Glutamate dehydrogenase in cerebellar mutant mice: gene localization and enzyme activity in different tissues

Spontaneous and induced mouse mutations with cerebellar dysfunctions: behavior and neurochemistry

Grid2(Lc) (Lurcher), Grid2(ho) (hot-foot), Rora(sg) (staggerer), nr (nervous), Agtpbp1(pcd) (Purkinje cell degeneration), Reln(rl) (reeler), and Girk2(Wv) (Weaver) are spontaneous mutations with cerebellar atrophy, ataxia, and deficits in motor coordination tasks requiring balance and equilibrium. In addition to these signs, the Dst(dt) (dystonia musculorum) spinocerebellar mutant displays dystonic postures and crawling. More recently, transgenic models with human spinocerebellar ataxia mutations and alterations in calcium homeostasis have been shown to exhibit cerebellar anomalies and motor coordination deficits. We describe neurochemical characteristics of these mutants with respect to regional brain metabolism as well as amino acid and biogenic amine concentrations, uptake sites, and receptors.

Regional brain variations of cytochrome oxidase activity inRelnrl-orl mutant mice

Cell malpositioning has been described in laminated structures of the spontaneous mutation, reeler, including the cerebellum, the hippocampus, and the neocortex. Despite the ectopic positions of different neuronal populations, the specificity of synaptic connections is maintained. The metabolic consequences of this form of neuropathology were examined in Reln(rl) mutant mice by quantitative measures of cytochrome oxidase (CO) activity, a mitochondrial enzyme essential for oxidative metabolism in neurons. Despite severe tissue disorganization but in line with the intact synaptic organization, the reeler mutation did not affect global metabolic activity of the laminated structures of the brain. CO activity, however, was altered in specific subregions of the cerebellum, hippocampus, and neocortex, as well as in septum and various brainstem (medial pontine, paramedial reticular, paragigantocellular reticular) regions anatomically related to these structures, attesting to large functional alterations in Reln(rl-orl) brain. Metabolic activity variations were also detected in the ventral tegmental area and ventral neostriatum of the mesolimbic dopaminergic pathway. The results are discussed and compared to the regional CO variations found in other ataxic mice, in regard to the structural defects, the integrity of the connections, and the mutation-specific effects.

Autoradiography of glutamate receptor binding in adult Lurcher mutant mice

The mutation Lurcher, resulting from a gain of malfunction of the delta2 glutamate receptor expressed specifically by cerebellar Purkinje cells, causes a primary total loss of these neurons of the cerebellar cortex, as well as the secondary degeneration of cerebellar granule and inferior olive neurons. The distributions of glutamate receptors sensitive to amino-methylisoxazole-propionic acid (AMPA), to kainic acid (KA), and to N-methyl-D-aspartic acid (NMDA) as well as metabotropic sites (MET1 and MET2) were examined in wild type and Lurcher mice by quantitative autoradiography. This study was undertaken to determine the gene effect on the distribution of the various glutamate receptor subtypes, as well as how the cerebellar lesion affects the glutamatergic system in other brain regions. In cerebellum, there were postsynaptic AMPA and metabotropic receptors on Purkinje cells, postsynaptic NMDA receptors on granule cells, as well as KA receptors on granule cells or on parallel fibers. Taking into account surface areas, binding to all receptor subtypes was lower in the cerebellar cortex of Lurcher mutants than in wild type mice, while in the deep cerebellar nuclei only KA receptors were diminished. In other brain regions, the alterations followed always the same pattern characterized by a decrease of NMDA and KA receptors but with an increase of AMPA sites; these reciprocal changes were seen in thalamus. neostriatum, limbic regions, and motor cerebral cortical regions. Comparisons of glutamate receptor distribution in Lurcher mutants and in human autosomal cerebellar ataxia may permit further understanding of the role of glutamate-induced toxicity on neuronal death in these heredo-degenerative diseases.

Visuospatial abilities

The importance of the hippocampus and its anatomical connections, including the medial septum, thalamic nuclei, and neocortical regions in many spatial tasks including the Morris water maze, has been emphasized. Studies in mutant mice with cerebellar atrophy and in rats with electrolytic lesions of the cerebellum have indicated that the cerebellum has a role in visuospatial and visuomotor processes in the Morris maze. Directional deficits in the water have also been noted in rats whose cerebellum was exposed to X-rays during different developmental stages. Cerebellar interactions with the superior colliculus, the hippocampus, and the neocortex via thalamic nuclei are suggested to be the basis of the cerebellar modulation of directional sense in maze tests.

Haloperidol reduces K(+)-evoked Ca(2+)-dependent D-[3H]aspartate release from rat hippocampal slices

Rat hippocampal slices preloaded with D-[3H]aspartate, a non metabolizable analogue of L-glutamate, were superfused with artificial CSF. Depolarization was induced by 53.5 mM K+, in the presence of Ca2+ (1.3 mM) or Mg2+ (5 mM) to determine the Ca2+ dependent release. Haloperidol added in the superfusion medium at 100 microM reduced by about 60% the Ca2+ dependent release of D-[3H]aspartate. This drug at 20 microM or 100 microM inhibited the non-activated glutamate dehydrogenase (GDH) but had no effect on GDH activated by ADP (2 mM) or leucine (5 mM). In addition no effect was observed on phosphate activated glutaminase (PAG) in the presence either of 20 mM or 5 mM phosphate. These results indicate that the effect of haloperidol is exerted on presynaptic mechanisms regulating neurotransmitter release.

Isolation and characterization of the rat gene encoding glutamate dehydrogenase

The concentration of glutamate dehydrogenase (GDH) varies strongly between different organs and between different regions within organs. To permit further studies on the regulation of GDH expression, we isolated and characterized the rat gene encoding the GDH protein. This gene contains 13 exons and spans approximately 34 kbp. The GDH gene is present as a single, autosomally located copy in the Wistar rat genome, but shows an extensive restriction-fragment-length polymorphism for several enzymes. Promoter activity of the 5'-flanking sequence is shown by transient transfection experiments. The 5'-flanking sequence contains a TTAAAA sequence at position -29, instead of a consensus TATA box and, like many other TATA-less promoters, is characterized by a very high G + C content. In addition, consensus sequences for the binding sites of the transcription factors Sp1 and Zif268 are present in the G + C-rich upstream region.

Polymorphisms revealed by PCR with single, short-sized, arbitrary primers are reliable markers for mouse and rat gene mapping

Ten single, arbitrarily designed oligodeoxynucleotide primers, with 50-70% (G+C) content, were used to amplify by polymerase chain reaction (PCR) sequences with DNA templates from several mouse species (Mus spretus, Mus musculus musculus, and Mus musculus domesticus), as well as DNA from the laboratory rat (Rattus norvegicus). Eight of these ten primers, used either individually or associated in pairs, generated a total of 13 polymorphic products which were used as genetic markers. All of these polymorphic sequences but one were mapped to a particular mouse chromosome, by use of DNA panels prepared either from interspecific backcross progeny of the type (C57BL/6 x Mus spretus)F1 x C57BL/6 or DNA samples prepared from two sets of recombinant inbred (RI) strains (AKXL and BXD). Six rat-specific DNA segments were also assigned to a particular chromosome with DNA panels prepared from 18 rat/mouse somatic cell hybrids segregating rat chromosomes. From these experiments we conclude that, under precisely standardized PCR conditions, the DNA molecules amplified with these arbitrarily designed primers are useful and reliable markers for genetic mapping in both mouse and rat.