Intrastriatal Dopamine-rich Implants Reverse the Increase of Dopamine D2 Receptor mRNA Levels Caused by Lesion of the Nigrostriatal Pathway: A Quantitative In Situ Hybridization Study

Antidepressant-Like Properties of Intrastriatal Botulinum Neurotoxin-A Injection in a Unilateral 6-OHDA Rat Model of Parkinson's Disease

Parkinson’s patients often suffer from depression and anxiety, for which there are no optimal treatments. Hemiparkinsonian (hemi-PD) rats were used to test whether intrastriatal Botulinum neurotoxin-A (BoNT-A) application could also have antidepressant-like properties in addition to the known improvement of motor performance. To quantify depression- and anxiety-like behavior, the forced swim test, tail suspension test, open field test, and elevated plus maze test were applied to hemi-PD rats injected with BoNT-A or vehicle. Furthermore, we correlated the results in the forced swim test, open field test, and elevated plus maze test with the rotational behavior induced by apomorphine and amphetamine. Hemi-PD rats did not show significant anxiety-like behavior as compared with Sham 6-OHDA- + Sham BoNT-A-injected as well as with non-injected rats. However, hemi-PD rats demonstrated increased depression-like behaviors compared with Sham- or non-injected rats; this was seen by increased struggling frequency and increased immobility frequency. Hemi-PD rats intrastriatally injected with BoNT-A exhibited reduced depression-like behavior compared with the respective vehicle-receiving hemi-PD animals. The significant effects of intrastriatally applied BoNT-A seen in the forced swim test are reminiscent of those found after various antidepressant drug therapies. Our data correspond with the efficacy of BoNT-A treatment of glabellar frown lines in treating patients with major depression and suggest that also intrastriatal injected BoNT-A may have some antidepressant-like effect on hemi-PD.

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.

Dopamine, Noradrenaline and Serotonin Receptor Densities in the Striatum of Hemiparkinsonian Rats following Botulinum Neurotoxin-A Injection

Parkinson's disease (PD) is characterized by a degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc) that causes a dopamine (DA) deficit in the caudate-putamen (CPu) accompanied by compensatory changes in other neurotransmitter systems. These changes result in severe motor and non-motor symptoms. To disclose the role of various receptor binding sites for DA, noradrenaline, and serotonin in the hemiparkinsonian (hemi-PD) rat model induced by unilateral 6-hydroxydopamine (6-OHDA) injection, the densities of D₁, D₂/D₃, α₁, α₂, and 5HT_2A receptors were longitudinally visualized and measured in the CPu of hemi-PD rats by quantitative in vitro receptor autoradiography. We found a moderate increase in D₁ receptor density 3 weeks post lesion that decreased during longer survival times, a significant increase of D₂/D₃ receptor density, and 50% reduction in 5HT_2A receptor density. α₁ receptor density remained unaltered in hemi-PD and α₂ receptors demonstrated a slight right-left difference increasing with post lesion survival. In a second step, the possible role of receptors on the known reduction of apomorphine-induced rotations in hemi-PD rats by intrastriatally injected Botulinum neurotoxin-A (BoNT-A) was analyzed by measuring the receptor densities after BoNT-A injection. The application of this neurotoxin reduced D₂/D₃ receptor density, whereas the other receptors mainly remained unaltered. Our results provide novel data for an understanding of the postlesional plasticity of dopaminergic, noradrenergic and serotonergic receptors in the hemi-PD rat model. The results further suggest a therapeutic effect of BoNT-A on the impaired motor behavior of hemi-PD rats by reducing the interhemispheric imbalance in D₂/D₃ receptor density.

Changes in Dopamine Signalling Do Not Underlie Aberrant Hippocampal Plasticity in a Mouse Model of Huntington's Disease

Altered dopamine receptor labelling has been demonstrated in presymptomatic and symptomatic Huntington's disease (HD) gene carriers, indicating that alterations in dopaminergic signalling are an early event in HD. We have previously described early alterations in synaptic transmission and plasticity in both the cortex and hippocampus of the R6/1 mouse model of Huntington's disease. Deficits in cortical synaptic plasticity were associated with altered dopaminergic signalling and could be reversed by D1- or D2-like dopamine receptor activation. In light of these findings we here investigated whether defects in dopamine signalling could also contribute to the marked alteration in hippocampal synaptic function. To this end we performed dopamine receptor labelling and pharmacology in the R6/1 hippocampus and report a marked, age-dependent elevation of hippocampal D1 and D2 receptor labelling in R6/1 hippocampal subfields. Yet, pharmacological inhibition or activation of D1- or D2-like receptors did not modify the aberrant synaptic plasticity observed in R6/1 mice. These findings demonstrate that global perturbations to dopamine receptor expression do occur in HD transgenic mice, similarly in HD gene carriers and patients. However, the direction of change and the lack of effect of dopaminergic pharmacological agents on synaptic function demonstrate that the perturbations are heterogeneous and region-specific, a finding that may explain the mixed results of dopamine therapy in HD.

Understanding graft-induced dyskinesia

The transplantation of dopaminergic cells for the treatment of symptoms of Parkinson’s disease has several hurdles to overcome before it can be considered a successful therapeutic approach. One issue is the development of abnormal involuntary movements in the absence of L-3,4-dihydroxyphenylalanine following the transplantation of fetal ventral mesencephalon identified in three different clinical trials. Hypotheses as to the cause of these movements include: the composition of the graft, size of the graft, L-3,4-dihydroxyphenylalanine exposure and L-3,4-dihydroxyphenylalanine-induced dyskinesia prior to transplantation and inflammatory responses in and around the graft. We evaluate the clinical evidence supporting these hypotheses and the preclinical models upon which experiments are being based to resolve them.

Priming for L-DOPA-induced abnormal involuntary movements increases the severity of amphetamine-induced dyskinesia in grafted rats

In some patients, graft-induced dyskinesia develops following intrastriatal transplantation of embryonic neural tissue for the treatment of Parkinson's disease. The mechanisms underlying these involuntary movements need to be clarified before this approach to clinical cell therapy can be developed further. We previously found that rats with 6-OHDA lesions, primed with L-DOPA treatment and that have subsequently undergone intrastriatal graft surgery exhibit involuntary movements when subjected to amphetamine. This model of amphetamine-induced AIMs reflects a pattern of post-graft behaviours that in the absence of robust spontaneous GID in the rat is the closest approximation that we currently have available. We now show that they are associated with the chronic administration of L-DOPA prior to the transplantation surgery. We also demonstrate that neither changes in c-fos nor FosB/DeltaFosB expression in the lateral striatum are associated with the expression of these behaviours. Taken together, these data reveal that the severity of abnormal movements elicited by amphetamine in grafted animals may relate to previous L-DOPA exposure and dyskinesia development, but they develop through mechanisms that are independent of FosB/DeltaFosB upregulation.

Positron emission tomography imaging demonstrates correlation between behavioral recovery and correction of dopamine neurotransmission after gene therapy

In vivo gene transfer using viral vectors is an emerging therapy for neurodegenerative diseases with a clinical impact recently demonstrated in Parkinson's disease patients. Recombinant adeno-associated viral (rAAV) vectors, in particular, provide an excellent tool for long-term expression of therapeutic genes in the brain. Here we used the [(11)C]raclopride [(S)-(-)-3,5-dichloro-N-((1-ethyl-2-pyrrolidinyl)methyl)-2-hydroxy-6-methoxybenzamide] micro-positron emission tomography (PET) technique to demonstrate that delivery of the tyrosine hydroxylase (TH) and GTP cyclohydrolase 1 (GCH1) enzymes using an rAAV5 vector normalizes the increased [(11)C]raclopride binding in hemiparkinsonian rats. Importantly, we show in vivo by microPET imaging and postmortem by classical binding assays performed in the very same animals that the changes in [(11)C]raclopride after viral vector-based enzyme replacement therapy is attributable to a decrease in the affinity of the tracer binding to the D(2) receptors, providing evidence for reconstitution of a functional pool of endogenous dopamine in the striatum. Moreover, the extent of the normalization in this non-invasive imaging measure was highly correlated with the functional recovery in motor behavior. The PET imaging protocol used in this study is fully adaptable to humans and thus can serve as an in vivo imaging technique to follow TH + GCH1 gene therapy in PD patients and provide an additional objective measure to a potential clinical trial using rAAV vectors to deliver l-3,4-dihydroxyphenylanaline in the brain.

The impact of graft size on the development of dyskinesia following intrastriatal grafting of embryonic dopamine neurons in the rat

Intrastriatal transplants of embryonic ventral mesencephalon can cause dyskinesia in patients with Parkinson's disease (PD). We assessed the impact of transplant size on the development of graft-induced dyskinesia. Rats with unilateral 6-hydroxydopamine lesions were primed to exhibit L-DOPA-induced dyskinesia. They were then intrastriatally grafted with different quantities of embryonic ventral mesencephalic tissue to give small and large grafts. Without drug treatment, discrete dyskinetic-like movements were observed in most rats with large grafts 2-6 weeks after transplantation, but disappeared later. Amphetamine evoked severe abnormal involuntary movements (AIMs) in grafted animals, which were more striking with large grafts. The AIMs coincided with contralateral rotation, but displayed a different temporal profile and pharmacological properties. Thus, selective dopamine uptake blockade elicited rotational behavior, whereas coadministration of both dopamine and serotonin uptake blockers was required to evoke significant orolingual and limb AIMs. In conclusion, robust and reproducible AIMs were evoked in rats with large grafts by blockade of monoamine reuptake. These AIMs may provide a new tool for assessing dyskinetic effects of neural grafting.

Graft placement and uneven pattern of reinnervation in the striatum is important for development of graft-induced dyskinesia

In two recent double-blind clinical trials of fetal ventral mesencephalic cell transplants into the striatum in patients with Parkinson's disease (PD), a significant proportion of the grafted patients developed dyskinetic side effects, which were not seen in the sham operated patients. Comparison between dyskinetic and non-dyskinetic grafted patients in one of the trials suggested that an uneven pattern of striatal reinnervation might be the leading cause of the dyskinesias. Here, we studied the importance of graft placement for the development of dyskinesias in parkinsonian rats. Abnormal involuntary movements resembling peak-dose dyskinesias seen in PD patients were induced by daily injections of L-DOPA for 6 weeks. The dyskinetic animals received about 130.000 fetal ventral mesencephalic cells as single grafts placement in the rostral or the caudal aspect of the head of striatum. The results show that grafts placed in the caudal, but not the rostral, part are effective in reducing the L-DOPA-induced limb and orolingual dyskinesia, predominantly seen as hyperkinesia. The same grafts, however, also induced a new type of dyskinetic behavior after activation with amphetamine, which were not seen in non-grafted lesion controls. The severity of these abnormal involuntary movements was significantly correlated with a higher graft-derived dopaminergic reinnervation in the caudal aspect of the head of striatum relative to the rostral part. The results indicate that graft-induced dyskinesias in PD patients may be linked to single, small graft deposits that provide an uneven, patchy reinnervation of the putamen.

Regulation of neuropeptide mRNA expression in the basal ganglia by intrastriatal and intranigral transplants in the rat Parkinson model

Previous studies have shown that intrastriatal transplants of dopamine (DA)-rich fetal ventral mesencephalic (VM) tissue can correct denervation-induced changes in the cellular expression of neuropeptide and receptor mRNAs in the rat Parkinson model. However, with the standard transplantation approach normalization of all cellular parameters has not been obtained. This may be due either to the incomplete striatal reinnervation achieved by these transplants, or to the ectopic placement of the grafts. In the present study we have used a microtransplantation approach to obtain a more complete reinnervation of the denervated striatum (20 micrograft deposits spread over the entire structure). Neurons were also implanted directly into the substantia nigra. In rats with multiple intrastriatal VM transplants the lesion-induced upregulation of mRNAs encoding for preproenkephalin (PPE), the D(2)-type DA-receptor, and the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD(67)) was normalized throughout the striatum, whereas the lesion-induced downregulation of preprotachykinin mRNA was unaffected. Intranigral grafts of either fetal DA-rich VM tissue or GABA-rich striatal tissue did not induce any changes in striatal neuropeptide and D(2)-receptor mRNA expression despite significant behavioral improvement. Comparison of the behavioral data with levels of neuropeptide expression showed that in rats with intrastriatal VM transplants a complete normalization of striatal PPE and GAD(67) mRNA expression did not translate into a complete recovery of spontaneous motor behaviors. The results show that extensive DA reinnervation of the host striatum by multiple VM microtransplants is insufficient to obtain full recovery of all lesion-induced changes at both the cellular and the behavioral level. A full reconstruction of the nigrostriatal pathway or, alternatively, modulation of basal ganglia function by grafting in non-striatal regions may be required to further improve the functional outcome in the DA-denervated brain.

Dopaminergic mRNA expression in the intact substantia nigra of unilaterally 6-OHDA-lesioned and grafted rats: an in situ hybridization study

The present study was performed to investigate the influence of intrastriatal fetal mesencephalic grafts on dopaminergic mRNA expression in the non-lesioned substantia nigra pars compacta of unilaterally 6-hydroxydopamine-lesioned rats. The expression of dopamine transporter mRNA, synaptic vesicular monoamine transporter mRNA and tyrosine hydroxylase mRNA was assessed in adjacent cryostat sections using in situ hybridization. Rotational behavior induced by apomorphine and amphetamine as well as hybridization of striatal sections cut at the grafting coordinates were used to prove the functional recovery and the presence of grafted cells, respectively. After grafting, the number of rotations was decreased and hybridization signals overlying cells in the grafted striatum were detected. Mean grain densities overlying labeled neurons in the substantia nigra pars compacta of grafted rats were compared to those of shamgrafted rats and revealed differential expression of dopamine transporter mRNA, whereas synaptic vesicular monoamine transporter mRNA and tyrosine hydroxylase mRNA expression showed no difference. The results will be discussed in relation to previous in vitro and in vivo studies suggesting a reduction of functional dopamine transporter molecules in the contralateral striatum.

Real-time dynamics of dopamine released from neuronal transplants in experimental Parkinson's disease

Intrastriatal transplantation of foetal midbrain dopamine (DA) neurons ameliorates the fundamental symptoms of dopaminergic denervation in clinical and experimental parkinsonism despite providing only restricted reinnervation. To understand how DA function is restored by these grafts we used fast-scan cyclic voltammetry at a carbon-fiber microelectrode in vitro to monitor directly and in "real time" the dynamics of graft-derived DA. Simulations of Michaelis-Menten kinetics were used to model the experimental observations. We show that the concentration of DA released by a single depolarizing pulse is significantly lower in grafted than intact striata. On the other hand, the extracellular lifetime of DA in grafts is extended due to a marked reduction in the rate maximum (V(max)) for DA reuptake by the DA transporter. Moreover, variations in V(max) and release occur in parallel: where DA release is lowest, V(max) is lowest and vice versa. The consequences of these dynamics are twofold. First, during repeated depolarization at a physiological firing frequency, when net extracellular concentrations reflect DA release versus uptake, ambient levels of extracellular DA within the graft are restored to normal. Second, the protracted extracellular lifetime of DA will increase the number and extracellular sphere of its postsynaptic actions. This effect will be most prominent where DA availability (and thus V(max)) is most restricted. Thus, these data demonstrate that dopaminergic grafts restore striatal dopaminergic function with extracellular dynamics of DA that are different from those of intact striatum but which can normalize ambient DA levels and permit transmission over an extended sphere.

Compensatory mechanisms in experimental and human parkinsonism: towards a dynamic approach

This paper provides an overview of the compensatory mechanisms which come into action during experimental and human parkinsonism. The intrinsic properties of the dopaminergic neurones of the substantia nigra pars compacta (SNc) which degenerate during Parkinson's disease are described in detail. It is generally considered that the nigrostriatal pathway is principally responsible for the compensatory preservation of dopaminergic function. It is also becoming clear that the morphological characteristics of dopaminergic neurones and the dual character, synaptic and asynaptic, of striatal dopaminergic innervation engender two modes of transmission, wiring and volume, and that both these modes play a role in the preservation of dopaminergic function. The plasticity of the dopamine neurones, extrinsic or intrinsic to the striatum, can thus be regarded as another compensatory mechanism. Recent anatomical and electrophysiological studies have shown that the SNc receives both glutamatergic and cholinergic inputs. The dynamic role this innervation plays in compensatory mechanisms in the course of the disease is explained and discussed. Recent developments in the field of compensatory mechanisms speak for the urgence to develop a valid chronic model of Parkinson's disease, integrating all the clinical features, even resting tremor, and illustrating the gradual evolution of nigral degeneration observed in human Parkinson's disease. Only a dynamic approach to the physiopathological study of compensatory mechanisms in the basal ganglia will be capable of elucidating these complex questions.

Unilateral fetal mesencephalic grafts in intact rats reduce amphetamine-induced dopamine release in both striata. An in vivo voltammetric study

This study investigated amphetamine-induced striatal dopamine release after intraventricular unilateral fetal mesencephalic grafts in otherwise intact rats. Dopamine was monitored in vivo by differential pulse voltammetry. In grafted animals, amphetamine-induced dopamine release was decreased compared to sham-grafted, age-matched controls. This decrease was observed in the grafted as well as in the contralateral striatum five months after intraventricular grafting. There was no measurable effect of the graft on the amphetamine-induced rotational behaviour. Our results exceed former observations reporting decreased amphetamine-induced dopamine release in the contralateral striatum of 6-hydroxydopamine-lesioned and unilaterally-grafted rats which had been attributed to a reduction of dopamine transporters. Furthermore, it was shown that concerning this effect ventral mesencephalic grafts are independent of a previous 6-hydroxydopamine lesion.

Effects of graft-derived dopaminergic innervation on the target neurons of patch and matrix compartments of the striatum

Fetal dopaminergic neurons grafted into the dopamine-depleted striatum have previously been shown to normalize neurochemical and behavioural abnormalities. However, the extent of graft-induced recovery of striatal compartments, which differ in their ontogeny, neurochemical properties and function, is still not clear. The striosome and matrix compartments of the striatum provide a segregated projection to somatostatin-containing GABAergic neurons of the rostral part of the entopeduncular nucleus and somatostatin-negative GABAergic neurons of the caudal part of the entopeduncular nucleus, respectively. In the present study, preprosomatostatin and glutamate decarboxylase messenger RNA levels in the rostral and caudal parts of the entopeduncular nucleus were determined six and 18 months postgrafting in rats with complete recovery of rotational behaviour following apomorphine challenge, and in rats with unilateral 6-hydroxydopamine lesions or sham lesions and no grafts. Sections were processed for in situ hybridization using 35S-labelled cRNA probes for glutamate decarboxylase (67,000 mol. wt isoform; GAD67) and preprosomatostatin. Autoradiographs showed a marked increase in preprosomatostatin messenger RNA within the ipsilateral entopeduncular nucleus in 6-hydroxydopamine-lesioned rats, and a substantially lower increase six months postgrafting. At 18 months postgrafting, the preprosomatostatin messenger RNA levels were symmetrical within the entopeduncular nucleus. Unilateral depletion of striatal dopamine resulted in a moderate increase in GAD67 messenger RNA levels within the ipsilateral entopeduncular nucleus, along with a substantial decrease in GAD67 levels within the contralateral nucleus. By six months postgrafting, the GAD67 levels had decreased considerably within the ipsilateral entopeduncular nucleus, while the messenger RNA levels had returned to normal within the contralateral nucleus. Interestingly, at 18 months postgrafting, the GAD67 levels remained decreased within the ipsilateral entopeduncular nucleus and were significantly lower than the normal value. The results indicate that fetal nigral grafts placed within the dopamine-depleted striatum can restore the neurochemical alterations seen in striatal target areas such as the entopeduncular nucleus. This may form the neurochemical basis of graft-induced behavioural recovery, as the normalization of neurotransmitter messenger RNA levels in the entopeduncular nucleus reflects the restoration of overall activity in both direct and indirect striatal output pathways. The results also indicate that the graft-derived dopaminergic innervation restores the output of both striosome and matrix compartments of the striatum. The present results also showed a progressive recovery leading to over-compensation of neurotransmitter messenger RNA levels following grafting, perhaps indicating the importance of feedback regulation of grafted dopaminergic neurons by the host.

DA uptake sites, D1 and D2 receptors, D2 and preproenkephalin mRNAs and Fos immunoreactivity in rat striatal subregions after partial dopaminergic degeneration

Stereotaxic injection of a limited amount of 6-hydroxydopamine in the lateral part of the rat substantia nigra induces a partial degeneration of the nigrostriatal dopaminergic system. This animal model in which the destruction of the dopaminergic nigral cell population reaches approximately 50% could be considered as a preclinical Parkinson's model. Autoradiography of dopaminergic uptake sites performed with a specific marker ([3H]GBR 12935) allowed the precise determination of dopaminergic denervated and non-denervated areas in the striatum 1 month after partial lesion of the substantia nigra pars compacta. In both striatal areas, dopaminergic D1 and D2 receptor densities and dopaminergic D2 and preproenkephalin mRNAs levels were measured by autoradiography and in situ hybridization coupled to an image analysis system. Our results show that in the denervated striatal subregion, none of the dopaminergic targets were modified, contrary to the observations made after complete lesion of the nigrostriatal DA system at the same post-lesion delay. However, striatal Fos activation induced by amphetamine (5 mg/kg i.p., 2 h before killing) revealed that the number of Fos-positive cells detected in the denervated striatal subregion was lower than that observed in the non-denervated one. These data argue in favour of the existence of compensatory mechanisms different from the up-regulation of DA receptor densities, thereby allowing the maintenance of striatal dopaminergic transmission. Such mechanisms could contribute to the delay of the appearance of neurological symptoms (which are reported to be clinically apparent only when depletion of striatal dopamine levels reaches near 80%) in Parkinsonian patients.

Phenotype of striatal cells expressing c-Fos following amphetamine treatment of rats with intrastriatal dopaminergic grafts

Activation of the nigrostriatal dopaminergic system by psychostimulants such as amphetamine increases c-Fos expression in the striatum, mostly in the striatonigral substance P-ergic pathway. This effect is greatly reduced in the neostriatum deprived of dopaminergic afferents. Dopaminergic grafts implanted into the denervated neostriatum restore the reactivity of the striatum to amphetamine. However, the number of striatal neurons expressing c-Fos is greatly increased in the graft-bearing striatum compared with the normal striatum. We examined whether this increase in the number of c-Fos-expressing neurons corresponds to the recruitment of a new neuron population, or whether it reflects an increase in the proportion of substance P-ergic neurons exhibiting activation of c-Fos. Adult rats received a unilateral 6-hydroxydopamine lesion of the ascending dopaminergic mesotelencephalic pathway, and a suspension of embryonic mesencephalic neurons was subsequently implanted into the denervated neostriatum. Three months after implantation, animals were injected with d-amphetamine (5 mg/kg) and killed 2 h later. In the first experiment, striatal sections were processed to visualize both c-Fos protein, by immunohistochemistry, and preproenkephalin A or substance P, by in situ hybridization. In the second experiment, c-Fos and neuropeptide Y were visualized on the same sections. In addition, some sections incubated with anti-c-Fos antibody were counterstained with toluidine blue in order to determine whether cholinergic neurons were expressing c-Fos following amphetamine treatment. The density of neurons expressing c-Fos following amphetamine treatment was three-fold higher in the graft-bearing striata than in the striata of control animals. Approximately 75% of the c-Fos expressing cells were substance P-ergic in control animals whereas 6% were enkephalinergic and only a few were neuropeptide Y-ergic or cholinergic. Similar proportions were found in the graft-bearing striatum, signifying that the pattern of activation of c-fos following amphetamine administration is not changed by the graft. Thus, the increased expression of c-Fos predominantly reflects a graft-induced increase in the proportion of neurons expressing c-Fos within the same population of neurons which normally expresses c-Fos in the striatum, i.e. the striatonigral substance P-ergic neurons; there is no recruitment of a new neuronal population. This increased activation of the striatonigral substance P-ergic pathway may underlie the abnormal behavioural reactions brought about by amphetamine-induced stimulation of the implanted dopaminergic neurons.

Expression of dopamine transporter mRNA and its binding site in fetal nigral cells transplanted into the striatum of 6-OHDA lesioned rat

Neurological disorders in rat model of hemi-Parkinson's disease can be compensated by the transplantation of fetal nigral cells. However, the role of the dopamine transporter (DAT) in this recovery has not been clarified. To clarify this mechanism, we examined the expression of DAT in the caudate putamen (CPu) by in situ hybridization histochemistry (mRNA) and autoradiography (using the ligand [125I] beta-CIT, which labels DAT) and compared them with the recovery of motor disturbance revealed with methamphetamine-induced rotation. Models were made with the stereotaxic injection of 6-hydroxydopamine into the left side of the substantia nigra pars compacta. Cell suspensions from rat fetus (embryonic day 14-15) were transplanted into the lesioned side of CPu. Methamphetamine-induced rotation, expression of DAT mRNA, and [125I] beta-CIT binding were evaluated 2, 4 and 12 weeks after the transplantation. Methamphetamine-induced rotation recovered partly in the 2nd week and significantly in the 4th week. [125I] beta-CIT binding increased with time and the dense binding was detected 4 and 12 weeks after the transplantation. In all transplanted rats, cells expressing DAT mRNA were found in CPu. These results indicated that transplanted fetal dopaminergic cells maturated in CPu of host animals and extended nerve terminals where high density of DAT binding sites were found.

Changes in striatal immediate early gene expression following neonatal dopaminergic lesion and effects of intrastriatal dopaminergic transplants

To evaluate the functional integration of neonatal dopaminergic transplants within host brain we studied the postsynaptic effects induced by their stimulation by following the expression of immediate early genes c-fos, c-jun and egr-1. This study was conducted nine months after the intrastriatal implantation of embryonic mesencephalic neurons to rat pups having sustained a unilateral lesion of the nigrostriatal dopaminergic system. We examined whether, when challenged with d-amphetamine: (1) dopaminergic grafts transplanted into the previously denervated neonatal neostriatum lead to a normal activation of postsynaptic striatal neurons in term of immediate early genes activation; and (2) whether this activation is related to the action of the dopamine released from the grafts using a dopaminergic D1 antagonist. Following a mild stress-injection of saline-c-fos expression was high in the lesioned neostriatum when compared with control animals. This effect was only partially counteracted by a pre-treatment with the D1 antagonist SCH 23390, but was abolished by the graft. Administration of d-amphetamine increased c-fos expression in the neostriatum and the globus pallidus of the control group. This activation was partially blocked by the lesion. The transplant reversed the effect of the lesion and, moreover, led to a c-fos over-expression in the dorsolateral neostriatum and the globus pallidus. These overcompensations positively correlated with the abnormal rotation induced by d-amphetamine in the same animals. Pre-treatment with SCH 23390 blocked the effect of d-amphetamine on c-fos expression in control and grafted animals. Similar results were found for egr-1 but not c-jun expression. It is concluded that the neonatal lesion of the nigrostriatal dopaminergic pathway, in contrast to the adult-stage lesion, modifies the reactivity of c-fos in the neostriatum to stress, presumably in relation with compensatory reorganizations occurring following the neonatal lesion. Grafts made into neonates, when challenged with amphetamine, induce an abnormal c-fos expression which can predict the degree of overshoot observed for rotation activity. This over-expression, which depends upon the stimulation of D1 receptors, indicate an abnormal activation of postsynaptic target cells by the grafts.

Partial reversal of increased preproenkephalin messenger ribonucleic acid (mRNA) and decreased preprotachykinin mRNA by foetal dopamine cells in unilateral 6-hydroxydopamine-lesioned rat striatum parallels functional recovery

In situ hybridization histochemistry was used to investigate the expression of striatal preproenkephalin and preprotachykinin messenger ribonucleic acid (mRNA) in rats with 6-hydroxydopamine lesions of the nigrostriatal pathway followed 4 weeks later by implantation of foetal dopamine cells into the denervated striatum. Striatal dopamine deafferentation caused an (+)-amphetamine-induced rotational asymmetry, an increase in striatal preproenkephalin mRNA message, and a decrease in striatal preprotachykinin mRNA message relative to control animals. Two months after grafting a foetal ventral mesencephalon suspension, there was reversal of the rotational asymmetry to (+)-amphetamine. At this time the increase in striatal preproenkephalin mRNA was significantly attenuated and the decrease in preprotachykinin mRNA was partially reversed compared to animals with a 6-hydroxydopamine lesion alone. Subregional analysis showed the attenuation of the increase in preproenkephalin mRNA to occur in dorsolateral, dorsomedial and ventromedial, but not ventrolateral, striatal subdivisions. The partial reversal of the decreased preprotachykinin mRNA density after grafting was only statistically significant in the DM and VM subdivisions. These results demonstrate graft-induced partial recovery of striatal function, as judged by preproenkephalin and preprotachykinin mRNA levels, within 2 months of transplantation.

Neonatal 6-hydroxydopamine lesions lead to opposing changes in the levels of dopamine receptors and their messenger RNAs

Previous studies have established that selective damage to the early-developing components of the mesostriatal dopamine system produces profound changes in dopamine D1 receptor-mediated behaviors, while decreasing D1 receptor density. In order to better understand the effects of early intrastriatal 6-hydroxydopamine lesions, we studied the ontogenetic expression (postnatal days 7, 14, 35 and 90) of D1 and D2 receptors, and their corresponding messenger RNAs, in rats that had received intrastriatal 6-hydroxydopamine or vehicle lesions on postnatal day 1. Using receptor autoradiography, significant (P < 0.05) decreases in [3H]SCH 23390 binding to D1 receptors in the rostral and caudal dorsomedial and ventromedial caudate of 6-hydroxydopamine-lesioned animals were evident by postnatal day 7, and remained depressed at all future time points. A significant decrease in D1 receptor concentration occurred in the dorsolateral caudate at later time points (postnatal days 35 and 90). [3H]Spiperone binding to D2 receptor sites was unchanged throughout the entire study. In situ hybridization for D1 and D2 messenger RNA expression showed contrasting results. 6-Hydroxydopamine induced significant decreases of D1 messenger RNA levels in the dorsolateral and dorsomedial caudate by postnatal day 7. By postnatal day 14, messenger RNA expression was significantly elevated in the dorsomedial and ventromedial caudate of the 6-hydroxydopamine group, and remained elevated thereafter. D1 messenger RNA levels became elevated in the lateral caudate at later time points (postnatal days 35 and 90). The opposing changes in D1 receptor concentrations and the messenger RNA encoding the protein did not occur as a consequence of increased transport of D1 receptors to striatonigral terminals. D2 messenger RNA levels in the dorsal caudate were significantly decreased on postnatal day 7, and became higher than controls at postnatal day 14, but were unchanged from controls at later time points. Together, the D1 receptor and D1 messenger RNA findings suggest that the normal relationship between levels of D1 receptor transcript and D1 receptor protein is permanently altered following the early loss of dopamine. In contrast, the results indicate that dopamine plays a minor role in the early postnatal development of the D2 receptor protein and transcript. These findings suggest that dopamine may be involved in the coordinated expression of some dopamine receptors and their corresponding messenger RNAs during development.

Time dependent changes in DA uptake sites, D1 and D2 receptor binding and mRNA after 6-OHDA lesions of the medial forebrain bundle in the rat brain

Quantitative receptor autoradiography and in situ hybridization techniques were used to examine the temporal pattern of changes in dopamine uptake sites, D1 and D2 receptors and their transcripts in the striata of animals lesioned with 6-hydroxydopamine. Animals were unilaterally lesioned in the medial forebrain bundle and the brains were analyzed at 1, 2, 4, 6, 8, and 16 weeks postlesion. Degeneration of the nigrostriatal pathway induced a significant loss of dopamine uptake sites in the ipsilateral caudate putamen of all lesioned animals. D1 receptor binding was significantly increased in the caudate putamen on the lesioned side from 1 week to 16 weeks postlesion, whereas the expression of D1 receptor mRNA did not show any change during this period. There was a significant upregulation of D2 receptor binding as well as D2 mRNA from 2 weeks to 8 weeks postlesion. However, at 16 weeks postlesion, D2 receptor binding continued to increase, whereas the mRNA appeared to compensate. These studies show that a different regulatory mechanism may exist between these two DA receptor subtypes. D1 receptor changes occur at the post-transcriptional or translational level, whereas D2 alterations occur by both transcriptional and translational processes. These studies also indicate that the postsynaptic supersensitivity observed in D1 receptors may not be accompanied by a corresponding increase in D1 receptor mRNA.

The neonatal lesion of the meso-telencephalic dopaminergic pathway increases intrastriatal D2 receptor levels and synthesis and this effect is reversed by neonatal dopaminergic rich-graft

The ascending dopaminergic pathway of 3-day-old rats has been unilaterally destroyed by the injection of 6-hydroxydopamine into the lateral hypothalamus. Five days later, a suspension containing embryonic dopaminergic neurones was injected in the lesioned neostriatum. Rotational responses to dopaminergic agonists were tested eight months after grafting and animals were killed one month later. Neostriatal dopaminergic D1 and D2 receptors were examined using autoradiography while changes in D2 receptor mRNA levels were studied by in situ hybridization. The lesion induced a behavioural hypersensitivity - as manifested in contralateral rotations - to dopaminergic D1 (SKF 38393) or D2 (LY 171555) agonists which was abolished by the graft. Density of D1 receptors was not affected by the lesion while D2 receptors density was increased by 20-25% in the more rostral part of the neostriatum. Changes in D2 mRNA after the lesion paralleled those observed for D2 receptor density, i.e. D2 mRNA level was increased by 15-19% in the rostral neostriatum. The graft did not influence D1 receptor densities but reversed the post-lesion increase of D2 receptors associated parameters. It is concluded that dopaminergic grafts implanted in neonatal hosts are able to normalise the density of D2 receptors by an action on their synthesis.

Transection of corticostriatal afferents abolishes the hyperexpression of Fos and counteracts the development of rotational overcompensation induced by intrastriatal dopamine-rich grafts when challenged with amphetamine

The present study was carried out to test whether the abnormally high striatal Fos activation induced by amphetamine and the overcompensation of amphetamine-induced rotation in 6-hydroxydopamine-lesioned rats receiving transplants of fetal nigral neurons can be reduced by a lesion of the corticostriatal projection. Fetal ventral mesencephalic tissue was transplanted as a cell suspension into the dopamine-denervated striatum of unilaterally 6-hydroxydopamine-lesioned rats. Rats in which the transplants had produced a complete compensation or reversal of the lesion-induced rotational asymmetry in response to amphetamine (5 mg/kg, i.p.) were divided into two equal groups, sustaining either a knife-cut transection of prefrontal corticofugal efferents ipsilaterally to the grafts, or a sham-lesion. The animals were re-tested for amphetamine-induced rotation one week post-operatively, and were perfusion-fixed two hours after drug administration. Adjacent sections through the striatum were processed for Fos and tyrosine hydroxylase immunohistochemistry. At the amphetamine rotation test performed after cortical lesion surgery, the frontocortically deafferented animals exhibited a low rate of rotation in the direction ipsilateral to the dopaminergically denervated and grafted side, while sham-lesioned rats rotated towards the intact side. In sham-lesioned controls, the density of Fos-immunoreactive nuclei (no. of nuclei/mm2) was significantly higher in the reinnervated portion of the grafted striatum than on the contralateral side (+54 to 316%). In the frontocortically deafferented-grafted striata, Fos expression was not different from that measured on the contralateral side and significantly lower than in the sham-lesioned controls (-65-79%).(ABSTRACT TRUNCATED AT 250 WORDS)

Fetal mesencephalic grafts influence the dopamine release in the non-lesioned striatum of 6-OHDA-lesioned rats: a behavioral and in vivo voltammetric study

This study was performed to investigate the effect of intraventricular fetal mesencephalic grafts on the non-lesioned nigro-striatal system of rats with unilateral lesions of dopaminergic neurones in the medial forebrain bundle and to analyze the involvement of the non-lesioned side in functional recovery due to grafts in this model. Grafts placed to the lesioned striatum produced a continuous decrease of apomorphine (APO, 0.25 mg/kg intraperitoneally (i.p.)) and amphetamine (AMPH, 5 mg/kg, i.p.) induced rotations over 7 months after grafting. Using differential pulse voltammetry (DPV) in anaesthetized and pargyline (75 mg/kg, i.p.) pretreated rats we found that 8 months after grafting in the lesioned striatum AMPH (5 mg/kg, i.p.) produced a higher increase of the dopamine (DA) signal (i.e., it became measurable), whereas in the non-lesioned striatum the same treatment produced a smaller increase of the DA signal, both compared to that in sham-grafted controls. After grafting onto the non-lesioned striatum, only a slight decrease of APO-induced rotations was observed, whereas AMPH-induced rotations were increased. In these animals AMPH did not produce a measurable DA signal in the lesioned striatum. The DA signal in the non-lesioned striatum was slightly higher than that of non-grafted controls. These results show clearly that unilateral fetal mesencephalic grafts producing behavioural recovery in the unilateral 6-OHDA model of the rat produce changes at dopaminergic mechanisms in the non-lesioned striatum.

Evidence for dopamine D2 receptor mRNA expression by striatal astrocytes in culture: in situ hybridization and polymerase chain reaction studies

The expression of dopamine D2 receptor mRNA in cultured rat striatal and cerebellar astrocytes was examined by in situ hybridization (ISH) and polymerase chain reaction (PCR). Cells double-labelled for glial fibrillary acidic protein (GFAP) immuno-histochemistry and dopamine D2 receptor mRNA (ISH) provide evidence that striatal but not cerebellar astrocytes express the dopamine D2 gene in vitro. These results were confirmed by polymerase chain reaction studies. As judged by GFAP immunostaining and morphology of the cells, this gene is almost exclusively expressed by astrocytes type 1. The expression of dopamine D2 receptor mRNA by striatal astrocytes in vitro, as found in this study, brings thus evidences for the existence of dopamine D2 receptors in such glial cells. This had been previously suggested from ligand binding studies but the typical dopaminergic nature of the binding to striatal astrocytes was left questionable. Our results with molecular biological techniques thus suggest that striatal dopamine might modulate the functions of striatal astrocytes.

Changes of D1 and D2 receptors in adult rat neostriatum after neonatal dopamine denervation: quantitative data from ligand binding, in situ hybridization and iontophoresis

The specific binding of [3H]SCH23390 to D1 and of [3H]raclopride to D2 dopamine receptors was measured by autoradiography in the rostral and caudal halves of neostriatum and in the substantia nigra of adult rats subjected to near total destruction of nigrostriatal dopamine neurons by intraventricular 6-hydroxydopamine soon after birth. Three months after this lesion, [3H]SCH23390 binding (D1 receptors) was slightly but significantly decreased in the rostral neostriatum (22%), but unchanged in its caudal half and in the substantia nigra. In contrast, [3H]raclopride binding (D2 receptors) was considerably increased throughout the neostriatum (10-40%), while markedly decreased in the substantia nigra (80%). In the rostral neostriatum, there were no parallel changes in D2 receptor messenger RNA levels, as measured by in situ hybridization on adjacent sections. Caudally, however, slight but significant increases in D2 messenger RNA could be observed (10-20%). As assessed by quantitative iontophoresis, there was a marked enhancement (63%) of the inhibitory responsiveness of spontaneously firing units in the rostral neostriatum to dopamine and the D1 agonist, SKF38393, in neonatally lesioned compared to control rats. On the other hand, responsiveness to PPHT, a potent D2 agonist, appeared to be unchanged. Such opposite changes in the number of D1 and D2 binding sites, dissociated from the expression of D2 receptor messenger RNA and from the sensitivity to dopamine and D1 and D2 agonists, suggested independent adaptations of these various parameters following the neonatal dopamine denervation of neostriatum. They also provided further evidence for mechanisms other than the dopamine innervation in the control of the expression of neostriatal D2 receptor messenger RNA during ontogenesis, and emphasized that the effects of dopamine and its D1 and D2 agonists in neostriatum do not depend strictly on the number of D1 and D2 primary ligand recognition sites.

Neuropeptide messenger RNA expression in the 6-hydroxydopamine-lesioned rat striatum reinnervated by fetal dopaminergic transplants: differential effects of the grafts on preproenkephalin, preprotachykinin and prodynorphin messenger RNA levels

In situ hybridization histochemistry was used to analyse the expression of the messenger RNAs encoding for enkephalin, substance P and dynorphin in the striatum of normal rats, rats subjected to a unilateral 6-hydroxydopamine lesion of the mesostriatal dopamine pathway and lesioned rats bearing intrastriatal transplants of fetal nigral neurons. About half of the rats in each group received twice-daily subcutaneous injections of 5 mg/kg apomorphine and the other half received control injections of saline, for nine days. Three hours after the last injection, the rats were killed by decapitation. Cryostat sections through the striatum were incubated with, 35S-labeled oligodeoxyribonucleotide probes hybridizing with preproenkephalin, preprotachykinin or prodynorphin messenger RNA. One additional series of sections was incubated with [3H]GBR 12935 in order to label dopamine uptake sites. Quantitative evaluation of the hybridization signal was performed both at the macroscopic level (autoradiographic film analysis) and at the cellular level (optical density of silver grains over identified cells). The grafted nigral neurons reversed the lesion-induced up-regulation of preproenkephalin messenger RNA in the whole striatal complex. By contrast, the graft-induced effect on the lesion-induced down-regulation of preprotachykinin messenger RNA was restricted to the region of the host striatum where the graft-derived dopamine fibers exhibited their densest distribution (up to 0.5 mm from the border of the grafts). However, following chronic treatment with apomorphine, preprotachykinin messenger RNA expression approached control levels in a wider portion of the grafted striata (up to 1 mm from the border of the grafts). Basal prodynorphin messenger RNA expression, which was also down-regulated in the lesioned striata, was only partially restored by the transplants. Repeated injections of apomorphine enhanced prodynorphin messenger RNA in the lesioned striata to levels several fold higher than normal. This massive increase in prodynorphin messenger RNA expression was completely prevented by the transplants over a large volume of the host striatum (> 1 mm from the graft-host border), but a trend towards an abnormally high prodynorphin messenger RNA expression was still present in peripheral striatal areas that were not reached by graft-derived dopamine fibers. The present results indicate that fetal nigral neurons transplanted to the 6-hydroxydopamine-lesioned striatum have differential effects on the activity of enkephalin-containing (i.e. mainly striatopallidal) and substance P- or dynorphin-containing (i.e. mainly striatonigral) neurons. An inhibitory control over the activity of striatopallidal neurons is completely restored by the grafts, even in non-reinnervated striatal regions, suggesting that neurohumoral mechanisms underlie this effect.(ABSTRACT TRUNCATED AT 400 WORDS)

Time-course of changes in striatal levels of DA uptake sites, DA D2 receptor and preproenkephalin mRNAs after nigrostriatal dopaminergic denervation in the rat

Changes in striatal dopamine uptake sites, D2 receptor and preproenkephalin (PPE) mRNA levels provoked by unilateral 6-hydroxydopamine-induced lesion of the nigrostriatal dopaminergic (DA) pathway were studied by quantitative autoradiography and in situ hybridization (ISH) in rats sacrificed at different post-lesion delays. The disappearance of DA terminals as visualized with the labelling of dopamine uptake sites with [3H]GBR 12935 became significant 36 h after the lesion and was almost complete at a delay of 7 days. PPE mRNA amounts significantly increase (+24%) already at the shortest delay studied (9 h after the lesion) while the labelling of the uptake sites on DA terminals was not affected. The time course increase of PPE mRNA levels was progressive until 21 days post-lesion where it reached its maximum (+132%) and remained stable up to the latest delay studied (60 days). Conversely D2 mRNA contents remained unchanged up to 5 days post-surgery and then increased relatively quickly since at 7 days post-lesion their levels were near (+21%) the maximum observed which was reached at 21 days post-lesion (+32%). This study suggests a time-dependent differential sensitivity to the degree of DA denervation of both major components implicated in the striatopallidal output.

Transplantation of fetal nigral cells reverses the increase of preproenkephalin mRNA levels in the rat striatum caused by 6-OHDA lesion of the dopaminergic nigrostriatal pathway: a quantitative in situ hybridization study

Unilateral 6-hydroxydopamine (6-OHDA)-induced lesion of the nigrostriatal dopamine (DA) pathway causes a significant increase of preproenkephalin (PPE) messenger RNA (mRNA) levels in the DA-depleted striatum in rat brain. Using an in situ hybridization (ISH) technique and computer-assisted microdensitometry, we quantified the changes in PPE mRNA levels in the striatum. Seven months after lesion, levels of PPE mRNA were 75% higher in the DA-depleted striatum than in the contralateral control striatum of the same animal or in the striatum of sham control animals. The implantation of embryonic dopaminergic neurons into the denervated striatum led to a complete reversal of this increase and, in grafted animals, levels of PPE mRNA were at control values. Moreover, this reversal extended beyond the areas reinnervated by the grafted dopaminergic neurons.

Intrastriatal transplants of embryonic dopaminergic neurons counteract the increase of striatal enkephalin immunostaining but not serotoninergic sprouting elicited by a neonatal lesion of the nigrostriatal dopaminergic pathway

The aim of the our experiment was to compare the ability of intrastriatal implants of embryonic dopaminergic neurons to reverse two kinds of postlesion modification in the host brain: the change in the activity level of neurons in the denervated area and morphological modifications, e.g. collateral sprouting. The ascending dopaminergic system of 3-day-old rat pups was unilaterally lesioned by an intrahypothalamic injection of the neurotoxin 6-hydroxydopamine. This lesion has been described previously to induce an increase in the level of activity of striatal enkephalinergic neurons. The same lesion leads also to sprouting of the serotoninergic afferents in the striatum, leading to hyperinnervation of this structure. The existence of these modifications thus offers the possibility of testing the influence of grafts in one structure of the same animal on two lesion-induced reactions of different nature. A cell suspension obtained from mesencephali of embryonic day 14 rats and containing dopaminergic neurons was implanted into the denervated striatum of lesioned animals 5 days after the lesion. Nine months later the animals were killed and immunohistochemistry was performed on striatal sections using antibodies directed against tyrosine hydroxylase, methionine enkephalin and serotonin. Intensity of immunostaining (methionine enkephalin and serotonin) as well as innervation density (serotonin) was quantified through the use of a computer-assisted image analyser. The lesion led to the disappearance of striatal dopaminergic innervation. Implanted dopaminergic neurons were found scattered in the striatum and restored a dopaminergic innervation in a large portion of this structure. There was a marked increase in striatal methionine enkephalin immunostaining in lesioned animals, which was most pronounced in the dorsolateral part of the striatum (+ 150% compared to control values), while in the ventral part it was slight or non-existent. The density of striatal serotoninergic innervation was also increased by approximately 250% relative to control values. In grafted animals striatal enkephalin immunostaining was similar to that observed in control animals. On the other hand, the serotoninergic hyperinnervation was still present in the graft-bearing striata. These results suggest that while intrastriatal implants of embryonic dopaminergic neurons are able to counteract modifications in the functioning of local striatal neuronal systems such as the increase in enkephalinergic activity or receptor hypersensitivity occurring as a result of the lesion, they might be unable to reverse postlesion morphological modifications.

Dopaminergic transplants in experimental parkinsonism: cellular mechanisms of graft-induced functional recovery

The ability of intrastriatal grafts of fetal mesencephalic dopamine neurons to ameliorate the symptoms of experimental and clinical parkinsonism has raised the question of the mechanisms underlying the transplant-induced functional effects. Recent studies have taken advantage of quantitative cytochemical and in situ hybridization techniques to study functional graft-host interactions at the cellular level in the rat Parkinson model. The results provide evidence that behaviorally functional grafts restore dopaminergic neurotransmission and normalize dopamine receptor function in the denervated striatum, and that these effects are likely to depend on both synaptic and extrasynaptic mechanisms.