Amphetamine withdrawal does not produce a depressive-like state in rats as measured by three behavioral tests

Encore: Behavioural animal models of stress, depression and mood disorders

Animal studies over the past two decades have led to extensive advances in our understanding of pathogenesis of depressive and mood disorders. Among these, rodent behavioural models proved to be of highest informative value. Here, we present a comprehensive overview of the most popular behavioural models with respect to physiological, circuit, and molecular biological correlates. Behavioural stress paradigms and behavioural tests are assessed in terms of outcomes, strengths, weaknesses, and translational value, especially in the domain of pharmacological studies.

Behavioral Effects of 4-CMC and 4-MeO-PVP in DBA/2J Mice After Acute and Intermittent Administration and Following Withdrawal from Intermittent 14-Day Treatment

Synthetic cathinones appeared on the market in the 2000s as new psychoactive substances and gained significant prevalence among drug abusers. Cathinones produce psychostimulant and empathogenic effects by enhancing dopaminergic, noradrenergic, and serotoninergic neurotransmission in the brain, and those which potently and selectively enhance dopaminergic transmission are considered to have higher abuse potential. The present study examines the behavioral effects related to psychostimulant properties, abuse potential, and addiction in DBA/2J mice of two cathinones with different profile of action on monoamine system, 4-chloromethcathinone (4-CMC), and 4-methoxy-pyrrolidinopentiophenone (4-MeO-PVP). 4-CMC and 4-MeO-PVP increase spontaneous locomotor activity after acute treatment and produce behavioral sensitization after 7-day intermittent treatment, which is a common feature of drugs of abuse. 4-MeO-PVP, but not 4-CMC, produces conditioned place preference after 4 days, indicating its rewarding properties. Finally, the ability of 4-CMC and 4-MeO-PVP to induce withdrawal symptoms after discontinuation from 14-day treatment was assessed using a battery of tests for behavioral markers of depression in mice: a tail suspension test, a forced swim test, measuring despair, and a sucrose preference test, measuring anhedonia. None of the three tests revealed increased depressive symptoms. Moreover, neither spontaneous locomotor activity nor motor performance on a rotarod was impaired after 14-day treatment with the tested compounds. These results indicate that 14-day treatment of mice with 4-CMC or 4-MeO-PVP does not induce significant withdrawal symptoms after cessation, nor significant impairment of dopaminergic circuitry resulting in motor impairment. The current study shows that 4-CMC and 4-MeO-PVP produce abuse-related behavioral changes in mice, which are more pronounced after more dopamine-selective 4-MeO-PVP.

Involvement of NO/NMDA-R pathway in the behavioral despair induced by amphetamine withdrawal

Abrupt discontinuation of chronic amphetamine consumption leads to withdrawal symptoms including depression, anhedonia, dysphoria, fatigue, and anxiety. These irritating symptoms may result in continuing to take the drug or can lead to suicidal behavior. Past studies have shown the involvement of various biologic systems in depression induced following amphetamine withdrawal (AW). However, there is no evidence about the relation between nitric oxide (NO) with NMDA receptors on depression following AW. In this study, we examined the involvement of the NO/NMDA pathways on depressive-like behaviors after 24 h withdrawal following 5 continuous days of amphetamine administration in male NMRI mice. Behavioral tasks used for depression assessment included the forced swimming test (FST), the Splash test and the open field test (OFT). In order to evaluate the role of NO/NMDA pathways animals treated with MK-801 (NMDA-R antagonist), Aminoguanidine (AG), a selective iNOS inhibitor, Nω-Nitro-l-arginine (L-NNA), a non-selective NOS inhibitor and 7-Nitro indazole (7-NI), a selective nNOS inhibitor. We also measured the level of nitrite in the hippocampus. Our data showed that AW induced the depressive-like effect in the FST and the Splash test. We showed that administration of AG, L-NNA, and MK-801 mitigated AW induced depression, however, 7-NI was failed to decrease depressive-like behaviors. Also, the antidepressant-like effect of co-injection of sub-effective doses of MK-801 with AG suggested that inducible nitric oxide synthase (iNOS) is associated with NMDA-R in AW induced depression. In conclusion, both NO and NMDA-R pathways are involved and related to each other in depression induced following AW.

Ultrasound of alternating frequencies and variable emotional impact evokes depressive syndrome in mice and rats

Emotional stress is primarily triggered by the cognitive processing of negative input; it is regarded as a serious pathogenetic factor of depression that is challenging to model in animals. While available stress paradigms achieve considerable face and construct validity in modelling depressive disorders, broader use of naturalistic stressors instead of the more prevalent models with artificial challenges inducing physical discomfort or pain may substantially contribute to the development of novel antidepressants. Here, we investigated whether a 3-week exposure of Wistar rats and Balb/c mice to unpredictably alternating frequencies of ultrasound between the ranges of 20-25 and 25-45kHz, which are known to correspond with an emotionally negative and with a neutral emotional state, respectively, for small rodents in nature, can induce behavioural and molecular depressive-like changes. Both rats and mice displayed decreased sucrose preference, elevated "despair" behaviour in a swim test, reduced locomotion and social exploration. Rats showed an increased expression of SERT and 5-HT2A receptor, a decreased expression of 5-HT1A receptor in the prefrontal cortex and hippocampus, diminished BDNF on gene and protein levels in the hippocampus. Fluoxetine, administered to rats at the dose of 10mg/kg, largely precluded behavioural depressive-like changes. Thus, the here applied paradigm of emotional stress is generating an experimental depressive state in rodents, which is not related to any physical stressors or pain. In essence, this ultrasound stress model, besides enhancing animal welfare, is likely to provide improved validity in the modelling of clinical depression and may help advance translational research and drug discovery for this disorder.

Effects of maternal L-tryptophan depletion and corticosterone administration on neurobehavioral adjustments in mouse dams and their adolescent and adult daughters

Major depressive disorder (MDD), a pathology characterized by mood and neurovegetative disturbances, depends on a multi-factorial contribution of individual predisposition (e.g., diminished serotonergic transmission) and environmental factors (e.g., neonatal abuse or neglect). Despite its female-biased prevalence, MDD basic research has mainly focused on male rodents. Most of present models of depression are also devalued due to the fact that they typically address only one of the aforementioned pathogenetic factors. In this paper we first describe the basic principles behind mouse model development and evaluation and then articulate that current models of depression are intrinsically devalued due to poor construct and/or external validity. We then report a first attempt to overcome this limitation through the design of a mouse model in which the genetic and the environmental components of early risk factors for depression are mimicked together. Environmental stress is mimicked through the supplementation of corticosterone in the maternal drinking water while biological predisposition is mimicked through maternal access to an L-tryptophan (the serotonin precursor) deficient diet during the first week of lactation. CD1 dams and their offspring exposed to the L-tryptophan deficient diet (T) and to corticosterone (80mg/l; C) were compared to animal facility reared (AFR) subjects. T and C mice served as intermediate reference groups. Adolescent TC offspring, compared to AFR mice, showed decreased time spent floating in the forced-swim test and increased time spent in the open sectors of an elevated 0-maze. Adult TC offspring showed reduced preference for novelty, decreased breakpoints in the progressive ratio operant procedure and major alterations in central BDNF levels and altered HPA regulation. The route of administration and the possibility to control the independent variables predisposing to depressive-like symptoms disclose novel avenues towards the development of animal models with increased external and construct validity. Furthermore, the observation that, compared to adult subjects, adolescent mice display an opposite profile suggests that peri-pubertal developmental processes may interact with neonatal predispositions to calibrate the adult abnormal phenotype.

Pre- and/or postnatal protein restriction in rats impairs learning and motivation in male offspring

Suboptimal developmental environments program offspring to lifelong health complications including affective and cognitive disorders. Little is known about the effects of suboptimal intra-uterine environments on associative learning and motivational behavior. We hypothesized that maternal isocaloric low protein diet during pregnancy and lactation would impair offspring associative learning and motivation as measured by operant conditioning and the progressive ratio task, respectively. Control mothers were fed 20% casein (C) and restricted mothers (R) 10% casein to provide four groups: CC, RR, CR, and RC (first letter pregnancy diet and second letter lactation diet), to evaluate effects of maternal diet on male offspring behavior. Impaired learning was observed during fixed ratio-1 operant conditioning in RC offspring that required more sessions to learn vs. the CC offspring (9.4±0.8 and 3.8±0.3 sessions, respectively, p<0.05). Performance in fixed ratio-5 conditioning showed the RR (5.4±1.1), CR (4.0±0.8), and RC (5.0±0.8) offspring required more sessions to reach performance criterion than CC offspring (2.5±0.5, p<0.05). Furthermore, motivational effects during the progressive ratio test revealed less responding in the RR (48.1±17), CR (74.7±8.4), and RC (65.9±11.2) for positive reinforcement vs. the CC offspring (131.5±7.5, p<0.05). These findings demonstrate negative developmental programming effects due to perinatal isocaloric low protein diet on learning and motivation behavior with the nutritional challenge in the prenatal period showing more vulnerability in offspring behavior.

Withdrawal from chronic exposure to amphetamine, but not nicotine, leads to an immediate and enduring deficit in motivated behavior without affecting social interaction in rats

Psychostimulant withdrawal leads to depressive symptoms, such as anhedonia and social dysfunction. We determined the effects of withdrawal from chronic exposure to nicotine (9 mg/kg/day salt, 28 days) or amphetamine (10 mg/kg/day salt, 7 days) on the motivated response for a sucrose reward and on social interaction in rats. Both nicotine and amphetamine exposure increased the motivated response for sucrose. However, only spontaneous amphetamine withdrawal led to an immediate and persistent decrease in motivated behavior, which was not correlated with body weight loss. Social interaction was not affected during withdrawal from either drug. These results indicate that withdrawal from chronic amphetamine exposure leads to an immediate and enduring anhedonic state.

Recapitulation and reversal of a persistent depression-like syndrome in rodents

Alterations in multiple biological functions, such as transcription factor activity, are implicated in the neurobiology of depression, based primarily on the characterization of antidepressant efficacy in naïve rodents rather than on models that capture the protracted feelings of anhedonia and helplessness that typify depression. This unit presents rat and mouse models of depression that involve chronic oral exposure to the stress-associated adrenal hormone, corticosterone (CORT), resulting in anhedonic- and helplessness-like behaviors that are persistent yet reversible by chronic antidepressant treatment. Prior CORT exposure also chronically influences molecular targets hypothesized to contribute to negative mood. One example is phosphorylation of cAMP response element binding protein in the hippocampus and nucleus accumbens. Prior chronic CORT exposure provides an alternative method to chronic mild stress models of depression that is easily replicable and persists well beyond the CORT exposure period, thereby modeling the persistent depressive-like state in humans.

Derivation and validation of murine histologic alterations resembling asthma, with two proposed histologic grade parameters

BACKGROUND

The objective was to define murine histologic alterations resembling asthma in a BALB/c OVA model and to suggest grading criteria. Identified were six salient histologic findings in lungs with putative allergic inflammation: 1) bronchoarterial space inflammation; 2) peri-venular inflammation; 3) inflammation about amuscular blood vessels; 4) inter-alveolar space inflammation, not about capillaries; 5) pleural inflammation; and 6) eosinophils within the inflammatory aggregates. An initial study comprised six groups of twelve mice each: 1) stressed, control; 2) stressed, sensitized; 3) stressed, challenged; 4) not physically stressed, control; 5) not physically stressed, sensitized; 6) not physically stressed, challenged. A second study comprised four experimental groups of twenty mice each: 1) stressed, control; 2) stressed, challenged; 3) not physically stressed, control; 4) not physically stressed, challenged. A third study evaluated two grading criteria, 1) the proportion of non-tracheal respiratory passages with inflammatory aggregates and 2) mitoses in the largest two non-tracheal respiratory passages, in five groups of five mice each, evaluated at different times after the last exposure.

RESULTS

The first study suggested the six histological findings might reliably indicate the presence of alterations resembling asthma: whereas 82.4% of mice with a complete response had detectable interleukin (IL)-5, only 3.8% of mice without one did; whereas 77.8% of mice with a complete response were challenged mice, only 6.7% of mice without complete responses were. The second study revealed that the six histological findings provided a definition that was 97.4% sensitive and 100% specific. The third study found that the odds of a bronchial passage's having inflammation declined 1) when mitoses were present (OR = 0.73, 0.60 - 0.90), and 2) with one day increased time (OR = 0.75, 0.65 - 0.86).

CONCLUSION

A definition of murine histologic alterations resembling asthma in the BALB/c OVA mouse was developed and validated. The definition will be of use in experiments involving this model to ensure that all mice said to have undergone an asthmatic attack did indeed reveal allergic pulmonary inflammation. Proposed grading criteria should be further evaluated with additional studies using physiologic measures of attack severity and increased airway resistance.

Acute stress affects the physiology and behavior of allergic mice

Physical and psychological stressors have been implicated in acute asthma exacerbation. The objective of the current study was to determine the effects of forced swimming stress (FST) on allergic pulmonary inflammation in BALB/c mice. Eighty female mice were allocated to one of four treatments arranged in a 2 x 2 factorial consisting of two levels of allergy and two levels of stress. The effects of stress and allergy were assessed by examination of cytokines and leukocyte differentials in the bronchoalveolar lavage fluid, corticosterone and immunoglobulin (Ig) E in the plasma, leukocyte differentials in the peripheral blood, natural killer cytotoxicity, and histopathology of the lungs. Behavior was recorded during the FST. Stress and allergy increased plasma corticosterone in mice. Allergy increased IgE concentrations and pulmonary inflammation. Interleukin-4 was greater among allergic stressed and non-stressed mice and stressed, non-allergic mice compared with non-stressed, non-allergic mice. Interleukin-5 (IL-5) and 6 (IL-6) were greater among allergic stressed and non-stressed mice compared with non-allergic mice. Interleukin-5 and 6 were reduced among stressed-allergic mice compared with non-stressed, allergic mice. Stress and allergy shifted mice towards a T-helper 2 response as shown by increased interleukin-4. Stress reduced IL-5 and IL-6 in allergic mice but not non-allergic mice. Pulmonary inflammation was not reduced among allergic stressed mice in spite of elevated glucocorticoids. Mice induced to be allergic responded to FST differently than non-allergic mice. Our findings suggest that stress induces a differential response among allergic and non-allergic mice.

Exposure to stressors during juvenility disrupts development-related alterations in the PSA-NCAM to NCAM expression ratio: potential relevance for mood and anxiety disorders

Childhood trauma is associated with higher rates of both mood and anxiety disorders in adulthood. The exposure of rats to stressors during juvenility has comparable effects, and was suggested as a model of induced predisposition for these disorders. The neural cell adhesion molecule (NCAM) and its polysialylated form PSA-NCAM are critically involved in neural development, activity-dependent synaptic plasticity, and learning processes. We examined the effects of exposure to stressors during juvenility on coping with stressors in adulthood and on NCAM and PSA-NCAM expression within the rat limbic system both soon after the exposure and in adulthood. Exposure to stressors during juvenility reduced novel-setting exploration and impaired two-way shuttle avoidance learning in adulthood. Among naive rats, a development-related decrease of about 50% was evident in the PSA-NCAM to NCAM expression ratio in the basolateral amygdala, in the CA1 and dentate gyrus regions of the hippocampus, and in the entorhinal cortex. In juvenile-stressed rats, we found no such decrease, but rather an increase in the polysialylation of NCAM ( approximately 50%), evident soon after the exposure to juvenile stress and also in adulthood. Our results suggest that exposure to stressors during juvenility alters the maturation of the limbic system, and potentially underlies the predisposition to exhibit stress-related symptoms in adulthood.

The amphetamine-induced sensitized state as a model of schizophrenia

Schizophrenia is a serious psychiatric disorder which impacts a broad range of cognitive, behavioural and emotional domains. In animals, exposure to an intermittent, escalating dose regimen of amphetamine induces a sensitized state that appears to share a number of behavioural and neurochemical similarities with schizophrenia. In humans repeated exposure to amphetamine, or other psychomotor stimulants, can induce sensitization as well as psychosis. The following paper evaluates the evidence for the amphetamine-induced sensitized state as an animal model of schizophrenia, focussing separately on the positive, cognitive and negative symptoms associated with this disease. Current evidence supports the use of amphetamine sensitization as a model of the positive symptoms observed in schizophrenia. Additionally, there is increasing evidence for long-lasting cognitive deficits in sensitized animals, especially in the area of attention and/or cognitive flexibility. Other areas of cognition, such as long-term memory, appear to be unaltered in sensitized animals. Finally, little evidence currently exists to either support or refute the use of amphetamine sensitization as a model of negative symptoms. It is concluded that amphetamine sensitization likely impacts behaviour by altering the functioning of mesolimbic dopamine systems and prefrontal cortical function and can serve as a model of certain domains of schizophrenia.

Neurochemical consequences of dysphoric state during amphetamine withdrawal in animal models: a review

Chronic abuse of amphetamines, such as d-amphetamine (AMPH) and d-methamphetamine, results in psychological dependence, a condition in which the drug produces a feeling of satisfaction and a drive that requires periodic or continuous administration of the drug to produce overwhelming pleasure or to avoid discomfort such as dysphoria. The dysphoric state of AMPH withdrawal has been recognized as depressive syndromes, such as anhedonia, depression, anxiety, and social inhibition, in early drug abstinence. Medication for treatment of the dysphoric state is important for AMPH abusers to avoid impulsive self-injurious behavior or acts that are committed with unconscious or uncontrolled suicidal ideation. However, successful treatments for AMPH withdrawal remain elusive, since the exact molecular basis of the expression of dysphoria has not been fully elucidated. This review focuses on the molecular aspects of AMPH withdrawal as indexed by neurochemical parameters under a variety of injection regimens (for example, levels of brain monoamines and their metabolites, and gamma-aminobutyric acid, expression of genes and proteins involved in neuronal activity, and monoamine metabolism and availability) in rodent models which exhibit significant phenotypic features relevant to the syndromes of AMPH withdrawal in humans.

Effects of short-term abstinence from escalating doses of D-amphetamine on drug and sucrose-evoked dopamine efflux in the rat nucleus accumbens

Abstinence from high doses of psychostimulant drugs, in both humans and rodents, is linked to adverse psychological effects including anhedonia, a core symptom of major depression, manifested behaviorally as decreased responding for rewarding stimuli. The present study used brain microdialysis in freely moving rats to examine the effect of D-amphetamine (D-amph) withdrawal on changes in extracellular dopamine (DA) levels in the nucleus accumbens (NAc) evoked by D-amph or behavior related to sucrose consumption. D-amph was administered intraperitoneally (i.p.) according to an escalating dose (ED) schedule (from 1 to 10 mg/kg, 3 doses/day). We first confirmed the development of tolerance by monitoring DA efflux in the NAc in response to 5 and 10 mg/kg doses of D-amph administered during the ED schedule of drug administration and again in response to the 5 mg/kg dose of D-amph 72 h following the last 10 mg/kg D-amph injection. In a separate study, DA efflux in the NAc was first shown to be increased significantly during both preparatory and consummatory phases of responding for a 4% sucrose solution. Withdrawal from the ED schedule of D-amph caused a selective attenuation of DA efflux only during the preparatory phase of the sucrose test. These results provided convincing evidence of neurochemical adaptation within the mesocorticolimbic DA pathway during and following the administration of an ED schedule of D-amph as well as suppressed neurochemical responses to a psychostimulant drug and cues associated with a natural reward after withdrawal from drug treatment. Accordingly, these findings support the hypothesis that downregulation of mesocorticolimbic DA function maintained during D-amph withdrawal may account for the selective disruption of motivated behavior reported in studies employing psychostimulant drug withdrawal as a model of depression in rodents.

Early deprivation leads to altered behavioural, autonomic and endocrine responses to environmental challenge in adult Fischer rats

Depression is diagnosed on the basis of abnormal positive affects (anhedonia) and negative affects (low mood, helplessness, coping deficit, fatigue), and associated physiological abnormalities include hyperactivity of the HPA endocrine system and autonomic nervous system. Adverse early life environments, including parent-offspring emotional and physical neglect, are associated with traits of altered physiological and neurobiological function and long-term predisposition to depression. Animal studies based on early life adversity can potentially yield environmental models of the developmental behavioural neurobiology of depression. In Wistar rats, we demonstrated that isolation of pups from dam and littermates at room temperature for 4 h per day on P1-14 (early deprivation, ED) led to adulthood anhedonia-like traits of reduced motivation to obtain gustatory reward and reduced social motivation, relative to subjects left undisturbed during infancy (non-handling, NH). We hypothesized that the depression-like effects of ED would be even more pronounced and multiple in the stress hyper-responsive Fischer rat strain. The effects of ED were studied relative to NH and 15 min of daily isolation (early handling, EH). Relative to NH and EH, which exhibited remarkably similar phenotypes, ED led, principally in males, to chronic traits of: reduced motivation for and consumption of gustatory reward; increased activity in the pre-test and test phases of the forced swim test; reduced coping behaviour in an aversive environment; attenuated plasma corticosterone stress response to a normal plasma ACTH stress response; increased hypertensive response to a novel environment; and increased prefrontal cortical serotonin. High sensitivity to an aversive early environment in male Fischer rats therefore constitutes an important model for the study of affective development and its neurobiology.

Amphetamine withdrawal leads to behavioral sensitization and reduced HPA axis response following amphetamine challenge

Withdrawal from repeated amphetamine (AMPH) administration leads to behavioral sensitization following a drug or a stress challenge and is commonly used to model anhedonia in rats, a core symptom of depression in humans. It is proposed that corticosteroids are involved in the mediation of sensitization and depression. The aim of the present study was to investigate stress and AMPH- induced release of adrenocorticotropic hormone (ACTH) and corticosterone (CORT) during withdrawal from an escalating dosage schedule of AMPH known to produce depression-like effects in rats. Wistar rats were given 3 injections (i.p.) per day over 3 days, escalating from 1 mg/kg to 9 mg/kg and a final injection of 10 mg/kg AMPH or saline on day 4. On day 2 of withdrawal, the animals were tested in the Porsolt swim test. HPA axis activity in response to restraint stress was tested on withdrawal day 14 and in response to AMPH challenge on withdrawal day 30. We found no effect of AMPH withdrawal in the Porsolt swim test and on the ACTH or CORT response following restraint stress. AMPH withdrawn animals expressed behavioral sensitization in terms of locomotion and reduced ACTH and CORT plasma levels following a 1 mg/kg AMPH challenge in comparison to the controls. We conclude that there is no critical involvement of a sensitized HPA axis stress response in the long-term expression of behavioral sensitization.

Withdrawal from continuous amphetamine administration abolishes latent inhibition but leaves prepulse inhibition intact

RATIONALE

Schizophrenia has been associated with dysregulation of dopamine (DA) transmission and impairment in a number of experimental tasks, including sensorimotor gating assessed using prepulse inhibition (PPI) and selective attention assessed using latent inhibition (LI). We have demonstrated in previous studies that after withdrawal from escalating (ESC) dosages of amphetamine (AMPH), animals exhibited disruption of LI but no alteration of PPI. Moreover, these animals always showed behavioural sensitization to an AMPH challenge.

OBJECTIVE

In this study, we were interested in testing whether a different administration schedule would elicit disruption of both LI and PPI.

METHODS

Animals were treated with continuous AMPH release (via osmotic mini-pumps at a dosage of 10 mg kg(-1) day(-1) for 7 days) and tested for their performance in L and PPI during withdrawal in a drug free state. Rats received AMPH treatment during the induction phase in their home cages or in the activity chambers. Following withdrawal, the expression of behavioural sensitization to an AMPH challenge was tested in both cases in the activity chambers.

RESULTS

Animals pretreated with AMPH from both groups did not exhibit behavioural sensitization. Withdrawal from continuous administration induced LI attenuation with no effect on PPI.

CONCLUSIONS

These findings are similar to what was previously found with respect to an ESC AMPH regime. The only difference between the schedules was that the ESC AMPH schedule led to behavioural sensitization whereas the continuous AMPH did not. It is suggested that the expression of sensitization may not be a prerequisite for observed LI disruption.

Dopamine challenge tests as an indicator of psychological traits

After discussing some introductory considerations about the value of challenge tests in general for discriminating personality dimensions which are considered extrapolations of psychopathological diseases, the present paper outlines the matter of responsivity to agonistic and antagonistic dopaminergic drugs or drugs of different mechanisms of action in the dopaminergic system, and elucidates that different hormones elicited by dopaminergic substances (prolactin, growth hormone) may indicate personality related differences in susceptibility of different brain areas. A further point was to demonstrate not only the well known relationship of dopaminergic hyperactivity with reward seeking and motivational factors associated with extraversion and novelty seeking, but also the relationship of dopaminergic hypofunction with the personality dimension of depression which had already been reported in studies on animals and psychiatric patients. A final point was to demonstrate that besides size of hormone responses additional parameters like time of response onset and initial prolactin increase can be used as biochemical indicators for identifying certain personality types, like highly depressive neurotic persons characterized by lower and later dopamine responses as compared to low depressives, and extraverted sensation-seeking types responding by an initial prolactin peak as opposed to low sensation seekers.

Withdrawal from repeated amphetamine administration leads to disruption of prepulse inhibition but not to disruption of latent inhibition

The present study represents a continuous effort to develop an animal model of schizophrenia based on the "endogenous dopamine sensitization" hypothesis. To achieve this goal, withdrawal from an escalating amphetamine (AMPH) regime administration [three injections per day over a period of 4 days and increasing doses from 1 to 10 mg/kg of AMPH or an equivalent volume of saline (SAL)] was employed. Animals exposed to this treatment were evaluated on their performance in attentional (Latent inhibition, LI) and sensorimotor gating (Prepulse inhibition, PPI) tasks in a drug free state and tested for locomotor sensitization following a low dose of AMPH challenge administration.LI using active avoidance, tested on withdrawal day 4, was unaffected. PPI of the acoustic startle response, measured on withdrawal days 6 and 70, was disrupted. On the 76th day of withdrawal, a low challenge dose of AMPH (1 mg/kg) led to a clear locomotor sensitization effect.

Early deprivation under specific conditions leads to reduced interest in reward in adulthood in Wistar rats

Early life adversity can lead to increased vulnerability to psychiatric disease including depression, with symptoms of depressed mood, impaired coping with negative events, anhedonia, reduced appetite, and elevated stress hormone activity. In rats, postnatal manipulation studies have focused on behavioural and endocrine anxiety effects, and have demonstrated that mild pup stimulation in the form of early handling (EH) is chronically anxiolytic relative to no stimulation in the form of non-handling (NH). Furthermore, apparently severe manipulations in the form of 3-4 h daily litter-dam separation (maternal separation) or pup-litter-dam separation (early deprivation, ED) are either without effect or even EH-like, relative to NH. In this Wistar rat study, we investigated the effects of ED under different circadian and thermal conditions on adulthood behavioural and endocrine responsiveness to environmental challenge, relative to NH. ED was performed on days 1-14, during either the Light or Dark phase and at either 21 degrees C (cold) or 32 degrees C (warm). Dark-cold ED adults exhibited reduced motivation to obtain sucrose in a progressive ratio schedule, tended to be less mobile in a forced swim test, but did not exhibit an escape deficit in a foot-shock pre-exposure/shuttle box test, or altered basal or stress endocrine activity. Light ED was completely without effect on adult phenotype. Even relative to stringent NH comparison, dark-cold ED leads to a long-term trait of mild gustatory anhedonia in Wistar rats.

Long-term effects of early-life environmental manipulations in rodents and primates: Potential animal models in depression research

Depression is one of the most common human illnesses and is of immense clinical and economic significance. Knowledge of the neuro-psychology, -biology and -pharmacology of depression is limited, as is the efficacy of antidepressant treatment. In terms of depression aetiology, whilst the evidence for causal mechanisms is sparse, some genomic and environmental factors associated with increased vulnerability have been identified. With regards to the latter, the environments in which human infants and children develop are fundamental to how they develop, and parental loss, emotional and physical neglect, and abuse have been shown to be associated with: traits of depression, traits of predisposition to depression triggered by subsequent life events, and associated physiological abnormalities, across the life span. Studies of postnatal environmental manipulations in rodents and primates can potentially yield evidence that abnormal early-life experience leading to dysfunction of the neurobiology, physiology and behaviour of emotion is a general mammalian characteristic, and therefore, that this approach can be used to develop animal models for depression research, with aetiological, face, construct and predictive validity. The establishment of models with such validity, if at all achievable, will require a sophisticated combination of (1) appropriate postnatal manipulations that induce acute stress responses in the infant brain which in turn lead to long-term neurobiological consequences, and (2) appropriate behavioural and physiological assays to identify and quantify any depression-like phenotypes resulting from these long-term neurobiological phenotypes. Here, we review some of the evidence-positive and negative-that neglect-like environments in rat pups and monkey infants lead to long-term, depression-like behavioural traits of reduced motivation for reward and impaired coping with adversity, and to altered activity in relevant physiological homeostatic systems.

Psychostimulant withdrawal as an inducing condition in animal models of depression

A large body of evidence indicates that the withdrawal from high doses of psychostimulant drugs in humans induces a transient syndrome, with symptoms that appear isomorphic to those of major depressive disorder. Pharmacological treatment strategies for psychostimulant withdrawal in humans have focused mainly on compounds with antidepressant properties. Animal models of psychostimulant withdrawal have been shown to demonstrate a wide range of deficits, including changes in homeostatic, affective and cognitive behaviors, as well as numerous physiological changes. Many of these behavioral and physiological sequelae parallel specific symptoms of major depressive disorder, and have been reversed by treatment with antidepressant drugs. These combined findings provide strong support for the use of psychostimulant withdrawal as an inducing condition in animal models of depression. In the current review we propound that the psychostimulant withdrawal model displays high levels of predictive and construct validity. Recent progress and limitations in the development of this model, as well as future directions for research, are evaluated and discussed.

Transient disruption of attentional performance following escalating amphetamine administration in rats

RATIONALE

Attentional deficits are thought to be critically involved in the development of positive symptoms in schizophrenia. The present experiment tests the general hypothesis that sensitization of the mesolimbic dopaminergic system contributes to the attentional deficits in schizophrenia.

OBJECTIVES

The present study assessed attentional performance following administration of an escalating amphetamine regimen and subsequent "challenge" amphetamine administration in rats.

METHODS

Rats were trained to perform a two-lever sustained attention task that involved discrimination of visual signals and no signal presentation. After reaching criterion, subjects were assigned to receive escalating amphetamine or saline. Attentional performance was assessed immediately following escalating amphetamine, following "challenge" amphetamine administration (1.0 mg/kg) to amphetamine-pretreated rats, and for 3 days after the challenge session. At the end of this experiment, a dose-response study was conducted with saline-pretreated rats to confirm the appropriateness of the challenge dose.

RESULTS

Amphetamine-pretreated animals demonstrated a transient increase in errors on nonsignal trials following escalating amphetamine administration. The latency to press a lever was decreased during and after challenge amphetamine administration. Administration of 1.0 mg/kg amphetamine did not alter accuracy of amphetamine-pretreated animals or of saline-pretreated animals in the dose-response experiment.

CONCLUSIONS

Prior escalating amphetamine administration transiently disrupted attention, increasing incorrect "claims" for a signal on trials when no signal was presented. The present data support the existing literature that escalating amphetamine regimens may be useful to model the attentional deficits that contribute to the psychotic symptoms in schizophrenia.

The impaired coping induced by early deprivation is reversed by chronic fluoxetine treatment in adult fischer rats

The symptoms of depression include feelings of reduced coping ability and increased helplessness. Early life adversity increases vulnerability to depression. In rats, the quantification of ability to cope with adverse challenge can be achieved using preexposure to an inescapable aversive stimulus and subsequent assessment of escape or avoidance deficits in the same environment. Here we investigated the predictive validity of a model in which, in the Fischer rat strain, postnatal isolation leads in adulthood to a state of increased sensitivity to develop an escape or avoidance deficit. On days 1-14 rat pups were isolated for 4 hours (early deprivation, ED) or for 15 minutes (early handling, EH), or were left completely undisturbed (non-handling, NH). In adulthood, subjects were placed in a shuttle box and half were exposed to brief, mild foot shocks (preexposure, PE) and the other half were non-preexposed (NPE). Half of the PE and NPE subjects were then treated for 21 days with fluoxetine and the other half with vehicle. In males, although there was no overall preexposure effect on avoidance behaviour, ED-PE and ED-NPE and EH-PE and EH-NPE demonstrated an avoidance deficit relative to NH. Fluoxetine attenuated this deficit and most notably in ED-PE. In females, vehicle ED-PE demonstrated an avoidance deficit relative to NH-PE; fluoxetine attenuated this ED effect. These findings provide supportive evidence for the predictive validity of this depression model.

Rats with congenital learned helplessness respond less to sucrose but show no deficits in activity or learning

Inbred rat strains for congenital learned helplessness (cLH) and for congenital resistance to learned helplessness (cNLH) were investigated as a model to study genetic predisposition to major depression. Congenitally helpless rats respond less to sucrose under a progressive ratio schedule. This is not confounded by locomotor hypoactivity: in contrast, cLH rats show a slight hyperactivity during the first 5 min of an open field test. cLH rats acquire operant responding to sucrose as readily as cNLH rats and exhibit normal memory acquisition and retrieval in the Morris water maze, thus ruling out general learning deficits as the cause of the decreased response to sucrose. Reduced total responses and reduced breaking points for sucrose in the cLH strain argue for anhedonia, which is an analogue to loss of pleasure essential for the diagnosis of major depressive episodes, and thus confirm the validity of congenitally learned helpless rats as a model of major depression.

In search of a depressed mouse: utility of models for studying depression-related behavior in genetically modified mice

The ability to modify mice genetically has been one of the major breakthroughs in modern medical science affecting every discipline including psychiatry. It is hoped that the application of such technologies will result in the identification of novel targets for the treatment of diseases such as depression and to gain a better understanding of the molecular pathophysiological mechanisms that are regulated by current clinically effective antidepressant medications. The advent of these tools has resulted in the need to adopt, refine and develop mouse-specific models for analyses of depression-like behavior or behavioral patterns modulated by antidepressants. In this review, we will focus on the utility of current models (eg forced swim test, tail suspension test, olfactory bulbectomy, learned helplessness, chronic mild stress, drug-withdrawal-induced anhedonia) and research strategies aimed at investigating novel targets relevant to depression in the mouse. We will focus on key questions that are considered relevant for examining the utility of such models. Further, we describe other avenues of research that may give clues as to whether indeed a genetically modified animal has alterations relevant to clinical depression. We suggest that it is prudent and most appropriate to use convergent tests that draw on different antidepressant-related endophenotypes, and complimentary physiological analyses in order to provide a program of information concerning whether a given phenotype is functionally relevant to depression-related pathology.

Amphetamine withdrawal modulates FosB expression in mesolimbic dopaminergic target nuclei: effects of different schedules of administration

Different patterns of psychostimulant intake can elicit widely varying behavioral and neurochemical consequences. Accordingly, rats were studied during withdrawal from either of two schedules of amphetamine administration, one consisting of 6 days of low-dose (1.5 mg/kg, i.p.) daily intermittent (INT) amphetamine (AMPH) injections, and the other of 6 days of moderately high-dose (1-5 mg/kg, i.p.) escalating (ESC) AMPH injections, for the effects of these treatments on numbers of FosB-positive nuclei and monoamine utilization in dopaminergic target areas. Withdrawal from AMPH pretreatment according to the ESC schedule markedly increased FosB expression in the nucleus accumbens shell and basolateral amygdala. In contrast, withdrawal from INT-AMPH administration did not increase FosB expression in any of the regions examined. Post-mortem neurochemical analyses of these same brain regions did not reveal effects of withdrawal from either INT or ESC administration of AMPH. These results suggest that withdrawal from a moderately high-dose AMPH regimen modifies patterns of gene expression in mesocorticolimbic dopaminergic target nuclei without significantly affecting basal monoamine levels. The strength of these effects in the nucleus accumbens shell and basolateral nucleus of the amygdala are consistent with behavioral and clinical data indicating the importance of these areas in the neuroadaptive changes which characterize addiction and withdrawal states.