GABAergic system and imipramine-induced impairment of memory retention in rats

The effect of GABA-B receptors in the basolateral amygdala on passive avoidance memory impairment induced by MK-801 in rats

MK-801 (dizocilpine) is a potent non-competitive N-methyl-[D]-aspartate (NMDA) receptor antagonist that affects cognitive function, learning, and memory. As we know, NMDA receptors are significantly involved in memory function, as well as GABA (Gamma-Aminobutyric acid) receptors. In this study, we aimed to discover the effect of GABA-B receptors in the basolateral amygdala (BLA) on MK-801-induced memory impairment. We used 160 male Wistar rats. The shuttle box was used to evaluate passive avoidance memory and locomotion apparatus was used to evaluate locomotor activity. MK-801 (0.125, 0.25, and 0.5 μg/rat), baclofen (GABA-B agonist, 0.0001, 0.001, and 0.01 μg/rat) and phaclofen (GABA-B antagonist, 0.0001, 0.001, and 0.01 μg/rat) were injected intra-BLA, after the training. The results showed that MK-801 at the dose of 0.5 μg/rat, baclofen at the doses of 0.001 and 0.01 μg/rat, and phaclofen at the doses of 0.001 and 0.01 μg/rat, impaired passive avoidance memory. Locomotor activity did not alter in all groups. Furthermore, the subthreshold dose of both baclofen (0.0001 μg/rat) and phaclofen (0.0001 μg/rat) restored the impairment effect of MK-801 (0.5 μg/rat) on memory. Also, both baclofen (0.0001 μg/rat) potentiated the impairment effect of MK-801 (0.125 μg/rat) and phaclofen (0.0001 μg/rat) potentiated the impairment effect of MK-801 (0.125 and 0.25 μg/rat) on passive avoidance memory. In conclusion, our results indicated that BLA GABA-B receptors can alter the effect of NMDA inactivation on passive avoidance memory.

Imipramine alleviates memory impairment and hippocampal apoptosis in STZ-induced sporadic Alzheimer's rat model: Possible contribution of MAPKs and insulin signaling

Alzheimer's disease (AD) is the most common age-related neurodegenerative disease, associated with several pathophysiological complaints. Impaired insulin signaling in the brain, is one of the important characteristic features of AD which is accompanied by cognitive deficits. According to the multifactorial and complicated pathology of AD, no modifying therapy has been approved yet. Imipramine is a kind of tricyclic antidepressant with reported anti-inflammatory and anti-oxidant effects in the brain. There are controversial studies about the effect of this drug on spatial memory. This study investigates the effect of imipramine on streptozotocin (STZ) induced memory impairment in rats. Pursuing this objective, rats were treated with imipramine 10 or 20 mg/kg i.p. once a day for 14 days. 24 h after the last injection, memory function was evaluated by the Morris water maze (MWM) test in 4 consecutive days. Then, hippocampi were removed and the activity of caspase-3, mitogen activated protein kinases (MAPKs) family and inhibitory phosphorylation of insulin receptor substrate-1 (IRS-1_ser307) were analyzed using Western blotting. Results showed that imipramine prevents memory impairment in STZ induced rats and this improvement was accompanied with an increase in ERK activity, reduction of caspase-3 and JNK activity, as well as partial restoration of P38 and IRS-1 activity. In conclusion, our study demonstrated that at least some members of the MAPK family are involved in the neuroprotective effect of imipramine.

Role of GABA(B) receptors in learning and memory and neurological disorders

Although it is evident from the literature that altered GABAB receptor function does affect behavior, these results often do not correspond well. These differences could be due to the task protocol, animal strain, ligand concentration, or timing of administration utilized. Because several clinical populations exhibit learning and memory deficits in addition to altered markers of GABA and the GABAB receptor, it is important to determine whether altered GABAB receptor function is capable of contributing to the deficits. The aim of this review is to examine the effect of altered GABAB receptor function on synaptic plasticity as demonstrated by in vitro data, as well as the effects on performance in learning and memory tasks. Finally, data regarding altered GABA and GABAB receptor markers within clinical populations will be reviewed. Together, the data agree that proper functioning of GABAB receptors is crucial for numerous learning and memory tasks and that targeting this system via pharmaceuticals may benefit several clinical populations.

Memory Impairment following Acute Tricyclic Antidepressants Overdose

Background. Psychiatric consultation is necessary for all patients with intentional poisoning and its reliability depends on the proper function of patients' memory performance. This study aimed to determine the possible memory impairment following acute TCAs' poisoning. Materials and Methods. In this cross-sectional study, patients with acute TCAs poisoning were allocated to two groups of severe poisoning (with coma, seizures, cardiac arrhythmias, hypotension, and a wide QRS complex) and mild-to-moderate poisoning according to their clinical presentation at the time of hospital admission. All patients underwent memory performance test both immediately and 24 hours after their initial consciousness after admission, using Wechsler Memory Scale (WMS-IV). Results. During the study period, 67 TCA-poisoned patients (aged, 20-64 years) were evaluated, of which 67.2% were female. The mean memory scores of patients immediately and 24 hours after the initial consciousness were 31.43 ± 9.02 and 50.62 ± 9.12, respectively (P < 0.001). Twenty-four hours after the initial consciousness, memory score was statistically correlated with the amount of ingested drug and the intoxication severity. Conclusion. Following the recovery from somatic symptoms of acute TCA poisoning, patients may still suffer from memory impairment and it seems that this time is not suitable for performing a reliable psychiatric consultation.

Effect of fendiline on the maintenance and expression of methamphetamine-induced conditioned place preference in Sprague-Dawley rats

RATIONALE

Fendiline is a GABAB receptor-positive allosteric modulator and L-type Ca²⁺ channel blocker that is safe for human use. Based on these pharmacological properties, fendiline may be useful to disrupt associative memories that can drive relapse to drug use in drug-addicted individuals

OBJECTIVE

The current study evaluated the potential of fendiline to inhibit the maintenance and expression of learned associations between methamphetamine (meth) and an environmental context using conditioned place preference (CPP) in rats, to model for the associative learning that occurs during drug abuse by humans

METHODS

Following meth conditioning (1 mg/kg), fendiline (5 mg/kg) was administered at various post-conditioning times to ascertain if there was a temporal window during which fendiline would be effective.

RESULTS

Two once-daily injections of fendiline did not influence the maintenance of CPP regardless of the post-conditioning treatment time while 10 once-daily fendiline treatments inhibited CPP maintenance (p < 0.05). Fendiline administered immediately prior to the CPP test inhibited expression of meth-induced CPP in rats with a fendiline treatment history of 10 once-daily injections (p < 0.05) or those that received two injections that corresponded to the last 2 days of the 10-day treatment (p < 0.05). Fendiline did not produce preference or aversion on its own, nor did it alter motivated motor behavior.

CONCLUSION

Maintenance and expression of meth CPP is mitigated by repeated fendiline treatments when administered during the days that precede CPP testing. Reduction in the significance of meth-associated cues can reduce relapse; therefore, fendiline may be of value for addiction therapy in abstinent, meth-addicted humans.

High serum androstenedione levels correlate with impaired memory in the surgically menopausal rat: a replication and new findings

After natural menopause in women, androstenedione becomes the primary hormone secreted by the residual follicle-depleted ovaries. In two independent studies, in rodents that had undergone ovarian follicular depletion, we found that higher endogenous serum androstenedione levels correlated with increased working memory errors. This led to the hypothesis that higher androstenedione levels impair memory. The current study directly tested this hypothesis, examining the cognitive effects of exogenous androstenedione administration in rodents. Middle-aged ovariectomised rats received vehicle or one of two doses of androstenedione. Rats were tested on a spatial working and reference memory maze battery including the water-radial arm maze, Morris water maze (MM) and delay match-to-sample task. Androstenedione at the highest dose impaired reference memory as well as the ability to maintain performance as memory demand was elevated. This was true for both high temporal demand memory retention of one item of spatial information, as well as the ability to handle multiple items of spatial working memory information. We measured glutamic acid decarboxylase (GAD) protein in multiple brain regions to determine whether the gamma-aminobutyric acid (GABA) system relates to androstenedione-induced memory impairments. Results showed that higher entorhinal cortex GAD levels were correlated with worse MM performance, irrespective of androstenedione treatment. These findings suggest that androstenedione, the main hormone produced by the follicle-depleted ovary, is detrimental to working memory, reference memory and memory retention. Furthermore, while spatial reference memory performance might be related to the GABAergic system, it does not appear to be altered with androstenedione administration, at least at the doses used in the current study.

Brain region-selective cellular redistribution of mGlu5 but not GABA(B) receptors following methamphetamine-induced associative learning

Alterations in receptor expression and distribution between cell surface and cytoplasm are means by which psychostimulants regulate neurotransmission. Metabotropic glutamate receptor group I, subtype 5 (mGluR5) and GABA(B) receptors (GABA(B) R) are critically involved in the development and expression of stimulant-induced behaviors, including conditioned place preference (CPP), an index of drug-seeking. However, it is not known if psychostimulant-induced CPP alters the trafficking of these receptors. To fill this gap, this study used methamphetamine (Meth)-induced CPP in rats to ascertain if receptor changes occur in limbic brain regions that regulate drug-seeking, the medial prefrontal cortex (mPFC), nucleus accumbens (NAc), and ventral pallidum (VP). To do so, ex vivo tissue was assessed for changes in expression and surface vs. intracellular distribution of mGluR5 and GABA(B) Rs. There was a decrease in the surface to intracellular ratio of mGluR5 in the mPFC in Meth-conditioned rats, commensurate with an increase in intracellular levels. mGluR5 levels in the NAc or the VP were unaltered. There were no changes for GABA(B) R in any brain region assayed. This ex vivo snapshot of metabotropic glutamate and GABA receptor cellular distribution following induction of Meth-induced CPP is the first report to determine if these receptors are differentially altered after Meth-induced CPP. The results suggest that this Meth treatment paradigm likely induced a compensatory change in mGluR5 surface to intracellular ratio such that the surface remains unaltered while an increase in intracellular protein occurred.

Administration of GABA(B) receptor positive allosteric modulators inhibit the expression of previously established methamphetamine-induced conditioned place preference

Little is known about the role of GABA(B) receptors (GABA(B)Rs) in the maintenance of memories associated with using abused substances. We have embarked on a series of studies designed to determine if enhancing the efficacy of GABA-occupied GABA(B)Rs with positive allosteric modulators (PAMs) can negate previously established conditioned place preference (CPP) induced by methamphetamine. In the current study, we evaluated the effects of acute administration of GABA(B)R PAMs, GS39783 and CGP7930. We determined that post-conditioning treatments with these PAMs, administered in the home cage, blocked the subsequent expression of methamphetamine-induced CPP. These data indicate that selectively augmenting GABA-occupied GABA(B)R signaling is sufficient to reduce memory maintenance and/or the salience of contextual cues previously associated with methamphetamine.

Tanshinone I enhances learning and memory, and ameliorates memory impairment in mice via the extracellular signal-regulated kinase signalling pathway

BACKGROUND AND PURPOSE

The intracellular signalling kinase, extracellular signal-regulated kinase 1/2 (ERK1/2) is required for new memory formation, suggesting that control of ERK signalling might be a target for the treatment of cognitive dysfunction. Previously, we reported that tanshinone congeners have ameliorating effects on drug-induced memory impairment in mice. Here, we have investigated possible modes of action of tanshinone I on learning and memory, associated with ERK phosphorylation.

EXPERIMENTAL APPROACH

Using immunohistochemical, Western blot techniques, and behavioural testing, we studied the effect of tanshinone I on memory impairment induced by diazepam or dizocilpine (MK-801) in mice.

KEY RESULTS

Tanshinone I (2 or 4 mg.kg(-1), p.o.) increased latency times versus vehicle-treated control group in the passive avoidance task. Western blot analysis and immunohistochemical data showed that tanshinone I (4 mg.kg(-1)) increased levels of phosphorylated cAMP response element binding protein (pCREB) and phosphorylated ERK (pERK) in the hippocampus. These increases in pCREB and pERK were blocked by U0126 (inhibitor of ERK1/2), which also prevented the increase in passive avoidance task latency time after tanshinone I. In models of learning and memory impairment induced by diazepam and MK-801, tanshinone I (4 mg.kg(-1)) reversed learning and memory impairments detected by the passive avoidance test. Western blot analysis showed that tanshinone I reversed the diazepam- and MK-801-induced inhibitions of ERK and CREB activation in hippocampal tissues. These effects were also blocked by U0126.

CONCLUSIONS AND IMPLICATIONS

Tanshinone I ameliorates the learning and memory impairments induced by diazepam and MK-801 through activation of ERK signalling.

Blocking GABA-A receptors in the medial septum enhances hippocampal acetylcholine release and behavior in a rat model of diencephalic amnesia

Wernicke-Korsakoff syndrome (WKS), a form of diencephalic amnesia caused by thiamine deficiency, results in severe anterograde memory loss. Pyrithiamine-induced thiamine deficiency (PTD), an animal model of WKS, produces cholinergic abnormalities including decreased functional hippocampal acetylcholine (ACh) release and poor spatial memory. Increasing hippocampal ACh levels has increased performance in PTD animals. Intraseptal bicuculline (GABA(A) antagonist) augments hippocampal ACh release in normal animals and we found it (0.50 microg/microl and 0.75 microg/microl) also increased in-vivo hippocampal ACh release in PTD animals. However, the 0.75 microg/microl dose produced a greater change in hippocampal ACh release in control animals. The 0.50 microg/microl dose of bicuculline was then selected to determine if it could enhance spontaneous alternation performance in PTD animals. This dose of bicuculline significantly increased hippocampal ACh levels above baseline in both PTD and control rats and resulted in complete behavioral recovery in PTD animals, without altering performance in control rats. This suggests that balancing ACh-GABA interactions in the septohippocampal circuit may be an effective therapeutic approach in certain amnestic syndromes.

Acute cold exposure and rewarming enhanced spatial memory and activated the MAPK cascades in the rat brain

Cold is a common stressor that is likely to occur in everyday occupational or leisure time activities. Although there is substantial literature on the effects of stress on memory from behavioral and pharmacologic perspectives, the effects of cold stress on learning and memory were little addressed. The aims of the present work were to investigate the effects of acute cold exposure on Y-maze learning and the activation of cerebral MAPK cascades of rats. We found that the 2-hour cold exposure (-15 degrees C) and a subsequent 30-min rewarming significantly increased the performance of the rats in the Y-maze test. Serum corticosterone (CORT) level was increased after the cold exposure. After a transient reduction following the cold exposure, the P-ERK levels in the hippocampus and PFC drastically increased 30 min later. The levels of P-JNK increased gradually after the cold exposure in all the three brain regions we investigated, but the level of P-p38 only increased in the PFC. The levels of GABAA receptor alpha1 subunit remained unchanged after the cold exposure. Furthermore, the performance of rats treated with cold plus muscimol or bicuculline in the Y-maze test was similar to that of the rats treated with those GABAergic agents alone. These results demonstrated that acute cold exposure and the subsequent rewarming could result in enhanced performance of spatial learning and memory, and the activation of MAPKs in the brain. However, GABAA receptor may not be involved in the acute cold exposure-induced enhancement of memory.

Antidepressant drugs and memory: insights from animal studies

This is a selective review of the literature concerning the effects of antidepressant drugs on animal memory, which was performed with the aid of the PubMed database. Monoamine oxidase inhibitors tend to either have no effect on memory or result in its improvement. Studies with cyclic antidepressants have reported no effect or, more often, memory impairments. Pre-training administration of selective serotonin reuptake inhibitors (SSRIs) has been shown to have either no effect on memory or undermine it (with some isolated exceptions, in which improvements have been recorded), while post-training administration of SSRIs has been demonstrated to improve memory or have no effect. A small group formed by the remaining antidepressants has been shown to improve memory, with the exception of trazodone, which impairs memory. These findings are discussed in the light of knowledge regarding the actions of antidepressants on several neurotransmission systems. The possibility that the effects of antidepressants on memory are the core of the therapeutic effects of these drugs is also considered.

GABAA receptor RDL inhibits Drosophila olfactory associative learning

In both mammals and insects, neurons involved in learning are strongly modulated by the inhibitory neurotransmitter GABA. The GABAA receptor, resistance to dieldrin (Rdl), is highly expressed in the Drosophila mushroom bodies (MBs), a group of neurons playing essential roles in insect olfactory learning. Flies with increased or decreased expression of Rdl in the MBs were generated. Olfactory associative learning tests showed that Rdl overexpression impaired memory acquisition but not memory stability. This learning defect was due to disrupting the physiological state of the adult MB neurons rather than causing developmental abnormalities. Remarkably, Rdl knockdown enhanced memory acquisition but not memory stability. Functional cellular imaging experiments showed that Rdl overexpression abolished the normal calcium responses of the MBs to odors while Rdl knockdown increased these responses. Together, these data suggest that RDL negatively modulates olfactory associative learning, possibly by gating the input of olfactory information into the MBs.

Evidence for a role of GABAA receptor in the acute restraint stress-induced enhancement of spatial memory

Stress exerts complex effects on learning and memory; however, the understanding of the molecular mechanisms involved in stress effects on brain and behavior is rather limited. In this study, we investigated the regulation of the activation of MAPK (mitogen-activated protein kinase) cascades in the rat brain by GABAA receptor in a learning and memory task under acute restraint stress conditions. We found that the acute restraint stress improved the performance of the rats in the Morris water maze. Furthermore, the acute restraint stress significantly increased the phosphorylation of ERK and JNK in the hippocampus and prefrontal cortex (PFC), but not in the striatum. The increase paralleled the time course of the decrease of the level of GABAA receptor alpha1 subunit. The increase of P-ERK levels was inhibited by the agonist of GABAA receptor, muscimol, and further increased by the antagonist of the receptor, bicuculline. However, neither muscimol nor bicuculline affected the levels of P-JNK and P-p38. Finally, injection of muscimol partly reversed the acute restraint stress-induced enhancement of performance in the Morris water maze, and injection of bicuculline improved it. These results demonstrated that the changes in ERK phosphorylation in hippocampus and PFC were regulated by GABAA receptor in a learning and memory paradigm under acute restraint stress conditions.

Effects of Milnacipran in Animal Models of Anxiety and Memory

Serotonin (5-HT) and noradrenaline (NA) are involved in both pathogenesis and recovery from depression and anxiety. We examined the effects of acute and chronic treatment with milnacipran, a serotonin/noradrenaline reuptake inhibitors (SNRIs) antidepressant, on anxiety and memory retention in rats. Male Wistar rats received acute or chronic administration of milnacipran (12.5, 25 or 50 mg/kg) or saline (control group). The animals were separately submitted to elevated plus-maze, inhibitory avoidance and open-field tasks 1 h after injection, in the acute group, or 23 h after last injection, in the chronic group. Our results showed an anxiolytic-like effect after chronic administration of milnacipran at doses of 25 and 50 mg/kg. The treatment does not interfere in memory retention and habituation to a novel environment at any doses studied. These findings support that milnacipran, an established SNRIs antidepressant, can also be useful in the treatment of anxiety disorders.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

Effect of the GABAergic System on Memory Formation and State-Dependent Learning Induced by Morphine in Rats

In the present study, the effects of intraperitoneal injections of GABA(A) receptor agonist and antagonist on memory formation and morphine state-dependent learning were investigated in rats. Pre-training administration of morphine (1-15 mg/kg) in a step-down passive avoidance task induced state-dependent learning with impaired memory retrieval on the test day. The impairment of memory was restored after the pre-test administration of the same dose of morphine. The pre-test administration of the GABA(A) receptor agonist, muscimol (0.01, 0.05 and 0.1 mg/kg), significantly decreased state-dependent retrieval induced by pre-test morphine (5 mg/kg). The state-dependency effect of morphine (1 mg/kg) was significantly potentiated by the pre-test administration of the GABA(A) receptor antagonist, bicuculline (0.125, 0.25 and 0.5 mg/kg). Furthermore, the pre-training injection of muscimol (0.01 mg/kg) impaired memory retrieval which was restored by pre-test morphine (1, 3 and 5 mg/kg) administration. However, the pre-training administration of bicuculline did not affect retention by itself. In addition, amnesia induced by pre-training morphine (5 mg/kg) was significantly reversed in rats which had received pre-test injections of muscimol (0.01, 0.05 and 0.1 mg/kg). Pre-test injections of bicuculline (0.125, 0.25 and 0.5 mg/kg) significantly decreased morphine-induced amnesia. It is concluded that the GABA(A) receptor mechanisms may be involved in the memory formation and it is postulated that these receptors may play an important role in morphine state-dependent learning.

Cholecystokinin and endogenous opioid peptides: interactive influence on pain, cognition, and emotion

It is well documented that stressful life experiences contribute to the etiology of human mood disorders. Cholecystokinin (CCK) is a neuropeptide found in high concentrations throughout the central nervous system, where it is involved in numerous physiological functions. A role for CCK in the induction and persistence of anxiety and major depression appears to be conspicuous. While increased CCK has been associated with motivational loss, anxiety and panic attacks, an increase in mesocorticolimbic opioid availability has been associated with coping and mood elevation. The close neuroanatomical distribution of CCK with opioid peptides in the limbic system suggests that there may be an opioid-CCK link in the modulation and expression of anxiety or stressor-related behaviors. In effect, while CCK induces relatively protracted behavioral disturbances in both animal and human subjects following stressor applications, opioid receptor activation may change the course of psychopathology. The antagonistic interaction of CCK and opioid peptides is evident in psychological disturbances as well as stress-induced analgesia. There appears to be an intricate balance between the memory-enhancing and anxiety-provoking effects of CCK on one hand, and the amnesic and anxiolytic effects of opioid peptides on the other hand. Potential anxiogenic and mnemonic influences of site-specific mesocorticolimbic CCK and opioid peptide availability, the relative contributions of specific CCK and opioid receptors, as well as the time course underlying neuronal substrates of long-term behavioral disturbances as a result of stressor manipulations, are discussed.

A parametric assessment of GABA antagonist effects on paired-pulse facilitation in the rat anterior cingulate cortex

Paired-pulse facilitation (PPF) is a form of short-term plasticity that can be used qualitatively to characterize the synaptic effects of neuroactive compounds. As we have shown previously, CNQX has a marked effect on PPF which can be measured quantitatively. The aim of the present study was to examine quantitatively possible differences in the effects of the post- and pre-synaptic GABA antagonists on PPF in vitro. Experiments were performed on slices taken from the coronal anterior cingulate cortex (ACC) of Sprague-Dawley rats. The stimuli consisted of a pair of biphasic pulses with an inter-pulse interval of 40ms. Evoked extracellular field potentials in layers 2/3 of the ACC were recorded. Quantitative assessment of PPF was achieved by calculating two parameters, the PPFmax (theoretical maximal PPF) and the Stmax (stimulus intensity that produces the PPFmax). Picrotoxin treatment produced increases in both the PPFmax and Stmax, by increasing the stimulus producing the half-maximal effect. In contrast, CGP-55845 treatment produced an increase in only the PPFmax, which was due to an alteration in the asymptotic values of the response amplitudes. Our findings show that the effect of different GABA receptor antagonists on short-term synaptic facilitation in the ACC may be assessed and specified quantitatively.

Induced depressive behavior impairs learning and memory in rats

While it is generally accepted that cognitive processes such as learning and memory are affected by emotion, the impact of depression on learning and memory has rarely been directly studied in experimental animals. Effects of induced depressive behavior on learning and memory were determined in rats, using an open space swim test, a novel animal model of depressive behavior that is developed recently in our laboratory. The model indexes searching activity of the animals, with the induced depressive immobility behavior showing specific sensitivity to three major prototypic classes of antidepressants and a selective serotonin reuptake inhibitor. The induced depressive behavior in rats showed a delayed response to chronic antidepressant treatment and had a lasting effect on the ability of rats to learn and recall the learned experience. It impaired the subsequent ability of rats to learn and recall both a spatial water maze task and a multi-trial passive avoidance task. These impairments were all sensitive to antidepressant therapeutics, but not to buspirone, an anxiolytic. By way of contrast, the ability of the rats to sense and move to a visible platform and to escape from an unconditioned shock stimulus was neither impaired by inducing the depressive behavior nor altered by the drug treatment, suggesting that non-specific changes in sensorimotor ability were not involved. These impairments of learning and memory indicate that the depressive behavior-induced deficits show generalizability and are not context-limited. This animal model of depressive behavior shows promising potential as a screen for novel antidepressive therapeutics and as a disease model for revealing network/cellular/molecular mechanisms in the pathophysiology of depression and depression-induced cognitive deficits.