Dani Brunner

Altered fear circuits in 5-HT1A receptor KO mice

The study of genetically altered mice has been used successfully to determine the influence of different neurotransmitter receptors on fear and anxiety. Mice with a genetic deletion of the serotonin 1A receptor (5-HT(1A)R knockout [KO]) have been shown to be more fearful in a number of behavioral conflict tests, confirming the important role of this receptor in modulating anxiety. Factor analysis of the behavior of WT and 5-HT(1A)R KO mice in the open field test shows that locomotion and anxiety measures segregate independently, supporting the idea that the anxious behavior of the KO mice is not the result of altered locomotion. KO mice also show increased anxiety in the novelty-suppressed feeding task, which differs from the other conflict tests in the motivational drive of the animals. In response to a discrete aversive stimulus, foot shock, the KO mice show increased freezing and increased tachycardia. However, activation of the hypothalamic-pituitary-adrenal axis in response to stress appears to be slightly blunted in the KO animals. Together, these data support the idea that the 5-HT(1A)R modulates an important fear circuit in the brain. The dual function of the 5-HT(1A)R as both a presynaptic autoreceptor, negatively regulating serotonin activity, and a postsynaptic heteroreceptor, inhibiting the activity of nonserotonergic neurons in forebrain structures, has complicated interpretation of the anxious phenotype of these KO mice. A more complete understanding of the function of the 5-HT(1A)R awaits further study of its role in behaving animals using tissue-specific antagonists and novel transgenic mice with tissue-specific expression of the receptor.

Comprehensive behavioral and molecular characterization of a new knock-in mouse model of Huntington's disease: zQ175.

Huntington’s disease (HD) is an autosomal dominant neurodegenerative disorder characterized by motor, cognitive and psychiatric manifestations. Since the mutation responsible for the disease was identified as an unstable expansion of CAG repeats in the gene encoding the huntingtin protein in 1993, numerous mouse models of HD have been generated to study disease pathogenesis and evaluate potential therapeutic approaches. Of these, knock-in models best mimic the human condition from a genetic perspective since they express the mutation in the appropriate genetic and protein context. Behaviorally, however, while some abnormal phenotypes have been detected in knock-in mouse models, a model with an earlier and more robust phenotype than the existing models is required. We describe here for the first time a new mouse line, the zQ175 knock-in mouse, derived from a spontaneous expansion of the CAG copy number in our CAG 140 knock-in colony [1]. Given the inverse relationship typically observed between age of HD onset and length of CAG repeat, since this new mouse line carries a significantly higher CAG repeat length it was expected to be more significantly impaired than the parent line. Using a battery of behavioral tests we evaluated both heterozygous and homozygous zQ175 mice. Homozygous mice showed motor and grip strength abnormalities with an early onset (8 and 4 weeks of age, respectively), which were followed by deficits in rotarod and climbing activity at 30 weeks of age and by cognitive deficits at around 1 year of age. Of particular interest for translational work, we also found clear behavioral deficits in heterozygous mice from around 4.5 months of age, especially in the dark phase of the diurnal cycle. Decreased body weight was observed in both heterozygotes and homozygotes, along with significantly reduced survival in the homozygotes. In addition, we detected an early and significant decrease of striatal gene markers from 12 weeks of age. These data suggest that the zQ175 knock-in line could be a suitable model for the evaluation of therapeutic approaches and early events in the pathogenesis of HD.

Anxiety, motor activation, and maternal-infant interactions in 5HT-sub(1B ) knockout mice.

This study describes the development of anxiety and motor activation in mice lacking the serotonin (5HT) 1B receptor and in wild type controls and characterizes their early mother-infant interactions. In the isolation-induced ultrasonic vocalization paradigm, 5HT1B knockout pups vocalized less and were hyperactive, rearing, jumping, and rolling more often than wild type pups. One week postpartum, 5HT1B knockout mothers spent 20% more of their time outside the nest and were also hyperactive, rearing and climbing to the edge of the cage more often than the wild type mothers. There were no genotype effects on pup retrieval. Knockout adults were less anxious in the elevated plus-maze, defecated less, and head-dipped more, although none of the standard measures of anxiety (time and entries in the open arms) were different. 5HT1B knockout mice of both sexes were hyperactive during both the light and the dark phases of the 24-hr cycle. Thus, 5HT1B knockout mice show reduced anxiety and are hyperactive throughout their life.

Timing Deficits in Aging and Neuropathology

The capacity to capture the temporal information embedded in biologically relevant events is a necessary and ubiquitous ability of higher organisms. The cognitive apparatus that supports timing is integrally entwined with those supporting other cognitive processes including memory and attention. In this chapter, we argue that timing deficits consistently occur with aging and in specific neurodegenerative disorders (i.e., Parkinson’s disorder and Huntington disease), and might depend on and reflect attentional deficits that are also characteristic of normal aging and in these clinical populations. We review the impairments in temporal information processing seen in the elderly and in neural disease, and evaluate them in relation with the structural and neurochemical brain markers. Given the good correspondence between the psychophysical properties of interval timing across nonhuman and humans, we further argue that interval timing might serve as a quantitative model for cognitive aging that offers promise in the translation from preclinical to clinical studies.

In need of high-throughput behavioral systems

One of the current major bottlenecks in drug discovery is in vivo testing of candidate drugs in behavioral paradigms in normal or genetically altered mice. This testing is essential in discovering gene function and predicting potential efficacy of CNS drugs in humans. New efforts in the biotech community aim to alleviate this bottleneck by developing higher-throughput systems of behavioral, neurological and physiological analyses. Together with large pharmacological databases, equipped with state-of-the-art bioinformatic and/or data-mining algorithms, these systems will provide rapid and accurate indices of the therapeutic potential of novel drugs. By providing a substantial increase in the speed of behavioral testing, new high-throughput systems will facilitate current behavioral research with faster, more reliable approaches. Furthermore, screening whole drug-libraries and comparing the profiles of novel compounds to those of known compounds will facilitate the discovery of novel drugs. Target validation will also become more efficient with the fast characterization of novel mutant mice.

Discovery of Isoxazole Analogues of Sazetidine-A as Selective α4β2-Nicotinic Acetylcholine Receptor Partial Agonists for the Treatment of Depression

Depression, a common neurological condition, is one of the leading causes of disability and suicide worldwide. Standard treatment, targeting monoamine transporters selective for the neurotransmitters serotonin and noradrenaline, is not able to help many patients that are poor responders. This study advances the development of sazetidine-A analogues that interact with α4β2 nicotinic acetylcholine receptors (nAChRs) as partial agonists and that possess favorable antidepressant profiles. The resulting compounds that are highly selective for the α4β2 subtype of nAChR over α3β4-nAChRs are partial agonists at the α4β2 subtype and have excellent antidepressant behavioral profiles as measured by the mouse forced swim test. Preliminary absorption, distribution, metabolism, excretion, and toxicity (ADMET) studies for one promising ligand revealed an excellent plasma protein binding (PPB) profile, low CYP450-related metabolism, and low cardiovascular toxicity, suggesting it is a promising lead as well as a drug candidate to be advanced through the drug discovery pipeline.

Memory for inter-reinforcement interval variability and patch departure decisions in the starling,Sturnus vulgaris

An experiment with starlings was conducted to investigate the effect of variability in inter-reinforcement intervals on foraging decisions. The experimental design simulated an environment in which food was distributed in patches. Patches contained zero to four food items which could be collected by pecking at a key. All patches ended with sudden depletion. The time elapsed since the last reinforcement was the only way to detect the depletion of the patch. Once a patch was depleted, a new patch could be reached by completion of a travel requirement of 20 flights between two perches. Key pecks within a patch and the time of the last response in a patch (giving-in time) were recorded. The level of variability in the inter-reinforcement intervals was varied between different conditions. An increase in inter-reinforcement interval variability resulted in a flattening of response rate functions and giving-in time distributions, and in more asymmetry of the response functions, but not of the giving-in time distributions. Two theoretical models of decision making are presented, which differ in the assumptions about memory constraints. In one case, all inter-reinforcement intervals are remembered but in the other, only the intervals with extreme values are remembered. Both models accommodate response rates as a function of trial time, but only the second is compatible with the observed departure decision. Our results are compatible with net rate maximization.

Mnemonics for variability: remembering food delay.

Three experiments with White Carneaux pigeons (Columba livia) investigated memory and decision processes under fixed and variable reinforcement intervals. Response rate was measured during the unreinforced trials in the discrete-trial peak procedure in which reinforced trials were mixed with long unreinforced trials. Two decision models differing in assumptions about memory constraints are reviewed. In the complete-memory model (J. Gibbon, R.M. Church, S. Fairhurst, & A. Kacelnik, 1988), all interreinforcement intervals were remembered, whereas in the minimax model (D. Brunner, A. Kacelnik, & J. Gibbon, 1996), only estimates of the shortest and longest possible reinforcement times were remembered. Both models accommodated some features of response rate as a function of trial time, but only the second was compatible with the observed cessation of responding.

Identification of novel α4β2-nicotinic acetylcholine receptor (nAChR) agonists based on an isoxazole ether scaffold that demonstrate antidepressant-like activity.

There is considerable evidence to support the hypothesis that the blockade of nAChR is responsible for the antidepressant action of nicotinic ligands. The nicotinic acetylcholine receptor (nAChR) antagonist, mecamylamine, has been shown to be an effective add-on in patients that do not respond to selective serotonin reuptake inhibitors. This suggests that nAChR ligands may address an unmet clinical need by providing relief from depressive symptoms in refractory patients. In this study, a new series of nAChR ligands based on an isoxazole-ether scaffold have been designed and synthesized for binding and functional assays. Preliminary structure-activity relationship (SAR) efforts identified a lead compound 43, which possesses potent antidepressant-like activity (1 mg/kg, IP; 5 mg/kg, PO) in the classical mouse forced swim test. Early stage absorption, distribution, metabolism, excretion, and toxicity (ADME-Tox) studies also suggested favorable drug-like properties, and broad screening toward other common neurotransmitter receptors indicated that compound 43 is highly selective for nAChRs over the other 45 neurotransmitter receptors and transporters tested.

Circadian Abnormalities in Motor Activity in a BAC Transgenic Mouse Model of Huntington's Disease.

Huntington’s disease (HD) is a progressive neurodegenerative disease marked by psychiatric and motor problems. Recently, these findings have been extended to deficits in sleep and circadian function that can be observed in HD patients and in HD mouse models, with abnormal sleep patterns correlating with symptom severity in patients. Here, we studied the behavior of the BAC HD mouse model using an 24/7 automated system; the results indicate significant lengthening of the circadian period in the mutant mice. These results reinforce previous findings in HD models and symptomatic HD patients, indicating that circadian dysfunction is a core feature of HD.