Resolution of stroke deficits following contralateral grafts of conditionally immortal neuroepithelial stem cells.

BACKGROUND AND PURPOSE: Grafts of MHP36 cells have previously been shown to reduce dysfunction after global ischemia in rats. To test their efficacy after focal ischemia, MHP36 cells were grafted 2 to 3 weeks after transient intraluminal middle cerebral artery occlusion (tMCAO) in rats. METHODS: MHP36 cells were implanted into the hemisphere contralateral to the lesion, with 8 deposits of 3 microL of cell suspension (25 000 cells per microliter). Sham grafted rats received equivalent volumes of vehicle. Three groups, sham-operated controls (n=11), MCAO+sham grafts (n=10), and MCAO+MHP36 grafts (n=11), were compared in 3 behavioral tests. RESULTS: In the bilateral asymmetry test, MCAO+MHP36 grafted rats exhibited neglect before grafting but subsequently showed no significant dysfunction, whereas MCAO+sham grafted rats showed stable sensorimotor deficits over 18 weeks relative to controls. MCAO+sham grafted rats demonstrated spontaneous motor asymmetry and increased rotational bias after injection of dopamine agonists. MCAO+MHP36 and control groups exhibited no bias in either spontaneous or drug-induced rotation. In contrast to motor recovery, MCAO+MHP36 grafted rats showed no improvement relative to MCAO+sham grafted rats in spatial learning and memory in the water maze. MCAO produced large striatal and cortical cavitations in both occluded groups. Lesion volume was significantly reduced (P<0.05) in the MCAO+MHP36 grafted group. The majority of MHP36 cells were identified within the intact grafted hemisphere. However, MHP36 cells were also seen in the cortex, striatum, and corpus callosum of the lesioned hemisphere. CONCLUSIONS: MHP36 cells may improve functional outcome after MCAO by assisting spontaneous reorganization in both the damaged and intact hemispheres.

Functional reconstruction of the hippocampus: fetal versus conditionally immortal neuroepithelial stem cell grafts.

Late fetal CA1 hippocampal grafts and stem cell grafts from the conditionally immortal MHP36 clonal line derived from the H-2Kb-tsA58 transgenic mouse neuroepithelium both improved spatial deficits in rats with ischaemic CA1 damage induced by four-vessel occlusion (4VO). However, the distribution of fetal and MHP36 grafts differed. Fetal cells lodged in clumps around the implant sites and along the corpus callosum, whilst MHP36 grafts infiltrated the area of CA1 ischaemic damage, achieving apparent architectural reconstruction of the hippocampus. The migration of MHP36 cells is damage-dependent. Few cells were found in intact brain; after 15 min of 4VO cells repopulated only the discrete area of CA1 cell loss, whereas with more extensive damage after 30 min occlusion cells migrated to all hippocampal fields and to cortex. A higher proportion of grafted MHP36 cells differentiated into neurons in the host CA1 field than grafts of striatal or cortical expanded cell populations. Cortical population grafts were as effective as MHP36 grafts in improving water maze learning, whereas striatal or ventral mesencephalic cells were ineffective, indicating a degree of stem cell specificity. The efficacy of MHP36 cells extends to primates. In marmosets with profound impairments in conditional discrimination tasks after lesions of the CA1 field, MHP36 cells improved performance as effectively as fetal grafts and migrated evenly through the CA1 field, in contrast to clustered fetal cells. These findings suggest that MHP36 stem cell grafts are as effective as fetal grafts in functional repair of hippocampal damage, and that their preference for areas of cell loss and adoption of appropriate morphologies is consistent with a point-to-point repair mechanism.

Conditionally immortal neuroepithelial stem cell grafts reverse age-associated memory impairments in rats.

In order to investigate the effects of stem cell grafts on water maze deficits in aged (22-month-old) rats, three groups of aged rats, assigned by pre-training latency scores to unimpaired, impaired control and impaired grafted groups, were compared with young (five-month-old) controls, six to eight weeks after implantation of cells from the conditionally immortal Maudsley hippocampal stem cell line, clone 36 (MHP36 stem cell line), in the cortex, striatum and hippocampus. Grafted rats were substantially superior to their matched impaired aged controls, and learned to find the platform as rapidly as unimpaired aged rats, although young controls were more efficient than all aged groups in several measures of spatial search during training. On the probe trial, however, aged rats with grafts showed significantly better recall of the precise position of the platform than any other group, including young controls, possibly indicating some perseveration. A further comparison found that groups of unimpaired and moderately impaired aged rats showed far less improvement from water maze pre-training to acquisition phases than young controls, indicative of progressive deficits over time. Histological investigation showed that beta-galactosidase-positive MHP36 cells migrated widely from the implantation sites to infiltrate the striatal matrix, all hippocampal fields and areas of the cortex. Grafted cells showed both astrocytic and neuronal morphologies, with cells of pyramidal and granular appearance in appropriate hippocampal strata.Taken together, these results indicate that neuroepithelial stem cell grafts extensively colonize the aged rat brain and substantially reverse progressive cognitive decline associated with ageing.

Neurological sequelae and long-term behavioural assessment of rats with transient middle cerebral artery occlusion.

Animal models of stroke, notably transient middle cerebral artery occlusion (MCAo), are used to assess the efficacy of pharmacological and transplant treatments. Long-term studies (>1 month) of the functional effects of treatments in animal models are required to predict treatments likely to improve dysfunctions associated with stroke damage. These pre-clinical studies require (1) optimum post-operative care to ensure long-term survival, (2) methods for assignment of rats to groups with equivalent impairments to reduce variability and enhance detection of treatment effects, and (3) behavioural tests that detect long-term stable deficits. For long-term functional assessment, a battery of behavioural tests sensitive to a range of deficits observed after MCAo was developed. The bilateral asymmetry test evaluated the time course of sensory neglect. Deficits of motor integration were examined in the footfault test, and motor bias was assessed by pharmacological stimulation of rotation. The water maze was used to detect long-term deficits in spatial information processing. Long-term differences between control and MCAo animals in this battery of tests indicate that the protocol provides an efficient assessment suitable for evaluating treatment outcomes in pre-clinical studies of stroke, and that the post-operative care procedure and method of assignment to groups were effective.