Restorative Neurology and Neuroscience

Fetal neocortical block transplants were implanted into the excitotoxically ablated sensorimotor cortex of adult rats in order to examine the density of innervation and distribution of presumptive host derived afferent fibers within these transplants. Cholinergic fiber innervation was examined at 3 months post grafting by measuring acetylcholinesterase (AChE) and choline acetyl-transferase (ChAT) enzyme activities within the grafts and within the corresponding host cortex by radiochemical enzyme assays as well as by AChE histochemistry for the visualization of AChE positive fibers. Noradrenergic and serotonergic inputs were examined by high performance liquid chromatography (HPLC) measurements of noradrenaline (NA) and serotonin (5-hydroxytryp-tamine, 5-HT) concentrations as well as by tyrosine hydroxylase (TH) and 5-HT immunocytochemistry for the visualization of monoaminergic fiber distribution. Our results demonstrated that the grafts contained significantly lower levels of neurotransmitter markers when compared to normal unablated cortex. The anatomical analysis showed an unequal fiber distribution within the transplants. Areas adjacent to the host tissue revealed a relatively dense fiber innervation when compared to the density observed within the more central parts of the transplants, and the anatomical data therefore supported the biochemical data in suggesting an overall lower cholinergic and monoaminergic innervation of fetal neocortical transplants placed into the lesioned adult cortex when compared to normal cortex.

The neural cell adhesion molecule, N-CAM, makes critical contributions to the development of the nervous system. It mediates the stability of homophilic adhesion in embryonic neurons and participates in morphologic differentiation. The goal of these studies was to determine N-CAM contributions to nerve regeneration and recovery of function in two species with an excised segment of sciatic nerve. N-CAM was isolated from embryonic brains, affinity purified and admixed in collagen gel for administration. Recovery was compared 30 days after surgery for two types of N-CAM delivery: entubulization versus direct application. For control nerves, tubes contained gel only. In preliminary chicken studies, latency of nerve responses was measured to demonstrate N-CAM's ability to improve upon spontaneous recovery. In subsequent studies of rodent nerves, the direct application of N-CAM significantly improved recovery in evoked nerve response amplitude, number of regenerated axons and behavioral activity. Results demonstrate N-CAM's ability to augment nerve regeneration and suggest a potential for therapeutic use.

To characterize the influence of primary afferent activation on the development of histopathological changes in the spinal cord after reversible ischemia, the left sciatic nerve was stimulated at the intensity of myelinated fibers before, during and for 1 h after 10 min of abdominal aortic ligation in halothane anesthetized rabbits. In control animals, only 10 min of spinal cord ischemia or sciatic nerve stimulation was employed. One hour after reperfusion all animals were perfusion fixed with 4% paraformaldehyde. Histopathological analysis using the suppressive Nauta method revealed significantly higher number of argyrophilic neurons in dorsal horns and in the intermediate zone in animals in which spinal cord ischemia was combined with sciatic nerve stimulation in comparison with the animals with spinal cord ischemia, but without stimulation. These histopathological changes corresponded with signs of irreversible damage analyzed on the ultrastructural level. Stimulation of sciatic nerve, but without ischemia did not evoke any detectable neuronal changes. The data from the present study suggest that increased activity of spinal cord neurons evoked by peripheral nerve stimulation can be an important factor in determining the extent of irreversible damage after short lasting ischemia.

Right-hemisphere-damaged (RHD) patients with contralesional neglect in the visual modality (n = 8) were found to differ from normal controls (n = 8), and also from RHD patients without visual neglect (n = 7), in their ability to identify auditory stimuli delivered through a loudspeaker on the left side. When the same stimuli on the left were administered in the presence of a fictitious source of sound (a dummy loudspeaker) visible in the homolesional space, a significant increase in the identification score was obtained (the ‘ventriloquist effect’). The result is in keeping with a notion of a strong coupling between auditory and visual systems. It is attributed to the activation by the fictitious stimulus of the audio-visual map in the left hemisphere. We draw attention to the possibility that the symptomatic relief associated with the above effect could be translated into certain clinical gains over time.

Fibrin sealing of nerves has become a commonly used technique in the treatment of brachial plexus injuries as it is quicker than microsuture, but the tensile strength of the fibrin has been in question. A new fibrin (Tisseel-DUO®, Immuno; Austria) is now available which we have previously studied and with which we had no anastomotic failures. This study is a continuation of our previous work and the aim was to evaluate further the histological and functional outcome after repair with this new product. The sciatic nerves in 15 rats were divided and rejoined with fibrin. The animals were allowed to survive for 3 months and their movement was unrestricted from immediately after the operation. The numbers of myelinated and unmyelinated axons were evaluated after regeneration at × 5000 and × 14 000 respectively. Regenerated function of polymodal nociceptors and low threshold mechano-receptors were evaluated in hairy and glabrous skin. Results from normal rats (n = 15) and rats that had undergone neurotomy and microsuture (n = 15) were used for comparison. After regeneration, counts of myelinated and unmyelinated axons in branches to hairy and glabrous skin differed significantly (P ≤ 0.05) when fibrin was used compared with microsuture, but this difference was not reflected in the functional regeneration. We conclude that this product may be a time saving alternative to microsuture of peripheral nerves in patients.

Regeneration distances were studied in nerves from vibration-exposed limbs. One hind limb of anaesthetized rats was attached to a vibration exciter and exposed to vibration (80 Hz/32 m/s²) for 5 h/day for 2 or 5 days. Seven days after the latest vibration period a 10-mm long nerve graft was taken from the vibrated sciatic nerve and sutured into a corresponding defect in the con-tralateral sciatic nerve and vice versa, thereby creating two different models within the same animal: (i) regeneration from a freshly transected unvibrated nerve into a vibrated graft and (ii) regeneration from a vibrated nerve into a fresh nerve graft (vibrated recipient side). Four, 6 or 8 days postoperatively (p.o.) the distances achieved by the regenerating axons were determined using the pinch reflex test. Two days of vibration did not influence the regeneration, but 5 days of vibration reduced the initial delay period and a slight reduction of regeneration rate was observed. After 5 days of vibration an increased regeneration distance was observed in both models at day 4 p.o. and at day 6 p.o. in vibrated grafts. This study demonstrates that vibration can condition peripheral nerves and this may be caused by local changes in the peripheral nerve trunk and in the neuron itself.

Bisbenzimide-labelled astrocytes were transplanted into the spinal white matter of the rat using three different injection techniques and the variability of the longitudinal distance over which they were found was compared 30 min later. Cells spread up to 5.02 mm and the greatest variability was seen when they were injected as a bolus (54%), compared with 26% when injected over 2 min. These results show the importance of establishing the extent of passive spread of cells and its variability when performing studies in cell migration.