Nerve fibers immunoreactive for substance P and calcitonin gene-related peptide in the cervical spinal ventral roots of the mouse

Myenteric Plexus Immune Cell Infiltrations and Neurotransmitter Expression in Crohn's Disease and Ulcerative Colitis

BACKGROUND AND AIMS

Pain is a cardinal symptom in inflammatory bowel disease [IBD]. An important structure in the transduction of pain signalling is the myenteric plexus [MP]. Nevertheless, IBD-associated infiltration of the MP by immune cells lacks in-depth characterisation. Herein, we decipher intra- and periganglionic immune cell infiltrations in Crohn´s disease [CD] and ulcerative colitis [UC] and provide a comparison with murine models of colitis.

METHODS

Full wall specimens of surgical colon resections served to examine immune cell populations by either conventional immuno-histochemistry or immunofluorescence followed by either bright field or confocal microscopy. Results were compared with equivalent examinations in various murine models of intestinal inflammation.

RESULTS

Whereas the MP morphology was not significantly altered in IBD, we identified intraganglionic IBD-specific B cell- and monocyte-dominant cell infiltrations in CD. In contrast, UC-MPs were infiltrated by CD8+ T cells and revealed a higher extent of ganglionic cell apoptosis. With regard to the murine models of intestinal inflammation, the chronic dextran sulphate sodium [DSS]-induced colitis model reflected CD [and to a lesser extent UC] best, as it also showed increased monocytic infiltration as well as a modest B cell and CD8+ T cell infiltration.

CONCLUSIONS

In CD, MPs were infiltrated by B cells and monocytes. In UC, mostly CD8+ cytotoxic T cells were found. The chronic DSS-induced colitis in the mouse model reflected best the MP-immune cell infiltrations representative for IBD.

Acromioclavicular Disk as a Potential Source of Pain in AC Joint Injuries

BACKGROUND

Injuries of the acromioclavicular joint (ACJ) are common shoulder injuries that often lead to pain and dysfunction of the affected shoulder. Regardless of operative or nonoperative treatment, a relatively large number of patients remain symptomatic and experience pain. However, the specific source of persistent pain in the ACJ remains ambiguous.

PURPOSE

To investigate the presence of sensory nerve fibers or pain-generating neurotransmitters within the intra-articular disk of the ACJ to determine its potential role as an independent pain generator in ACJ disorders.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Twelve paired ACJs from 6 fresh human cadavers (mean age, 56 years; range, 41-82 years) were harvested and freed from surrounding soft tissues, leaving only the ACJ capsule intact. The specimens were placed in 4.5% formaldehyde fixative for a minimum of 48 hours. Coronal plane sections were obtained and demineralized in EDTA for a week, embedded in paraffin for 12 hours, and dehydrated overnight. With a rotation microtome, 2-μm sections were cut and stained with hematoxylin and eosin to investigate tissue architecture and confirm the presence of a fibrocartilaginous intra-articular disk. The sections were immunohistochemically stained with antisera against S100, neuropeptide Y (NPY), and substance P (SP) to detect for neural tissue. Additionally, a nerve fiber count per 10 high-power fields representing an area of 0.2 mm² was conducted for S100 stains. All sections were examined for the presence of positive immunoreactivity to S100, NPY, and SP.

RESULTS

The presence of a fibrocartilaginous intra-articular disk could be observed in all 12 examined ACJs. In all specimens, an immunoreactivity to S100, NPY, and SP could be observed within the superior peripheral region of the intra-articular disk. High-power field nerve counts of the S100 stains revealed a mean ± SD of 7.9 ± 2.28 nerves per 10 high-power fields (range, 4-12).

CONCLUSION

The documented immunoreactivity to S100, NPY, and SP indicates the presence of somatic and autonomic nerve fibers within the intra-articular disk of the ACJ.

CLINICAL RELEVANCE

Confirming the presence of nerve fibers within the intra-articular disk of the ACJ suggests that the disk itself could be an independent source of pain after injury and thus a possible explanation for recalcitrant pain after treatment.

Developmental localization of calcitonin gene-related peptide in dorsal sensory axons and ventral motor neurons of mouse cervical spinal cord

Calcitonin gene-related peptide (CGRP) is a 37-amino-acid neuropeptide, synthesized by alternative splicing of calcitonin gene mRNA. CGRP is characteristically distributed in the nervous system, and its function varies depending on where it is expressed. To reveal developmental formation of the CGRP network and its function in neuronal maturation, we examined the immunohistochemical localization of CGRP in the developing mouse cervical spinal cord and dorsal root ganglion. CGRP immunolabeling (IL) was first detected in motor neurons on E13, and in ascending axons of the posterior funiculus and DRG neurons on E14. CGRP-positive sensory axon fibers entered Laminae I and II on E16, and Laminae I through IV on E18. The intensity of the CGRP-IL gradually increased in both ventral and dorsal horns during embryonic development, but markedly decreased in the ventral horn after birth. These results suggest that CGRP is expressed several days after neuronal settling and entry of sensory fibers, and that the CGRP network is formed in chronological and sequential order. Furthermore, because CGRP is markedly expressed in motor neurons when axons are vastly extending and innervating targets, CGRP may also be involved in axonal elongation and synapse formation during normal development.

Differential distribution of nerve fibers immunoreactive for substance P and calcitonin gene-related peptide in the superficial and deep muscle layers of the dorsum of the rat

We compared the distribution of substance P (SP) and calcitonin gene-related peptide (CGRP) fibers of the superficial muscle layer (trapezius muscle), median muscle layer (rhomboideus muscle), and deep muscle layer (longissimus and spinalis muscles) of the dorsum of the rat. SP- and CGRP-immunoreactive fibers were seen along the walls of various types of blood vessels and within nerve bundles in skeletal muscles of all layers. Coexistence of SP and CGRP was evident in nerve fibers along the blood vessel walls. The total number of CGRP varicosities per millimeter square of muscle surface area was evaluated quantitatively, and CGRP varicosities were found to be significantly more numerous in the superficial muscle layer than in the deeper ones. After capsaicin treatment, most of the SP and CGRP fibers along the blood vessel walls were eliminated. These results suggest that sensory nerve fibers containing SP and CGRP are distributed more abundantly in the superficial muscle layer than in the deeper ones and that they might be involved in the regulation of local blood flow. The finding of SP- and CGRP-immunoreactive nerve fibers along the blood vessel walls connecting the trapezius muscle and the hypodermis raises the possibility that sensory stimuli to the skin affect the local blood flow of superficial muscle through collaterals of cutaneous fibers.

The role of capsaicin-sensitive muscle afferents in fatigue-induced modulation of the monosynaptic reflex in the rat

1. The role of group III and IV afferent fibres of the lateral gastrocnemious muscle (LG) in modulating the homonymous monosynaptic reflex was investigated during muscle fatigue in spinalized rats. 2. Muscle fatigue was induced by a series of increasing tetanic electrical stimuli (85 Hz, 600 ms) delivered to the LG muscle nerve. Series consisted of increasing train numbers from 1 to 60. 3. Potentials from the spinal cord LG motor pool and from the ventral root were recorded in response to proprioceptive afferent stimulation and analysed before and during tetanic muscle activations. Both the pre- and postsynaptic waves showed an initial enhancement and, after a '12-train' series, an increasing inhibition. 4. The enhancement of the responses to muscle fatiguing stimulation disappeared after L3-L6 dorsal root section, while a partial reflex inhibition was still present. Conversely, after section of the corresponding ventral root, there was only a reduction in the inhibitory effect. 5. The monosynaptic reflex was also studied in animals in which a large number of group III and IV muscle afferents were eliminated by injecting capsaicin (10 mM) into the LG muscle. As a result of capsaicin treatment, the fatigue-induced inhibition of the pre- and postsynaptic waves disappeared, while the response enhancement remained. 6. We concluded that the monosynaptic reflex inhibition, but not the enhancement, was mediated by those group III and IV muscle afferents that are sensitive to the toxic action of capsaicin. The afferents that are responsible for the response enhancement enter the spinal cord through the dorsal root, while those responsible for the inhibition enter the spinal cord through both the ventral and dorsal roots.

Selective motor hyperreinnervation using motor rootlet transfer: an experimental study in rat brachial plexus

Misdirection of sensory fibers into motor pathways is, in part, responsible for the poor results obtained after peripheral nerve repair. After avulsion of the C-5 root in rats, the authors connected a C-4 ventral rootlet to the musculocutaneous nerve by means of a sural nerve graft. In this way, they were able to increase the number of regenerating motor fibers and avoid growth of sensory fibers into the nerve grafts. Functional recovery was evaluated electrophysiologically and histologically. The origin of the axons that reinnervated the nerve graft was analyzed by means of morphological studies including retrograde labeling procedures. Motor neurons survived and regenerated after the rootlet transfer and there was no functional impairment. Many neurons were retrograde labeled in the ventral horn and widespread biceps muscle reinnervation was demonstrated with recovery of nearly normal electrophysiological properties. Motor hyperreinnervation of the musculocutaneous nerve was observed. This high degree of reinnervation in a long (40-mm) graft was attributed to the good chance that a muscle fiber can be reinnervated by a motor fiber when the number of regenerating motor neurons is increased and when competitive sensory fibers are excluded from reinnervation.

Ganglionic axons in motor roots and pia mater

In addition to motor axons and preganglionic axons, ventral roots contain unmyelinated or thin myelinated sensory axons and postganglionic sympathetic axons. It has been said that ventral roots channel sensory axons to the CNS. However, it now seems that these axons end blindly, shift to the pia or loop and return towards the periphery and that these units reach the CNS via dorsal roots. Sensory ventral root axons project from a variety of somatic or visceral receptors; some of them are third branches of dorsal root afferents and some seem to lack a CNS projection. Many ventral root afferents contain substance P (SP) and/or calcitonin gene-related peptide (CGRP). These fibres are not affected by neonatal capsaicin treatment and they cannot induce radicular or pial extravasation. Some thin ventral root axons are sympathetic and relate to blood vessels. Afferents containing SP and/or CGRP and sympathetic axons also occur in the spinal pia mater. The sensory axons mediate pain. They might also have vasomotor, tissue-regulatory and/or mechanoreceptive functions. The motor roots of cranial nerves IV, VI and XI contain unmyelinated axons arranged like in ventral roots outside the autonomic outflow. However, the motor root of cranial nerve V channels some unmyelinated axons into the CNS. The occurrence of thin axons in ventral roots and pia mater changes during development and ageing. After peripheral nerve injury, ipsilateral ventral roots and pia are invaded by new sensory and postganglionic sympathetic axons.

Coiled mechanoreceptors in Aplysia revealed by sensorin immunofluorescence and confocal microscopy

Identified mechanosensory neurons of Aplysia are established model neurons for studies on learning and memory, and for examining responses to axonal injury. Although many characteristics of these sensory neurons have received intensive study, the nature of the peripheral mechanoreceptive endings remains unknown. Identification of a peptide, sensorin, specific in Aplysia for mechanosensory neurons, led to the development of an antibody which proved useful in studying the peripheral morphology of these neurons. Immunostaining for sensorin in tail body wall revealed that sensorin is present in peripheral arborizations. Examination of sensorin-positive fibers in the periphery revealed that they terminate as coiled structures in the muscle layer of the body wall. These coiled structures (approximately 0.5 microns diameter processes, 2-3 microns across the coil, approximately 60 microns long) run parallel to muscle fibers and have a pitch of about one turn per 4 microns. Sensorin immunostaining was particularly intense in varicosities, both along peripheral fibers and along the coiled structure. The localization of sensorin suggests that it may be released peripherally where it could have various paracrine and/or autocrine neuromodulatory actions.