Behavioral Effects of Neural Transplantation

A comparison of dopaminergic cells from the human NTera2/D1 cell line transplanted into the hemiparkinsonian rat

Human NT cells derived from the NTera2/D1 cell line express a dopaminergic phenotype making them an attractive vehicle to supply dopamine to the depleted striatum of the Parkinsonian patient. In vitro, hNT neurons express tyrosine hydroxylase (TH), depending on the length of time they are exposed to retinoic acid. This study compared two populations of hNT neurons that exhibit a high yield of TH+ cells, MI-hNT and DA-hNT. The MI-hNT and DA-hNT neurons were intrastriatally transplanted into the 6-OHDA hemiparkinsonian rat. Amelioration in rotational behavior was measured and immunohistochemistry was performed to identify surviving hNT and TH+ hNT neurons. Results indicated that both MI-hNT and DA-hNT neurons can survive in the striatum, however, neither maintained their dopaminergic phenotype in vivo. Other strategies used in conjunction with hNT cell replacement are likely needed to enhance and maintain the dopamine expression in the grafted cells.

Cell delivery to the central nervous system

A dysfunctional central nervous system (CNS) resulting from neurological disorders and diseases impacts all of humanity. The outcome presents a staggering health care issue with a tremendous potential for developing interventive therapies. The delivery of therapeutic molecules to the CNS has been hampered by the presence of the blood-brain barrier (BBB). To circumvent this barrier, putative therapeutic molecules have been delivered to the CNS by such methods as pumps/osmotic pumps, osmotic opening of the BBB, sustained polymer release systems and cell delivery via site-specific transplantation of cells. This review presents an overview of some of the CNS delivery technologies with special emphasis on transplantation of cells with and without the use of polymer encapsulation technology.

Implications of neurological rehabilitation for advancing intracerebral transplantation

Neurological rehabilitation involves the systematic presentation of environmental stimuli and challenges that enable the patient to learn strategies for minimizing their disabilities. Rehabilitation therapy of transplant recipients may be an important factor in enhancing the efficacy of the transplanted organ or tissue to promote functional recovery. Laboratory research and clinical trials on neural transplantation, as an experimental treatment for neurological disorders (e.g., Parkinson's disease, Huntington's disease, and cerebral ischemia), have focused primarily on devising effective surgical implantation strategies with little attention devoted to the interaction between environmental factors and restorative neurosurgery. Exercise training as part of neurological rehabilitation may be an important factor for neural transplantation therapy for Parkinson's disease. Rehabilitation providers are particularly well placed to provide the environment and the support to optimize the behavioral functioning of neural transplant patients in learning to use the new grafted tissue.

Testis-derived Sertoli cells have a trophic effect on dopamine neurons and alleviate hemiparkinsonism in rats

Neural tissue transplantation has become an alternative treatment for Parkinson's disease (PD) and other neurodegenerative disorders. The clinical use of neural grafts as a source of dopamine for Parkinson's disease patients, although beneficial, is associated with logistical and ethical issues. Thus, alternative graft sources have been explored including polymer-encapsulated cells and nonneural cells (that is, adrenal chromaffin cells) or genetically modified cells that secrete dopamine and/or trophic factors. Although progress has been made, no current alternative graft source has ideal characteristics for transplantation. Emerging evidence suggests the importance of trophic factors in enhancing survival and regeneration of intrinsic dopaminergic neurons. It would be desirable to transplant cells that are readily available, immunologically accepted by the central nervous system and capable of producing dopamine and/or trophic factors. Sertoli cells have been shown to secrete CD-95 ligand and regulatory proteins, as well as trophic, tropic, and immunosuppressive factors that provide the testis, in part, with its "immunoprivileged" status. The present study demonstrated that transplantation of rat testis-derived Sertoli cells into adult rat brains ameliorated behavioral deficits in rats with 6-hydroxydopamine-induced hemiparkinsonism. This was associated with enhanced tyrosine hydroxylase (TH) immunoreactivity in the striatum in the area around the transplanted Sertoli cells. Furthermore, in vitro experiments demonstrated enhanced dopaminergic neuronal survival and outgrowth when embryonic neurons were cultured with medium in which rat Sertoli cells had been grown. Transplantation of Sertoli cells may provide a useful alternative treatment for PD and other neurodegenerative disorders.

Transplantation of mesencephalic cell suspension in dopamine-denervated striatum of the rat. II. Effects on corticostriatal transmission

The present study has been designed to investigate whether intrastriatal implantation of mesencephalic dopamine (DA)-synthetizing neurons into the striatum (ST) of rats whose substantia nigra (SN) was previously destroyed by 6-hydroxydopamine (6-OHDA) restores the pattern of corticostriatal transmission from the medial prelimbic and sensorimotor cortices. In 6-month-old normal animals electrical stimulation of these two functionally unrelated cortices evoked a short latency and brief excitation in 81.6% of neurons recorded in the dorsolateral ST. This percentage decreased significantly (70.6%) in age-matched animals whose dopaminergic nigrostriatal pathway was unilaterally destroyed by 6-OHDA 3 months before recording. However a significant increase in neurons (36.9%) which could be simultaneously activated from the two cortices in comparison to intact rats was noted. In addition the lesion caused a significant decrease in the threshold current required to evoke activation of striatal neurons from the sensorimotor cortex. The increase in the number of striatal neurons responding simultaneously to cortical stimulations demonstrates that destruction of the dopaminergic nigrostriatal pathway causes a loss of the focusing action of DA on corticostriatal transmission. Transplantation of embryonic mesencephalic neurons appears to reestablish this action since the number of convergent responses was significantly decreased in grafted animals (23.5%) in comparison to denervated (36.9%) and sham-grafted (35.1%) animals. Furthermore, the grafts showed a trend to increase current intensities required to evoke activation of striatal cells from both cortices. The action of grafted mesencephalic neurons over prelimbic and sensorimotor cortical inputs to the dorsal ST could be involved in recovery of grafted animals in the correct execution of complex sensorimotor tasks requiring integration of different cortical signals within the ST.

Neural transplantation as an experimental treatment modality for cerebral ischemia

Cerebrovascular disease exemplifies the poor regenerative capacity of the CNS. While there are methods to prevent cerebral infarction, there is no effective therapy available to ameliorate the anatomical, neurochemical and behavioral deficits which follow cerebral ischemia. Focal and transient occlusion of the middle cerebral artery (MCA) in rodents has been reported to result in neuropathology similar to that seen in clinical cerebral ischemia. Using specific techniques, this MCA occlusion can result in a well-localized infarct of the striatum. This review article will provide data accumulated from animal studies using the MCA occlusion technique in rodents to examine whether neural transplantation can ameliorate behavioral and morphological deficits associated with cerebral infarction. Recent advances in neural transplantation as a treatment modality for neurodegenerative disorders such as Parkinson's disease, have revealed that fetal tissue transplantation may produce neurobehavioral recovery. Accordingly, fetal tissue transplantation may provide a potential therapy for cerebral infarction. Preliminary findings in rodents subjected to unilateral MCA occlusion, and subsequently transplanted with fetal striatal tissue into the infarcted striatum have produced encouraging results. Transplanted fetal tissue, assessed immunohistochemically, has been demonstrated to survive and integrate with the host tissue, and, more importantly, ameliorate the ischemia-related behavioral deficits, at least in the short term. Although, this review will focus primarily on cerebral ischemia, characterized by a localized CNS lesion within the striatum, it is envisioned that this baseline data may be extrapolated and applied to cerebral infarction in other brain areas.

Adrenal chromaffin cells on microcarriers exhibit enhanced long-term functional effects when implanted into the mammalian brain

Rat adrenal chromaffin cells attached to either collagen-coated dextran (Cytodex 3) or glass bead microcarriers, both of 90-200 microns diameter, were used as dopamine-secreting implants in the caudate-putamen of rats with 6-hydroxydopamine-induced unilateral lesions of the substantia nigra. As controls, beads without cells and cells in suspension alone were implanted. Chromaffin cells adhered to microcarriers reduced apomorphine-induced rotation by 75% in lesioned animals. Animals that were lesioned but not receiving cell implants or receiving beads alone showed no reduction. Animals implanted with cells not attached to beads also showed a reduction in rotation but this effect lasted less than three months. Microcarrier-attached cells, however, maintained their effect in reducing rotation for at least eight months (rotations were reduced from a control mean of 10.9 +/- 1.4 to 3.6 +/- 1.1 turns/min) without any "drop-off" of the effect. Histological examination showed that eight months post-implant the cells pre-adhered to beads were still present and could be stained by anti-tyrosine hydroxylase antibody. Sections stained with hematoxylin-eosin showed no signs of an inflammatory response. In contrast to beads implanted into the striatum, Cytodex bead implants injected into the lateral ventricle induced a histopathological response appearing to involve the ependyma and choroid plexus. Results suggest that the striatal parenchyma but not the ventricle is amenable to studies using the microcarrier approach to transplantation.

Locomotor and passive avoidance deficits following occlusion of the middle cerebral artery

The characterization of sensory, motor and cognitive dysfunctions following occlusion of the middle cerebral artery (MCA) is prerequisite to investigations of treatment intervention in animal models of ischemia. Different strategies are used to induce ischemia, but the focal, transient occlusion of the MCA has been reported to result in neuropathology most similar to that seen in clinical cerebral ischemia. If the MCA occlusion technique results in a stroke animal model, then the behavioral impairments inherent in stroke should be manifested in this model. The present study provides a further characterization of behavioral alterations associated with MCA occlusion. Sprague-Dawley rats underwent temporal occlusion of the right MCA, and at 1 mo and 2 mo postischemia, were subsequently tested in passive avoidance behavior, motor coordination, asymmetrical motor behavior, neurological functioning, nocturnal spontaneous and amphetamine-induced locomotor activity, and haloperidol-induced catalepsy. Results revealed that ischemic rats showed long-term impairments in sensory, motor and cognitive functions. The discrepancy with other studies reporting temporal MCA-induced behavioral deficits may be due to techniques used to induce ischemia and consequent CNS damage, differences in time period of testing (i.e., immediate vs. later postischemia, nighttime vs. daytime), number of test-retests over the course of the experiment, and age of the animals. The mechanism involved in the MCA-induced behavioral changes may be represented by loss of dopamine receptors on striatal neurons. Histological analysis revealed damage limited to the lateral aspect of the striatum. These behavioral and anatomical data support MCA occlusion as a model of ischemia, and elucidate important factors that should be controlled for in characterizing the MCA-induced neuropathological alterations.

Asymmetrical motor behavior in rats with unilateral striatal excitotoxic lesions as revealed by the elevated body swing test

Severe degeneration of basal ganglia neurons, particularly the intrinsic neurons of the striatum, is the major underlying neuropathology implicated in clinical attributes of Huntington's disease (HD). The excitotoxin-lesioned striatum provides a useful model for evaluating behavioral parameters of HD. Animals with unilateral excitotoxic lesions exhibit asymmetrical rotational behavior in response to dopamine agonists, such as apomorphine. However, the observed behavior is a pharmacological reaction, and subject to sensitization effects. A behavioral test using undrugged animals may demonstrate a more natural response of the animals to the lesion effects. Recently, we have developed the 'drug-free' elevated body swing test (EBST), and demonstrated that hemiparkinsonian rats exhibited significant biased swing activity. In the present study, we observed that animals with unilateral intrastriatal 3-nitropropionic acid or quinolinic acid lesions displayed a significant biased swing activity with the direction ipsilateral to the lesioned side of the brain. This ipsilateral swing corresponded to the ipsilateral rotational behavior exhibited by the lesioned animals when challenged with apomorphine. The present results demonstrated that the EBST is a sensitive measure for characterizing asymmetrical behavior in animals with striatal lesions.