Evaluation of Lewis and SHR rat strains as a genetic model for the study of anxiety and pain

Applying the Research Domain Criteria to Rodent Studies of Sex Differences in Chronic Stress Susceptibility

Women have a 2-fold increased rate of stress-associated psychiatric disorders such as depression and anxiety, but the mechanisms that underlie this increased susceptibility remain incompletely understood. Historically, female subjects were excluded from preclinical studies and clinical trials. Additionally, chronic stress paradigms used to study psychiatric pathology in animal models were developed for use in males. However, recent changes in National Institutes of Health policy encourage inclusion of female subjects, and considerable work has been performed in recent years to understand biological sex differences that may underlie differences in susceptibility to chronic stress-associated psychiatric conditions. Here, we review the utility as well as current challenges of using the framework of the National Institute of Mental Health's Research Domain Criteria as a transdiagnostic approach to study sex differences in rodent models of chronic stress including recent progress in the study of sex differences in the neurobehavioral domains of negative valence, positive valence, cognition, social processes, and arousal.

Dorsal peduncular cortex activity modulates affective behavior and fear extinction in mice

The medial prefrontal cortex (mPFC) is critical to cognitive and emotional function and underlies many neuropsychiatric disorders, including mood, fear and anxiety disorders. In rodents, disruption of mPFC activity affects anxiety- and depression-like behavior, with specialized contributions from its subdivisions. The rodent mPFC is divided into the dorsomedial prefrontal cortex (dmPFC), spanning the anterior cingulate cortex (ACC) and dorsal prelimbic cortex (PL), and the ventromedial prefrontal cortex (vmPFC), which includes the ventral PL, infralimbic cortex (IL), and in some studies the dorsal peduncular cortex (DP) and dorsal tenia tecta (DTT). The DP/DTT have recently been implicated in the regulation of stress-induced sympathetic responses via projections to the hypothalamus. While many studies implicate the PL and IL in anxiety-, depression-like and fear behavior, the contribution of the DP/DTT to affective and emotional behavior remains unknown. Here, we used chemogenetics and optogenetics to bidirectionally modulate DP/DTT activity and examine its effects on affective behaviors, fear and stress responses in C57BL/6J mice. Acute chemogenetic activation of DP/DTT significantly increased anxiety-like behavior in the open field and elevated plus maze tests, as well as passive coping in the tail suspension test. DP/DTT activation also led to an increase in serum corticosterone levels and facilitated auditory fear extinction learning and retrieval. Activation of DP/DTT projections to the dorsomedial hypothalamus (DMH) acutely decreased freezing at baseline and during extinction learning, but did not alter affective behavior. These findings point to the DP/DTT as a new regulator of affective behavior and fear extinction in mice.

Three methods of behavioural testing to measure anxiety - A review

Behavioural test is very useful to assess the anxiety activity, screen new anxiolytic drugs, explore the pathogenesis of anxiety disorders. Methods of behavioural testing that reflects different aspects of anxiety emotionality simultaneously have always been a critical issue for academics. In this paper, we reviewed previous methods to use behavioural test to evaluate the anxiety activity. A single test was used to measure only one aspect of anxiety emotionality. A battery of behavioural tests could get a comprehensive information of anxiety profile. In one single trial, open field test, elevated plus maze and light/dark box are integrated to assess different types of emotional behaviours. This new paradigm is useful for evaluating multiple dimensions of behaviours simultaneously, minimizing general concerns about previous test experience and inter-test intervals between tests. It is proposed as a promising alternative to using test battery.

Long-term effects of neonatal pain and sucrose treatment

Purpose

In neonatal intensive care units, applying sucrose solution for analgesia is now a routine treatment for mild procedural pain. Studies of animal and human infants provide clear evidence of benefits in the short term, but few studies have investigated the long term benefits. Thus, we determined whether sucrose could ameliorate painful stimulation during infancy in Sprague-Dawley rats and also explored the long-term effects of repeated sucrose administration during infancy. Female and male rats were included to investigate sex-related differences.

Methods

Rat pups were stimulated either with painful or tactile stimuli for the first 14 days of their lives. Pups were pretreated either with sucrose or not treated before stimulation. Behavioral tests were conducted during adolescence and adulthood. Hotplate, rotarod, open field, elevated plus maze, and radial arm water maze tests were employed to assess the behavioral consequences of early life manipulations and treatments.

Results

Painful stimulation during infancy increased the sensitivity to pain later in life, and sucrose did not remedy this effect. Motility, coordination, anxiety, and cognition tests in adulthood obtained mixed results. Pain during infancy appeared to increase anxiety during adulthood. Learning and memory in adulthood were affected by pain during infancy, and sucrose had a negative effect even in the absence of pain. No sex-related differences were observed in any of the behavioral tests by employing this model of neonatal pain.

Conclusion

Painful stimulation during infancy resulted in deficiencies in some behavioral tests later in life. Sucrose pretreatment did not mitigate these shortcomings and it actually resulted in negative outcomes.

Toll-like receptor 3 neuroimmune signaling and behavior change: A strain comparison between Lewis and Wistar rats

There are many unanswered questions about the interaction between the immune system and behavior change, including the contributions of individual differences. The present study modeled individual differences in the immune system by comparing inbred Lewis rats, which have dysregulated stress and immune systems, to their genetically diverse parent strain, Wistar rats. The objective was to examine the consequences of an immune challenge on behavior and neuroimmune signaling in both strains. Peripheral administration of the toll-like receptor 3 (TLR3) agonist and viral memetic polyinosinic-polycytidylic acid (poly(I:C)) induced behavior changes in both strains, reducing locomotor activity and increasing avoidance behavior (time on the dark side of the light-dark box). Furthermore, poly(I:C) induced hyperarousal and increased avoidance behavior more in female Lewis than female Wistar rats. Baseline strain differences were also observed: Lewis rats had higher avoidance behavior and lower startle response than Wistars. Lewis rats also had lower levels of peripheral inflammation, as measured by spleen weight. Finally, poly(I:C) increased expression of genes in the TLR3 pathway, cytokine genes, and CD11b, a gene associated with proinflammatory actions of microglia, in the prelimbic cortex and central amygdala, with greater expression of cytokine genes in male rats. Lewis rats had lower baseline expression of some neuroimmune genes, particularly CD11b. Overall, we found constitutive strain differences in immune profiles and baseline differences in behavior, yet poly(I:C) generally induced similar behavior changes in males while hyperarousal and avoidance behavior were heightened in female Lewis rats.

Pimavanserin reverses multiple measures of anxiety in a rodent model of post-traumatic stress disorder

Pimavanserin is a highly selective 5-HT_2A inverse agonist in current medical use. Prior studies suggest that 5-HT_2A serotonin receptors may play a role in anxiety and emotional memory. Therefore, pimavanserin was tested in a rat model of PTSD to determine whether it might ameliorate PTSD-like symptoms. The lifetime prevalence of PTSD is estimated to be 125% higher in women than men. Consequently, in an effort to create a robust model of PTSD that was more representative of human PTSD prevalence, 20-week old female rats of the emotionally hyperreactive Lewis strain were used for these studies. The rats were single-housed and exposed twice to restraint stress coupled with predator odor or to a sham-stressed condition. Twenty days after the second stress or sham-stress exposure, rats were injected with saline alone or with 0.3 or 1.0 mg/kg pimavanserin, doses that were confirmed to substantially block 5-HT_2A receptor activity in this study without causing any non-specific behavioral or adverse effects. One hour later, rats were tested for anxiety through acoustic startle response, the elevated plus-maze and three parameters of open field behavior. Five days later, blood was sampled for plasma corticosterone. The stressed/saline-injected rats had higher anxiety scores and corticosterone levels than sham-stressed/saline-injected rats. Pimavanserin significantly and generally dose-dependently reversed these persistent stress effects, but had no significant effect on the behavioral measures in normal, non-stressed rats. These results, consistent with a role for the 5-HT_2A receptor, suggest that pimavanserin might have potential to reduce some consequences of traumatic stress.

Spontaneously hypertensive rats manifest deficits in emotional response to 22-kHz and 50-kHz ultrasonic playback

Many symptoms used routinely for human psychiatric diagnosis cannot be directly observed in animals which cannot describe their internal states. However, the ultrasonic vocalizations (USV) rodents use to communicate their emotional states can be measured. USV have therefore become a particularly useful tool in brain disease models. Spontaneously hypertensive rats (SHR) are considered an animal model of attention deficit hyperactivity disorder (ADHD) and schizophrenia. However, the specifics of SHR's behavior have not been fully described and there is very little data on their USV. Recently, we developed a communication model, in which Wistar rats are exposed to pre-recorded playbacks of aversive (22-kHz) or appetitive (50-kHz) USV, and their vocal responses depend on the extent of prior fear conditioning (0, 1, 6 or 10 shocks). Here, we investigated SHR's behavior and heart rate (HR) in our communication model, in comparison to Wistar rats employed as controls. In general, SHR emitted typical USV categories, however, they contained more short 22-kHz and less 50-kHz USV overall. Moreover, fewer SHR, in comparison with Wistar rats, emitted long 22-kHz USV after fear conditioning. SHR did not show a 50-kHz playback-induced HR increase, while they showed a profound 22-kHz playback-induced HR decrease. Finally, the number of previously delivered conditioning shocks appeared to have no effect on the investigated vocal, locomotor and HR responses of SHR. The phenomena observed in SHR are potentially attributable to deficits in emotional perception and processing. A lower number of 50-kHz USV emitted by SHR may reflect observations of speech impairments in human patients and further supports the usefulness of SHR to model ADHD and schizophrenia.

Are cognitive aspects of defense a core feature of anxiety and depression?

Anxiety and depression are highly prevalent behavior disorders, particularly in women. Recent preclinical work using animal models has been suboptimal in predicting the efficacy of drugs targeted at these conditions, suggesting a potential discrepancy between such models and the human disorders. Notably female animals tend to be equal to, or less responsive than, males in these tasks. A number of analyses suggest that mammalian defense patterns are complex: In addition to relatively discrete and immediate fight, flight, and freezing responses, a risk assessment pattern may occur in response to threat stimuli or situations with ambiguous elements. This pattern combines defensiveness with a number of cognition-linked behaviors such as sensory attention and orientation, approach, contact, and investigation of the potential threat. Studies measuring elements of this pattern suggest that female rats, and perhaps female mice, show higher levels than equivalent males. Higher female involvement may also occur in tasks involving learning/generalization/extinction of defensiveness to conditioned stimuli. Such findings are consonant with recent analyses of "female survival strategies" based on differential adaptiveness of cognitive components of defensiveness in females, due to the necessity of female care of offspring until they are independent. These data suggest the value of additional behavioral and functional analyses of cognitive aspects of defensive behavior; contributing to both an understanding of their underlying mechanisms, and providing more sensitive measures of drug responsivity for use with animal models.

The influence of chromosome 4 on high ethanol consumption and blood pressure

The Spontaneously Hypertensive Rats (SHR) strain was developed through selective breeding for high systolic blood pressure. In our laboratory, we established a congenic rat strain named SHR.Lewis-Anxrr16 (SLA16). The SLA16 rat strain is genetically identical to the SHR except for the inserted Anxrr16 region in chromosome 4. Our objective was to evaluate the influence of this genomic region on ethanol consumption and blood pressure. First, we exposed SHR and SLA16 male and female rats to ethanol consumption. Results showed that, regardless of strain, females consumed more ethanol than males during forced (10% v/v) and spontaneous ethanol consumption (SEC; 2.5-20% v/v). Then, females from both strains were used to evaluate sensitivity to ethanol. No strain differences in the loss of righting reflex were observed after ethanol treatment (3 g/kg, 20% w/v, intraperitoneal [i.p.]). But, in the triple test, female SHR rats presented lower sensitivity to the ethanol (1.2 g/kg, 14% w/v, i.p.). Surprisingly, female SHR rats also presented higher blood pressure after SEC (10% v/v). Finally, losartan treatment was effective in decreasing the blood pressure of female rats of both strains, but had specific effects on SHR ethanol consumption. Our data suggest that SLA16 female rats consume less ethanol (10%), are more sensitive to its effects, and present lower blood pressure than SHR female rats. We demonstrated that the Anxrr16 locus in chromosome 4 is a genetic candidate to explain high ethanol consumption and blood pressure, at least in females.

Light-Dark Open Field (LDOF): A novel task for sensitive assessment of anxiety

BACKGROUND

Pre-clinical studies of psychiatric disorders often include a measure of anxiety-like behavior. Several tasks exist that serve this purpose, but because anxiety is complex with a myriad of anxiogenic stimuli, researchers are often compelled to use multiple tasks. The Light-Dark Open Field (LDOF) combines concepts from two such tasks, Light-Dark Box and Open Field, into one task with the synergistic effect of enhanced discrimination of anxiety-like behavior.

NEW METHODS

Our goal was to increase the sensitivity of the Open Field task with the addition of a shadow, conceptually similar to the Light-Dark Box, to detect concealed differences even under bright light, which is highly anxiogenic. The resulting LDOF allows assessment of anxiety due to bright light and open space simultaneously, while retaining the ability to assess the impact of each with custom indices. In addition, it maintains all the advantages and measures of the Open Field.

RESULTS

Using custom created indices from measures collected in the LDOF one can assess anxiety induced by light, open space, or light and open space combined and thus elucidate anxiety-inducing factors. Using two strains of rats: an outbred strain, Sprague-Dawley (SD), and a strain that exhibits high trait anxiety, Lewis rats, we found that increased discrimination for anxiety-like behavior can be achieved with the Light-Dark Open Field.

COMPARISON WITH EXISTING MODELS

The LDOF allows researchers to extract the traditional measures of an Open Field, including valuable information about locomotion and habituation while adding a further layer of discrimination with the light-dark component. Because the LDOF is a combination of two different tests, it saves time compared to running multiple experiments in series that then need to be counterbalanced to reduce artefacts and task order effects. In addition, it detects differences even when traditional tasks of anxiety have reached their ceiling sensitivity (i.e. EPM under bright light conditions).

CONCLUSION

We present the Light-Dark Open Field: a simple modification of an existing Open Field apparatus that incorporates aspects of the Light-Dark Box with the addition of a shadow. The shadow (Dark Perimeter) allows for increased discrimination in detecting anxiety-like behaviors. Comparison of anxiety-like behavior between Lewis and SD rats allowed us to develop the construct and face validity of the LDOF as well as demonstrate its sensitivity even under bright light conditions. In addition, we developed 3 indices that allow one to parse out, from one set of data, the effect of two anxiogenic stimuli- bright light and open space.

Effect of Estrous Cycle on Behavior of Females in Rodent Tests of Anxiety

Anxiety disorders are more prevalent in women than in men. In women the menstrual cycle introduces another variable; indeed, some conditions e.g., premenstrual syndrome, are menstrual cycle specific. Animal models of fear and anxiety, which form the basis for research into drug treatments, have been developed almost exclusively, using males. There remains a paucity of work using females and the available literature presents a confusing picture. One confound is the estrous cycle in females, which some authors consider, but many do not. Importantly, there are no accepted standardized criteria for defining cycle phase, which is important given the rapidly changing hormonal profile during the 4-day cycle of rodents. Moreover, since many behavioral tests that involve a learning component or that consider extinction of a previously acquired association require several days to complete; the outcome may depend on the phase of the cycle on the days of training as well as on test days. In this article we consider responsiveness of females compared to males in a number of commonly used behavioral tests of anxiety and fear that were developed in male rodents. We conclude that females perform in a qualitatively similar manner to males in most tests although there may be sex and strain differences in sensitivity. Tests based on unconditioned threatening stimuli are significantly influenced by estrous cycle phase with animals displaying increased responsiveness in the late diestrus phase of the cycle (similar to the premenstrual phase in women). Tests that utilize conditioned fear paradigms, which involve a learning component appear to be less impacted by the estrous cycle although sex and cycle-related differences in responding can still be detected. Ethologically-relevant tests appear to have more translational value in females. However, even when sex differences in behavior are not detected, the same outward behavioral response may be mediated by different brain mechanisms. In order to progress basic research in the field of female psychiatry and psychopharmacology, there is a pressing need to validate and standardize experimental protocols for using female animal models of anxiety-related states.

Sex differences in the elevated plus-maze test and large open field test in adult Wistar rats

There is a growing need for a better understanding of sex differences in animal models of psychiatric disorders. The elevated plus-maze (EPM) test and large open field (LOF) test are widely used to study anxiety-like behavior in rodents. Our studies explored sex differences in anxiety and activity parameters in the LOF and EPM and determined whether these parameters correlate within and between tests. Drug naïve adult male and female Wistar rats (n = 47/sex) were used for the studies, and the rats were tested for 5 min in the EPM and 10 min in the LOF. The females spent more time on the open arms of the EPM and made more open arms entries than the males. The females also spent more time in the center zone of the LOF and made more center zone entries. The females traveled a greater distance in the LOF and EPM. There was a moderate positive correlation between time on the open arms of the EPM and time in the center zone of the LOF. There was also a moderate positive correlation between open arms entries in the EPM and center zone entries in the LOF. A hierarchical cluster analysis revealed one cluster with LOF parameters, one cluster with EPM parameters, and one cluster with parameters related to the avoidance of open spaces. In conclusion, these findings indicate that female rats display less anxiety-like behavior in the EPM and LOF. Furthermore, there are sex differences for almost all behavioral parameters in these anxiety tests.

Gender-specific approach in psychiatric diseases: Because sex matters

In both animals and human beings, males and females differ in their genetic background and hormonally driven behaviour and show sex-related differences in brain activity and response to internal and external stimuli. Gender-specific medicine has been a neglected dimension of medicine for long time, and only in the last three decades it is receiving the due scientific and clinical attention. Research has recently begun to identify factors that could provide a neurobiological basis for gender-based differences in health and disease and to point to gonadal hormones as important determinants of male-female differences. Animal studies have been of great help in understanding factors contributing to sex-dependent differences and sex hormones action. Here we review and discuss evidence provided by clinical and animal studies in the last two decades showing gender (in humans) and sex (in animals) differences in selected psychiatric disorders, namely eating disorders (anorexia nervosa, bulimia nervosa, binge eating disorder), schizophrenia, mood disorders (anxiety, depression, obsessive-compulsive disorder) and neurodevelopmental disorders (autism spectrum disorders, attention-deficit/hyperactivity disorder).

Centrally acting antihypertensives change the psychogenic cardiovascular reactivity

Clonidine (CL) and Rilmenidine (RI) are among the most frequently prescribed centrally acting antihypertensives. Here, we compared CL and RI effects on psychogenic cardiovascular reactivity to sonant, luminous, motosensory, and vibrotactile stimuli during neurogenic hypertension. The femoral artery and vein of Wistar (WT - normotensive) and spontaneously hypertensive rats (SHR) were catheterized before (24 h interval) i.p. injection of vehicle (NaCl 0.9%, control - CT group), CL (10 µg/kg), or RI (10 µg/kg) and acute exposure to luminous (5000 lm), sonant (75 dB sudden tap), motor (180° cage twist), and air-jet (10 L/min - restraint and vibrotactile). Findings showed that: (i) CL or RI reduced the arterial pressure of SHR, without affecting basal heart rate in WT and SHR; (ii) different stimuli evoked pressor and tachycardic responses; (iii) CL and RI reduced pressor response to sound; (iv) CL or RI reduced pressor responses to luminous stimulus without a change in peak tachycardia in SHR; (v) cage twist increased blood pressure in SHR, which was attenuated by CL or RI; (vi) air-jet increased pressure and heart rate; (vii) CL or RI attenuated the pressor responses to air-jet in SHR while RI reduced the chronotropic reactivity in both strains. Altogether, both antihypertensives relieved the psychogenic cardiovascular responses to different stimuli. The RI elicited higher cardioprotective effects through a reduction in air-jet-induced tachycardia.

The influence of rat strain on the development of neuropathic pain and comorbid anxio-depressive behaviour after nerve injury

Back-translating the clinical manifestations of human disease burden into animal models is increasingly recognized as an important facet of preclinical drug discovery. We hypothesized that inbred rat strains possessing stress hyper-reactive-, depressive- or anxiety-like phenotypes may possess more translational value than common outbred strains for modeling neuropathic pain. Rats (inbred: LEW, WKY, F344/ICO and F344/DU, outbred: Crl:SD) were exposed to Spared Nerve Injury (SNI) and evaluated routinely for 6 months on behaviours related to pain (von Frey stimulation and CatWalk-gait analysis), anxiety (elevated plus maze, EPM) and depression (sucrose preference test, SPT). Markers of stress reactivity together with spinal/brain opioid receptor expression were also measured. All strains variously developed mechanical allodynia after SNI with the exception of stress-hyporesponsive LEW rats, despite all strains displaying similar functional gait-deficits after injury. However, affective changes reflective of anxiety- and depressive-like behaviour were only observed for F344/DU in the EPM, and for Crl:SD in SPT. Although differences in stress reactivity and opioid receptor expression occurred, overall they were relatively unaffected by SNI. Thus, anxio-depressive behaviours did not develop in all strains after nerve injury, and correlated only modestly with degree of pain sensitivity or with genetic predisposition to stress and/or affective disturbances.

ADHD-like behaviors caused by inactivation of a transcription factor controlling the balance of inhibitory and excitatory neuron development in the mouse anterior brainstem

The neural circuits regulating motivation and movement include midbrain dopaminergic neurons and associated inhibitory GABAergic and excitatory glutamatergic neurons in the anterior brainstem. Differentiation of specific subtypes of GABAergic and glutamatergic neurons in the mouse embryonic brainstem is controlled by a transcription factor Tal1. This study characterizes the behavioral and neurochemical changes caused by the absence of Tal1 function. The Tal1^cko mutant mice are hyperactive, impulsive, hypersensitive to reward, have learning deficits and a habituation defect in a novel environment. Only minor changes in their dopaminergic system were detected. Amphetamine induced striatal dopamine release and amphetamine induced place preference were normal in Tal1^cko mice. Increased dopamine signaling failed to stimulate the locomotor activity of the Tal1^cko mice, but instead alleviated their hyperactivity. Altogether, the Tal1^cko mice recapitulate many features of the attention and hyperactivity disorders, suggesting a role for Tal1 regulated developmental pathways and neural structures in the control of motivation and movement.

Pre-Gestational intake of Lactobacillus helveticus NS8 has anxiolytic effects in adolescent Sprague Dawley offspring

INTRODUCTION

Adolescence is a period of heightened susceptibility to anxiety disorders. Probiotic supplementation had a positive impact on reducing anxiety. The maternal microbiome plays an important role in child health outcomes and in the establishment of the offspring microbiome. Few studies have investigated the impact of gestational probiotic supplementation on the offspring's anxiety.

METHODS

The present study examined the impact of prenatal Lactobacillus helveticus NS8 supplementation (LAC) on Sprague Dawley rat offspring's anxiety-like behavior. The behaviors tested in the present study include the elevated plus maze (EPM), the open field test (OFT), and prepulse inhibition (PPI). Analyses of variance were utilized.

RESULTS

(a) The performance of LAC adolescent rats in the EPM was similar to that in the OFT, both of which reflect that LAC caused an antianxiety effect in adolescent offspring rats and the antianxiety effect without sex differences; (b) LAC did not change performance in PPI and did not change the sex and age differences in PPI; and c. LAC decreased the body mass of rat offspring.

CONCLUSION

Lactobacillus helveticus NS8 supplementation during gestation might have a moderate antianxiety effect in both males and females (especially adolescents) and be helpful for avoiding excessive body mass.

Caffeine Consumption plus Physical Exercise Improves Behavioral Impairments and Stimulates Neuroplasticity in Spontaneously Hypertensive Rats (SHR): an Animal Model of Attention Deficit Hyperactivity Disorder

Attention deficit hyperactivity disorder (ADHD) is a prevalent and disabling disorder, mainly characterized by hyperactivity, inattention, and impulsivity, but also by olfactory and memory impairments that frequently persist throughout lifetime. The pathophysiology of ADHD is complex, involving several brain regions and neural pathways including alterations in adenosine neuromodulation. The administration of caffeine (a non-selective adenosine receptor antagonist) and physical exercise have been independently pointed as effective approaches for the management of ADHD symptoms. Here, we evaluated the effects of caffeine consumption (0.3 mg/mL in drinking water) plus physical exercise in running wheels during 6 weeks-starting during either adolescence (30 days old) or adulthood (4-5 months old)-on behavioral performance (including olfactory discrimination, open field, object recognition, and water maze tests) on the brain levels of monoamines (by high-performance liquid chromatography), on proteins related to synaptic plasticity and on brain-derived neurotrophic factor signaling (by Western blot analysis) in spontaneously hypertensive rats (SHRs), a validated animal model of ADHD. SHRs displayed persistent impairments of olfactory and short-term recognition memory from adolescence to adulthood, which were accompanied by lower levels of synaptosomal-associated protein 25 (SNAP-25) in the prefrontal cortex and hippocampus. The association of caffeine plus physical exercise during adolescence or adulthood restored the olfactory discrimination ability and, in an independent manner, improved short-term recognition memory of SHRs. These benefits were not associated to alterations in locomotor activity or in the hypertensive phenotype. The association of caffeine consumption plus physical exercise during adolescence increased the levels of SNAP-25, syntaxin, and serotonin in the hippocampus and prefrontal cortex, and striatal dopamine levels in SHRs. These results provide new evidence of the potential of caffeine and physical exercise, starting at adolescence or adult life, to improve behavioral impairments and stimulate neuroplasticity in ADHD.

Pain in neuropsychiatry: Insights from animal models

Pain is the most common symptom reported in clinical practice, meaning that it is associated with many pathologies as either the origin or a consequence of other illnesses. Furthermore, pain is a complex emotional and sensorial experience, as the correspondence between pain and body damage varies considerably. While these issues are widely acknowledged in clinical pain research, until recently they have not been extensively considered when exploring animal models, important tools for understanding pain pathophysiology. Interestingly, chronic pain is currently considered a risk factor to suffer psychiatric disorders, mainly stress-related disorders like anxiety and depression. Conversely, pain appears to be altered in many psychiatric disorders, such as depression, anxiety and schizophrenia. Thus, pain and psychiatric disorders have been linked in epidemiological and clinical terms, although the neurobiological mechanisms involved in this pathological bidirectional relationship remain unclear. Here we review the evidence obtained from animal models about the co-morbidity of pain and psychiatric disorders, placing special emphasis on the different dimensions of pain.

Losartan suppresses the kainate-induced changes of angiotensin AT1 receptor expression in a model of comorbid hypertension and epilepsy

AIMS

Experimental and clinical studies have demonstrated that components of renin-angiotensin system are elevated in the hippocampus in epileptogenic conditions. In the present work, we explored the changes in the expression of angiotensin II receptor, type 1 (AT₁ receptor) in limbic structures, as well as the effect of the AT1 receptor antagonist losartan in a model of comorbid hypertension and epilepsy.

MAIN METHODS

The expression of AT₁ receptors was compared between spontaneously hypertensive rats (SHRs) and Wistar rats by using immunohistochemistry in the kainate (KA) model of temporal lobe epilepsy (TLE). The effect of losartan was studied on AT₁ receptor expression in epileptic rats that were treated for a period of 4weeks after status epilepticus.

KEY FINDINGS

The naive and epileptic SHRs were characterized by stronger protein expression of AT₁ receptor than normotensive Wistar rats in the CA1, CA3a, CA3b, CA3c field and the hilus of the dentate gyrus of the dorsal hippocampus but fewer cells were immunostained in the piriform cortex. Increased AT₁ immunostaining was observed in the basolateral amygdala of epileptic SHRs but not of epileptic Wistar rats. Losartan exerted stronger and structure-dependent suppression of AT₁ receptor expression in SHRs compared to Wistar rats.

SIGNIFICANCE

Our results confirm the important role of AT₁ receptor in epilepsy and suggest that the AT₁receptor antagonists could be used as a therapeutic strategy for treatment of comorbid hypertension and epilepsy.

Individual differences in circadian locomotor parameters correlate with anxiety- and depression-like behavior

Disrupted circadian rhythms are a core feature of mood and anxiety disorders. Circadian rhythms are coordinated by a light-entrainable master clock located in the suprachiasmatic nucleus. Animal models of mood and anxiety disorders often exhibit blunted rhythms in locomotor activity and clock gene expression. Interestingly, the changes in circadian rhythms correlate with mood-related behaviours. Although animal models of depression and anxiety exhibit aberrant circadian rhythms in physiology and behavior, it is possible that the methodology being used to induce the behavioral phenotype (e.g., brain lesions, chronic stress, global gene deletion) affect behavior independently of circadian system. This study investigates the relationship between individual differences in circadian locomotor parameters and mood-related behaviors in healthy rats. The circadian phenotype of male Lewis rats was characterized by analyzing wheel running behavior under standard 12h:12h LD conditions, constant dark, constant light, and rate of re-entrainment to a phase advance. Rats were then tested on a battery of behavioral tests: activity box, restricted feeding, elevated plus maze, forced swim test, and fear conditioning. Under 12h:12h LD conditions, percent of daily activity in the light phase and variability in activity onset were associated with longer latency to immobility in the forced swim test. Variability in onset also correlated positively with anxiety-like behavior in the elevated plus maze. Rate of re-entrainment correlated positively with measures of anxiety in the activity box and elevated plus maze. Lastly, we found that free running period under constant dark was associated with anxiety-like behaviors in the activity box and elevated plus maze. Our results provide a previously uncharacterized relationship between circadian locomotor parameters and mood-related behaviors in healthy rats and provide a basis for future examination into circadian clock functioning and mood.

Effects of physical exercise and social isolation on anxiety-related behaviors in two inbred rat strains

We investigated the effects of physical exercise (PE) on locomotor activity and anxiety-like behavior in Lewis (LEW) and Spontaneously Hypertensive Rats (SHR) male rats. Rats received either four weeks of forced training, 5days/week, on a treadmill (experiment 1) or were given 21days of free access to running wheels (experiment 2). We also tested the effects of social isolation (SI) (seven days of isolation - experiment 3) on behavior. In experiment 1, 20% of LEW rats and 63% of SHR rats completed the training protocol. PE significantly increased central and peripheral locomotion in the open field (OF) and entries into the open arms in the elevated plus-maze (EPM) in both strains. In experiment 2, the distance traveled by SHR rats on running wheels was significantly higher compared with LEW rats. PE on running wheels also increased the time spent in the center of the OF in SHR rats only. In experiment 3, SI decreased central and peripheral locomotion in the OF in both strains. In summary, forced PE on a treadmill reduced anxiety-like behavior and increased locomotion in male rats of both strains, whereas voluntary PE on running wheels decreased anxiety-like behavior in SHR rats only. SI decreased locomotion in both strains in the OF. This study suggests that spontaneous activity levels are genotype-dependent and the effects of PE depend on the type of exercise performed.

Role of the Orexin/Hypocretin System in Stress-Related Psychiatric Disorders

Orexins (hypocretins) are critically involved in coordinating appropriate physiological and behavioral responses to aversive and threatening stimuli. Acute stressors engage orexin neurons via direct projections from stress-sensitive brain regions. Orexin neurons, in turn, facilitate adaptive behavior via reciprocal connections as well as via direct projections to the hypophysiotropic neurons that coordinate the hypothalamic-pituitary-adrenal (HPA) axis response to stress. Consequently, hyperactivity of the orexin system is associated with increased motivated arousal and anxiety, and is emerging as a key feature of panic disorder. Accordingly, there has been significant interest in the therapeutic potential of pharmacological agents that antagonize orexin signaling at their receptors for the treatment of anxiety disorders. In contrast, disorders characterized by inappropriately low levels of motivated arousal, such as depression, generally appear to be associated with hypoactivity of the orexin system. This includes narcolepsy with cataplexy, a disorder characterized by the progressive loss of orexin neurons and increased rates of moderate/severe depression symptomology. Here, we provide a comprehensive overview of both clinical and preclinical evidence highlighting the role of orexin signaling in stress reactivity, as well as how perturbations to this system can result in dysregulated behavioral phenotypes.

Genetic evidence for chromosome 4 loci influencing learning and memory

The Lewis (LEW) and SHR (Spontaneously Hypertensive Rats) inbred rat strains differ in several anxiety/emotionality and learning/memory-related behaviors. We aimed to search quantitative trait locus (QTL) that influence these behaviors and confirm their effects in a congenic rat strain SLA16 (SHR.LEW.Anxrr16). LEW females and SHR males were intercrossed to produce F2 rats (96/sex), which were all tested in the plus-maze discriminative avoidance task (PMDAT), open-field (OF), object recognition (OR), spontaneous alternation (SA) and fear conditioning (FC). All animals were genotyped for microsatellite markers located on chromosome (Chr) 4. Behavioral and genotypic data were used to perform factor and QTL analyses. Also, to confirm the QTL effects, we tested male and female SLA16 rats and their isogenic control SHR in the same behavioral tests. A factor analysis of the F2 population revealed a correlation between anxiety/emotionality related behaviors and learning/memory in both sexes. QTL analysis revealed two significant QTL in males and three in females, on behavioral parameters in the PMDAT, OF and FC. Four QTL found herein were confirmed in SLA16 rats. The SLA16 strain displayed lower levels of anxiety/emotionality, higher locomotor activity and deficits in learning/memory in comparison with SHR strain. The Chr 4 contains genes influencing anxiety/emotionality and learning/memory behaviors and the SLA16 strain represents a valuable tool in the search for them. The use of the SLA16 strain as a genetic model for studying behavioral phenomena and their implications for psychiatric disorders are discussed.

Long-Term Treatment with Losartan Attenuates Seizure Activity and Neuronal Damage Without Affecting Behavioral Changes in a Model of Co-morbid Hypertension and Epilepsy

Over the last 10 years, accumulated experimental and clinical evidence has supported the idea that AT1 receptor subtype is involved in epilepsy. Recently, we have shown that the selective AT1 receptor antagonist losartan attenuates epileptogenesis and exerts neuroprotection in the CA1 area of the hippocampus in epileptic Wistar rats. This study aimed to verify the efficacy of long-term treatment with losartan (10 mg/kg) after kainate-induced status epilepticus (SE) on seizure activity, behavioral and biochemical changes, and neuronal damage in a model of co-morbid hypertension and epilepsy. Spontaneous seizures were video- and EEG-monitored in spontaneously hypertensive rats (SHRs) for a 16-week period after SE. The behavior was analyzed by open field, elevated plus maze, sugar preference test, and forced swim test. The levels of serotonin in the hippocampus and neuronal loss were estimated by HPLC and hematoxylin and eosin staining, respectively. The AT1 receptor antagonism delayed the onset of seizures and alleviated their frequency and duration during and after discontinuation of treatment. Losartan showed neuroprotection mostly in the CA3 area of the hippocampus and the septo-temporal hilus of the dentate gyrus in SHRs. However, the AT1 receptor antagonist did not exert a substantial influence on concomitant with epilepsy behavioral changes and decreased 5-HT levels in the hippocampus. Our results suggest that the antihypertensive therapy with an AT1 receptor blocker might be effective against seizure activity and neuronal damage in a co-morbid hypertension and epilepsy.

Hypotensive and diuretic effect of the butanolic soluble fraction of the hydroethanolic extract of bark of Scutia buxifolia Reissek in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Scutia buxifolia, a native tree popularly known as "coronilha", is widely used in Brazilian folk medicine for diuretic and anti-hypertensive purposes.

AIM OF THE STUDY

We investigated the effects of a butanolic (BuOH) soluble fraction of the hydroethanolic extract (HESB) of bark of Scutia buxifolia on both blood pressure and urinary excretion of rats. The involvement of the nitric oxide/guanylate cyclase pathway in the hypotensive effect found was also explored.

MATERIAL AND METHODS

We tested the effect of the BuOH soluble fraction of HESB on the mean arterial pressure (MAP) of anesthetized rats. The fraction was administered at doses of 1, 3 and 10mg/kg (i.v.) in normotensive rats during continuous infusion of vehicle (10 μl/min), or phenylephrine (4 μg/kg/min), or l-NAME (7 mg/kg/min), two approaches able to induce a sustained hypertensive state. In some experiments, a bolus injection of ODQ (2mg/kg) was administered in animals infused with phenylephrine before the administration of the BuOH soluble fraction of HESB. We also measured the effects of the BuOH soluble fraction on the MAP of spontaneously hypertensive rats (SHR). Separate groups of rats were treated orally with either HESB (10, 30 or 100mg/kg), or its BuOH soluble fraction (3, 10 or 30 mg/kg), and were subjected to measurement of diuresis and blood pressure.

RESULTS

The BuOH soluble fraction of HESB (10mg/kg, i.v.) reduced the MAP of both phenylephrine-infused and SHR rats by 20.6 ± 6.0 and 41.8 ± 8.3 mm Hg, respectively. However, no hypotensive effect was found in normotensive animals infused with l-NAME, a non-selective inhibitor of nitric oxide synthase, or animals previously treated with the soluble guanylate cyclase inhibitor ODQ. The urinary excretion was increased by 70% at 6-8h after a single oral administration of the BuOH soluble fraction of HESB (10mg/kg), without change in urinary density, pH, or Na(+) and K(+) concentrations. In addition, MAP was lower 3h after the acute oral treatment with the BuOH soluble fraction (82.1 ± 3.8 mm Hg), compared with MAP of animals from the control group (97 ± 3.2 mm Hg).

CONCLUSION

This study demonstrates that the BuOH soluble fraction of the hydroethanolic bark of Scutia buxifolia, which has its bark used in folk medicine for the treatment of hypertension mainly by its presumed diuretic properties, possesses both diuretic and hypotensive effects in rats, and that at least the hypotensive effect is fully dependent on activation of the nitric oxide/guanylate cyclase pathway.

Peri-pubertal exposure to testicular hormones organizes response to novel environments and social behaviour in adult male rats

Previous research has shown that exposure to testicular hormones during the peri-pubertal period of life has long-term, organizational effects on adult sexual behaviour and underlying neural mechanisms in laboratory rodents. However, the organizational effects of peri-pubertal testicular hormones on other aspects of behaviour and brain function are less well understood. Here, we investigated the effects of manipulating peri-pubertal testicular hormone exposure on later behavioural responses to novel environments and on hormone receptors in various brain regions that are involved in response to novelty. Male rodents generally spend less time in the exposed areas of novel environments than females, and this sex difference emerges during the peri-pubertal period. Male Lister-hooded rats (Rattus norvegicus) were castrated either before puberty or after puberty, then tested in three novel environments (elevated plus-maze, light-dark box, open field) and in an object/social novelty task in adulthood. Androgen receptor (AR), oestrogen receptor (ER1) and corticotropin-releasing factor receptor (CRF-R2) mRNA expression were quantified in the hypothalamus, hippocampus and medial amygdala. The results showed that pre-pubertally castrated males spent more time in the exposed areas of the elevated-plus maze and light-dark box than post-pubertally castrated males, and also confirmed that peri-pubertal hormone exposure influences later response to an opposite-sex conspecific. Hormone receptor gene expression levels did not differ between pre-pubertally and post-pubertally castrated males in any of the brain regions examined. This study therefore demonstrates that testicular hormone exposure during the peri-pubertal period masculinizes later response to novel environments, although the neural mechanisms remain to be fully elucidated.

Behavioral and locomotor measurements using an open field activity monitoring system for skeletal muscle diseases

The open field activity monitoring system comprehensively assesses locomotor and behavioral activity levels of mice. It is a useful tool for assessing locomotive impairment in animal models of neuromuscular disease and efficacy of therapeutic drugs that may improve locomotion and/or muscle function. The open field activity measurement provides a different measure than muscle strength, which is commonly assessed by grip strength measurements. It can also show how drugs may affect other body systems as well when used with additional outcome measures. In addition, measures such as total distance traveled mirror the 6 min walk test, a clinical trial outcome measure. However, open field activity monitoring is also associated with significant challenges: Open field activity measurements vary according to animal strain, age, sex, and circadian rhythm. In addition, room temperature, humidity, lighting, noise, and even odor can affect assessment outcomes. Overall, this manuscript provides a well-tested and standardized open field activity SOP for preclinical trials in animal models of neuromuscular diseases. We provide a discussion of important considerations, typical results, data analysis, and detail the strengths and weaknesses of open field testing. In addition, we provide recommendations for optimal study design when using open field activity in a preclinical trial.

Acute total sleep deprivation potentiates cocaine-induced hyperlocomotion in mice

Sleep deprivation is common place in modern society. Nowadays, people tend to self-impose less sleep in order to achieve professional or social goals. In the social context, late-night parties are frequently associated with higher availability of recreational drugs with abuse potential. Physiologically, all of these drugs induce an increase in dopamine release in the mesolimbic dopaminergic system, which leads to hyperlocomotion in rodents. Sleep deprivation also seems to play an important role in the events related to the neurotransmission of the dopaminergic system by potentiating its behavioral effects. In this scenario, the aim of the present study was to investigate the effects of total sleep deprivation (6h) on the acute cocaine-induced locomotor stimulation in male mice. Animals were sleep deprived or maintained in their home cages and subsequently treated with an acute i.p. injection of 15mg/kg cocaine or saline and observed in the open field. Total sleep deprivation for 6h potentiated the hyperlocomotion induced by acute cocaine administration. In addition, the cocaine sleep deprived group showed a decreased ratio central/total locomotion compared to the cocaine control group, which might be related to an increase in the impulsiveness of mice. Our data indicate that acute periods of sleep loss should be considered risk factors for cocaine abuse.

Sex differences in animal models of psychiatric disorders

Psychiatric disorders are characterized by sex differences in their prevalence, symptomatology and treatment response. Animal models have been widely employed for the investigation of the neurobiology of such disorders and the discovery of new treatments. However, mostly male animals have been used in preclinical pharmacological studies. In this review, we highlight the need for the inclusion of both male and female animals in experimental studies aiming at gender-oriented prevention, diagnosis and treatment of psychiatric disorders. We present behavioural findings on sex differences from animal models of depression, anxiety, post-traumatic stress disorder, substance-related disorders, obsessive-compulsive disorder, schizophrenia, bipolar disorder and autism. Moreover, when available, we include studies conducted across different stages of the oestrous cycle. By inspection of the relevant literature, it is obvious that robust sex differences exist in models of all psychiatric disorders. However, many times results are conflicting, and no clear conclusion regarding the direction of sex differences and the effect of the oestrous cycle is drawn. Moreover, there is a lack of considerable amount of studies using psychiatric drugs in both male and female animals, in order to evaluate the differential response between the two sexes. Notably, while in most cases animal models successfully mimic drug response in both sexes, test parameters and treatment-sensitive behavioural indices are not always the same for male and female rodents. Thus, there is an increasing need to validate animal models for both sexes and use standard procedures across different laboratories.

Prolonged consumption of trans fat favors the development of orofacial dyskinesia and anxiety-like symptoms in older rats

Polyunsaturated fatty acids (FAs) are cell membrane components involved in brain functions. We hypothesized that long-term trans fat consumption is able to modify the membrane FAs composition impairing behavioral parameters related to aging. In this study, a comparison of behavioral parameters at 10 and 15 months of trans fat consumption by male Wistar rats was made. Animals were fed for 10 and 15 months from weaning with diets containing either 20% w/w soybean oil (SO), rich in n-6 PUFA, hydrogenated vegetable fat (HVF), rich in trans FAs, or a standard diet (control - C). At both evaluation times, HVF-fed rats showed progressively increased parameters of orofacial dyskinesia, fear and anxiety-like symptoms. The HVF diet reduced locomotor and exploratory activities progressively over 10 and 15 months of supplementation, while the standard and SO diets did not. In this study, we showed that chronic trans FAs consumption from weaning is able to favor the development of neuromotor and neuropsychiatric diseases, whose intensity was time dependent.

Low-anxiety rat phenotypes can be further reduced through genetic intervention

BACKGROUND

A previous study using an intercross between the inbred rat strains Lewis (LEW) and Spontaneously Hypertensive Rats (SHR) identified a locus on chromosome 4, named Anxrr16, influencing an experimental index of anxiety and showing a transgressive effect, with alleles from the LEW strain (more anxious) decreasing rather than increasing anxiety.

OBJECTIVE

To confirm the location and isolate the effect of a rat genome region named Anxrr16 through a planned genomic recombination strategy, where the target locus in SHR rats was replaced with LEW genetic material.

METHODS

A new congenic strain, named SHR.LEW-Anxrr16 (SLA16), was developed from a cross between LEW (donor) and SHR (receptor) rats and then evaluated in several anxiety-related tests. The activity and attention levels of the new strain were also evaluated, since hyperactivity was observed during its construction and because SHR is a model of attention deficit hyperactivity disorder.

RESULTS

Significant effects of Anxrr16 were found for open field central locomotion, as well as for other indices of anxiety from the light/dark box, triple test and T-maze. In all cases, the low-anxiety levels of SHR rats were further reduced by the insertion of LEW alleles. Differences in locomotor activity were found only in unfamiliar (hence stressful) environments and no genetic effects were observed in indices of attention.

CONCLUSION

The SLA16 strain can help in the identification of the molecular pathways involved in experimental anxiety and it demonstrates how apparently extreme phenotypes sometimes hide major opposite-acting genes.

Neurobiology of stress-induced hyperalgesia

The intensity and severity of perceived pain does not correlate consistently with the degree of peripheral or central nervous system tissue damage or with the intensity of primary afferent or spinal nociceptive neurone activity. In this respect, the modulation of pain by emotion and context is now widely recognized. In particular, stress, fear and anxiety exert potent, but complex, modulatory influences on pain. Stress can either suppress pain (stress-induced analgesia) or exacerbate it (stress-induced hyperalgesia; SIH) depending on the nature, duration and intensity of the stressor. Herein, we review the methods and models used to study the phenomenon of SIH in rodents and humans and then present a detailed discussion of our current understanding of neural substrates and neurobiological mechanisms. The review provides perspectives and challenges for the current and future treatment of pain and the co-morbidity of pain with stress-related psychiatric disorders including anxiety and depression.

Acute total sleep deprivation potentiates amphetamine-induced locomotor-stimulant effects and behavioral sensitization in mice

It has been demonstrated that a prolonged period (48 h) of paradoxical sleep deprivation (PSD) potentiates amphetamine (AMP)-induced behavioral sensitization, an animal model of addiction-related neuroadaptations. In the present study, we examined the effects of an acute short-term deprivation of total sleep (TSD) (6h) on AMP-induced behavioral sensitization in mice and compared them to the effects of short-term PSD (6 h). Three-month-old male C57BL/6J mice underwent TSD (experiment 1-gentle handling method) or PSD (experiment 2-multiple platforms method) for 6 h. Immediately after the sleep deprivation period, mice were tested in the open field for 10 min under the effects of saline or 2.0 mg/kg AMP. Seven days later, to assess behavioral sensitization, all of the mice received a challenge injection of 2.0 mg/kg AMP and were tested in the open field for 10 min. Total, peripheral, and central locomotion, and grooming duration were measured. TSD, but not PSD, potentiated the hyperlocomotion induced by an acute injection of AMP and this effect was due to an increased locomotion in the central squares of the apparatus. Similarly, TSD facilitated the development of AMP-induced sensitization, but only in the central locomotion parameter. The data indicate that an acute period of TSD may exacerbate the behavioral effects of AMP in mice. Because sleep architecture is composed of paradoxical and slow wave sleep, and 6-h PSD had no effects on AMP-induced hyperlocomotion or sensitization, our data suggest that the deprivation of slow wave sleep plays a critical role in the mechanisms that underlie the potentiating effects of TSD on both the acute and sensitized addiction-related responses to AMP.

Sex differences in anxiety and emotional behavior

Research has elucidated causal links between stress exposure and the development of anxiety disorders, but due to the limited use of female or sex-comparative animal models, little is known about the mechanisms underlying sex differences in those disorders. This is despite an overwhelming wealth of evidence from the clinical literature that the prevalence of anxiety disorders is about twice as high in women compared to men, in addition to gender differences in severity and treatment efficacy. We here review human gender differences in generalized anxiety disorder, panic disorder, posttraumatic stress disorder and anxiety-relevant biological functions, discuss the limitations of classic conflict anxiety tests to measure naturally occurring sex differences in anxiety-like behaviors, describe sex-dependent manifestation of anxiety states after gestational, neonatal, or adolescent stressors, and present animal models of chronic anxiety states induced by acute or chronic stressors during adulthood. Potential mechanisms underlying sex differences in stress-related anxiety states include emerging evidence supporting the existence of two anatomically and functionally distinct serotonergic circuits that are related to the modulation of conflict anxiety and panic-like anxiety, respectively. We discuss how these serotonergic circuits may be controlled by reproductive steroid hormone-dependent modulation of crfr1 and crfr2 expression in the midbrain dorsal raphe nucleus and by estrous stage-dependent alterations of γ-aminobutyric acid (GABAergic) neurotransmission in the periaqueductal gray, ultimately leading to sex differences in emotional behavior.

Classical and novel approaches to the preclinical testing of anxiolytics: A critical evaluation

Over 80% of current anxiety studies employ one of the tests that were developed earlier than, or concurrently with the elevated plus-maze, i.e. before 1985. Considering 1985 as a historical reference point, we briefly review here 115 new tests and models of anxiety, the development of which was likely prompted by the poor predictive validity of classical tests as shown here by the comparison of preclinical and clinical findings with putative novel anxiolytics. The new approaches comprise major innovations to classical tests, the pre-test application of manipulations that mimic etiological factors of anxiety disorders, and entirely new approaches including anxiety disorder-specific tests. Thus, intensive test development over the last 27 years created a large pool of novel approaches. However, these are infrequently used and as such, their impact on anxiolytic drug development remains low. We suggest here that test/model development should step over the intensive phase when several new methods are proposed each year and should start selecting and establishing the methodologies that would successfully replace or complement classical tests. We propose here a novel strategy for improving the validity of anxiety testing that includes the retrospective analysis of the predictive validity of new procedures (as opposed to classical pharmacological validation), and a call for concerted international efforts at both the conceptual and practical levels. Similar endeavors proved recently successful with other psychiatric disorders.

Differential effects of intermittent and continuous exposure to novel environmental stimuli on the development of amphetamine-induced behavioral sensitization in mice: implications for addiction

BACKGROUND

Previous studies have demonstrated a preventive effect of continuous environmental enrichment during early development on the vulnerability of rodents to drug addiction-related behaviors. Recently, it was demonstrated that a continuous environmental enrichment could eliminate already established addiction-related behaviors in mice. The present study compared the effects of intermittent or continuous exposure to novel stimuli during repeated amphetamine (Amp) treatment on the development of behavioral sensitization (an animal model of addiction-related neuroadaptations) in adult mice.

METHODS

Three-month-old male Swiss mice were treated with 2.5mg/kg Amp every other day for 13 days in their home cages. Novel objects were presented in their home cages for 2h on non-drug treatment days (experiment 1) or for 24h/day during the 13 days of drug treatment (experiment 2). Seven days after the drug treatment had finished, the mice were challenged with 2.5mg/kg Amp, and their locomotor activity was quantified in a familiar open field for 10 min.

RESULTS

Intermittent exposure to the novel objects did not modify the acute Amp locomotor stimulatory effect but potentiated the development of Amp-induced locomotor sensitization. This enhanced sensitization was due to increased locomotion in the central squares of the apparatus, which suggests anxiolysis or increased impulsiveness. Conversely, continuous exposure to the novel objects potentiated the acute Amp locomotor stimulatory effect and blunted the development of Amp-induced locomotor sensitization.

CONCLUSIONS

We conclude that addiction-related behaviors can be differentially and critically modified depending on the schedule and period of the novelty exposure.

Selectively bred rodents as models of depression and anxiety

Stress related diseases such as depression and anxiety have a high degree of co morbidity, and represent one of the greatest therapeutic challenges for the twenty-first century. The present chapter will summarize existing rodent models for research in psychiatry, mimicking depression- and anxiety-related diseases. In particular we will highlight the use of selective breeding of rodents for extremes in stress-related behavior. We will summarize major behavioral, neuroendocrine and neuronal parameters, and pharmacological interventions, assessed in great detail in two rat model systems: The Flinders Sensitive and Flinders Resistant Line rats (FSL/FRL model), and rats selectively bred for high (HAB) or low (LAB) anxiety related behavior (HAB/LAB model). Selectively bred rodents also provide an excellent tool in order to study gene and environment interactions. Although it is generally accepted that genes and environmental factors determine the etiology of mental disorders, precise information is limited: How rigid is the genetic disposition? How do genetic, prenatal and postnatal influences interact to shape adult disease? Does the genetic predisposition determine the vulnerability to prenatal and postnatal or adult stressors? In combination with modern neurobiological methods, these models are important to elucidate the etiology and pathophysiology of anxiety and affective disorders, and to assist in the development of new treatment paradigms.

Effects of antipsychotics and amphetamine on social behaviors in spontaneously hypertensive rats

We have recently reported that spontaneously hypertensive rats (SHRs) exhibit a deficit in contextual fear conditioning that is specifically reversed by antipsychotic and potentiated by psychostimulants and other manipulations thought to produce schizophrenia-like states in rodents. Based on these findings, we suggested that this deficit in fear conditioning could be used as an experimental model of emotional processing impairments observed in schizophrenia. This strain has also been suggested as a model by which to study attention deficit/hyperactivity disorder (ADHD). Considering that schizophrenia and ADHD are both characterized by poor social function, this study aimed to investigate possible behavioral deficits of SHRs in a social context. Furthermore, we sought to examine the effects of typical and atypical antipsychotics (used for the treatment of schizophrenia) and a psychostimulant (used to treat ADHD) on these behaviors. Pairs of unfamiliar rats of the same or different (i.e., Wistar) strains were treated with one of the aforementioned drugs and placed in an open-field for 10min. During this time, social behaviors, locomotion and rearing frequencies were scored. Atypical antipsychotics increased social interaction in Wistar rats (WRs) and improved the deficit in social interaction exhibited by SHRs. In addition, the SHR group displayed hyperlocomotion that was attenuated by all antipsychotics (quetiapine and clozapine also decreased locomotion in WRs) and potentiated by amphetamine (which also increased locomotion in WRs). Our results reveal that the behavioral profile of the SHR group demonstrates that this strain can be a useful animal model to study several aspects of schizophrenia.

Overexpression or knockdown of rat tryptophan hyroxylase-2 has opposing effects on anxiety behavior in an estrogen-dependent manner

Previous studies showed that chronic estrogen treatment increases tryptophan hydroxylase-2 (TpH2) mRNA in the caudal dorsal raphe nucleus (DRN), and this increase was associated with decreased anxiety. The present study explored the interaction of estrogen and targeted, bidirectional manipulation of TpH2 expression in the caudal DRN by knockdown or viral overexpression, to decrease or increase tryptophan hydroxylase expression respectively, on anxiety behavior. Rats were ovariectomized and replaced with empty or estradiol capsules (OVX, OVX/E, respectively). Animals received microinfusions of either antisense TpH2 or control morpholino oligonucleotides into caudal DRN and were later tested in the open field test. A separate group of animals were microinfused with TpH2-GFP or GFP-only herpes simplex viral vectors into caudal DRN and tested in the open field. The bidirectional impact of manipulations on TpH2 expression was confirmed using a combination of quantitative protein and mRNA measurements; TpH2 expression changes were limited to discrete subregions of DRN that were targeted by the manipulations. Estradiol decreased anxiety in all behavioral measures. In the OVX/E group, TpH2 knockdown significantly decreased time spent in the center of the open field, but not in the OVX group, suggesting that TpH2 knockdown reduced the anxiolytic effects of estrogen. Conversely, TpH2 overexpression in the OVX group mimicked the effects of estrogen, as measured by increased time spent in the center of the open field. These results suggest that estrogen and TpH2 in the caudal DRN have a critical interaction in regulating anxiety-like behavior.

A role for delta opioid receptors in the central nucleus of the amygdala in anxiety-like behaviors

RATIONALE

Compounds acting on delta opioid receptors (DOR) modulate anxiety-like behaviors, yet the site of action underlying this effect is unknown. DOR mRNA and protein are expressed in the central nucleus of the amygdala, a region that plays an important role in processing fear, stress, and anxiety. We hypothesized that this brain region may contribute to the modulation of anxiety by DOR drugs.

OBJECTIVE

The present study investigated the role of DOR in the central amygdala in anxiety-like behaviors.

METHODS

The selective DOR agonist [D-Pen 2,5]-enkephalin (DPDPE) or antagonist naltrindole was bilaterally microinjected into the central nucleus of the amygdala of adult male Sprague Dawley rats and anxiety-like behaviors were assessed using the elevated plus maze. The effects of DOR agonists on heightened anxiety produced by stress were also investigated.

RESULTS

Rats injected with DPDPE into the central nucleus of the amygdala demonstrated less anxiety-like behavior, as evidenced by significantly greater number of open-arm entries and time spent in the open arms than controls. Naltrindole administered alone did not affect the duration or number of entries onto the open arms; however, naltrindole pre-treatment blocked the anxiolytic effects produced by DPDPE. Systemic administration of the selective DOR agonist, SNC80, or microinjection of DPDPE into the central amygdala prior to a swim stress blocked the anxiogenic effect produced by the swim stress.

CONCLUSIONS

These findings provide direct evidence that activation of DOR in the central amygdala reduces anxiety-like behavior and suggest that DOR in this area are important for regulating anxious states.

The effects of strain and prenatal nicotine exposure on ethanol consumption by adolescent male and female rats

Two studies of variables affecting voluntary ethanol consumption by adolescent male and female rats are reported. Sprague-Dawley (SD) and spontaneously hypertensive rats (SHRs) were compared in Experiment 1. Starting on postnatal day 30 all had 24-h access to 2%, then 4%, and then 6% ethanol, followed by 1-h access to the 6% until intake stabilized. During the 1-h access SHR females consumed more ethanol than all other groups. In Experiment 2, the same procedure was used to compare SD groups prenatally exposed to nicotine, with controls. Nicotine-exposed females consumed more ethanol during 1-h access than both nicotine-exposed and control males; but after using water intake as a covariate, the differences were not significant. These data show that deprivation conditions need to be considered when generalizing the results of voluntary consumption studies, and that estrogens may be a modulator of addictive behavior.

Diurnal rhythms of spontaneous recurrent seizures and behavioral alterations of Wistar and spontaneously hypertensive rats in the kainate model of epilepsy

Attention deficit hyperactivity disorder (ADHD) can coexist with epilepsy. Spontaneously hypertensive rats (SHRs) are considered to model ADHD with overactivity, impulsiveness, deficient sustained attention, and alterations in circadian autonomic profiles. The present study explored spontaneous recurrent seizures (SRSs) and behavioral diurnal activity rhythms in normotensive Wistar rats and SHRs in the kainate model of epilepsy. Rats were video monitored (24 h/3 months) to detect SRSs. SHRs manifested a lower seizure frequency during the light phase in the 8th and 10th weeks and a lower frequency of SRSs during the night phase accompanied by attenuated responses in hyperexcitability tests. Both epileptic strains were hyperactive, with lower anxiety levels, and their diurnal rhythms were abolished. Epileptic Wistar rats and SHRs exhibited less exploration during the dark phase. This study suggests that SHRs may be useful in modeling some aspects (particularly hypertension-related diurnal rhythm disturbance) of behavior associated with epilepsy.

Emotional reactivity and cognitive performance in aversively motivated tasks: a comparison between four rat strains

BACKGROUND

Cognitive function might be affected by the subjects' emotional reactivity. We assessed whether behavior in different tests of emotional reactivity is correlated with performance in aversively motivated learning tasks, using four strains of rats generally considered to have a different emotional reactivity.

METHODS

The performance of male Brown Norway, Lewis, Fischer 344, and Wistar Kyoto rats in open field (OF), elevated plus-maze (EPM), and circular light-dark preference box (cLDB) tasks, which are believed to provide measures of emotional reactivity, was evaluated. Spatial working and reference memory were assessed in two aversively motivated learning and memory tasks: the standard and the "repeated acquisition" versions of the Morris water maze escape task, respectively. All rats were also tested in a passive avoidance task. At the end of the study, levels of serotonin (5-HT) and 5-hydroxyindoleacetic acid, and 5-HT turnover in the hippocampus and frontal cortex were determined.

RESULTS

Strain differences showed a complex pattern across behavioral tests and serotonergic measures. Fischer 344 rats had the poorest performance in both versions of the Morris water escape task, whereas Brown Norway rats performed these tasks very well but the passive avoidance task poorly. Neither correlation analysis nor principal component analysis provided convincing support for the notion that OF, EPM, and cLDB tasks measure the same underlying trait.

CONCLUSIONS

Our findings do not support the hypothesis that the level of emotional reactivity modulates cognitive performance in aversively motivated tasks. Concepts such as "emotional reactivity" and "learning and memory" cannot adequately be tapped with only one behavioral test. Our results emphasize the need for multiple testing.

Environmental enrichment reduces the impact of novelty and motivational properties of ethanol in spontaneously hypertensive rats

The present study investigated the consequences of environmental enrichment on the impact of novelty and motivational properties of ethanol in spontaneously hypertensive rats (SHR), a validated model of attention deficit hyperactivity disorder (ADHD). This rat strain displays increased sensitivity to distinct classes of abused drugs, which makes it an interesting model for the study of the association between ADHD and drug abuse. Female SHR reared from weaning to adulthood in standard (SE) or enriched (EE) environment were tested on novelty-induced locomotion, saccharin consumption, ethanol consumption (forced and free-choice schedules) and ethanol-induced conditioned place preference (CPP). SHR reared in an EE showed reduced novelty-induced locomotion, consumed less saccharin and ethanol in a forced schedule and showed less ethanol preference in a free-choice schedule compared to SE rats. Moreover, EE rats did not develop CPP, whereas SE rats developed preference for ethanol (1.2g/kg). These results show that exposure to stimuli mimicking positive life experiences (environmental enrichment) induces persistent changes in the reward/motivational system of female SHR, suggesting an important role of the familiar environment during early stages of the neurodevelopment on the co-morbidity of ADHD and drug abuse.