Are neuronal markers and neocortical graft-host interface influenced by housing conditions in rats with cortical infarct cavity?

Bioscaffold-Induced Brain Tissue Regeneration

Brain tissue lost after a stroke is not regenerated, although a repair response associated with neurogenesis does occur. A failure to regenerate functional brain tissue is not caused by the lack of available neural cells, but rather the absence of structural support to permit a repopulation of the lesion cavity. Inductive bioscaffolds can provide this support and promote the invasion of host cells into the tissue void. The putative mechanisms of bioscaffold degradation and its pivotal role to permit invasion of neural cells are reviewed and discussed in comparison to peripheral wound healing. Key differences between regenerating and non-regenerating tissues are contrasted in an evolutionary context, with a special focus on the neurogenic response as a conditio sine qua non for brain regeneration. The pivotal role of the immune system in biodegradation and the formation of a neovasculature are contextualized with regeneration of peripheral soft tissues. The application of rehabilitation to integrate newly forming brain tissue is suggested as necessary to develop functional tissue that can alleviate behavioral impairments. Pertinent aspects of brain tissue development are considered to provide guidance to produce a metabolically and functionally integrated de novo tissue. Although little is currently known about mechanisms involved in brain tissue regeneration, this review outlines the various components and their interplay to provide a framework for ongoing and future studies. It is envisaged that a better understanding of the mechanisms involved in brain tissue regeneration will improve the design of biomaterials and the methods used for implantation, as well as rehabilitation strategies that support the restoration of behavioral functions.

Importance of behavioral manipulations and measures in rat models of brain damage and brain repair

The relevance of careful behavioral measures and manipulations in animal research on neural plasticity and brain damage has become increasingly clear. Recent research in adult rats indicates that an understanding of neural restructuring after brain damage requires an understanding of how it is influenced by postinjury behavioral experiences. Other research indicates that optimizing pharmacological and other treatments for brain damage may require their combination with rehabilitative training. Assessing the efficacy of a treatment approach in animal models requires the use of sensitive behavioral measures of functional outcome. In research on restorative plasticity after brain damage, procedures for handling and housing rats should promote the quality of behavioral measures and manipulations.

Restoration of function by neural transplantation in the ischemic brain

Stroke remains a major brain disorder that often renders patients severely impaired and permanently disabled. There is no available treatment for reversing these deficits. Hippocampal, striatal and cortical grafting studies demonstrate that fetal cells/tissues, immortalized cells, and engineered cell lines can survive grafting into the ischemic adult brain, correct neurotransmitter release, establish both afferent and efferent connections with the host brain, and restore functional and cognitive deficits in specific models of stroke. The success of neural transplantation depends on several factors: the stroke model (location, extent, and degree of infarction), the donor cell viability and survival at pre- and post-transplantation, and the surgical technique, among others. Further exploitation of knowledge of neural transplantation therapy already available from our experience in treating Parkinson's disease needs to be critically considered for stroke therapy. While the consensus is to create a functional neuronal circuitry in the damaged host brain, there is growing evidence that trophic action of the grafts and host, as well as exogenous application of trophic factors may facilitate functional recovery in stroke. Current treatment modules, specifically that of rehabilitative medicine, should also be explored with neural transplantation therapy. However, validation of neural transplantation and any other treatment for stroke should be critically assessed in laboratory experiments and limited clinical trials. No direct treatment is recognized as safe and effective for reversing the stroke-induced brain damage and functional/cognitive deficits. The first clinical trial of neural transplantation in stroke patients is a mile-stone in stroke therapy, but subsequent large-scale trials should be approached with caution.

Neuronal and fibre organization in neocortical grafts placed in post-ischaemic adult rat brain: a three-dimensional confocal microscopy study

The dendritic morphology in neocortical grafts was studied with three-dimensional confocal laser scanning microscopy after microinjection of Lucifer Yellow into individual cells. The grafts had been implanted into infarct cavities in the neocortex of hypertensive rats 46 weeks earlier. The carbocyanine dye method was used to identify afferent (host to transplant) and efferent (transplant to host) connections. Pyramidal, nonpyramidal and glial cells were present in the transplants. Some dendrites had an almost normal appearance, but abnormalities (atypical orientation of apical, basal or oblique apical dendrites) were observed. Some bi-apical pyramidal neurons and pyramidal neurons with obliquely oriented apical dendrites were also observed. Carbocyanine dye-labelled fibres of different diameter formed a dense network in the transplant, enabling the border between transplant and host tissue to be clearly recognized. No labelled fibres were observed to enter the host brain. Fibres with "boutons en passant" and no preferential orientation were noted. It is proposed that Lucifer Yellow microinjection may be a useful method in studies aimed at improving graft morphology. Failure to demonstrate host to transplant connections with the carbocyanine dye method was contrary to earlier studies in which tracers were applied in vivo. A combined use of in-vivo and post-mortem tracer techniques is needed to establish the reason for the discrepancy.

Expression of zinc-positive cells and terminals in fetal neocortical homografts to adult rat depends on lesion type and rearing conditions

Zinc-positive neurons and terminals, known to be associated with the glutamatergic projections in the brain, can be demonstrated by the histochemical Timm method and later modifications thereof. The adult rat neocortex contain a uniform lamination of zinc-positive cells with specific projections to, e.g., the striatum. We have previously reported that fetal neocortical grafts implanted in the adult rat neocortex combined with rearing in an enriched environment can improve behavioral functions and reduce the secondary atrophy of thalamus after cortex infarction in adult rats. In order to examine whether the expression of zinc positivity is ontogenetically inherent to neocortical neurons we grafted fetal neocortical tissue to aspiration or ischemic lesions of the frontoparietal neocortex of adult rats, followed by histochemical visualization of the vesicular zinc pool by selenite or sulfide. One further aim of the study was to elucidate to what extent the distribution of zinc-containing neurons and terminals in the grafts depended on rearing under different environmental conditions. The foremost finding of the present study was that the overall density of zinc-containing terminals in fetal cortical transplants placed in brain infarcts of adult spontaneously hypertensive rats is higher when the rats are reared in an enriched environment. Moreover, the presence and expression of zinc-positive neurons and terminals do not seem to be ontogenetically inherent to the cortical neurons as the fetal neocortical grafts placed in aspiration lesions contained no zinc-selenide-positive neurons and few or no zinc-selenide-positive terminals. The presence or expression of zinc-positive cells may thus be induced by ingrowth of fibers and terminals from the host brain as transplants placed in the ischemic lesions expressed both zinc-positive neurons and terminals.