Albert Gramsbergen

At what age is the developing cerebral cortex of the rat comparable to that of the full-term newborn human baby?

By means of a comparative study of experimental data from the literature we estimated at what age the rat cerebral cortex corresponds to that of the full-term newborn human infant with regard to the degree of maturation. As a result of this study we suggest that the 12-13-day-old rat pup fulfills this criterion. This finding should be of use to scientists who use the rat for studying certain processes assumed to occur in the human cerebral cortex around full-term birth.

Methods to evaluate functional nerve recovery in adult rats: walking track analysis, video analysis and the withdrawal reflex

The aim of this study was to compare different methods for the evaluation of functional nerve recovery. Three groups of adult male Wistar rats were studied. In group A, a 12-mm gap between nerve ends was bridged by an autologous nerve graft; in rats of group B we performed a crush lesion of the sciatic nerve and group C consisted of non-operated control rats. The withdrawal reflex, elicited by an electric stimulus, was used to evaluate the recovery of sensory nerve function. To investigate motor nerve recovery we analyzed the walking pattern. Three different methods were used to obtain data for footprint analysis: photographic paper with thickened film developer on the paws, normal white paper with finger paint, and video recordings. The footprints were used to calculate the sciatic function index (SFI). From the video recordings, we also analyzed stepcycles. The withdrawal reflex is a convenient and reproducible test for the evaluation of global sensory nerve recovery. Recording walking movements on video and the analysis of footplacing is a perfect although time-consuming method for the evaluation of functional aspects of motor nerve recovery.

Transection of peripheral nerves, bridging strategies and effect evaluation

Disruption of peripheral nerves due to trauma is a frequently occurring clinical problem. Gaps in the nerve are bridged by guiding the regenerating nerves along autologous grafts or artificial guides. This review gives an overview on the different methods of nerve repair techniques. Conventional suturing techniques are discussed as well as the use of e.g. biological, synthetic, non-degradable or degradable nerve guides. Functional assessment showed that repair of a gap with a bio-degradable guide is superior to that with autologous grafts. But still, long lasting changes were observed in the Sciatic Function Index (SFI), abnormal walking patterns, disturbed Electro Myo Graphic (EMG) patterns, next to shifts in the histochemical properties of the muscles and longlasting abnormalities in neuromuscular contacts. These phenomena are explained by an at-random reinnervation. When transecting the nerve at young ages, this did not lead to enhanced recovery. Rearing rats operated at adult age in an enriched environment, also had no beneficial effect. Future research should aim at developing longer guides, possibly lined with Schwann cells, or additives, improving specific reinnervation of the former target areas.

Sciatic nerve transection in the adult rat: Abnormal EMG patterns during locomotion by aberrant innervation of hindleg muscles

The effects of lesions in the sciatic nerve were studied in adult rats. In the left hindleg, a segment 12 mm long was resected from the proximal part of the nerve, before the bifurcation into the peroneal and tibial nerves. This segment in a reversed orientation was used as a nerve graft. EMG patterns in the tibialis anterior and the gastrocnemius muscles at both sides were recorded during locomotion in six rats after recovery periods varying from 15 to 21 weeks. The specificity of axonal outgrowth was studied in nine rats by retrogradely labeling the motoneurons with unconjugated Cholera Toxin subunit B (CTB) after injections into the gastrocnemius, the soleus, and the tibialis anterior muscles at both sides. EMG patterns at the operated side were irregular and we often observed coactivation of the gastrocnemius and tibialis anterior muscle. Moreover, burst activity was badly adjusted to the phases of the stepcycle. Retrogradely labeling indicated that the pools of motoneurons innervating the respective muscles at the left side had increased in volume. Neuronal diameters were slightly decreased but a considerable decrease was observed in dendritic branching and dendrite bundles in the pools of the SOL and in the GC were absent. No consistent trends in neuronal numbers at the affected side in comparison to the right side were detected. We conclude that axons, sprouting from the proximal stump of the sciatic nerve, innervate the muscles aselectively and that the motoneurons of origin maintain their original activation pattern.

Toe out angle : a functional index for the evaluation of sciatic nerve recovery in the rat model

In experimental peripheral nerve studies, the rat sciatic nerve model is widely used to examine functional outcome following nerve injury and repair. A variety of evaluation methods exist in the literature, but an adequate selection continues to be a critical point for the researcher. Rats with sciatic nerve injury typically ambulate with an external rotation of the foot. A new functional assessment instrument, the toe out angle (TOA) is quantified using computerized gait analysis. We compared Sciatic Functional Index (SFI) with TOA parameter after peripheral nerve transection and entubulation repair. We found a good correlation between SFI and TOA measurements in terms of predicting functional recovery. Moreover, the TOA provides information on the biomechanical consequences of the external rotation of the foot in the stance phase of walking.

Functional assessment of sciatic nerve reconstruction: Biodegradable poly (DLLA-epsilon-CL) nerve guides versus autologous nerve grafts

The aim of this study was to compare functional nerve recovery after reconstruction with a biodegradable p(DLLA‐ϵ‐CL) nerve guide filled with modified denatured muscle tissue (MDMT), or an autologous nerve graft. We evaluated nerve recovery using walking track analysis (measurement of the sciatic function index [SFI]) and electrostimulation tests. Functional nerve recovery after reconstruction with a biodegradable p(DLLA‐ϵ‐CL) nerve guide filled with MDMT was faster when compared with nerve reconstruction using an autologous nerve graft. We conclude that in case of a short nerve gap in the rat, reconstruction can best be carried out using a p(DLLA‐ϵ‐CL) biodegradable nerve guide filled with MDMT.

Reinnervation of muscles after transection of the sciatic nerve in adult rats

Functional recovery after transection of the sciatic nerve in adult rats is poor, probably because of abnormalities in reinnervation. Denervation and reinnervation patterns were studied morphologically in the lateral gastrocnemius (LGC), tibialis anterior (TA), and soleus (SOL) muscles for 21 weeks after nerve transection (motor endplates by acetylcholinesterase staining; nerves by silver impregnation). Motor endplates in the TA showed improving morphology with age, and, at 21 weeks, three‐quarters of these were normal. Poorest recovery was observed in the SOL, as, at 21 weeks, only one‐third of the motor endplates had a normal morphology. Polyneuronal innervation initially was more pronounced in the SOL, but, at 21 weeks, 10% of the motor endplates in all three muscles were still polyneuronally innervated. Our results indicate important differences in the reinnervation of these three hindleg muscles, and, even at 5 months, abnormalities were still present. These factors may in part explain the abnormal locomotion in rats as well as the limited recovery of function observed clinically in humans after nerve transection.

Posture and locomotion in the rat: independent or interdependent development?

In this essay, recent research into the relation between postural control and the development of walking in the rat is reviewed. The adult-like walking pattern develops at the 15th to 16th day (P15-P16). Until this age, postural control, as indicated by EMG activity in the longissimus muscle in the trunk, is poorly phased in relation to the stepcycle. After P15-P16, accuracy increases but only after P21 is the adult pattern of EMG activity in the trunk muscles in relation to locomotor activity in the hindpaw muscles established. Neuroanatomical research revealed that those muscles in trunk and extremities which fulfil important postural tasks are innervated by motoneuronal pools containing conspicuous dendrite bundles. These bundles emerge at about the age when the adult type of postural control starts to develop. As spinal transsection at P10 abolishes their development, we hypothesize that the development of dendrite bundles is dependent on the ingrowth or the becoming functional of descending projections. On the basis of the neurophysiological and neuroanatomical results we conclude that the development of postural control, which reaches its final stage 5-6 days after the adult-like pattern of walking has developed, is dependent on the maturation of suprasegmental structures and their spinal projections.

CNS plasticity after hemicerebellectomy in the young rat. Quantitative relations between aberrant and normal cerebello-rubral projections

The double labelling technique has been applied to study the quantitative relations between aberrant and normal cerebello-rubral projections in rats hemicerebellectomized on the 2nd, 5th, 10th, 20th or 30th day after birth, respectively. In the group of rats lesioned on the 2nd day about 30% of cells in the lateral nucleus and 20% in the interpositus nuclei are labelled retrogradely by the fluorescent tracer injected in the aberrant ipsilateral projection area. These values decreased in the groups of rats operated on the 5th or 10th day and reached values of about 1-2% in rats lesioned on the 20th or 30th day. These values have been also found in control rats. Both in experimental rats and in control rats less than 0.5% of cells are double labelled from both projection areas. This implies that the aberrant cerebello-rubral fibres stem from separate parent cells and are not collaterals from normally projecting fibres.

Corticotropin-releasing factor and urocortin differentially modulate rat Purkinje cell dendritic outgrowth and differentiation in vitro

The precise outgrowth and arborization of dendrites is crucial for their function as integrators of signals relayed from axons and, hence, the functioning of the brain. Proper dendritic differentiation is particularly resonant for Purkinje cells as the intrinsic activity of this cell‐type is governed by functionally distinct regions of its dendritic tree. Activity‐dependent mechanisms, driven by electrical signaling and trophic factors, account for the most active period of dendritogenesis. An as yet unexplored trophic modulator of Purkinje cell dendritic development is corticotropin‐releasing factor (CRF) and family member, urocortin, both of which are localized in climbing fibers. Here, we use rat organotypic cerebellar slice cultures to investigate the roles of CRF and urocortin on Purkinje cell dendritic development. Intermittent exposure (12 h per day for 10 days in vitro) of CRF and urocortin induced significantly more dendritic outgrowth (45% and 70%, respectively) and elongation (25% and 15%, respectively) compared with untreated cells. Conversely, constant exposure to CRF and urocortin significantly inhibited dendritic outgrowth. The trophic effects of CRF and urocortin are mediated by the protein kinase A and mitogen‐activating protein kinase pathways. The study shows unequivocally that CRF and urocortin are potent regulators of dendritic development. However, their stimulatory or inhibitory effects are dependent upon the degree of expression of these peptides. Furthermore, the effects of CRF and urocortin on neuronal differentiation and re‐modeling may provide a cellular basis for pathologies such as major depression, which show perturbations in the expression of these stress peptides.