Morphometric analysis of the inferior alveolar nerve fails to demonstrate sexual dimorphism

PURPOSE

With regard to the incidence of inferior alveolar nerve (IAN) damage after an IAN block or following oral and maxillofacial surgical procedures, there are reports of sexual dimorphism, no sexual dimorphism, and little sexual dimorphism. However, details of the morphology and sexual dimorphism in the characteristics of the IAN have not been available in textbooks. We morphometrically analyzed the human IAN and clarified these issues.

MATERIALS AND METHODS

The materials were obtained from 22 cadavers (11 female and 11 male), aged 59 to 84 years (average age: 74.1 yr), and dentulous. The causes of death did not influence the nervous system, so the IANs were considered to be normal. Human IANs were resected at the mandibular foramen. We counted the myelinated axons and measured the transverse area, perimeter, and circularity ratio of the myelinated axons.

RESULTS

We estimated the average total number of myelinated axons in the female IAN to be 25,230, with an average transverse area of 34.1 microm(2), an average perimeter of 21.8 microm, and an average circularity ratio of 0.86, with the same measurements in the male IAN being 20,278, 31.7 microm(2), 20.7 microm, and 0.87, respectively. Our data showed no significant difference between the female and male specimens in any measured item (P < .05).

CONCLUSIONS

We assumed that the sex difference in the incidence of IAN damage was not affected by the morphometric findings. Our findings might partly explain why there is no significant sex difference in the incidence of IAN damage.

Modification of classical neurochemical markers in identified primary afferent neurons with Aβ-, Aδ-, and C-fibers after chronic constriction injury in mice

It is functionally important to differentiate between primary afferent neurons with A-fibers, which are nociceptive or nonnociceptive, and C-fibers, which are mainly nociceptive. Neurochemical markers such as neurofilament 200 (NF200), substance P (SP), and isolectin B4 (IB4) have been useful to distinguish between A- and C-fiber neurons. However, the expression patterns of these markers change after peripheral nerve injury, so that it is not clear whether they still distinguish between fiber types in models of neuropathic pain. We identified neurons with Abeta-, Adelta-, and C-fibers by their conduction velocity (corrected for utilization time) in dorsal root ganglia taken from mice after a chronic constriction injury (CCI) of the sciatic nerve and control mice, and later stained them for IB4, SP, calcitonin gene-related peptide (CGRP), NF200, and neuropeptide Y (NPY). NF200 remained a good marker for A-fiber neurons, and IB4 and SP remained good markers for C-fiber neurons after CCI. NPY was absent in controls but was expressed in A-fiber neurons after CCI. After CCI, a group of C-fiber neurons emerged that expressed none of the tested markers. The size distribution of the markers was investigated in larger samples of unidentified dorsal root ganglion neurons and, together with the results from the identified neurons, provided only limited evidence for the expression of SP in Abeta-fiber neurons after CCI. The extent of up-regulation of NPY showed a strong inverse correlation with the degree of heat hyperalgesia.

Enzyme replacement therapy improves function of C-, Adelta-, and Abeta-nerve fibers in Fabry neuropathy

BACKGROUND

Peripheral neuropathy in Fabry disease predominantly involves small nerve fibers. Recently, enzyme replacement therapy (ERT) with recombinant human alpha-galactosidase A has become available.

OBJECTIVE

To evaluate whether ERT improves Fabry neuropathy.

METHODS

In 22 Fabry patients (age 27.9 +/- 8.0 years) undergoing ERT with recombinant human alpha-galactosidase A (agalsidase beta) for 18 (n = 11) or 23 (n = 11) months and in 25 control subjects (age 29.0 +/- 10.4 years), the authors performed quantitative sensory testing using the 4, 2, and 1 stepping algorithm (CASE IV). Detection thresholds of vibration (VDT) on the first toe were assessed; cold detection thresholds (CDT), heat-pain onset (HP 0.5), and intermediate heat-pain (HP 5.0) assessments were made on the dorsum of the feet. Patient values above mean + 2.5 SD of control values were considered abnormal.

RESULTS

Before ERT, VDT, CDT, HP 0.5, and HP 5.0 were higher in patients than control subjects (p < 0.05). Following ERT, patients developed lower thresholds than prior to ERT for VDT (15.5 +/- 3.5 vs 14.3 +/- 4.1; p < 0.05), HP 0.5 (22.3 +/- 6.7 vs 19.4 +/- 1.3; p < 0.01), and HP 5.0 (27.3 +/- 5.6 vs 22.5 +/- 2.3; p < 0.01). Moreover, fewer patients had abnormal results of VDT (2 vs 4), CDT (7 vs 12), HP 0.5 (0 vs 9), and HP 5.0 (4 vs 20) after than before ERT.

CONCLUSIONS

ERT therapy with agalsidase beta significantly improves function of C-, Adelta-, and Abeta-nerve fibers and intradermal vibration receptors in Fabry neuropathy. Lack of recovery in some patients with abnormal cold or heat-pain perception suggests the need for early ERT, prior to irreversible nerve fiber loss.

A myelo-architectonic method for the structural classification of cortical areas

We describe an automatic and reproducible method to analyze the histological design of the cerebral cortex as applied to brain sections stained to reveal myelinated fibers. The technique provides an evaluation of the distribution of myelination across the width of the cortical mantle in accordance with a model of its curvature and its intrinsic geometry. The profile lines along which the density of staining is measured are generated from the solution of a partial differential equation (PDE) that models the intermediate layers of the cortex. Cortical profiles are classified according to significant components that emerge from wavelet analysis. Intensity profiles belonging to each distinct class are normalized and averaged to produce area-specific templates of cortical myelo-architecture.

Capsaicin responses in heat-sensitive and heat-insensitive A-fiber nociceptors

The recently cloned vanilloid receptor (VR1) is postulated to account for heat and capsaicin sensitivity in unmyelinated afferents. We sought to determine whether heat and capsaicin sensitivity also coexist in myelinated nociceptive afferents. Action potential (AP) activity was recorded from single A-fiber nociceptors that innervated the hairy skin in monkey. Before intradermal injection of capsaicin (10 microg/10 microl) into the receptive field, nociceptors were classified as heat-sensitive (threshold, </=53 degrees C, 1 sec) or heat-insensitive afferents and as mechanically sensitive (von Frey threshold, <6 bar) or mechanically insensitive afferents. All heat-sensitive afferents (n = 16) were insensitive to mechanical stimuli but responded to the intradermal injection of capsaicin (69 +/- 7 APs in 10 min). Responsiveness to mechanical stimuli, thermal stimuli, and capsaicin varied in their receptive fields; the majority of receptive field sites (24 of 36) were responsive to only one or two stimulus modalities, whereas only eight sites responded to all three modalities. For most heat-insensitive afferents, the activity induced by the capsaicin injection did not exceed the activity induced by needle insertion alone. However, the largest response to capsaicin (314 +/- 98 APs in 10 min) was observed for five afferents that were insensitive to heat as well as mechanical stimuli and therefore may be classified as cutaneous chemoreceptors. These results suggest that A-fiber nociceptors play a role in the pain and hyperalgesia associated with capsaicin injection. Our finding that a subgroup of capsaicin-sensitive A-fiber nociceptors are insensitive to heat predicts the existence of heat-insensitive capsaicin receptors.

The classification and properties of nociceptive afferent units from the skin of the anaesthetized pig

The afferent properties of nerve fibres innervating the hairy skin of the pig hind limb were investigated by recording from 142 single units from the saphenous nerve. Identified single units were isolated using maximal electrical stimulation of the nerve trunk. Afferent units were classified on the basis of their responses to a range of stimuli, both thermal (heating to 60 degrees C and cooling to 10 degrees C) and mechanical (air jet, von Frey type filaments with forces of 0.1-250 mN, and strong pressure with a blunt needle). A-fibre units (conduction velocity 6.3-64 m/s, n = 60) fell into categories that have been described in hairy skin in other mammalian species. Most were mechanoreceptors, although seven typical A-fibre mechanical nociceptors with large, multipoint fields were also isolated. No cutaneous receptive field could be found for 15% of A-fibre units. Out of 62 C-fibre units (conduction velocity 0.49-2 m/s) 40% had no cutaneous field for pressure, heat or cold. Of the C-fibre units with cutaneous fields, 42% were polymodal nociceptors, 38% were mechanoreceptors with a variety of properties, including some excited by noxious heat, and 19% were heat-only nociceptors. C-polymodal nociceptors had large receptive fields up to 12.5 mm across and did not sensitize following strong heating. Twenty units conducted at 2-6.3 m/s, between the main C- and A-fibre bands, and were varied in their responses. Some had properties identical to C-fibre mechanoreceptors whilst four were sensitive cold thermoreceptors and one was a polymodal nociceptor. Two units were mechanical nociceptors with small receptive fields.(ABSTRACT TRUNCATED AT 250 WORDS)

Peripheral neuropathy in myotonic dystrophy: a nerve biopsy study

Sural nerve biopsies from 13 unselected myotonic dystrophy patients and 6 normal controls were studied morphometrically. The myelinated fiber density was reduced in 11 of the 13 myotonic dystrophy patients, with preferential loss of large myelinated fibers. Unmyelinated fiber densities and diameters were normal. Teased fiber studies commonly revealed focal areas of remyelination and abnormal wrinkling of the myelin sheath. Measurement of internodal length disclosed features of both axonal regeneration and focal demyelination-remyelination. These findings are consistent with a chronic axonopathy of moderate severity, possibly due to axonal atrophy.