Tritiated Thymidine Identification of Embryonic Neostriatal Transplants

Behavioral Effects of Neural Transplantation

Considerable evidence suggests that transplantation of fetal neural tissue ameliorates the behavioral deficits observed in a variety of animal models of CNS disorders. However, it is also becoming increasingly clear that neural transplants do not necessarily produce behavioral recovery, and in some cases have either no beneficial effects, magnify existing behavioral abnormalities, or even produce a unique constellation of deficits. Regardless, studies demonstrating the successful use of neural transplants in reducing or eliminating behavioral deficits in these animal models has led directly to their clinical application in human neurodegenerative disorders such as Parkinson's disease. This review examines the beneficial and deleterious behavioral consequences of neural transplants in different animal models of human diseases, and discusses the possible mechanisms by which neural transplants might produce behavior recovery.

Migration of cells from primary transplants of allo- and xenografted foetal striatal tissue in the adult rat brain

Primary neural cells derived from human xenografts migrate extensively following transplantation into the adult rat CNS. However, it is unknown whether cells from allografts have the same capability to migrate within the adult rat brain. Moreover, it is unclear whether human-derived cells migrate to this extent as an inherent property of being in a xenograft environment, or whether it is due to the large size of the developed human brain compared with the adult rat brain. In order to address these issues we have designed an experimental paradigm to investigate the potential for cells derived from grafts of primary rat, mouse and human foetal striatal tissue to migrate following intrastriatal transplantation in an adult rat model of Huntington's disease (HD). Green fluorescent protein (GFP)-expressing rat and mouse donors and an antibody specific to human nuclear antigen enabled identification of graft-derived cells within the host brain, and double-labelling with GFP and neuronal nuclear antigen or immunostaining with human-specific tau identified graft-derived neurons. Twelve weeks post-transplantation, cells had migrated throughout the host in all groups; however, human cells and neurons had migrated significantly more than rat or mouse cells. These results demonstrate that neural cells derived from allografts are capable of migrating in the adult rat CNS and that the extent of migration is most likely determined by the size of the mature donor adult brain. This has important implications for the use of allo- and xenogeneic tissue as a source for transplantation in treating diffuse neurodegenerative disorders such as HD.

Neural cells from primary human striatal xenografts migrate extensively in the adult rat CNS

Primary neural cells do not appear to migrate significantly following transplantation into the adult rodent CNS, which is in contrast to expanded neural precursor cells where migration is well-documented. However, most transplant studies of primary neural tissue have been performed in an allograft situation in which it is difficult to identify graft-derived cells. We have, therefore, used a xenograft paradigm to investigate the potential for cells derived from grafts of primary human fetal striatal tissue (gestational age of 66-72 days) to migrate following intrastriatal transplantation in an athymic adult rat model of Huntington's disease. The use of an antibody specific to human nuclear antigen enabled clear identification of graft-derived cells within the host brain, and specific neural phenotypes were determined using human-specific tau for neurons, glial fibrillary acidic protein for mature astrocytes and Ki67 for proliferative cells. At 6 weeks, the graft mass was very dense with a high proliferative index, few cells had migrated away from the graft, and the cells that had differentiated both within and away from the graft were mainly neurons. In contrast, at 6 months, the graft core was dispersed significantly more and a large number of graft-derived cells had migrated throughout the brain as far rostral as the olfactory bulb and as caudal as the substantia nigra. Cells had differentiated into both neurons and astrocytes and the level of proliferation was significantly lower within the graft. These results demonstrate that primary neural xenografts contain proliferative cells that possess the ability to migrate and differentiate into both neurons and astrocytes, and suggest that these cells could contribute to normal graft function. This property may be a consequence of the xenograft situation and could potentially be exploited to provide the opportunity to target regions of distant pathology in neurodegenerative diseases using xenotransplantation of embryonic neural tissue.

Receptor characteristics and recovery of function following kainic acid lesions and fetal transplants of the striatum. I. Cholinergic systems

The relationship between striatal muscarinic cholinergic receptor development and locomotor activity/T-maze alternation behavior in adult female rats with kainic acid lesions (kal) and fetal transplants of the striatum (str) was examined. Kal led to a number of deficits under conditions of spontaneous locomotion, including: (1) decreased stereotypical and increased horizontal movements during spontaneous overnight locomotion, (2) decreased spontaneous alternation on a T-maze, and (3) deficits on a sensorimotor neurological exam. Lesion-induced deficits following injection with cholinergic agonists (pilocarpine)/antagonists (scopolamine) included: (1) hypoactivity on vertical activity and stereotypical activity following scopolamine injection, and (2) increased stereotypical activity and decreased horizontal activity following pilocarpine injection. Transplants differentially affected the different types of behavioral deficits. Transplants reversed some of the deficits under conditions of spontaneous locomotion, including the hyperactivity noted during the night period, but only partially reversed the sensorimotor neurological exam and had no effect on spontaneous alternations in the T-maze. The transplants did not reverse the lesion-induced deficits following scopolamine injection, but partially reversed the lesion-induced changes in locomotion following pilocarpine injection. The striatal transplants had reduced numbers of M1 but increased numbers of M2 muscarinic cholinergic receptors. Cholinergic receptor density correlated with scores on the sensorimotor functioning and alternation tasks, but not with the locomotor measures. Conversely, the cross-sectional area of the str correlated strongly with the transplant-induced recovery in the lesion group. These results suggest that the development of cholinergic receptor systems within the transplants proceeds abnormally, and that the abnormal development of the transplant may impact on the transplant's ability to remediate lesion-induced deficits.