Transplants of fetal ventral mesencephalic tissue are known to contain a mixture of two major dopamine (DA) neuron types: the A9 neurons of the substantia nigra pars compacta (SNpc) and the A10 neurons of the ventral tegmental area (VTA). Previous studies have suggested that these two DA neuron types may differ in their growth characteristics, but, because of technical limitations, it has so far been difficult to identify the two subtypes in fetal ventral mesencephalon (VM) grafts and trace their axonal projections. Here, we have made use of a transgenic mouse expressing green fluorescent protein (GFP) under the tyrosine hydroxylase promoter. The expression of the GFP reporter allowed for visualization of the grafted DA neurons and their axonal projections within the host brain. We show that the SNpc and VTA neuron subtypes in VM grafts can be identified on the basis of their morphology and location within the graft, and their expression of a G-protein-gated inwardly rectifying K+ channel subunit (Girk2) and calbindin, respectively, and also that the axonal projections of the two DA neuron types are markedly different. By retrograde axonal tracing, we show that dopaminergic innervation of the striatum is derived almost exclusively from the Girk2-positive SNpc cells, whereas the calbindin-positive VTA neurons project to the frontal cortex and probably also other forebrain areas. The results suggest the presence of axon guidance and target recognition mechanisms in the DA-denervated forebrain that can guide the growing axons to their appropriate targets and indicate that cell preparations used for cell replacement in Parkinson's disease will be therapeutically useful only if they contain cells capable of generating the correct nigral DA neuron phenotype.

https://www.jneurosci.org/content/jneuro/25/27/6467.full.pdf

Identification of dopaminergic neurons of nigral and ventral tegmental area subtypes in grafts of fetal ventral mesencephalon based on cell morphology, protein expression, and efferent projections.

Dopaminergic innervation of the caudate nucleus in adult rats can be partially restored by the grafting of embryonic substantia nigra into the overlying parietal cortex with concomitant compensation of certain behavioral abnormalities. In this study the function of such grafts was investigated neurochemically by quantification of transmitter metabolism and glucose utilization in the reinnervated target. Rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal bundle received a single graft to the dorsal caudate-putamen and were screened for rotational behavior following 5 mg/kg methamphetamine. The grafts restored dopamine concentrations in the caudate-putamen from initially less than 0.5% to an average of 13.6% of normal in rats with behavioral compensation. The ratio of 3,4-dihydroxyphenylacetic acid to dopamine, which is a measure of the rate of transmitter turnover, were equivalent in transplanted and normal control rats. Moreover, measurements of DOPA accumulation for a 30-min period after DOPA decarboxylase inhibition indicated similar fractional dopamine turnover rates in normal and transplant-reinnervated tissues. Correlations between rotational behavior and dopamine concentrations showed that reinnervation to only 3% of normal was sufficient to counterbalance the motor asymmetry. Measurements of glucose utilization by (14C)deoxyglucose autoradiography indicated equivalent metabolic rates for the grafted tissue and the intact substantia nigra. Overall the results indicate that behaviorally functional neuronal grafts spontaneously metabolize dopamine and utilize glucose at rates characteristic of the intact nigrostriatal system. This provides further evidence that ectopic intracortical nigral transplants can reinstate dopaminergic neurotransmission in regions of the host brain initially denervated by the 6-hydroxydopamine lesion.

Functional activity of substantia nigra grafts reinnervating the striatum: neurotransmitter metabolism and (14C)2-deoxy-D-glucose autoradiography. [Rats]

Improved graft survival and striatal reinnervation by microtransplantation of fetal nigral cell suspensions in the rat Parkinson model

Grafts of foetal ventral mesencephalon, used in cell replacement therapy for Parkinson’s disease, are known to contain a mix of dopamine neuronal subtypes including the A9 neurons of the substantia nigra and the A10 neurons of the ventral tegmental area. However, the relative importance of these subtypes for functional repair of the brain affected by Parkinson’s disease has not been studied thoroughly. Here, we report results from a series of grafting experiments where the anatomical and functional properties of grafts either selectively lacking in A9 neurons, or with a typical A9/A10 composition were compared. The results show that the A9 component of intrastriatal grafts is of critical importance for recovery in tests on motor performance, in a rodent model of Parkinson’s disease. Analysis at the histological level indicates that this is likely to be due to the unique ability of A9 neurons to innervate and functionally activate their target structure, the dorsolateral region of the host striatum. The findings highlight dopamine neuronal subtype composition as a potentially important parameter to monitor in order to understand the variable nature of functional outcome better in transplantation studies. Furthermore, the results have interesting implications for current efforts in this field to generate well-characterized and standardized preparations of transplantable dopamine neuronal progenitors from stem cells.

The A9 dopamine neuron component in grafts of ventral mesencephalon is an important determinant for recovery of motor function in a rat model of Parkinson's disease.

Girk2 expression in the ventral midbrain, cerebellum, and olfactory bulb and its relationship to the murine mutation weaver

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

Degeneration and graft-induced restoration of dopamine innervation in the weaver mouse neostriatum: a quantitative radioautographic study of [3H]dopamine uptake.

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

S. Seth

Author Tools

Chat about Author

Papers

Degeneration and graft-induced restoration of dopamine innervation in the weaver mouse neostriatum: a quantitative radioautographic study of [3H]dopamine uptake.