Grafted cerebellar cells in a mouse model of hereditary ataxia express IGF-I system genes and partially restore behavioral function.

Fetal grafts of normal cerebellar tissue were implanted into the cerebellum of Purkinje cell degeneration mutant mice (pcd/pcd), a model of adult-onset recessively inherited cerebello-olivary atrophy, in an attempt at correcting their cellular and motor impairment. Donor cerebellar cells engrafted in the appropriate sites, as evidenced by the pattern of expression of insulin-like growth factor-I (IGF-I) system genes. Bilateral cerebellar grafts led to an improvement of motor behaviors in balance rod tests and in the open field, providing evidence for functional integration into the atrophic mouse cerebellum and underscoring the potential of neural transplantation for counteracting the human cerebellar ataxias.

Nerve cell atrophy and loss in the inferior olivary complex of "Purkinje cell degeneration" mutant mice.

The genetically determined loss of cerebellar Purkinje cells (PCs) in "Purkinje cell degeneration" (pcd) mutant mice deprives inferior olivary (IO) neurons of their major postsynaptic target. The degeneration of PCs starts on postnatal day (P) 17 and loss of these neurons is virtually complete by P45. We examined the inferior olivary complex (IOC) of normal and pcd mutant mice by quantitative light microscopy to determine whether the degeneration of PCs is associated with atrophy and loss of their presynaptic neurons in the IOC. The number of IO neurons in 17-day-old mutants did not differ significantly from controls (P greater than .1). IO neurons in 23-day-old mutants were 23% (95% confidence limits: 12-34%) fewer than in age-matched controls, and in 300-day-old mutants they were 48% (95% confidence limits: 37-58%) fewer than in their controls (P less than .001 in both cases). The decline of the number of IO neurons in pcd mice between days 17 and 300 was 49% (P less than .0001; 95% confidence limits: 38-57%). The medial accessory olive (MAO) appeared less affected than the principal (PO) and the dorsal accessory olive (DAO). The mean neuronal diameter in control mice was 11.6 micron at 23 days and 10.8 micron at 300 days of age. The respective values in pcd mutants were 11.5 micron and 8.7 micron. Diameters in old mutants were significantly smaller than those in both age-matched controls and young mutants (P less than .001). These findings suggest that in the mature olivocerebellar system the stability of IO neurons depends on the state of their postsynaptic PCs.

Freud's contribution to neuroanatomy.

Sigmund Freud, the acknowledged father of psychoanalysis, started his scientific career as a very promising neurohistologist. This report gives an overview of his early neuroanatomic articles and pioneering contributions to 19th-century neurologic science.

The effect of dexamethasone on L-alpha-lysophosphatidyl choline (lysolecithin)-induced demyelination of the rat spinal cord.

Adult male Sprague-Dawley rats were injected intraspinally with 2 microL of 1% lysolecithin to induce demyelination. This was followed by systemic treatment with dexamethasone acetate for two weeks. Control groups were injected with lysolecithin but not treated. The animals were perfused at 8, 12, 28, and 60 days postoperatively, and the spinal cords were processed and examined histopathologically. The intraspinal injection of lysolecithin produced a focal area of primary demyelination followed by remyelination. In the steroid-treated groups, there was a suppression of the mononuclear phagocytic response, accompanied by slow clearance of the disrupted myelin sheaths and an apparent reduction in lesion size. Remyelination was substantially retarded in comparison with the controls. The findings suggest that steroids interfere with the process of remyelination, as they are known to do with myelination during development. Thus, dexamethasone appears to have a dual effect, decreasing demyelination but delaying remyelination.

Monoaminergic nerve terminals in the cerebellar cortex of Purkinje cell degeneration mutant mice: fine structural integrity and modification of cellular environs following loss of Purkinje and granule cells.

The cerebellar cortex of normal and Purkinje cell degeneration mutant mice was examined by electron microscopy after fixation with potassium permanganate for the demonstration of small granular vesicles in monoaminergic nerve terminals. In control mice, monoaminergic terminals were found mainly in apposition to Purkinje cell dendrites. After the degeneration of Purkinje cells, which constitute the major target for monoaminergic fibres in the cerebellum, monoaminergic terminals persisted in the cerebellar cortex of Purkinje cell degeneration mutant mice. They were ensheathed by astroglial processes in most of the instances. They were also apposed to boutons that contained agranular vesicles, and to stellate cells in the molecular layer. Clear synaptic specializations in the form of thickening of the synaptic membranes were not observed in either control or mutant mice. It is hypothesized that the survival of monoaminergic axons following loss of their target cells may be attributed to the lack of intimate adhesion to their target elements, to a possible functional interaction with the glia, or to the integrity of the extracerebellar terminal fields of the monoamine axon collaterals.

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.

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)

Altered IGFBP5 gene expression in the cerebellar external germinal layer of weaver mutant mice.

The IGF system components play important roles in cerebellar development as demonstrated by their specific spatial-temporal expression. IGF-I, type I IGF receptor (IGFR-I), IGFBP2 and IGFBP5 mRNA are localized in distinct cell populations, and all are expressed at the highest levels at the peak of Purkinje cell growth, active synaptogenesis and dendritic formation. To understand IGF-I's action at the cellular level, in situ hybridization was employed to investigate the distribution of IGF system gene transcripts in the cerebellum of weaver mutant mice (wv/wv). Although located ectopically, the surviving Purkinje cells express IGF-I mRNA at the same level in wv/wv as in +/+. No alteration in the cellular distribution or mRNA levels was observed with IGFBP2, or IGFR-I mRNAs. However, the pattern of IGFBP5 expression is altered in the external germinal layer of wv/wv mice. Not only is IGFBP5 expressed by more granule cell precursors of wv/wv cerebellum, but its mRNA level is 2.3 fold that of +/+. The altered IGFBP5 gene expression in granule cell precursors may modulate the interaction of IGF-I with IGFR-I in ways that contribute to their massive death occurring in the development of wv/wv cerebellum.

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.

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).

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.

Graft-induced restoration of function in hereditary cerebellar ataxia.

Fetal cerebellar cell suspensions, prepared from wild-type (+/+) mice, were implanted bilaterally into the cerebellum of Purkinje cell degeneration' (pcd) mutant mice, a model of adult-onset recessively inherited cerebellar ataxia, to study the functional effects of the grafts on motor coordination and fatigue resistance in a rotating rod treadmill paradigm. The viability of transplanted Purkinje cells was verified with immunocytochemistry for calbindin-D28k and for glutamate receptor 2/3 subunits and with in situ hybridisation histochemistry for insulin-like growth factor I mRNA, biochemical markers normally expressed by Purkinje cells in the cerebellum. Sham injections of vehicle did not appreciably modify the performance of pcd mutants in the rota-rod tests. On the other hand, bilateral cerebellar grafts led to a 3.5-fold increase in the time period that recipient pcd mice were able to stay on the rotating drum based on the comparison of mean scores (of three trials) or a 5.5-fold increase based on the comparison of maximum scores (of the three trials). These findings provide evidence for a motor enhancement in the pcd mouse model of hereditary cerebellar ataxia following intracerebellar transplantation of primordial Purkinje cells.

Transplantation of mesencephalic cell suspensions from wild-type and heterozygous Weaver mice into the denervated striatum: assessing the role of graft-derived dopaminergic dendrites in the recovery of function.

The Weaver (wv) mutation leads to a loss of mesencephalic dopamine cells and nigrostriatal dopamine axons in homozygosity (wv/wv) and to a deficiency of nigral dopaminergic dendrites without a concomitant loss of dopamine cell somata or axons in heterozygosity (wv/+). Previous studies have shown that grafts of foetal dopamine cells from wild-type (+/+) donors can survive when implanted into the wv/wv striatum, supply both an axonal and a dendritic innervation to the host, establish synaptic connections with host striatal neurons, and bring about a functional recovery evidenced by rotational asymmetry tests. The aims of the present study were to examine whether wv/+ dopamine cells maintain a "dendrite-poor" phenotype after transplantation to the denervated striatum, and to compare their functional effects with those of wild-type (+/+) grafts in reversing amphetamine-induced turning behaviour. To that end, +/+ and wv/+ ventral mesencephalic tissue (dissected out from E10-E12 foetal mice and made into a cell suspension by enzymatic and mechanical dissociation) was stereotactically grafted into the right striatum of either wv/wv hosts or +/+ hosts subjected in advance to 6-OHDA lesions of the right substantia nigra. Viability and morphology of grafted neurons were assessed by tyrosine hydroxylase immunocytochemistry on serial sections of the host forebrains. Dopamine cell bodies survived in comparable numbers in the grafts regardless of donor genotype; however, grafts of either genotype contained fewer dopaminergic cells when they were hosted in the wv/wv striatum as compared to the striatum of +/+ mice with 6-OHDA lesions. Despite the survival of cell somata, the dendritic arborisation of wv/+ cells was strikingly poorer than that of +/+ cells in grafts placed into both host types, most likely reflecting their in situ phenotypic abnormality. Recipient wv/wv mice with +/+ and wv/+ grafts exhibited 88% and 83% left rotations, respectively; 6-OHDA hosts with +/+ and wv/+ grafts showed 178% and 165% reversals of asymmetry, respectively. The differences between the effects of +/+ and wv/+ grafts were not statistically significant.(ABSTRACT TRUNCATED AT 400 WORDS)

Amelioration of the behavioral phenotype in genetically ataxic mice through bilateral intracerebellar grafting of fetal Purkinje cells.

We have previously applied neural grafting to "Purkinje cell degeneration" mutant mice (gene symbol pcd, mouse chromosome 13), a model of recessively inherited cerebello-olivary atrophy, to create appropriate interactions between wild-type and mutant cells in elucidating gene effects on the involved neuron populations and to address issues of the structural integration of donor Purkinje cells into the disrupted cerebellar loop. Behaviorally, pcd homozygotes manifest ataxic signs beginning at 3-4 wk of age. The functional effects of cerebellar transplants on motor performance have long remained an open question. The aim of the present study was to determine the recovery of motor responses in pcd mutants in a battery of behavioral tasks after bilateral transplantation of cerebellar cell suspensions (prepared from wild-type mice) into the parenchyma of the deep cerebellar nuclei of the hosts, according to a protocol that emphasizes the reconstruction of the missing inhibitory cortico-nuclear projection. With this approach, the denervated deep nuclei of the host receive a new Purkinje axonal innervation; further, most transplanted Purkinje cells end up occupying cortical localities anyway and display a correct dendritic tree orientation toward the pia. Motor coordination and fatigue resistance were assessed in a rotarod treadmill apparatus, a behavioral paradigm useful in studying various brain abiotrophies and treatments, including developmental perturbations of the cerebellar cytoarchitecture. Locomotor activity was quantified by the number of squares mice crossed as they moved about in an open-field matrix. Grafted pcd mice performed significantly better than sham-operated mutants in both of these tasks. Moreover, graft-recipient mice were able to sustain their abdomen above the floor on their limbs during movement, contrasting to the typical lowered, widened stance of sham-operated pcd mutants. These findings clearly demonstrate that bilateral transplants of fetal Purkinje cells have functional effects on motor performance in the pcd model of hereditary cerebellar ataxia.

Cerebellar grafts partially reverse amino acid receptor changes observed in the cerebellum of mice with hereditary ataxia: quantitative autoradiographic studies.

We used quantitative autoradiography of [3H]CNQX (200 nM), [3H]muscimol (13 nM), and [3H]flunitrazepam (10 nM) binding to study the distribution of non-NMDA and GABA(A) receptors in the cerebellum of pcd mutant mice with unilateral cerebellar grafts. Nonspecific binding was determined by incubation with 1 mM Glu, 200 microM GABA, or 1 microM clonazepam, respectively. Saturation parameters were defined in wild-type and mutant cerebella. In mutants, non-NMDA receptors were reduced by 38% in the molecular layer and by 47% in the granule cell layer. The reduction of non-NMDA receptors in the pcd cerebellar cortex supports their localization on Purkinje cells. [3H]CNQX binding sites were visualized at higher density in grafts that had migrated to the cerebellar cortex of the hosts (4.1 and 11.0 pmol/mg protein, respectively, at 23 and 37 days after grafting) than in grafts arrested intraparenchymally (2.6 and 6.2 pmol/mg protein, respectively, at 23 and 37 days after grafting). The pattern of expression of non-NMDA receptors in cortical vs. parenchymal grafts suggests a possible regulation of their levels by transacting elements from host parallel fibers. GABA(A) binding levels in the grafts for both ligands used were similar to normal molecular layer. Binding was increased in the deep cerebellar nuclei of pcd mutants: the increase in [3H]muscimol binding over normal was 215% and the increase in [3H]flunitrazepam binding was 89%. Such increases in the pcd deep cerebellar nuclei may reflect a denervation-induced supersensitivity subsequent to the loss of Purkinje axon terminal innervation. In the deep nuclei of pcd mutants with unilateral cerebellar grafts, [3H]muscimol binding was 31% lower in the grafted side than in the contralateral nongrafted side at 37 days after transplantation; [3H]flunitrazepam binding was also lower in the grafted side by 15% compared to the nongrafted side. Such changes in GABA(A) receptors suggest a significant, albeit partial, normalizing trend of cerebellar grafts on the state of postsynaptic supersensitive receptors in the host cerebellar nuclei.

Ventral mesencephalic grafts in the neostriatum of the weaver mutant mouse: structural molecule and receptor studies.

Mesencephalic cell suspensions were prepared from E12 wild-type (+/+) mouse embryos and stereotaxically implanted into the dorsal neostriatum of weaver mutant mice (wv/wv), which have a genetic mesostriatal dopamine (DA) deficiency. Survival of DA neurons in the grafts was documented by tyrosine hydroxylase (TH) immunocytochemistry. Axon growth was monitored by immunocytochemistry using a battery of antibody markers, and the cellular localization of structural protein and receptor RNA transcripts was studied by in situ hybridization histochemistry using [32P]oligonucleotide probes. The cell suspension grafts exhibited strong immunoreactivity for neural cell adhesion molecule (N-CAM), growth-associated phosphoprotein GAP-43, microtubule-associated protein 2 (MAP2), beta-amyloid protein precursor (beta APP), and phosphorylated neurofilament epitopes (clone SMI-31); intermediate-to-high levels of immunoreactivity were seen for synaptophysin. High levels of hybridization were found in the grafts for the RNA transcripts of GAP-43, MAP2, and isoforms beta APP695, beta APP714 and beta APP751 of the beta APP. No hybridization signal was detected in the grafts for DA D2 or neurotensin receptor mRNAs, both of which are normally expressed by nigral DA neurons. DA receptor autoradiography using the D2/D3 agonist [3H]CV 205-502 as a ligand showed no binding in the transplants, indicating an apparent abnormality of grafted cells; neurotensin binding sites, labeled with [125I]neurotensin, were visualized in the suspensions, indicating the possibility that receptors could be present but that RNA message levels might be too low to allow detection. These findings offer a molecular correlate of axonal, dendritic and structural protein expression by transplanted mesencephalic neurons; further, they suggest that specific functional properties of grafted nigral cells are maintained after transplantation, while other aspects of their cellular biology may be compromised.

[3H]CNQX and NMDA-sensitive [3H]glutamate binding sites and AMPA receptor subunit RNA transcripts in the striatum of normal and weaver mutant mice and effects of ventral mesencephalic grafts.

Levels of excitatory amino acid receptors were studied in the weaver mouse model of DA deficiency after unilateral intrastriatal transplantation of E12+/+ mesencephalic cell suspensions. Graft integration was verified by turning behavior tests and from the topographical levels of the DA transporter, tagged autoradiographically with 3 nM [3H]GBR 12935 (average increase in grafted dorsal striatum compared to nongrafted side, 60%). Autoradiography of 80 nM [3H]CNQX and 100 nM NMDA-sensitive [3H]glutamate binding was carried out to visualize the topography of non-NMDA and NMDA receptors, respectively, in +/+ mice and in recipient weaver mutants 3 months after grafting. Increases of 30% or more were found for [3H]CNQX binding in the dorsal nongrafted weaver striatum compared to +/+, and a further 6-9% increase in grafted weaver compared to nongrafted side. The added increase of non-NMDA receptors in the transplanted striatum might be explained by a presence of such receptors on DA presynaptic endings of graft origin. A 20% increase in NMDA-sensitive [3H]glutamate binding was measured in the dorsal nongrafted weaver striatum compared to +/+. NMDA-sensitive [3H]glutamate binding in the transplanted side of weaver mutants tended to be slightly higher in all areas of the striatal complex compared to the nongrafted side, without reaching conventional levels of statistical significance. Using in situ hybridization histochemistry with synthetic 32p labeled oligonucleotide probes, we investigated RNA transcripts encoding the four AMPA receptor subunits. RNA transcripts in the striatum are seen with a decreasing signal intensity in the following order: GluRB > GluRA > GluRC > GluRD. The weaver caudate-putamen shows a 12% increase in GluRA subunit mRNA compared to +/+, whereas mesencephalic neuron transplantation leads to slight increases (3%) in the levels of GluRB mRNA in the nucleus accumbens. The results are placed in the context of the important interaction between the converging glutamatergic corticostriatal and the DAergic nigrostriatal pathways in controlling the functional output of the basal ganglia in Parkinson's disease and in experimental models of DA deficiency.

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.

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.