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.     

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.     

PACAP facilitate the nerve regeneration factors in the facial nerve injury

Pituitary adenylate cyclase-activating polypeptide (PACAP) has been reported as a strong neurotrophic factor in the various sites of nervous system. The facial nerve injury is one of the common problems in patients at the Otolaryngology since the nerve damage could occur easily due to the anatomical characteristics. Once it happens, the regeneration is little observed and functional recovery is poor. Thus, we investigated that PACAP might have some influence for regeneration after the facial nerve transaction in the guinea pig. PACAP treatment accelerated time for the appearance of compound muscle action potentials (CMAP) after the nerve transaction (first appeared at 1 versus 2 weeks in control) and shortened the latency at 4 weeks. The number of myelinated fibers increased at 4 weeks. Histochemical demonstration of GAP-43, a growth cone protein, was observed at the injury area at 2-4 days. PACAP increased the level of glial cell line-derived neurotrophic factor (GDNF), a neurotrophin, in facial target muscles at 1 day-4 weeks. These data indicated that PACAP promotes the regeneration factors and increases the possibility of functional recovery following the facial nerve injury.     

Aberrant cutaneous nerve of the thigh arising from the sciatic nerve in the human

An aberrant cutaneous nerve of the thigh arising from the peroneal portion of the human sciatic nerve or common peroneal nerve was observed in 9 cases (4.6% of sides). After giving a branch to the short head of the biceps femoris muscle and a branch to the knee joint, this cutaneous nerve reaches the subcutaneous tissue by passing between the short head of the biceps femoris and the vastus lateralis or by piercing through the biceps femoris. The authors presume that the cutaneous nerve shows the presence of the potential cutaneous nerve routes from the common peroneal nerve to the skin of the lateral aspect of the thigh.     

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.     

An alternative to the classical nerve graft for the management of the short nerve gap

Reconstruction of a short nerve gap by a nerve graft produces donor-site scarring, loss of donor nerve function, and neuroma formation. This study compared the regeneration achieved after 1 year in 16 monkeys across a 3-cm upper arm ulnar nerve gap with a bioabsorbable polyglycolic acid nerve conduit with the regeneration achieved with a classical interfascicular interpositional sural nerve graft. The results demonstrated electrophysiologic and histologic evidence of neural regeneration across the gaps in all experimental groups. The bioabsorbable nerve conduit groups and the sural nerve graft group had mean fiber diameters, amplitudes, and conduction velocities each significantly less than those of normal control ulnar nerves. There was, however, no significant difference between any of the experimental groups. Electromyography demonstrated recovery of 19 of the 28 (68 percent) intrinsic muscles studied. These results demonstrate that the primate peripheral nerve can regenerate across short nerve gaps when guided by an appropriate nerve conduit, suggesting that a single-stage biodegradable polyglycolic acid conduit may be used as an alternative to a short interfascicular nerve graft.     

On the nerve impulse equation: The dynamic responses of nerve impulse

With the assumption of dipole interaction with the membrane matrix, the dipole barrier under an applied field shows a minimum in its time transient. Kinetic equations governing the migration of ions are presented. Na⁺ activation, Na⁺ inactivation and K⁺ delay are all part of the same mechanism in this model with no other separate assumptions needed. Voltage Clamp equation and action potential equation are presented. Supported in part by Physics Research Center, National Science Council, The Republic of China.     

On the maxillary nerve

The trigeminal, the fifth cranial nerve of vertebrates, represents the rostralmost component of the nerves assigned to pharyngeal arches. It consists of the ophthalmic and maxillomandibular nerves, and in jawed vertebrates, the latter is further divided into two major branches dorsoventrally. Of these, the dorsal one is called the maxillary nerve because it predominantly innervates the upper jaw, as seen in the human anatomy. However, developmentally, the upper jaw is derived not only from the dorsal part of the mandibular arch, but also from the premandibular primordium: the medial nasal prominence rostral to the mandibular arch domain. The latter component forms the premaxillary region of the upper jaw in mammals. Thus, there is an apparent discrepancy between the morphological trigeminal innervation pattern and the developmental derivation of the gnathostome upper jaw. To reconcile this, we compared the embryonic developmental patterns of the trigeminal nerve in a variety of gnathostome species. With the exception of the diapsid species studied, we found that the maxillary nerve issues a branch (nasopalatine nerve in human) that innervates the medial nasal prominence derivatives. Because the trigeminal nerve in cyclostomes also possesses a similar branch, we conclude that the vertebrate maxillomandibular nerve primarily has had a premandibular branch as its dorsal element. The presence of this branch would thus represent the plesiomorphic condition for the gnathostomes, implying its secondary loss within some lineages. The branch for the maxillary process, more appropriately called the palatoquadrate component of the maxillary nerve (V₂), represents the apomorphic gnathostome trait that has evolved in association with the acquisition of an upper jaw. J. Morphol. 275:17–38, 2014. © 2013 Wiley Periodicals, Inc.     

Neural conduction velocity of the human auditory nerve: bipolar recordings from the exposed intracranial portion of the eighth nerve during vestibular nerve section

We measured the conduction velocity of the intracranial portion of the auditory nerve in 3 patients undergoing vestibular nerve section to treat Ménière's disease. The conduction velocity varied from patient to patient, with an average value of 15.1 m/sec. The latency of peak III of the brain-stem auditory evoked potentials (BAEPs) increased by an average of 0.5 msec as a result of exposure of the eighth nerve, and if that increase is assumed to affect the entire length of the auditory nerve (2.6 cm) evenly, then the corrected estimate of conduction velocity would be 22.0 m/sec. Estimates of conduction velocity based on the interpeak latencies of peaks I and II of the BAEP, assuming that peak II is generated by the mid-portion of the intracranial segment of the auditory nerve, yielded similar values of conduction velocities (about 20 m/sec).