Sensory C-fibers in rat ventral roots are capsaicin-insensitive and they do not mediate extravasation from pial vessels

Brachial plexus dorsal rhizotomy in hemiplegic cerebral palsy

Brachial plexus dorsal rhizotomy releases spasticity, improving the functional use of the hand. Grasping and pinch strength are augmented, together with movement speed and dexterity. Even when four dorsal roots have been sectioned, hand sensibility is largely preserved. Movement control is improved and equally advantageous in athetotic patients. Brachial plexus dorsal rhizotomy does not exclude the use of tendon lengthening or transfer procedures, but it is the authors' opinion that orthopedic procedures should be performed after dorsal rhizotomy. Children aged 5-6 years without muscle contractures are the ideal candidates to benefit fully from dorsal rhizotomy.

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.

Capsaicin blocks tetrodotoxin-resistant sodium potentials and calcium potentials in unmyelinated C fibres of biopsied human sural nerve in vitro

Topical application of capsaicin has been tested recently for treatment of painful peripheral neuropathy. In the present study, effects of capsaicin were explored on compound action potentials of isolated fascicles from human sural nerve biopsies. Capsaicin reduced the C fibre component by 30-60%; the remaining C fibres were not sensitive to the drug. A good correlation was found between the sensitivity of C fibres to capsaicin and their resistance to tetrodotoxin (TTX), i.e. C fibre action potentials recorded in the presence of TTX were completely blocked by capsaicin. Calcium action potentials seen after inhibition of axonal potassium conductances were also completely suppressed. The data indicate that application of capsaicin nearby human peripheral nerves might prevent action potential conduction in specific subtypes of C fibres.

Postnatal development and aging of the rat ventral root L5: electron microscopic and immunohistochemical studies

The ventral root L5 of neonatal and adult rats has been used in many experimental studies on ganglionic C-fibers. Since the normal presence of such axons in L5 roots from animals of different ages is unknown, the results of these studies cannot be appropriately interpreted. In the present study we examine L5 ventral roots from developing and aging rats in this respect. Electron microscopic examination revealed that C-fibers occur in neonatal roots. The adult proportion has been established at day 30. Immunohistochemical analysis showed that thin ganglionic fibers with substance P/calcitonin gene-related peptide- or tyrosine hydroxylase-like immunoreactivity in the L5 root and the spinal pia mater seem to increase postnatally from low levels at birth. In roots from aged rats, myelinated fibers with a variety of aberrant features occur in normal numbers. The occurrence of unmyelinated axons is elevated. The increased presence of fibers with calcitonin gene-related peptide- or tyrosine hydroxylase-like immunoreactivity in aged roots indicates that the extra unmyelinated fibers may represent motor sprouts and sympathetic fibers, respectively. We conclude that the rat ventral root L5 contains a variable number of putative sensory and sympathetic axons at all ages.

Teeth and tooth nerves

(1) Although our knowledge on teeth and tooth nerves has increased substantially during the past 25 years, several important issues remain to be fully elucidated. As a result of the work now going on at many laboratories over the world, we can expect exciting new findings and major break-throughs in these and other areas in a near future. (2) Dentin-like and enamel-like hard tissues evolved as components of the exoskeletal bony armor of early vertebrates, 500 million years ago, long before the first appearance of teeth. It is possible that teeth developed from tubercles (odontodes) in the bony armor. The presence of a canal system in the bony plates, of tubular dentin, of external pores in the enamel layer and of a link to the lateral line system promoted hypotheses that the bony plates and tooth precursors may have had a sensory function. The evolution of an efficient brain, of a head with paired sense organs and of toothed jaws concurred with a shift from a sessile filter-feeding life to active prey hunting. (3) The wide spectrum of feeding behaviors exhibited by modern vertebrates is reflected by a variety of dentition types. While the teeth are continuously renewed in toothed non-mammalian vertebrates, tooth turnover is highly restricted in mammals. As a rule, one set of primary teeth is replaced by one set of permanent teeth. Since teeth are richly innervated, the turnover necessitates a local neural plasticity. Another factor calling for a local plasticity is the relatively frequent occurrence of age-related and pathological dental changes. (4) Tooth development is initiated through interactions between the oral epithelium and underlying neural crest-derived mesenchymal cells. The interactions are mediated by cell surface molecules, extracellular matrix molecules and soluble molecules. The possibility that the initiating events might involve a neural component has been much discussed. With respect to mammals, the experimental evidence available does not support this hypothesis. In the teleost Tilapia mariae, on the other hand, tooth germ formation is interrupted, and tooth turnover ceases after local denervation. (5) Prospective dental nerves enter the jaws well before onset of tooth development. When a dental lamina has formed, a plexus of nerve branches is seen in the subepithelial mesenchyme. Shortly thereafter, specific branches to individual tooth primordia can be distinguished. In bud stage tooth germs, axon terminals surround the condensed mesenchyme and in cap stage primordia axons grow into the dental follicle.(ABSTRACT TRUNCATED AT 400 WORDS)

Invasion of the rat ventral root L5 by putative sympathetic C-fibers after neonatal sciatic nerve crush

The present study examines the occurrence of C-fibers in lumbar ventral roots after sciatic nerve crush in neonatal and adult rats. Electron microscopic analysis showed that the number of C-fibers in the ventral root L5 increased significantly on the lesion side after neonatal but not adult sciatic nerve crush and that the number of C-fibers was higher in the ventral root L5 on the unoperated side compared to this root in normal control rats. In order to determine whether the new C-fibers in the L5 root on the lesion side are sensory or sympathetic we made immunohistochemical studies on roots from neonatally crushed rats. We found that there was no obvious lesion side/contralateral side or operated rat/control rat difference with respect to the occurrence and general configuration of axons with substance P-, calcitonin gene-related peptide- or vasoactive intestinal polypeptide-like immunoreactivity. However, the occurrence of axons with tyrosine hydroxylase-like immunoreactivity appeared clearly higher in the ventral root L5 on the lesion side compared to the unoperated side in neonatally crushed rats. Moreover, these axons seemed to be more numerous also in the ventral root L5 on the unoperated side compared to normal control rats. No lesion side/contralateral side or operated rat/control rat differences were seen in the ventral root L4. We propose that the ventral root L5 is invaded by putative sympathetic C-fibers after sciatic nerve crush lesions in newborn rats.

Shoulder region of the rat: anatomy and fiber composition of some suprascapular nerve branches

BACKGROUND

The pathophysiology of chronic supraspinatus tendinitis is not fully understood. This may be due to the scarcity of experimental studies on this issue.

METHODS

In search for a system suitable for experimental analysis, the present study describes the relevant gross anatomy of the rat shoulder region (dissection), and examines the fiber composition of relevant supra-scapular nerve branches (electron microscopy, selective denervations).

RESULTS

The rat shoulder region is similar to the human shoulder in terms of gross anatomy. The average suprascapular nerve (SSC) is derived mainly from the spinal cord segment C5 and contains 3,435 axons, 74% of which are unmyelinated. The supraspinatus branch (SSP) contains 627 fibers. Of the SSP fibers, 52% are myelinated, including 32% motor and 20% sensory axons. Of the C-fibers in the SSP 16% are sympathetic efferents and 32% are sensory. Many of the latter disappear after neonatal capsaicin treatment. The SSC emits a subacromial articular branch (ART), with some 260 axons, about 90% of which are unmyelinated. The myelinated ART fibers are sensory, and of the unmyelinated ones about 24% are sympathetic efferents and 66% are afferents. The latter resist neonatal capsaicin treatment.

CONCLUSIONS

In view of the anatomy of the supraspinatus muscle, of the subacromial space, and of relevant nerves, the rat shoulder should be appropriate for experimental studies on inflammatory conditions in the subacromial space.