly after the induction of arthritis, the synovial cavity was enlarged and filled with leukocytes. From day 4 onward, small sprouting blood vessels penetrated the avascular mass of cells in the joint cavity. After 1 week, the vascular sprouting activity and GAP-43 immunoreactivity were maximal, and after 2 weeks, vascular sprouting activity diminished. In the subsequent period, the synovia slowly regained their prearthritic appearance and thickness. The most pronounced changes in the general staining pattern of CGRP, SP, VIP, and TH were found in the periosteum. From 2 days to 4 weeks after the induction of arthritis, the layer of SP, CGRP, and VIP fibers in the femoral periosteum was thicker and more irregular. GAP-43 staining showed many terminal varicosities, which suggested sprouting of nerve fibers. From 2 days to 2 weeks after the induction of arthritis, the SP and CGRP fibers in the periosteum showed gradual depletion. In the thickened subsynovial tissues that were revascularized, no ingrowth of neural elements was found. As the total number of nerve fibers in the synovial tissue did not change, large parts of the synovia directly facing the joint cavity were not innervated at 1 week after the induction of arthritis. These results strongly suggest that periosteal SP and CGRP fibers were depleted during arthritis. Synovial proliferation without concomitant fiber growth is the main cause of the reduced number of immunocytochemically detectable fibers in the mouse arthritic knee joint.

Substance P and calcitonin gene-related peptide expression at the extensor carpi radialis brevis muscle origin: implications for the etiology of tennis elbow

With use of immunohistochemistry and antibodies to substance P and calcitonin gene-related peptide, nerve fibers showing substance P-like and calcitonin gene-related peptide-like immunoreactivity were demonstrated at the origin of the extensor carpi radialis brevis muscle in patients with tennis elbow (n = 6) and in healthy controls (n = 6). The nerve fibers were distributed in association with a subpopulation of small blood vessels and in nerve bundles but were not distributed in the tunica media-adventitia junction of the arterioles. There were no inflammatory-cell infiltrates and few solitary mast cells. The present study gives further evidence to previous suggestions that tennis elbow is not an inflammatory process in the sense of involving inflammatory cells. Frequent mechanical involvement affects sensory innervation, and substance P and calcitonin gene-related peptide may have various important efferent effects, including microvascular leakage and local edema formation; therefore, the observations from this study constitute a morphological substrate for possible effects of substance P and calcitonin gene-related peptide at the origin of the extensor carpi radialis brevis muscle.

Examination of colocalization of calcitonin gene-related peptide- and substance P-like immunoreactivity in the knee joint of the dog

It is generally assumed that the majority of substance P (SP)-containing afferents are also immunoreactive for calcitonin gene-related peptide (CGRP). In order to determine whether this is also the case in articular afferents where the contents of these peptides are low, we carried out a double labeling study using Fast Blue (FB) as a retrograde tracer injected into the center of the knee joint cavity of the dog together with immunohistochemistry for SP and CGRP. After 7-36 days of survival, dorsal root ganglia (DRGs, L4-S1) were removed. Labeled cells were found mainly (94%) in L5 - 6 DRGs, and SP- and CGRP-like immunoreactivity was found in about 17 and 29% of FB-labeled cells, respectively. The coexistence of SP and CGRP was observed in 10.4% of articular afferents and only 62.7% of SP-positive articular neurons contained CGRP, a much lower ratio than in other afferents of the dog such as testicular afferents. Our data suggest that these peptides are not always released together and that they do not always work together in the joint under normal conditions.

Quantification of cat's articular afferents containing calcitonin gene-related peptide or substance P innervating normal and acutely inflamed knee joints

In cats with an acute (32 h) unilateral knee joint inflammation the proportion of calcitonin gene-related peptide-(CGRP) and substance P-(SP) immunoreactive articular afferents, retrogradely labelled by Fast Blue (FB), were determined using immunohistochemistry. The proportion of neurons containing CGRP was significantly higher on the inflamed side (52%) than on the contralateral side (39%) and in controls (42%). However, the proportion of SP-immunoreactive articular perikarya on the inflamed side (26%) did not differ from the contralateral side (24%) and the control cats (22%). These data indicate that acute inflammation induces the synthesis of CGRP but not of SP in joint afferents.

Number, distribution and neuropeptide content of rat knee joint afferents

Retrograde tracing with Fluoro-Gold was used to identify the complete population of knee joint afferents in the lumbar dorsal root ganglia of adult female Wistar rats. There was an average of 581 +/- 31 (mean +/- S.D.) afferents supplying each joint. These were found distributed from L1 to L5 with the great majority localised in the L3 and L4 ganglia. Electron microscopy of the posterior articular nerve of the knee revealed an average of 103 +/- 15 (mean +/- S.D.) myelinated and 513 +/- 39 unmyelinated axonal profiles. Since about 50-60% of the unmyelinated profiles would be expected to be sympathetic efferents, these numbers are consistent with the numbers of afferents found by Fluoro-Gold retrograde tracing and suggest that the posterior articular nerve contains about 50% of the total number of knee joint afferents in the rat. Immunohistochemistry revealed that an average of 10% of identified joint afferents expressed substance P-like immunoreactivity and that 33% expressed calcitonin gene-related peptide-like immunoreactivity.

Morphological and immunohistochemical examination of nerves in normal and injured collateral ligaments of rat, rabbit, and human knee joints

BACKGROUND

Knee joints possess an abundant nerve supply that relays sensory and motor information on such aspects as proprioception, nociception, and vasoregulation. Although synovial innervation has been well documented, little is known of the nerves that supply the collateral ligaments.

METHODS

The morphology of rabbit and human collateral ligament nerves was examined by silver impregnation. Immunohistochemistry was performed on rabbit and rat collateral ligaments to determine the presence of peptidergic nerves in these tissues. A 6-week gap injury was performed on three rabbit medial collateral ligaments, and the localisation of peptidergic nerves in these tissues was determined.

RESULTS

Irrespective of species or type of ligament examined, the greatest density of nerve fibres was found in the epiligament. Nerve fibres commonly accompanied blood vessels along the long axis of the ligament and then entered the substance of the tissue before ramifying in the deeper layers. Substance P and calcitonin gene-related peptide-immunoreactive nerve fibres were found in the collateral ligaments of the rat and rabbit. Injured ligaments showed a higher than normal level of immunoreactivity in and around the healing zone; however, the nerve fibres appeared tangled and truncated.

CONCLUSIONS

Like other structures in knee joints, collateral ligaments possess a complex nerve supply. The presence of peptidergic nerves suggests that ligaments may be susceptible to neurogenic inflammation and may be centres of articular nociception.

Sensitisation of articular afferents in normal and inflamed knee joints by substance P in the rat

To examine whether substance P (SP) influences the response properties of fine articular afferents in normal and acutely inflamed joints, single units were recorded from the rat knee during normal and noxious joint rotations. Only three of 39 units were activated by a single bolus injection of 0.1 mM SP. However, 35% (7/20) of the nerve fibres from the normal joint and 21% (4/19) of the units from the inflamed joint significantly increased their responses to movements after the SP injection. This was most prominent during noxious movements in normal joints, whereas in inflamed joints increase of responses occurred mainly during normal movements. These data indicate that SP may also be involved in the process of sensitisation of primary afferents during an inflammation.

Microtopography of the autonomic nerves in the rat knee: a fluorescence microscopic study

BACKGROUND

The autonomic innervation of the joint is involved in different functions, such as sensory inputs, modulation of the function of immune cells, and trophic actions. To have a basis for further studies of the arthritic knee joint we have investigated the topographical distribution of different neuropeptides in knees of newborn and adult rats and in adult rats after arthritis induction.

METHODS

The distribution of the neuropeptides calcitonin gene-related peptide (CGRP), neurokinin A (NKA), substance P (SP), and neuropeptide Y (NPY) was analyzed using fluorescence immunohistochemistry. Samples were investigated after fixation by perfusion and decalcification by a special method which allows studies in bone tissue. Vascular structures were analyzed by scanning electron microscopy (SEM) of vascular resin casts.

RESULTS

In all tissues of the joint (synovial membrane, vessels, fibrous structures, bone, and cartilagineous tissues) CGRP and NKA are the most frequent neuropeptides. They are localized in free or perivascular fibers predominantly around arteries and arterioles. The NPY-ergic perivascular fibers even enter the vessel wall. Generally, SP-ergic fibers occur rarely. Free NKA- and CGRP-ergic nerve fibers spread out in the synovial lining layer reaching the synovial cavity and the outer layers of the articular and metaphyseal cartilage. In the cartilagineous tissue these nerves contact the chondrocytes. The density of NKA- and CGRP-immunoreactive fibers is lower in newborn rats than in adult rats. Six hours after arthritis induction SP-, NKA-, and CGRP-immunoreactivity is enhanced especially in perivascular fibers. The related vessels are dilated substantially.

CONCLUSIONS

The distribution pattern of the autonomic nerves found in this study might reflect the functions of these nerves: control of the microcirculation, sensory and even trophic functions. The new finding of CGRP- and NKA-ergic fibers in the outer layer of the cartilage can also have implications for the pathogenesis of rheumatoid arthritis.

[Projections and fiber characteristics of sensory afferents of the anterior cruciate ligament in an animal experiment]

The sensory innervation of the rabbit anterior cruciate ligament was studied by retrograde tracing technique using wheat-germ-agglutinin-horseradish-peroxidase (WGA-HRP) and Fast Blue as neuronal tracers. Injection of the tracer into the ligament was followed by histo- and immunohistochemical investigation of labelled nerve cell bodies located in the dorsal root ganglia. In 4 animals we injected the tracer into the joint cavity to label general joint afferents. The segmental distribution of retrogradely labelled neurons following injection into the anterior cruciate ligament (L6, L7, S1) is significantly different from the distribution pattern after injection into the knee joint (L4-S2). Retrogradely labelled nerve cells innervating the anterior cruciate ligament were further investigated using immunohistochemical and morphometric analysis. The sensory innervation of the anterior cruciate ligament is therefore comprised of at least 2 different qualities of sensory afferent nerves: 1. Small neurones immunoreactive to the inflammatory peptide substance P most likely transmitting nociceptive information centrally (44%). 2. Large, presumably fast conducting A-fibre-afferents characterized by neurofilament proteins transmitting proprioceptive information from corpuscular mechanoreceptors (43%). The results of this study put further weight to the importance of the sensory role of the anterior cruciate ligament using neuroanatomical and immunohistochemical techniques.

Calcitonin gene-related peptide is involved in the spinal processing of mechanosensory input from the rat's knee joint and in the generation and maintenance of hyperexcitability of dorsal horn-neurons during development of acute inflammation

In an electrophysiological study in anaesthetized rats, the involvement of calcitonin gene-related peptide in the spinal processing of mechanosensory information from the normal and inflamed knee joint was investigated. Calcitonin gene-related peptide(8-37), a specific antagonist at calcitonin gene-related peptide 1 receptors was administered ionophoretically close to nociceptive neurons with input from the knee joint before, during, and after development of acute inflammation in the knee induced by the intra-articular injections of kaolin and carrageenan. Calcitonin gene-related peptide (8-37) selectively antagonized the effects of ionophoretically applied calcitonin gene-related peptide but not those of ionophoretically applied substance P, neurokinin A, and (R,S)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid. Before inflammation, calcitonin gene-related peptide (8-37) reduced the responses to noxious pressure applied to the knee in 22 of 23 neurons; in 14 of 22 neurons, the responses to innocuous pressure were also reduced. In eight neurons calcitonin gene-related peptide (8-37) was administered during induction and in three periods within the first 90 min of inflammation. In these neurons the developing inflammation evoked a significantly smaller increase of the responses to innocuous and noxious pressure applied to the injected knee than in 13 control neurons which were not treated by the antagonist during induction of inflammation. In 16 of 16 neurons, calcitonin gene-related peptide (8-37) reduced the responses to innocuous and noxious pressure once inflammation and hyperexcitability of the spinal cord neurons were established. These data show that calcitonin gene-related peptide is involved in the spinal processing of mechanosensory input from the normal joint. Furthermore, this peptide and its spinal receptors significantly contribute to the generation and expression of inflammation-evoked hyperexcitability of spinal cord neurons during the development of inflammation. Finally, calcitonin gene-related peptide is involved in the maintenance of inflammation-evoked hyperexcitability. By these effects calcitonin gene-related peptide receptors may significantly contribute to the neuronal basis of hyperalgesia and allodynia associated with inflammation.

The role of spinal neurokinin-2 receptors in the processing of nociceptive information from the joint and in the generation and maintenance of inflammation-evoked hyperexcitability of dorsal horn neurons in the rat

In spinal cord neurons in anesthetized rats, the role on neurokinin A and neurokinin-2 receptors in the processing of nociceptive information from the knee joint was studied. The specific non-peptide antagonist at the neurokinin-2 receptor, SR48968, its inactive R-enantiomer, SR48965, neurokinin A, substance P and (RS)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), were administered ionophoretically close to neurons with input from the knee joint. SR48968 reduced the effects of exogenous neurokinin A, but not those of exogenous substance P and AMPA, indicating selective blockade of neurokinin-2 receptors. In most neurons with input from the normal knee joint, SR48968 reduced dose-dependently the responses to noxious pressure with applied to the knee, and in approximately 50% of the neurons the responses to innocuous pressure. The administration of SR48968 during the induction of an experimental joint inflammation markedly attenuated the development of inflammation-evoked hyperexcitability. In hyperexcitable neurons with input from the inflamed joint, SR48968 reduced the responses to noxious and innocuous pressure. The relative reduction of the responses was more pronounced than in neurons with input from the normal joint. None of the effects of SR48968 was mimicked by SR48965. These data show that neurokinin-2 receptors are involved in the spinal processing of nociceptive information from the normal joint. Furthermore, neurokinin-2 receptors must be coactivated at an early stage of inflammation, to allow the generation of hyperexcitability. Finally, neurokinin-2 receptors are involved in maintenance of hyperexcitability during inflammation. In summary, spinal neurokinin-2 receptors are important in the generation of pain in the normal and inflamed joint.

A simple method for a specific retrograde labelling of dorsal root and sympathetic ganglion cells innervating the knee joint of the cat

To examine the biochemical characteristics of primary afferents and sympathetic efferents innervating the normal and inflamed knee joint of the cat, the corresponding perikarya have to be labelled retrogradely. In the present study we used an injection of the fluorescent dye Fast Blue through the intact skin and the patellar ligament into the centre of the knee joint cavity and examined the efficiency of this kind of labelling. The segmental distributions of labelled cell profiles in cryostat sections of dorsal root ganglia (DRG) and paravertebral ganglia of the sympathetic trunk agreed with data obtained previously after applying the dye at the transected end of the two main articular nerves. The soma size distribution of labelled DRG cells was identical to previous results indicating that the perikarya labelled in the present study may be a representative proportion of the knee joint innervation. Axotomy of the medial and posterior articular nerves reduced the number of labelled cell profiles of about 85%. Taken together, these data indicate that an injection of Fast Blue into the knee joint cavity of the cat revealed a highly specific and efficient retrograde labelling of the neuronal cell bodies innervating the knee joint.

The effect of a unilateral inflammation at the rat's ankle joint on the expression of preprotachykinin-A mRNA and preprosomatostatin mRNA in dorsal root ganglion cells--a study using non-radioactive in situ hybridization

In rats with an acute (2 days) and chronic (20 days) unilateral ankle joint inflammation (induced by Freund's complete adjuvant), the proportion of dorsal root ganglion cells containing preprotachykinin-A mRNA or preprosomatostatin mRNA was determined using non-radioactive in situ hybridization. At the acute stage of inflammation, the proportion of neurons containing preprotachykinin-A mRNA was similar to that in control rats. At the chronic stage, the proportion of neurons expressing preprotachykinin-A mRNA was significantly higher on the inflamed side than on the contralateral side. The proportion of dorsal root ganglion cells containing preprosomatostatin mRNA did not change. These data suggest that inflammation influences the synthesis of substance P but not of somatostatin in afferent neurons.

Changes in innervation of long bones after insertion of an implant: immunocytochemical study in goats with antibodies to calcitonin gene-related peptide and B-50/GAP-43

In this study, we describe the distribution of fibres that contain calcitonin gene-related peptide in normal bones and in bones that are remodeling after insertion of an implant. With routine histology and antibodies to calcitonin gene-related peptide, small neural and free-running fibres staining positively for calcitonin gene-related peptide were found in the periosteum, endosteum, and cortical bone of the tibia in the goat. In many cases, the free-running fibres were associated with blood vessels that entered the bone through Volkmann's canals. The endosteal blood supply was destroyed as a result of insertion of the implant. The necrotic bone was no longer innervated, as shown by the lack of staining for the antibodies. At 6 weeks, a repair phase started with revascularization and remodeling of the necrotic endosteal bone. During this repair phase, there was increased innervation with fibres containing calcitonin gene-related peptide in the remodeling cavities at the interface between living and necrotic bone. These fibres ended blindly, with many large varicosities, and could be demonstrated by immunostaining with monoclonal antibodies to B-50/growth associated protein-43, an antibody to outgrowing neuronal fibres. The correlative occurrence between extensive sprouting of fibres containing calcitonin gene-related peptide and the remodeling of necrotic endosteal bone suggests that sensory fibres with calcitonin gene-related peptide have a regulatory role in the control of angiogenesis or of bone remodeling associated with the insertion of an implant, or with both processes.

Plasticity in the synthesis and storage of substance P and calcitonin gene-related peptide in primary afferent neurons during peripheral inflammation

Several indices of peptidergic, primary afferent neural transmission in rat at the level of the lumbar spinal cord exhibited differential changes over time in response to adjuvant-induced inflammation of the hindpaw. The indices were measurements of the production of messenger RNA encoding the precursors for substance P and calcitonin gene-related peptide in dorsal root ganglia, the storage of substance P and calcitonin gene-related peptide in the dorsal spinal cord and the release of the peptides evoked by application of capsaicin to the dorsal spinal cord. A 47% decrease in the content of immunoreactive substance P in the dorsal half of the lumbar spinal cord, as determined by radioimmunoassay, was measured at 6 h following the injection of complete Freund's adjuvant into the hindpaw. Decreased content of immunoreactive SP persisted for four days, but was no longer present at eight days after the adjuvant injection. The content of immunoreactive calcitonin gene-related peptide in the dorsal spinal cord was decreased by 29% at one day following the injection of adjuvant into the rat hindpaw and 43% at two days; the content then increased to a level greater than that of control animals at eight days. The amount of messenger RNA encoding preprotachykinin and prepro-calcitonin gene-related peptide in L4-L6 dorsal root ganglia was determined from northern blot analysis of the total messenger RNA extracted from the dorsal root ganglia. Each species of messenger RNA had increased compared to the control animals at two days following the injection of adjuvant into the rat hindpaws and remained elevated after eight days. Thus, an increase in the messenger RNAs encoding substance P and calcitonin gene-related peptide in the dorsal root ganglia preceeded the recovery of the content of the peptides in the spinal cord. Morphometric studies of calcitonin gene-related peptide-immunoreactive perikarya in the L4 dorsal root ganglia indicated that the increase in messenger RNA occurred in neurons of the size that normally express calcitonin gene-related protein. Radioimmunoassay of the superfusate of the dorsal half of the lumbar spinal cord was used to measure the release of immunoreactive substance P and immunoreactive calcitonin gene-related protein in vitro. Although the basal release of immunoreactive substance P and immunoreactive calcitonin-gene related protein from the dorsal spinal cord was constant throughout the time points examined, changes occurred in the release of peptide evoked by 10 microM capsaicin. The capsaicin-evoked release of immunoreactive substance P was decreased at 6 h and eight days post-injection of adjuvant.(ABSTRACT TRUNCATED AT 400 WORDS)

Origin of the calcitonin gene-related peptide-immunoreactive nerve fibers in the rat shoulder joint

The rat shoulder joint capsule is innervated by thin sympathetic and sensory nerve fibers, most of which contain calcitonin gene-related peptide (CGRP). In order to establish the origin and distribution of CGRP-immunoreactive (IR) fibers, wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) was injected into the shoulder joints of rats via a dorsal surgical approach. After WGA-HRP injection, the cervico-thoracic dorsal root ganglia (DRG) were removed and processed using both HRP histochemistry and CGRP immunohistochemistry. In the C4 to C7 DRG, small to medium-sized neurons (20-40 microns) were labeled by this combined method. The number and size of the labeled neurons were measured in the cervical 4th-7th DRG. The number of double-labeled neurons was one quarter of the total number of HRP-labeled neurons and 1/20 of the CGRP-IR neurons. Most of the double-labeled cells were located in the C6 ganglion, and the mean number of double-labeled neurons was 13 at this level. This distribution and function of the CGRP-IR fibers in the rat shoulder joint capsule are discussed.

Somatostatin-like immunoreactivity in primary afferents of the medial articular nerve and colocalization with substance P in the cat

The proportion of somatostatin-containing dorsal root ganglion cells innervating the knee joint of the cat via the medial articular nerve was determined by using retrograde labeling with fast blue and immunohistochemistry. Immunoreactivity was found in 8.6% of labeled cell bodies. In colchicine-treated ganglia, the proportion increased to 16.8%. Only small and intermediate-sized perikarya showed somatostatin-like immunoreactivity, indicating that this neuropeptide is synthesized predominantly in primary afferent units with unmyelinated sensory axons but may also be present in primary afferents with thinly myelinated sensory fibers. Colchicine treatment had no influence on the cell size distribution. Colocalization of somatostatin with substance P was determined by comparing the proportions of immunopositive dorsal root ganglion cells after incubation with antibodies against substance P or somatostatin or with a mixture of both. Substance P-like immunoreactivity was found in 18.1% (untreated ganglia) and 19.6% (colchicine treated ganglia) of the labeled neurons. After incubation with a mixed antibody solution, 18.2% of joint afferents in untreated and 19.9% of the cells in colchicine-treated ganglia were immunopositive. Comparing this result with the results obtained using somatostatin and substance P antibodies alone, one can calculate that both neuropeptides are colocalized in about 17% of the cat's knee joint afferents. About 3% of the neurons contain only substance P, whereas almost none of the neurons contain only somatostatin. Based on this fact, one can assume that both neuropeptides are coreleased in peripheral tissue as well as in the central nervous system.

Changes in the innervation of rabbit craniomandibular joint tissues associated with experimental induction of anterior disk displacement: histochemical and immunohistochemical studies

We have previously reported that surgical induction of anterior disk displacement (ADD) in a rabbit craniomandibular joint (CMJ) leads to histopathological changes consistent with osteoarthritis. This paper reports the changes that were noted in the innervation of rabbit CMJ tissues following surgical induction of ADD. The right joint of 30 rabbits was exposed surgically and the discal attachments were severed except for the posterior discal attachment (bilaminar zone). The disk was then displaced anteriorly and sutured to the zygomatic arch. The left joints was used as sham-operated control. CMJ tissues were then removed after fixation and processed for histochemical localization of nerve fibers using the silver impregnation technique and immunohistochemical localization of neurofilaments using monoclonal antibodies. The results showed an absence of nerve fibers in the control and experimental disks and their presence in the control and experimental bilaminar zones. The bilaminar zone adhesions to the experimental condyles were also innervated. The spread of nerve fibers into the pathological fibrous adhesions surrounding the arthritic condyles in this animal model of ADD may indicate a possible mechanism of nociception in this disease.

NADPH-diaphorase reactivity in articular afferents of a normal and inflamed knee joint in the cat

The distribution of NADPH-diaphorase was studied in retrogradely labelled dorsal root ganglion cells innervating the knee joint of the cat. A strong staining reaction was found in 7.5 +/- 1.9% (mean +/- S.D. of 9 normal joints and 6393 labelled perikarya) of the articular afferents. An acute inflammation (32 h) significantly increased this proportion to 10.9 +/- 2.2% (mean +/- S.D. of 5 inflamed joints and 3933 labelled perikarya). The diameter distribution of the somata with a positive NADPH-diaphorase reaction ranged from 18 to 46 microns with a maximum at 24-28 microns. These data indicate that a small proportion of knee joint primary afferents may be able to release nitric oxide playing a role in synaptic transmission and in regulatory functions within the peripheral tissue under normal and pathophysiological conditions.

The involvement of substance P and neurokinin-1 receptors in the responses of rat dorsal horn neurons to noxious but not to innocuous mechanical stimuli applied to the knee joint

In 29 anesthetized rats, the involvement of substance P and neurokinin-1 receptors in the spinal processing of mechanosensory innocuous and noxious information from the knee and ankle joint was investigated. In 21 rats, multibarrel electrodes were used to record from 46 spinal cord neurons with afferent input from the knee joint and to administer agonists and antagonists by microinophoresis. In 35 of 46 nociceptive neurons, substance P (ejected at 20-120 nA) caused an excitation and/or an increase in responses to innocuous and noxious pressure applied to the knee and ankle. These effects were reduced by ionophoretic application of the specific neurokinin-1 receptor antagonist CP96,345 (ejected at 25-80 nA) but not by CP96,344, its inactive enantiomer. CP96,345 dose-dependently reduced the responses to noxious pressure applied to the knee joint in 28/28 substance P-sensitive neurons but not those to innocuous pressure in 23/23 substance P-sensitive wide dynamic range neurons. CP96,345 did not affect responses to pressure in substance P-insensitive neurons and the inactive enantiomer CP96,344 had no effect in any of the neurons tested. Using microprobes coated with antibody to substance P, intraspinal release of immunoreactive substance P was found to be evoked by noxious pressure applied to the knee but not by innocuous pressure in 8 rats. Both sets of data suggest a role for substance P and neurokinin-1 receptors in the neuronal mechanisms in the spinal cord related to nociception and pain in the normal joint.

Intraspinal release of immunoreactive calcitonin gene-related peptide during development of inflammation in the joint in vivo--a study with antibody microprobes in cat and rat

This study addressed the intraspinal release of immunoreactive calcitonin gene-related peptide in vivo during mechanical stimulation of the normal joint and during the development of an acute experimental inflammation in the knee joint in the anaesthetized cat (spinalized) and rat (not spinalized). Release was assessed using microprobes coated with antibody to calcitonin gene-related peptide; inhibition of binding of [125I]calcitonin gene-related peptide to these probes following insertion into the spinal cord is equated with intraspinal release of the endogenous (unlabelled) peptide. Probes inserted prior to inflammation showed marked basal release of immunoreactive calcitonin gene-related peptide in the dorsal horn with a maximum in the superficial dorsal horn in the absence of intentional stimulation. The pattern of binding of [125I]calcitonin gene-related peptide was not or only minimally changed by innocuous mechanical stimuli (flexion of and innocuous pressure to the knee in the cat and innocuous pressure to the knee of the rat) but was significantly altered by electrical stimulation of the tibial nerve in the cat (sufficient to excite unmyelinated afferent fibres), indicating release of the peptide by the latter stimulus. During the first hours of the development of an experimental inflammation in the knee joint induced by intra-articular injections of kaolin and carrageenan, the pattern of binding of [125I]calcitonin gene-related peptide changed. In the cat, the level of immunoreactive calcitonin gene-related peptide showed a persistent increase in the gray matter and up to the surface of the cord and release was slightly increased by innocuous stimuli. In the rat, increased levels of immunoreactive calcitonin gene-related peptide were mainly seen in the superficial and deep dorsal horn during innocuous pressure (this stimulus did not evoke release of the peptide prior to inflammation) and noxious pressure applied to the injected knee, whereas increased basal levels were only observed at later stages. These data show that the development of an acute experimental inflammation in the joint is associated with an enhancement of the intraspinal release of immunoreactive calcitonin gene-related peptide. Since the changes in the release were noted at an early stage, within the first hours, they could contribute to the generation of inflammation-evoked changes of the responsiveness of spinal cord neurons and hence to the mechanisms inducing inflammatory pain.

Innervation of the patella. An immunohistochemical study in mice

In the mouse, arthritis was induced by a single sub-patellar intraarticular injection of bacterial collagenase. This procedure induces also patellar malalignment. A rich innervation of thin varicose calcitonin gene-related peptide (CGRP) and substance P (SP) immunoreactive fibers was found in the joint capsule, in the periosteum of the patella, in the synovial tissues at the lateral border of the patella, in the femoral groove, and in the subchondral bone of the patella and femur. Moreover, fibers were found in plica tissues between the quadriceps and patellar tendon, and the femoral groove. After the collagenase treatment, the general innervation pattern was comparable to that of the controls, but CGRP and SP innervation was no longer detectable with the antibodies in the plica tissues, and was to a lesser extent detectable in the fat pad of the patella, in the lateral borders of the patella and in the proliferated synovial tissues. Signs of degenerated axonal profiles were observed in these locations with a polyclonal antibody to the growth-associated protein GAP-43/B-50. At all the other peripheral locations, such as the muscles, the GAP-43/B-50 distribution was normal.

Nerve supply of anterior cruciate ligaments and of cryopreserved anterior cruciate ligament allografts: a new method for the differentiation of the nervous tissues

We investigated the nerve supply of anterior cruciate ligaments ((ACLs) and of cryopreserved bone-ACL-bone allografts in a rabbit model with immunohistochemical methods to establish the distribution pattern of the nervous tissues and to determine the reinnervation rate of ACL allografts. The ACL is innervated by three different classes of nerve fibre: (1) fibres of large diameter, characterized by neurofilament immunoreactivity, which are fast-conducting mechanoreceptive sensory afferents; (2) fibres of small diameter, characterized by substance P-immunoreactivity, which are slow-conducting nociceptive sensory afferents; and (3) sympathetic efferent vasomotor fibres, characterized by their immunoreactivity to the rate-limiting enzyme of noradrenaline synthesis, tyrosine hydroxylase. The ACLs showed numerous fibres of all three nerve classes; as specialised sensory nerve endings only Ruffini corpuscles were observed. All nerve fibres were located subsynovially, none within the collagen core of the ligament itself. No nerve fibres were detected in the ACL allografts at 3 and 6 weeks. Sparse fibres were detected at 12 weeks, while the 24-, 36- and 52-week specimens showed plenty of all three fibre types. No mechanoreceptors were found in the ACL allografts. To our knowledge, this method for the first time allows a differentiation of the nerve fibres of ACLs and ACL allografts into three different nerve fibre classes with known neurophysiological functions.

Innervation of the dura mater encephali of cat and rat: ultrastructure and calcitonin gene-related peptide-like and substance P-like immunoreactivity

Ultrastructural, immunocytochemical, and immunoelectron microscopical examinations are reported that describe the morphology of putative sensory nerve endings in the dura mater encephali of the rat and the cat. Morphometrical measurements and reconstructions showed that in the cat the mean diameter of axons, the bare area of axolemma, and the content of mitochondria and vesicles are highly variable in dural nerve endings. Nerve fibers with a high volume density of mitochondria are thought to be sensory, while nerve fibers containing many small vesicles are considered autonomic. There is, however, a broad overlap of mitochondria-rich and vesicle-rich nerve fibers in the dura, so that discrimination between sensory and autonomic endings by these characteristics frequently fails. Whole-mount preparations treated cytochemically for detection of substance P- and calcitonin gene-related peptide-like immunoreactivity in the rat and the cat showed a network of immunopositive nerve fibers in the vicinity of dural blood vessels. Most of these peptidergic and probably sensory nerve fibers were found terminating in the dural connective tissue far from vessels. Calcitonin gene-related peptide-positive nerve fibers were much more abundant than substance P-positive fibers. Immunoelectron microscopic preparations revealed that calcitonin gene-related peptide- and substance P-like immunoreactivity is found in a small proportion of generally thin unmyelinated nerve fibers. These proportions were very similar in the rat and the cat. Summarizing the recent literature, the morphological characteristics of putative sensory nerve fibers in the dura mater are discussed in relation to their possible functional significance for neurogenic inflammation and nociception.

Acute and chronic phases of unilateral inflammation in rat's ankle are associated with an increase in the proportion of calcitonin gene-related peptide-immunoreactive dorsal root ganglion cells

Using immunocytochemical methods, the proportion of calcitonin gene-related peptide immunoreactive perikarya was determined in dorsal root ganglia L4-L6 in four control rats and in ten rats with a unilateral inflammation in the ankle region of the left hindlimb. The inflammation was induced by subdermal injection of Freund's complete adjuvant at the ankle. Swelling and cellular infiltration of the ankle region developed within 2 days, and were stable and restricted to the injected ankle for the duration of the 3-week study. In control rats approximately 24% of 20,419 perikarya showed calcitonin gene-related peptide (CGRP)-like immunoreactivity. In rats with unilateral inflammation the proportion of CGRP-positive neurons was increased on the inflamed side to approximately 32% of 11,454 cells at day 2 (P < 0.001 with respect to ganglia in normal rats) and approximately 29% of 10,739 perikarya at day 20 post inoculation (P < 0.01). By contrast, no significant changes were found between ganglia in the non-injected side (approximately 25% at day 2 and approximately 24% at day 20). These results demonstrate that peripheral inflammation is associated with an increase in the proportion of neurons in the dorsal root ganglia that synthetize CGRP. This up-regulation is already present at an early stage of inflammation but also at later stages, suggesting that the increased synthesis of CGRP is an important neurobiological reaction associated with the acute and chronic phases of inflammation.