Microtubule stability along mammalian peripheral nerves

Microtubule (MT) number, axonal area, and MT density were examined in unmyelinated axons of rat cervical vagus nerve. Study of nerve regions proximal (1-5 mm) and distal (35-40 mm) to the nodosum ganglion in controls (incubation at 37 degrees C for 1 h) showed that the number of MT per axon is significantly less in distal than in proximal nerve regions. Cooling (incubation at 0 degree C for 1 h) caused a significant reduction in the number of MT per axon in both nerve regions. The unmyelinated axons from both nerve regions showed a comparable reduction in MT number by cooling, indicating that axonal MT stability to cold was not significantly different between these two nerve regions. In these nerves no detectable changes were found in cross-axonal area of unmyelinated axons between distal and proximal nerve regions. In another experimental series, in distal nerve regions (35-40 mm from the nodosum ganglion) the number of MT was not further reduced in nerves incubated at 0 degree C by increasing the incubation time. Similar results were obtained from colchicine treated nerves (incubation at 37 degrees C, with 10 mM colchicine for 1 and 2 h). Distal nerve regions (35-40 mm from the nodosum ganglion) showed a similar reduction in the number of MT per axon when nerves were incubated at 0 degree C or with colchicine, suggesting that this drug, as well as cold, may be affecting a similar population of axonal MT, i.e., MT susceptible to anti-MT agents. These results indicate that approximately one-half of the axonal MT are stable to cold as well as to colchicine in rat unmyelinated axons.     

Cellular migration and axonal outgrowth from adult mammalian peripheral nerves in vitro

It is known that following peripheral nerve transections, sheath cells proliferate and migrate to form a bridge between nerve stumps, which may facilitate axonal regeneration. In the present investigations, cellular migration and axonal outgrowth from nerves of adult mice were studied in vitro using collagen gels. During the first 3 days in culture, profuse migration of fibroblasts and macrophages occurred from the ends of sciatic nerve segments, which had been lesioned in situ a few days prior to explanation, but not from segments of normal nerves. The mechanism of cellular activation in the lesioned nerves was not determined, but migration was blocked by suramin, which inhibits the actions of several growth factors. The migrating cells, which form the bridge tissue, may promote axonal regeneration in two ways. Firstly, axonal outgrowth from isolated intercostal nerves was significantly increased in co-cultures with bridges from lesioned sciatic nerves. This stimulatory effect was inhibited by antibodies to 2.5S nerve growth factor. Secondly, the segments of bridge tissue contracted when removed from animals. It is possible that fibroblasts within the bridge exert traction that would tend to pull the lesioned stumps of peripheral nerve together, as in the healing of skin wounds. The traction may also influence deposition of extracellular matrix materials, such as collagen fibrils, which could orient the growth of the regenerating axons toward the distal nerve stump. © 1996 John Wiley & Sons, Inc.     

Comparative studies on myelin proteins in mammalian peripheral nerve.

Myelin proteins in mammalian peripheral nerve were studied comparatively. 1. While each content of P1 and P2 in the myelin varied among species, additional content of P1 and P2 are relatively constant. 2. The antigenic determinants of P2 for induction of experimental allergic neuritis were reported. 3. Amino acid sequence analysis of P0 revealed that P0 is conserved across species and belongs to the immunoglobulin superfamily. 4. The characteristic carbohydrate chain of P0 containing sulfate and sialic acid showed a positive reaction to the molecule-related immunity and adhesion. 5. Molecular architecture of the myelin is discussed.     

Sensory nerves in central and peripheral control of pancreatic integrity by leptin and melatonin.

Central nervous system affects pancreatic secretion of enzymes however, the neural modulation of acute pancreatitis has not been investigated. Leptin and melatonin have been recently reported to affect the inflammatory response of various tissues. The identification of specific receptors for both peptides in the pancreas suggests that leptin and melatonin could contribute to the pancreatic protection against inflammation. The aim of this study was: 1/ to compare the effect of intracerebroventricular (i.c.v.) or intraperitoneal (i.p.) administration of leptin or melatonin on the course of caerulein-induced pancreatitis (CIP) in the rat, 2/ to examine the involvement of sensory nerves (SN) and calcitonin gene-related peptide (CGRP) in pancreatic protection afforded by leptin or melatonin, 3/ to assess the effect of tested peptides on lipid peroxidation products (MDA + 4-HNE) in the pancreas of CIP rats, 4/ to investigate the influence of leptin or melatonin on nitric oxide (NO) release from isolated pancreatic acini and 5/ to determine the effects of caerulein and leptin on leptin receptor gene expression in these acini by RT-PCR. CIP was induced by subcutaneous (s.c.) infusion of caerulein (25 microg/kg) to the conscious rats, confirmed by the significant increases of pancreatic weight and plasma amylase and by histological examination. This was accompanied in marked reduction of pancreatic blood flow and significant rise of MDA + 4-HNE in the pancreas. Leptin or melatonin were administered i.p. or i.c.v. 30 min prior to the start of CIP. Deactivation of SN was produced by s.c. capsaicin (100 mg/kg). An antagonist of CGRP, CGRP 8-37 (100 microg/kg i.p.), was given together with leptin or melatonin to the CIP rats. MDA + 4-HNE was measured using LPO commercial kit. NO was determined using the Griess reaction. Pretreatment of CIP rats with i.p. leptin (2 or 10 microg/kg) or melatonin (10 or 50 mg/kg) significantly attenuated the severity of CIP. Similar protective effects were observed following i.c.v. application of leptin (0.4 or 2 microg/rat) but not melatonin (10 or 40 microg/rat) to the CIP rats. Capsaicin deactivation of SN oradministration of CGRP 8-37 abolished above beneficial effects of leptin on CIP, whereas melatonin-induced protection of pancreas was unaffected. Pretreatment with i.p. melatonin (10 or 50 mg/kg), but not leptin, significantly reduced MDA + 4-HNE in the pancreas of CIP rats. Leptin (10(-10) - 10(-6) M) but not melatonin (10(-8) - 10(-5) M) significantly stimulated NO release from isolated pancreatic acini. Leptin receptor gene expression in these acini was significantly increased by caerulein and leptin. We conclude that 1/ central or peripheral pretreatment with leptin protects the pancreas against its damage induced by CIP, whereas melatonin exerts its protective effect only when given i.p., but not following its i.c.v. adminstration, 2/ activation of leptin receptor in the pancreatic acini appears to be involved in the beneficial effects of leptin on acute pancreatitis, 3/ the protective effects of leptin involve sensory nerves, CGRP and increased generation of NO whereas melatonin-induced protection of the pancreas depends mainly on the antioxidant local effect of this indole, and scavenging of the radical oxygen species in the pancreatic tissue.     

Proprioceptive afferent fibers in the cranial nerves III, IV and VI.

The purpose of the present works was to clarify whether the cranial nerves III, IV and VI carry proprioceptive afferent fibres from the extrinsic ocular muscles. In sheep the picture is now clear. The cranial nerves III, IV and VI carry many large proprioceptive fibres (12-16 micrometer) to the central nervous system. These nerves also contain many small fibres of the y-range (2-6 micrometer) which innervate the intrafusal muscle fibres in the spindles. In man the picture is still vague: most of the spindles are not typical, the large proprioceptive fibres (12-16 micrometer) and the small y-fibres (2-6 micrometer) are very few in the cranial nerves III, IV and VI. It is to be concluded that in sheep the cranial nerves III, IV and VI are not purely motor nerves to the extrinsic ocular muscles, but they also carry many of the large fibres of the proprioceptive function. In man, such large fibres are not found and the pathway of proprioceptive afferents from the orbital muscles is still not certain.     

Hemopexin is synthesized in peripheral nerves but not in central nervous system and accumulates after axotomy.

In adult mammals, injured axons regrow over long distances in peripheral nerves but fail to do so in the central nervous system. Analysis of molecular components of tissue environments that allow axonal regrowth revealed a dramatic increase in the level of hemopexin, a heme-transporting protein, in long-term axotomized peripheral nerve. In contrast, hemopexin did not accumulate in lesioned optic nerve. Sciatic nerve and skeletal muscle, but not brain, were shown to be sites of synthesis of hemopexin. Thus, hemopexin expression, which can no longer be considered to be liver-specific, correlates with tissular permissivity for axonal regeneration.     

Distribution of tau proteins in the normal human central and peripheral nervous system

In human brain, antibodies to tau proteins primarily label abnormal rather than normal structures. This might reflect altered immunoreactivity owing to post-mortem proteolysis, disease, or species differences. We addressed this issue by comparing the distribution of tau in bovine and human post-mortem nervous system tissues and in human neural cell lines, using new monoclonal antibodies (MAb) specific for phosphate-independent epitopes in bovine and human tau. In neocortex, hippocampus, and cerebellum, immunoreactive tau was widely expressed but segregated into the axon-neuropil domain of neurons. In spinal cord and peripheral nervous system, tau immunoreactivity was similarly segregated but less abundant. No immunoreactive tau was detected with our MAb in glial cells or in human neural cell lines that express neurofilament or glial filament proteins. Post-mortem delays in tissue denaturation of less than 24 hr did not affect the distribution of tau, but the method used to denature tissues did, i.e., microwave treatment preserved tau immunoreactivity more effectively than chemical fixatives such as Bouin's solution, and formalin-fixed tissue samples reacted poorly with our anti-tau MAb. We conclude that the distribution of tau proteins in human nervous system is similar to that described in perfusion-fixed experimental animals, and that visualization of normal immunoreactive tau in human tissues is critically dependent on the procedures used to denature post-mortem tissue samples. Furthermore, microenvironmental factors in different neuroanatomical sites may affect the regional expression of tau.