Mechanisms of action of neural grafts in the limbic system

This review summarizes the range of possible mechanisms of action of neuronal grafts in the central nervous system. It aims to illustrate the capacity and limitations of the transplanted tissue in the promotion of neurological recovery after experimental surgical insults.     

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.     

Adenovirus-mediated over-expression of TGFbeta1 in the striatum decreases dopaminergic cell survival in embryonic nigral grafts.

Neurotrophic factors may be valuable for improving the survival and the functional efficacy of fetal nigral grafts to treat Parkinson's disease (PD). However, further characterization of their effects is required. New methods of protein delivery also need to be explored to supply sustained and regulated levels of these molecules. Gene transfer via adenoviral vectors is a promising strategy for this purpose. We show herein the effect of adenovirus-mediated transforming growth factor beta1 (TGFbeta1) gene transfer on fetal nigral grafts in a rat model of PD. Direct injection of AdTGFbeta1 into the dopamine-depleted striatum decreased the survival of the transplanted tyrosine hydroxylase-positive (TH+) neurons and impaired the functional efficacy of grafts. Viral toxicity to the graft was avoided by separating the site of viral infection from the transplant by a distance that allowed TGFbeta1 effect on the graft. This infection protocol may be useful for delivering secreted molecules with neurotrophic effects to dopaminergic grafts.     

Differential effects of autologous peripheral nerve grafts to the corpus striatum of adult rats on the regeneration of axons of striatal and nigral neurons and on the expression of GAP-43 and the cell adhesion molecules N-CAM and L1

A segment of tibial nerve was autografted to the right corpus striatum of deeply anesthetized adult rats; the distal graft was left beneath the scalp. Horseradish peroxidase (HRP) conjugates were injected into the distal graft after 2–30 weeks, and the animals were killed 2–3 days later. Small numbers of neostriatal perikarya were HRP labeled at all survival times; most were large (ca. 20 μm in diameter), and many contained acetycholine esterase (AChE). Many more neurons were labelled in the substantia nigra pars compacta (SNpc) 4 weeks or more after grafting. When the graft encroached on the globus pallidus, numerous pallidal neurons, most of them AChE positive, were also labeled. Nigrostriatal neurons, a population of pallidal cholinergic neurons, and a subclass (or classes) of neostriatal neurons, including cholinergic interneurons, thus can be classified as central nervous system (CNS) neurons with a relatively strong regenerative response. In a second experimental series, animals were killed 1–4 weeks after grafting, and sections were probed for the expression of mRNAs encoding growth-associated protein 43 (GAP-43) and the cell adhesion molecules N-CAM and L1. Subpopulations of mostly large neurons scattered throughout the neostriatum gave moderate signals for GAP-43 and N-CAM mRNAs and a stronger signal for L1 mRNAs. Most SNpc neurons were strongly labeled with all three probes. Neostriatal grafts had no apparent effect on the expression of any of the mRNAs in the SNpc or on L1 and N-CAM mRNAs in the striatum. However, GAP-43 mRNA levels were increased in a few, mainly large neostriatal neurons around the graft tip, resembling the HRP-labeled cells. In contrast, previous work has shown upregulation (from an undetectable level) of GAP-43 and L1 mRNAs in neurons regenerating axons into grafts placed in the thalamus and cerebellum. Thus, GAP-43 and L1 mRNA expression, but not necessarily marked upregulation, may correlate with, and be intrinsic determinants of, the ability of CNS neurons to regenerate their axons. J. Comp. Neurol. 391:259–273, 1998. © 1998 Wiley-Liss, Inc.     

In vivo measurement of spontaneous release and metabolism of dopamine from intrastriatal nigral grafts using intracerebral dialysis

Spontaneous release and metabolism of dopamine (DA) from intrastriatal grafts of fetal mesencephalic DA neurons was measured by intracerebral dialysis. Mesencephalic DA cell suspensions were implanted into the head of the caudate-putamen in rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the mesostriatal DA pathway. Four months later, when tests for amphetamine-induced turning behaviour showed that the grafts had become functional, loops of dialysis tubing were implanted into the striatum on the grafted side and the contralateral non-lesioned side of the grafted rats, and in a similar position in the denervated caudate-putamen of 6-OHDA lesioned control rats. Dialysis perfusates collected from the 6-OHDA lesioned striata showed a reduction of about 95-98% in DA and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). In the grafted animals these levels had recovered to about 40% of control for DA and to 12-16% of control for HVA and DOPAC. In addition, the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) was increased in the grafted striata compared to both the lesioned and non-lesioned controls. Amphetamine had little or no effect on DA release in the 6-OHDA lesioned rats, but caused a marked increase in DA release in the grafted rats, this response being proportional to that seen in intact striata. Since the subsequent histochemical analysis showed that the dialysis probe had been located in the transplant-reinnervated part of the caudate-putamen, the results provide additional evidence that the grafted DA neurons exert their functional effects through a continuous active transmitter release from their newly-established terminals in the reinnervated host target.     

Localization of striatal and nigral tachykinin receptors in the rat

The effects of lesioning mesostriatal dopamine projections or striatal neurons on tachykinin binding in the basal ganglia were assessed in the rat. 6-Hydroxydopamine lesions of the medial forebrain bundle destroyed striatal dopamine terminals as assessed by [³H]mazindol autoradiography, but did not significantly affect the binding of NK-1 ([³H][Sar⁹, Met(O₂)¹¹]substance P) or NK-3 ([³H]senktide) tachykinin ligands in the striatum. 6-Hydroxydopamine lesions significantly reduced NK-3 binding in the substantia nigra pars compacta, but not the ventral tegmental area. In contrast, striatal quinolinic acid lesions reduced both NK-1 and NK-3 binding in the striatum, but failed to affect NK-3 binding in the substantia nigra. These findings suggest that both NK-1 and NK-3 receptors within the striatum are predominantly post-synaptic with respect to dopamine neurons, whereas nigral NK-3 receptors are located on dopaminergic neurons.     

Characterization of epidermal neural crest stem cell (EPI-NCSC) grafts in the lesioned spinal cord

We have characterized in the contusion-lesioned murine spinal cord the behavior of acutely implanted epidermal neural crest stem cells (EPI-NCSC, formerly eNCSC). EPI-NCSC, a novel type of multipotent adult stem cell, are remnants of the embryonic neural crest. They reside in the bulge of hair follicles and have the ability to differentiate into all major neural crest derivatives (Sieber-Blum, M., Grim, M., Hu, Y.F., Szeder, V., 2004. Pluripotent neural crest stem cells in the adult hair follicle. Dev. Dyn. 231, 258-269). Grafted EPI-NCSC survived, integrated, and intermingled with host neurites in the lesioned spinal cord. EPI-NCSC were non-migratory. They did not proliferate and did not form tumors. Significant subsets expressed neuron-specific beta-III tubulin, the GABAergic marker glutamate decarboxylase 67 (GAD67), the oligodendrocyte marker, RIP, or myelin basic protein (MBP). Close physical association of non-neuronal EPI-NCSC with host neurites was observed. Glial fibrillary acidic protein (GFAP) immunofluorescence was not detected. Collectively, our data indicate that intraspinal EPI-NCSC demonstrate several desirable characteristics that may include local neural replacement and re-myelination.     

Comparative effects of estrogens and prolactin on nigral and striatal GAD activity

The comparative effects of a 10 day estrogen treatment and estrogen independent hyperprolactinemia on nigral and striatal glutamic acid decar☐ylase (GAD, EC 4.1.1.15) activity were investigated in male rats. Data obtained show that estrogen treatment decreases GAD activity in substantia nigra, while an increase was observed in conditions of hyperprolactinemia induced by modulation of strio-nigral GABAergic system by estrogens and prolactin is suggested.     

Levodopa replacement therapy alters enzyme activities in striatum and neuropeptide content in striatal output regions of 6-hydroxydopamine lesioned rats.

The effects of striatal dopamine denervation and levodopa replacement therapy on neuronal populations in the rat striatum were assessed by measurement of glutamic acid decarboxylase (GAD) and choline acetyltransferase (CAT) activities in the striatum, dynorphin and substance P concentrations in the substantia nigra, and enkephalin concentration in the globus pallidus. Rats with a unilateral 6-hydroxydopamine (6-OHDA) lesion of the nigrostriatal pathway were treated for 21 days with levodopa (100 mg/kg/day, i.p., with 25 mg/kg benserazide) on either an intermittent (b.i.d.) or continuous (osmotic pump infusion) regimen and sacrificed following a three day drug washout. In saline-treated control rats, striatal GAD activity and globus pallidus enkephalin content were elevated and nigral substance P content was reduced ipsilateral to the 6-OHDA lesion. Intermittent levodopa treatment further increased GAD activity, decreased CAT activity, restored substance P to control levels, markedly increased dynorphin content, and had no effect on enkephalin. In contrast, continuous levodopa elevated globus pallidus enkephalin beyond the levels occurring with denervation, but had no effect on any of the other neurochemical measures. These results indicate that striatal neuronal populations are differentially affected by chronic levodopa therapy and by the continuous or intermittent nature of the treatment regimen. With the exception of substance P, levodopa did not reverse the effects of the 6-OHDA lesion but, rather, either exacerbated the lesion-induced changes (e.g. GAD and enkephalin) or altered neurochemical markers which had been unaffected by the lesion (e.g. CAT and dynorphin).(ABSTRACT TRUNCATED AT 250 WORDS)     

Chronic cocaine administration depletes tyrosine hydroxylase immunoreactivity in the rat brain nigral striatal system: Quantitative light microscopic studies

Chronic administration of cocaine (10 mg/kg, i.p., every 12 h for 10 consecutive days) produced a large decrease in tyrosine hydroxylase-staining axons and terminal boutons in the caudate nucleus in rats when examined 60 days after the final cocaine injection. This effect was quantitated using the Leitz data acquisition and display system (DADS) which revealed that there was a 63% decrease in tyrosine hydroxylase-positive processes in the caudate nucleus. In addition, this cocaine treatment regimen produced a large decrease in the number of tyrosine hydroxylase-positive staining neuronal perikarya in the pars compacta of the substantia nigra. Use of the Leitz-DADS system revealed that there was a 51% decrease in tyrosine hydroxylase-positive material in the substantia nigra. These data demonstrated that chronic administration of cocaine produced a long-term loss of tyrosine hydroxylase in both the cell bodies of the substantia nigra and the nerve terminals of the caudate nucleus. Further studies are required to determine whether the observed changes are due to degeneration of the neurons or some metabolic effect.     

A glial cell line-derived neurotrophic factor-secreting clone of the Schwann cell line SCTM41 enhances survival and fiber outgrowth from embryonic nigral neurons grafted to the striatum and to the lesioned substantia nigra.

We have developed a novel Schwann cell line, SCTM41, derived from postnatal sciatic nerve cultures and have stably transfected a clone with a rat glial cell line-derived neurotrophic factor (GDNF) construct. Coculture with this GDNF-secreting clone enhances in vitro survival and fiber growth of embryonic dopaminergic neurons. In the rat unilateral 6-OHDA lesion model of Parkinson's disease, we have therefore made cografts of these cells with embryonic day 14 ventral mesencephalic grafts and assayed for effects on dopaminergic cell survival and process outgrowth. We show that cografts of GDNF-secreting Schwann cell lines improve the survival of intrastriatal embryonic dopaminergic neuronal grafts and improve neurite outgrowth into the host neuropil but have no additional effect on amphetamine-induced rotation. We next looked to see whether bridge grafts of GDNF-secreting SCTM41 cells would promote the growth of axons to their striatal targets from dopaminergic neurons implanted orthotopically into the 6-OHDA-lesioned substantia nigra. We show that such bridge grafts increase the survival of implanted embryonic dopaminergic neurons and promote the growth of axons through the grafts to the striatum.     

Functional fetal nigral grafts in a patient with Parkinson's disease: Chemoanatomic,ultrastructural, and metabolic studies

A patient with Parkinson's disease received bilateral fetal human nigral implants from six donors aged 6.5 to 9 weeks post-conception. Eighteen months following a post-operative clinical course characterized by marked improvement in clinical function, this patient died from events unrelated to the grafting procedure. Post-mortem histological analyses revealed the presence of viable grafts in all 12 implant sites, each containing a heterogeneous population of neurons and glia. Approximately 210,146 implanted tyrosine hydroxylase-immunoreactive (TH-ir) neurons were found. A greater number of TH-ir grafted neurons were observed in the right (128,162) than the left (81,905) putamen. Grafted TH-ir neurons were organized in an organotypic fashion. These cells provided extensive TH-ir and dopamine transporter-ir innervation to the host striatum which occurred in a patch-matrix fashion. Quantitative evaluations revealed that fetal nigral grafts reinnervated 53% and 28% of the post-commissural putamen on the right and left side, respectively. Grafts on the left side innervated a lesser area of the striatum, but optical density measurements were similar on both sides. There was no evidence that the implants induced sprouting of host TH-ir systems. Electron microscopic analyses revealed axo-dendritic and occasional axo-axonic synapses between graft and host. In contrast, axo-somatic synapses were not observed. In situ hybridization for TH mRNA revealed intensely hybridized grafted neurons which far exceeded TH mRNA expression within residual host nigral cells. In addition, γ-amino butyric acid (GABA)-ergic neurons were observed within the graft that formed a dense local neuropil which was confined to the implant site. Serotonergic neurons were not observed within the graft. Cytochrome oxidase activity was increased bilaterally within the grafted post-commissural putamen, suggesting increased metabolic activity. In this regard, a doubling of cytochrome oxidase activity was observed within the grafted post-commissural putamen bilaterally relative to the non-grafted anterior putamen. The grafts were hypovascular relative to the surrounding striatum and host substantia nigra. Blood vessels within the graft stained intensely for GLUT-1, suggesting that this marker of blood-brain barrier function is present within human nigral allografts. Taken together, these data indicate that fetal nigral neurons can survive transplantation, functionally reinnervate the host putamen, establish synaptic contacts with host neurons, and sustain many of the morphological and functional characteristics of normal nigral neurons following grafting into a patient with PD. © 1996 Wiley-Liss, Inc.     

Autosomal dominant adult neuronal ceroid lipofuscinosis: parkinsonism due to both striatal and nigral dysfunction.

We describe a family with adult neuronal ceroid lipofuscinosis, with apparent autosomal dominant inheritance, observed in six affected individuals in three generations. Disease onset was usually in the fifth decade, but was earlier in the youngest generation. Early symptoms consisted of myoclonus in face and arms, epilepsy, auditory symptoms, cognitive decline, or depression. Parkinsonism occurred a few years after disease onset, with stooped posture, shuffling gait, bradykinesia, and mask face. Four subjects deteriorated to a state of severe handicap, with severe dementia, contractures, dysphagia, and dysarthria. Leg weakness evolved to flaccid paraparesis in two patients. Diagnosis was confirmed by brain biopsy in one patient and full autopsy in two patients. Abundant intraneuronal storage of autofluorescent material was found throughout the brain. Electron microscopy showed granular osmiophilic deposits and scarce fingerprint profiles. Striking loss of neurons in the substantia nigra pars compacta and reticulata was found. (123)I-IBZM Single photon emission computed tomography in two patients showed loss of postsynaptic D2 receptor binding in the striatum. We conclude that parkinsonism in ANCL is likely to be caused by both presynaptic nigral cell loss and postsynaptic striatal degeneration.     

Motor training effects on recovery of function after striatal lesions and striatal grafts

Environment, training, and experience can influence plasticity and recovery of function after brain damage. However, it is less well known whether, and how, such factors influence the growth, integration, and functional recovery provided by neural grafts placed within the brain. To explore this process, rats were pretrained on the skilled staircase test, then lesioned unilaterally in the lateral dorsal striatum with quinolinic acid. Half of the animals were given suspension grafts prepared from E15 whole ganglionic eminence implanted into the lesioned striatum. For the following 5 months, half of the animals in each group were trained daily in a bilateral manual dexterity task. Then, 23 weeks after surgery, all animals were retested on the staircase test. The grafts promoted recovery in the reaching task, irrespective of the additional dexterity training, and within the trained group recovery was proportional to the volume of the striatal-like tissue in the graft, suggesting that training influenced the pattern of graft-induced functional recovery. The additional training also benefited the rats with lesions alone, raising their performance close to level of the grafted groups. In separate tests of rotation, the grafts reduced drug-induced ipsilateral turning in response to both amphetamine and apomorphine, an effect that was greater in the grafted rats given extra training. The results suggest that both nonspecific motor training and cell transplantation can contribute to recovery of lost function in tests of spontaneous and skilled lateralized motor function after striatal damage, and that these two factors interact in a task-specific manner.     

Cortical and nigral deafferentation and striatal cholinergic markers in the rat dorsal striatum: different effects on the expression of mRNAs encoding choline acetyltransferase and muscarinic m1 and m4 receptors

The regulation of the striatal m1 and m4 muscarinic receptor mRNA as well as the choline acetyltransferase (ChAT) mRNA expression by nigral dopaminergic and cortical glutamatergic afferent fibres was investigated using quantitative in situ hybridization histochemistry. The effects induced by a unilateral lesion of the medial forebrain bundle and a bilateral lesion of the sensorimotor (SM) cortex were analysed in the dorsal striatum 3 weeks after the lesions. Dopaminergic denervation of the striatum resulted in a marked decrease in the levels of m4 mRNA throughout the striatum, while the levels of muscarinic m1 mRNA and ChAT mRNA in cholinergic neurons were unaffected by the lesion. In contrast, following bilateral cortical ablation, the levels of the muscarinic m1 mRNA were significantly increased in the striatal projection area of the SM cortex, whereas the expression of m4 mRNA remained unchanged. Single cholinergic cell analysis by computer-assisted grain counting revealed a decreased labelling for ChAT mRNA per neuron following cortical ablation. However, in contrast to the topographical m1 mRNA changes, the decreased ChAT mRNA expression was evenly distributed within the striatum, suggesting an indirect cortical control upon striatal cholinergic interneurons. Altogether, these data suggest that dopaminergic nigral and glutamatergic cortical afferents modulate differentially cholinergic markers, at the pre- and post-synaptic levels. Beside the fact that nigral and cortical inputs exert an opposite control on cholinergic neurotransmission, our study further shows that this control involved different muscarinic receptor subtypes: the m4 and m1 receptors, respectively.     

NGF-producing transfected 3T3 cells: Behavioral and histological assessment of transplants in nigral lesioned rats

The rodent fibroblast clonal cell line, 3T3, was retrovirally transfected with the rat nerve growth factor (NGF) gene and selected for NGF synthesis. This study tested the hypothesis that transplanted 3T3 cells, transfected to secrete nerve growth factor (3T3^NGF+), change motor behavioral indices created by striatal denervation in a dose-dependent fashion. 3T3^NGF+ cells were transplanted into the lateral ventricle of rats following ipsilateral lesions of the substantia nigra pars compacta by stereotaxic injections of 6-hydroxydopamine (10 μg), an established lesion model. Control groups included vehicle injections and transplanted untransfected cells. The extent of the lesions was measured by determining rotational behavior before and two weeks after transplantation. Immediately prior to transplantation, cells were incubated with the fluorescent dye marker, Dil. To assess cell viability, whole brains were cryosectioned and examined for Dil-labeled 3T3 cells using fluorescent microscopy. The number Uf Dil-labeled profiles in five animals per group were counted in at least five noncontiguous sections per animal. From these data a statistically derived estimate of viable, transplanted 3T3 cells was obtained. The number of surviving transplanted cells correlated with the behavioral changes measured. The 3T3NGF + transplants reduced rotational behavior, while control 3T3 transplants exacerbated rotational behavior. Thus, while NGF delivery was found to be beneficial, it was apparent that naive 3T3 had detrimental effects. These results underscore the importance of making doseresponse measurements when attempting transplantbased modifications of CNS behavior. © 1995 Wiley-Liss, Inc.     

Effects of AMPA and D1 receptor activation on striatal and nigral GABA efflux

The ability of locally-administered AMPA and D1 receptor ligands to modulate in vivo striatal and nigral GABA efflux was determined in awake, intact male rats using a dual-probe microdialysis technique. Intrastriatal perfusion of AMPA (100 μM) produced a 50–100% increase in striatal GABA efflux that was totally blocked by co-perfusion with TTX (10.0 μM). This AMPA-stimulated, TTX-sensitive GABA efflux was similar across repeated dialsysis perfusions. The effects of intrastriatal perfusion of the full D1-like agonist SKF 81297 were complex. Perfusion of the higher dose (100 μM) of SKF 81297 enhanced GABA efflux, whereas perfusion of the lower dose (10 μM) decreased GABA efflux. Both of these effects were blocked by co-perfusion with the D1-like antagonist SCH 23390 (10 μM). Intrastriatal perfusion of AMPA (100 μM), SKF 81297 (100 μM), or AMPA + SKF 81297 did not stimulate GABA efflux in the substantia nigra. These bidirectional effects of D1 agonists and the apparent dissociation, under certain conditions, between striatal and nigral GABA efflux highlight the complexities of DA- and Glu-modulated striatonigral activity in situ. Synapse 26:254–268, 1997. © 1997 Wiley-Liss Inc.     

Expanded mesencephalic precursors develop into grafts of densely packed dopaminergic neurons that reinnervate the surrounding striatum and induce functional responses in the striatal neurons

The search for alternative sources of dopaminergic cells, other than primary fetal tissue for transplantation in Parkinson's disease has become a major focus of research. Different methodological approaches have led to generation in vitro of cells expressing DA-cell markers, although these cells are frequently unable to survive for a long time in vivo after transplantation and/or induce functional effects in the host brain. In the present study, we grafted cell aggregates treated with antibodies against fibroblast growth factor 4 into dopaminergic-denervated striata in rats. Furthermore, we grafted cell suspensions from primary mesencephalic fetal tissue. Grafts from expanded precursors were able to survive (at least 3 months postgrafting) and most decreased the lesion-induced ipsiversive rotation. In addition, immunolabeling for tyrosine hydroxylase and/or Fos showed that the grafts reinnervated the surrounding striatal tissue with dopaminergic terminals, and induced the expression of Fos in the striatal neurons of the reinnervated area after administration of amphetamine to the host rat. The number of dopaminergic cells in grafts from expanded precursors inducing rotational recovery was usually lower (1,226+/-314) than that in grafts from primary fetal tissue (1,671+/-122), but they were more densely packed in grafts that were of smaller volume and did not have the characteristic central nondopaminergic area observed in grafts from primary fetal tissue. The results suggest that long-term survival and functional integration into the DA-denervated striatum can be achieved with grafts of expanded mesencephalic precursors.