Effects of desipramine and alprazolam in the forced swim test in rats after long-lasting termination of chronic exposure to picrotoxin and pentylenetetrazol

Upregulations of α1 adrenergic receptors and noradrenaline synthases in the medial prefrontal cortex are associated with emotional and cognitive dysregulation induced by post-weaning social isolation in male rats

Early-life social isolation induces emotional and cognitive dysregulation, such as increased aggression and anxiety, and decreases neuron excitability in the medial prefrontal cortex (mPFC). The noradrenergic system in the mPFC regulates emotion and cognitive function via α₁ or α_2A adrenergic receptors, depending on noradrenaline levels. However, social isolation-induced changes in the mPFC noradrenergic system have not been reported. Here, male Wistar rats received post-weaning social isolation for nine consecutive weeks and were administered behavioral tests (novel object recognition, elevated plus maze, aggression, and forced swimming, sequentially). Protein expression levels in the mPFC noradrenergic system (α₁ and α_2A adrenergic receptors, tyrosine hydroxylase, and dopamine-β-hydroxylase used as indices of noradrenaline synthesis and release) were examined through western blotting. Social isolation caused cognitive dysfunction, anxiety-like behavior, and aggression, but not behavioral despair. Socially-isolated rats exhibited increased protein levels of the α₁ adrenergic receptor, tyrosine hydroxylase, and dopamine-β-hydroxylase in the mPFC; there was no significant difference between the groups in the α_2A adrenergic receptor expression levels. Preferential activation of the α₁ adrenergic receptor caused by high noradrenaline concentration in the mPFC may be involved in social isolation-induced emotional and cognitive regulation impairments. Targeting the α₁ adrenergic receptor signaling pathway is a potential therapeutic strategy for psychiatric disorders with symptomatic features such as emotional and cognitive dysregulation.

From Inhibition of GABA-A Receptor-Mediated Synaptic Transmission by Conventional Antidepressants to Negative Allosteric Modulators of Alpha5-GABA-A Receptors as Putative Fast-Acting Antidepressant Drugs: Closing the Circle?

The present perspective paper shortly and specifically addresses the issues of whether inhibition of GABA-A receptor-mediated synaptic transmission may be involved in antidepressant-like actions and the therapeutic effects of conventional antidepressant (AD) drugs, and whether the recent development of negative allosteric modulators (NAMs) of the alpha5-GABA-A receptor may constitute significant progress in our knowledge on the neurobiology and the treatment of depression.

Pharmacological characterization of the forced swim test in Drosophila melanogaster

The forced swim test is commonly used as a preclinical screen of antidepressant medication efficacy in rats and mice. Neckameyer and Nieto-Romero (Stress 18:254-66, 2015) adopted the forced swim test for use with the fruit fly Drosophila melanogaster and showed that behavior in this test is sensitive to several physiologically relevant stressors. However, whether this test might be sensitive to the effects of antidepressant medications or other compounds is unknown. In the current studies, we fed drugs to male and female flies that we expected to either decrease or increase the duration of immobility in the forced swim test, including fluoxetine, desipramine, picrotoxin, reserpine, 3-iodo-tyrosine, and ethanol. Fluoxetine was the only drug tested that affected behavior in this test, and surprisingly, the direction of the effect depended on the duration of feeding. Short-term (30 min) feeding of the drug prior to test resulted in the expected increase in latency to immobility, while a longer feeding duration (20-24 h) decreased this measure. These results suggest that the pharmacological profile of the fly FST is more restricted than that of the rat or mouse FST, and that the duration of drug exposure is an important consideration in pharmacological research using flies.

Down-regulation of hippocampal BDNF and Arc associated with improvement in aversive spatial memory performance in socially isolated rats

Rats deprived of social contact with other rats at a young age experience a form of prolonged stress that leads to long-lasting changes in behavioral profile. Such isolation is thought to be anxiogenic for these normally gregarious animals, and the abnormal reactivity of isolated rats to environmental stimuli is thought to be a product of prolonged stress. We now show that isolation of rats at weaning reduced immobility time in the forced swim test, decreased sucrose intake and preference, and down-regulated both brain-derived neurotrophic factor (BDNF) and activity-regulated cytoskeletal associated protein (Arc) in the hippocampus. In the Morris water maze, isolated rats showed a reduced latency to reach the hidden platform during training, indicative of an improved learning performance, compared with group-housed rats. The cumulative search error during place training trials indicated a reliable difference between isolated and group-housed rats on days 4 and 5. The probe trial revealed a significant decrease of the average proximity to the target location in the isolated rats suggesting an improvement in spatial memory. Isolated rats also showed an increase in the plasma level of corticosterone on the 5th day of training and increased expression of BDNF and Arc in the hippocampus on both days 1 and 5. These results show that social isolation from weaning in rats results in development of depressive-like behavior but has a positive effect on spatial learning, supporting the existence of a facilitating effect of stress on cognitive function.

A postpartum model in rat: behavioral and gene expression changes induced by ovarian steroid deprivation

BACKGROUND

Postpartum depression (PPD) affects approximately 10% to 20% of women during the first 4 weeks of the postpartum period and is characterized by labile mood with prominent anxiety and irritability, insomnia, and depressive mood. During the postpartum period, elevated ovarian hormones abruptly decrease to the early follicular phase levels that are postulated to play a major role in triggering PPD. However, the underlying neurobiological mechanisms that contribute to PPD have not been determined.

METHODS

In the present study, we examined the effect of ovarian steroids, administered at levels that occur during human pregnancy followed by rapid withdrawal to simulate postpartum conditions, on behavior and gene expression in the rat.

RESULTS

The results of behavioral testing reveal that the hormone-simulated postpartum treatment results in the development of a phenotype relevant to PPD, including vulnerability for helplessness, increased anxiety, and aggression. Real-time quantitative polymerase chain reaction (PCR) demonstrated transient regulation of several genes, including Ca(2+)/calmodulin-dependent protein kinase II (CAMKII), serotonin transporter (SERT), myocyte enhancer factor 2A (MEF2A), brain-derived neurotrophic factor (BDNF), gamma-aminobutyric acid type A receptor alpha 4 (GABAARA4), mothers against decapentaplegic homolog 4 (SMAD4), and aquaporin 4 (AQP4) that could underlie these behavioral effects.

CONCLUSIONS

These studies provide an improved understanding of the effects of withdrawal from high doses of ovarian hormones on behavior and gene expression changes in the brain that could contribute to the pathophysiology of PPD.

Anxiogenic-like behavioral phenotype of mice deficient in phosphodiesterase 4B (PDE4B)

Phosphodiesterase-4 (PDE4), an enzyme that catalyzes the hydrolysis of cyclic AMP and plays a critical role in controlling its intracellular concentration, has been implicated in depression- and anxiety-like behaviors. However, the functions of the four PDE4 subfamilies (PDE4A, PDE4B, PDE4C, and PDE4D) remain largely unknown. In animal tests sensitive to anxiolytics, antidepressants, memory enhancers, or analgesics, we examined the behavioral phenotype of mice deficient in PDE4B (PDE4B-/-). Immunoblot analysis revealed loss of PDE4B expression in the cerebral cortex and amygdala of PDE4B-/- mice. The reduction of PDE4B expression was accompanied by decreases in PDE4 activity in the brain regions of PDE4B-/- mice. Compared to PDE4B+/+ littermates, PDE4B-/- mice displayed anxiogenic-like behavior, as evidenced by decreased head-dips and time spent in head-dipping in the holeboard test, reduced transitions and time on the light side in the light-dark transition test, and decreased initial exploration and rears in the open-field test. Consistent with anxiogenic-like behavior, PDE4B-/- mice displayed increased levels of plasma corticosterone. In addition, these mice also showed a modest increase in the proliferation of neuronal cells in the hippocampal dentate gyrus. In the forced-swim test, PDE4B-/- mice exhibited decreased immobility; however, this was not supported by the results from the tail-suspension test. PDE4B-/- mice did not display changes in memory, locomotor activity, or nociceptive responses. Taken together, these results suggest that the PDE4B subfamily is involved in signaling pathways that contribute to anxiogenic-like effects on behavior.

Role of GABA in anxiety and depression

This review assesses the parallel data on the role of gamma-aminobutyric acid (GABA) in depression and anxiety. We review historical and new data from both animal and human experimentation which have helped define the key role for this transmitter in both these mental pathologies. By exploring the overlap in these conditions in terms of GABAergic neurochemistry, neurogenetics, brain circuitry, and pharmacology, we develop a theory that the two conditions are intrinsically interrelated. The role of GABAergic agents in demonstrating this interrelationship and in pointing the way to future research is discussed.

Kindling epileptogenesis in immature rats leads to persistent depressive behavior

Depression is a frequent comorbidity in epilepsy patients. A variety of biological factors may underlie epilepsy-associated depression. We examined whether kindling-induced chronic increase in seizure susceptibility is accompanied by behavioral symptoms of depression. Three-week-old Wistar rats underwent rapid kindling: 84 initially subconvulsant electrical stimulations of ventral hippocampus delivered every 5 minutes, followed by depression-specific behavioral tests performed 2 and 4 weeks later. Kindled animals exhibited a sustained increase in immobility time in the forced swim test and the loss of taste preference toward calorie-free saccharin, as compared with controls. Initial loss of preference toward the intake of calorie-containing sucrose was followed by the increased consumption at 4 weeks. At both time points, animals exhibited enhanced seizure susceptibility on test stimulations of the hippocampus. We conclude that neuronal plastic changes associated with the kindling state are accompanied by the development of depressive behavior.

The convulsive and electroencephalographic changes produced by nonpeptidic delta-opioid agonists in rats: comparison with pentylenetetrazol

delta-Opioid agonists produce convulsions and antidepressant-like effects in rats. It has been suggested that the antidepressant-like effects are produced through a convulsant mechanism of action either through overt convulsions or nonconvulsive seizures. This study evaluated the convulsive and seizurogenic effects of nonpeptidic delta-opioid agonists at doses that previously were reported to produce antidepressant-like effects. In addition, delta-opioid agonist-induced electroencephalographic (EEG) and behavioral changes were compared with those produced by the chemical convulsant pentylenetetrazol (PTZ). For these studies, EEG changes were recorded using a telemetry system before and after injections of the delta-opioid agonists [(+)-4-[(alphaR)-alpha-[(2S,5R)-2,5-dimethyl-4-(2-propenyl)-1-piperazinyl]-(3-methoxyphenyl)methyl]-N,N-diethylbenz (SNC80) and [(+)-4-[alpha(R)-alpha-[(2S,5R)-2,5-dimethyl-4-(2-propenyl)-1-piperazinyl]-(3-hydroxyphenyl)methyl]-N,N-diethylbenzamide [(+)-BW373U86]. Acute administration of nonpeptidic delta-opioid agonists produced bilateral ictal and paroxysmal spike and/or sharp wave discharges. delta-Opioid agonists produced brief changes in EEG recordings, and tolerance rapidly developed to these effects; however, PTZ produced longer-lasting EEG changes that were exacerbated after repeated administration. Studies with antiepileptic drugs demonstrated that compounds used to treat absence epilepsy blocked the convulsive effects of nonpeptidic delta-opioid agonists. Overall, these data suggest that delta-opioid agonist-induced EEG changes are not required for the antidepressant-like effects of these compounds and that neural circuitry involved in absence epilepsy may be related to delta-opioid agonist-induced convulsions. In terms of therapeutic development, these data suggest that it may be possible to develop delta-opioid agonists devoid of convulsive properties.

Behavioral differences between subgroups of rats with high and low threshold to clonic convulsions induced by DMCM, a benzodiazepine inverse agonist

In epileptic patients, there is a high incidence of psychiatric comorbidities, such as anxiety. Gamma-aminobutyric acid (GABA) ionotropic receptor GABA(A)/benzodiazepine allosteric site is involved in both epilepsy and anxiety. This involvement is based on the fact that benzodiazepine allosteric site agonists are anticonvulsant and anxiolytic drugs; on the other hand, benzodiazepine inverse agonists are potent convulsant and anxiogenic drugs. The aim of this work was to determine if subgroups of rats selected according to their susceptibility to clonic convulsions induced by a convulsant dose 50% (CD50) of DMCM, a benzodiazepine inverse agonist, would differ in behavioral tests commonly used to measure anxiety (elevated plus-maze, open field) and depression (forced swimming test). In the first experiment, subgroups of adult male Wistar rats were selected after a single dose of DMCM and in the second experiment they were selected after two injections of DMCM given after an interval of 1 week. Those rats presenting full clonic convulsions were termed Low Threshold rats to DMCM-induced clonic convulsions (LTR) and those not having clonic convulsions High Threshold rats to DMCM-induced clonic convulsions (HTR). In both experiments, only those rats presenting full clonic convulsions induced by DMCM and those not showing any signs of motor disturbances were used in the behavioral tests. The results showed that the LTR subgroup selected after two injections of a CD50 of DMCM spent a significantly lower time in the open arms of the elevated plus-maze and in the off the walls area of the open field; moreover, this group also presented a higher number of rearings in the open field. There were no significant differences between HTR and LTR subgroups in the forced swimming test. LTR and HTR subgroups selected after only one injection of DMCM did not differ in the three behavioral tests. To verify if the behavioral differences between HTR and LTR subgroups of rats selected after two injections of DMCM were due to the clonic convulsion, another experiment was carried out in which subgroups of rats susceptible and nonsusceptible to clonic convulsions induced by a CD50 of picrotoxin, a GABA(A) receptor channel blocker, were selected and submitted to the elevated plus-maze and open field tests. The results obtained did not show any significant differences between these two subgroups in the elevated plus-maze and open field tests. In another approach to determine the relation between fear/anxiety and susceptibility to clonic convulsions, subgroups of rats were selected in the elevated plus-maze as more or less fearful/anxious. The CD50 for clonic convulsions induced by DMCM was determined for each of these two subgroups. The results showed a significantly lower CD50 for the more fearful/anxious subgroup, which means a higher susceptibility to clonic convulsions induced by DMCM. The present findings show a relation between susceptibility to clonic convulsions and fear/anxiety and vice versa which may be due to differences in the assembly of GABA(A)/allosteric benzodiazepine site receptors in regions of the brain.

Prenatal exposure to diazepam and alprazolam, but not to zolpidem, affects behavioural stress reactivity in handling-naïve and handling-habituated adult male rat progeny

A gentle long-lasting handling produces persistent neurochemical and behavioural changes and attenuates the impairment in the behavioural reactivity to novelty induced by the prenatal exposure to diazepam (DZ) in adult male rat progeny. This study investigated the consequences of a late prenatal treatment with three GABA/BDZ R agonists (DZ) alprazolam (ALP) and zolpidem (ZOLP)), on different stress-related behavioural patterns, in non-handled (NH), short-lasting handled (SLH) and long-lasting handled (LLH) adult male rats exposed to forced swim test (FST), acoustic startle reflex (ASR) and Vogel test (VT). The effects on motor activity were evaluated in the open field and in the Skinner box. The seizure sensitivity to picrotoxin (PTX) was investigated as an index of the functional state of GABA/BDZ Rs. A single daily s.c. injection of DZ (1.25-2.50 mg/kg) and ALP (0.125-0.250 mg/kg) over gestational days 14-20 induced a decrease in immobility time in the FST in NH rats, no change in SLH rats and an increase in LLH rats; DZ induced an increase in the peak amplitude of the ASR in NH rats, no change in SLH rats and a reduction in LLH rats; ALP was ineffective in all groups. DZ and ALP reduced the number of punished licks in the VT in NH, SLH and LLH rats while the unpunished licks were not modified. DZ decreased locomotion and the lever pressing responses while ALP increased them. DZ and ALP increased the seizure sensitivity to PTX (2.5-4.0 mg/kg i.p.). These findings indicate a convergence on anxiety-related behaviours in the effects of prenatal exposure to DZ and ALP and a differentiation on motor activity. Long-lasting handling was able to overcompensate the increased behavioural stress reactivity induced by the prenatal exposure to DZ and ALP.

Blockade of latent inhibition following pharmacological increase or decrease of GABA(A) transmission

The latent inhibition (LI) phenomenon refers to the retardation in learning of an association between a stimulus and a consequence if that stimulus had been previously experienced without consequence. An earlier study demonstrated that the benzodiazepine receptor agonist chlordiazepoxide (CDP), when administered before the phase of preexposure to the to-be-conditioned stimulus, impaired animals' ability to develop LI. The present study was designed to investigate the effect of the anxiogenic drugs pentylenetetrazole (PTZ) and the benzodiazepine partial inverse agonist Ro15-4513 on LI. Both anxiogenics, in contrast to CDP, are known for their GABA inhibitory action. The effects produced by the combined administration of a GABAergic function facilitator and inhibitor (CDP/PTZ and CDP/Ro15-4513) were also investigated. Both anxiogenic drugs led to an attenuation of LI, and, similarly to CDP, this attenuation was exclusively due to their administration prior to the preexposure stage of the experiment. However, this effect was abolished when anxiolytic and anxiogenic drugs were administered together, suggesting a pharmacological rather than behavioral summation of effects. These data also demonstrate the bidirectional GABAergic modulation of the LI phenomenon: both increased and decreased GABA(A) receptor activation led to reduced LI, thereby suggesting that an optimal receptor activation level is necessary for the normal establishment of LI.

Agastache mexicana may produce anxiogenic-like actions in the male rat

Behavioral effects of a water-soluble extract of Agastache mexicana, a plant with purported anxiolytic actions, were studied in male Wistar rats. In the elevated plus-maze test, various doses of the plant extract (3.0 mg/kg body wt.; 9.0 mg/kg body wt.; 12.0 mg/kg body wt.) administered intraperitoneally (i.p.) decreased the exploration of open arms, showing an anxiogenic-like effect. Agastache mexicana (12 mg/kg body wt.; i.p.) did not change immobility in the forced swimming test (i.e., had no anti-depressant effect) but increased the anti-immobility action of 32.0 mg/kg body wt. (i.p.) of desipramine (i.e., increased the antidepressant-like effect of desipramine). A. mexicana had no effect on exploratory activity in an open field test, indicating that it had no sedative effect at the doses used. It is concluded that effects of the water extract of A. mexicana are more consistent with an anxiogenic-like property than an anxiolytic-like one.

Chronic treatment with desipramine induces an estrous cycle-dependent anxiolytic-like action in the burying behavior, but not in the elevated plus-maze test

The effect of chronic desipramine (DMI, 2.5 mg/kg x 21-26 days) treatment in female rats in two anxiety paradigms was assessed: the burying behavior (BB) and the elevated plus-maze (EPM) tests. In the BB test DMI produced a significant decrease in burying in ovariectomized rats, an effect considered as anxiolytic-like. In cycling females, DMI also reduced the cumulative BB most notably in proestrus rats. However, in diestrus rats no anxiolytic-like actions were observed. In addition, DMI increased BB latencies in proestrus and estrus rats. In the EPM test, DMI produced anxiolytic-like actions only in ovariectomized rats, while no significant actions were found in cycling females. Finally, the chronic treatment with DMI produced a general reduction in the ambulatory behavior of rats in all estrous cycle phases. Results are discussed on the basis of the differences between both anxiety paradigms and the probable relationship between the steroids secreted during proestrus and chronic DMI treatment.

Locomotor and antidepressant-like effects of 5-HT(1A) agonist LY 228729 in prenatally benzodiazepine-exposed rats

Locomotor activity and antidepressant-like effect in the forced swim test (FST) of 5-HT(1A) agonist LY 228729 were investigated in adult rats prenatally exposed at doses of diazepam (DZ) and alprazolam (ALP) which induce persistent downregulation of GABA/ benzodiazepine (BZ) receptors. Prenatal exposure to ALP and DZ did not modify the efficacy of subchronic LY 228729 to decrease immobility time in the FST. Prenatal DZ and ALP potentiated the facilitatory effect of subchronic LY 228729 on locomotor activity; prenatal DZ was more effective than prenatal ALP. Moreover, prenatal DZ increased stereotypic movements induced by LY 228729. These data suggest that the persistent downregulation of GABA/BZ receptors, induced by prenatal BZs, does not play a role in the anti-immobility effect in the FST of 5-HT(1A) agonist LY 228729 while it can increase locomotor activity and stereotypic movements. Moreover, this study indicates that increases in locomotor activity do not seem to influence the anti-immobility effect in the FST of LY 228729 in rats.

Strain differences in pentylenetetrazol-kindling development and subsequent potentiation effects

Rats from two different strains, i.e. Wistar rats and Lister hooded rats, were investigated for their ability to acquire the kindling syndrome. After having received 13 kindling stimulations (injection of pentylenetetrazol), the animals were tested for subsequent alterations in induction and maintenance of hippocampal long-term potentiation (LTP) and, moreover in glutamate binding. It was found that rats from both strains did not differ in the response to the initial injection of pentylenetetrazol (PTZ) and the amplitude of the population spike. This suggests that some aspects of basic central excitability are equivalent. Wistar rats acquired the kindling syndrome rapidly whereas seizure outcome was poor in Lister rats. As regards hippocampal LTP, the population spike was only dramatically increased in Wistar rats after kindling completion. Glutamate binding was not altered in animals from the Lister strain. The results suggest that changes in glutamate binding and the increase in the population spike are characteristic consequences of kindling.