Early life blockade of 5-hydroxytryptamine 1A receptors normalizes sleep and depression-like behavior in adult knock-out mice lacking the serotonin transporter.

In serotonin transporter knock-out (5-HTT-/-) mice, extracellular serotonin (5-HT) levels are markedly elevated in the brain, and rapid eye movement sleep (REMS) is enhanced compared with wild-type mice. We hypothesized that such sleep impairment at adulthood results from excessive serotonergic tone during early life. Thus, we assessed whether neonatal treatment with drugs capable of limiting the impact of 5-HT on the brain could normalize sleep patterns in 5-HTT-/- mutants. We found that treatments initiated at postnatal day 5 and continued for 2 weeks with the 5-HT synthesis inhibitor para-chlorophenylalanine, or for 4 weeks with the 5-HT(1A) receptor (5-HT(1A)R) antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexane carboxamide (WAY 100635), induced total or partial recovery of REMS, respectively, in 5-HTT-/- mutants. Early life treatment with WAY 100635 also reversed the depression-like behavior otherwise observed in these mutants. Possible adaptive changes in 5-HT(1A)R after neonatal treatment with WAY 100635 were investigated by measuring 5-HT(1A) binding sites and 5-HT(1A) mRNA in various REMS- and/or depression-related brain areas, as well as 5-HT(1A)R-mediated hypothermia and inhibition of neuronal firing in the dorsal raphe nucleus. None of these characteristics were modified in parallel with REMS recovery, suggesting that 5-HT(1A)Rs involved in wild-type phenotype rescue in 5-HTT-/- mutants are located in other brain areas or in 5-HT(1A)R-unrelated circuits where they could be transiently expressed during development. The reversal of sleep alterations and depression-like behavior after early life blockade of 5-HT(1A)R in 5-HTT-/- mutants might open new perspectives regarding preventive care of sleep and mood disorders resulting from serotonin transporter impairments during development.

Anxiety in mice: a principal component analysis study.

Two principal component analyses of anxiety were undertaken investigating two strains of mice (ABP/Le and C57BL/6ByJ) in two different experiments, both classical tests for assessing anxiety in rodents. The elevated plus-maze and staircase were used for the first experiment, and a free exploratory paradigm and light-dark discrimination were used for the second. The components in the analyses produced definitions of four fundamental behavior patterns: novelty-induced anxiety, general activity, exploratory behavior, and decision making. We also noted that the anxious phenotype was determined by both strain and experimental procedure. The relationship between behavior patterns and the use of specific tests plus links with the genetic background are discussed.

From the behavioral pharmacology of beta-carbolines to seizures, anxiety, and memory.

A number of beta-carbolines are inverse agonists of the GABA-A receptor complex, acting on the benzodiazepine site. They show convulsive properties when administered at high doses, anxiogenic properties at moderate doses, and learning-enhancing effects at low doses. These data suggest a possible physiological relationship, through the GABA-A receptor channel, between memory processes, anxiety, and ultimately, in pathological states, epileptic seizures. This relationship seems to be confirmed partially by experiments on mouse strains selected for their resistance (BR) and sensitivity (BS) to a single convulsive dose of a beta-carboline. These two strains also show differences in anxiety and learning abilities. However, some opposite results found while observing the behavior of the two strains suggest that in addition to pharmacologically induced anxiety, there is spontaneous anxiety, no doubt involving other brain mechanisms.

Mouse lines selected for difference in sensitivity to beta-CCM also differ in memory processes.

Methyl-beta-carboline-3-carboxylate (or beta-CCM) is a benzodiazepine receptor ligand with inverse agonist properties. Two strains of mice were selected, one for sensitivity (BS) and one for resistance (BR) to a convulsive dose of beta-CCM. These two strains were then shown to differ in several biochemical, pharmacological and behavioral characteristics; specifically BS mice were less anxious than BR mice. The present work provides evidence of differences in the learning abilities of the two strains. Three different learning tasks were used: spatial delayed discrimination on the 4-hole board, a learned choice between a lit and a dark compartment in a T-maze, and place-learning in an 8-arm radial maze. In all three tasks, BS mice had consistently better performance levels than BR mice.

Spatio-temporal analysis of locomotion in BALB/cByJ and C57BL/6J mice in different environmental conditions.

We analysed spatial and temporal characteristics of mouse locomotion and investigated whether mouse gait differed between strains and environments. To this end, we used two inbred strains of mice (BALB/cByJ and C57BL/6J) known for their contrasting inherent level of anxiety, in three different visual surroundings. The animal position was determined relative to each environment. Gait cycle, defined as the sequence of limb movements, was analysed relative to time. We also recorded spatial parameters of gait such as stride length, track width and footfall characteristics. These measures allowed us to obtain an accurate description of locomotion and to assess subtle modifications of the gait. We found that mice adjusted their position in space, posture and gait in order to either stabilize their body on the ground in a potentially unsafe environment, or to optimize propulsion and maneuverability in a safer location. In addition, the two strains of mice used different strategies, suggesting that the inherent level of emotionality may affect the organization of locomotion in mice. We further concluded that higher structures of the central nervous system are involved in the online control of locomotion.

GABA-A receptor complex and memory processes.

Considerable evidence has been provided these last years for the involvement of the GABAA receptor complex in memory processes. Compounds that enhance the action of GABA, such as benzodiazepines, impair memory processing. On the contrary, compounds that reduce the action of GABA, such as -CCM, pentylenetetrazol or picrotoxin, have the opposite action, that is : enhance memory processing. All these actions seem to focus mainly on the acquisition (learning) processes. Depending on the dose, the same compounds also have effects on anxiety and on seizuring. Benzodiaze-pines are well-known anxiolytic and anticonvulsant agents whereas compounds that reduce the action of GABA have been found to produce anxiogenic and convulsant actions. The GABAA receptor complex might thus be the location of a possible link between a pathological state (epilepsy) and two normal functions (anxiety and learning). This link is likely to involve common genetic pathways. In the normal subject, these data also emphasize the idea that normal memory processing involves a moderate level of anxiety.

Chronic ultra-mild stress improves locomotor performance of B6D2F1 mice in a motor risk situation.

Chronic low grade stress predispose to psychopathological disorders. We consistently showed that chronic ultra-mild stress (CUMS) applied to B6D2F1 female mice induced behavioral disinhibition in several conflict exploration models. Insufficient reactivity to conflicts may be maladaptive and lead to inappropriate appreciation of potential risks and impaired ability to cope with those. Therefore, the purpose of the study was to assess the effect of a CUMS procedure on the behavior of mice in a motor risk situation based on multisensory conflict. Following three weeks exposure to various mild stressors, stressed and control B6D2F1 mice were tested on the rotating beam to determine how CUMS exposure affected balance control, posture stability and locomotor performance in response to a sensory-motor challenge. Detailed behavioral analysis included several parameters, both postural (height of the trunk, tail angle, number of imbalances, falls and head movements) and kinetic (mean velocity on the beam, distance covered with large and small movements, plus time spent in no-motion episodes). Comparisons between control and stressed mice showed that CUMS exposure increased mean velocity and improved locomotor performance in the learning task. In addition, sensitivity to sensory conflict seemed to be reduced in stressed mice, which displayed fewer behavioral adjustments to the increasing difficulty of the test compared to control mice. The results are discussed in terms of the possible influence of disturbances in behavioral and attentional inhibitory processes following CUMS exposure. Whether longer periods of CUMS exposure would shift the performance on the RTB from improvement to deterioration remain to be established.

A new method for the assessment of spatial orientation and spatial anxiety in mice.

The implication of integrated functional sensory relations of the body to space in anxiety disorders is a very important issue which encourages the development of animal models, in particular, for pharmacological perspectives and for the functional assessment of the deficits induced by genetic manipulation in the mouse or the rat. A new experimental device is presented here: It is comprised of a rotating tunnel and a rotating-beam controlled by computer which can be used for multiple visuo-idiothetic and kinesthetic sensory conflict situations during active locomotor behaviour by mice. The system is linked to a digital video system, Video-Track trade mark, designed to track and record the movements of the animals. Anxious BALB/cByJ mice were compared to non-anxious C57BL/6J mice and were seen to display highly disturbed locomotor behaviour in a sensory conflict situation. The model highlights the advantages of video-digital analysis for animal behavioural sciences.

Posture and balance responses to a sensory challenge are related to anxiety in mice.

Anxiety disorders and balance disorders share common clinical features related to perception such as spatial disorientation or dizziness. The search for the mechanism underlying this core of symptoms led us to investigate impairments in multisensory integration. In mice, the 'rotating beam test' allows analysis of changes in balance control and posture in response to a multisensory challenge. We used the BALB/c and C57BL/6 inbred strains of mice, known for their contrasted anxiety-related behavior. The level of anxiety was also manipulated using anxiolytic and anxiogenic pharmacological compounds. Despite equal sensori-motor abilities, anxious mice were more prone to fall off the rotating beam and showed more imbalance than non-anxious mice. Striking inter-strain differences in posture were also observed. Diazepam and beta-CCM reversed these strain-specific responses in opposite directions. We demonstrated that balance and postural strategies developed in response to a multisensory challenge vary as a function of the level of anxiety in mice.

Behavioral models for anxiety and multisensory integration in animals and humans.

Complaints related to dizziness, balance problems and spatial disorientation in psychiatry have seldom been considered as a possible manifestation of a distorted multisensory integrative ability. Several kinds of mismatches among simultaneous sensory information are encountered in everyday life but despite these, the central nervous system usually manages to update the internal representation of the body in the surrounding space. In some cases, a sensory mismatch may elicit an erroneous perception of the body in space, resulting in anxiety, dizziness and balance problems. As vestibular system dysfunction leads to dizziness and disorientation, it has been hypothesized that a peripheral vestibular abnormality could explain the presence of certain symptoms related to sensory mismatches in anxiety disorders. Several studies tried to find a link between panic disorder with or without agoraphobia and vestibular system dysfunction. Yet, even though some vestibular abnormalities have been demonstrated in these patients, it is difficult to demonstrate a cause-and-effect relationship between panic disorder and vestibular dysfunction. However, this does not rule out a possible influence of anxiety on normal vestibular function. The study of the relation between vestibular system and anxiety has to take into account that the vestibular system has three main functions: to maintain equilibrium through the vestibular spinal reflexes; to stabilize the visualization of the world through the vestibular-ocular reflex; to contribute to perception and orientation in space. We will review different studies in humans, which have particularly paid attention to the third function and its relation to anxiety. Animal experiments offer possibilities to more precisely analyze the different parameters underlying the behavioral results, as well as possible pharmacological actions on them. Two attempts have been made by our group to model, in mice, the preceding human data on integrated functional sensory relations of the body to space in anxiety disorders: the rotating beam and the rotating tunnel. We summarize here the main results obtained.

Pharmacological alterations of anxious behaviour in mice depending on both strain and the behavioural situation.

A previous study comparing non-emotive mice from the strain C57BL/6/ByJ with ABP/Le mice showed ABP/Le to be more anxious in an open-field situation. In the present study, several compounds affecting anxiety were assayed on ABP/Le and C57BL/6/ByJ mice using three behavioural models of anxiety: the elevated plus-maze, the light-dark discrimination test and the free exploratory paradigm. The compounds used were the full benzodiazepine receptor agonist, chlordiazepoxide, and the antagonist, flumazenil, the GABA(A) antagonist, bicuculline, the full 5-HT(1A) agonist 8-OH-DPAT, and the mixed 5-HT(1A)/5-HT(1B) agonist, RU 24969. Results showed the effect of the compounds to be dependent on both the strain and the behavioural task. Several compounds found to be anxiolytic in ABP/Le mice had an anxiogenic effect on C57BL/6/ByJ mice. More behavioural changes were observed for ABP/Le in the elevated plus-maze, but the clearest findings for C57BL/6/ByJ mice were observed in the light-dark discrimination apparatus. These data demonstrate that anxious behaviour is a complex phenomenon which cannot be described by a single behavioural task nor by the action of a single compound.