Regional brain variations of cytochrome oxidase activity and motor coordination in Girk2(Wv) (Weaver) mutant mice.

The Girk2(Wv) (weaver) phenotype, caused by a mutated inward rectifying potassium channel, is characterized by degeneration of cerebellar granule cell population as well as midbrain dopamine-containing cells of the nigrostriatal pathway. To investigate the regional brain metabolic consequences of this combined pathology, cytochrome oxidase (CO) activity was measured by histochemistry from brain regions of wild-type and homozygous Girk2(Wv) mutant mice and correlated with motor performances. CO activity of Girk2(Wv) mutants was abnormal in cerebellar cortex, dentate nucleus, and brainstem regions (medial and lateral vestibular nuclei, prepositus, superior colliculus, lateral cuneiform nucleus, and reticular nuclei) implicated in the gaze system. CO activity increased in midbrain dopaminergic regions after correcting for tissue density, regions with severe depletion of tyrosine hydroxylase activity. Forebrain regions were relatively spared in term of CO activity, except for subthalamic nucleus, lateral geniculate nucleus, and cortical eye field. Similarly to the Rora(sg) cerebellar mutant, metabolic alterations in cerebellar and vestibular regions were linearly correlated with poor motor coordination, underlining the sensitivity of these tests to cerebellar dysfunction.

Opposite behaviours in the forced swimming test are linked to differences in spatial working memory performances in the rat.

Despite consistent evidence of an association between depression and impaired memory performance, only a few studies have investigated memory processes in animal models of depression. The aim of the present study was to determine if rats selected for marked differences in their immobility response in the forced swimming test (FST, i.e. high-immobility, [HI] and low-immobility [LI] rats) exhibit differences in spatial and non-spatial memory performances. In a classic radial maze elimination task, we observed that HI rats made significantly more errors than LI rats, and their first error appeared significantly earlier. In a delayed spatial win-shift procedure where rats have to hold spatially relevant information in working memory across a 30 min delay, HI rats tended initially to perform more poorly than LI rats. HI rats made more across-phase errors, the occurrence of the first error was earlier and by the end of the experiment the differences between the two groups disappeared. Thus, HI rats present more difficulties to learn the rules in a spatial task and show weaker performances in spatial working memory in comparison to LI rats. On the other hand, performances in the two groups of animals were similar in a non-spatial task, the object recognition task. Complementary behavioral data indicate that the differences observed between the two groups are not attributable to opposite locomotor activities or to different levels of anxiety. Overall we can conclude that opposite swimming behavior in the FST could parallel some differences in cognitive performances, more specifically linked to spatial working memory.

Decreased densities of dopamine and serotonin transporters and of vesicular monoamine transporter 2 in severely kainic acid lesioned subregions of the striatum.

Fifteen days after a striatal kainic acid (KA) injection, we have examined presynaptic modifications of dopamine and serotonin terminals in the striatum through (i) autoradiographic labeling of dopamine, serotonin and vesicular monoamine transporters respectively with 3H-mazindol, 3H-citalopram and 3H-dihydrotetrabenazine, and (ii) determination of the contents in dopamine, serotonin and their metabolites. Acetylcholinesterase histochemical labeling enabled the definition of severely and moderately KA-lesioned subregions within the striatum. A significant decrease of the three transporters labeling density was observed only in the severely lesioned subregions. The strong decrease in serotonin transporter labeling revealed here has not been described until now. Besides, the striatal contents of homovanillic acid (dopamine metabolite) and 5-hydroxyindolacetic acid (serotonin metabolite) were significantly increased in the lesioned striatum. The whole data evidence an incomplete sparing of dopamine and serotonin terminals in the striatum 15 days after a KA injection, especially in the areas where the degeneration of postsynaptic neurons was the most extensive.

Reserpine or chronic paroxetine treatments do not modify the vesicular monoamine transporter 2 expression in serotonin-containing regions of the rat brain.

To date, very little information is available about the regulation of vesicular monoamine transporter in central serotonergic regions. The expression of the vesicular monoamine transporter 2 (VMAT2) has been studied in the serotonergic system of the rat brain after an 18 day treatment with the serotonin selective-reuptake inhibitor paroxetine (10 mg/kg, i.p., once daily). This treatment, while increasing serotonergic transmission, did not modify either VMAT2 mRNA expression or (3)H-dihydrotetrabenazine binding site density in any of the studied regions. These results suggest that VMAT2 regulation in the central serotonergic system is not involved in the mechanism of action of antidepressants. In addition, a single administration of reserpine (5 mg/kg, s.c.), while blocking the vesicular monoamine uptake function, had no effect on VMAT2 immunoreactivity in the dorsal raphe nucleus 2 or 30 days after injection. It is concluded that neither a reduction (reserpine) nor an enhancement (paroxetine) of the serotonin transmission induces VMAT2 regulation in serotonergic system in the rat brain.

Differential expression of glutamate decarboxylase messenger RNA in cerebellar Purkinje cells and deep cerebellar nuclei of the genetically dystonic rat.

The genetically dystonic rat exhibits a motor syndrome that closely resembles the human disease, generalized idiopathic dystonia. Although in humans dystonia is often the result of pathology in the basal ganglia, previous studies have revealed electrophysiological abnormalities and alterations in glutamate decarboxylase, the synthetic enzyme for GABA, in the cerebellum of dystonic rats. In this study, we further characterized the alterations in cerebellar GABAergic transmission in these mutants by examining the expression of the messenger RNA encoding glutamate decarboxylase (67000 mol. wt) with in situ hybridization histochemistry at the single cell level in Purkinje cells and neurons of the deep cerebellar nuclei. Glutamate decarboxylase (67000 mol. wt) messenger RNA levels were increased in the Purkinje cells and decreased in the deep cerebellar nuclei of dystonic rats compared to control littermates, suggesting opposite changes in GABAergic transmission in Purkinje cells and in their target neurons in the deep cerebellar nuclei. In contrast, levels of glutamate decarboxylase (67000 mol. wt) messenger RNA in the pallidum, and of enkephalin messenger RNA in the striatum, were unaffected in dystonic rats. The data indicate that both the Purkinje cells and GABAergic neurons of the deep cerebellar nuclei are the site of significant functional abnormality in the dystonic rat.

Locomotor sensitization and decrease in [3H]mazindol binding to the dopamine transporter in the nucleus accumbens are delayed after chronic treatments by GBR12783 or cocaine.

Rats were treated once daily for 15 consecutive days with either cocaine or the specific dopamine uptake inhibitor 1-[2- (diphenylmethoxy)ethyl]-4-(3-phenyl-2-(propenyl)-piperazine (GBR12783) at a dose (10 mg/kg) that given acutely increases locomotor activity. Two or 14 days after the last administration, the motor stimulant responses of rats to a challenge dose (5 mg/kg) of the drug administered previously were compared with the motor stimulant responses of rats daily injected with solvent. A sensitization to the acute stimulant locomotor effect of these drugs was only observed 14 days after cessation of chronic treatments. After this withdrawal period, autoradiographic analysis revealed a significant decrease in the desipramine-insensitive [3H]mazindol binding to the dopamine transporter in the shell of the nucleus accumbens. No change was noticed in other regions with high dopamine content: core of nucleus accumbens, striatum, olfactory tubercle, substantia nigra and ventral tegmental area. Absence of concomitant decrease in [3H]dihydrotetrabenazine labeling, which indicates lack of effect on vesicular monoamine transporters, suggests that the decrease in accumbal [3H]mazindol binding did not result from a cytotoxic effect on corresponding dopamine neurons. In addition, 14 days after the last administration of GBR12783, the levels of dopamine and metabolites (dihydroxy-phenylacetic acid, homovanillic acid) and the ability of acute GBR12783 to synergize with haloperidol-induced increase in these metabolites were not modified either in the whole nucleus accumbens or in the striatum.

Reserpine affects differentially the density of the vesicular monoamine transporter and dihydrotetrabenazine binding sites.

We have studied the effect of a single injection of reserpine (5 mg/kg, s.c.) on the synaptic vesicle monoamine transporter (VMAT) density in the rat striatum, using two labelling procedures: radioimmunolabelling with an antibody against VMAT, and binding of the specific ligand [(3)H]dihydrotetrabenazine ([(3)H]TBZOH). In the rostral and medial striatum, the distribution of VMAT immunoreactivity displayed the highest density in the lateral subregions. In the caudal part of the striatum, VMAT immunoreactivity showed increasing density from dorsal to ventral subregions. The VMAT immunoreactivity was not altered 2 and 30 days after the reserpine injection, whereas [(3)H]TBZOH binding site density, measured on adjacent slices, showed a dramatic decrease at day 2 and a moderate recovery at day 30, suggesting that despite a persistent blockade of [(3)H]TBZOH binding sites, VMAT protein density was unchanged.

Time-course of modifications elicited by reserpine on the density and mRNA synthesis of the vesicular monoamine transporter, and on the density of the membrane dopamine uptake complex.

The long-term effects of a unique injection of reserpine (5 mg/kg s.c.) on the vesicular monoamine transporter and dopamine uptake complex have been investigated, in parallel with behavioral and neurochemical effects. Early after treatment, a dramatic decrease in locomotor activity, as well as a marked depletion in striatal dopamine (DA), associated with a prominent enhancement in dopaminergic turnover were observed in reserpine-treated rats. From 2 to 60 days after reserpine injection, a recovery in locomotor activity occurred, in parallel with an increased DA content in the striatum, reaching about 50% of controls at day 60. At this time, the dopamine turnover was quite normal. The density of the dopamine uptake sites in the striatum, studied with 3H GBR12783, was unchanged after reserpine treatment at any time studied up to 60 days. By contrast, the density of binding sites for 3H dihydrotetrabenazine (3H TBZOH), a marker for the vesicular monoamine transporter, remained dramatically decreased in the striatum all over the time of the study (> -90% of controls at day 2 and -80% at day 30 and 60). A lesser decrease (-60%) was observed in the substantia nigra pars compacta (SNc), 2 and 30 days after reserpine treatment. This suggests that at least 60% of the vesicular monoamine transporter is sensitive to reserpine in this cell bodies region, indicating that this proportion of the transporter is integrated in functional vesicles, a prerequisite for reserpine binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Short-term treatments with haloperidol or bromocriptine do not alter the density of the monoamine vesicular transporter in the substantia nigra.

[3H]dihydrotetrabenazine ([3H]TBZOH) was used to label the monoamine vesicular transporter in the rat substantia nigra. An accumulation of neuronal vesicles in the substantia nigra pars compacta was observed after blockade of the fast axonal transport by a microinjection of colchicine (10 micrograms/2 microliters) into the medial forebrain bundle. This accumulation was measured after sustained 2-day pharmacological modifications of the central dopaminergic transmission. It was not modified after s.c. administration of either the direct dopamine (DA) receptor agonist bromocriptine (four injections of 4 or 6 mg/kg) or the DA receptor antagonist haloperidol (four injections of 0.5-1-1.5-2 mg/kg). Thus, it appears that these pharmacological modifications, imposed to the activity of the nigro-striatal dopaminergic system during 2 days, have no consequence on the rate of synthesis of its vesicles.

Invariance of the density of dopamine uptake sites and dopamine metabolism in the rat brain after a chronic treatment with the dopamine uptake inhibitor GBR 12783.

A chronic treatment (10 mg/kg, twice daily during 9 days) with the dopamine uptake inhibitor GBR 12783 was performed in rats at a dose increasing their locomotor activity. Forty-eight hours after the last administration, animals were sacrificed and 3H mazindol binding was performed on brain slices. Autoradiographic analysis revealed no change in this binding relatively to control animals in regions with high dopamine contents: striatum, nucleus accumbens, olfactory tubercle, substantia nigra and ventral tegmentum area. The treatment did not either modify the levels of dopamine (DA) and metabolites (HVA, DOPAC) both in the striatum and the nucleus accumbens. Thus, early after the end of the treatment, the chronic blockade of the dopamine uptake complex regulates neither the dopamine uptake complex nor the dopamine metabolism.

Consequences of an intrastriatal injection of kainic acid on the dopaminergic neuronal and vesicular uptake systems.

Intrastriatal kainic acid injection destroys the neurons originating from the striatum, including those on which terminals of the nigro- and meso-striatal dopaminergic neurons project. We have studied at various times the consequences of this lesion on dopamine metabolism and on the neuronal and vesicular transporters. Two and 15 days after kainic acid injection, whereas dopamine turnover was increased and the dopamine content unchanged, there was no modification in the binding of [3H]GBR 12783, a marker of the neuronal uptake complex, but the binding of [3H]dihydrotetrabenazine, a marker of the vesicular transporter, was significantly decreased. At later times (30 and 60 days) when the dopamine turnover was decreased as well as the dopamine content, the binding of [3H]dihydrotetrabenazine was more dramatically decreased (about 30% of controls) than that of [3H]GBR 12783. In addition autoradiography showed an increase in the density of [3H]dihydrotetrabenazine binding sites in the substantia nigra. Thus it appears that the long-term (60 days) repercussions of a kainic acid lesion affect simultaneously the dopamine turnover (which is decreased) and the vesicular transporter whereas the dopamine uptake complex is little affected.

Kainic acid lesion of the striatum increases dopamine release but reduces 3-methoxytyramine level.

Kainic acid lesion of the striatum leads to the disruption of the striatonigral regulatory loop. Although microdialysis showed an increase in dopamine release, two days after kainic acid injection, 3-methoxytyramine levels are dramatically decreased. This suggests that the postsynaptic membrane-bound catechol-O-methyltransferase (COMT), but not the glial COMT, is responsible for the formation of measured 3-methoxytyramine.