Open field locomotion and neurotransmission in mice evaluated by principal component factor analysis-effects of housing condition, individual activity disposition and psychotropic drugs

Effect of sacubitril/valsartan on cognitive impairment in colchicine-induced Alzheimer's model in rats

Alzheimer's disease (AD) is a complex neurodegenerative disease. There is epidemiological evidence that heart failure (HF) patients are at higher risk of developing AD, and the impact of sacubitril/valsartan, the first angiotensin receptor-neprilysin inhibitor (ARNI) approved for HF, on cognitive functions is still controversial. To investigate the effect of sacubitril/valsartan on cognitive functions in colchicine-induced AD rat model. Forty adult male Wistar rats were equally allocated into four groups (each of 10 rats): Group I: normal control, Group II: intracerebroventricular injection of colchicine (15 μg/5 μl/bilaterally), Group III: colchicine (15 μg/5 μl/bilaterally, icv) + oral sacubitril/valsartan (100 mg/kg/day) for 25 days, and Group IV: colchicine (15 μg/5 μl/bilaterally, icv) + oral valsartan (50 mg/kg/day) for 25 days. Behavioral assessment was done using Morris water maze and passive avoidance tasks. Biochemically, β-amyloid (1-40 and 1-42) peptides, oxidative stress (malondialdehyde and superoxide dismutase) and inflammatory (tumor necrosis factor-alpha) parameters were measured in hippocampus and prefrontal cortex. Sacubitril/valsartan exaggerated colchicine-induced cognitive impairment in both Morris water maze and passive avoidance tasks and was associated with significant increase in β-amyloid accumulation, oxidative stress, and inflammation versus valsartan. Sacubitril/valsartan caused deleterious effect on cognitive impairment and biochemical alterations in colchicine-induced AD rat model. Hence, special caution should be taken following long-term intake of ARNI on cognitive functions.

Differential Effects of a Novel Opioid Ligand UTA1003 on Antinociceptive Tolerance and Motor Behaviour

Analgesic tolerance is a major problem in the clinic for the maintenance of opioid-induced long-term pain relief. Opioids with mixed activity on multiple opioid receptors promise reduced antinociceptive tolerance in preclinical studies, but these compounds typically show poor bioavailability upon oral, subcutaneous, intraperitoneal, or intravenous administration. We designed UTA1003 as a novel opioid that acts as a mu (MOP) and kappa (KOP) opioid receptor agonist and a partial agonist for delta (DOP) opioid receptor. In the present study, its antinociceptive effects, as well as its effects on antinociceptive tolerance and motor behaviour, were investigated in male rats. Acute antinociception was measured before (basal) and at different time points after subcutaneous injection of UTA1003 or morphine using the tail flick and hot plate assays. Various motor behavioural activities, including horizontal locomotion, rearing, and turning, were automatically measured in an open-field arena. The antinociceptive and behavioural effects of repeated administration of UTA1003 and morphine were determined over eight days. UTA1003 induced mild antinociceptive effects after acute administration but induced no tolerance after repeated treatment. Importantly, UTA1003 co-treatment with morphine prevented antinociceptive tolerance compared to morphine alone. UTA1003 showed less motor suppression than morphine in both acute and sub-chronic treatment regimens, while it did not affect morphine-induced motor suppression or hyper-excitation. Based on these activities, we speculate that UTA1003 crosses the blood-brain barrier after subcutaneous administration and, therefore, could be developed as a lead molecule to avoid opioid-induced antinociceptive tolerance and motor suppression. Further structural modifications to improve its antinociceptive effects, toxicity profile, and ADME parameters are nevertheless required.

Long-term scopolamine treatment altered locomotor, exploratory and anxiety-like behaviours of albino rats

Background

Animal models are used to provide an adequate investigation of brain-behaviour, physiological and path physiological relationships to give insight into human behaviour and the underlying processes of drugs affecting the nervous system. Scopolamine; SCO (alkaloid l-(2)-scopolamine [l-(2)-hyoscine]) has a competitive inhibitory effect on muscarinic receptors for acetylcholine. Thus, this study was designated to investigate the effect of long-term SCO treatment on locomotor, exploratory and anxiety-like behaviours of rats using open field test.

Results

The long-term SCO treatment induced a prominent increase in locomotion (hyperactivity) and exploratory behaviour of rats. In addition, anxiety-like behavioural patterns showed a non-significant difference in SCO treated compared to control. Serotonin level was significantly decreased in the scopolamine treated group in comparison with the control group.

Conclusions

Data suggested that long-term SCO treatment resulted in marked neurobehavioural alterations in a rat as an animal model.

Alfa2-adrenoblockers attenuate the elevated plasma cholesterol, anxiety levels and restore impaired spatial memory of rats under the chronic noise exposure

Noise is considered one of the environmental hazards that negatively affect health. It can cause damage to the auditory, neurological, hormonal and cardiovascular systems, in addition to impairing psychological and cognitive functions. Considering the significance of vascular disturbances and oxidative stress in the development of the aforementioned negative effects, the purpose of our investigation was to study the level of high density lipoprotein-cholesterol (HDL-Cl), low density lipoprotein-cholesterol (LDL-Cl), and total cholesterol (TCl) in plasma, in addition to the behavioral characteristics of white rats, and the effects of the α₂-adrenoblockers beditin and mesedin to reveal their antiatherogenic effect during noise exposure. The "Open field" and "Y-maze" tests were used in order to evaluate the behavioral states of the rats. Investigations were carried out on albino rats divided into 4 groups. The 1^st group of rats served as a control. The 2^nd, 3^rd and 4^th groups were exposed to 91 dBA of noise; the duration of exposure was 8 h per day for 60 days. The 3^rd group was injected with beditin and the 4^th group with mesedin, both intraperitoneally and repeatedly. According to our results, the chronic exposure to high-volume noise leads to the increase of plasma TCl and LDL-Cl concentrations and the decrease of HDL-Cl levels, resulting in increase of the atherogenic coefficient, which is estimated to be one of the main cardiovascular disease risk factors. The "Open field" and "Y-maze" tests revealed that chronic noise exposure caused disturbances in the behavioral activity, a noise duration-dependent delay in movement and orientation, increased anxiety and deficit in the animals' spatial memory. The administration of α₂-adrenoblockers to the noise-exposed animals had a regulatoryeffects of varying intensities, depending on the medication used and the studied parameters under the conditions of chronic acoustic stress.

Adrenergic alpha-2 receptor antagonists cease augmented oxidation of plasma proteins and anxiety of rats caused by chronic noise exposure

BACKGROUND

Noise is one of the environmental factors, which is considered as a powerful stressor for the organism. Generally, the acoustic stress affects the behavior and physiological state of humans and animals.

AIMS

The goal of this study is to investigate the relationship between chronic noise exposure and the effects of adrenergic alpha-2 receptor antagonists, beditin and mesedin, on the anxiety and oxidation of plasma proteins and fibrinogen in rats.

METHODS

The experiments were carried out on non-linear albino male rats, divided into four groups (six animals in each): 1. Healthy controls 2. Exposed to noise of a level 91 dB(A), eight hours daily, during 7, 30 and 60 days; 3. Injected with 2 mg/kg of beditin (2-(2-amino-4-thiazolyl)-1,4-benzodioxane hydrochloride)); 4. Injected with 10 mg/kg mesedin (2-(2-methyl-amino-thiozolyl)-1,4-benzodioxane hydrochloride). For evaluating the cognitive impairment, the Any-maze test was applied. The level of carbonylation of proteins was assessed by reaction with 2,4-dinitrophenylhydrazine, spectrophotometrically.

RESULTS

Chronic noise decreased locomotor activity and increased anxiety and oxidation of plasma protein and fibrinogen. Intensity of these changes were dependent on the duration of noise exposure.

CONCLUSION

The Alpha 2 adrenoblockers alleviate oxidative modification of plasma proteins and reduce the cognitive impairment caused by chronic exposure to noise.

Evaluation of the antianxiety and antidepressant activities of mosapride in Wistar albino rats

Background The 5HT4 receptor agonists are antidepressants with a unique mode of action. Many studies have been done on investigational drugs, and mosapride has been shown to have a 5HT3 antagonistic property. In this study, we assessed the potential anxiolytic and antidepressant effects of mosapride on Wistar albino rats. Methods The rats were randomly assigned to two models containing 4 groups of 6 animals each. In the anxiety model, four groups included 0.5 mL of 0.5% carboxymethyl cellulose (CMC), mosapride 1.5 mg/kg, mosapride 3 mg/kg and diazepam 2 mg/kg. They were dosed for 5 days. On the 3rd day, the elevated plus maze (EPM) was conducted, and on the 5th day, the open field (OF) tests were conducted. In the depression model, four groups included 0.5 mL of 0.5% CMC, mosapride 1.5 mg/kg, mosapride 3 mg/kg and imipramine 30 mg/kg. After 3 days of dosing, the forced swim test (FST) was conducted, followed by a washout period of 1 month. Then, the rats were subjected to chronic unpredictable stress with sucrose preference. Results Compared with the control, the mosapride-treated animals showed significant anxiolytic behavior at both high and low doses in the EPM and OF tests. In the FST, both high and low doses of mosapride reduced immobility. The climbing behavior was prominent at a high dose of mosapride, whereas swimming was prominent at a low dose. In the chronic stress model, both doses of mosapride preserved sucrose preference comparable to imipramine. Conclusion These findings suggest that mosapride has anxiolytic and antidepressant activities at clinically used doses.

Exploratory rearing: a context- and stress-sensitive behavior recorded in the open-field test

Stressful experiences are linked to anxiety disorders in humans. Similar effects are observed in rodent models, where anxiety is often measured in classic conflict tests such as the open-field test. Spontaneous rearing behavior, in which rodents stand on their hind legs to explore, can also be observed in this test yet is often ignored. We define two forms of rearing, supported rearing (in which the animal rears against the walls of the arena) and unsupported rearing (in which the animal rears without contacting the walls of the arena). Using an automated open-field test, we show that both rearing behaviors appear to be strongly context dependent and show clear sex differences, with females rearing less than males. We show that unsupported rearing is sensitive to acute stress, and is reduced under more averse testing conditions. Repeated testing and handling procedures lead to changes in several parameters over varying test sessions, yet unsupported rearing appears to be rather stable within a given animal. Rearing behaviors could therefore provide an additional measure of anxiety in rodents relevant for behavioral studies, as they appear to be highly sensitive to context and may be used in repeated testing designs.

Animal models in psychiatric research: The RDoC system as a new framework for endophenotype-oriented translational neuroscience

The recently proposed Research Domain Criteria (RDoC) system defines psychopathologies as phenomena of multilevel neurobiological existence and assigns them to 5 behavioural domains characterizing a brain in action. We performed an analysis on this contemporary concept of psychopathologies in respect to a brain phylogeny and biological substrates of psychiatric diseases. We found that the RDoC system uses biological determinism to explain the pathogenesis of distinct psychiatric symptoms and emphasises exploration of endophenotypes but not of complex diseases. Therefore, as a possible framework for experimental studies it allows one to evade a major challenge of translational studies of strict disease-to-model correspondence. The system conforms with the concept of a normality and pathology continuum, therefore, supports basic studies. The units of analysis of the RDoC system appear as a novel matrix for model validation. The general regulation and arousal, positive valence, negative valence, and social interactions behavioural domains of the RDoC system show basic construct, network, and phenomenological homologies between human and experimental animals. The nature and complexity of the cognitive behavioural domain of the RDoC system deserve further clarification. These homologies in the 4 domains justifies the validity, reliably and translatability of animal models appearing as endophenotypes of the negative and positive affect, social interaction and general regulation and arousal systems’ dysfunction.

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The RDoC system encourages endophenotype-oriented experimental studies in human and animals.

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The system conforms with the normality-pathology continuum concept.

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The RDoC system appears to be a suitable framework for basic research.

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Four RDoC domains show construct and phenomenological homology in human and animals.

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Endophenotype-based models of affective psychopathologies appear most reliable.

The drug candidate, ADX71441, is a novel, potent and selective positive allosteric modulator of the GABAB receptor with a potential for treatment of anxiety, pain and spasticity

Positive allosteric modulation of the GABA_B receptor is a promising alternative to direct activation of the receptor as a therapeutic approach for treatment of addiction, chronic pain, anxiety, epilepsy, autism, Fragile X syndrome, and psychosis. Here we describe in vitro and in vivo characterization of a novel, potent and selective GABA_B positive allosteric modulator (PAM) N-(5-(4-(4-chloro-3-fluorobenzyl)-6-methoxy-3,5-dioxo-4,5-dihydro-1,2,4-triazin-2(3H)-yl)-2-fluorophenyl)acetamide (ADX71441). In vitro, Schild plot and reversibility tests at the target confirmed PAM properties of the compound. In mice and rats ADX71441 is bioavailable after oral administration and is brain penetrant. A single dose of ADX71441 had an anxiolytic-like profile in the mouse marble burying test (minimum effective dose; MED 3 mg/kg) as well as in the elevated plus maze test in mice and rats (both MED 3 mg/kg). Also, in mice, acute administration of ADX71441 reduced visceral pain-associated behaviors in the acetic acid-induced writhing test. ADX71441 dose-dependently reduced time on rotarod in rats (MED 10 mg/kg) indicative of muscle-relaxant qualities. ADX71441 reduced locomotor activity in mice (10 mg/kg) and rats (3 mg/kg) after single dose; however, following sub-chronic administration in mice, 30 mg/kg ADX71441 was associated with normal locomotor activity. While acute administration of ADX71441 reduced body temperature in rats and mice (both MED 10 mg/kg), the effect in the former was transient, rapidly returning to normal levels despite high concentrations of the compound remaining in plasma. Thus, the GABA_B PAM ADX71441 represents a valid therapeutic approach for development of novel treatment of anxiety, pain and spasticity.

Evaluation of peripheral versus central effects of GABA(B) receptor activation using a novel, positive allosteric modulator of the GABA(B) receptor ADX71943, a pharmacological tool compound with a fully peripheral activity profile

BACKGROUND AND PURPOSE

The GABA(B) receptor agonist, baclofen, has shown promising effects in patients suffering from pain, post-traumatic stress disorder, alcoholism, overactive bladder and gastroesophageal reflux disease. However, baclofen's short duration of action and side effects limit its wider use. Here we characterized a novel, GABA(B) receptor positive allosteric modulator (PAM) ADX71943.

EXPERIMENTAL APPROACH

In vitro, ADX71943 was assessed for pharmacological activity and selectivity using recombinant and native GABA(B) receptors. In vivo ADX71943 was assessed in the acetic acid-induced writhing (AAW) test in mice and formalin tests (FTs) in mice and rats. Marble burying (MB) and elevated plus maze (EPM) tests, rotarod, spontaneous locomotor activity (sLMA) and body temperature (BT) tests in mice and rats were used to investigate centrally-mediated effects.

KEY RESULTS

In vitro, in the presence of GABA, ADX71943 increased the potency and efficacy of agonists and showed selectivity at the GABA(B) receptor. ADX71943 reduced pain-associated behaviours in AAW; an effect blocked by GABA(B) receptor antagonist CGP63360. ADX71943 reduced pain in the FT in mice and rats, but was inactive in the MB and EPM despite reaching high concentrations in plasma. ADX71943 had no effect on BT, rotarod and sLMA.

CONCLUSIONS AND IMPLICATIONS

ADX71943 showed consistent and target-related efficacy in tests of disorders that have a significant peripheral component (acute and chronic pain), while having no effect in those associated with centrally-mediated anxiety-like reactivity and side effects. Thus, ADX71943 is a useful pharmacological tool for delineation of peripherally- versus centrally-mediated effects of GABA(B) receptor activation.

Four factors underlying mouse behavior in an open field

The observation of the locomotor and exploratory behaviors of rodents in an open field is one of the most fundamental methods used in the field of behavioral pharmacology. A variety of behaviors can be recorded automatically and can readily generate a multivariate pattern of pharmacological effects. Nevertheless, the optimal ways to characterize observed behaviors and concomitant drug effects are still under development. The aim of this study was to extract meaningful behavioral factors that could explain variations in the observed variables from mouse exploration. Behavioral data were recorded from male C57BL/6J mice (n=268) using the Behavioral Pattern Monitor (BPM). The BPM data were subjected to the exploratory factor analysis. The factor analysis extracted four factors: activity, sequential organization, diversive exploration, and inspective exploration. The activity factor and the two types of exploration factors correlated positively with one another, while the sequential organization factor negatively correlated with the remaining factors. The extracted factor structure constitutes a behavioral model of mouse exploration. This model will provide a platform on which one can assess the effects of psychoactive drugs and genetic manipulations on mouse exploratory behavior. Further studies are currently underway to examine the factor structure of similar multivariate data sets from humans tested in a human BPM.

Parallel declines in cognition, motivation, and locomotion in aging mice: association with immune gene upregulation in the medial prefrontal cortex

Aging in humans is associated with parallel changes in cognition, motivation, and motoric performance. Based on the human aging literature, we hypothesized that this constellation of age-related changes is mediated by the medial prefrontal cortex and that it would be observed in aging mice. Toward this end, we performed detailed assessments of cognition, motivation, and motoric behavior in aging mice. We assessed behavioral and cognitive performance in C57Bl/6 mice aged 6, 18, and 24 months, and followed this with microarray analysis of tissue from the medial prefrontal cortex and analysis of serum cytokine levels. Multivariate modeling of these data suggested that the age-related changes in cognition, motivation, motor performance, and prefrontal immune gene expression were highly correlated. Peripheral cytokine levels were also correlated with these variables, but less strongly than measures of prefrontal immune gene upregulation. To determine whether the observed immune gene expression changes were due to prefrontal microglial cells, we isolated CD11b-positive cells from the prefrontal cortex and subject them to next-generation RNA sequencing. Many of the immune changes present in whole medial prefrontal cortex were enriched in this cell population. These data suggest that, as in humans, cognition, motivation, and motoric performance in the mouse change together with age and are strongly associated with CNS immune gene upregulation.

Urine from stressed rats increases immobility in receptor rats forced to swim: Role of 2-heptanone

The present study was aimed to determine whether the urine from donor rats, which were physically stressed (UD-PS) by unavoidable electric footshocks, produces despair in receptor partner rats (RP) in the long-term. For each trial, an RP rat was placed during 10 min once per day for 21 days in a small non-movement-restricting cage impregnated with the urine collected from a UD-PS rat. Control rats, free of stimulation, maintained their locomotion and immobility scores at basal values throughout the 21-day test. After 21 days of stressing experience [F(2,90)=15.22, P<0.0001] locomotion significantly increased in RP rats (r=0.938, P<0.01), whereas in the UD-PS group locomotion decreased (r=-0.606, P<0.05). The RP and UD-PS groups displayed the longest time of immobility [F(2,90)=8.83, P<0.001] in the forced-swim test (RP, r=0.886, P<0.05; UD-PS, r=0.962, P<0.001) compared with the control group (r=-0.307, NS). We conclude that the RP became similarly despaired as the UD-PS group through the action of 2-heptanone, a ketonic compound identified in UD-PS urine by HS-GC/MS techniques. This ketone was found to be increased [F(2,15)=3.50, P<0.05] from the 1st day of unavoidable electric footshocks, and to induce despair, an effect reverted [F(2,21)=16.5, P<0.0001] by imipramine (5.0 mg/kg) in another group of rats.

Serotonin 1A and 2A receptor densities, neurochemical and behavioural characteristics in two closely related mice strains after long-term isolation

Knowledge about individual differences in behavioural traits and their neurostructural and neurochemical correlates should improve therapeutic approaches of corresponding psychopathology. The presented investigations are aimed to reveal interrelationships between central nervous serotonergic [5-HT] receptor densities and neurochemical as well as behavioural traits in two mice strains. Male AB-Halle [ABH] and AB-Gatersleben [ABG] mice differing in aggression were investigated after 6 weeks of isolation housing. 5-HT1A and 5-HT2A receptors were analysed in different brain regions by in vitro autoradiography. HPLC determinations of aminergic transmission in the cortex, hippocampus, striatum as well as in the raphe-region and radioimmunoassay determination of serum corticosterone were done before (basal condition) and after behavioural tests (challenge condition). Receptor autoradiography revealed higher 5-HT1A receptor densities, especially in limbic regions, and lower 5-HT2A receptor densities in the basal ganglia of ABH mice. Furthermore, ABH mice characterized as behaviourally more active in the open field and plus maze as well as more reactive and aggressive during the social interaction test showed lower basal 5-hydroxyindolacetic acid [5-HIAA] concentrations in the hippocampus, cortex and raphe-region as well as a different activation pattern in serotonergic, dopaminergic and noradrenergic brain systems after challenge in comparison to ABG mice. Additionally lower corticosterone concentrations were found in ABH mice. Lower basal serotonergic and striatal dopaminergic, but higher basal cortical dopaminergic metabolism in contrast to enhanced challenge-induced central nervous serotonergic and cortical dopaminergic reactivities are discussed to be crucial for an enhanced reactive behavioural trait, which could secondarily result in aggression-related behaviours, where higher 5-HT1A receptor and lower 5-HT2A receptor densities may be essential.

Housing environment alters delayed-type hypersensitivity and corticosterone concentrations of individually housed male C57BL/6 mice

Housing conditions can alter both the physiology and behaviour of laboratory animals. Forced-air-ventilated micro-isolation systems increase the efficient use of space, decrease the incidence of disease among laboratory rodents, and provide better working conditions for animal care staff; however, such systems can increase breeding variability and mortality. We examined the possibility that stressors associated with automated housing conditions evoke subtle changes among immune, endocrine, and behavioural parameters in mice housed in a static versus a forced-air-ventilated micro-isolation system. In addition, we assessed the effects of housing in the forced-air-ventilated micro-isolation system both with and without the use of an automatic watering system. Housing in the forced-air-ventilated micro-isolation system, using the automatic watering system, suppressed delayed-type hypersensitivity (DTH) responses, a measure of cell mediated immune function, compared with the responses of mice housed in static cages. Hypothalamic–pituitary–adrenal axis function was also altered by housing in the forced-air-ventilated micro-isolation system with the use of the automatic watering system, such that mice in this housing system had lower resting corticosterone concentrations and increased reactivity to restraint. Despite these changes in corticosterone, housing condition did not alter activity level or exploratory, anxiety-like, or depressive-like behaviours. These results suggest that investigators should carefully consider housing conditions in studies of immune and endocrine function.

Autoradiographic analyses of 5-HT1A and 5-HT2A receptors after social isolation in mice

Social isolation of rodents is used to model human psychopathological processes. In the present study, the effects of intermediate and long term isolation housing on postsynaptic 5-HT(1A) and 5-HT(2A) receptors were analyzed in male mice housed in groups or isolation for 4 and 12 weeks. [3H]8-OH-DPAT and [3H]ketanserin were used to label 5-HT(1A) and 5-HT(2A) receptors. Four representative sagittal sections (planes 1-4) were scored by in vitro autoradiography. Whereas after 4 weeks of housing both receptor densities were lowered significantly in isolated mice, after 12 weeks of housing only marginal isolation effects were seen. Intermediate isolation reduced 5-HT(1A) receptors especially in the lateral frontal, parietal and entorhinal cortex (-63%), in the lateral CA1-3 and dentate gyrus region of the hippocampus (-68%), in the basolateral, basomedial, central and medial amygdaloid nuclei (between -38 and -66%), and in the hypothalamus (-28%). 5-HT(2A) receptors were strongly reduced in the frontal cortex (between -47 and -74%), in the hippocampus (between -47 and -95%), in the striatum (between -66 and -76%), and in the accumbens nucleus (between -59 and -73%) in comparison to group housed control mice. After 12 weeks of isolation in the hippocampus continuously decreased 5-HT(1A) receptor densities were demonstrated (between -24 and -61%). But increased 5-HT(2A) receptor densities were seen in the lateral striatum (+86%) compared to control mice. Age-dependent effects were also found. After 12 weeks of group housing the 5-HT(1A) and 5-HT(2A) receptor densities were decreased (between -28 and -54%) in all analyzed brain regions in comparison to 4 weeks of group housing. Isolated animals showed diminished 5-HT(1A) receptor densities in the cortex (-14%) and hippocampus (-15%), but increased 5-HT(1A) receptor densities in the amygdala (+33%) after 12 weeks. The 5-HT(2A) receptor densities were increased in all analyzed regions (between +31 and +96%) after 12 weeks of isolation compared to 4 weeks. To explain these dynamic, time-dependent pattern of isolation-induced changes different regulation processes are supposed regarding 5-HT(1A) and 5-HT(2A) receptors. Besides metabolism-related adaptation processes also neurotransmitter and hormonal (e.g., glucocorticoid) interactions especially in limbic regions have to be considered.

Effects of the social conditions of housing through testing on cocaine-induced contextual sensitisation and conditioned locomotion in C57BL/6J mice

The potential differential effects of isolated and collective housing through the testing phase on sensitisation to cocaine-induced locomotion, the subsequent conditioned locomotion and the context-dependent expression of sensitisation were examined in C57Bl/6J male mice. Sensitisation was first generated in mice receiving seven once-daily subcutaneous injections of either saline or 10 mg/kg cocaine, before being placed in a testing chamber (singly) or in their home cage. On Day 8, mice were tested for conditioned locomotion (under saline). On Day 12, after three daily sessions of reinstatement of sensitisation, they were tested for contextual sensitisation (under cocaine). Whereas little or no effect of housing on the development of sensitisation was found, postsensitisation conditioned activity was significantly greater in isolation-kept mice (in comparison with the group-kept animals) and the likelihood of inducing a context-dependent expression of sensitisation was greater in grouped-housed mice. The results indicate that some of the aspects of contextual sensitisation can be influenced by the social conditions of lodging, not only when these conditions start several weeks before or during previous developmental periods of animals life (as previously published), but also when social isolation or social grouping are initiated after sexual maturity and applied through the period of treatments and testing. Moreover, the differential effect of social conditions of lodging on conditioned activity and contextual expression of sensitisation disagrees with the excitatory conditioning account of contextual sensitisation.

Home-cage activity in heterogeneous stock (HS) mice as a model of baseline activity

Behavioral genetic work in humans indicates that clinical hyperactivity is best viewed as the extreme end of activity levels in the population. However, current animal models of hyperactivity are not studied as quantitative traits as they are either knockout models or inbred strains. Furthermore, these animal models generally demonstrate elevated locomotion in novel environments, but not in their home-cages. This is the opposite of the symptoms seen in the human condition where childhood hyperactivity is generally more pronounced in constant, unstimulating situations. In this study we filmed an outbred population of 44 heterogeneous stock (HS) mice under red light during their active phase, to assess the reliability of individual differences in home-cage behavior and extract an index of home-cage activity (HCA) level. We then compared this measure to locomotor behavior in a novel environment--the open-field. Reliable individual differences in home-cage behaviors such as running, swinging on bars, and burrowing were found, and principal component factor analysis yielded a general activity factor, which accounted for 32% of the variance and correlated 0.90 with a subjective impression of activity level. The correlation between HCA and locomotor activity in the open-field was 0.23, which was non-significant. However, the association with HCA level appeared to increase over the five minutes of the open-field, presumably as the mice habituated. Furthermore, although mice displaying particularly high and low HCA were indistinguishable early in the open-field task, they became significantly differentiated over time. We conclude that home-cage behaviors and the open-field, after habituation, display good face and construct validity, and may provide a good model of baseline activity for quantitative trait loci (QTL) discovery and functional genomics in the HS mice.

Behavioral and neurochemical effects of anpirtoline and citalopram in isolated and group housed mice

Acute effects of serotonergic drugs acting via different mechanisms were investigated by a social interaction test and subsequent determination of serotonin and dopamine metabolisms in mice housed in groups or isolated for 6 weeks. A resident/intruder test was performed with anpirtoline (5-HT1B receptor agonist in rodents; 1 mg/kg), citalopram (SSRI; 0.5 mg/kg) and saline treatment before animals were decapitated and different brain regions were frozen for subsequent HPLC-analyses. Behavioral investigations indicated a strong increase of aggressive behavior after 6 weeks of isolation housing. Acute citalopram treatment did not influence behavioral parameters of isolated and group housed mice. In contrast, anpirtoline antagonized isolation induced aggressive behavioral components in a specific manner. Analysis of dopamine and serotonin metabolism revealed that citalopram treatment did not affect dopamine metabolism, but reduced serotonin metabolism in the striatum, hippocampus, cortex and midbrain independent of housing conditions. In contrast, anpirtoline treatment increased dopamine metabolism in cortex, striatum and midbrain as well as influenced serotonin metabolism in a structure- and state-specific manner. Whereas anpirtoline decreased serotonin metabolism in the cortex, the midbrain and the hippocampus independent of housing conditions, in the striatum anpirtoline abolished the isolation induced decrease of serotonin metabolism. These results indicate that anpirtoline might induce antiaggressive effects via postsynaptic receptor- and structure-specific activation of serotonergic but also dopaminergic processes, whereas structure independent increase of synaptic serotonin via citalopram was ineffective to reverse aggressivity in isolated mice.