Electrical phenomena in nerve; crab nerve

The resting and action potentials of the leg nerves of the spider crab are reduced by procaine, cocaine, iodoacetate, KCl, and veratrine. The first three agents depress the sensitivity of the resting potential to anoxia, while the last can be shown to augment it. Glucose sustains activity and the polarized state in the absence of oxygen, an effect blocked by iodoacetate; corresponding concentrations of lactate and pyruvate are inert under most experimental conditions. DDT and veratrine both induce repetitive activity following an impulse, but only the latter does so with a marked increase in negative after-potential. The negative after-potential induced by veratrine is decreased by KCl relatively more than the spike or the resting potential. Elevation of the calcium content of the medium increases this after-potential. Neither ion appreciably alters the time constant of repolarization. The recovery is more rapid than that obtained following prolonged activity of both veratrinized and unveratrinized nerves. Repolarization following a tetanus is accelerated by an increase in the volume of solution in contact with the fibers; associated with this is an augmentation of the positive after-potential which normally follows a bout of activity. Yohimbine induces a positive after-potential following individual spikes which is depressed by an elevation of the potassium or calcium content of the medium. These observations are discussed from the standpoint of the available evidence for the involvement of potassium at the surface of the fibers as regulated by a labile permeability and metabolism. The potassium liberated by the action potential, calculated from the polarization changes, agrees closely with an available analytical figure; less direct observations are also found to be consistent with this view.     

Decline of IXth nerve taste responses following nerve transection

Summated impulse discharges to taste solutions were recordedfrom intact and transected IXth nerves in the Mongolian gerbil(Meriones unguiculatus). Five taste stimuli were used: 0.3 MNH₄Cl, 0.3 M NaCl, 0.01 M HCl, 0.01 M quinine hydrochloride,and 0.5 M sucrose. 0.3 M NH₄Cl was the most effective stimulus.Taste responses from intact nerves were stable for more than10 hours. Following IXth nerve transection, the peak summatedresponse to 0.3 M NH₄Cl declined by 50% in a mean of 119 min.(Some animals failed to show this taste response decline inthe winter months.) The transected IXth nerve's spontaneousactivity and responses to other taste solutions also typicallydeclined. The continued presence of normal compound action potentialsindicated that the transection-induced decline in taste responsesdid not result from a failure of impulse propagation mechanismsin the nerve trunk. The results are consistent with the propositionthat transection interferes with axonal transport of materialsvital to the short-term maintenance of taste responses.     

After-depolarization of the frog nerve and single nerve fiber

Experiments on frogs (Rana ridibunda) showed that, unlike in the whole nerve, prolonged after-depolarization and the associated phase of summation are absent in the single node of Ranvier of isolated nerve fibers. If, however, special measures are taken to prevent the stretching of the Ranvier node of single fibers, prolonged after-depolarization can be found in them. It is concluded that the absence of prolonged after-depolarization in single Ranvier nodes of nerve fibers isolated without additional precautions is the result of injury to the excitable membrane or to disturbance of the integrity of the ionic barrier surrounding it as a result of stretching of the fibers during dissection.     

Adrenergic nerve fibers in the human fetal sciatic nerve.

The adrenergic innervation was studied in the human sciatic nerve at the gestational age of 16, 17, 18 and 21 weeks. Formaldehyde-induced catecholamine fluorescence, tyrosine hydroxylase (TH) and neuropeptide Y (NPY) peroxidase-antiperoxidase immunohistochemistry methods were used. At the gestational age of 16, 17 and 18 weeks no adrenergic or NPY-positive nerve fibers were seen. At 21 weeks both fluorescence microscopy and TH immunohistochemistry showed adrenergic nerve fibers around arterioles in the epiperineurium and single nerve fibers in the endoneurium not related to blood vessels. The number of adrenergic nerve fibers appeared to be higher in the sciatic than in the tibial segment of the nerve. At this age, as at earlier stages of gestation, no NPY-positive nerve fibers were seen either in the epiperineurium or in the endoneurium. The results suggest that adrenergic nerve fibers may be associated with the epiperineurial blood vessels in the human sciatic nerve, and that the innervation starts to develop between 18 and 21 weeks of gestational age.     

Target-specific nerve regeneration through a nerve guide in the rat

Nerve regeneration across a gap in peripheral nerve has been achieved through various nonneural nerve guides in both lower and primate species. This technique can only be useful if the regenerated nerve cable grows specifically to and reinnervates the appropriate distal target. In this study, the proximal peroneal fascicle of rat sciatic nerve was inserted into the proximal limb of a Y-shaped nerve guide. Distal peroneal and tibial fascicles were placed within the two distal limbs of the same Y. The proximal peroneal nerve grew preferentially by a 2:1 ratio to the appropriate distal peroneal fascicle suggesting that target-specific reinnervation is possible through a nerve guide.     

Stretch-induced nerve conduction deficits in guinea pig ex vivo nerve

In the current communication, we characterized supraphysiologic elongations that elicited short-term nerve dysfunction. This was accomplished by assessing the electrophysiology of guinea pig tibial and peroneal nerves at predetermined elongation magnitudes. Results showed that a longitudinal supraphysiological stretch of lambda = 1.05 caused a 16% reduction in the mean compound action potential (CAP) amplitude. Upon relaxation to physiologic length, a full recovery in the CAP was observed. At lambda = 1.10, the CAP decreased by 50% with an 88% recovery after relaxation. For a supraphysiologic stretch of lambda = 1.20, severe conduction block with minimal acute recovery was observed. Latency also increased during periods of stretch and was proportional to the stretch magnitude. Additional studies showed some electrophysiological recovery during the sustained stretch phase. This attribute may be related to internal stress relaxation mechanisms. Since whole nerve elongations are averaged global deformations, we also used an incremental digital image correlation (DIC) technique to characterize the strain at the micro-tissue level. The DIC analysis revealed considerable heterogeneity in the planar strain field, with some regions exhibiting strains above the macroscale stretch. This non-uniformity in the strain map arises from structural inconsistencies of the nerve and we presume that zones of high local strain may translate into the observed conduction deficits.     

P311 accelerates nerve regeneration of the axotomized facial nerve

In axotomized adult neurons, a process of axonal regrowth and re-establishment of the neuronal function has to be activated. Developmentally regulated factors may be reactivated during neuronal regeneration. Here we identify a gene, previously designated P311, that is up-regulated in the axotomized facial motoneurons. Ectopically expressed P311 localizes in the cytoplasm and the nucleus. Over-expression of P311 induces p21(WAF1/Cip1) expression, leading PC12 cells to differentiate and to have neuron-like morphologies. Adenovirus-mediated P311 gene transfer promotes neurite outgrowth of postnatal dorsal root ganglion neurons and embryonic hippocampal neurons in vitro. This effect is abolished by the activation of Rho kinase. P311 also facilitates nerve regeneration following facial nerve injury in vivo. Our data provide evidence that genes involved in the differentiation process contribute to the regeneration of injured mature neurons, and may provide a practical molecular target.     

Use new PLGL-RGD-NGF nerve conduits for promoting peripheral nerve regeneration

ABSTRACT: BACKGROUND: Nerve conduits provide a promising strategy for peripheral nerve injury repair. However, the efficiency of nerve conduits to enhance nerve regeneration and functional recovery is often inferior to that of autografts. Nerve conduits require additional factors such as cell adhesion molecules and neurotrophic factors to provide a more conducive microenvironment for nerve regeneration. METHODS: In the present study, poly{(lactic acid)-co-[(glycolic acid)-alt-(L-lysine)]} (PLGL) was modified by grafting Gly-Arg-Gly-Asp-Gly (RGD peptide) and nerve growth factor (NGF) for fabricating new PLGL-RGD-NGF nerve conduits to promote nerve regeneration and functional recovery. PLGL-RGD-NGF nerve conduits were tested in the rat sciatic nerve transection model. Rat sciatic nerves were cut off to form a 10 mm defect and repaired with the nerve conduits. All of the 32 Wistar rats were randomly divided into 4 groups: group PLGL-RGD-NGF, group PLGL-RGD, group PLGL and group autograft. At 3 months after surgery, the regenerated rat sciatic nerve was evaluated by footprint analysis, electrophysiology, and histologic assessment. Experimental data were processed using the statistical software SPSS 10.0. RESULTS: The sciatic function index value of groups PLGL-RGD-NGF and autograft was significantly higher than those of groups PLGL-RGD and PLGL. The nerve conduction velocities of groups PLGL-RGD-NGF and autograft were significantly faster than those of groups PLGL-RGD and PLGL. The regenerated nerves of groups PLGL-RGD-NGF and autograft were more mature than those of groups PLGL-RGD and PLGL. There was no significant difference between groups PLGL-RGD-NGF and autograft. CONCLUSIONS: PLGL-RGD-NGF nerve conduits are more effective in regenerating nerves than both PLGL-RGD nerve conduits and PLGL nerve conduits. The effect is as good as that of an autograft. This work established the platform for further development of the use of PLGL-RGD-NGF nerve conduits for clinical nerve repair.     

Olfactory nerve fibers

Cross sections of olfactory nerves present a unique appearance. They indicate the presence of large numbers of very small nerve fibers, with a modal diameter of about 0.2 µ and a narrow range for their size variation. From one side of the nasal septum of a pig the yield of fibers was estimated at 6,000,000; the number arising from the turbinates would be considerably larger. The fibers are attached to the membranes of the Schwann sheaths in large bundles through mesaxons longer and more branched than those that have been seen in other nerves. Continuity of the axons between the nerves and the bipolar cells was traced in an examination of the olfactory mucous membrane; and the indication of a one-to-one relationship between cells and axons was reinforced by a comparative count. After the axons leave the bipolar cells they become incased in the central projections of the sustentacular cells. Where the latter come into contact with the basal cells the axons emerge to push back the plasma membranes of the basal cells in the first step in acquiring their nerve sheaths. Later steps are described. When the axons are delivered by the basal cells to the collecting Schwann tubes, they are already aggregated into small bundles with sheaths fundamentally the same as those they will possess until they are delivered to the glia in the olfactory bulb. Some of the aspects of the cytology of the bipolar cells and adjoining sustentacular cells are described. A survey of the physiological properties of olfactory nerve fibers was made in some experiments on the olfactory nerve of the pike. Almost all of the action potential is encompassed within a single elevation, manifesting at its front a conduction velocity of 0.2 m./sec. For a comparison, the last elevation in the C action potential in the sciatic nerve of the frog is cited as an example of conduction at the same velocity. Though expressed through long time constants, the properties of the pike olfactory fibers conform to the generalized schema for properties of vertebrate nerve fibers. This conformity signalizes that they differ from the exceptional properties of the unmedullated fibers of dorsal root origin. An afferent function for unmedullated nerve fibers does not imply that the fibers concerned are alike in their physiological properties.