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Notes: Summary The ventral mesencephalon, containing the developing dopaminergic neurons of the substantia nigra-ventral tegmental region, was obtained from aborted human fetuses of 9–19 weeks of gestation. The tissue was grafted into the striatum of rats previously subjected to a 6-hydroxydopamine lesion of the mesostriatal dopamine pathway. The graft recipients were immunosuppressed by daily injections of Cyclosporin A. Amphetamine-induced motor asymmetry was reduced, and finally totally reversed, only in rats receiving grafts from the 9-week old fetal donor. The fluorescence microscopic analysis revealed large numbers of surviving dopamine neurons, and extensive fiber outgrowth into the host striatum, in these rats. By contrast, rats receiving grafts from 11–19 week old donors had at most only few surviving dopamine neurons. These results indicate that human fetal mesencephalic tissue may be an efficient source of dopamine neurons for functional intracerebral grafting in patients with Parkinson's disease.

Notes: Summary We have used a rat model of Parkinson's disease (PD) to address issues of importance for a future clinical application of dopamine (DA) neuron grafting in patients with PD. Human mesencephalic DA neurons, obtained from 6.5–8 week old fetuses, were found to survive intracerebral cell suspension xenografting to the striatum of rats immunosup-pressed with Cyclosporin A. The grafts produced an extensive new DA-containing terminal network in the previously denervated caudate-putamen, and they normalized amphetamine-induced, apomorphine-induced and spontaneous motor asymmetry in rats with unilateral lesions of the mesostriatal DA pathway. Grafts from an 11.5-week old donor exhibited a lower survival rate and smaller functional effects. As assessed with the intracerebral dialysis technique the grafted DA neurons were found to restore spontaneous DA release in the reinnervated host striatum to normal levels. The neurons responded with large increases in extracellular striatal DA levels after the intrastriatal administration of the DA-releasing agent d-amphetamine and the DA-reuptake blocker nomifensine, although not to the same extent as seen in striata with an intact mesostriatal DA system. DA fiber outgrowth from the grafts was dependent on the localization of the graft tissue. Thus, grafts located within the striatum gave rise to an extensive axonal network throughout the whole host striatum, whereas grafted DA neurons localized in the neocortex had their outgrowing fibers confined within the grafts themselves. In contrast to the good graft survival and behavioural effects obtained in immunosuppressed rats, there was no survival, or behavioural effects, of human DA neurons implanted in rats that did not receive immunosuppression. In addition, we found that all the graft recipients were immunized, having formed antibodies against antigens present on human T-cells. This supports the notion that the human neurons grafted to the non-immunosuppressed rats underwent immunological rejection. Based on an estimation of the survival rate and extent of fiber outgrowth from the grafted human fetal DA neurons, we suggest that DA neurons that can be obtained from one fetus may be sufficient to restore significant DA neurotransmission unilaterally, in one putamen, in an immunosuppressed PD patient.

Notes: Summary The afferent and efferent connections of grafts of fetal caudate-putamen, implanted into the ibotenic acid (IA)-lesioned striatum of adult rats, have been studied with wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP) as a combined retrograde and anterograde tracer, and with aldehyde fluorescence histochemistry for the visualisation of dopamine-containing nigrostriatal afferents from the host. The WGA-HRP was deposited in crystalline form (within a capillary tip) either into the depth of the graft tissue, or into the IA lesioned host striatum as a control. Labelling was only evaluated in specimens where the WGA-HRP deposit was entirely confined within the graft. Retrogradely labelled neurons were most consistently found in the ipsilateral host substantia nigra and the spared portions of the host CP, and in one case also in the midline and intralaminar thalamic nuclei normally projecting to the striatum. Some neurons, although weakly labelled, occurred in the deep layers of the frontal cortex in all grafted rats. Signs of anterograde WGA-HRP labelling in the host were found in one of the five animals in the ipsilateral globus pallidus and substantia nigra, pars reticulata. Fluorescence histochemistry revealed extensive ingrowth of dopamine-containing fibres from the host striatum into the grafted striatal tissue. The ingrowing fibres formed distinct and partly interconnected patches, most prominently in the peripheral regions of the grafts. The results provide evidence that intrastriatal grafts of fetal striatal tissue receive extensive dopaminergic afferents from the host substantia nigra, and that they may be capable of establishing connections also with thalamus, neocortex and globus pallidus of the host, as well as with the spared portions of the host caudate-putamen. The afferent connections from the thalamus and neocortex were notably more variable and sparse. However, since the control WGA-HRP deposits (into the lesioned host striatum) labelled the cortical and thalamic afferent neurons only poorly, it appears that the cortico-striatal and thalamo-striatal afferents (in contrast to the nigro-striatal ones) had undergone substantial degenerative changes (atrophy and/or cell death) in the long-term (6–11 months) IA-lesioned rats. The sparse thalamic and cortical afferent connections to the grafts may thus reflect an inability of the grafted striatal tissue to prevent the course of degenerative changes in these striatal input systems.

Notes: Summary Fetal mesencephalic mouse tissue, rich in dopamine neurons, was xenografted as a dissociated cell suspension into the striatum of rats with unilateral 6-hydroxydopamine induced lesions of the mesostriatal pathway. The rats were either assigned to a 10-day, 21-day or 42-day Cyclosporin A (CyA) immunosuppression scheme, or given no immunosuppression. The functional effects of the grafts were followed over 6 months by monitoring changes in the recipient rats' amphetamine-induced turning behaviour. Without immunosuppression no grafts were functional at the end of the experiment. In the 10-, 21-and 42-day CyA treatment groups there was a significant reduction of rotational asymmetry at some timepoint following grafting in 26 of the 33 rats. However, by 6 months only 8 grafts remained functional suggesting that in several rats an immunological rejection took place following the termination of immunosuppression. This was supported by catecholamine histofluorescence analysis which revealed evidence of surviving grafts only in the few rats which had shown sustained functional graft effects at 6 months after grafting. In animals in which the grafts had undergone rejection, there was scarlike tissue in the striatum which appeared more extensive in rats that had lost their grafts after several weeks compared to rats in which the grafts were rejected at an early time-point. In a subgroup of the grafted animals the humoral antibody response against major transplantation antigens present on the grafted cells was investigated. All the studied rats were found to be immunized against the grafted mouse tissue following the intrastriatal implantation. This occurred irrespective of prior immunosuppressive treatment. In a parallel group of rats, the leakage of the blood-brain barrier was studied following intrastriatal implantation of a syngeneic fetal neural cell suspension. Evans Blue was infused into rats 3–12 days following transplantation surgery. At the early time-points there was a marked barrier leakage at the implantation site. This subsided with time such that there was minor leakage after 7–8 days and no leakage after 12 days. In summary, the results indicate the CyA is effective in promoting survival of intracerebral xenografts of fetal neural tissue, but that cessation of immunosuppressive treatment in most cases results in rejection of the grafted tissue. Temporary CyA treatment, even exceeding the time it takes for the blood-brain barrier to reform after transplantation surgery, is thus not sufficient to reliably support long term survival of xenografted dopamine neurons.

Notes: Summary In vivo voltammetry was used to monitor dopamine (DA) neuron activity during the course of reinnervation of the initially denervated caudateputamen by grafted mesencephalic neurons. Fetal DA neurons were implanted as a cell suspension into the depth of the caudate-putamen in adult 6-hydroxydopamine-lesioned recipient rats. Recordings were performed over a period of 2.5–4 months, starting within a week after transplantation, using chronically implanted surface-treated multifiber carbon electrodes. The voltammetric method used in this study has generated considerable discussion centred on the ability of the multifiber electrodes to measure DA alone in vivo, but the results of previous studies have led to the conclusion that changes in the voltammetric signal most probably reflect dopaminergic terminal activity. It seems therefore possible to follow the time-course of changes in the voltammetric signal amplitude during the process of dopaminergic reinnervation of the host striatum from the grafts. A 6-hydroxydopamine lesion of the mesostriatal dopamine pathway caused a substantial (〉 80%) reduction of the voltammetric signal within 8–10 days, and the low residual signal remained essentially unchanged for time periods up to at least 5 months in the non-grafted control rats. In 7 of 11 rats with DA-rich grafts there was a recovery of the signal amplitude to levels within, or close to, the range recorded from the striatum of normal intact rats. The increase was observed 6–8 weeks after grafting in the rats which had received the largest transplants, and at about 13–14 weeks after grafting in the rats which had received the smallest ones. The recovery of the signal amplitude, from baseline to maximal response, was quite rapid and typically developed between two or three recording sessions, i.e. over a period of one to two weeks. In contrast to the intact striatum, the recovered signal in the graft-reinnervated striata showed a progressive decline within one hour of sampling time at high sampling frequencies (1 per min to 1 per 3 min). Grafted striata also showed a larger response to systemically administered amphetamine than did intact striata. Since the changes in the voltammetric signal recorded with the multifiber electrode mainly reflect dopaminergic terminal activity, the results provide evidence that the intrastriatal DA-rich grafts are spontaneously active, and that the grafted DA neurons can restore DA neuro-transmission in the reinnervated part of the host caudate-putamen to levels which are within the normal range. From the time-course of changes in the voltammetric signal it can be estimated that the outgrowing DA fibers, after an initial maturation period, expand from the graft into the host striatum at a maximum rate of about 0.1 mm per week, and that the advancing front of graft-derived fibers may be capable of saturating the area around the electrode tip with new terminals within a time period of about 1–2 weeks. The characteristics of the signal seem compatible with the view that the activity of the individual grafted DA neurons is greater than that of the mesostriatal DA neurons in situ.

Notes: Summary The survival of grafts of dissociated allogeneic fetal neural dopamine (DA) rich tissue in the striatum has been studied after transplantation between inbred strains of mice differing at defined immunogenetical loci between donor and recipient. Six to 7 weeks and 15 weeks after grafting, surviving grafted DA neurons were found in the brains of all the recipients, albeit with a large variation in numbers, located either within the striatum or within the adjacent lateral ventricle. The mean number of surviving DA neurons did not differ between the syngeneic controls and the histoincompatible donor-host combinations, and there was no difference in survival between grafts that differed at single or multiple major histocompatibility complex (MHC) loci, and those that differed at multiple non-MHC loci. The amount of inflammatory cells in the graft area did not differ between the groups, and none of the animals showed massive infiltration of inflammatory cells. The in situ immunogenicity of the grafted neural tissue after intracerebral implantation was monitored by means of Simonsen's alloimmunization test, at 6–7 weeks after transplantation, which provides a sensitive measure primarily of the cellular immunological response. Most, but not all, graft recipients showed immunization with a Spleen Index (S.I.) close to that seen in recipients of an orthotopical skin graft of the same histoincompatibility combination. In contrast to the prolonged survival of the intracerebral neural transplants, none of the skin grafts survived longer than 3 weeks, thus demonstrating the immunologically privileged status of the brain. We conclude that intracerebrally grafted allogeneic neural tissue is capable of provoking a cellular immune response. Despite host immunization, however, the dissociated fetal neural allografts survived for at least 15 weeks without any overt signs of rejection, regardless of the donor-host combination used.

Notes: Summary The purpose of the present study was to investigate the amplifying function of the nucleus accumbens septi region (NAS) in 6-hydroxydopamine (6-OHDA)-induced rotational behaviour by implanting fetal dopamine (DA)-rich mesencephalic cell suspensions unilaterally in the NAS of rats previously subjected to combined mesostriatal (MS) and NAS 6-OHDA lesions. First, all the rats received a unilateral 6-OHDA lesion of the ascending MS DA pathway, which produced an amphetamine-induced rotational asymmetry towards the lesioned side. In a second step, the rats received a local bilateral 6-OHDA lesion of the NAS which, as previously shown, caused a significant attenuation of the amphetamine-induced locomotor (1.5 mg/kg) and rotational (5 mg/kg) behaviour. Finally, some of these MS + NAS lesioned rats received a unilateral mesencephalic DA graft into the NAS ipsilateral to the original MS lesion. The unilateral DA-rich grafts in the NAS significantly elevated the amphetamine-induced locomotion and ipsilateral circling (opposite to the direction of rotation produced when a graft is placed in the ipsilateral caudate-putamen), suggesting that the NAS plays only an amplifier role in locomotor behaviour and not a directional role. In addition, these grafts significantly attenuated the supersensitive locomotor response observed in lesioned rats when given apomorphine (0.05 mg/kg). The findings emphasize the amplifying role of the NAS in locomotion and circling behaviour and they extend previous findings demonstrating the functional heterogeneity of the striatal complex as well as the regional specificity of the graft-derived functional effects. Moreover, the results argue against the notion that DA grafts can function through a diffusion of transmitter over large distances since, despite the large size of the grafts, the functional graft effects were well localized to the reinnervated NAS and ventromedial striatal regions. We conclude, therefore, that graft-induced amelioration of postural and locomotor deficits are affected through different parts of the striatal complex, and that multiple graft placements are required to produce more complete recovery of motoric behaviour in the DA-depleted brain.

Notes: Summary Human fetal mesencephalic dopamine (DA) neurons, obtained from 6.5–9 week old aborted fetuses, were grafted to the striatum of immunosuppressed rats with 6-hydroxydopamine lesions of the ascending mesostriatal DA pathway. The effects on amphetamine-induced motor asymmetry were studied at various timepoints after grafting. At eight weeks, functional graft effects were not evident but after 11 weeks small effects on motor asymmetry could be monitored and rats tested 19–21 weeks after grafting exhibited full reversal of the lesion-induced rotational behaviour. Four rats were sacrificed at different timepoints between 8 and 20 weeks and the grafted DA neurons were studied in tyrosine hydroxylase (TH) immunocytochemically stained sections at the light and electronmicroscopic level. The grafts contained a total of 500–700 TH-positive neurons in each rat. In one rat sacrificed 8 weeks after grafting the grafted neurons were TH-positive but exhibited virtually no fiber outgrowth. In another rat, sacrificed after 11 weeks, a sparse TH-positive fiber plexus was seen to extend into the adjacent host neostriatum. Two rats sacrificed after 20 weeks both contained TH-positive neurons that gave rise to a rich fiber network throughout the entire host neostriatum, and this fiber network was also seen to extend into the globus pallidus and nucleus accumbens. Very coarse TH-positive processes, identified as dendrites in the electron microscope, projected up to 1.5–2.0 mm from the graft into the host striatum. Ultrastructural analysis revealed that the grafted neurons had formed no TH-positive synaptic contacts with host striatal neurons after 8 weeks, and at 11 weeks some few TH-positive synapses were identified. Twenty weeks after transplantation, abundant TH-positive synaptic contacts with host neurons were seen throughout the neostriatum, and such contacts were identified in the globus pallidus as well. Thus, the present study provides tentative evidence for a time-link between the development of synaptic contacts and the appearance of functional graft effects. Similar to the normal mesostriatal DA pathway, ingrowing TH-positive axons formed symmetric synapses and were mainly seen to contact dendritic shafts and spines. However, in comparison to the normal rat striatum there was a higher incidence of TH-immunoreactive boutons forming synapses onto neuronal perikarya. The TH-positive dendrites that extended into the host striatum were seen to receive non-TH-immunoreactive synaptic contacts, presumably arising from the host neurons. These results suggest that human fetal DA neurons are able to develop a reciprocal synaptic connectivity with the host rat when grafted to the adult brain. Grafting of human fetal DA neurons may therefore be expected to provide a means of restoring regulated synaptic DA release in patients with Parkinson's disease.

Notes: Summary A recently introduced quantitative radioautographic technique was used to characterize the striatal dopaminergic deficit in weaver mutant mice and to evaluate the extent of DA reinnervation resulting from cell suspension grafts of fetal ventral mesencephalic tissue. Brain slices from normal mice and unilaterally grafted weaver mice were incubated in [3H]DA, in the presence of desipramine and pargyline, 3–5 months after graft surgery. Semi-thin sections from the fixed and resin-embedded slices were subsequently exposed on tritium sensitive film and afterwards dipped in nuclear emulsion for light microscope radioautography. Alternate slices were embedded in Epon for post-embedding tyrosine hydroxylase (TH) immunocytochemistry. The grain density of the film radioautographs matched well the distribution of TH positive fibers. Both methods revealed an almost complete absence of DA axons in the dorsomedial quadrant of the weaver neostriatum and an increasing density of DA innervation towards the ventrolateral areas. In the light microscope radioautographs, only the ventral striatum (i.e. nucleus accumbens and olfactory tubercle) and a narrow ventral and periventricular zone of the caudate-putamen were covered by silver grain clusters typical of DA varicosity labeling. Such labeled varicosities were nevertheless found in reduced numbers in the lateral portion of both nucleus accumbens and the olfactory tubercle. The remaining neostriatum was overlaid by diffuse silver grains, suggesting a deficient DA uptake and storage mechanism in the residual DA fibers in this region. Immunocytochemistry using antibodies specific for DA or TH provided further evidence that the residual DA innervation in the weaver neostriatum was biochemically defective. Weaver mice with grafts of ventral mesencephalic tissue in the right neostriatum showed an amphetamine-induced rotational bias to the contralateral side, which was not seen in the sham-operated animals. In contrast to the intrinsic weaver neostriatal DA innervation, DA fibers of graft origin exhibited the normal, clustered type of varicosity labeling. The computerized image analysis of silver grain density in film radioautographs was calibrated by counting these labeled varicosities in selected areas of light microscope radioautographs from the same sections. Results showed a mean DA reinnervation of neostriatal tissue surrounding the graft of about 20%, in some cases up to 80%, of the density seen in wild type mice, with a gradual decrease with distance up to 1–1.4 mm from the graft. The ventral parts of the neostriatum, which contained higher numbers of residual intrinsic DA fibers, were much more sparsely reinnervated than the dorsal and dorsomedial areas. These data show that a quantitatively significant DA reinnervation of the weaver neostriatum can be provided by fetal mesencephalic cell suspension grafts and that these DA fibers become functional, at least with respect to their DA uptake and storage mechanisms, in a neostriatal environment where intrinsic weaver DA axons are strongly deficient. However, observations in long-term weaver mice (9 months after transplantation) suggested that the graft-derived DA fiber outgrowth was reduced with time in the affected striatum, in spite of good survival of the grafted neurones.

Notes: Summary Intrahippocampal cell suspension grafts, prepared from the locus coeruleus region of rat fetuses, have previously been shown to retard seizure development in rats made hypersensitive to hippocampal kindling by a lesion of the forebrain noradrenergic system. The objective of the present study was to provide evidence that the seizure-suppressant effect elicited by the grafts is mediated via noradrenergic mechanisms. Two groups of rats received 6-hydroxydopamine in the lateral ventricle and then bilateral intrahippocampal locus coeruleus grafts. After 3 months, the grafted animals and a group of normal rats were subjected to hippocampal kindling. One group of grafted animals and the normal rats were injected intraperitoneally with the alpha-2 adrenergic receptor blocker idazoxan before each kindling stimulation. The other grafted rats received vehicle injections. The development of seizures was significantly faster in the grafted and normal rats that had been given idazoxan than in the grafted rats that had not been subjected to alpha-2 receptor blockade. Our data suggest that the seizure-suppressant action exerted by grafts of fetal locus coeruleus in hippocampal kindling is mediated via noradrenergic mechanisms, most likely via activation of postsynaptic alpha-2 adrenoreceptors.