Functional effects of fetal striatal 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.

Neural Transplantation: Prospects for Clinical use

Neural transplantation has been extensively applied in Parkinson's disease, including numerous clinical studies, studies in animal models, and related basic research on cell biology. There is evidence that the clinical trials of both adrenal medulla transplantation and fetal substantia nigra transplantation have produced a detectable clinical effect, although it is not yet clear whether the clinical benefit is sufficient to justify a more widespread application of these procedures. Studies of long-term outcome and quantitative tests are important in assaying the degree of benefit produced by transplantation procedures in Parkinson's disease and for developing improved and refined procedures. Other disease-related applications of neural transplantation are beginning to be developed. These include Huntington's disease, chronic pain, epilepsy, spinal cord injury, and perhaps even demyelinating diseases and cortical ischemic injury. Although most of these applications lie in the future, it is not too soon to begin to consider the scientific justification that should be required for initiation of human clinical trials.

Neural Transplantation for Huntington's Disease: Experimental Rationale and Recommendations for Clinical Trials

Huntington's disease (HD) is a neurodegenerative disorder affecting motor function, personality, and cognition. This paper reviews the experimental data that demonstrate the potential for transplantation of fetal striatum and trophic factor secreting cells to serve as innovative treatment strategies for HD. Transplantation strategies have been effective in replacing lost neurons or preventing the degeneration of neurons destined to die in both rodent and nonhuman primate models of HD. In this regard, a logical series of investigations has proven that grafts of fetal striatum survive, reinnervate the host, and restore function impaired following excitotoxic lesions of the striatum. Furthermore, transplants of cells genetically modified to secrete trophic factors such as nerve growth factor protect striatal neurons from degeneration due to excitotoxicity or mitochondrial dysfunction. Given the disabling and progressive nature of HD, coupled with the absence of any meaningful medical therapy, it is reasonable to consider clinical trials of neural transplantation for this disease. Fetal striatal implants will most likely be the first transplant strategy attempted for HD. This paper describes the variable parameters we believe to be critical for consideration for the design of clinical trials using fetal striatal implants for the treatment of HD.

Neural transplants in patients with Huntington's disease undergo disease-like neuronal degeneration

The clinical evaluation of neural transplantation as a potential treatment for Huntington's disease (HD) was initiated in an attempt to replace lost neurons and improve patient outcomes. Two of 3 patients with HD reported here, who underwent neural transplantation containing striatal anlagen in the striatum a decade earlier, have demonstrated marginal and transient clinical benefits. Their brains were evaluated immunohistochemically and with electron microscopy for markers of projection neurons and interneurons, inflammatory cells, abnormal huntingtin protein, and host-derived connectivity. Surviving grafts were identified bilaterally in 2 of the subjects and displayed classic striatal projection neurons and interneurons. Genetic markers of HD were not expressed within the graft. Here we report in patients with HD that (i) graft survival is attenuated long-term; (ii) grafts undergo disease-like neuronal degeneration with a preferential loss of projection neurons in comparison to interneurons; (iii) immunologically unrelated cells degenerate more rapidly than the patient's neurons, particularly the projection neuron subtype; (iv) graft survival is attenuated in the caudate in comparison to the putamen in HD; (v) glutamatergic cortical neurons project to transplanted striatal neurons; and (vi) microglial inflammatory changes in the grafts specifically target the neuronal components of the grafts. These results, when combined, raise uncertainty about this potential therapeutic approach for the treatment of HD. However, these observations provide new opportunities to investigate the underlying mechanisms involved in HD, as well as to explore additional therapeutic paradigms.

Neural progenitor implantation restores metabolic deficits in the brain following striatal quinolinic acid lesion

Neural progenitor transplantation is a potential treatment for neurodegenerative diseases, including Huntington's disease (HD). In the current study, we tested the potential of rat embryonic neural progenitors expanded in vitro as therapy in the rat quinolinic acid-lesioned striatum, a model that demonstrates some of the pathological features of HD. We used positron emission tomography (PET) to demonstrate that the intrastriatal injection of cultured rat neural progenitors results in improved metabolic function in the striatum and overlying cortex when compared to media-injected controls. Transplanted progenitors were capable of surviving, migrating long distances and differentiating into neurons and glia. The cortices of transplanted animals contained greater numbers of neurons in regions that had shown metabolic improvement. However, histological analysis revealed that only a small fraction of these increased neurons could be accounted for by engrafted cells, indicating that the metabolic sparing was likely the result of a trophic action of the transplanted cells on the host. Behavioral testing of the implanted animals did not reveal improvement in apomorphine-induced rotation. These data demonstrate that progenitor cell implantation results in enhanced metabolic function and sparing of neuron number, but that these functions do not necessarily result in the restoration of complex circuitry.

Intrastriatal grafts derived from fetal striatal primordia--IV. Host and donor neurons are not intermixed

Embryonic striatal grafts transplanted into excitotoxin-damaged host striatum develop a heterogeneous structure in which some regions resemble striatum but others do not. In the experiments reported here, we tested for the possibility that the regions resembling striatum were actually derived from host neurons that migrated into the grafts, rather than being derived from donor cells. We placed embryonic striatal grafts into host brains in which striatal cells had been multiply pulse-labeled with [3H]thymidine. Four groups of host rats were exposed to [3H]thymidine at embryonic days 12 and 13-15, 15-18, 16-19, or 20 to postnatal day 1, and were allowed to reach maturity. One week prior to grafting, lesions of the caudoputamen were made unilaterally in each host rat by injecting ibotenic acid. At grafting, dissociated cells from embryonic days 14-16 rat striatal primordia were injected bilaterally into the host caudoputamen. The locations of [3H]thymidine-labeled neurons were analysed by autoradiography eight to 16.5 months post-grafting. Despite the presence of many intensely labeled neurons in the host striatum of rats in all four groups, intensely labeled neurons were rarely found in the cores of grafts. A few weakly labeled small cells appeared in the graft cores, and occasional strongly or weakly labeled medium-sized cells appeared at the margins of the graft zones. Some perivascular cells associated with blood vessels in the grafts were also weakly labeled, but the gliotic tissue surrounding the graft zones was not labeled. These results suggest that very few host striatal neurons migrate into the cores of intrastriatal grafts, or that, if they do, such neurons return to the host striatum or do not survive. At most, surviving host striatal neurons have limited spatial interactions with donor cells at the margins of the grafts, both in the damaged and in the intact host striatal environment. These observations, combined with our previous finding that [3H]thymidine-labeled cells derived from embryonic day 15 striatal primordia do not appear in the host striatum, indicate that no extensive mutual migrations of striatal donor neurons and host neurons occur in the zones of grafting.

Behavioral effects of fetal neural transplants: relevance to Huntington's disease

Animal models of Huntington's disease (HD) and other neurological disorders have proven useful for examining the anatomical, neurochemical, and behavioral alterations in these diseases. Investigators have taken advantage of new excitotoxic models that appear to successfully simulate the neurobiological and behavioral characteristics of HD with remarkable homology. Selective excitotoxic compounds allow for a more precise and controlled lesion with which to examine the relationship between striatal damage and behavioral abnormalities. In addition, these models provide new approaches for developing and testing various treatments for HD. Fetal neural tissue transplanted into the excitotoxin-lesioned animal can integrate with the host brain and promote neurochemical and functional recovery. Neural grafting paradigms may be viewed as potential therapies for treating neurodegenerative diseases and as aids in deciphering the regenerative mechanisms of the central nervous system. Further research is necessary, however, to determine the negative and positive effects of neural transplantation. In addition, existing behavioral models need to be refined to allow for better evaluation of the subtle topographic changes in behavior resulting from fetal tissue transplantation.

Intrastriatal transplantation of cross-species fetal striatal cells reduces abnormal movements in a primate model of Huntington disease

Huntington disease is a neurological movement disorder involving massive neuronal death in the caudate-putamen region of the brain. Neither preventive nor curative therapy exists for this disease. The implantation of cross-species striatal neural precursor cells into the lesioned striatum of nonhuman primates (baboons) reduced the abnormal movements seen in the disease model. These abnormal movements reappeared after immunological rejection of the implanted striatal cells and were not modified by transplantation with nonstriatal cells. These findings encourage further experimentation toward the use of cell sources other than human fetal cells in a potential clinical application to Huntington disease.

Striatal, ventral mesencephalic and cortical transplants into the intact rat striatum: a neuroanatomical study

Intrastriatal transplantation of fetal striatal (STR), cortical (CTX), or ventral mesencephalic (VM) tissue into the normal striatum has been shown to produce behavioral deficits (38). Here, we have examined the cellular elements of the transplants and their connectivity with the host using histochemistry for cytochrome oxidase (CO) and acetylcholinesterase (AChE), immunocytochemistry for glial fibrillary acidic protein (GFAP), OX42, tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), serotonin (5-HT), and cholecystokinin (CCK). Autoradiography for dopamine D1 and D2, muscarinic cholinergic, and serotonin 5-HT1 and 5-HT2 receptors at 5-15 months after transplantation was also investigated. CO staining showed that all transplants were metabolically active. The STR and VM transplants contained AChE-positive neurons and fibers. The CTX transplants exhibited AChE terminals with an appearance similar to that of the host cortex. AChE staining within the STR transplants was patchy. 5-HT-, TH-, and DBH-immunoreactive (IR) fibers were found in the STR and CTX transplants. In two of six CTX transplants, many TH-IR neurons were present. The VM transplants contained many TH-IR, 5-HT-IR, and DBH-IR cell bodies and fibers. CCK-IR stain was found in the VM transplant and was coextensive with regions containing TH-IR cell bodies. Fibers stained by all markers crossed the transplant and host border. Receptor autoradiography revealed that muscarinic cholinergic and 5-HT2 receptors were present in the STR, CTX, and VM transplants. In addition, dopamine D1 and D2 receptors were present in the STR transplants. Intermittent heavy staining for GFAP and OX42 were observed along the border of most transplants and the hosts. It was noted that high densities and hypertrophy of GFAP- or OX42-stained astrocytes or microglia, respectively, were present in the transplants and adjacent host. OX42-stained macrophages were found in many transplants. The present results indicate that intrastriatal transplants into the intact normal brain express numerous histochemical, immunocytochemical, and receptor features characteristic of the appropriate adult tissues. The afferents from the host extend into the STR and CTX transplants, and neural fibers from the VM transplants grew into surrounding host tissue, suggesting possible anatomical connection. Ultrastructural evidence is needed to determine if these fibers form synaptic connections. The results from GFAP and OX42 immunocytochemical staining support the possibility suggested by behavioral studies that damage to the host brain is induced by neural transplantation.

A method for culturing rat oviduct gamma-aminobutyric acid cells

A technique for the culture of rat oviduct gamma-aminobutyric acid (GABA) cells is described. The technique involves first explaining the fimbria and preampulla, which are the oviduct divisions with the highest density of GABA cells. The explanted tissue is cultured in a serum-free medium, to propagate the outgrowing cells. Under the experimental conditions we describe, the majority of the cells maintain GABA expression, as determined by immunostaining with a GABA antiserum.

Striatal implants protect the host striatum against quinolinic acid toxicity

Quinolinic acid (QA) and related excitotoxins produce a pattern of neuronal loss and neurochemical changes in the rat striatum similar to that of patients suffering from Huntington's disease, suggesting neurotoxicity is important in the etiology of that disease. Thus, strategies for limiting excitotoxin-induced striatal damage, like that caused by QA, may be of great benefit to these individuals. Accordingly, we tested the ability of both neural and non-neural tissue implants to protect the rat striatum against a subsequent QA challenge. Our results demonstrated that recipients of fetal striatal grafts were significantly less affected by striatal injections of QA than non-grafted animals. In contrast to the latter, fetal striatal tissue recipients did not exhibit apomorphine-induced rotation behavior and showed a sparing of cholinergic and enkephalinergic systems normally lost following QA injections. Animals grafted with adult rat sciatic nerve, adrenal medulla or adipose tissue all showed a less dramatic behavioral protection and sparing of cholinergic and enkephalinergic systems. These results suggest that fetal striatal tissue exerts an optimal, and perhaps specific protective influence on the host brain.

Female rats are more sensitive to the locomotor alterations following quinolinic acid-induced striatal lesions: effects of striatal transplants

The effects of sex differences and hormonal factors on the locomotor alterations following intrastriatal injections of quinolinic acid (QA) and the ability of fetal striatal transplants to reverse those effects were examined. Male, female, or ovariectomized female rats received bilateral injections of 150 nmol QA or vehicle into the striatum. Using a multidimensional analysis of spontaneous nocturnal locomotor behavior, a significant increase in locomotion was observed in female but not male or ovariectomized female rats. The increases in activity observed in the lesioned females were attenuated at 6 and 10 weeks following transplantation of rat fetal (E17) striatal tissue into the lesioned striata. Transplanted striatal tissue had no effect on locomotion in male or ovariectomized female rats. Cytochrome oxidase histochemistry revealed that QA produced a marked loss of metabolic activity in regions exhibiting cell loss. Within these areas there was a marked loss of striatal neurons including those reactive for NADPH diaphorase. Despite the sex-related differences in QA-induced locomotion, there were no apparent differences in the extent of striatal pathology or survival of the grafts in any of the groups receiving QA. These experiments demonstrate a sex-dependent dissociation between the behavioral and neurobiological consequences of QA and suggest that sex and hormonal variables play an important role in the locomotor changes following excitotoxic-induced striatal damage.

Intraspinal transplants

Transplants of embryonic central nervous system tissue have long been used to study axon growth during development and regeneration, and more recently to promote recovery in models of human diseases. Transplants of embryonic substantia nigra correct some of the deficits found in experimental Parkinson's disease, for example, by mechanisms that are thought to include release of neurotransmitter and reinnervation of host targets, as well as by stimulating growth of host axons. Similar mechanisms appear to allow intraspinal transplants of embryonic brainstem to reverse locomotor and autonomic deficits due to experimental spinal cord injuries. Embryonic spinal cord transplants offer an additional strategy for correcting the deficits of spinal cord injury because, by replacing damaged populations of neurons, they may mediate the restoration of connections between host neurons. We have found that spinal cord transplants permit regrowth of adult host axons resulting in reconstitution of synaptic complexes within the transplant that in many respects resemble normal synapses. Transplants of fetal spinal cord may also contribute to behavioral recovery by rescuing axotomized host neurons that otherwise would have died. Electrophysiological and behavioral investigations of functional recovery after intraspinal transplantation are preliminary, and the role of transplants in the treatment of human spinal cord injury is uncertain. Transplants are contributing to our understanding of the mechanisms of recovery, however, and are likely to play a role in the development of rational treatments.

Behavioral effects of neural transplants into the intact striatum

The behavioral effects of fetal brain tissue and adrenal medulla transplants into the intact striatum of rats were investigated. Following a bilateral injection of 1.5, 3 or 6 microliters of fetal striatal tissue, a volume-related weight loss was found in all transplanted groups, including the SHAM group, during the first 7 days after the surgery. Rearing behavior was changed in a transplant volume-related manner. Histological analysis suggested that the locomotor effects of transplants into the intact striatum are related to the volume of the transplants. Following bilateral transplantation of fetal cortex (CTX), substantia nigra (SN), striatum (STR), or adrenal medulla (AM) into the striatum, the different behavioral deficits were observed among these transplant groups. The SN group showed a decrease in spontaneous locomotion, significantly increased rearing activity in response to administration of amphetamine, reduction of food intake and water intake and a reduction in body weight. The CTX and AM groups showed a marked increase in spontaneous rearing activities. Hyporesponsiveness to the administration of apomorphine (1 mg/kg) and amphetamine (1 mg/kg) was evident in the CTX, STR, AM groups and SHAM groups. In contrast, the haloperidol-induced catalepsy scores of the CTX, STR, SN and AM were significantly higher than those of a normal control group. In addition, the CTX group showed a deficit in the delayed reward alternation test. These results indicated that the behavioral deficits produced by transplants into normal striatum may be related to both mechanical destruction due to transplant expansion and specific neurochemical interactions of each tissue type between the host and the transplant. Therefore, potential negative consequences of neural transplantation therapy should be considered as well as the beneficial effects.

T1 and T2 weighted magnetic resonance imaging of excitotoxin lesions and neural transplants in rat brain in vivo

On T1- and T2-weighted magnetic resonance (MR) images obtained at 0.14 T the rat brain was visible in the rat head as an area of relative high signal intensity. The enlarged lateral ventricles produced by intrastriatal injections of the excitotoxin kainic acid (KA) were clearly visible as areas of low signal intensity in T1-weighted images but could not be differentiated from normal brain tissue on T2-weighted images for the protocols utilized. Repeated T1-weighted MR images of individual rats demonstrated a progression in the extent of the lesions over an approximately 14-week period following the injection of KA. On the T2-weighted images, areas of relatively high signal intensity corresponding to tissue on the lesioned side of the brain were evident. As the lesion progressed and the remaining tissue visible on the T1-weighted images decreased, the region of high signal intensity visible on the T2-weighted images diminished. This area of high signal intensity on the T2-weighted images appeared to correspond to tissue undergoing a neurodegenerative process. MR images from contiguous slices of brain demonstrated the extent of the KA-induced degeneration throughout the brain, although volume averaging of multiple brain structures was a possible confounding factor. Features apparently corresponding to fetal striatal tissue transplants growing within the enlarged lateral ventricle were visible on T1-weighted images but could not be discriminated on the T2-weighted images. MR imaging is useful for monitoring in vivo the anatomical location and progression of excitotoxin lesions and the location of fetal striatal tissue transplants in lesioned rat brain.

A preliminary study of homotopic fetal cortical and spinal cotransplants in adult rats

Neocortical and spinal tissue from a given E16-17 rat fetus were homotopically transplanted into lesion sites of adult rats which had undergone combined cortical and complete lower thoracic spinal cord lesions. Spinal cord transplants were placed either directly into the gap in host spinal cord or embedded in a collagen matrix. Animals were killed from 4 days to 8 months and tissues were processed for light microscopy. All cortical transplants survived and integrated with host brain. Many axons appeared to grow between the cortical transplant and subjacent host parenchyma. Only collagen-embedded spinal transplants survived. At 8 months, two animals underwent spinal cord transection and HRP implantation two vertebral segments rostral to the spinal cord transplantation site. Both animals revealed HRP-labeled neurons in the cortical transplants. It was concluded that 1) homotopically transplanted fetal cortical tissue can survive and may be capable of extending axons to midthoracic levels, and 2) a collagen matrix may enhance the survival of fetal tissues transplanted into a complete gap in host spinal cord.

A magnetic resonance imaging contrast agent differentiates between the vascular properties of fetal striatal tissue transplants and gliomas in rat brain in vivo

The tumors formed by rat C-6 glioma cells were isointense with the normal rat brain on precontrast T1 weighted magnetic resonance (MR) images. Following i.v. peripheral administration of the MR imaging contrast agent gadolinium (Gd)-DTPA, there was no significant change in the signal intensity from normal brain tissue. However, the tumor appeared as areas of high signal intensity demonstrating the abnormal vascular properties of the tumor. Fetal rat striatal tissue transplanted into unlesioned adult rat striatum appeared isointense with the host brain on precontrast T1 weighted images and there was no evidence for enhancement of the transplanted tissue relative to host brain following i.v. administration of Gd-DTPA. Using this technique we found no evidence with respect to permeability of the contrast agent of an abnormal blood-brain barrier within the striatal transplant in vivo.

Fetal striatal tissue grafts into excitotoxin-lesioned striatum: pharmacological and behavioral aspects

In an excitotoxin animal model of Huntington's disease (HD), fetal striatal tissue transplants survive and grow in the host brain and reverse the behavioral, and, hence, functional deficits produced by the lesion. In the present study we found recovery of apomorphine-induced rotation behavior in unilateral excitotoxin-lesioned rats indicating that the transplant reverses this functional pharmacologic deficit induced by the lesion. It might, therefore, by expected that the transplanted fetal striatal tissue would possess similar pharmacological characteristics as the host striatum. However, autoradiographic localization of D1 and D2 dopamine receptors demonstrated that the transplanted tissue expressed relatively small numbers of these receptor subtypes. Furthermore, there was a relative deficit of [3H]forskolin binding to the stimulatory guanine nucleotide regulatory subunit/adenylate cyclase complex in the fetal striatal tissue transplants. Therefore, transplanted tissue which is neurochemically dissimilar to the host striatum is capable of reversing deficits in both drug-induced and spontaneous locomotor activity.

Magnetic resonance imaging of rat brain following kainic acid-induced lesions and fetal striatal tissue transplants

Use of a small diameter (5.1 cm) radiofrequency coil provided relatively high resolution magnetic resonance (MR) images of rat heads at 0.14 Tesla. On T1-weighted images, the rat brain was clearly visible in the rat head as a region of high signal intensity. No structures were distinguished within the normal rat brain. In contrast, in the brains of rats receiving unilateral kainic acid lesions of the striatum, enlarged lateral ventricles, which are characteristic of the lesion, were clearly visible as dark areas of low signal intensity. Extrastriatal damage on the lesioned side of the brain was also evident in some of the images. Fetal striatal tissue transplants growing within the lesioned striata were also identified in the MR images. The transplanted tissue appeared as areas of high and intermediate signal intensity, similar to the host brain. MR imaging is a useful technique for monitoring excitotoxin lesions of brain and fetal striatal tissue transplants in vivo.