Biomedical subjects

R Hen

Publications and source records attributed to R Hen.

At least 19 recordsLinked to original sources

PubMed2007

A novel conditional knockout strategy applied to serotonin receptors.

Here we demonstrate the feasibility of a doubly regulatable transgenic mouse design that allows for gene manipulation by both Cre-recombinase and the tetracycline inducible system. Using a knock-in strategy to insert both elements of the tetracycline inducible system and a neomycin (neo) cassette flanked by loxP sequences (floxed) into the wild-type locus, we generated mice that express the 5-HT(1B) receptor in a conditional manner. In the presence of a floxed neo-cassette, receptor expression was silenced. Removal of this cassette by Cre-mediated recombination led to 5-HT(1B) receptor expression, which was highly regulatable when doxycycline, a derivative of tetracycline, was administered to the mice. This system allowed for a determination of an in vivo time course of receptor half-life and recovery. Physiological studies also demonstrated that rescued 5-HT(1B) receptors were functional, and that this functionality was reversible upon treatment with doxycycline. Crossing mice where the 5-HT(1B), or the 5-HT(1A), receptors were silenced by the neo-cassette, with mice expressing either Cre-recombinase or the tetracycline transactivator (tTA) under the control of tissue-specific promoters, led to tissue-specific re-expression of these receptors. Our studies thus demonstrate the potential of this strategy for achieving both a classic knockout, as well as subsequent tissue-specific and/or inducible knockouts.

Animals↗

PubMed2005

Molecular heterogeneity along the dorsal-ventral axis of the murine hippocampal CA1 field: a microarray analysis of gene expression.

There has been increasing interest in functional heterogeneity along the septotemporal, dorsal-ventral (D-V) axis of the hippocampus. Although anatomical connectivity and lesion studies point to discrete roles for these sub-regions, the contribution of differential gene expression across this axis has not been systematically studied. Here we present findings from an Affymetrix microarray screen aimed at identifying genes in the CA1 region of the adult murine hippocampus that show significant differential expression along the D-V axis. Our results indicate that the vast majority of monitored genes (>90%) had tissue expression levels that differed by less than 20% between regions, while less than 0.1% of genes had expression levels that varied more than three-fold by sub-region. Only 23 probes showed a CA1 dorsoventral signal intensity ratio greater than three: 18 enriched dorsally and five enriched ventrally. Probes with the greatest difference in expression levels represent a range of genes with known functions in patterning and signaling, as well as genes without known function. Selective screening with digoxigenin-labeled in situ hybridization confirms the existence of CA1 sub-regionalized expression, with some genes exhibiting a graded expression pattern across the D-V axis, and others restricted to a discrete region. Our findings demonstrate that there are gene expression differences across the D-V axis of the adult murine hippocampus within traditionally recognized cytoarchitecturally defined boundaries. Combined with the previously recognized differences in connectivity and results from lesion studies, our data further confirm the existence of functional heterogeneity along the D-V axis.

Animals↗

PubMed2003

Serotonin 1B knockout mice exhibit a task-dependent selective learning facilitation.

Serotonin 1B knockout (KO) mice exhibit better spatial reference memory performance in the Morris water maze than their wild type (WT) controls. The present study was aimed at dissecting the underlying cognitive bases of this facilitation using a stepwise water maze paradigm. The performance of KO mice did not differ from WT in a single start-goal task, nor when using two opposite starts. However, KO mice exhibited better performance in stages requiring cognitive flexibility or the higher level of spatial navigation planning (standard version). In a short-term memory version of the task, no such genotype effect was observed, confirming our previous findings. These results suggest that the serotonin 1B receptor gene deletion selectively enhances learning performance when the cognitive requirement of the task is elevated.

Animals↗

PubMed2003

Enkephalin contributes to the locomotor stimulating effects of 3,4-methylenedioxy-N-methylamphetamine.

3,4-methylenedioxy-N-methylamphetamine (MDMA, 'Ecstasy') is a potent inhibitor of serotonin uptake, which induces both an increase in locomotion and a decrease in exploratory activity in rodents. Serotonin 5-HT1B receptors, located on the terminals of striatal efferent neurons, have been suggested to mediate these motor effects of MDMA. Striatal neurons projecting to the globus pallidus contain met-enkephalin, whilst those projecting to the substantia nigra contain substance P. We therefore analysed the levels of both peptides using radioimmunocytochemistry after MDMA administration (10 mg/kg, 3 h) in wild-type and 5-HT1B receptor knockout mice. Our results demonstrate that MDMA induces a decrease in pallidal met-enkephalin immunolabelling in wild-type, but not in 5-HT1B receptor knockout mice. Similar results were obtained following treatment with the 5-HT1A/1B agonist RU24969 (5 mg/kg, 3 h), suggesting that activation of 5-HT1B receptors leads to a reduction in met-enkephalin levels in the globus pallidus. In contrast, MDMA had no effect on the nigral substance P levels. We have previously shown that both MDMA and RU24969 fail to stimulate locomotor activity in 5-HT1B receptor knockout mice. Our present data indicate that the opioid antagonist naloxone suppressed the locomotor effects of MDMA. This study is the first to demonstrate that Enk contributes to MDMA-induced increases in locomotor activity. Such an effect may be related to the 5-HT control of pallidal met-enkephalin levels via the 5-HT1B receptors.

Animals↗

PubMed2003

Effects of chronic paroxetine treatment on dialysate serotonin in 5-HT1B receptor knockout mice.

The role of serotonin (5-HT)1B receptors in the mechanism of action of selective serotonin re-uptake inhibitors (SSRI) was studied by using intracerebral in vivo microdialysis in conscious, freely moving wild-type and 5-HT1B receptor knockout (KO 5-HT1B) mice in order to compare the effects of chronic administration of paroxetine via osmotic minipumps (1 mg per kg per day for 14 days) on extracellular 5-HT levels ([5-HT]ext) in the medial prefrontal cortex and ventral hippocampus. Basal [5-HT]ext values in the medial prefrontal cortex and ventral hippocampus, approximately 20 h after removing the minipump, were not altered by chronic paroxetine treatment in both genotypes. On day 15, in the ventral hippocampus, an acute paroxetine challenge (1 mg/kg i.p.) induced a larger increase in [5-HT]ext in saline-pretreated mutant than in wild-type mice. This difference between the two genotypes in the effect of the paroxetine challenge persisted following chronic paroxetine treatment. Conversely, in the medial prefrontal cortex, the paroxetine challenge increased [5-HT]ext similarly in saline-pretreated mice of both genotypes. Such a challenge produced a further increase in cortical [5-HT]ext compared with that in saline-pretreated groups of both genotypes, but no differences were found between genotypes following chronic treatment. To avoid the interaction with raphe 5-HT1A autoreceptors, 1 micro m paroxetine was perfused locally through the dialysis probe implanted in the ventral hippocampus; similar increases in hippocampal [5-HT]ext were found in acutely or chronically treated wild-type mice. Systemic administration of the mixed 5-HT1B/1D receptor antagonist GR 127935 (4 mg/kg) in chronically treated wild-type mice potentiated the effect of a paroxetine challenge dose on [5-HT]ext in the ventral hippocampus, whereas systemic administration of the selective 5-HT1A receptor antagonist WAY 100635 did not. By using the zero net flux method of quantitative microdialysis in the medial prefrontal cortex and ventral hippocampus of wild-type and KO 5-HT1B mice, we found that basal [5-HT]ext and the extraction fraction of 5-HT were similar in the medial prefrontal cortex and ventral hippocampus of both genotypes, suggesting that no compensatory response to the constitutive deletion of the 5-HT1B receptor involving changes in 5-HT uptake capacity occurred in vivo. As steady-state brain concentrations of paroxetine at day 14 were similar in both genotypes, it is unlikely that differences in the effects of a paroxetine challenge on hippocampal [5-HT]ext are due to alterations of the drug's pharmacokinetic properties in mutants. These data suggest that there are differences between the ventral hippocampus and medial prefrontal cortex in activation of terminal 5-HT1B autoreceptors and their role in regulating dialysate 5-HT levels. These presynaptic receptors retain their capacity to limit 5-HT release mainly in the ventral hippocampus following chronic paroxetine treatment in mice.

Animals↗

PubMed2002

Decreased G-protein coupling of serotonin 5-HT(1A) receptors in the brain of 5-HT(1B) knockout mouse.

The firing of central serotonin (5-hydroxytryptamine, 5-HT) neurons and their capacity to release 5-HT are subjected to a receptor-mediated auto-control via 5-HT(1A) and 5-HT(1B) receptors respectively located on the somata/dendrites (5-HT(1A) autoreceptors) and preterminal axon arborizations (5-HT(1B) autoreceptors) of these neurons. To further characterize mutual adaptations of these two receptor subtypes in the absence of one of them, activation of G-protein coupling by agonist was measured and compared to wild-type (WT) in 5-HT(1A) and 5-HT(1B) homozygous knockout (KO) mice. As expected, in WT, the non-selective 5-HT(1A/1B) receptor agonist 5-carboxyamidotryptamine (5-CT) stimulated guanosine 5'-O-(gamma-[(35)S]thio)triphosphate ([(35)S]GTP(gamma)S) incorporation in many brain regions endowed with one and/or the other receptor. In the respective KOs, no stimulation was measured in regions known to express only or mainly the deleted receptor. In the 5-HT(1A) KOs, the amplitude of G-protein activation in regions endowed with 5-HT(1B) receptors was unchanged by comparison to WT. In the 5-HT(1B) KOs, the magnitude of the 5-CT stimulation was the same as WT in all regions containing 5-HT(1A) receptors, except in the amygdala, where it was significantly lower, even if this region was one of the most strongly activated in the WT. A similar result was obtained in the amygdala of 5-HT(1B) KOs after activation by the selective 5-HT(1A) receptor agonist R-(+)8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT). Under these conditions, however, there was in addition a significant lowering of the stimulated (but not basal) [(35)S]GTP(gamma)S incorporation by comparison to WT in all regions endowed with 5-HT(1A) receptors, including the dorsal raphe nucleus. Thus, eventhough agonist radioligand binding to either 5-HT(1A) or 5-HT(1B) receptors is unchanged in the reciprocal KOs, it appears that a compensatory decrease in the efficiency of G-protein coupling to 5-HT(1A) receptors has developed in the 5-HT(1B) mutant. This could represent the first indication of a cross-talk between these two 5-HT receptor subtypes, at least in brain regions where they are co localized in the same neurons.

Animals↗

PubMed2002

Lack of 5-HT(1B) receptor and of serotonin transporter have different effects on the segregation of retinal axons in the lateral geniculate nucleus compared to the superior colliculus.

We have shown previously that raised levels of serotonin (5-hydroxytryptamine or 5-HT) during development prevent retinal ganglion cell axons from segregating into eye-specific regions in their principal targets: the superior colliculus and the dorsal lateral geniculate nucleus. Possible mediators of 5-HT in this system include its plasma membrane transporter, which is transiently expressed by a sub-population of retinal ganglion cells, and the presynaptic 5-HT(1B) receptor carried on retinal ganglion cell axons. We analysed the retinal projections of 5-HT(1B) knockout (n=15), serotonin transporter knockout (n=14), serotonin transporter/5-HT(1B) double knockout (n=4) and monoamine oxidase A/5-HT(1B) double knockout (n=3) mice. In all four different knockout mice, the ipsilateral retinal projection to the superior colliculus was more diffuse and lost its characteristic patchy distribution. The alterations were most severe in the serotonin transporter knockout mice, where the ipsilateral retinal fibres covered the entire rostrocaudal and mediolateral extent of the superior colliculus, whereas in the 5-HT(1B) and double knockout mice, fibres retracted from the caudal and lateral superior colliculus. Abnormalities in the 5-HT(1B) knockout mice appeared only after postnatal day (P) 4. Treatment with parachlorophenylalanine (at P1-P12) to decrease serotonin levels caused an exuberance of the ipsilateral retinal fibres throughout the superior colliculus (n=9). In the dorsal lateral geniculate nucleus in contrast, the distribution and size of the ipsilateral retinal projection was normal in all four knockout mice. In the serotonin transporter knockout mice however, the contralateral retinal fibres failed to retract from the mediodorsal dorsal lateral geniculate nucleus, an abnormality that was reversed by early treatment with parachlorophenylalanine and in the serotonin transporter/5-HT(1B) double knockout. OUR OBSERVATIONS INDICATE: (1) that the lack of 5-HT transporter and the associated changes in 5-HT levels impair the segregation of retinal axons in both the superior colliculus and the dorsal lateral geniculate nucleus; (2) that 5-HT and 5-HT(1B) receptors are necessary for the normal refinement of the ipsilateral retinal fibres in the superior colliculus, but are not essential for the establishment of eye-specific segregation in the thalamus. Thus, both an excess and a lack of 5-HT affect the refinement of the superior colliculus retinal projection, while the establishment of eye-specific patterns in the dorsal lateral geniculate nucleus appears not to be sensitive to the lack of 5-HT or 5-HT(1B) receptors.

Animals↗

PubMed2001

Proteasomal-dependent aggregate reversal and absence of cell death in a conditional mouse model of Huntington's disease.

Neuronal intranuclear inclusions are a histopathological hallmark of Huntington's disease. Nevertheless, the precise mechanism by which they are formed and their relevance to neuronal cell death and/or dysfunction remains unclear. We recently generated a conditional mouse model of Huntington's disease (HD94) in which silencing expression of mutated huntingtin led to the disappearance of intranuclear aggregates and amelioration of the behavioral phenotype. Here, we analyze primary striatal neuronal cultures from HD94 mice to explore the dynamics of aggregate formation and reversal, the possible mechanisms involved, and the correlation between aggregates and neuronal death. In parallel, we examine symptomatic adult HD94 mice in similar studies and explored the relationship between aggregate clearance and behavioral reversal. We report that, in culture, aggregate formation and reversal were rapid processes, such that 2 d of transgene expression led to aggregate formation, and 5 d of transgene suppression led to aggregate disappearance. In mice, full reversal of aggregates and intranuclear mutant huntingtin was more rapid than reported previously and preceded the motor recovery by several weeks. Furthermore, the proteasome inhibitor lactacystin inhibited the aggregate clearance observed in culture, thus indicating that aggregate formation is a balance between the rate of huntingtin synthesis and its degradation by the proteasome. Finally, neither expression of the mutant huntingtin nor aggregates compromised the viability of HD94 cultures. This correlated with the lack of cell death in symptomatic HD94 mice, thus demonstrating that neuronal dysfunction, and not cell loss, triggered by mutant huntingtin underlies symptomatology.

Acetylcysteine↗

PubMed2001

Interaction between 5-HT(1A) and 5-HT(1B) receptors: effects of 8-OH-DPAT-induced hypothermia in 5-HT(1B) receptor knockout mice.

To test for adaptive compensatory changes that may have occurred in the functional activity of somatodendritic 5-HT(1A) receptors during the development of constitutive "knockout" mice lacking the 5-HT(1B) receptor subtype (5-HT(1B) -/- KO), we assayed for decrease in body temperature induced by an acute subcutaneous injection of the 5-HT(1A) receptor agonist, 8-hydroxy 2(di-n-propyl(amino)tetralin (8-OH-DPAT), either alone or in the presence of a selective 5-HT(1A) receptor antagonist, N-[4-(2-methoxyphenyl)-1-piperazinyl]-N-(2-pyridinyl) cyclo-hexanecarboxamide (WAY 100635). We compared dose-response curves, time course study, calculated ED(50) values (potency), maximal response to 8-OH-DPAT (efficacy) as well as measurements of the dose-dependent blockade of this response by WAY 100635 between wild-type controls and mutant mice. We found a higher efficacy of 8-OH-DPAT-induced hypothermia in 5-HT(1B) -/- KO compared to wild-type mice suggesting that an adaptive thermoregulatory process involving the functional activity of somatodendritic 5-HT(1A) receptors is altered in mutant mice lacking 5-HT(1B) receptors.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed2001

Human 5-HT(5) receptors: the 5-HT(5A) receptor is functional but the 5-HT(5B) receptor was lost during mammalian evolution.

We have isolated from a human genomic library the human 5-hydroxytryptamine 5-HT(5A) and 5-HT(5B) genes. The human 5-HT(5A) gene encodes a protein with similar characteristics to its mouse homologue. When expressed in monkey COS-7 cells, the human 5-HT(5A) receptor displayed a high affinity for tritiated 5-carbamidotryptamine ([3H]5-CT; K(D)=2.8 nM) and iodinated lysergic acid diethylamide ([125I]LSD; K(D)=187 pM). These binding sites displayed the following displacement profile: Ergotamine>Methiothepin>5-CT, Ritanserin>5-HT. Reverse transcriptase polymerase chain reaction (RT-PCR) experiments revealed the presence of human 5-HT(5A) mRNA in the central nervous system but not in peripheral organs. When expressed in Xenopus oocytes, the 5-HT(5A) receptor was able to couple to the inwardly rectifying K(+) channel, GIRK(1). In contrast to the human 5-HT(5A) gene and the mouse 5-HT(5B) gene, the human 5-HT(5B) gene does not encode a functional protein because its coding sequence is interrupted by stop codons. Our results suggest, therefore, that the 5-HT(5B) receptor has been lost during evolution after the divergence between rodents and primates. The 5-HT(5B) receptor is the first example of a brain-specific protein that is absent in human.

3T3 Cells↗

PubMed2001

Absence of 5-HT(1B) receptors is associated with impaired impulse control in male 5-HT(1B) knockout mice.

BACKGROUND: Serotonin (5-HT) plays a complex regulatory role in processes like anxiety, depression, aggression, and impulse control. Due to the large amount of serotonergic receptors, knockout mice offer an important opportunity to investigate the role of specific receptors. The 5-HT(1B) receptor is thought to mediate aggression and impulse control. This was studied here in mice lacking 5-HT(1B) receptors (5-HT(1B) KO). METHODS: Wild type and 5-HT(1B) KO mice were exposed to several types of entrained and nonentrained stimuli. With telemetry, body temperature, heart rate, and locomotor activity were measured continuously during the different experiments. RESULTS: To nonentrained stimuli like disturbance stress and confrontation with an intruder, 5-HT(1B) KO mice showed exaggerated physiologic and behavioral responses. These mice displayed behavioral disinhibition, measured as increased social interest and aggression to an intruder mouse. However, in response to well-entrained stimuli like daily light transitions, responses were smaller in 5-HT(1B) KO than in wild type mice, suggesting that hyperreactivity is stimulus specific. CONCLUSIONS: Serotonin 1B receptors are essential in impulse control by inhibiting responses to nonentrained stimuli. Therefore, the 5-HT(1B) KO mouse might be an important additional model for studying aspects of disinhibition in aggression and impulse control.

Aggression↗

PubMed2001

Stress-induced hyperthermia in the 5-HT(1A) receptor knockout mouse is normal.

BACKGROUND: Several studies on serotonin 1A (5-HT(1A)) receptor knockout mice in different genetic backgrounds indicate that such mice display a more anxious phenotype than their corresponding wild types. We hypothesized that the 5-HT(1A) receptor knockout mice would show a different phenotype than the wild type mice in the stress-induced hyperthermia (SIH) paradigm, which tests putative anxiolytic effects of drugs. Moreover, on pharmacologic challenges with the 5-HT(1A) receptor agonist flesinoxan we expected an absence of the functional response in knockout mice relative to wild type mice. METHODS: Effects of the 5-HT(1A) receptor agonist flesinoxan, alone or in combination with the 5-HT(1A) receptor antagonist WAY-100635, and the gamma-aminobutyric acid A (GABA(A))-benzodiazepine receptor agonist diazepam were studied in the SIH paradigm in male 129/Sv 5-HT(1A) receptor knockout and wild type mice. In addition, the effects of flesinoxan on plasma corticosterone concentrations were determined. RESULTS: Plasma corticosterone concentrations were dose dependently elevated by flesinoxan in wild type mice but not in knockout mice. Flesinoxan dose dependently decreased SIH in wild type mice but not in knockout mice. The flesinoxan effect in wild type mice was blocked by WAY-100635. Furthermore, diazepam decreased SIH in both genotypes. There were no differences in basic SIH responses between wild type and knockout mice. CONCLUSIONS: 5 -HT(1A) receptor knockout mice display a normal SIH response, and results indicate, based on the SIH, that the GABA(A)-benzodiazepine receptor complex functions normally.

Animals↗

PubMed2001

Hyperactivity and impaired response habituation in hyperdopaminergic mice.

Abnormal dopaminergic transmission is implicated in schizophrenia, attention deficit hyperactivity disorder, and drug addiction. In an attempt to model aspects of these disorders, we have generated hyperdopaminergic mutant mice by reducing expression of the dopamine transporter (DAT) to 10% of wild-type levels (DAT knockdown). Fast-scan cyclic voltammetry and in vivo microdialysis revealed that released dopamine was cleared at a slow rate in knockdown mice, which resulted in a higher extracellular dopamine concentration. Unlike the DAT knockout mice, the DAT knockdown mice do not display a growth retardation phenotype. They have normal home cage activity but display hyperactivity and impaired response habituation in novel environments. In addition, we show that both the indirect dopamine receptor agonist amphetamine and the direct agonists apomorphine and quinpirole inhibit locomotor activity in the DAT knockdown mice, leading to the hypothesis that a shift in the balance between dopamine auto and heteroreceptor function may contribute to the therapeutic effect of psychostimulants in attention deficit hyperactivity disorder.

3,4-Dihydroxyphenylacetic Acid↗

PubMed2001

Excessive activation of serotonin (5-HT) 1B receptors disrupts the formation of sensory maps in monoamine oxidase a and 5-ht transporter knock-out mice.

Deficiency in the monoamine degradation enzyme monoamine oxidase A (MAOA) or prenatal exposure to the monoamine uptake inhibitor cocaine alters behavior in humans and rodents, but the mechanisms are unclear. In MAOA knock-out mice, inhibiting serotonin synthesis during development can prevent abnormal segregation of axons in the retinogeniculate and somatosensory thalamocortical systems. To investigate this effect, we crossed MAOA knock-outs with mice lacking the serotonin transporter 5-HTT or the 5-HT1B receptor, two molecules present in developing sensory projections. Segregation was abnormal in 5-HTT knock-outs and MAOA/5-HTT double knock-outs but was normalized in MAOA/5-HT1B double knock-outs and MAOA/5-HTT/5-HT1B triple knock-outs. This demonstrates that the 5-HT1B receptor is a key factor in abnormal segregation of sensory projections and suggests that serotonergic drugs represent a risk for the development of these projections. We also found that the 5-HT1B receptor has an adverse developmental impact on beam-walking behavior in MAOA knock-outs. Finally, because the 5-HT1B receptor inhibits glutamate release, our results suggest that visual and somatosensory projections must release glutamate for proper segregation.

Animals↗

PubMed2001

Genetic and pharmacological disruption of neurokinin 1 receptor function decreases anxiety-related behaviors and increases serotonergic function.

Alterations in serotonin (5-hydroxytriptamine, 5-HT), norepinephrine, and gamma-aminobutyric acid have been linked to the pathophysiology of anxiety and depression, and medications that modulate these neurotransmitters are widely used to treat mood disorders. Recently, the neuropeptide substance P (SP) and its receptor, the neurokinin 1 receptor (NK1R), have been proposed as possible targets for new antidepressant and anxiolytic therapies. However, animal and human studies have so far failed to provide a clear consensus on the role of SP in the modulation of emotional states. Here we show that both genetic disruption and acute pharmacological blockade of the NK1R in mice result in a marked reduction of anxiety and stress-related responses. These behavioral changes are paralleled by an increase in the firing rate of 5-HT neurons in the dorsal raphe nucleus, a major source of serotonergic input to the forebrain. NK1R disruption also results in a selective desensitization of 5-HT1A inhibitory autoreceptors, which resembles the effect of sustained antidepressant treatment. Together these results indicate that the SP system powerfully modulates anxiety and suggest that this effect is at least in part mediated by changes in the 5-HT system.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed2001

5-HT1B receptor knockout, but not 5-HT1A receptor knockout mice, show reduced startle reactivity and footshock-induced sensitization, as measured with the acoustic startle response.

To investigate whether the hyperreactivity to mild environmental and novel stimuli in 5-HT1B receptor knockout (1BKO) mice, as suggested by measures of exploratory, aggressive, and impulsive behaviors, can be extended to phasic stimuli, 1BKO and wildtype mice were tested in acoustic startle reactivity and plasticity paradigms, including habituation, prepulse inhibition, and footshock-induced sensitization of the startle response. Furthermore, we compared 5-HT1A receptor knockout (1AKO) and 1BKO mice to further test the suggested opposite behavioral profiles in these two genotypes. Results show that startle reactivity and footshock-induced sensitization was reduced in 1BKO mice, with no changes in habituation or PPI. In contrast, 1AKO mice did not differ from WT mice in any of the measures. These results indicate that an absence of 5-HT1B receptors, but not of 5-HT1A receptors, affects the modulation of startle reactivity and footshock-induced sensitization, without influencing startle plasticity. Moreover, this study suggests that 1AKO mice display a distinct, but not opposite behavioral profile from 1BKO mice. Furthermore, it is concluded that the hyperreactivity in 1BKO mice cannot be generalized to all stimuli, including the startling stimuli used in this study, but is probably restricted to mild environmental stimuli only.

Acoustic Stimulation↗

PubMed2001

Decreased nuclear beta-catenin, tau hyperphosphorylation and neurodegeneration in GSK-3beta conditional transgenic mice.

Glycogen synthase kinase-3beta (GSK-3beta) has been postulated to mediate Alzheimer's disease tau hyperphosphorylation, beta-amyloid-induced neurotoxicity and presenilin-1 mutation pathogenic effects. By using the tet-regulated system we have produced conditional transgenic mice overexpressing GSK-3beta in the brain during adulthood while avoiding perinatal lethality due to embryonic transgene expression. These mice show decreased levels of nuclear beta-catenin and hyperphosphorylation of tau in hippocampal neurons, the latter resulting in pretangle-like somatodendritic localization of tau. Neurons displaying somatodendritic localization of tau often show abnormal morphologies and detachment from the surrounding neuropil. Reactive astrocytosis and microgliosis were also indicative of neuronal stress and death. This was further confirmed by TUNEL and cleaved caspase-3 immunostaining of dentate gyrus granule cells. Our results demonstrate that in vivo overexpression of GSK-3beta results in neurodegeneration and suggest that these mice can be used as an animal model to study the relevance of GSK-3beta deregulation to the pathogenesis of Alzheimer's disease.

Animals↗

PubMed2001

The ons and offs of inducible transgenic technology: a review.

Classical transgenic and gene-targeted mouse mutants are powerful model systems in which to study the pathogenesis of neurodegenerative diseases. However, a number of issues of fundamental importance to neurodegenerative research cannot be addressed using classical techniques. These include identification of the earliest events in disease pathogenesis and a determination of whether a particular pathogenic protein produces a inexorable or a reversible disease process. Both of these issues have profound implications for the rational development of new therapies. To address these questions, genetic techniques that allow pathogenic proteins to be expressed or knocked out with temporal and regional specificity have been developed. We have reviewed these systems, highlighting the tetracycline-regulated system because of its demonstrated utility in mice and its reversibility. These regulatable systems are a new and powerful tool for the neurobiologist and allow one to address a new set of important questions in an in vivo setting.

Animals↗