Fetal nigral grafts in the anterior eye chamber of adult rats: a long-term morphological study

Studies of histogenetic and neurodegenerative processes in the nervous system using heterotopic neurotransplantation

The aim of the present article is to summarize our own experimental and published data on neurotransplantation into ectopic sites such as peripheral nerves (mainly) and the anterior chamber of the eye in rats. The review addresses questions touching on the following problems: the histogenesis and survival of nervous tissue after transplantation, the interaction between transplanted tissues with recipient tissues, assessment of long-term living transplants, simultaneous transplantation of different embryonic rudiments, transplantation of spinal cord ganglia, and the effects of trophic factors on the development of transplants. New data on stem cell transplantation into peripheral nerves are discussed.

Fetal hippocampal CA3 cell grafts transplanted to lesioned CA3 region of the adult hippocampus exhibit long-term survival in a rat model of temporal lobe epilepsy

Intracerebroventricular administration of kainic acid in the adult rat, a widely used model for studying human temporal lobe epilepsy, results in widespread degeneration of CA3-pyramidal neurons. Transplantation of specific fetal hippocampal CA3 cell grafts into the lesioned CA3-region at a prolonged post lesion delay of 45-day leads to 31% graft cell survival at 1 month postgrafting and significantly facilitates appropriate recovery of the lesioned host hippocampus. However, the capability of hippocampal CA3 cell grafts for enduring survival in this model is unknown. We hypothesize that a significant fraction of fetal CA3 cells grafted into the lesioned CA3 region of the adult hippocampus at 45-days postlesion exhibit long-term survival. We measured the extent of cell survival within 5'-bromodeoxyuridine-labeled CA3 cell grafts at 1 year postgrafting, following their transplantation at 45 days postlesion into the lesioned CA3-region. Quantification of absolute graft cell survival using BrdU immunostaining and the optical fractionator counting method revealed survival of 36% of grafted cells at 1 year postgrafting. Thus, over a third of fetal hippocampal CA3 cells transplanted to the lesioned CA3-region at 45 days postlesion exhibit long-term survival. Further, the extent of cell survival in these grafts is highly analogous to the degree of cell survival in CA3 grafts analyzed earlier at 1 month postgrafting, suggesting that specific fetal cells that survive the first month of grafting into the lesioned CNS area are capable of exhibiting enduring survival.

Development of fetal hippocampal grafts in intact and lesioned hippocampus

Functional recovery observed in Parkinson's disease patients following grafting of fetal substantia nigra has encouraged the development of similar grafting therapy for other neurological disorders. Fetal hippocampal grafting paradigms are of considerable significance because of their potential to treat neurological disorders affecting primarily hippocampus, including temporal lobe epilepsy, cerebral ischemia, stroke, and head injury. Since many recent studies of hippocampal transplants were carried out with an aim of laying the foundation for future clinical applications, an overview of the development of fetal hippocampal transplants, and their capability for inducing functional recovery under different host conditions is timely. In this review, we will summarize recent developments in hippocampal transplants, especially the anatomical and/or functional integration of grafts within the host brain under specific host conditions, including a comparison of intact hippocampus with various types of hippocampal lesions or injury. Improvements in grafting techniques, methods for analysis of graft integration and graft function will be summarized, in addition to critical factors which enhance the survival and integration of grafted cells and alternative sources of donor cells currently being tested or considered for hippocampal transplantation. Viewed collectively, hippocampal grafting studies show that fetal hippocampal tissue/cells survive grafting, establish both afferent and efferent connections with the host brain, and are also capable of ameliorating certain learning and memory deficits in some models. However, the efficacy of intracerebral fetal hippocampal grafts varies considerably in different animal models, depending on several factors: the mode of donor tissue preparation, the method of grafting, the state of host hippocampus at the time of grafting, and the placement of grafts within the hippocampus. Functional improvement in many models appeared to be caused partially by re-establishment of damaged circuitry and partially by a trophic action of grafts. However, exact mechanisms of graft-mediated behavioral recovery remain to be clarified due to the lack of correlative analysis in the same animal between the degree of graft integration and behavioral recovery. Issues of mechanisms of action, degree of restoration of host circuitry and amelioration of host pathological conditions will need to be sorted out clearly prior to clinical use of fetal hippocampal transplants for susceptible neurological conditions.

Ultrastructure of developing substantia nigra in humans

Electron microscopy of the maturing neurons and developing and maturing synapses in the substantia nigra of 14 human embryos/foetuses of 8-24 weeks of gestation are reported. At 8 weeks, cells were immature with very little cytoplasm and cellular organelles. Contact sites of processes appeared more electron dense than the other areas. At 12 weeks, many of the cells had acquired more cytoplasm and cellular organelles and could be identified as neurons. Asymmetric synapses with clear, round synaptic vesicles also were identifiable at this age. Such synapses, first to appear in the developing substantia nigra, are reported to be formed by recurrent collateral nigro-striatal fibres. Substance P fibres from the striatum also are contributing to this type of synapse. At 15-16 weeks, not only was the number of such synapses increased, but many appeared morphologically mature. Symmetric synapses having clear round vesicles along with a few dense core vesicles also appeared at this stage, suggesting striatal input. By 24 weeks of gestation, most of the neurons had cytological features comparable to that of the mature neurons. There was an increase in the total number of synapses and the individual variety from 15 to 24 weeks of gestation. The present study indicates that synaptogenesis starts at 8 weeks and continues beyond 24 weeks of gestation.

Sympathetic neurons outlive the original host after transplantation to the rat submandibular gland

Sympathetic ganglion tissue of aged (36 months) Wistar rats was allotransplanted into the submandibular gland (SMG) of young (3 months) animals to study whether sympathetic neurons can outlive the original host. The viability of the transplants was evaluated one year postgrafting, using the formaldehyde-induced fluorescence technique (FIF) for histochemical demonstration of catecholamines, tyrosine hydroxylase (TH) immunohistochemistry, and morphometry. One year after transplantation, grafted superior cervical ganglion (SCG) cells demonstrated catecholamine fluorescence and tyrosine hydroxylase immunoreactivity. The transplants consisted of groups of sympathetic neurons dispersed in a fibrous matrix. After long postgrafting time, the sympathetic neurons of aged rats showed several signs of enhanced degeneration; increased autofluorescent lipopigment, decreased neuronal density and reduced catecholamine fluorescence. The mean diameter of the transplanted aged neurons was significantly decreased. The histograms of grouped diameter values showed a shift to smaller cells in ganglion transplants. A subpopulation of small and medium-sized grafted neurons sent out fluorescent fibers, which were located in a fibrous scar area but did not extend into submandibular host tissue. The results indicate that a long postgrafting time induced degeneration which is comparable to normal aging changes in grafted very old neurons. Thus, aged sympathetic neurons maintain plasticity to survive as transplants, and under favourable conditions these neurons outlive the original host.

Motor function, graft survival and gliosis in rats with 6-OHDA lesions and foetal ventral mesencephalic grafts chronically treated with L-dopa and carbidopa

In rats with a unilateral 6-OHDA lesion of the nigrostriatal pathway, foetal ventral mesencephalic grafts implanted into the 6-OHDA-lesioned striatum produced a reduction in apomorphine-induced contralateral rotation, and complete abolition of (+)-amphetamine-induced ipsilateral rotation. The graft-induced reduction of apomorphine and (+)-amphetamine-induced rotation was not affected by chronic 27 week administration of L-DOPA and carbidopa to rats receiving foetal grafts. TH-immunohistochemistry revealed greater than 96% loss of dopamine cells in the substantia nigra ipsilateral to the 6-OHDA lesion in all animals, but cell loss in the ipsilateral ventral tegmental area was more variable (21-46% of the intact side). TH-positive cells in the intact substantia nigra and ventral tegmental area were not affected by chronic treatment with L-DOPA and carbidopa. In the lesioned striatum of rats receiving sham grafts, no TH-positive cells or fibres were seen. In the 6-OHDA-lesioned striatum of animals receiving foetal grafts, many TH-positive cells were seen in the grafts and chronic treatment with L-DOPA and carbidopa did not reduce cell survival. GFA-P immunohistochemistry revealed that a unilateral 6-OHDA lesion followed by a sham graft was not associated with a reactive gliosis reaction in the striatum at the time of study (38 weeks after lesion surgery and 30 weeks after sham-graft), and treatment of such rats with L-DOPA and carbidopa was also without effect on glia. In contrast there was a marked gliosis in the striatum surrounding foetal grafts which was unaffected by chronic treatment with L-DOPA and carbidopa. The grafts themselves were surrounded by a rim of glial cells, and the glial density within the grafts was higher in animals receiving chronic L-DOPA and carbidopa treatment. However, there was no obvious relationship between the number of TH-positive cells within the grafts, or graft volume, and glial cell density within the grafts. These results suggest that long-term treatment with L-DOPA and carbidopa does not impair either the behavioural recovery produced by foetal ventral mesencephalic grafts in rats or the long-term survival of grafts as revealed by TH-immunohistochemistry. The presence of a foetal graft is associated with a reactive gliosis in the implanted striatum, which was not altered by long-term treatment with L-DOPA and carbidopa. However such treatment did result in an increase in glial density within the grafts themselves.