Intrastriatal grafts derived from fetal striatal primordia. III. Induction of modular patterns of fos-like immunoreactivity by cocaine

Neuronal Replacement as a Tool for Basal Ganglia Circuitry Repair: 40 Years in Perspective

The ability of new neurons to promote repair of brain circuitry depends on their capacity to re-establish afferent and efferent connections with the host. In this review article, we give an overview of past and current efforts to restore damaged connectivity in the adult mammalian brain using implants of fetal neuroblasts or stem cell-derived neuronal precursors, with a focus on strategies aimed to repair damaged basal ganglia circuitry induced by lesions that mimic the pathology seen in humans affected by Parkinson’s or Huntington’s disease. Early work performed in rodents showed that neuroblasts obtained from striatal primordia or fetal ventral mesencephalon can become anatomically and functionally integrated into lesioned striatal and nigral circuitry, establish afferent and efferent connections with the lesioned host, and reverse the lesion-induced behavioral impairments. Recent progress in the generation of striatal and nigral progenitors from pluripotent stem cells have provided compelling evidence that they can survive and mature in the lesioned brain and re-establish afferent and efferent axonal connectivity with a remarkable degree of specificity. The studies of cell-based circuitry repair are now entering a new phase. The introduction of genetic and virus-based techniques for brain connectomics has opened entirely new possibilities for studies of graft-host integration and connectivity, and the access to more refined experimental techniques, such as chemo- and optogenetics, has provided new powerful tools to study the capacity of grafted neurons to impact the function of the host brain. Progress in this field will help to guide the efforts to develop therapeutic strategies for cell-based repair in Huntington’s and Parkinson’s disease and other neurodegenerative conditions involving damage to basal ganglia circuitry.

Fetal striatal transplants reinstate the electrophysiological response of pallidal neurons to systemic apomorphine challenge in rats with excitotoxic striatal lesions

Previous studies with single-unit recording and 2-[14C]deoxyglucose quantitative autoradiography have shown that systemic administration of apomorphine increases the functional activity of pallidal neurons, and that the enhancement in the globus pallidus (GP) activity is abolished by striatal lesions. The present study employing electrophysiological techniques tested whether embryonic striatal tissue implanted in the excitotoxically damaged striatum of rats may affect the lesion-induced alteration in the neuronal response of GP to apomorphine. Systemically administered apomorphine significantly increased spontaneously firing rates of GP cells. The blockade of dopamine receptors with haloperidol reversed the increased rate to baseline levels. Quinolinate-induced striatal lesions attenuated the rate-increasing effect of apomorphine. Embryonic striatal grafts placed in the lesioned striatum restored the response of GP cells to systemic apomorphine. The graft-mediated restoration of the GP neuron response to apomorphine were accompanied by an improvement in the motor asymmetry induced by this drug. Considering previous anatomical data to demonstrate extensive innervation of the GP by embryonic striatal grafts, the present results suggest that the grafts reconstruct the functional striatopallidal pathway which is capable of transmitting apomorphine-induced changes in the neuronal activity.

Fetal tissue transplants in animal models of Huntington's disease: the effects on damaged neuronal circuitry and behavioral deficits

Accumulating evidence indicates that grafts of embryonic neurons achieve the anatomical and functional reconstruction of damaged neuronal circuitry. The restorative capacity of grafted embryonic neural tissue is most illustrated by studies with striatal tissue transplantation in animals with striatal lesions. Striatal neurons implanted into the lesioned striatum receive some of the major striatal afferents such as the nigrostriatal dopaminergic inputs and the gluatmatergic afferents from the neocortex and thalamus. The grafted neurons also send efferents to the primary striatal targets, including the globus pallidus (GP, the rodent homologue of the external segment of the globus pallidus) and the entopeduncular nucleus (EP, the rodent homologue of the internal segment of the globus pallidus). These anatomical connections provide the reversal of the lesion-induced alterations in neuronal activities of primary and secondary striatal targets. Furthermore, intrastriatal striatal grafts improve motor and cognitive deficits seen in animals with striatal lesions. Since the grafts affect motor and cognitive behaviors that are critically dependent on the integrity of neuronal circuits of the basal ganglia, the graft-mediated recovery in these behavioral deficits is most likely attributable to the functional reconstruction of the damaged neuronal circuits. The fact that the extent of the behavioral recovery is positively correlated to the amount of grafted neurons surviving in the striatum encourages this view. Based on the animal studies, embryonic striatal tissue grafting could be a viable strategy to alleviate motor and cognitive disorders seen in patients with Huntington's disease where massive degeneration of striatal neurons occurs.

Heatstroke induces c-fos expression in the rat hypothalamus

We induced heat stress in urethane-anesthetized rats (the animals were exposed to an ambient temperature at 42 degrees C), and monitored their colon temperature, mean arterial pressure and local cerebral blood flow. Rats 0, 20, 40 or 80 min after heat stress were sacrificed for determination of c-fos mRNA and protein expression in the paraventricular nucleus (PVN), supraoptic nucleus (SON) and preoptic nucleus (PON). The heatstroke, which appears as profound decreases in both mean arterial pressure and local cerebral blood flow and increases in colon temperature, is produced 80 min after heat stress. We show the c-fos mRNA and protein is strongly induced in all these nuclei of rat hypothalamus after the onset of heatstroke. We conclude that c-fos expression in the hypothalamus during rat heatstroke is associated with hyperthermia, arterial hypotension and cerebral ischemia.

Embryonic striatal grafts restore neuronal activity of the globus pallidus in a rodent model of Huntington's disease

It has been demonstrated in rats that embryonic striatal grafts placed in the excitotoxically lesioned striatum establish neuronal connections with the host globus pallidus. In order to determine whether the morphologically verified connections between the grafts and host are functional, the present study investigated the effects of embryonic striatal grafts on changes in the neuronal activity of the globus pallidus in rats with quinolinic acid-induced striatal lesions. The activity of pallidal neurons was determined by use of quantitative cytochrome oxidase histochemistry and an electrophysiological technique. Striatal lesions induced an increase in both the cytochrome oxidase activity and the spontaneous firing rate of the globus pallidus ipsilateral to the lesions. Grafts derived from the lateral ganglionic eminence, but not the medial ganglionic eminence, reversed the lesion-induced increase in the cytochrome oxidase activity of the globus pallidus with concomitant reduction of apomorphine-induced rotational asymmetry. The lateral ganglionic eminence grafts also attenuate the increase in the firing rate of pallidal neurons in rats with striatal lesions. The present results provide evidence that striatal lesions lead to the loss of a tonic inhibitory input to the globus pallidus with consequent increase in the activity of pallidal neurons, and that intrastriatal striatal grafts reverse the altered activity of pallidal neurons. The findings strongly suggest that embryonic striatal grafts functionally repair the damaged striatopallidal pathway.

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 positron emission tomography scanner, using ligands to the dopamine D1 and D2 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 D1 and D2 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 D1 and D2 dopamine receptors measured by positron emission tomography, i.e. a more extensive integration of the graft with the host brain.

Co-transplantation of fetal lateral ganglionic eminence and ventral mesencephalon can augment function and development of intrastriatal transplants

Methods to increase the development and sustained function of embryonic mesencephalic dopamine cells after transplantation into dopamine (DA)-depleted striatum are currently under investigation. Elements that are crucial for the maturation and connectivity of neurons during normal development of the brain may also play a role in the development and integration of grafted embryonic tissue. Based on in vitro and in vivo observations of the enhancing effects of striatal tissue on nigral dopaminergic cell development and survival, we demonstrate that inclusion of embryonic striatal cells, specifically from the lateral ganglionic eminence (LGE), produces dopaminergic transplants with augmented functional effects. Rats neonatally DA-depleted and co-transplanted with embryonic nigral and LGE cells developed improved functional outcome when compared with animals receiving only nigral cells, and they required the transplantation of fewer nigral cells to produce a strong behavioral effect. Anatomically, the inclusion of LGE cells produced increased DA cell survival, a higher density of reinnervation into the DA-depleted host striatum, and patches of DA fibers within the co-transplants. There were also an increased number of host striatal cells which induced the immediate-early gene c-fos in co-transplanted animals compared to animals receiving nigral cells alone, indicating a higher degree of host-cell activation. The ability to enhance function, cell survival, reinnervation, and host activation with nigral-striatal co-transplants in the presence of fewer nigral cells supports the hypothesis of a trophic influence of striatal cells on nigral DA cells.

Expression of c-fos, jun D and pp60c-src+ mRNAs in the developing and grafted rat striatum

Expression of the mRNAs of the proto-oncogenes pp60c-src+, c-fos and jun D were studied using in-situ hybridisation histochemistry in the developing striatum and in striatal grafts. The temporal patterns of mRNA expression were monitored in the striatum of the normal developing rat from the 12th day of gestation (E12) to 10 days postnatally, and were compared to the changes in gene expression observed in E13-E14 primordial striatal tissue grafts 7, 15 and 30 days after implantation in the ibotenic acid-lesioned striatum of adult rats. During development, all three proto-oncogenes were most highly expressed just before birth, at E19. Striatal expression of all three proto-oncogenes was markedly reduced after birth and remained at a low level through to adulthood. A different mode of expression was observed in the transplanted striatum which was unique to each particular gene. jun D and pp60c-src+ were expressed for a longer time period in the grafted primordial cells than in normal development, whereas no c-fos expression could be detected in the grafts. These results suggest that transplantation of embryonic neural cells into the host brain may affect the normal developmental regulation of such cells and their expression of some proto-oncogenes.

Intrathalamic striatal grafts survive and affect circling behaviour in adult rats with excitotoxically lesioned striatum

Current models of basal ganglia disorders suggest that choreoathetosis is the end result of reduced GABAergic inhibition of the motor thalamus. Graft-derived release of GABA from intrastriatal striatal grafts has also been reported. In the present work, cell suspension grafts from embryonic day 14-15 rat striatal primordia were implanted close to the ventromedial thalamic nucleus to investigate whether they can develop and survive in this ectopic location, and whether they induce changes in the circling behaviour of the host. The grafts were implanted either in normal rats or in rats whose striatum had been lesioned with ibotenic acid. These grafts were implanted either ipsilateral or contralateral to the lesioned striatum. Additionally, some rats received intrastriatal grafts, and lesioned but non-grafted rats and lesioned rats that had received injections of saline or of cell suspensions from fetal spinal cord in the thalamus were used as control. Four to eight months after transplantation, circling behaviour after amphetamine or apomorphine injection was evaluated. Serial sections were stained with Cresyl Violet and studied immunohistochemically with antibodies against DARPP-32 (dopamine- and adenosine 3',5'-monophosphate-regulated phosphoprotein, as striatal marker), Fos protein, glutamate decarboxylase (67,000 mol. wt), glutamate decarboxylase (65,000 mol. wt) and GABA. Cresyl Violet sections showed that the intrathalamic striatal grafts developed into tissue masses resembling those observed in intrastriatal striatal grafts. DARPP-32 immunohistochemistry revealed that the grafts were composed of DARPP-32 immunoreactive (striatum-like) and DARPP-32-negative patches. The intrathalamic grafts of rats which had received a low dose of apomorphine (0.25 mg/kg) 2 h before perfusion showed clusters of intensely Fos-immunoreactive nuclei throughout the transplant, indicating that these cells had developed dopamine receptors and supersensitivity to dopamine agonists. Double Fos and DARPP-32 immunohistochemistry revealed that the Fos-positive nuclei were located in the striatum-like areas. Finally, the intrathalamic grafts also contained neurons immunoreactive to GABA and glutamate decarboxylase (65,000 and 67,000 mol. wt). Rats that had received intrathalamic grafts contralateral to the lesioned striatum (i.e. contralateral to the lesion-induced turning direction) showed a significant reduction of circling both after amphetamine (78% reduction) or apomorphine (77% reduction) injection. Rats that had received grafts ipsilateral to the lesioned striatum showed a 75% decrease in amphetamine-induced circling, but no significant change in apomorphine-induced circling. No significant drug-induced circling was observed in non-lesioned and grafted rats. Sham grafting (saline) or grafting of weakly GABAergic tissue (fetal spinal cord) had no significant effects on lesion-induced circling behaviour.(ABSTRACT TRUNCATED AT 400 WORDS)

Rationale for intrastriatal grafting of striatal neuroblasts in patients with Huntington's disease

Huntington's disease is a genetic disease, autosomal and dominant, that induces motor disorders, an inexorable deterioration of higher brain functions and psychiatric disturbances. At present, there are no known therapeutics against Huntington's disease. The Network of European CNS Transplantation and Restoration (NECTAR) has begun a program aimed at defining the conditions under which intrastriatal transplantation of fetal striatal cells could be attempted as an experimental treatment for Huntington's disease. This review presents the reasons why our group is considering participating in these trials. The validity of this therapeutic approach is supported by three main series of data: (i) neuropathological, clinical and imaging data indicate that Huntington's disease is, above all, a localized affection of a specific neuronal population ("medium-spiny" neurons) in the striatum; (ii) a large body of experimental results, obtained in rats and non-human primates, demonstrates that transplanted fetal striatal cells are able to integrate the host brain and to substitute for previously lesioned host striatal neurons; (iii) expertise in clinical neural transplantation has now been acquired from the treatment of patients with Parkinson's disease. These different sets of data are presented and discussed in this review. There are a number of problems which do not yet appear to be entirely resolved, nor are they likely to be using the experimental models currently available. These problems are identified and explicitly presented as working hypotheses. (1) Anatomo-functional results obtained in rodents and non-human primates with excitotoxic striatal lesions can serve as a basis for the extrapolation of what can be obtained from patients with Huntington's disease. (2). Huntington's disease can be efficiently fought by substituting degenerated striatal neurons alone. (3) Huntington's disease is due to a genetic defect which either hits the neurons that carry it directly or hits them indirectly only after several decades. Transplanted neurons, because they do not carry the gene or because they are of fetal origin, will not be rapidly affected by the ongoing disease process. Given the current state of knowledge, intracerebral transplantation appears to be the most serious opportunity (if not the only one that has been experimentally validated) for clinical improvement to be obtained in patients with Huntington's disease. The purpose of this review is to open a scientific discussion on its experimental bases before actual clinical trials start.

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.

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-immunohistochemstry 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.

Cortical stimulation induces fos expression in intrastriatal striatal grafts

Innervation of intrastriatal grafts of fetal striatal tissue by host corticostriatal projections has been shown in a number of previous studies in rats. In the work reported here, induction of Fos protein in grafted striatal neurons by electrical stimulation of the host frontoparietal cortex has been used as cell-level marker of corticostriatal postsynaptic responses within the striatal grafts. Unilateral cortical stimulation 30 min before sacrifice led to bilateral widespread and intense Fos induction throughout the normal striatum, although the response was somewhat more intense ipsilaterally and in the dorsolateral rostral striatum. In adult rats whose striatum had been lesioned with ibotenic acid 10-12 days prior to implantation of fetal striatal tissue, 3- and 18-month-old striatal grafts showed Fos immunoreactivity in a considerable number of cells after either bilateral, or ipsilateral (approximately 30-40% of the density of Fos-immunoreactive cells in the normal striatum) or contralateral cortical stimulation. Double-Fos and -DARPP-32 immunohistochemistry revealed that the Fos-immunoreactive nuclei were concentrated in the DARPP-32-positive (i.e. striatum-like) patches, which contained approximately 60% of the density of Fos-positive nuclei in the normal striatum after either ipsilateral or bilateral stimulation. However, Fos-immunoreactive nuclei were unevenly distributed within the DARPP-32-positive compartment of the graft, with some clusters of Fos-immunoreactive nuclei at 2-3 x the density observed in the normal striatum and other areas with Fos-immunoreactive nuclei present at lower density or absent. Fos induction was also observed in 4-week-old grafts, indicating that functional corticostriatal synaptic contacts develop rapidly. Striatal grafts implanted either in non-lesioned host striatum or in long-term (18 months) lesioned striatum, similarly showed Fos-positive nuclei after cortical stimulation, indicating that host corticostriatal fibers are equally capable of establishing functional synaptic contacts under these conditions. These results indicate that host corticostriatal fibres not only form an axonal network within the graft but also induce postsynaptic responses which may contribute to the observed graft-induced amelioration of lesion-derived behavioural deficits.

Comparison between normal developing striatum and developing striatal grafts using drug-induced Fos expression and neuron-specific enolase immunohistochemistry

The cell-level functional maturation of cell suspension grafts from embryonic day 14-15 rat striatal primordia implanted unilaterally into ibotenic acid lesioned striata of adult female rats was studied from two days to 10 weeks post-grafting. The functional and morphological characteristics of the grafts were compared with those of adult grafts (one year after implantation), normal adult striata and postnatal developing striata (up to four weeks after birth). Serial sections were stained with Cresyl Violet and investigated immunohistochemically with antibodies against dopamine- and adenosine 3',5'-monophosphate-regulated phosphoprotein (DARPP-32, as a striatal marker), tyrosine hydroxylase (as a marker of dopaminergic fibres), Fos protein (as a cell-level marker of functional dopaminergic host-graft interactions), and neuron-specific enolase (correlated to differentiation and functional maturation of neuronal cells). Selected sections were double-stained for DARPP-32 and either tyrosine hydroxylase, Fos or neuron-specific enolase. The rats used to study dopamine receptor-activated expression of Fos were killed 2 h after administration of either the dopamine-releasing agent D-amphetamine (5 mg/kg intraperitoneally) or the dopamine-receptor agonist apomorphine (0.25 mg/kg subcutaneously, at which dosage it is active only on supersensitive receptors of denervated neurons). In normally developing rats, amphetamine induced Fos expression in both the striatum and globus pallidus by two weeks after birth; by four weeks, the pattern of amphetamine-induced Fos immunoreactivity was similar to that observed in adults. In the globus pallidus of both two- and three-week-old rats, amphetamine induced greater expression of Fos than in adults. Apomorphine did not induce appreciable Fos activation in either the striatum or the globus pallidus at any stage of development. In striatal grafts, amphetamine induced Fos expression from three weeks after implantation onwards, and by five to 10 weeks post-grafting the pattern of Fos immunoreactivity was similar to that observed in adult grafts. However, apomorphine induced a considerable number of Fos-positive nuclei in striatal grafts at three and four weeks after grafting. Neuron-specific enolase immunoreactivity was moderate in normal adult striatum and very high in the adult globus pallidus, and mainly located in neuronal perikarya and processes. Before two weeks of age, most neuron-specific enolase immunoreactivity was observed in internal capsule fascicles and the striatal afferents. Between two and four weeks after birth, neuron-specific enolase immunoreactivity in striatal and globus pallidus neurons gradually increased, while that in afferent fibres decreased to adult levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Concurrent immediate early gene induction by epileptic seizures in heterotopic cortical grafts and neocortex

Cortical primordia of rat fetuses (gestation day 14) were stereotactically grafted into the rostral striatum of adult recipient rats. After 8 weeks, the transplants had developed into a highly differentiated population of mature neuroectodermal cells. Host rats were then subjected to 15 min of bicuculline-induced epileptic seizures or served as controls. Seizure-elicited immediate early gene (IEG) expression was investigated after various postictal survival times (up to 24 h), using immunocytochemistry with specific antisera against seven IEG encoded proteins (c-FOS, FOS B, c-JUN, JUN B, JUN D, KROX-24, KROX-20). Constitutive IEG expression in intra striatum grafted neocortical neurons was identical to that in the corresponding host neocortex. In particular, abundant KROX-24 and lack of c-JUN expression implies the establishment of synaptic contacts within the graft or with the host circuitry. Postictal expression kinetics of individual IEG encoded proteins within the transplants were strikingly similar to those seen in the neocortex in situ. c-FOS and KROX-24 were most rapidly induced, followed by c-JUN and JUN B, and a more delayed induction of FOS B, JUN D and KROX-20. Apart from a slightly prolonged c-FOS expression in grafts, individual transcription factors remained elevated for different time periods and showed a concurrent decline in transplants and in neocortex in situ. In conclusion, IEG induction in grafts closely paralleled that in the host neocortex but differed from the adjacent striatum which exhibited no c-JUN induction at any time point investigated. These results indicate that following an appropriate differentiation period, heterotopically grafted embryonic cortical neurons respond to extracellular stimuli with changes of gene expression that closely resemble the normal host cortex. This suggests development of a similar molecular phenotype, including proper acquisition and intracellular processing of information.

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.

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.

Characterization of GABA release from intrastriatal striatal transplants: dependence on host-derived afferents

Extracellular levels of GABA, derived from cell suspension transplants of embryonic day 14-15 rat striatal primordia implanted into the previously excitotoxically lesioned striatum, were measured using intracerebral microdialysis in halothane-anaesthetized rats. GABA overflow was monitored using loop type dialysis probes implanted into grafted, age-matched ibotenic acid-lesioned and intact striata, under baseline conditions and after different pharmacological manipulations. Basal and evoked GABA release, which was reduced by 58 and 96%, respectively, in the excitotoxin-lesioned striatum, was restored by the striatal grafts to levels close to or above those observed in normal striata. The graft-derived release of GABA was most likely of neuronal origin, since the K(+)-evoked (100 mM) GABA overflow was reduced by almost 80% when Ca++ was replaced by 20 mM Mg++ in the perfusion medium, and blockade of GABA uptake by nipecotic acid (0.5 mM), induced a greater than six-fold increase in GABA overflow. However, perfusion of the graft with 1 microM tetrodotoxin in combination with K+ (100 mM) resulted in little if any reduction in the K(+)-evoked overflow. Histological analysis demonstrated a dense tyrosine hydroxylase-positive fibre network in the grafts, which was removed after a 6-hydroxydopamine lesion of the ipsilateral nigrostriatal pathway. The dopamine denervating lesion resulted in an increased K(+)-evoked GABA overflow both in the intact (+76%) and the grafted striata (+181%), suggesting that the tonic dopaminergic inhibitory control of GABA release, seen in the intact striatum, is also present in the grafted striata. The glutamate analogue, kainic acid (1 mM added to the perfusion fluid), evoked a 60-74% increase in GABA overflow both in intact striata (with or without dopaminergic denervation) and in the striatal grafts. This effect seemed to be dependent on an intact corticostriatal projection, since knife-cut transections of the frontal cortex at the level of the forceps minor, abolished the response in both the intact and grafted striata. These results demonstrate that grafts of fetal striatal tissue implanted into the excitotoxically lesioned striatum restore striatal GABA overflow in a neuron-dependent manner, close to or above that seen in the normal intact striatum. Furthermore, the graft-derived GABA release appears to be under normal regulatory control from the host dopaminergic and glutamatergic systems. Since the GABAergic striatal output system is critical for the expression of striatum-related behaviours, it is proposed that the graft-induced behavioural recovery in the striatal lesion model, at least in part, may depend on the restoration of striatal GABAergic neurotransmission.

Differential regulation of neuropeptide mRNA expression in intrastriatal striatal transplants by host dopaminergic afferents

The effects of dopamine-specific manipulations on neuropeptide gene expression in intrastriatal grafts of fetal striatal tissue were studied by quantitative in situ hybridization histochemistry, using 35S-labeled oligonucleotide probes. Messenger RNA transcripts for the striatal neuropeptides preproenkephalin (PPE) and preprotachykinin (PPT) were detected in neurons forming discrete patches in the striatal grafts. The relative abundance of PPE and PPT mRNA-expressing neurons within the graft patches (51-54%) was similar to that found in normal caudate-putamen. In specimens with intact dopamine afferents the expression of PPE mRNA in grafted neurons was similar to that found in normal caudate putamen, whereas the hybridization signal for PPT mRNA was 27% higher in the graft neurons than in the normal caudate-putamen. Removal of host dopaminergic afferents by 6-hydroxydopamine lesions of the ipsilateral mesostriatal dopamine pathway increased the hybridization signal for PPE mRNA both in the grafts (+84%) and in the spared ipsilateral host caudate-putamen (+125%), whereas the PPT signal was reduced by 53% in the grafts and by 51% in the remaining host caudate-putamen. Similarly, chronic treatment of grafted animals with the dopamine receptor antagonist haloperidol (2 mg/kg per day for 10 days) produced a 146% increase in the PPE signal in the grafts and a 175% increase in the intact contralateral caudate-putamen, whereas the signal for PPT mRNA was again decreased by 52% and 51% in the grafts and host caudate-putamen, respectively. These results show that the host nigrostriatal dopamine pathway differentially regulates enkephalin and substance P gene expression within striatal grafts and thereby exerts a tonic functional influence over grafted striatal neurons.

Mapping of the motor pathways in rats: c-fos induction by intracortical microstimulation of the motor cortex correlated with efferent connectivity of the site of cortical stimulation

The general goal of the present study was to investigate structural components of a neural system anatomically as well as functionally. The rat motor system, which is reasonably well understood, was selected and a new procedure was developed to combine a functional marker with axonal tracing methods (in the same animal). This was achieved by mapping c-fos induction immunocytochemically as a result of intracortical microstimulation in the distal forelimb area of the motor cortex. The anterograde tracers Phaseolus vulgaris-leucoagglutinin or biocytin were deposited at the site of intracortical microstimulation, the former three weeks and the latter two to three days before stimulation. Neuronal nuclei, labeled for the expressed c-fos protein, were present and mapped in the following structures: motor cortex; basal ganglia (caudate-putamen, globus pallidus); thalamus (reticular, ventromedial and posterior nuclei); subthalamic nucleus; substantia nigra; tectum; red nucleus; pontine nuclei; inferior olive; external cuneate nucleus; cerebellar cortex; deep cerebellar nuclei. Labeling was often bilateral but generally more substantial ipsilaterally, except in the cerebellum where it was mainly contralateral. Axonal labeling, including terminal branches and boutons, was also found in most of the above structures with the exception of the globus pallidus, deep cerebellar nuclei, cerebellar cortex and external cuneate nucleus. These expected exceptions demonstrate that activity changes in these latter structures, as revealed by c-fos labeled neurons, were induced over more than one synapse. This combined procedure might, therefore, be useful in deciding whether two structures in a given system are linked directly (monosynaptically) or indirectly (polysynaptically) to each other. In contrast to the 2-deoxyglucose technique, functional mapping by means of c-fos induction provides cellular resolution, making it possible to establish fine details of axonal contacts with target neurons: boutons in close apposition to c-fos labeled neurons were clearly observed here, for instance in the cerebral cortex, caudate-putamen, thalamus, subthalamic nucleus and pontine nuclei. Surprisingly, the ventrolateral and ventrobasalis nuclei of the thalamus contained numerous and dense axon terminals labeled with Phaseolus vulgaris-leucoagglutinin or biocytin, but the contacted neurons in the ventrolateral and ventrobasalis nuclei were not marked with c-fos. However, with respect to directly connected structures, there was, in general, a good correlation between structures with axonal labeling and those with c-fos labeled neurons.

Fos expression in intrastriatal striatal grafts: regulation by host dopaminergic afferents

Previous studies have shown that transplants of fetal striatum, implanted into the ibotenic acid-lesioned striatum of adult rats, become innervated from the host nigrostriatal dopamine (DA) pathway. In the present study we have used DA-receptor-mediated expression of the Fos protein (i.e. the product of the immediate-early c-fos gene) as a cellular marker for functional dopaminergic host-graft interactions in the striatal grafts. Amphetamine (5 mg/kg; 2 h) induced Fos-like immunoreactivity in clusters of cells located mainly within the DARPP-32-positive areas within the transplants, i.e. within the striatum-like graft compartment which is preferentially innervated by the host DA afferents. As in the normal striatum, this effect was largely, although not completely, abolished by a 6-hydroxydopamine lesion of the ipsilateral nigrostriatal DA pathway. Apomorphine (0.25 mg/kg; 2 h) had no detectable effect in grafts with an intact host DA system. Two to 3 weeks after a 6-OHDA lesion of the host DA pathway (i.e. a time sufficient for DA receptor supersensitivity to develop), apomorphine-induced extensive Fos-activation selectively within the DARPP-32-positive areas of the graft. The magnitude of the response was similar to that seen in the DA-denervated host striatum. Dual Fos/DARPP-32 immunostaining revealed that the activated graft neurons were, at least in part, DARPP-32-positive. In intrastriatal grafts of fetal neocortical tissue, which were studied for comparison, the amphetamine- and apomorphine-induced effects on Fos expression were much smaller and similar to that seen in the DARPP-32-negative, non-striatal compartment within the striatal grafts.(ABSTRACT TRUNCATED AT 250 WORDS)