Walter C. Low

Cross-species embryonic septal transplants: restoration of conditioned learning behavior

Embryonic septal and hippocampal tissue from mice was transplanted between species into the brains of adult rat hosts as cell suspensions. Deficits in the ability to learn a conditioned, hippocampally mediated, forced alternation behavior, which were caused by a bilateral transection of the fornix-fimbria pathway, were ameliorated in the septal transplant recipients. The successful performance of the task was correlated to the density index of acetylcholinesterase in the hippocampal section.

Intrahippocampal transplants of septal cholinergic neurons : high-affinity choline uptake and spatial memory function

Recent studies have demonstrated that intrahippocampal cholinergic septal grafts can ameliorate deficits in spatial memory function and hippocampal cholinergic neurochemical activity in animals with disruptions of the septohippocampal system. However, no study has determined if the restoration of spatial memory function is correlated to the restoration of cholinergic activity, as measured by high-affinity choline uptake (HACU). The present study was designed to determine if such a correlation between behavioral and neurochemical restoration exists. Male Sprague-Dawley rats received either sham lesions (SHAM), bilateral lesions of the septohippocampal pathway (LES), or bilateral lesions along with intrahippocampal septal grafts (SG). After 8 months, rats were tested for their ability to perform spatial reference, spatial navigation and working memory tasks. Upon completion of the behavioral testing, neurochemical activity of the hippocampus was measured by HACU. The results indicate that animals in the SG group had significantly higher behavioral scores and hippocampal HACU rates than animals in the LES group. Regression analysis indicates that a significant correlation exists between performance on each behavioral task and HACU rates. These results demonstrate that hippocampal cholinergic activity, as measured by HACU, correlates significantly with performance on tests of spatial memory function.

Restoration of High Affinity Choline Uptake in the Hippocampal Formation Following Septal Cell Suspension Transplants in Rats with Fimbria-Fornix Lesions

Abstract: High affinity choline uptake (HACU) was investigated in the hippocampal formation following fetal septal cell suspension transplants into rats with fimbria‐fornix lesions. Nine‐14 weeks after transplantation, HACU was markedly decreased in hippocampi from animals with fimbria‐fornix lesions; this decrease was ameliorated by fetal septal cells transplanted into the host hippocampus. HACU related to septal transplantation was activated in vitro by K+, and in vivo by the administration of scopolamine and pic‐rotoxin. These findings suggest that fetal septal cell transplantation can restore HACU in the host hippocampus following fimbria‐fornix lesions, and that HACU related to the graft has pharmacological properties similar to those of the normal adult HACU system. The activation of HACU by picrotoxin, a γ‐aminobutyric acid (GABA) antagonist, suggests that transplanted cholinergic neurons receive either direct or indirect functional input from GABAergic afferents from the transplant and/or host hippocampus. Lesions of the fimbria‐fornix also resulted in an increased binding to muscarinic receptors in the dorsal hippocampus. This increase in binding was not significantly ameliorated by intrahippo‐campal grafts of cholinergic neurons.

Developmental expression of polypeptide PEP-19 in cerebellar cell suspensions transplanted into the cerebellum of pcd mutant mice

SummaryCerebellar cell suspensions were prepared from normal mouse embryos and implanted into the cerebellum of Purkinje cell degeneration (pcd) mutant mice, which are characterized by a virtually complete degeneration of Purkinje cells between postnatal day (P) 17 and P45. The expression of immunoreactivity for PEP-19, a developmentally-regulated brain-specific polypeptide, was analyzed in normal mouse cerebellum, as well as in pcd mutants with or without grafts. In the normal cerebellum, PEP-19 immunoreactivity was present in Purkinje cells. In unoperated mutants, 45 days of age or older, Purkinje cells were absent. In grafted pcd mice, numerous PEP-19 immunoreactive, neuroblast-like cells were seen in the graft at 5 days after transplantation. By 9 days, large PEP-19 immunoreactive neurons were found in the host molecular layer; by 17 days after transplantation, such neurons displayed an extensive dendritic tree and resembled differentiated Purkinje cells. The vast majority of PEP-19 immunoreactive cells was located in the molecular layer of the host at 9 days after transplantation and beyond; nonetheless, the same cells extended axonal processes toward the graft, indicating an affinity for co-grafted (possibly deep nuclei) neurons. These results point to the ability of donor Purkinje cells for survival, migration into the host brain and morphological and chemical differentiation following transplantation to the degenerated cerebellar cortex of the recipient mutants.

Chapter 40 Spatial memory deficit resulting from ischemia-induced damage to the hippocampus is ameliorated by intra-hippocampal transplants of fetal hippocampal neurons

Publisher Summary This chapter examines the extent to which an ischemically induced spatial memory performance deficit, in adult Mongolian gerbils, is ameliorated by hippocampal neurons, derived from fetal gerbils that are bilaterally transplanted into the CA 1 field of the ischemic dorsal hippocampal formation. In an experiment described in the chapter, transient cerebral ischemia was produced in 80–100 g adult male Mongolian gerbils. At the end of the ischemic interval, the clips were released and blood flow was observed to resume through each artery. Non-ischemic gerbils, serving as sham-operated controls, underwent the same surgical procedure except that the common carotid arteries were not occluded. The spatial probe test is used. After the spatial probe test, the ischemic gerbils were ranked according to the severity of their spatial memory performance deficit. Similarly, they were ranked on the basis of performance in an open field and a passive avoidance paradigm. When the number of platform crossings in the training quadrant prior to and after transplantation was determined, it was found that the ischemic gerbils that had undergone bilateral transplantation of a cell suspension derived from whole fetal hippocampi into the CA 1 field of the dorsal hippocampal formation had a significant improvement in their performance during the spatial probe test.

Cross-species neural transplants of embryonic septal nuclei to the hippocampal formation of adult rats

SummaryIn the absence of immunosuppressive treatment, suspensions of cells from the developing septal region of mouse embryos were transplanted successfully into the denervated hippocampal formations of adult rat hosts. The longitudinal recovery of acetylcholinesterase (AChE)-containing fibers in the host was the index of transplant success. In transplant recipients, the fornix-fimbrial interconnection between the septum and hippocampal formation was severed unilaterally, and two 5 μl aliquots of cell suspension were injected into the hippocampal formations of host rats. Five sets of controls included one in which animals received no surgical intervention (Normal Controls), and another which was subjected to a sham operation (Sham Controls). The fornix-fimbria pathway was transected unilaterally in Lesion Control animals, while Hippocampal Controls received the same lesion plus two injections of non-cholinergic cells from the hippocampal formations of mouse embryos. Injection Controls were subjected to a fornix-fimbria transection and given two injections of debris and dead cells in saline. The cross-species transplants induced the return of a normal AChE laminar pattern in the recipient rats. The density of the laminar pattern, quantified with laser densitometry, was greatest in transplants that had survived for one week, but only in sections adjacent to the injection sites. Although the density decreased from the first through third weeks of survival, overall density of AChE staining stabilized from the fourth through 17th weeks of survival. Because the success rates of these cross-species transplants were similar to those reported for homogenic tissue, it was concluded that the rat brain is a suitable host for xenogenic transplants of septal. neurons from embryonic mice.

Dopamine D2 receptors increase in the dorsolateral striatum of weaver mutant mice

Dopamine D2 receptors were studied in homozygous weaver mutant mice (wv/wv), heterozygous littermates (wv/+), and normal mice (+/+). Specific [3H]spiperone binding was significantly higher in the dorsolateral part of the striatum in the weaver mutant mice (wv/wv) than in normal mice (+/+). No significant differences among the 3 genotypes were found in other parts of the striatum or in the nucleus accumbens.

Functional innervation of the striatum by ventral mesencephalic grafts in mice with inherited nigrostriatal dopamine deficiency

Weaver mutant mice are characterized by a decrease in striatal dopamine (DA), which is associated with a progressive loss of DA neurones in the substantia nigra. This mutant thus provides the opportunity to examine the functional effects of DA neurones grafted to the striatum in a genetic model of parkinsonism. Ventral mesencephalic tissue from normal foetuses was placed on the surface of the right dorsal striatum of adult weaver mutants. After grafting, animals were tested for methamphetamine-induced circling behaviour. Mutants with DA containing grafts displayed a significant circling bias toward the left, non-grafted side. Mutants without grafts did not display any rotational bias to either side. These results demonstrate that grafted DA containing neurones establish a functional innervation of the weaver striatum and suggest that grafting of neural tissue is a viable approach in restoring function in genetic degenerative disorders of the nigrostriatal system.

Transplantation of cerebellar anlagen to hosts with genetic cerebellocortical atrophy

SummaryEmbryonic cerebellar grafts from genetically normal donors were implanted into the cerebellomedullary cistern of adult ‘Purkinje cell degeneration’ (pcd) and weaver mutant mice, which are respectively characterized by the selective loss of Purkinje and granule cells. Grafts placed into both mutant recipients exhibited a layered cellular organization reminiscent of the normal cerebellar cortex. Molecular, Purkinje, and granule cell layers were identifiable. Grafted Purkinje cells displayed characteristic cytological features, such as hypolemmal cisterns in association with mitochondria in the perikaryon, and lamellar structures in their axons. The cytological features of granule cell somata in the grafts appeared similar to those of mature granule cells. Electron microscopic examination of the molecular layer of the grafts revealed the presence of parallel fibers, which were not oriented in a parallel fashion; axon terminals of such fibers were often presynaptic to dendritic spines. The number of parallel fibers was markedly reduced in grafts implanted into both mutants compared to the normal cerebellar cortex; however, this phenomenon is commonly seen in cerebellum in tissue culture and in cerebellar transplants into normal hosts. It is concluded, therefore, that the environment of the mutant hosts does not affect the survival of Purkinje or granule cells and that transplantation of solid cerebellar grafts in the neurological mutants studied does not seem to pose any apparent limitations beyond those inherent to the process of cerebellar growth and differentiation outside its normal environment.

Chapter 13 Neural transplantation of horseradish peroxidase-labeled hippocampal cell suspensions in an experimental model of cerebral ischemia

Publisher Summary One of the major obstacles in assessing the use of neuronal transplants to replace cells that are lost because of ischemia is the inability to identify and distinguish homotypically-transplanted cells from similar cells in the host brain. This chapter discusses the use of horseradish peroxidase (HRP) to label cell suspensions of fetal rodent hippocampus that were injected into the hippocampi of post-ischemic rats to determine whether homotypically transplanted cells could be distinguished from those of the host. When homotypic cells are to be transplanted and are labeled with HRP, a label is required, which might help in distinguishing cells of transplant origin from those of the host. One factor influencing the transplant survival appears to be the placement of the cells within the hippocampus. Whether the minor differences in histocompatibility between the donor tissue and host in combination with the cytotoxicity factors influence cellular survival is an issue that remains to be resolved. The chapter suggests that neural transplantation may be feasible for treatment for focal lesions produced during ischemia. Sufficient cell growth and development that occurred in the four vessel occlusion (VO) animals, justify further transplantation experiments in this model.