A Golgi study of hypothalamic transplants in young and old host rats

Neural Transplantation in Animal Models of Dementia

Neural transplantation provides a powerful novel technique for investigating the neurobiological basis and potential strategies for repair of a variety of neurodegenerative conditions. The present review considers applications of this technique to dementia. After a general introduction (section 1), attempts to replace damaged neural systems by transplantation are considered in the context of distinct animal models of dementia. These include grafting into aged animals (section 2), into animals with neurotransmitter-selective lesions of subcortical nuclei, in particular involving basal forebrain cholinergic systems (section 3), and into animals with non-specific lesions of neocortical and hippocampal systems (section 4). The next section considers the alternative use of grafts as a source of growth/trophic factors to inhibit degeneration and promote regeneration in the aged brain (section 5). Finally, a number of recent studies have employed transplanted tissues to model and study the neurodegenerative processes associated with ageing and Alzheimer's disease taking place within the transplant itself (section 6). It is concluded (section 7) that although neural transplantation does not offer any immediate prospect of therapeutic repair in clinical dementia, the technique does offer a powerful neurobiological tool for studying the neuropathological processes involved in both spontaneous degeneration and specific diseases of ageing. New understandings derived from neural transplantation may be expected to lead to rational development of novel strategies to inhibit the neurodegenerative process and to promote regeneration in the aged brain.

Early neural grafts transiently reduce the behavioral effects of radiation-induced fascia dentata granule cell hypoplasia

X-irradiation of the neonatal rat hippocampus produces a selective hypoplasia of fascia dentata granule cells, locomotor hyperactivity, perseverative movements and deficits in passive avoidance. We previously reported that transplantation of fetal hippocampal tissue into the adult (age = 182 +/- 4 days) brain produced a partial recovery of these behavioral deficits. Since graft/host interconnections are more prominent when transplants are conducted soon after radiation-induced hippocampal damage, in this study we transplanted hippocampal or cerebral cortex neurons when host rats were 33 +/- 5 days of age (i.e. only 16 days after radiogenic brain damage). Behavioral evaluations were conducted 80 and 182 days after transplantation or surgical control procedures. In the first test series only, selective components of locomotion (e.g. stereotypy and total distance traveled) and perseverative turning (e.g. mean bout length and turning speed topography) were normalized by the hippocampal grafts. Radiation-induced changes in passive avoidance were less prominent in these studies than in past experiments. Still, transplantation of hippocampal tissue improved performance on this learning task as well. Cerebral cortex grafts did not produce reliable improvements in most behavioral measures. These data suggest that hippocampal grafts placed soon after X-ray induced fascia dentata hypoplasia reduce a broad range of behavioral deficits. However, these benefits are transient and, for the most part, depend on the use of transplant tissues homologous with those damaged.

Ultrastructural and immunohistochemical analysis of fetal mediobasal hypothalamic tissue transplanted into the aged rat brain

MBH tissue, which included the hypothalamic arcuate nucleus of fetal or neonatal rats, was transplanted into the third ventricle of aged (21-30-month-old) female rats. The brain and ovaries of each recipient were examined histologically 3 or 4 weeks after transplantation. Four grafted MBH tissues were examined ultrastructurally and immunohistochemically 4 weeks after transplantation. The appearance of the MBH grafts was similar to that of normal neural tissue. The neuropil in the grafts was fully occupied with numerous axons, dendrites, and glial processes. A number of axodendritic shaft and spine synapses were observed in the neuropil. Immunohistochemical analysis with antiserum to TH revealed stained (immunoreactive) neuronal perikarya and processes in the grafts. TH-immunoreactive processes originating from the TH-positive neurons in the grafts could be seen to extend across the graft-host interface. The ovaries of six out of nine females that received MBH grafts exhibited follicles of various sizes and healthy appearing corpora lutea. On the other hand, some follicles and masses of interstitial cells were prominent in the ovaries of the intact animals or controls that had received cortical grafts. In the females that received MBH grafts, the ovarian weight was significantly greater than that in the controls. These results suggest that the neural substrates in fetal MBH tissue can survive and develop well in the aged rat brain and that MBH grafts may play some role in the recovery of declined ovarian function in aged female rats.

Neural transplantation: a review of recent developments and potential applications to the aged brain

Mammalian neural transplantation has recently been recognized to be a valuable technique for studying normal development and regeneration in the central nervous system. In addition, the ability of grafted neurons to reinnervate damaged regions of the host brain and to ameliorate some neuroendocrine deficits, cognitive disorders and motoric dysfunctions in young adult rodents has suggested that transplantation therapy may be effective in treating human neurodegenerative diseases and neurotransmitter deficiencies related to aging. It is of particular interest that initial studies of neuron transplants in aged rodents indicate that cholinergic, dopaminergic and noradrenergic neurons all integrate to some extent with the aged brain, and that the product of this graft-host interaction is improved behavioral performance of aged subjects. The present paper critically reviews the present domain of neural transplantation, its application to studies on the properties of the aged mammalian brain and discusses the possible therapeutic use of transplants in ameliorating transmitter-specific abnormalities associated with Parkinson's disease and Alzheimer's disease.