Studies on the striatal dopamine uptake system of weaver mutant mice and effects of ventral mesencephalic grafts

The dopamine (DA) uptake system was investigated in the mesostriatal system of normal and weaver mutant mice, which lose mesencephalic DA neurons, as well as in weaver mutants with ventral mesencephalic grafts to the striatum. Assays of [3H]DA uptake in striatal synaptosomal fractions in vitro and autoradiography of [3H]mazindol binding in brain sections were carried out in wild-type mice (+/+) and in the two hemispheres of homozygous weaver mutants (wv/wv) that had received unilateral grafts of mesencephalic cell suspensions to the right side. Net [3H]DA uptake, expressed as pmol/mg-protein/2-min, was on the average 50.6 in the striatum of wild-type mice, 7.9 in the non-grafted, and 10.1 in the transplanted striatum of weaver mutants. [3H]DA uptake in wild-type mice differed significantly from both the grafted and non-grafted weaver striata (P < 0.001). Paired comparisons for [3H]DA uptake between right and left sides of recipient weaver mice showed a significant side effect (P < 0.02), the right side being 28-38% higher than the left side [mean of all individual (R-L)/L values]. The results of amphetamine-induced turning behavior tests were compared with the biochemical findings. Mice with grafts to the right side rotated an average of 22 turns to the left and 7 turns to the right during the five one-minute sessions; the mean value L/(L + R) was 64%. A plot of (L-R) rotations against (R-L) [3H]DA uptake gave a correlation coefficient of 0.552 (P < 0.05), indicating that animals with a strong rotational bias to the left tended to have higher [3H]DA on the right. Similarly, the animals that were used for [3H]mazindol binding autoradiographic studies displayed on the average 72% rotations to the left side. In the [3H]mazindol binding data, non-grafted weaver mutants showed the severest depletion relative to wild-type in the dorsomedial and dorsolateral caudate-putamen (86% and 87%, respectively). Mice with unilateral grafts to the right side showed an increase in [3H]mazindol binding signal in the transplanted side of 40-64% (depending on dorsoventral topography) over the contralateral, non-grafted side. These findings attest to the functional effects of the grafts at the anatomical, biochemical, and behavioral levels. The parallel measurements of motor performance and DA uptake in the same animals offers an index of behavioral recovery as a function of transmitter-related activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Correlated quantitative studies of the neostriatum, nucleus accumbens, substantia nigra, and ventral tegmental area in normal and weaver mutant mice

Normal mice (+/+) and homozygous weaver mutant mice (wv/wv) at 1 year of age were used for three-dimensional computer-aided reconstructions of the nucleus accumbens (NA) and neostriatum (ST) and for quantitative estimations of the total number of medium-sized neurons in the NA and ST, and for the total number of tyrosine hydroxylase (TH)-containing neurons in the ventral tegmental area (VTA) and substantia nigra (SN). The three-dimensional reconstructions showed that the weaver NA and ST are smaller than they are in +/+. Quantitative volumetric measurements of the NA and ST showed wv/wv were smaller than +/+ by nonsignificant differences of 14% and 13%, respectively. The wv/wv group showed statistically significant depletion of neurons in all four structures. On average, NA neurons are reduced by 27%, ST neurons by 22%, VTA-TH neurons by 40%, and SN-TH neurons by 79%. In wv/wv animals, there was a high positive correlation (r = 0.836) between the numbers of SN-TH neurons and ST neurons and a moderate positive correlation (r = 0.534) between the numbers of SN-VTA neurons and NA neurons. The nuclei in TH-containing neurons in wv/wv and +/+ had the same diameters, but in all animals, the SN-TH neurons contained larger nuclei than the VTA-TH neurons. Cytoarchitectonic measurements in control and weaver NA and ST were also similar. In all animals, the NA contains more densely packed neurons with smaller nuclei than those in the ST.

cDNA approaches to isolation of the mouse mutant weaver gene

The mouse autosomal recessive mutant gene weaver (wv) results in abnormalities in cerebellum, substantia nigra and testis. Although a substracted cDNA library prepared by removing P31 (wv/wv) sequences from a P1 (wv/+) library should contain mainly nonrepetitive neonatal sequences, unfortunately, repetitive sequences still appear during screening. Two clones, one repetitive, the other not, are used to illustrate the problems encountered in attempting to isolate the weaver gene from a substrated cDNA library.

Molecular characterization of a novel cDNA from murine cerebellum, developmental expression, and distribution in brain

Several novel cDNA clones were previously identified by immunoscreening a cerebellar cDNA expression library derived from heterozygous weaver (wu/+) mice at postnatal day one (P1) with an antigranule cell antiserum. One cDNA, GCAP-8 (granule cell antiserum-positive clone 8) has been further characterized. The 1.1 kb insert is a partial cDNA containing a segment near the 3' end of the full-length cDNA. The 5' end of the GCAP-8 cDNA contains a 259 nucleotide open reading frame (ORF) coding for the last 85 amino acids of the carboxy terminus of the encoded protein. The encoded polypeptide contains two highly hydrophobic segments interrupted by a basic stretch. The carboxy terminus of this protein is cysteine-rich, with 10 cysteine residues among the 85 amino acids. The GCAP-8 cDNA probably represents a single-copy gene. The GCAP-8 gene, designated Gcap1, was mapped to the distal region of mouse chromosome 5 by the analyses of two multilocus crosses. The distribution of the GCAP-8 mRNA in mouse brain was studied by in situ hybridization histochemistry. In the adult mouse brain, strong hybridization was detected in cerebellum, hippocampus, substantia nigra (SN), and cerebral cortex. In mouse cerebellum, hybridization was detected in granule cells, Purkinje cells, and in cells of the deep cerebellar nuclei (DCN). In human cerebellum, hybridization was detected in the granule cell layer. In the mouse, GCAP-8 is expressed at least as early as embryonic day 14 (E14) in the central nervous system (CNS).

Novel cDNA clones obtained by antibody screening of a mouse cerebellar cDNA expression library

In order to obtain cDNAs of genes that are expressed in cerebellar granule cells (GC), an antiserum was raised against GC isolated from mouse cerebella. Western blot analysis demonstrated that antibodies against multiple proteins were present and immunohistochemical analysis showed that at least some of these proteins were localized to cerebellar GC. The antiserum was used to screen an expression library derived from mouse cerebellar cDNA. Twenty-two granule cell antibody-positive (GCAP) clones were obtained. Of these, eight represented genes previously described and 14 were novel clones (not found in the GenBank database). In situ hybridization histochemistry showed that eight of the novel clones had moderate to strong expression in cerebellar GC and some of these clones were expressed also in the hippocampal formation. One such clone, GCAP-7, appears to represent a single-copy gene and the entire cDNA insert (2,688 bp) has been sequenced. The clone appears to consist primarily of the 3' untranslated portion, including a poly(A) tail and polyadenylation signals, of a 5 kb transcript. The GCAP clones should be useful for future studies of molecular biology of GC in normal individuals and in inherited neurologic disease with GC degeneration.

Alterations in dopamine and serotonin uptake systems in the striatum of the weaver mutant mouse

In the striatum of the homozygous weaver mutant mouse (wv/wv), dopamine content, uptake and tyrosine hydroxylase activity are decreased compared to wild-type (+/+) mice. In mice heterozygous for the weaver gene (wv/+), these dopaminergic parameters exhibit only minor reductions compared to +/+ mice. The wv/wv striatum has recently been shown to have an increase in serotonin content. In the present study, the serotonin uptake system of the weaver striatum was investigated. Synaptosomal uptake of [3H] serotonin was determined in the dorsal portion of wv/wv and +/+ striatum, and serotonin uptake sites were examined by the binding of [3H] citalopram in the striatum of wv/wv, wv/+ and +/+ mice. The dopamine uptake system was also investigated in all three genotypes via the binding of [3H] mazindol. Synaptosomal uptake of [3H] serotonin was increased by 79% in the dorsal portion of the wv/wv striatum compared to that seen in the +/+ striatum. The binding of [3H] citalopram was increased by 62% in the dorsolateral and by 111% in the dorsomedial portions of the wv/wv striatum compared to +/+. [3H] Citalopram binding in the wv/+ striatum was also higher than +/+, but this increase did not reach statistical significance. Within the wv/wv striatum, [3H] mazindol binding was almost completely absent (88-89% reduction) in the dorsal portion and severely reduced in the other striatal areas. These data support the notion that the dorsal portion of the wv/wv striatum, which has the severest reduction in dopamine uptake, is hyperinnervated by serotonin fibers.

Regional distribution of amyloid beta-protein precursor, growth-associated phosphoprotein-43 and microtubule-associated protein 2 messenger RNAs in the nigrostriatal system of normal and Weaver mutant mice and effects of ventral mesencephalic grafts

Using in situ hybridization histochemistry with [32P]oligonucleotide probes, we studied the cellular localization of RNA transcripts for amyloid beta-protein precursor (beta APP), growth-associated phosphoprotein-43 (GAP-43) and microtubule-associated protein 2 (MAP2) in the mesostriatal system of normal (+/+) and weaver (wv/wv) mutant mice, which lose mesencephalic dopamine neurons. In addition, expression of the same messages was studied in ventral mesencephalic cell suspensions transplanted to the weaver striatum. Transcripts encoding GAP-43, MAP2 and isoforms beta APP695, beta APP714 and beta APP751 were present in normal substantia nigra and progressively reduced in weaver substantia nigra; such a reduction was correlated with dopamine neuron loss. The survival of dopamine neurons in unilateral intrastriatal grafts was documented by methamphetamine-induced rotational asymmetry tests and by tyrosine hydroxylase immunocytochemistry. High hybridization signals were obtained for GAP-43, MAP2, beta APP695, beta APP714 and beta APP751 RNA transcripts in the grafted tissue; the beta APP770 species--normally seen in striatum and not substantia nigra--was not expressed in the grafts, but it was present in the recipient striatum. Following immunocytochemical labelling with antibodies, GAP-43 and MAP2 immunoreactivities were seen in cell processes in the grafts and surrounding tissue, whereas beta APP immunoreactivity was mainly found in grafted cell bodies. These results suggest that the transplanted mesencephalic cells mature very similarly to those in the normal substantia nigra, expressing different mRNAs that are normally present in the ventral midbrain and which are reduced in the weaver mutant as a consequence of dopamine neuron loss.

Cellular distribution of the RNA transcripts of a newly discovered gene in the brain of normal, weaver, Purkinje cell degeneration and reeler mutant mice as evidenced by in situ hybridization histochemistry

After we identified several novel cDNAs by screening a neonatal (P1) heterozygous weaver (wv/+) cerebellar cDNA expression library with a rabbit anti-mouse granule cell antiserum, we characterized and sequenced one cDNA, GCAP-8 (standing for granule cell antiserum positive, clone number 8). In this study we examined its expression and cellular distribution in adult cerebellar mutant mice as evidenced by in situ hybridization histochemistry. In wild-type (+/+) brain, strong hybridization signal is seen in cerebellum, hippocampus, substantia nigra (SN), and cerebral cortex; in the cerebellum, hybridization signal is seen in granule cells, Purkinje cells, and in cells of the deep cerebellar nuclei. In the granuloprival weaver (wv/wv) cerebellum, hybridization signal is seen mainly in Purkinje cells. GCAP-8 expression is reduced in wv/wv SN pars compacta, which is known to lose dopamine (DA) neurons. In Purkinje cell degeneration (pcd/pcd) mutants, granule cells show hybridization signal, but overall expression is decreased owing to the absence of Purkinje cells. In reeler (rl/rl) cerebellum, the strongest hybridization signal is found in a thin granule cell layer without the typical foliation pattern, while grain clusters representing ectopic Purkinje cells are observed in the subcortical white matter and the area of the deep cerebellar nuclei. GCAP-8 expression in the reeler hippocampus and cerebral cortex shows a mixing of layers, which is known to be an aspect of the histological phenotype of this mutant.(ABSTRACT TRUNCATED AT 250 WORDS)

Serotonin content is elevated in the dopamine deficient striatum of the weaver mutant mouse

In the present study, we measured the striatal serotonin content of weaver and control mice at different ages. Overall, weaver mutant mice exhibited 50% more striatal serotonin than controls. Neither a rostrocaudal gradient nor an age effect was found for either genotype. An analysis of serotonin content across the dorsoventral extent of the striatum revealed that in the dorsal striatum of the weaver, serotonin content was increased 200%, and in the ventral striatum, the increase amounted to 50% relative to control mice. Serotonin immunocytochemistry also revealed an increase in the dorsal striata of weaver mice. The major increase in striatal serotonin content seen in the weaver striatum occurs in the same region that exhibits the severest dopamine depletion. This observation is consistent with the notion that the increase in serotonin levels may be secondary to the decrease in dopamine content and may play an adaptive or compensatory role.

Regional distribution of the alternatively spliced isoforms of beta APP RNA transcript in the brain of normal, heterozygous and homozygous weaver mutant mice as revealed by in situ hybridization histochemistry

The cellular localization of amyloid beta-protein precursor (beta APP) RNA transcripts was studied by in situ hybridization histochemistry in normal, heterozygous and homozygous weaver (wv) mutant mice, which lose midbrain dopamine (DA) neurons, cerebellar granule cells, and Purkinje cells. The beta APP gene is located at the distal end of mouse chromosome (MMU) 16, on which the wv locus has been assigned as well. Transcripts encoding isoforms beta APP695, beta APP714 and beta APP751 were present in several different brain areas of normal (+/+) mice, including hippocampus, substantia nigra (SN) pars compacta and cerebellum. The same transcripts were progressively reduced in homozygous weaver (wv/wv) SN, in correlation with DA neuron loss. The beta APP770 species--normally seen in striatum and not SN--was present in the mutant striatum. There were not any obvious changes in beta APP expression in the nigrostriatal system of weaver heterozygotes (wv/+). In normal cerebellum, Purkinje cells showed very high levels of hybridization signal for beta APP695, beta APP714 and beta APP751 RNA transcripts, and a moderate signal for the beta APP770 species. In weaver heterozygotes and homozygotes, Purkinje cells, which are typically not arranged in a monolayer, showed strong hybridization signal. No changes in beta APP mRNAs were observed in brain areas other than the cerebellum and ventral midbrain of weaver mutants. These findings suggest that the decreased beta APP gene expression seen in the cerebellum and SN of weaver mutants most likely represents an epiphenomenon of the regional nerve cell loss and, therefore, the wv gene defect on MMU 16 does not seem to influence the expression of the closely linked beta APP gene in brain areas outside the nigrostriatal pathway and cerebellar cortex.

Serotonin fiber innervation of cerebellar cell suspensions intraparenchymally grafted to the cerebellum of pcd mutant mice

One aspect of integration of implanted neurons into the neuronal circuitry of a defective host brain is the re-establishment of a host-to-graft afferent innervation. We addressed this issue by using the adult cerebellum of 'Purkinje cell degeneration' (pcd) mutant mice, which lack virtually all Purkinje cells after postnatal day (P) 45. Purkinje cells constitute one of the cerebellar cell types being innervated by axons of raphé serotonin (5-HT) neurons. In normal mice, 5-HT-immunoreactive fibers are distributed to all cerebellar folia. Following Purkinje cell loss in pcd mice, cerebellar 5-HT-immunoreactive fibers persist. Cerebellar cell suspensions were prepared from embryonic day (E) 11-13 normal mouse embryos and were intraparenchymally grafted into the cerebellum of pcd mutants either directly or after pre-treatment with 5,7-dihydroxytryptamine (5,7-DHT) to selectively remove 5-HT cells of donor origin. The state of Purkinje cells and 5-HT axons was monitored in alternate sections by 28-kDa Ca(2+)-binding protein (CaBP) and 5-HT immunocytochemistry, respectively. Serotonin-immunoreactive axons were seen in the grafts from 5 to 32 days after transplantation. In some of the grafts which had not been pre-treated with 5,7-DHT, a small number of 5-HT-immunoreactive cell bodies was found, indicating that part of the 5-HT fiber innervation of the graft could actually derive from donor cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Intraparenchymal grafting of cerebellar cell suspensions to the deep cerebellar nuclei of pcd mutant mice, with particular emphasis on re-establishment of a Purkinje cell cortico-nuclear projection

In transplanting embryonic cerebellar grafts to the cerebellar cortex of "Purkinje cell degeneration" (pcd) mutant mice to replace missing Purkinje cells (PC), donor PC leave the graft and migrate to the molecular layer of the host. However, PC axons do not always reach the deep cerebellar nuclei of the host, which would be a key element in restoring much of the necessary inhibitory cortico-nuclear projection associated with normal cerebellar function. Rather, grafted PC axons often innervate a region containing deep cerebellar nuclei neurons inside the transplant, while the perikaryon migrates to the host molecular layer. In the present study, aimed at re-establishing a PC innervation of the deep nuclei, we implanted E12 cerebellar cell suspensions intraparenchymally to the deep cerebellar mass of the hosts. The development of grafted PC was monitored with 28-kDa calcium-binding protein (CaBP) immunocytochemistry at various times after transplantation. At short survival times (5 days after grafting), grafts were confined to the site of the original injection. At longer survival times (7-32 days after grafting), grafted PC formed a migratory stream that reached the cerebellar cortex of the host. The most robust graft development was seen 1 month after grafting, the longest survival time allowed in this series of experiments. At that time, clusters of donor PC were found both in the deep nuclei parenchyma and aligned along cortical folia. The orientation of the dendritic trees of PC that had migrated to the cortex was toward the pia. A CaBP-immunoreactive fibre plexus innervated the host deep cerebellar nuclei. The stream of grafted PC extended from the deep cerebellar nuclei to the cerebellar cortex of the host, indicating that donor PC could establish their axonal contacts in the deep nuclei and then move to their final cortical locality, thus recapitulating a migratory path normally taken during cerebellar ontogeny. It appears therefore that both from the pathophysiological and ontogenetic standpoints, the deep cerebellar nuclei represent the appropriate site for PC implantation in cerebellocortical atrophy.

Serotonin-immunoreactivity in the cerebellum of two neurological mutant mice and the corresponding wild-type genetic stocks

Using a serotonin (5-HT)-specific antibody, we examined the 5-HTergic innervation of the cerebellum in the normal mouse (+/+) and in two neurological mutants: weaver (wv/wv), which are characterized by a genetically determined loss of granule cells, and 'Purkinje cell degeneration' (pcd/pcd), which are characterized by a genetically determined loss of Purkinje cells. In normal cerebellum, serotonin-immunoreactive (5-HT-ir) fibers are discrete and ascend to all three layers of the cerebellar cortex. Serotonin-immunoreactive fibers have a much higher density in the atrophic cerebella of both weaver and pcd mutants, where they form multidirectional contours. These anatomical findings provide a profile of 5-HT axon innervation of mouse cerebellum and extend previous neurochemical observations on the metabolic state of cerebellar 5-HT in neurological mutants.

Stabilisation of neurone number in the inferior olivary complex of aged 'Purkinje cell degeneration' mutant mice

Virtually all cerebellar Purkinje cells degenerate in 'Purkinje cell degeneration' (pcd) mutant mice between postnatal day (P) 17 and P45. The inferior olivary complex (IOC) in these mutants undergoes atrophy subsequent to the deprivation of its major cortical target; the number of IOC neurones declines by 18% by P23 and by 49% by P300. In the present study we used control (+/?) and mutant (pcd/pcd) mice that were 14-15 months old to determine whether any further cell loss is observed in the pcd IOC after P300. Nerve cell counts were obtained from serial paraffin sections of the medulla oblongata. The corrected estimate of neurone number in the left IOC of control mice was 12,785 +/- 794 cells (mean +/- SD, n = 5); in pcd mutants that number was 6,722 +/- 535 (n = 5). The 47% difference between control and mutant mice was highly significant (p less than 0.001). The perikarya of surviving IOC neurones were atrophic. Compared to P17 mutants, pcd homozygotes manifest a 50% cell loss by P428-P446, which does not practically differ from the deficit found on P300. These results suggest that, once a critical neuronal mass degenerates in the IOC of pcd mutants, the remaining neurones become stabilised and no further loss is observed even at an advanced age.(ABSTRACT TRUNCATED AT 250 WORDS)

Unique cerebellar phenotype combining granule and Purkinje cell loss: morphological evidence for weaver* pcd double mutant mice

Weaver (wv/wv) mutant mice lose most granule cells of the cerebellum during the first 2 weeks of postnatal life; 'Purkinje cell degeneration' (pcd/pcd) mutants lose virtually all Purkinje cells between postnatal days 17 and 45. Both these neurological mutations are autosomal recessive. We designed a breeding protocol that, in theory, should result in the production of mice with a doubly mutant, wv/wv*pcd/pcd, genotype. Some of the offspring of such crosses had a novel cerebellar phenotype in which both granule and Purkinje cells underwent degeneration, leading to a highly atrophic cortex. This phenotype is what would be expected in wv/wv*pcd/pcd double mutants, and the proportion of such progeny obtained fits with genetic expectations. We propose that (1) wv/wv*pcd/pcd double mutant mice are viable, and (2) the anatomical phenotype of such mice is a combined expression of the component phenotypes.

Age-related changes in striatal dopamine D2 receptor binding in weaver mice and effects of ventral mesencephalic grafts

Dopamine (DA) D2 receptor binding is increased in the striatum of 5-6 months old weaver mutant mice (Kaseda et al. 1987). This may occur in response to the loss of DA neurons in the midbrain and the decrease in DA content in the striatum of homozygous mutants. One purpose of the present study was to determine if the diminished DA innervation is associated with changes in D2 receptors at earlier ages and if the increase in DA D2 receptor binding seen at 5-6 months is a lasting phenomenon. Specific [3H]spiperone binding was measured in the dorsolateral (DL), dorsomedial (DM) and ventrolateral (VL) striatum and in the nucleus accumbens (AC) of homozygous weaver mutant mice (wv/wv), heterozygous littermates (wv/+) and wild-type controls (+/+). Mice were studied at 20 days and 1, 3, 6, 9 and 12 months of age. The difference in specific [3H]spiperone binding in DL striatum between wv/wv and +/+ mice was significantly greater at 6 months than the difference at 1 month and at 12 months of age. Foetal ventral mesencephalic grafts survive and establish functional innervation in the striatum of weaver mice as shown by the induction of a contralateral turning bias (Low et al. 1987). The second aim of the present studies was to determine if such grafts would also reverse the increase in DA D2 receptor binding in the striatum. Aspiration cavities were prepared in the cortex of weaver mice, and ventral mesencephalic tissue from E14-E15 +/+ foetuses was subsequently placed on the surface of the right dorsal striatum when the recipients were 3 months old.(ABSTRACT TRUNCATED AT 250 WORDS)

Intrastriatal implants of mesencephalic cell suspensions in weaver mutant mice: ultrastructural relationships of dopaminergic dendrites and axons issued from the graft

Dissociated cell suspensions were prepared from the ventral midbrain of normal mouse foetuses and stereotaxically implanted into the neostriatum of 2-3 months old homozygous weaver mutant mice, which are severely deficient in dopamine. In tests of amphetamine-induced turning behaviour 60 days after grafting, recipient animals displayed a rotational bias opposite to the grafted side. Prior to perfusion, which was carried out at 80 days after transplantation surgery, the grafted striata of the weaver recipients were deprived of their intrinsic mesostriatal dopamine input by local injections of 6-hydroxydopamine into the ipsilateral substantia nigra in order to selectively study the innervation derived from the graft. Grafts were found to contain an estimated 100-700 tyrosine hydroxylase immunoreactive neurones. An ultrastructural analysis demonstrated that both axons and dendrites immunoreactive for tyrosine hydroxylase extended from the graft into the recipient striatum. In the host striatum proximal to the graft (i.e. at a distance of 0.0-0.5 mm from the graft) the proportion of dendrites to axons was about 1:2, whereas distal to the graft (i.e. at a distance of 0.5-1.0 mm) it was 1:20. Graft-derived tyrosine hydroxylase immunoreactive axons were primarily found in apposition with unlabelled dendrites or spines of the recipient striatum (greater than 90%). Graft-derived dopaminergic dendrites received synaptic input from unlabelled axon terminals and were opposed to the unlabelled somata of striatal neurones in a few instances. In conclusion, this study shows that mesencephalic cell suspensions survive in the weaver striatum and provide a functional dopamine innervation which comprises both axonal and dendritic processes.

The dendritic dopamine projection of the substantia nigra: phenotypic denominator of weaver gene action in hetero- and homozygosity

While cerebellar granule cell migration and survival are affected by the weaver (wv) mutation both in the heterozygous and homozygous states, the dopamine (DA) deficit of the nigrostriatal projection has been shown to involve only midbrain DA cell bodies and nigrostriatal DA axons of homozygous mutants. We have identified a cellular site which is defective in the mesencephalic DA system of mice both heterozygous and homozygous for the wv gene. That deficit involves the dendritic DA projection which extends from the substantia nigra pars compacta (SNc) into the pars reticulata (SNr). In the midbrain of heterozygotes, dopaminergic dendrites are reduced by 60% at 20 days of age, when DA neurone number in the midbrain, DA content in the neostriatum and pattern of synaptic connectivity of nigrostriatal axon terminals are normal. At the same age, the deficit of dopaminergic dendrites in the SNr of homozygotes (76%) is disproportionate to the loss of DA cell bodies (42%). These findings: (a) may provide clues to the aetiopathogenetic mechanisms of wv gene operation; and (b) may explain the generalised convulsions intermittently manifested by weaver heterozygotes, as the SN has been implicated in the pathophysiology of experimental seizures.

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

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 resinembedded slices were subsequently exposed on tritium sensitive film and afterwards dipped in nuclear emulsion for light microscope radioautography. Alternative 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 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.(ABSTRACT TRUNCATED AT 400 WORDS)

Developmental expression of polypeptide PEP-19 in cerebellar cell suspensions transplanted into the cerebellum of pcd mutant mice

Cerebellar cell suspensions were prepared from normal mouse embryos and implanted into the cerebellum of Purkinje cell degeneration (pcd) mutant mice, which are characterized by a virtually complete degeneration of Purkinje cells between postnatal day (P) 17 and P45. The expression of immunoreactivity for PEP-19, a developmentally-regulated brain-specific polypeptide, was analyzed in normal mouse cerebellum, as well as in pcd mutants with or without grafts. In the normal cerebellum, PEP-19 immunoreactivity was present in Purkinje cells. In unoperated mutants, 45 days of age or older, Purkinje cells were absent. In grafted pcd mice, numerous PEP-19 immunoreactive, neuroblast-like cells were seen in the graft at 5 days after transplantation. By 9 days, large PEP-19 immunoreactive neurons were found in the host molecular layer; by 17 days after transplantation, such neurons displayed an extensive dendritic tree and resembled differentiated Purkinje cells. The vast majority of PEP-19 immunoreactive cells was located in the molecular layer of the host at 9 days after transplantation and beyond; nonetheless, the same cells extended axonal processes toward the graft, indicating an affinity for co-grafted (possibly deep nuclei) neurons. These results point to the ability of donor Purkinje cells for survival, migration into the host brain and morphological and chemical differentiation following transplantation to the degenerated cerebellar cortex of the recipient mutants.

Layer-specific innervation of the dopamine-deficient frontal cortex in weaver mutant mice by grafted mesencephalic dopaminergic neurones

The dopamine innervation of the frontal cortex originates in the A9 and A10 mesencephalic dopamine cell groups. In weaver mutant mice, there is a 77% frontocortical dopamine deficiency associated with losses of dopamine neurones in areas A9 and A10. The dopamine-depleted cortical areas of weaver mutant mice are receptive to reinnervation by afferent fibres originating in dopamine-containing mesencephalic grafts from normal donor embryos. In the anteromedial frontal lobe, reinnervation by tyrosine hydroxylase immunoreactive fibres is largely confined to the basal cortical layers whereas in the anterior cingulate cortex, tyrosine hydroxylase immunoreactive fibres also occupy superficial layers, including the molecular layer. Normally, the dopaminergic innervation of the anteromedial frontal lobe is distributed among the basal cortical layers (IV-VI), and the dopaminergic innervation of the cingulate cortex occupies both basal and superficial cortical layers. The pattern of innervation following transplantation indicates that, in repopulating dopamine-deficient cortical areas of recipient weaver mutants, graft-derived dopamine fibres show a preference for those layers which are normally invested by dopamine afferents.

Reinstatement of synaptic connectivity in the striatum of weaver mutant mice following transplantation of ventral mesencephalic anlagen

Ventral mesencephalic anlagen survive following grafting to the striatum of weaver mutant mice and reinnervate the dopamine-depleted basal ganglia of the recipients. The aim of the present study was to examine the pattern of connectivity established by graft-deriving dopamine afferents in the host striatum. Grafts were obtained from normal embryos at a gestational age of 14-15 days and implanted into a surgical cavity overlying the dorsal striatum of adult weaver recipients. Tissue was processed for electron microscopic immunocytochemistry using a primary antiserum against tyrosine hydroxylase. At the time of examination, recipient weaver mutants were 8.5 months old and the grafts had survived for 4.5 months. Grafts were found to contain an estimated 100-1000 tyrosine hydroxylase immunoreactive neurons. Tyrosine hydroxylase immunoreactive fibres, displaying characteristic varicosities, innervated the dorsal striatum to a depth of 1000 micron. In the non-grafted striatum, 8% of the contacts of tyrosine hydroxylase immunoreactive nerve terminals were junctional. That proportion contrasted with the corresponding value of normal animals, which is 27%. In the grafted striatum, 29% of the contacts were junctional. That percentage approximated the value found in normal animals. By applying a stereological correction, it can be estimated from those numbers that the true proportion of junctional contacts in the non-grafted striatum of 8.5-month-old mutants may be 26%, whereas that in the grafted side may be 91%, which is close to the normal situation. The majority of contacts in the reinnervated striatum (84%) were made with dendrites and spines. However, the proportion of total axosomatic contacts in the reinnervated striatum was twice as high as that found in the striatum of normal animals, and the proportion of junctional synapses was three times higher than that found normally. We conclude that: (1) in spite of a genetically determined degenerative process, the dorsal neostriatum of weaver mutant mice is receptive to synaptic investment by dopamine afferents originating in normal donor tissue. (2) In repopulating the denervated weaver striatum, graft-deriving dopamine afferents display a connectional selectivity, i.e. they establish synaptic relations preferentially with those cellular domains that are normally innervated by dopamine nerve terminals. In this context, it is possible that dopamine fibres originating in the grafts invest postsynaptic sites that had either been vacated from the intrinsic dopamine input or had never received such an input. (3) The striatal connectivity following transplantation may retain features of immaturity as suggested by t