Pascal Hilber

Stress and anxious-related behaviors in Lurcher mutant mice.

Blood corticosterone levels (CORT) were measured before and after the completion of the elevated +-maze test in cerebellar Lurcher mutant and control mice. Consistent with the existence of a much more pronounced activation of the hypothalamo-pituitary-adrenal (HPA) system in the mutants, our results showed that while basal CORT were similar in mutants and controls, the surge of this stress indicator was enhanced in the Lurcher mice after completion of a behavioral test of anxiety. In contrast, at the behavioral level, we also observed that Lurcher exhibited significantly reduced anxiety related indices; they spent a significant greater amount of time in the aversive places of the apparatus and entered them more frequently than non mutant mice. It is proposed that rather than less anxious, the Lurcher mice are less inhibited than controls when placed in anxiogenic situation and that such poor inhibition could be causally related to changes in HPA system regulation. The overall patterns of our behavioral and endocrinological results thereby provided the evidence that cerebellar circuitry is involved in producing changes in physiological and behavioral stress-related emotional responses.

EFFECTS OF HARMALINE ON ANXIETY-RELATED BEHAVIOR IN MICE

Harmaline (HA) is a beta-carboline commonly known to provoke motor alterations through activation of cells in the inferior olive. In addition, this pharmacological agent also induces cognitive disturbances such as motor and spatial learning impairments. In order to complete and extend these data, we examined the effects of this drug on state anxiety in mice, employing elevated plus maze test. We report here that lower doses of harmaline (5-10 mg/kg) have anxiogenic since higher doses (20 mg/kg) have anxiolytic-like properties. Overall pattern of our behavioral results provides evidence that harmaline also acts on emotional reactivity in mice by influencing their decision making when placed in an anxiogenic situation.

Effects of chlordiazepoxide on the emotional reactivity and motor capacities in the cerebellar Lurcher mutant mice.

It is now well accepted that besides its roles in motor control, the cerebellum is involved in non-motor functions with emotional aspects. Consistent with this view, several studies highlighted that the cerebellar Lurcher mutant mice (+/Lc), with motor impairments, also exhibited altered emotional reactivity, previously interpreted in term of behavioural disinhibition. In this study, we investigated the effects of a classical anxiolytic on such disinhibition. For that, behaviours of +/Lc and control (+/+) mice injected with NaCl or chlordiazepoxide (CDP 5 and 7.5mg/kg) were evaluated in the elevated plus-maze test. The motor impact of the drug (7.5mg/kg only) was also evaluated in the hole-board and unstable platform tests. Our results showed that, compared to the +/+ mice, CDP injection greatly influenced the anxious-related behaviours in the +/Lc mice by reducing their preference to the open areas in the elevated plus-maze test. Furthermore, we found that injection of CDP at the dose of 7.5mg/kg aggravated motor coordination deficit, altered motor learning capabilities in the mutants and provoked equilibrium disturbances in the non-mutant mice in the unstable platform test. These results indicated that CDP was able to reduce behavioural disinhibition in the cerebellar +/Lc mice and were discussed in term of implication of the cerebellar connections into CDP-sensitive neural circuitries involved in both emotional and motor processes.

Influence of stimulation of the olivocerebellar pathway by harmaline on spatial learning in the rat.

Administration of harmaline to the rat, which activates synchronously and rhythmically the olivary neurons and the olivocerebellar pathway, elicits visuo-motor, spatial learning and spatial memory deficiencies which are dose-dependent. Since activation and lesion of the olivocerebellar pathway have similar effects, it is concluded that normal functioning of this pathway is required for spatial learning achievement.

Effect of training on motor abilities of heterozygous staggerer mutant (Rora+/Rorasg) mice during aging

Heterozygous cerebellar mutant (Rora(+)/Rora(sg)) mice and control (Rora(+)/Rora(+)) mice of the same C57Bl6/J strain, 3-24 months old, were subjected to motor training on a rotorod for 10 days. Falling latency and percentage of time spent walking were measured. A good correlation was found between falling latency and walking time: the mice which maintained equilibrium for a long time were those which were walking, and the mice which fell early were those which were gripping suggesting that walking is obviously the most adapted strategy to keep balance on the rotorod. In Rora(+)/Rora(+) mice, scores before training were altered very precociously (from 6 months of age). Moreover, scores of Rora(+)/Rora(sg) mice were lower than those of Rora(+)/Rora(+) mice from the age of 3 months, while neuronal number in the cerebellar cortex of these mutants was quite normal and similar to that of Rora(+)/Rora(+) mice. This suggests that the motor skill disability would be due to fine structural and/or biochemical changes preceding neuronal death. Such subtle changes would begin several months earlier in Rora(+)/Rora(sg) than in Rora(+)/Rora(+) mice. Training on the rotorod resulted in increased scores in both genotypes at all ages. Motor learning abilities were therefore preserved in animals with a moderate neuronal loss in the cerebellum. It may be that motor learning is partly compensated by the striatum, which is known to play a major role in learning of motor skills.

Motor effects of delta 9 THC in cerebellar Lurcher mutant mice

The present study evaluated the effects of the principal active component of marijuana (delta 9 THC) on motor abilities and motor learning in mice with cerebellar dysfunction. For this purpose, spontaneous locomotor activity, equilibrium abilities, muscular tone, motor coordination and motor learning were investigated in Lurcher mutant and non-mutant B6/CBA mice 20 min after i.p. administration of 4 or 8 mg kg(-1) of delta 9 tetra hydro cannabinol (delta 9 THC). The performances were compared to those obtained by Lurcher and non-mutant mice injected with vehicle (Tween 80). The results showed that at the dose of 4 mg kg(-1) but not at the dose of 8 mg kg(-1), the cannabinoid (CB) substance reduced deficits in motor coordination, equilibrium and muscular tone and facilitated motor learning in Lurcher mice. On the other hand, only a muscular strength decrease was observed in control B6/CBA mice injected with the dose of 8 mg kg(-1) of delta 9 THC. These results suggested that cannabinoid derivative could represent a new field of investigation concerning the treatment of cerebellar ataxic syndrome in humans.

Fear-related behaviors in Lurcher mutant mice exposed to a predator

The Lurcher mutant mice are characterized by massive cerebellar cortex degeneration. Besides their motor and cognitive disturbances, they exhibit both exaggerated blood corticosterone (CORT) level surge and behavioral disinhibition when confronted to anxiogenic conditions (i.e. to a potential threat). In this study, we assessed if such physiological and behavioral hyperactivity was also detectable in a fear‐eliciting situation (actual threat). For this purpose, the behaviors and CORT level elevations in Lurcher mice were compared with those of littermate controls in the predator exposure test: mice were exposed either to a rat (exposure) or to a brief wave of the experimenters hand (sham exposure). While the basal CORT concentrations (24 h before testing) were not significantly different between mice of both genotypes, the post‐exposure ones were higher in Lurcher than in control mice whatever the condition of the experimental design (exposure or sham exposure). Predator exposure did not provoke significant increase of CORT levels whatever the genotype. On the contrary, our data clearly showed that fear‐related behaviors of cerebellar mutants facing a real threat were exacerbated in comparison to those of control mice. These results suggest that the cerebellar cortex not only participates to fear conditioning and anxiety but also actively contributes to the modulation of the innate fear‐related behaviors.

Evaluation of the Impact of the Cancer Therapy Everolimus on the Central Nervous System in Mice

Cancer and treatments may induce cognitive impairments in cancer patients, and the causal link between chemotherapy and cognitive dysfunctions was recently validated in animal models. New cancer targeted therapies have become widely used, and their impact on brain functions and quality of life needs to be explored. We evaluated the impact of everolimus, an anticancer agent targeting the mTOR pathway, on cognitive functions, cerebral metabolism, and hippocampal cell proliferation/vascular density in mice. Adult mice received everolimus daily for 2 weeks, and behavioral tests were performed from 1 week after the last treatment. Everolimus-treated mice displayed a marked reduction in weight gain from the last day of the treatment period. Ex vivo analysis showed altered cytochrome oxidase activity in selective cerebral regions involved in energy balance, food intake, reward, learning and memory modulation, sleep/wake cycle regulation, and arousal. Like chemotherapy, everolimus did not alter emotional reactivity, learning and memory performances, but in contrast to chemotherapy, did not affect behavioral flexibility or reactivity to novelty. In vivo hippocampal neural cell proliferation and vascular density were also unchanged after everolimus treatments. In conclusion, two weeks daily everolimus treatment at the clinical dose did not evoke alteration of cognitive performances evaluated in hippocampal- and prefrontal cortex-dependent tasks that would persist at one to four weeks after the end of the treatment completion. However, acute everolimus treatment caused selective CO modifications without altering the mTOR effector P70S6 kinase in cerebral regions involved in feeding behavior and/or the sleep/wake cycle, at least in part under control of the solitary nucleus and the parasubthalamic region of the hypothalamus. Thus, this area may represent a key target for everolimus-mediating peripheral modifications, which has been previously associated with symptoms such as weight loss and fatigue.

Cooperation of the vestibular and cerebellar networks in anxiety disorders and depression

ABSTRACT The discipline of affective neuroscience is concerned with the neural bases of emotion and mood. The past decades have witnessed an explosion of research in affective neuroscience, increasing our knowledge of the brain areas involved in fear and anxiety. Besides the brain areas that are classically associated with emotional reactivity, accumulating evidence indicates that both the vestibular and cerebellar systems are involved not only in motor coordination but also influence both cognition and emotional regulation in humans and animal models. The cerebellar and the vestibular systems show the reciprocal connection with a myriad of anxiety and fear brain areas. Perception anticipation and action are also major centers of interest in cognitive neurosciences. The cerebellum is crucial for the development of an internal model of action and the vestibular system is relevant for perception, gravity‐related balance, navigation and motor decision‐making. Furthermore, there are close relationships between these two systems. With regard to the cooperation between the vestibular and cerebellar systems for the elaboration and the coordination of emotional cognitive and visceral responses, we propose that altering the function of one of the systems could provoke internal model disturbances and, as a result, anxiety disorders followed potentially with depressive states. HIGHLIGHTSAlteration of the vestibular system provokes self‐perception disorganization.Alteration of the cerebellar system could provoke internal model disorganization.Self‐perception and internal models could be involved in anticipation and anxiety.Alteration of internal models might provoke unsuited behavior as well as anxiety disorders and depression.

Impaired spatial performance in cerebellar-deficient Lurcher mice is not associated with their abnormal stress response

&NA; Both humans and laboratory animals suffering from cerebellar lesions exhibit cognitive as well as many emotional and behavioral abnormalities. These latter have been already observed in the cerebellar mutant mice currently used to highlight some aspect of autism spectrum disorders. The aim of this study was to investigate the influence of cerebellar‐related stress response abnormalities on spatial learning and memory. Cerebellar‐deficient Lurcher mutant mice were exposed to water environment without active escape possibility and then tested for spatial learning in the Morris water maze. As a marker of stress intensity we measured corticosterone in urine. Finally, the volumes of individual components of the adrenal gland were estimated. Though having spatial navigation deficit in the water maze, Lurcher mice preserved a substantial residuum of learning capacity. Lurcher mutants had a higher increase of corticosterone level after exposure to the water environment than wild type mice. We did not observe any decrease of this physiological stress marker between the start and the end of the spatial navigation task, despite significant improvement of behavioral performances. Furthermore, zona fasciculata and zona reticularis of the adrenal cortex as well as the adrenal medulla were larger in Lurcher mice, reflecting high stress reactivity. We conclude that for both genotypes water exposure was a strong stressor and that there was no habituation to the experiment independently to the increasing controllability of the stressor (e.g. ability to find the escape platform). Based on these findings, we suggest that the enhanced stress response to water exposure is not the main factor explaining the spatial deficits in these cerebellar mutant mice. HighlightsLurchers had a higher increase of corticosterone level after water exposure.Lurcher mice showed spatial navigation deficit with residuum of learning capacity.No decline of the corticosterone level was seen despite mild improving performance.Adrenal glands of Lurcher mice were larger than in wild type mice.Enhanced stress response is not the main factor causing spatial deficits in Lurchers.