Striatal Transplantation Research Articles

Human fetal striatal transplantation in an excitotoxic lesioned model of Huntington's disease.

Human fetal striatal transplantation in an excitotoxic lesioned model of Huntington's disease.

The effects of donor stage on the survival and function of embryonic striatal grafts in the adult rat brain: II. Correlation between positron emission tomography and reaching behaviour

Grafts of embryonic striatal primordia are able to elicit behavioural recovery in rats which have received an excitotoxic lesion to the striatum, and it is believed that the P zones or striatal-like tissue within the transplants play a crucial role in these functional effects. We performed this study to compare the effects of different donor stage of embryonic tissue on both the morphology (see accompanying paper) and function of striatal transplants. Both the medial and lateral ganglionic eminence was dissected from rat embryos of either 10 mm, 15 mm, 19 mm, or 23 mm crown-rump length, and implanted as a cell suspension into adult rats which had received an ibotenic acid lesion 10 days prior to transplantation. After four months the animals were tested on the “staircase task” of skilled forelimb use. At 10–14 months rats from the groups which had received grafts from 10 mm or 15 mm donor embryos were taken for positron emission tomography scanning in a small diameter postiron emission tomography scanner, using ligands to the dopamine D 1 and D 2 receptors, [ 11C]SCH 23390 and [ 11C]raclopride, respectively. A lesion-alone group was also scanned with the same ligands for comparison. Animals which had received transplants from the 10 mm donors showed a significant recovery with their contralateral paw on the “staircase test”. No other groups showed recovery on this task. Similarly, the animals with grafts from the youngest donors showed a significant increase in D 1 and D 2 receptor binding when compared to the lesion-alone group. No increase in signal was observed with either ligand in the group which had received grafts from 15 mm donors. Success in paw reaching showed a strong correlation to both the positron emission tomography signal obtained and the P zone volume of the grafts. These results suggest that striatal grafts from younger donors (10 mm CRL) give greater behavioural recovery than grafts prepared from older embryos. This recovery is due to both the increased proportion of striatal-like tissue within the grafts and an increase in functional D 1 and D 2 dopamine receptors measured by positron emission tomography, i.e. a more extensive integration of the graft with the host brain.

The age of striatum determines the pattern and extent of dopaminergic innervation: A nigrostriatal double graft study

In animal models of Parkinson's disease, transplanted fetal mesencephalic dopaminergic neurons can innervate the dopamine-depleted host brain, but it is unclear why large portions of the host striatum are left uninnervated. During normal development, the dopaminergic innervation first occurs in the form of a dense patchy pattern in the striatum, followed by a widespread nerve fiber network. Using intraocular double grafts we have investigated dopaminergic growth patterns initiated when ventral mesencephalic grafts innervate striatal targets. The fetal lateral ganglionic eminence was implanted into the anterior eye chamber. After maturation in oculo, fetal ventral mesencephalon was implanted and placed in contact with the first graft. In other animals the two pieces of tissue were implanted simultaneously. Tyrosine hydroxylase (TH) immunohistochemistry revealed a pattern of dense TH-positive patches throughout the total volume of the striatal grafts in simultaneously transplanted cografts, while a widespread, less dense, pattern was found when mature striatal transplants were innervated by fetal dopaminergic grafts. To investigate which type or types of growth patterns that developed after grafting to striatum in situ of an adult host, fetal ventral mesencephalic tissue was implanted into the lateral ventricle adjacent to the dopamine-lesioned striatum. After maturation of the mesencephalic graft, the fetal lateral ganglionic eminence was implanted into the reinnervated part of the host striatum. TH immunohistochemistry revealed a few nerve fibers within the striatal graft and the growth pattern was of the widespread type. In conclusion, grafted dopaminergic neurons preferably innervate mature striatum with a widespread sparse nerve fiber network, while the innervation of the immature striatum occurs in the form of dense patches. Furthermore, when the patchy pattern is formed, the total volume of the striatal target is innervated while growth of the widespread type terminates prior to reaching distal striatal parts. Thus, the growth pattern seems essential to the final volume that is innervated. Once the widespread growth pattern is initiated, the presence of immature striatum does not change the dopaminergic growth pattern.

Neuropsychological functioning following fetal striatal transplantation in Huntington's chorea: Three case presentations

Neurotransplantation has been proposed as a potential treatment for the neurodegenerative disorder of Huntington's disease (HD), which currently has no effective therapy. While patients with Parkinson's disease have received neurotransplantation, until recently no HD patients have undergone transplantation for HD with standardized evaluations of their progress following surgery. The current report presents the cognitive changes in three patients with HD who underwent bilateral transplantation of human fetal striatal tissue. As part of the pre- and postsurgical evaluation, all three patients were administered a neuropsychological battery sensitive to the cognitive effects of HD within 2 mo prior to surgery and at 4–6 mo following transplantation. Four to 6 mo subsequent to surgery, all patients demonstrated increased scores on some measures of cognitive functioning. However, the pattern of changes was not uniform across subjects. These findings suggest that fetal striatal transplantation may improve some of the cognitive symptoms associated with HD in the three reported patients.

The age of striatum determines the pattern and extent of dopaminergic innervation: a nigrostriatal double graft study.

In animal models of Parkinson's disease, transplanted fetal mesencephalic dopaminergic neurons can innervate the dopamine-depleted host brain, but it is unclear why large portions of the host striatum are left uninnervated. During normal development, the dopaminergic innervation first occurs in the form of a dense patchy pattern in the striatum, followed by a widespread nerve fiber network. Using intraocular double grafts we have investigated dopaminergic growth patterns initiated when ventral mesencephalic grafts innervate striatal targets. The fetal lateral ganglionic eminence was implanted into the anterior eye chamber. After maturation in oculo, fetal ventral mesencephalon was implanted and placed in contact with the first graft. In other animals the two pieces of tissue were implanted simultaneously. Tyrosine hydroxylase (TH) immunohistochemistry revealed a pattern of dense TH-positive patches throughout the total volume of the striatal grafts in simultaneously transplanted cografts, while a widespread, less dense, pattern was found when mature striatal transplants were innervated by fetal dopaminergic grafts. To investigate which type or types of growth patterns that developed after grafting to striatum in situ of an adult host, fetal ventral mesencephalic tissue was implanted into the lateral ventricle adjacent to the dopamine-lesioned striatum. After maturation of the mesencephalic graft, the fetal lateral ganglionic eminence was implanted into the reinnervated part of the host striatum. TH immunohistochemistry revealed a few nerve fibers within the striatal graft and the growth pattern was of the widespread type. In conclusion, grafted dopaminergic neurons preferably innervate mature striatum with a widespread sparse nerve fiber network, while the innervation of the immature striatum occurs in the form of dense patches. Furthermore, when the patchy pattern is formed, the total volume of the striatal target is innervated while growth of the widespread type terminates prior to reaching distal striatal parts. Thus, the growth pattern seems essential to the final volume that is innervated. Once the widespread growth pattern is initiated, the presence of immature striatum does not change the dopaminergic growth pattern.

Localization of dopamine receptors and associated mRNA in transplants of human fetal striatal tissue in rodents with experimental Huntington's Disease

Huntington's Disease (HD) is characterized by deficits in motor and cognitive functions. This neurodegenerative disease shows an extensive loss of medium-sized spiny projection neurons (GABAergic) within the neostriatum. With the loss of these neurons, there is a concomitant loss of associated receptors, such as those for GABA, glutamate, and dopamine. In the present study, we have addressed the question of whether dopamine receptors are re-established in the lesioned rodent striatum following the transplantation of human striatal cells. Human striatal cell suspension or saline (transplant controls) was injected into the striatum of rats previously lesioned with quinolinic acid (QA). Three–nine months following transplantation, the animals were sacrificed and the brains were processed for receptor autoradiography and in situ hybridization of dopamine D1 and D2 receptor subtypes. Our results demonstrate that animals transplanted with human striatal cells show a significant increase in D1 receptors following transplantation when compared to the lesion area in control animals, while D1 receptor mRNA remains unchanged. In contrast to D1 receptor binding, D2 receptor levels are not increased in the lesioned and transplanted area of the striatum when compared to controls; however, D2 receptor mRNA levels are significantly increased. These results demonstrate that at the times the animals were examined, D1 and D2 receptors were differentially regulated. Our results further indicate that human striatal primordium will survive following transplantation and will express D1 receptors and D2 receptor mRNA that are depleted in the QA lesioned rodent striatum. This study compliments and extends previous findings on human striatal cell transplantation in rodent models of HD.

Motor disturbance and brain functional imaging in Parkinson's disease.

18F-Dopa positron emission tomography (PET) provides a sensitive means of quantitating the loss of nigrostriatal dopaminergic fibres in Parkinson's disease and so can be used to diagnose its presence and to objectively follow the rate of disease progression. It can also be used, in principle, to determine the efficacy of putative neuroprotective agents and has already been extensively used to monitor the viability of striatal transplants of fetal mesencephalic tissue. Loss of dopaminergic projections produces significant changes in the patterns of both resting and activated cortical function. H2(15)O PET activation studies have suggested that the akinesia of Parkinson's disease is associated with failure to activate the supplementary motor and dorsal prefrontal areas, brain regions particularly involved in motor preparation and decision making. Activation of these cortical areas can be restored by administering dopaminergic medication, implanting the striatum with fetal mesencephalic tissue, and by pallidotomy. This article reviews the insight that PET studies have provided into the pathophysiology of Parkinson's disease.

Transplantation of human striatal tissue into a rodent model of Huntington's disease: Phenotypic expression of transplanted neurons and host-to-graft innervation

The present study was undertaken to investigate the phenotypic expression and integration of human striatal neurons transplanted into an animal model of Huntington's disease. Sprague-Dawley rats were anesthetized and subjected to quinolinic acid lesions of the left striatum. Three human fetal cadavers were utilized for transplantation in this study (7,8, and 10 weeks in gestation). The striatal primordia was dissected from each fetus and subsequently dissociated into cell suspensions. Following the initial lesion surgeries (3–4 months), the rats were reanesthetized and transplanted with human striatal cells (400,000 cells per rat). The animals were processed for histochemical analysis 9–17 weeks posttransplantation. Histochemistry was performed utilizing thionin (Nissl staining), acetylcholinesterase, NADPH-diaphorase, and antibodies against tyrosine hydroxylase and glial fibrillary acidic protein. Examination of stained brain sections demonstrate that human striatal transplants grow to fill a substantial portion of the remaining striatum, and contain clusters of immature and mature cells. Acetylcholinesterase activity is present in the transplant neuropil, varying in intensity, and distributed in a heterogeneous fashion. In addition, host afferent dopaminergic fibers penetrate into the transplant, and are occasionally found in patches. NADPH-diaphorase histochemistry revealed medium sized aspiny striatal neurons of donor origin in the transplants. The results of this study are similar to those obtained with rodent fetal striatal transplants, and suggest that human striatal tissue is capable of surviving, expressing normal striatal cell phenotypes, and receiving host dopaminergic innervation.

Development of the human striatum: Implications for fetal striatal transplantation in the treatment of Huntington's disease

Fetal neural transplantation has recently been demonstrated to ameliorate motor and other behavioral deficits in animal models of Huntington's disease, and reconstruct many of the damaged striatal circuits. However, there has been significant variability in the histological appearance of these grafts, most likely related to differences of the regions of dissection of the donor tissue. Selective dissection and transplantation of the lateral ventricular eminence in rodents has resulted in grafts consisting of primarily striatal-like tissue. This data, combined with data from our own and other laboratories has led to a description of the development of the human striatum, with a particular emphasis on the relevance of human striatal development to the field of fetal tissue transplantation for the treatment of Huntington's disease. If the goal of transplantation is to graft GABAergic striatal projection neurons, it is our impression that optimal grafting results will occur when transplants are derived from the lateral ventricular eminence and the lateral aspect of the body of the ventricular eminence anterior to the foramen of Monro. Optimal results are likely to occur when donor ages range from Stage 19 to 23, with possible graft success when donor age extends to as late as postovulatory week 22.

Projection neurons in fetal striatal transplants are predominantly derived from the lateral ganglionic eminence.

In the present study, we have characterized aspects of integration, growth and phenotypic differentiation of embryonic grafts derived from the selective dissection of either the lateral or medial portion of the ganglionic eminences of the rodent forebrain. Donor tissues were derived from embryonic day 15 rat, or embryonic day 14 mouse embryos, and injected, as single cell suspensions into the striatum or substantia nigra of adult rats previously subjected to an intrastriatal ibotenic acid lesion. Two to six weeks following grafting, immunocytochemical detection of DARPP-32, the 32,000 mol. wt dopamine- and cyclic AMP-regulated phosphoprotein, was used to identify areas with a striatum-like phenotype within both the intrastriatal and the intranigral grafts. It was thus revealed that all the lateral ganglionic eminence grafts, irrespective of their placement, were dominated by striatum-like tissue (up to 90% of the total graft volume), while the medial ganglionic eminence transplants were only sparsely positive (< 10% of the total graft volume). These striatum-like regions of the grafts were selectively innervated by tyrosine hydroxylase immunopositive fibres from the host substantia nigra. Furthermore, axons derived from the lateral ganglionic eminence mouse grafts placed in the striatum, as detected by the mouse-specific neuronal marker M6, showed a more extensive and directed outgrowth towards the globus pallidus when compared to fibres emanating from the medial ganglionic eminence grafts. Mouse lateral and medial ganglionic eminence grafts placed into the substantia nigra exhibited similar fibre outgrowth patterns; both types of grafts thus innervated the substantia nigra-pars reticulata and extended axons into the cerebral peduncle. These results show that DARPP-32-positive striatal projection neurons are derived, for the most part, from the lateral ganglionic eminence and that the restricted lateral ganglionic eminence dissection provides a more optimal source of striatal tissue for grafting in the rat Huntington model.

Development of the human striatum: implications for fetal striatal transplantation in the treatment of Huntington's disease.

Fetal neural transplantation has recently been demonstrated to ameliorate motor and other behavioral deficits in animals models of Huntington's disease, and reconstruct many of the damaged striatal circuits. However, there has been significant variability in the histological appearance of these grafts, most likely related to differences of the regions of dissection of the donor tissue. Selective dissection and transplantation of the lateral ventricular eminence in rodents has resulted in grafts consisting of primarily striatal-like tissue. This data, combined with data from our own and other laboratories has led to a description of the development of human striatum, with a particular emphasis on the relevance of human striatal development to the field of fetal tissue transplantation for the treatment of Huntington's disease. If the goal of transplantation is to graft GABAergic striatal projection neurons, it is our impression that optimal grafting results will occur when transplants are derived from the lateral ventricular eminence and the lateral aspect of the body of the ventricular eminence anterior to the foramen of Monro. Optimal results are likely to occur when donor ages range from Stage 19 to 23, with possible graft success when donor age extends to as late as postovulatory week 22.

Neurotransmitter-related gene expression in intrastriatal striatal transplants. III. Regulation by host cortical and dopaminergic afferents.

Grafted striatal neurons have previously been shown to receive innervation from both the host cerebral cortex and dopaminergic substantia nigra. In the present study, we have used quantitative in situ hybridization histochemistry for striatal neuropeptide mRNAs, to determine the extent of functional integration exhibited by these two afferent systems. DARPP-32, preproenkephalin (PPE) and preprotachykinin (PPT) mRNAs were all expressed within discrete patches of the graft (termed P-regions) which corresponded well with each other on adjacent sections. Dopamine-depleting 6-OHDA lesions resulted in a marked increase in PPE mRNA levels and a concomitant decrease in PPT mRNA expression both in the remaining host striatum and in the P-regions of the graft. In a previous report [7], we have shown that cortical and dopaminergic afferents to the striatum interact in the regulation of PPE mRNA expression, such that in the absence of functional dopaminergic inputs, intact prefrontal corticostriatal afferents are necessary in order to maintain increased PPE mRNA levels. In the present study, we observed that cortical knife cut lesions placed at the level of the foreceps minor in previously 6-OHDA-lesioned animals resulted in a normalization of PPE mRNA expression, not only in the remaining host striatum but also within the P-regions of striatal grafts. Cellular analysis showed that this normalization was most pronounced in the peripherally situated P-regions (along the graft borders), which are known to receive dense host-derived cortical input. The cortical lesions had no significant effect on the 6-OHDA-induced reduction of PPT mRNA levels neither in the remaining lost striatum nor in the striatal graft. The expression of DARPP-32 mRNA in the remaining host striatum or striatal graft was not affected by either 6-OHDA lesion or cortical transection, demonstrating the specificity of the cortical lesion effect. These results indicate that both cortical and dopaminergic afferents originating in the host, functionally regulate neuropeptide mRNA expression within the striatal grafts, and that the two afferent systems interact with each other in the regulation of enkephalin gene expression in grafted neurons. On basis of recent results [9] showing that the enkephalin-expressing neurons are identical, at least in part, to efferent graft neurons projecting to the host globus pallidus, it is proposed that the cortical-dopamine interaction demonstrated here may play an important role in the recovery of complex motor performance induced by the striatal transplants.

Asymmetrical behavior in rats following striatal lesions and fetal transplants: the elevated body swing test

Animals with unilateral neurotoxic lesions in the striatum exhibit a stereotypical biased rotational behavior in response to dopamine agonists. We recently argued that the rotational test may be subject to sensitization effects of the drug. Accordingly, we proposed the drug-free elevated body swing test (EBST) as an alternative behavioral index of motor asymmetry in striatal lesioned animals. EBST involves elevating the animal from the ground by holding its tail and simply recording the number of swings to either side made by the animal over 30 s. We previously reported that Sprague-Dawley, male 8-week-old rats, intrastriatally lesioned with 500 nanomoles of 3-nitropropionic acid or 225 nanomoles of quinolinic acid, exhibit biased swing activity at 7, 14, 21 and 28 days post-lesion. In the present study, we extended the efficacy of the EBST in measuring the recovery of motor function following fetal striatal transplants. At 2 months post-lesion, lesioned animals which show 70% or higher biased swing activity were transplanted with rat fetal striatal lateral eminence (16-day-old gestational age). When tested in the EBST at 1 and 3 months post-transplant, these transplanted animals displayed normalization of the biased swing activity. In contrast, animals transplanted with medium alone continued to exhibit a biased swing activity. The present study thus extends our previous EBST data to include successful behavioral characterization by EBST of recovery of motor function in lesioned animals receiving fetal transplants.

Neurotransmitter-related gene expression in intrastriatal striatal transplants--I. Phenotypical characterization of striatal and non-striatal graft regions.

In the present study, we have re-examined the heterogeneous nature of intrastriatal striatal transplants derived from embryonic day 14-15 rat striatal primordia implanted into the previously excitotoxically lesioned striatum of adult rats, using in situ hybridization histochemistry to localize neurotransmitter-related messenger RNAs. These grafts are characterized by discrete patches of DARPP-32 messenger RNA expression, which cover approximately one-third of the cross-sectional graft area. The messenger RNAs encoding for preproenkephalin (the enkephalin precursor), preprotachykinin (precursor to substance P), choline acetyltransferase, as well as the D1 and D2 dopamine receptors, which are abundant in the normal striatum, were all present in the striatal grafts and were expressed almost exclusively in the DARPP-32-positive graft regions. In these graft regions, the expression of the neurotransmitter-related messenger RNAs was generally similar to that seen in the intact striatum, although the level of expression of preproenkephalin and preprotachykinin messenger RNAs varied notably among the patches of expression. Cellular analysis performed on individual patches showed that the expression per cell of preproenkephalin and preprotachykinin messenger RNAs was inversely related, such that patches with higher than normal preproenkephalin messenger RNA levels displayed lower than normal preprotachykinin messenger RNA levels, and vice versa. Moreover, messenger RNA expression for the dopamine D2 receptor was overall lower than that for the dopamine D1 receptor, both with respect to the level per cell and the number of positive cells within the DARPP-32 patches. Glutamate decarboxylase messenger RNA was expressed throughout the grafts, in 98% of all neurons located in the DARPP-32-positive regions and in 75% of all neurons in the non-DARPP-32 regions of the graft. Interestingly, the cellular expression of glutamate decarboxylase messenger RNA was considerably higher in the non-DARPP-32 expressing regions than that in the DARPP-32 messenger RNA-rich areas, where it approximated that of the intact striatum. Furthermore, grafted neurons located outside the DARPP-32-expressing regions displayed similar levels of expression to those found in the overlying cortex and in the closely adjacent globus pallidus. To further characterize the DARPP and non-DARPP graft compartments, messenger RNAs encoding the alpha 1 and beta 2 subunits of the GABAA receptor were studied. These receptor subunits, which exhibit a high expression in the host cortex and pallidum but little in the intact striatum, were found in discrete patches situated outside, but often closely associated with, the DARPP-32-rich areas of the graft.(ABSTRACT TRUNCATED AT 400 WORDS)

Neurotransmitter-related gene expression in intrastriatal striatal transplants—II. Characterization of efferent projecting graft neurons

The phenotypic characteristics of identified graft neurons in intrastriatal striatal transplants which give rise to efferent projections innervating the host brain were examined using a combination of in situ hybridization histochemistry and fluorescent retrograde tracing. Cell suspension grafts of embryonic day 14-15 rat striatal primordia (including both the medial and lateral ganglionic eminences) were implanted into the previously excitotoxically lesioned striatum of adult rats, and after longer than one year the retrograde tracer Fluoro-Gold was injected bilaterally into either the globus pallidus or the substantia nigra. Injections into the globus pallidus resulted in significant retrograde labelling of graft neurons within most of the experimental animals, whereas very few graft cells were labelled after the nigral injections. The vast majority of the neurons retrogradely labelled from the globus pallidus occurred in clusters or patches in the caudal half of the transplants, which corresponded well with DARPP-32 messenger RNA expressing (i.e. striatal) regions of the grafts. Indeed, within these Fluoro-Gold-labelled graft patches, the proportion of retrogradely labelled cells found to contain DARPP-32 messenger RNA was identical to that observed in the intact striatum after similar pallidal injections (93%). In addition, some Fluoro-Gold-labelled cells were found scattered outside the DARPP-32-positive cell clusters; these cells were overall larger and rarely (c. 9%) DARPP-32 messenger RNA-positive. Messenger RNA encoding for glutamate decarboxylase (which was found in 95% of Fluoro-Gold-labelled neurons in the intact striatum) was detected in almost all retrogradely labelled graft neurons located in both the DARPP-32-positive patches of retrograde labelling (93%) and in the DARPP-32-negative regions (82%). In the intact striatum, neurons labelled after pallidal injections of Fluoro-Gold were observed to express preproenkephalin messenger RNA to a greater extent than preprotachykinin messenger RNA (81% vs 21%). Conversely, within the grafts, retrogradely labelled neurons in the patches of Fluoro-Gold-labelled cells were more often found to contain preprotachykinin messenger RNA (50%) than preproenkephalin messenger RNA (21%). The Fluoro-Gold-labelled cells scattered outside the patches of retrograde labelling rarely expressed either preproenkephalin or preprotachykinin messenger RNA. Fluoro-Gold injections into the host substantia nigra resulted in very few retrogradely labelled graft neurons; however, many (85%) of these cells were observed to express glutamate decarboxylase messenger RNA, while only rarely were they observed to contain either DARPP-32, preproenkephalin or preprotachykinin messenger RNAs (c. 10%).(ABSTRACT TRUNCATED AT 250 WORDS)

The lateral ganglionic eminence is the origin of cells committed to striatal phenotypes: neural transplantation and developmental evidence

In order to determine whether the lateral ganglionic eminence (LGE) of the fetal telencephalon is the primary source of striatal precursors in striatal transplants and tissue cultures, cells derived exclusively from the LGE of fetal rat brains were transplanted into the quinolinic-acid-lesioned striatum of adult rats. After 2–3 months they produced grafts that were almost entirely AChE-positive as well as DARPP-32-, TH-, and calbindin-immunoreactive. The grafts were integrated into the host striatum so that host corticofugal fiber tracts interdigitated with graft tissues similar to the way they penetrate the gray matter of the normal striatum. Fast Blue dye injected into the ipsilateral globus pallidus of LGE grafted produced retrogradely labeled neurons within the grafts, but Fluorogold dye injected into the ipsilateral substantia nigra did not. In a separate experiment using DARPP-32-immunohistochemistry as a striatal marker, fetal (E16) and neonatal (P2) rat brains showed DARPP-32 immunoreactivity in the LGE but not in the adjacent medial ganglionic eminence (MGE). In summary, both fetal LGE cells and LGE grafts express specific striatal markers, and LGE grafts integrate into the host striatum and innervate the major striatal efferent target within the host brain. These data suggest that the LGE is the origin of cells committed to striatal phenotypes in the developing brain.

Permeability of the Blood-Brain Barrier within Rat Intrastriatal Transplants Assessed by Simultaneous Systemic Injection of Horseradish Peroxidase and Evans Blue Dye

Both horseradish peroxidase (HRP) and Evans blue dye (EBD) have been used previously to characterize the status of the blood-brain barrier (BBB) within brain tissue transplants and host brain tissue. We investigated the possibility that a differential permeability of the vasculature to these two markers can account for discrepancies in the literature concerning the presence of an intact BBB within the grafted tissues. Intravascular injection of both HRP and EBD was used to evaluate the status of the BBB within intracerebral tissue transplants. Simultaneous injection of HRP and EBD in rats with adrenal medulla transplants or C-6 glioma tumors demonstrated a lack of a BBB within these grafts. Both markers produced consistent results within each tissue type, although HRP was generally a more sensitive marker. In contrast to the lack of a BBB in the C-6 gliomas or adrenal medulla transplants, 1-week-old fetal striatal transplants had a BBB essentially intact to both HRP and EBD. Any reported discrepancies in the characterization of the BBB are not likely due to differences between the properties of HRP or EBD. Fetal striatal transplants appear to have an intact BBB at 1 week following transplantation.

Retrograde degenerative changes in the substantia nigra pars compacta following an excitotoxic lesion of the striatum

The retrograde changes induced by an excitotoxic lesion of the striatum (Str) on the neurons in substantia nigra pars compacta (SNc) projecting to the neuron-depleted region were investigated in adult rats. The retrograde tracer Fluoro-Gold (FG) was injected bilaterally into the Str. 2 weeks later, the excitotoxic amino acid ibotenic acid (IA) was injected unilaterally into the same structure. At four different time points after the lesion (1 week and 1,2 and 3 months, respectively), the size of the FG-labelled cells and number of tyrosine hydroxylase (TH)-positive cells in the SNc were evaluated on the lesioned and control sides. Parallel groups of animals received suspension grafts of fetal striatal tissue into the lesioned striata. At 1 week and 1 month after lesion, there were no changes in cell size, number of TH-positive cells or number of FG-labelled cells expressing TH in the SNc. At 2 and 3 months, however, there was a significant 30% shrinkage of the FG-labelled SNc cells but no evident decrease in TH-positive cell number, or in the expression of the TH protein, on the lesioned side as compared with the non-lesioned control side. Striatal transplants placed into the lesioned Str did not counteract this effect. This finding that an axon-sparing lesion of target cells results in cell shrinkage but no cell loss of the neurons that project to the lesioned area is in line with that has been shown to occur after similar lesions in the cholinergic septohippocampal and basalo-cortical systems. These slowly developing atrophic changes, without cell loss, induced in the nigral dopamine neurons by removal of the striatal target neurons should provide a useful model for the in vivo evaluation of the effect of putative target-derived neurotrophic factors in the nigrostriatal dopamine system.

Re-initiated growth from mature ventral mesencephalon: an in oculo transplant study of nigrostriatal co-grafts.

The ability of mature dopaminergic neurons derived from ventral mesencephalon to re-initiate growth after making contact with a non-innervated target was studied using the intra-ocular grafting model. Foetal ventral mesencephalic tissue or brain stem including the locus coeruleus area was grafted to the anterior chamber of the eye. Two weeks, 6 weeks or 1 year after the first implantation, foetal striatal tissue was placed in contact with the nigral graft or grafted alone. The size of the transplants was measured through the cornea. The final size of the striatal grafts was significantly larger when placed alone than when co-grafted with 1-year-old or 6-week-old dopaminergic grafts. Striatum grafted together with 2-week-old nigra was larger than when grafted adjacent to mature substantia nigra, but not significantly so. Nerve fibre outgrowth into the iris from the nigral transplants did not increase after maturation, but the re-innervated area of the host iris progressively increased around the locus coeruleus grafts. Ingrowth of tyrosine hydroxylase (TH) immunoreactive nerve fibres into the striatal grafts was studied 6 weeks after the second implantation. TH immunohistochemistry revealed innervation of the striatal piece in all cases, except for the group where striatum alone was grafted. With the short survival time for co-grafts of 6 weeks, TH-positive nerve fibres innervated a larger volume, had a patchy appearance and the density was higher in striatum grafted to 2 week-old nigral transplants than that seen in striatal transplants grafted to mature nigral grafts. The patchy pattern of TH-immunoreactive nerve terminals was also seen in striatum co-grafted with 6-week-old or 1-year-old nigral transplants. No difference in striatal innervation volume was detected between those latter two groups. When striatum was implanted adjacent to mature ventral mesencephalon and grown together for 6 months--the longer survival time--the same dense TH-positive innervation as seen in striatum co-grafted with immature nigral tissue at the shorter survival time was found. Additionally, the nigral part of the co-grafts showed increased TH-immunoreactive nerve fibre density. In conclusion, dopaminergic neurites from mature ventral mesencephalic transplants can re-initiate growth if placed in contact with non-innervated striatal tissue. The nigral grafts do not progressively re-innervate the host iris, while locus coeruleus grafts do. The intra-ocular grafting model can be used to study the in vivo effects of trophic factors on mature dopaminergic neurons.

Huntington's disease: animal models and transplantation repair

Recent identification of the gene for Huntington's disease is currently attracting widespread attention. While having importance for predictive testing and the potential of elucidating the underlying disease process, this discovery does not yet provide any advances for therapeutic intervention. Here we review recent advances in the development of improved animal models of Huntington's disease and strategies for its repair. Novel toxins may better mimic the neuropathology, and provide important clues about the underlying metabolic disorder, of the human disease. In addition, recent experiments into the cellular morphology, development and function of striatal cell transplants in both rats and monkeys are now indicating the prospect of viable strategies for structural repair in this disorder.