Substantia Nigra Grafts Research Articles

Embryonic substantia nigra grafts in the mesencephalon send neurites to the host striatum in non‐human primate after overexpression of GDNF

In spite of partial success in treating Parkinson's disease by using ectopically placed grafts of dopamine-producing cells, restoration of the original neuroanatomical circuits, if possible, might work better. Previous evidence of normal anatomic projections from ventral mesencephalic (VM) grafts placed in the substantia nigra (SN) has been limited to neonatal rodents and double grafting or bridging procedures. This study attempted to determine whether injection of a potent growth-promoting factor, glial cell line-derived neurotrophic factor (GDNF), into the target regions or placement of fetal striatal co-grafts in the nigrostriatal pathway might elicit neuritic outgrowth to the caudate nucleus. Four adult St. Kitts green monkeys received embryonic VM grafts into the rostral mesencephalon near the host SN, and injections of adeno-associated virus 2 (AAV2)/GDNF or equine infectious anemia virus (EIAV)/GDNF into the caudate. Three adult monkeys were co-grafted with fetal VM tissue near the SN and fetal striatal grafts (STR) 2.5 mm rostral in the nigrostriatal pathway. Before sacrifice, the striatal target regions were injected with the retrograde tracer Fluoro-Gold (FG). FG label was found in tyrosine hydroxylase-labeled neurons in VM grafts in the SN of only those monkeys that received AAV2/GDNF vector injections into the ipsilateral striatum. All monkeys showed FG labeling in the host SN when FG labeling was injected on the same side. These data show that grafted dopaminergic neurons can extend neurites to a distant target releasing an elevated concentration of GDNF, and suggest that grafted neurons can be placed into appropriate loci for potential tract reconstruction.

Embryonic substantia nigra grafts in the mesencephalon send neurites to the host striatum in non-human primate after overexpression of GDNF

Embryonic substantia nigra grafts in the mesencephalon send neurites to the host striatum in non-human primate after overexpression of GDNF

Embryonic Substantia Nigra Grafts Show Directional Outgrowth to Cografted Striatal Grafts and Potential for Pathway Reconstruction in Nonhuman Primate

Transplantation of embryonic dopamine (DA) neurons has been tested as a therapy for Parkinson's disease. Most studies placed DA neurons into the striatum instead of the substantia nigra (SN). Reconstruction of this DA pathway could serve to establish a more favorable environment for control of DA release by grafted neurons. To test this we used cografts of striatum to stimulate growth of DA axons from embryonic SN that was implanted adjacent to the host SN in African green monkeys. Embryonic striatum was implanted at one of three progressive distances rostral to the SN. Immunohistochemical analysis revealed DA neuron survival and neuritic outgrowth from the SN grafts at 12-36 weeks after grafting. Each animal showed survival of substantial numbers of DA neurons. Most fibers that exited SN grafts coursed rostrally. Striatal grafts showed evidence of target-directed outgrowth and contained dense patterns of DA axons that could be traced from their origin in the SN grafts. A polarity existed for DA neurites that exited the grafts; that is, those seen caudal to the grafts did not appear to be organized into a directional outflow while those on the rostral side were arranged in linear profiles coursing toward the striatal grafts. Some TH fibers that reached the striatal grafts appeared to arise from the residual DA neurons of the SN. These findings suggest that grafted DA neurons can extend neurites toward a desired target over several millimeters through the brain stem and caudal diencephalon of the monkey brain, which favors the prospect of circuit reconstruction from grafted neurons placed into appropriate locations in their neural circuitry. Further study will assess the degree to which this approach can be used to restore motor balance in the nonhuman primate following neural transplantation.

Serotonergic activity in the rat striatum after intrastriatal transplantation of fetal nigra as measured by microdialysis

In vivo microdialysis was used to examine the effects of dopaminergic transplants on extracellular concentrations of dopamine (DA), serotonin (5-HT), and their precursors and major metabolites in the denervated rat striatum. Dialysis perfusates were collected from intact, 6-hydroxydopamine (6-OHDA) lesion plus sham grafted, and lesion plus fetal substantia nigra (SN) grafted striata. The SN transplants ameliorated the reduction of striatal DA and dihydroxyphenylacetic acid (DOPAC) levels in rats with unilateral 6-OHDA lesions of the mesostriatal pathway. The transplants also increased extracellular levels of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in the denervated striatum. In response to NSD-1015 (an inhibitor of aromatic l-amino acid decarboxylase), 5-hydroxytryptophan (5-HTP) levels were substantially elevated in the SN grafted striata as compared with those in the sham grafted controls, which continued even after subsequent administration of l-3,4-dihydroxyphenylalanine ( l-DOPA, 100 mg/kg i.p.). Immunohistochemical analysis showed hyperinnervation of 5-HT fibers in the grafted striatum, which was consistent with the results of microdialysis experiments. These results indicated that implantation of SN grafts into the 6-OHDA-lesioned striatum of rats induces hyperactivity of 5-HT synthesis, release and metabolism.

Permeability of the Blood–Brain Barrier to Protein and [3H]GABA in Intraparenchymal Fetal CNS Tissue Grafts

In the present study solid grafts of rat fetal neocortex or substantia nigra were transplanted into young adult rat cortex or striatum. To study the permeability to protein and potential changes in the blood–brain barrier (BBB), HRP was administered intravascularly or, to examine endogenous protein exudation, noninjected animals were evaluated after immunocytochemical stain for rat serum albumin. In addition, [3H]GABA, a neurotransmitter that does not cross the BBB, was systemically administered to cortical graft-bearing hosts in order to determine if a barrier to small potentially bioactive compounds was present. Postoperative periods ranged between 1 week and 15 months for the cortical grafts and between 1 week and 8 months for nigral grafts; the experiments were repeated several times at the same time point in order to determine the potential for variability in the model systems. The results show that a high percentage (80%) of both neocortical and nigral grafts lack a complete BBB to protein up to 2–3 weeks postoperative. After this time the majority of neocortical grafts were impermeable to protein yet 20–30% of longer-term specimens showed variable degrees of permeability to protein; permeability to [3H]GABA, which manifested in the transmitter being sequestered by graft neurons, was observed only up to 4 weeks postoperative. Nigral grafts after 4 weeks postoperative showed negligible permeability to serum protein. Although in all early CNS grafts protein permeation is extensive in both graft and adjacent host, the mature host brain resolved the exudation far more efficiently so that the reaction appeared exclusively in the graft or interface and not in the host by 2–3 weeks, suggesting that the graft tissue may lack appropriate mechanisms for clearance of extracellular materials. It is unclear why this phenomenon occurred consistently but in a minority percentage of cortical specimens. It is suggested that either frank pathology or immunopathology provides a subtle and incomplete rejection process that allows the interface vessel to be permeable over the life of the graft. Since nigral grafts appeared to have significantly less BBB dysfunction variation it is possible that the maturation levels or the ontogeny between different graft sources may play a role in differing responses to injury or vascular problems after transplant surgery.

Astrocytes and extracellular matrix following intracerebral transplantation of embryonic ventral mesencephalon or lateral ganglionic eminence

Transplantation of embryonic neurons to the adult mammalian central nervous system (CNS) offers the possibility of re-establishing neural functions lost after traumatic injuries or neurodegenerative disease. In the adult CNS, however, transplanted neurons and their growing neurites can become confined to the graft region, and there may also be a relative paucity of afferents innervating grafted neurons. Because glia may influence the development and regeneration of CNS neurons, the present study has characterized the distribution of astrocytes and developmentally regulated glycoconjugates (chondroitin-6-sulfate proteoglycan and tenascin) within regions of the embryonic mouse CNS used as donor tissues, and in and around these grafts to the adult striatum and substantia nigra. Both chondroitin-6-sulfate proteoglycan and tenascin are present in the embryonic ventral mesencephalon (in association with radial glia and their endfeet, and glial boundaries that cordon off the ventral mesencephalon dopamine neuron migratory zone) and lateral ganglionic eminence before transplantation, and they are conserved within grafts of these tissues to the adult mouse. Neostriatal grafts exhibit a heterogeneous pattern of astrocyte and extracellular matrix molecule distribution, unlike ventral mesencephalon grafts, which are rather homogeneous. There is evidence to suggest that, in addition to variation in astroglial/extracellular matrix immunostaining within different compartments in striatal grafts to either adult striatum or substantia nigra, there are also boundaries between these compartments that are rich in glial fibrillary acidic protein/extracellular matrix components. Substantia nigra grafts, with cells immunoreactive for tyrosine hydroxylase, are also rich in immature astroglia (RC-2- immunopositive), and as the astroglia mature (to glial fibrillary acidic protein-positive) over time the expression of chondroitin-6-sulfate proteoglycan and tenascin is also reduced. These same extracellular matrix constituents, however, are only slightly up-regulated in an area of the adult host which surrounds the grafted tissue. Glial scar components exhibit no obvious differences between grafts from different sources to homotopic (e.g., striatum to striatum) or heterotopic (e.g., substantia nigra to striatum) sites, and likewise grafts of non-synaptically associated structures (e.g., cerebellum to striatum), needle lesions or vehicle injections all yield astroglial/extracellular matrix scars in the host that are indistinguishable. Studies utilizing the ROSA-26 transgenic (β-galactosidase-positive) mouse as a host for non-5-bromo-4-chloro-3-indolyl-β- d-galactopyranoside-labeled grafts indicate that the early astroglial/extracellular matrix response to the graft is derived from the surrounding host structures. Furthermore, biochemical analysis of one of the “boundary molecules”, tenascin, from the developing ventral mesencephalon versus adult striatal lesions, suggests that different forms of the molecule predominate in the embryonic versus lesioned adult brain. Such differences in the nature and distribution of astroglia and developmentally regulated extracellular matrix molecules between donor and host regions may affect the growth and differentiation of transplanted neurons. The present study suggests that transplanted neurons and their processes may flourish within graft versus host regions, in part due to a confining glial scar, but also because the extracellular milieu within the graft site remains more representative of the developmental environment from which the donor neurons were obtained. [Gates [29]M. A., et al. (1994). See Neurosci. Abstr. 20, 471].

Sham surgery does not ameliorate MPTP-induced behavioral deficits in monkeys.

Parkinsonism has been reported to improve following transplantation of fetal mesencephalic tissue into the striatum of MPTP-exposed monkeys and humans and in patients with idiopathic Parkinson's disease. While there is good evidence for the survival of grafted tyrosine hydroxylase (TH)-positive cells in animal studies, it is not known whether they produce neuronal effects that account for behavioral improvement after transplantation or whether spontaneous or graft-induced changes in the host striatum are at least partly responsible. Are neuronal synaptic connections and dopamine release necessary, or would "toenails and talcum powder" do the job equally well? We have addressed these questions by studying several types of implantation surgeries, including sham surgery, the implantation of cerebellar tissue, and the implantation of mesencephalic TH-positive fetal tissue of various gestational ages into the striatum. Adult male African green monkeys received systemic MPTP administration (cumulative doses of 2.0-2.5 mg/kg) prior to these stereotaxic surgical manipulations. Subjects were matched for quantitative behavioral deficits prior to surgery. Subjects were examined and assessments made by "blinded" observers who scored individual spontaneous and elicited behaviors. Observers were trained and tested repeatedly for inter-rater reliability. A "parkinsonian summary score" derived and determined using a principal component factor analysis of a large sample of data from MPTP-treated and normal monkeys of the same species was used to assess behavior. Postmortem brain tissue was prepared for biochemical analysis of dopamine concentrations and TH immunohistochemical studies. The most dramatic improvement was seen in monkeys with "early" (< 4 cm fetal crown rump length) surviving substantia nigra grafts in the caudate nucleus. Some behavioral improvements were seen in MPTP-treated sham-operated monkeys, cerebellar-grafted monkeys, and "later" (> 14 cm fetal crown rump length) substantia nigra-grafted monkeys. These changes in monkeys which did not have surviving dopamine-producing grafts probably represent the recovery capacity of MPTP-treated host brain during this time interval since un-operated subjects showed similar changes. More variable effects were seen with substantia nigra grafts in the putamen. The most consistent correlate of behavioral improvement in all experimental groups was elevation in dopamine concentrations near the grafts compared with a distant striatal location which is believed to represent the depletion without the effects of the grafts. While these data do not establish the precise mechanism of action, they point to a hierarchy of factors which provide increasingly larger restorative effects, including sprouting of host neurons and increased dopamine production by grafted fetal dopamine neurons. Sham surgery appears to be significantly less effective than early fetal mesencephalic tissue which survives and releases dopamine.

Sham surgery does not ameliorate MPTP-induced behavioral deficits in monkeys

Parkinsonism has been reported to improve following transplantation of fetal mesencephalic tissue into the striatum of MPTP-exposed monkeys and humans and in patients with idiopathic Parkinson's disease. While there is good evidence for the survival of grafted tyrosine hydroxy-lase (TH)-positive cells in animal studies, it is not known whether they produce neuronal effects that account for behavioral improvement after transplantation or whether spontaneous or graft-induced changes in the host striatum are at least partly responsible. Are neuronal synaptic connections and dopamine release necessary, or would “toenails and talcum powder” do the job equally well? We have addressed these questions by studying several types of implantation surgeries, including sham surgery, the implantation of cerebellar tissue, and the implantation of mesencephalic TH-positive fetal tissue of various gestational ages into the striatum. Adult male African green monkeys received systemic MPTP administration (cumulative doses of 2.0–2.5 mg/kg) prior to these stereotaxic surgical manipulations. Subjects were matched for quantitative behavioral deficits prior to surgery. Subjects were examined and assessments made by “blinded” observers who scored individual spontaneous and elicited behaviors. Observers were trained and tested repeatedly for inter-rater reliability. A “parkinsonian summary score” derived and determined using a principal component factor analysis of a large sample of data from MPTP-treated and normal monkeys of the same species was used to assess behavior. Postmortem brain tissue was prepared for biochemical analysis of dopamine concentrations and TH immunohistochemical studies. The most dramatic improvement was seen in monkeys with “early” (<4 cm fetal crown rump length) surviving substantia nigra grafts in the caudate nucleus. Some behavioral improvements were seen in MPTP-treated sham-operated monkeys, cerebellar-grafted monkeys, and “later” (>14 cm fetal crown rump length) substantia nigra-grafted monkeys. These changes in monkeys which did not have surviving dopamine-producing grafts probably represent the recovery capacity of MPTP-treated host brain during this time interval since un-operated subjects showed similar changes. More variable effects were seen with substantia nigra grafts in the putamen. The most consistent correlate of behavioral improvement in all experimental groups was elevation in dopamine concentrations near the grafts compared with a distant striatal location which is believed to represent the depletion without the effects of the grafts. While these data do not establish the precise mechanism of action, they point to a hierarchy of factors which provide increasingly larger restorative effects, including sprouting of host neurons and increased dopamine production by grafted fetal dopamine neurons. Sham surgery appears to be significantly less effective than early fetal mesencephalic tissue which survives and releases dopamine.

Programmed Cell Death in Developing Grafts of Fetal Substantia Nigra

Intracerebral transplants of ventral mesencephalic (VM) tissue have been well characterized. VM grafts contain numerous tyrosine hydroxylase immunoreactive neurons which send axons into the host brain. Transplanted neurons in VM grafts develop normally in that they contain tyrosine hydroxylase and GAP43. An overlooked aspect of graft development is cell death. It has been suggested that cell death in VM grafts was mostly necrotic. However, recent work in this laboratory suggested that developing grafts contain numerous apoptotic cells. In the present paper morphological, histochemical, and molecular correlates of apoptosis were used to assay cell death during VM graft development. At early times (5-15 days) after grafting VM grafts contained numerous apoptotic cells. In older grafts (21 and 28 days) few apoptotic cells were observed. In situ end labeling of fragmented DNA with biotinylated dUTP showed that early grafts contained numerous positive cells. The expression of RP8, a molecular correlate of apoptotic cell death, occurred in early grafts, but was not detectable in older grafts. These results indicate that apoptosis is a normal part of VM graft development. As in naturally developing neural systems, cell death in grafts may function to eliminate cells that fail to connect to appropriate targets.

The combined method of transplantation of foetal substantia nigra and stereotactic thalamotomy for Parkinson's disease.

Five cases with late Parkinson's disease improved following treatment with a combination of foetal substantia nigra grafts and stereotactic thalamotomy. The average Webster's score decreased from 21 to 11 points. This modified method is simple, safe and effective.

Kainic acid lesions increase reafferentation of the striatum by substantia nigra grafts

Effects of kainic acid lesions of the striatum on reafferentation of the striatum produced by intraventricular substantia nigra (SN) grafts were investigated. Rats with unilateral 6-hydroxydopamine lesions of the SN received intrastriatal kainic acid lesions or sham lesions, and then received fetal (E16) SN or sciatic nerve grafts in the lateral ventricle. The depth of reafferentation of the striatum by catecholaminergic neurites from SN grafts was significantly increased in rats with kainic acid-induced striatal lesions, as compared to the sham-lesioned controls. No reafferentation was seen in the control animals with sciatic nerve grafts. These data suggest that striatal injury promotes the growth of dopaminergic neurites from SN grafts.

A Comparison of Solid Intraventricular and Dissociated Intraparenchymal Fetal Substantia Nigra Grafts in a Rat Model of Parkinson's Disease: Impaired Graft Survival Is Associated with High Baseline Rotational Behavior

It has been established that substantia nigra (SN) grafts can produce a behavioral effect in animal models of Parkinson's disease when transplanted either into the lateral ventricles as solid tissue fragments or directly into the striatum as dissociated cells. These two transplantation methods (solid-intraventricular and dissociated-intraparenchymal) were directly compared in the present study. Adult male rats received unilateral SN lesions by stereotaxic injection of 6-hydroxydopamine. Fetal ventral mesencephalon, containing the SN, was harvested from 15-day gestational rat fetuses. Equal weights of tissue were transplanted, either as solid-intraventricular or dissociated-intraparenchymal grafts. In the animals with surviving grafts, similar decreases in apomorphine-induced rotational behavior were seen in both dissociated (40.2% at 6 weeks, 29.6% at 12 weeks, N = 12) and solid (31.8% at 6 weeks, 51.0% at 12 weeks, N = 11) graft groups. Control animals receiving tectal grafts showed smaller decreases (dissociated: 12.6% at 6 weeks, 18.8% at 12 weeks, N = 20; solid: 4.1% at 6 weeks, 8.0% at 12 weeks, N = 20). There were no significant overall differences between the effects of the solid and dissociated grafts; however, in the subgroup of animals with high baseline levels of rotational behavior, the solid-intraventricular grafts produced a significantly larger effect then did the dissociated-intraparenchymal SN grafts. There was also a tendency for the effect of the solid-intraventricular grafts to increase gradually over the 12-week testing period, whereas the effects of the dissociated-intraparenchymal grafts were maximal by 6 weeks after transplantation. For both SN graft groups, there were significant correlations between decreases in rotation and numbers of surviving tyrosine hydroxylase-immunore-active neurons in the grafts. It was also found that animals with no surviving transplanted tyrosine hydroxylase-positive neurons had higher baseline levels of rotational behavior. Therefore, in the present model, solid-intraventricular and dissociated-intraparenchymal SN grafts have similar effects on apomorphine-induced rotational behavior, except that the solid-intra-ventricular grafts tended to produce a larger effect in animals with high baseline levels of rotational behavior.

2-Deoxyglucose autoradiographic evidence that fetal substantia nigra grafts exert contralateral effects in 6-hydroxydopamine-lesioned animals who recover motor asymmetries

Fetal substantia nigra grafts decrease turning behavior induced by dopaminergic agonists in rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal system. The purpose of this study was to determine, through the [ 14C]2-Deoxyglucose autoradiographic method, whether substantia nigra grafts have an effect on efferent striatal nuclei and other related structures. The results showed an unexpected enhancement of metabolic activity in the substantia nigra pars reticulata and striatum on the side contralateral to the lesion and a bilateral enhancement in the thalamus and frontoparietal cortex, in rats bearing fetal substantia nigra grafts. The results are discussed in terms of the possibility that recovery of turning behavior may in part be caused by an increased activity of the striatum contralateral to the grafted side.

Normalization of Striatal Proenkephalin and Preprotachykinin mRNA Expression by Fetal Substantia Nigra Grafts

The expression of striatal proenkephalin and preprotachykinin mRNA was studied in Wistar rats following unilateral injections of 6-hydroxydopamine into the nigrostriatal pathway and after grafting dopaminergic fetal cell suspensions into the dopamine-depleted striatum. Striatal dopaminergic deafferentation resulted in an amphetamine-induced rotational asymmetry, an increase in ipsilateral striatal proenkephalin mRNA, and a decrease in preprotachykinin mRNA expression. Twelve months following grafting, proenkephalin and preprotachykinin mRNA returned to near-normal levels in contrast to control nongrafted lesioned animals. In addition, reversal of the rotational asymmetry was routinely observed. This study has demonstrated long-term graft-induced functional recovery coincident with normalization of striatal proenkephalin and preprotachykinin mRNA expression.

Transplants in Parkinson's disease

The objectives of this review are, first, to summarize results from clinical trials on patients with Parkinson’s disease using grafts of either adrenal medulla or fetal substantia nigra and, second, t

Adrenal medulla and substantia nigra co-grafts in peripheral nerve: chromaffin cells survive for long time periods and prevent degeneration of nigral neurons

A series of degenerative cytoskeletal changes characterize grafts of embryonic substantia nigra when isolated for long time periods in the peripheral nervous system. This study was designed to determine whether the adrenal medulla could modulate the cytoskeletal changes in the substantia nigra when co-grafted within peripheral nerves. The sciatic nerves of young adult rats received single transplants of embryonic day 15 substantia nigra or co-transplants of substantia nigra plus young adult adrenal medulla in close proximity. Immunocytochemistry was used to examine the expression of tyrosine hydroxylase, phosphorylated (RT97) and non-phosphorylated (SMI-32) neurofilament proteins in the grafts. Single substantia nigra grafts, examined after 1 month, consisted of numerous neurons and fibers that expressed the epitope for tyrosine hydroxylase. Normal spatial distributions of the phosphorylated and non-phosphorylated neurofilament subunits were observed. In contrast, single 1-year-old nigral transplants were shrunken, contained significantly fewer tyrosine hydroxylase positive neurons and displayed abnormal neurofilament staining patterns including swollen axons, a reduction in the density of labeled axons and perikaryal accumulation of the phosphorylated neurofilament subunit. When co-grafted with the adrenal medulla, the nigral transplants did not show the degenerative cytoskeletal aspects evident in the single 1-year-old grafts. The loss of neurons was prevented and the neurofilament immunolabeling was indistinguishable from the young substantia nigra preparations. In addition, all the 1-year-old adrenal medulla grafts were viable within the peripheral nerves, consisting of hundreds of cells identified by immunoreactivity to tyrosine hydroxylase and the rat β-nerve growth factor receptor (192-IgG). The experiments illustrate a strong protective effect by the adrenal medulla on neurons of the substantia nigra in the peripheral nerve environment. It is suggested that a catecholaminergic trophic source and/or neural interactions with the adrenal medulla may be important factors in the long-term survival of neurons and maintenance of normal cytoskeletal characteristics in the grafted substantia nigra neurons under these experimental circumstances.

Dopaminergic innervation of substance P‐containing striatal neurons by fetal nigral grafts: An ultrastructural double‐labeling immunocytochemical study

Evidence for survival and growth of fetal substantia nigra grafts in host striatum and partial reversal of behavioural and biochemical deficits in the host animal is well documented. Afferent synaptic connections arising from the graft and contacting host structures have also been reported; however, the properties of the neurons receiving this input is less clear. The purpose of this study was to determine if substance P-containing neostriatal neurons receive a dopaminergic input from nigral grafts. Fetal substantia nigra cell suspensions were stereotaxically implanted in the deafferented neostriatum of Wistar rats 2 weeks after a unilateral 6-hydroxydopamine (6-OHDA) lesion in the ipsilateral substantia nigra or medial forebrain bundle. The ultrastructural features of the graft-host synaptic interactions were analysed by employing an electron microscope immunocytochemical double-labeling technique. Tyrosine hydroxylase (TH) and substance P-immunoreactive structures were simultaneously demonstrated by means of the peroxidase-antiperoxidase method using two different chromogens with distinct reaction products easily differentiated at the light and electron microscope levels. TH-immunoreactive sites were first demonstrated using 3,3'-diaminobenzidine tetrahydrochloride (DAB); then substance P immunoreactivity was localized using benzidine dihydrochloride (BDHC). TH-immunoreactive terminals of axons originating from the graft made synaptic contacts with substance P-positive cell bodies and dendrites from the host. These results indicate that at least partial restoration of the normal nigrostriatal circuitry can be achieved following nigral grafts. The demonstration of specific synaptic input on host substance P neurons provides an anatomical basis for direct functional modulation of the deafferented host neostriatum by the nigral graft.

Functional recovery of supersensitive dopamine receptors after intrastriatal grafts of fetal substantia nigra

Interruption of the ascending dopamine neurons of the nigrostriatal pathway, by 6-hydroxydopamine (6-OHDA) lesion in rats, produced a significant loss of the dopamine transport complexes labeled with the phencyclidine derivative [ 3H]BTCP. This loss of dopamine innervation in the striatum was present at least 12 to 14 months after lesioning and was functionally manifested by ipsilateral rotation of the animals in response to amphetamine. In these same animals, in comparison to controls, there was a significant increase in the number ( B max) of [ 3H]SCH 23390-labeled D-1 receptors in the striatum (36.7%) and the substantia nigra (35.1%) and a 54.4% increase in the number ( B max) of [ 3H]sulpiride-labeled striatal D-2 receptors without an apparent change in affinity ( K d ). Ten to twelve months after the transplantation of homologous fetal substantia nigra into the denervated striatum, there was a significant decrease in amphetamine-induced turning behavior. In these animals, there was an ingrowth of dopamine nerve terminals in the striatum as demonstrated by a return of [ 3H]BTCP binding. Accompanying this reinnervation was the normalization of D-1 and D-2 receptors to control values in the striatum as well as the return of D-1 receptors to prelesion densities in the substantia nigra. In a subgroup of transplanted rats, amphetamine continued to induce ipsilateral turning. In these animals both D-1 and D-2 receptors remained supersensitive. These results support the hypothesis that the functional recovery of transplanted animals is due, in part, to reinnervation of the striatum. In addition, long-term alterations in receptor density may be related to the behavioral deficits that are associated with the 6-OHDA-lesioned rat. Furthermore, dopamine receptor plasticity may play a role in the functional recovery of substantia nigra transplanted animals and graft viability seems to be a prerequisite for behavioral recovery as well as receptor normalization.

Downregulation of muscarinic receptors in the rat caudate-putamen after lesioning of the ipsilateral nigrostriatal dopamine pathway with 6-hydroxydopamine (6-OHDA): normalization by fetal mesencephalic transplants

The autoradiographic distribution and density of muscarinic receptors was studied in the neostriatum of rats with long-term unilateral 6-hydroxydopamine (6-OHDA) lesions of the nigrostriatal dopaminergic pathway and in lesioned rats who had additionally received embryonic substantia nigra grafts in the dopamine denervated striatum. Muscarinic receptors were labeled with [ 3H]quinuclidinyl benzilate (QNB), M 1 receptors were directly labeled with [ 3H]pirenzepine (PZ) and non-M 1 receptors were labeled by the competition of 100 nM PZ with [ 3H]QNB. The density and distribution of muscarinic receptors were directly compared to the sodium-dependent, high-affinity, choline uptake sites as labeled with [ 3H]hemicholinium-3 (HC-3). In the 6-OHDA-lesioned animals, there was a 25% reduction in muscarinic receptors labeled with [ 3H]QNB. Subtype analysis showed that there was a reduction of both M 1 (−26%) and non-M 1 (−33%) receptors. A normal density of both muscarinic receptor populations was found in animals with successful transplants. Saturation analysis demonstrated that the changes, in muscarinic receptor density, were due to a change in receptor number ( B max) and not affinity ( K d). There was no significant change in [ 3H]HC-3 binding in the 6-OHDA-lesioned or transplanted animals, indicating that alterations in muscarinic receptors were not due to transynaptic degeneration of striatal cholinergic interneurons. The findings of downregulation of muscarinic receptors following long-term dopamine denervation and the subsequent normalization of muscarinic receptor density after fetal mesencephalic transplantation suggests that transplanted substantia nigra cells are able to restore inhibitory control on striatal cholinergic interneurons.

Fetal substantia nigra and adrenal medullary grafts placed contralateral to the nigrostriatal lesion side induce a decrease in turning behavior but not in dopamine receptor density

Motor asymmetries as well as changes in the density of postsynaptic dopamine receptors produced by unilateral denervation of the striatum have been reduced by both substantia nigra (SN) and adrenal medullary (AM) grafts. Since to this date all studies have placed the grafts on the side ipsilateral to the lesion, the purpose of this study was to determine whether similar effects can be obtained when grafts are placed contralateral to the denervated side. The results of this study showed that 6-hydroxydopamine-lesioned rats followed up to 150 days with contralaterally placed intraventricular fetal substantia nigra grafts and fetal adrenal medulla grafts have a reduction of turning behavior of 41% and 34% respectively. However, contrary to ipsilateral grafts no normalization of dopamine receptor density as measured by [3H]spiperone autoradiography was observed 6 months after SN grafts, however, after AM grafts normalization did occur except in the anterior portion of the striatum. These results suggest that the compensatory motor changes induced by the grafted tissues could be mediated by mechanisms unrelated to changes in receptor density.