Allopregnanolone reduces immobility in the forced swimming test and increases the firing rate of lateral septal neurons through actions on the GABAA receptor in the rat

Antidepressant effects of activation of infralimbic cortex via upregulation of BDNF and β-catenin in an estradiol withdrawal model

RATIONALE

Clinical and preclinical studies have demonstrated that estradiol withdrawal after delivery is one of important factors involved in the pathogenesis of postpartum depression (PPD). The infralimbic cortex (IL) is related to anxiety and mood disorders. Whether IL neurons mediate PPD is still unclear.

OBJECTIVES

This study was to observe the antidepressant effect and expression of BDNF and β-catenin in IL by allopregnanolone (ALLO) treatment or the selective activation or inhibition of IL neurons using a chemogenetic approach in a pseudopregnancy model of PPD.

METHODS

Administration of estradiol combined with progesterone and the abrupt withdrawal of estradiol simulated the pregnancy and early postpartum periods to induce depression in ovariectomized rats. The relative expression levels of β-catenin and BDNF were observed by western blotting.

RESULTS

Immobility time was significantly increased in the forced swim test and open-arm movement was reduced in the elevated plus maze test in the estradiol-withdrawn rats. After ALLO treatment, the immobility time were lower and open-arm traveling times higher than those of the estradiol-withdrawn rats. Meanwhile, the expression level of BDNF or β-catenin in the IL was reduced significantly in estradiol-withdrawn rats, which was prevented by treatment with ALLO. The hM3Dq chemogenetic activation of pyramidal neurons in the IL reversed the immobility and open-arm travel time trends in the estradiol-withdrawal rat model, but chemogenetic inhibition of IL neurons failed to affect this. Upregulated BDNF and β-catenin expression and increased c-Fos in the basolateral amygdala were found following IL neuron excitation in model rats.

CONCLUSIONS

Our results demonstrated that pseudopregnancy and estradiol withdrawal produced depressive-like behavior and anxiety. ALLO treatment or specific excitement of IL pyramidal neurons relieved abnormal behaviors and upregulated BDNF and β-catenin expression in the IL in the PPD model, suggesting that hypofunction of IL neurons may be involved in the pathogenesis of PPD.

Mifepristone blocks the anxiolytic- and antidepressant-like effects of allopregnanolone in male rats

BACKGROUND

Allopregnanolone (3α, 5α-tetrahydroprogesterone) is an inhibitory neurosteroid synthesized from progesterone via 5α-reductase activity in the brain and has anxiolytic, antidepressant, sedative, anticonvulsant, and analgesic activity. Altered levels of allopregnanolone cause anxiety, depression, premenstrual syndrome, and psychiatric disorders. Although allopregnanolone exerts most of its actions by modulating GABAA receptor, NMDA receptor, BDNF expression, and PXR activity, a recent study showed its effects are blocked by mifepristone on lordosis behavior which indicates the involvement of progestin or glucocorticoid receptors in the effects of allopregnanolone since mifepristone blocks both these receptors. However, whether these receptors are involved in acute anxiolytic or antidepressant-like effects is unknown.

METHODS

Adult male Wistar rats were used to study whether the prior administration of mifepristone would alter the effects of allopregnanolone in the elevated plus maze (EPM) and forced swim test (FST) was evaluated.

RESULTS

10 mg/Kg dose of allopregnanolone increased percent open arm entries in the EPM, whereas 3 mg/Kg dose of allopregnanolone decreased percent immobility in the FST. Mifepristone administration resulted in a U-shaped response in the FST (with 1 mg/Kg, s.c., decreasing the immobility time) without significantly impacting the behavior in the EPM. In combination studies, mifepristone blocked the anxiolytic and antidepressant effects of allopregnanolone.

CONCLUSION

The current study provides evidence for the first time that progestin or glucocorticoid receptors are involved in the acute anxiolytic and antidepressant effects of allopregnanolone. Understanding the mechanism of action of allopregnanolone will help us design better therapeutic strategies to treat neuropsychiatric diseases such as depression and anxiety.

Behavioral Despair Is Blocked by the Flavonoid Chrysin (5,7-Dihydroxyflavone) in a Rat Model of Surgical Menopause

Women have a high susceptibility to the negative effects of stress. Hormonal changes experienced throughout their reproductive life partially contribute to a higher incidence of anxiety and depression symptoms, particularly, during natural or surgical menopause. In preclinical research, the flavonoid chrysin (5,7-dihydroxyflavone) exerts anxiolytic- and anti-despair-like effects; however, it is unknown whether chrysin exerts a protective effect against the behavioral changes produced by acute stress on locomotor activity and behavioral despair in rats at 12-weeks post-ovariectomy. Ovariectomized female Wistar rats were assigned to eight groups: vehicle group (10% DMSO), three groups with chrysin and three groups with the same dose of allopregnanolone (0.5, 1, and 2 mg/kg), and one group with diazepam (2 mg/kg). The treatments were administered for seven consecutive days and the effects were evaluated in the locomotor activity and swimming tests. Chrysin (2 mg/kg) increased the latency to first immobility and decreased the total immobility time in the swimming test as the reference drugs allopregnanolone and diazepam (2 mg/kg); while locomotor activity prevented the behavioral changes produced by swimming. In conclusion, chrysin exerts a protective effect against the behavioral changes induced by acute stress, similarly to the neurosteroid allopregnanolone and the benzodiazepine diazepam in rats subjected to a surgical menopause model.

Serotonergic and noradrenergic response of ethanol extract; opioidergic response of ethyl acetate extract of Dicranopteris linearis L. leaf

Background

Dicranopteris linearis L. is among the popular tribal plants used for various ailments, although many of its pharmacological potentials have not been investigated yet. The neuropharmacological potentials of the leaf, including sedative-anxiolytic potential, were previously studied however, the antidepressant activity was yet to be examined. Thus, this study was aimed to investigate the serotonergic, noradrenergic and opioidergic response of D. linearis leaf extracts.

Methods

The plant leaf was extracted in three solvents- water (DLAQ), ethanol (DLET) and ethyl acetate (DLEA) and applied each in 200 and 400 mg.kg− 1 per body weight of Swiss Albino mice. Forced Swim Test (FST) and Tail Suspension Test (TST) were conducted to evaluate antidepressant potential. In FST, latency and duration of immobility, swimming and climbing time were recorded. In TST, immobility, swinging, curling and pedaling were observed. Alongside, preliminary screening through acute toxicity study and pentobarbitone induced sleep test were performed.

Results

Both in FST and TST, the duration of immobility was reduced by the standard imipramine and DLET 200 and 400. In FST, DLEA 200 and 400 increased the climbing time suggesting noradrenergic mechanism of action and decreased the swimming time suggesting deficit of serotoninergic mechanism of action. Interestingly, DLET increased both the parameters presenting a dual action. However, in TST, DLEA decreased immobility but increased swinging and curling response which indicated its opioidergic mechanism. On the other hand, DLET proved to mediate through serotonin and/or NA reuptake mechanism by having decreased curling time.

Conclusion

Among the three extracts, the ethanol extract proved to be more potent. DLET mimicked the standard imipramine in all parameters except for the curling behavior. The result thus suggests D. linearis as a potent antidepressant agent however, recommends its medicinal use after further investigation to identify bioactive compounds.

Sex and estrous-phase dependent alterations in depression-like behavior following mild traumatic brain injury in adolescent rats

Following mild traumatic brain injury (TBI), high school and collegiate-aged females tend to report more emotional symptoms than males. Adolescent male and female rats (35 days old) were subjected to mild TBI and evaluated for anxiety- and depression-like behaviors using the elevated plus maze and forced swim test (FST), respectively, and cellular alterations. Injured brains did not exhibit an overt lesion, atrophy of tissue or astrocytic reactivity underneath the impact site at 6-week post-injury, suggestive of the mild nature of trauma. Neither male nor female brain-injured rats exhibited anxiety-like behavior at 2 or 6 weeks, regardless of estrous phase at the time of behavior testing. Brain-injured male rats did not exhibit any alterations in immobility, swimming and climbing times in the FST compared to sham-injured rats at either 2- or 6-week post-injury. Brain-injured female rats did, however, exhibit an increase in immobility (in the absence of changes in swimming and climbing times) in the FST at 6 weeks post-injury only during the estrus phase of the estrous cycle, suggestive of a depression-like phenotype. Combined administration of the estrogen receptor antagonist, tamoxifen, and the progesterone receptor antagonist, mifepristone, during proestrus was able to prevent the depression-like phenotype observed during estrus. Taken together, these data suggest that female rats may be more vulnerable to exhibiting behavioral deficits following mild TBI and that estrous phase may play a role in depression-like behavior.

The Role of HPA Axis and Allopregnanolone on the Neurobiology of Major Depressive Disorders and PTSD

Under stressful conditions, the hypothalamic-pituitary-adrenal (HPA) axis acts to promote transitory physiological adaptations that are often resolved after the stressful stimulus is no longer present. In addition to corticosteroids (e.g., cortisol), the neurosteroid allopregnanolone (3α,5α-tetrahydroprogesterone, 3α-hydroxy-5α-pregnan-20-one) participates in negative feedback mechanisms that restore homeostasis. Chronic, repeated exposure to stress impairs the responsivity of the HPA axis and dampens allopregnanolone levels, participating in the etiopathology of psychiatric disorders, such as major depressive disorder (MDD) and post-traumatic stress disorder (PTSD). MDD and PTSD patients present abnormalities in the HPA axis regulation, such as altered cortisol levels or failure to suppress cortisol release in the dexamethasone suppression test. Herein, we review the neurophysiological role of allopregnanolone both as a potent and positive GABAergic neuromodulator but also in its capacity of inhibiting the HPA axis. The allopregnanolone function in the mechanisms that recapitulate stress-induced pathophysiology, including MDD and PTSD, and its potential as both a treatment target and as a biomarker for these disorders is discussed.

Allopregnanolone in mood disorders: Mechanism and therapeutic development

The neuroactive steroid allopregnanolone (ALLO) is an endogenous positive allosteric modulator of GABA type A receptor (GABA_AR), and the down-regulation of its biosynthesis have been attributed to the development of mood disorders, such as depression, anxiety and post-traumatic stress disorder (PTSD). ALLO mediated depression/anxiety involves GABAergic mechanisms and appears to be related to brain-derived neurotrophic factor (BDNF), dopamine receptor, glutamate neurotransmission, and Ca²⁺ channel. In the clinical, brexanolone, as a newly developed intravenous ALLO preparation, has been approved for the treatment of postpartum depression (PPD). In addition, traditional antidepressants such as selective serotonin reuptake inhibitor (SSRI) could reverse ALLO decline. Recently, the translocation protein (TSPO, 18 kDa), which involves in the speed-limiting step of ALLO synthesis, and ALLO derivatization have been identified as new directions for antidepressant therapy. This review provides an overview of ALLO researches in animal model and patients, discusses its role in the development and treatment of depression/anxiety, and directs its therapeutic potential in future.

Allopregnanolone induces antidepressant-like effects through BDNF-TrkB signaling independent from AMPA receptor activation in a rat learned helplessness model of depression

Allopregnanolone (ALLO, 3α5α-tetrahydroprogesterone) was found to be effective for depressed patients. Animal models of depression indicate that ALLO is associated with the pathophysiology of depression. Traditional antidepressant drugs produce antidepressant effects via the monoamine system, with consequent up-regulation of brain-derived neurotrophic factor (BDNF). This study was designed to examine whether the antidepressant effects of ALLO involve BDNF-TrkB signaling or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor activation on the learned helplessness paradigm. The antidepressant-like effect of ALLO infusion into the cerebral ventricle was blocked by coinfusion of TrkB inhibitor ANA-12, but not by co-administration of AMPA receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfoamoylbenzo(f)quinoxaline (NBQX). Thus, the antidepressant-like effect of ALLO involves BDNF signaling independent from AMPA receptor activation.

The role of allopregnanolone in depressive-like behaviors: Focus on neurotrophic proteins

Allopregnanolone (3α,5α-tetrahydroprogesterone; pharmaceutical formulation: brexanolone) is a neurosteroid that has recently been approved for the treatment of postpartum depression, promising to fill part of a long-lasting gap in the effectiveness of pharmacotherapies for depressive disorders. In this review, we explore the experimental research that characterized the antidepressant-like effects of allopregnanolone, with a particular focus on the neurotrophic adaptations induced by this neurosteroid in preclinical studies. We demonstrate that there is a consistent decrease in allopregnanolone levels in limbic brain areas in rodents submitted to stress-induced models of depression, such as social isolation and chronic unpredictable stress. Further, both the drug-induced upregulation of allopregnanolone or its direct administration reduce depressive-like behaviors in models such as the forced swim test. The main drugs of interest that upregulate allopregnanolone levels are selective serotonin reuptake inhibitors (SSRIs), which present the neurosteroidogenic property even in lower, non-SSRI doses. Finally, we explore how these antidepressant-like behaviors are related to neurogenesis, particularly in the hippocampus. The protagonist in this mechanism is likely the brain-derived neurotrophic factor (BFNF), which is decreased in animal models of depression and may be restored by the normalization of allopregnanolone levels. The role of an interaction between GABA and the neurotrophic mechanisms needs to be further investigated.

Acute effect of an infusion of Montanoa tomentosa on despair-like behavior and activation of oxytocin hypothalamic cells in Wistar rats

Background and aim

In Mexican traditional medicine, Montanoa tomentosa (Mt) has been used as a remedy for reproductive impairments and mood swings. In pre-clinical research, both the extract and some of its active metabolites have produced oxytocinergic-like effects on female reproductive organs; however, there are no detailed studies of its effects on mood swing and brain structures. The aim of this study, was to analyze the behavioral effects of acute administration of a Mt infusion on male rats, during the Open Field (OFT) and Forced Swim (FST) Tests, and their association with the activation of oxytocin (OXT) cells, indicated by Fos protein (Fos/OXT) in the paraventricular (PVN) and supraoptic nuclei (SON).

Experimental procedure

52 adult male Wistar rats were assigned to two conditions; with FST (n = 8), or without (n = 5). Each integrated condition included four groups [Control, Vehicle, Fluoxetine (Flx; 10 mg/kg), and Mt (50 mg/kg), p.o.].

Results and conclusion

Mt and Flx treatment produced an anti-despair-like effect on the FST, but no significant changes in locomotor activity. Also, the Mt infusion -but not Flx-significantly increased the number of Fos/OXT cells in the PVN and SON, regardless of the condition, compared to the control and vehicle groups. These results show that Mt, but not Flx, produces an anti-despair-like effect that could be associated with the activation of OXT cells in PVN and SON. This study thus contributes to our knowledge of the pharmacological activity of Mt infusions, which could be a natural antidepressant agent with future clinical relevance.

Cyclic changes and actions of progesterone and allopregnanolone on cognition and hippocampal basal (stratum oriens) dendritic spines of female rats

Ovarian steroids modulate the neuronal structure and function during the estrous cycle, contrasting peak effects during the proestrus cycle and low effects during the metestrus cycle. An ovariectomy (OVX) decreases gonadal hormones and tests the effects of substitutive therapies. We studied female rats with a normal estrous cycle and we also studied the effects of systemic progesterone (P4, 4.0 mg/kg) or its reduced metabolite allopregnanolone (ALLO, 4.0 mg/kg, both for 10 days) in females who had had an OVX 16.5 weeks prior to the study (long-term OVX) with the novel object recognition test (NORT) for associative memory. The dendritic shape and spine density in Golgi-impregnated basal dendrites (stratum oriens) of hippocampal pyramidal neurons was also studied. Proestrus females had a better performance than metestrus or OVX females in short-term memory (tested 1 h after the acquisition phase). Proestrus and metestrus females showed better results than OVX females for long-term memory (24 h after the initial phase). Both P4 and ALLO recovered the cognitive impairment induced by long-term OVX. Also, proestrus females had a higher density of dendritic spines than metestrus females, OVX reduced the density of spines when compared to intact females, whereas both P4 and ALLO treatments increased the dendritic spine density, number of dendritic branches along the dendritic length, and branching order compared to vehicle. These data add the dendrites of the stratum oriens as an additional site for naturally occurring changes in spine density during the estrous cycle and evidence the actions of progestins in both behavioral recovery and the structural dendritic rearrangement of hippocampal pyramidal neurons in long-term OVX female rats.

Estradiol Fluctuation, Sensitivity to Stress, and Depressive Symptoms in the Menopause Transition: A Pilot Study

The menopause transition is associated with an increased risk of depressed mood. Preliminary evidence suggests that increased sensitivity to psychosocial stress, triggered by exaggerated perimenopausal estradiol fluctuation, may play a role. However, accurately quantifying estradiol fluctuation while minimizing participant burden has posed a methodological challenge in the field. The current pilot project aimed to test the feasibility of capturing perimenopausal estradiol fluctuation via 12 weekly measurements of estrone-3-glucuronide (E1G), a urinary metabolite of estradiol, using participant-collected urine samples in 15 euthymic perimenopausal women ages 45-55 years. Furthermore, it aimed to correlate E1G fluctuation (standard deviation across the 12 E1G measurements) with weekly mood and cardiovascular, salivary cortisol, and subjective emotional responses to the Trier Social Stress Test (TSST) at weeks 4, 8, and 12. Protocol acceptability and adherence was high; furthermore, E1G fluctuation was positively associated with anhedonic depressive symptoms and weekly negative affect. E1G fluctuation was also associated with increased heart rate throughout the TSST as well as higher levels of rejection, anger, and sadness. E1G fluctuation was not significantly associated with TSST blood pressure or cortisol levels. This study suggests a feasible method of assessing estradiol fluctuation in the menopause transition and provides support for the hypothesis that perimenopausal estradiol fluctuation increases sensitivity to psychosocial stress and vulnerability to depressed mood.

Cortical GABAergic Dysfunction in Stress and Depression: New Insights for Therapeutic Interventions

Major depressive disorder (MDD) is a debilitating illness characterized by neuroanatomical and functional alterations in limbic structures, notably the prefrontal cortex (PFC), that can be precipitated by exposure to chronic stress. For decades, the monoaminergic deficit hypothesis of depression provided the conceptual framework to understand the pathophysiology of MDD. However, accumulating evidence suggests that MDD and chronic stress are associated with an imbalance of excitation-inhibition (E:I) within the PFC, generated by a deficit of inhibitory synaptic transmission onto principal glutamatergic neurons. MDD patients and chronically stressed animals show a reduction in GABA and GAD67 levels in the brain, decreased expression of GABAergic interneuron markers, and alterations in GABA_A and GABA_B receptor levels. Moreover, genetically modified animals with deletion of specific GABA receptors subunits or interneuron function show depressive-like behaviors. Here, we provide further evidence supporting the role of cortical GABAergic interneurons, mainly somatostatin- and parvalbumin-expressing cells, required for the optimal E:I balance in the PFC and discuss how the malfunction of these cells can result in depression-related behaviors. Finally, considering the relatively low efficacy of current available medications, we review new fast-acting pharmacological approaches that target the GABAergic system to treat MDD. We conclude that deficits in cortical inhibitory neurotransmission and interneuron function resulting from chronic stress exposure can compromise the integrity of neurocircuits and result in the development of MDD and other stress-related disorders. Drugs that can establish a new E:I balance in the PFC by targeting the glutamatergic and GABAergic systems show promising as fast-acting antidepressants and represent breakthrough strategies for the treatment of depression.

Effect of blackberry juice (Rubus fruticosus L.) on anxiety-like behaviour in Wistar rats

The present study evaluated the effects of blackberry juice that is rich in different concentrations of anthocyanins and polyphenols (2.6 mg/kg anthocyanins, 14.57 mg/kg polyphenols; 5.83 mg/kg anthocyanins, 27.10 mg/kg polyphenols; 10.57 mg/kg anthocyanins, 38.40 mg/kg polyphenols) on anxiety-like behaviour in Wistar rats. The rats were treated with blackberry juice for 21 days and then tested in the elevated plus maze, locomotor activity test and forced swim test. The results were compared with a reference anxiolytic drug diazepam (2.0 mg/kg) and vehicle (8.7 ml/kg). The intermediate dose of blackberry juice exerted an anxiolytic-like effect that was similar to diazepam, without affecting locomotive activity. The low and high doses of blackberry juice exerted no significant effects on anxiety-like behaviour compared with vehicle. In the forced swim test, both the high and intermediate doses of blackberry juice reduced total immobility time, suggesting a protective effect against behavioural changes that are induced by acute stress. These findings suggest a potential therapeutic effect of blackberry juice on anxiety that is associated with a stressful event.

Cortical GABAergic Dysfunction in Stress and Depression: New Insights for Therapeutic Interventions

Major depressive disorder (MDD) is a debilitating illness characterized by neuroanatomical and functional alterations in limbic structures, notably the prefrontal cortex (PFC), that can be precipitated by exposure to chronic stress. For decades, the monoaminergic deficit hypothesis of depression provided the conceptual framework to understand the pathophysiology of MDD. However, accumulating evidence suggests that MDD and chronic stress are associated with an imbalance of excitation-inhibition (E:I) within the PFC, generated by a deficit of inhibitory synaptic transmission onto principal glutamatergic neurons. MDD patients and chronically stressed animals show a reduction in GABA and GAD67 levels in the brain, decreased expression of GABAergic interneuron markers, and alterations in GABA_A and GABA_B receptor levels. Moreover, genetically modified animals with deletion of specific GABA receptors subunits or interneuron function show depressive-like behaviors. Here, we provide further evidence supporting the role of cortical GABAergic interneurons, mainly somatostatin- and parvalbumin-expressing cells, required for the optimal E:I balance in the PFC and discuss how the malfunction of these cells can result in depression-related behaviors. Finally, considering the relatively low efficacy of current available medications, we review new fast-acting pharmacological approaches that target the GABAergic system to treat MDD. We conclude that deficits in cortical inhibitory neurotransmission and interneuron function resulting from chronic stress exposure can compromise the integrity of neurocircuits and result in the development of MDD and other stress-related disorders. Drugs that can establish a new E:I balance in the PFC by targeting the glutamatergic and GABAergic systems show promising as fast-acting antidepressants and represent breakthrough strategies for the treatment of depression.

Advances in the Preclinical Study of Some Flavonoids as Potential Antidepressant Agents

Flavonoids are phenolic compounds found commonly in plants that protect them against the negative effects of environmental insults. These secondary metabolites have been widely studied in preclinical research because of their biological effects, particularly as antioxidant agents. Diverse flavonoids have been studied to explore their potential therapeutic effects in the treatment of disorders of the central nervous system, including anxiety and depression. The present review discusses advances in the study of some flavonoids as potential antidepressant agents. We describe their behavioral, physiological, and neurochemical effects and the apparent mechanism of action of their preclinical antidepressant-like effects. Natural flavonoids produce antidepressant-like effects in validated behavioral models of depression. The mechanism of action of these effects includes the activation of serotonergic, dopaminergic, noradrenergic, and γ-aminobutyric acid-ergic neurotransmitter systems and an increase in the production of neural factors, including brain-derived neurotrophic factor and nerve growth factor. Additionally, alterations in the function of tropomyosin receptor kinase B and activity of the enzyme monoamine oxidase A have been reported. In conclusion, preclinical research supports the potential antidepressant effects of some natural flavonoids, which opens new possibilities of evaluating these substances to develop complementary therapeutic alternatives that could ameliorate symptoms of depressive disorders in humans.

Identification of a novel, fast-acting GABAergic antidepressant

Current pharmacotherapies for depression exhibit slow onset, side effects and limited efficacy. Therefore, identification of novel fast-onset antidepressants is desirable. GLO1 is a ubiquitous cellular enzyme responsible for the detoxification of the glycolytic byproduct methylglyoxal (MG). We have previously shown that MG is a competitive partial agonist at GABA-A receptors. We examined the effects of genetic and pharmacological inhibition of GLO1 in two antidepressant assay models: the tail suspension test (TST) and the forced swim test (FST). We also examined the effects of GLO1 inhibition in three models of antidepressant onset: the chronic FST (cFST), chronic mild stress (CMS) paradigm and olfactory bulbectomy (OBX). Genetic knockdown of Glo1 or pharmacological inhibition using two structurally distinct GLO1 inhibitors (S-bromobenzylglutathione cyclopentyl diester (pBBG) or methyl-gerfelin (MeGFN)) reduced immobility in the TST and acute FST. Both GLO1 inhibitors also reduced immobility in the cFST after 5 days of treatment. In contrast, the serotonin reuptake inhibitor fluoxetine (FLX) reduced immobility after 14, but not 5 days of treatment. Furthermore, 5 days of treatment with either GLO1 inhibitor blocked the depression-like effects induced by CMS on the FST and coat state, and attenuated OBX-induced locomotor hyperactivity. Finally, 5 days of treatment with a GLO1 inhibitor (pBBG), but not FLX, induced molecular markers of the antidepressant response including brain-derived neurotrophic factor (BDNF) induction and increased phosphorylated cyclic-AMP response-binding protein (pCREB) to CREB ratio in the hippocampus and medial prefrontal cortex (mPFC). Our findings indicate that GLO1 inhibitors may provide a novel and fast-acting pharmacotherapy for depression.

The Aqueous Crude Extracts of Montanoa frutescens and Montanoa grandiflora Reduce Immobility Faster Than Fluoxetine Through GABAA Receptors in Rats Forced to Swim

BACKGROUND

Montanoa frutescens and Montanoa grandiflora have been indistinctly used for centuries in traditional Mexican medicine for reproductive impairments, anxiety, and mood disorders. Preclinical studies support their aphrodisiac and anxiolytic properties, but their effects on mood are still unexplored.

METHODS

The effects of 25 and 50 mg/kg of M frutescens and M grandiflora extracts were evaluated on days 1, 7, 14, 21, and 28 of treatment, and compared with fluoxetine (1 mg/kg) and Remotiv (7.14 mg/kg) in Wistar rats. The participation of GABAA receptor in the effects produced by the treatments was explored.

RESULTS

Montanoa extracts reduced immobility since day 1 of treatment, while fluoxetine and Remotiv required 14 days. The GABAA antagonism blocked the effects of Montanoa extracts, but not of fluoxetine or Remotiv.

CONCLUSIONS

Montanoa extracts prevented quickly the stress-induced behaviors in the swimming test through action at the GABAA receptor, exerting a protective effect different to the typical antidepressants drugs.

A Fatty Acids Mixture Reduces Anxiety-Like Behaviors in Infant Rats Mediated by GABAA Receptors

Fatty acids (C6-C18) found in human amniotic fluid, colostrum, and maternal milk reduce behavioral indicators of experimental anxiety in adult Wistar rats. Unknown, however, is whether the anxiolytic-like effects of fatty acids provide a natural mechanism against anxiety in young offspring. The present study assessed the anxiolytic-like effect of a mixture of lauric acid, myristic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, elaidic acid, and linoleic acid in Wistar rats on postnatal day 28. Infant rats were subjected to the elevated plus maze, defensive burying test, and locomotor activity test. Diazepam was used as a reference anxiolytic drug. A group that was pretreated with picrotoxin was used to explore the participation of γ-aminobutyric acid-A (GABAA) receptors in the anxiolytic-like effects. Similar to diazepam, the fatty acid mixture significantly increased the frequency of entries into and time spent on the open arms of the elevated plus maze and decreased burying behavior in the defensive burying test, without producing significant changes in spontaneous locomotor activity. These anxiolytic-like effects were blocked by picrotoxin. Results suggest that these fatty acids that are contained in maternal fluid may reduce anxiety-like behavior by modulating GABAergic neurotransmission in infant 28-day-old rats.

Chronic treatment with estradiol restores depressive-like behaviors in female Wistar rats treated neonatally with clomipramine

Neonatal administration of clomipramine (CMI) induces diverse behavioral and neurochemical alterations in adult male rats that resemble major depression disorder. However, the possible behavioral alterations in adult female rats subjected to neonatal treatment with clomipramine are unknown. Therefore, the aim of this study was to explore the effect of neonatal treatment with CMI on adult female rats in relation to locomotion and behavioral despair during the estrus cycle. Also evaluated was the effect of chronic treatment with E2 on these female CMI rats. We found no effects on spontaneous locomotor activity due to neonatal treatment with CMI, or after 21days of E2 administration. In the FST, neonatal treatment with CMI increased immobility and decreased active swimming and climbing behaviors. Influence of the ovarian cycle was detected only in relation to climbing behavior, as the rats in the MD phase displayed less climbing activity. Chronic E2 administration decreased immobility but increased only swimming in CMI rats. These results suggest that neonatal treatment with CMI induces despair-like behavior in female rats, but that chronic E2 administration generates antidepressant-like behavior by decreasing immobility and increasing swimming, perhaps through interaction with the serotonergic system.

Maternal care and affective behavior in female offspring: Implication of the neurosteroid/GABAergic system

In female rats, the proestrus phase of the estrous cycle is associated with decreased levels of anxiety-like and depressive-like behavior relative to the metestrus phase. Progesterone likely modulate these behaviors, in part through the influence of its metabolite, allopregnanolone (THP) on hippocampal GABA_AR subunit expression. As natural variations in maternal care have been found to influence both progesterone levels at proestrus and anxiety-like behavior in female offspring, we sought to investigate the importance of maternal care and the estrous cycle on affective behavior in female rats that had received Low or High levels of licking/grooming (LG) during early life. Subjects were tested for anxiety-like behavior in the elevated plus maze at proestrus or metestrus or for estrous cycle-dependent changes in depressive-like anhedonic behavior with a saccharin preference test. GABA_AR subunit expression, and THP levels in the dorsal hippocampus and in plasma were also evaluated. Estrous cycle phase influenced saccharine preference and hippocampal THP level in both phenotypes. Low LG animals showed higher levels of hedonic behavior and anxiety-like behavior, irrespective of estrous cycle phase, as well as lower THP levels within the dorsal hippocampus when compared to High LG animals. Only High LG animals showed positive correlations between hippocampal THP levels and GABA_AR subunit expression, suggesting a relative insensitivity to THP's modulation of these receptor subunits in Low LG offspring. These findings suggest that natural variations in maternal care influence anxiety-like and hedonic behavior through the modulation of the neurosteroid/GABAergic system.

Social Plasticity Relies on Different Neuroplasticity Mechanisms across the Brain Social Decision-Making Network in Zebrafish

Social living animals need to adjust the expression of their behavior to their status within the group and to changes in social context and this ability (social plasticity) has an impact on their Darwinian fitness. At the proximate level social plasticity must rely on neuroplasticity in the brain social decision-making network (SDMN) that underlies the expression of social behavior, such that the same neural circuit may underlie the expression of different behaviors depending on social context. Here we tested this hypothesis in zebrafish by characterizing the gene expression response in the SDMN to changes in social status of a set of genes involved in different types of neural plasticity: bdnf, involved in changes in synaptic strength; npas4, involved in contextual learning and dependent establishment of GABAergic synapses; neuroligins (nlgn1 and nlgn2) as synaptogenesis markers; and genes involved in adult neurogenesis (wnt3 and neurod). Four social phenotypes were experimentally induced: Winners and Losers of a real-opponent interaction; Mirror-fighters, that fight their own image in a mirror and thus do not experience a change in social status despite the expression of aggressive behavior; and non-interacting fish, which were used as a reference group. Our results show that each social phenotype (i.e., Winners, Losers, and Mirror-fighters) present specific patterns of gene expression across the SDMN, and that different neuroplasticity genes are differentially expressed in different nodes of the network (e.g., BDNF in the dorsolateral telencephalon, which is a putative teleost homolog of the mammalian hippocampus). Winners expressed unique patterns of gene co-expression across the SDMN, whereas in Losers and Mirror-fighters the co-expression patterns were similar in the dorsal regions of the telencephalon and in the supracommissural nucleus of the ventral telencephalic area, but differents in the remaining regions of the ventral telencephalon. These results indicate that social plasticity relies on multiple neuroplasticity mechanisms across the SDMN, and that there is not a single neuromolecular module underlying this type of behavioral flexibility.

Diagnosis and Treatment of Anxiety in the Aging Woman

The peri- and postmenopausal periods represent a window of vulnerability for emergence of anxiety symptoms and disorders in the life cycle of adult women. Compared to depression, anxiety symptoms and disorders remain largely unexplored during this phase of a woman's life, despite the significant impact on quality of life if not diagnosed and treated. Here, we review the literature to present our current understanding of the epidemiology, causal factors, diagnosis, and treatment of anxiety in the aging woman.

Ovarian hormone fluctuation, neurosteroids, and HPA axis dysregulation in perimenopausal depression: a novel heuristic model

OBJECTIVE

In this conceptual review, the authors propose a novel mechanistic candidate in the etiology of depression with onset in the menopause transition ("perimenopausal depression") involving alterations in stress-responsive pathways, induced by ovarian hormone fluctuation.

METHOD

The relevant literature in perimenopausal depression, including prevalence, predictors, and treatment with estrogen therapy, was reviewed. Subsequently, the growing evidence from animal models and clinical research in other reproductive mood disorders was synthesized to describe a heuristic model of perimenopausal depression development.

RESULTS

The rate of major depressive disorder and clinically meaningful elevations in depressive symptoms increases two- to threefold during the menopause transition. While the mechanisms by which ovarian hormone fluctuation might impact mood are poorly understood, growing evidence from basic and clinical research suggests that fluctuations in ovarian hormones and derived neurosteroids result in alterations in regulation of the HPA axis by γ-aminobutyric acid (GABA). The authors' heuristic model suggests that for some women, failure of the GABAA receptor to regulate overall GABA-ergic tone in the face of shifting levels of these neurosteroids may induce HPA axis dysfunction, thereby increasing sensitivity to stress and generating greater vulnerability to depression.

CONCLUSIONS

The proposed model provides a basis for understanding the mechanisms by which the changing hormonal environment of the menopause transition may interact with the psychosocial environment of midlife to contribute to perimenopausal depression risk. Future research investigating this model may inform the development of novel pharmacological treatments for perimenopausal depression and related disorders, such as postpartum depression and premenstrual dysphoric disorder.

Multifunctional aspects of allopregnanolone in stress and related disorders

Allopregnanolone (3α-hydroxy-5α-pregnan-20-one) is a major cholesterol-derived neurosteroid in the central nervous system and is synthesized from progesterone by steroidogenic enzymes, 5α-reductase (the rate-limiting enzyme) and 3α-hydroxysteroid dehydrogenase. The pathophysiological role of allopregnanolone in neuropsychiatric disorders has been highlighted in several investigations. The changes in neuroactive steroid levels are detected in stress and stress-related disorders including anxiety, panic and depression. The changes in allopregnanolone in response to acute stressor tend to restore the homeostasis by dampening the hyper-activated HPA axis. However, long standing stressors leading to development of neuropsychiatric disorders including depression and anxiety are associated with decrease in the allopregnanolone levels. GABAA receptor complex has been considered as the primary target of allopregnanolone and majority of its inhibitory actions are mediated through GABA potentiation or direct activation of GABA currents. The role of progesterone receptors in producing the late actions of allopregnanolone particularly in lordosis facilitation has also been described. Moreover, recent studies have also described the involvement of other multiple targets including brain-derived neurotrophic factor (BDNF), glutamate, dopamine, opioids, oxytocin, and calcium channels. The present review discusses the various aspects of allopregnanolone in stress and stress-related disorders including anxiety, depression and panic.

Single unit activity in the lateral septum and central nucleus of the amygdala in the elevated plus-maze: a model of exposure therapy?

The central nucleus of the amygdala (CeA) is a major output region of the amygdala involved in organizing the expression of fear. There is also evidence that the lateral septum (LS) provides inhibitory control of neurons in CeA and is involved in the relief of fear. This study examined single unit activity in the lateral septum (LS) and the central nucleus of the amygdala (CeA) in the open and closed arms of the elevated plus-maze, a highly validated animal model of fear and anxiety. The general presumption is that animals normally avoid the open arms because the open arms are relatively more anxiety provoking than the closed arms which represent relative safety. It was expected that neurons in CeA would increase their activity in the open arms relative to the closed arms indicative of increased anxiety and that LS neurons would decrease their activity on the open arms. Contrary to expectations it was found that the preponderance of units in CeA decreased their firing rates on the open arms compared to the closed arms. An increase in firing rates in LS was seen in the open arms compared to the closed arms. The data suggest that when animals are placed on the open arms a compensatory process takes place to suppress fear so that the animal can engage in adaptive behavior. We liken this process to that which takes place in exposure therapy for phobias in humans which involves the inhibition of fear resulting from Pavlovian extinction.

The aqueous crude extract of Montanoa frutescens produces anxiolytic-like effects similarly to diazepam in Wistar rats: involvement of GABAA receptor

ETHNOPHARMACOLOGICAL RELEVANCE

Cihuapatli is the Nahuatl name assigned to some medicinal plants grouped in the genus Montanoa, where Montanoa frutescens (Family: Asteraceae, Tribe: Heliantheae) is included. The crude extract from these plants has been used for centuries in the Mexican traditional medicine as a remedy for reproductive impairments and mood disorders. Experimental studies have systematically corroborated the traditional use of cihuapatli on reproductive impairments and sexual motivation, however, the effect on mood and "nervous" disorders, remains to be explored.

MATERIALS AND METHODS

The anxiolytic-like effect of aqueous crude extract of M. frutescens (25, 50 and 75 mg/kg) was investigated in male Wistar rats evaluated in the elevated plus-maze and compared with several doses of diazepam (1, 2 and 4 mg/kg) as a reference anxiolytic drug. Picrotoxin (1 mg/kg), a noncompetitive antagonist of the GABA(A) receptor, was used in experimental procedures to evaluate if this receptor could be involved in the anxiolytic-like effects produced by M. frutescens. To discard hypoactivity, hyperactivity, or no changes associated with treatments, which could interfere with the behavioral activity in the elevated plus-maze, rats were subjected to the open field test.

RESULTS

M. frutescens at 50 mg/kg showed anxiolytic-like activity similarly to 2 mg/kg of diazepam, without disrupts in general motor activity. The anxiolytic-like effect of M. frutescens detected in the elevated plus-maze was blocked by picrotoxin, indicating that GABA(A) receptors are involved in the modulation of this effect.

CONCLUSIONS

The results corroborate the use of M. frutescens in folk Mexican ethnomedicine as a potential anxiolytic agent and suggest that this effect is mediated by the GABA(A) receptors. Additionally, some sedative effects with high doses of M. frutescens were detected in the present study.

Long-term ovariectomy modulates the antidepressant-like action of estrogens, but not of antidepressants

Controversial results related to effectiveness of estrogen replacement therapy (ERT) to alleviate depression are frequently reported. The discrepancies could be related to (a) time when ERT is initiated after the beginning of menopause and/or (b) type of estrogen used. Furthermore, estrogens modulate the antidepressant effect of different compounds; therefore, the effectiveness of antidepressant drugs could also depend on the menopausal status. The aim of the present study was to analyze whether the time after estrogen decline can influence antidepressant-like effects of two estrogens and/or two antidepressants. Thus, the antidepressant-like actions of 17β-estradiol (E(2)), 17α-ethynyl-estradiol (EE(2)), fluoxetine (FLX) and desipramine (DMI) were studied at different periods (1, 3 and 12 weeks) after ovariectomy (OVX), using the forced swimming test (FST). Results showed that OVX increased depressive-like behavior only 1 week after OVX. The antidepressant-like actions of E(2), but not those of EE(2), were cancelled 12 weeks after OVX. Conversely, antidepressant-like actions of FLX and DMI were observed at 1, 3 and 12 weeks after OVX. In conclusion, while the antidepressant-like effects of estrogens depended on the time at which treatment is initiated after OVX as well as on the estrogenic compound used, antidepressant-like effects of FLX and DMI were not blocked by OVX.

Progesterone attenuates depressive behavior of younger and older adult C57/BL6, wildtype, and progesterone receptor knockout mice

Progesterone may have actions independent of intracellular progestin receptors (PRs) to influence depressive behavior. To investigate this, we examined effects of progesterone (P; 10mg/kg, SC) on the depressive behavior of mice in the forced swim test (FST). In Experiment 1, subjects were 4 to 6 months old, intact or ovariectomized (OVX) female and intact or gonadectomized (GDX) male, C57/BL6 mice. Progesterone reduced depressive behavior of young diestrous and OVX mice but male mice were impervious to effects of P. In Experiment 2, subjects were intact aged (20-28 months old) C57/BL6 female and male mice. Progesterone reduced depressive behavior of aged female and male C57/BL6 mice, albeit effects were greater among males. In Experiment 3, effects of P were examined in 4 to 6 months old, gonadally-intact, female and male mice that were wildtype or PR knockouts (PRKOs). Progesterone decreased depressive behavior of young adult, wildtype and PRKO mice, which showed greater immobility than did their wildtype counterparts. In Experiment 4, subjects were 18-24 months old wildtype or PRKO mice (Exp 4). Progesterone decreased immobility among wildtype and PRKO mice (which were not different in terms of their baseline depressive behavior). Together these data demonstrate that P decreases depressive behavior of young and older adult C57/BL6, wildtype and PRKO mice, which suggest that acute anti-depressant effects of P may occur independent of actions at "classic" PRs.

Antidepressant-like effects of mineralocorticoid but not glucocorticoid antagonists in the lateral septum: interactions with the serotonergic system

The lateral septum (LS) is a limbic brain region that receives serotonergic projections from raphe neurons and participates in the modulation of stress responses and affective states. The present study determined whether mineralocorticoid receptors (MRs) and/or glucocorticoid receptors (GRs) located in the LS interact with the serotonergic system in the regulation of depressive-like behavior of rats subjected to the forced swimming test (FST). We also studied the effect of corticosterone release induced by the FST on MR- and GR-mRNA expression in the LS. Specifically, we studied the antidepressant-like effects of spironolactone (a MR antagonist), mifepristone (a GR antagonist), and the antidepressant clomipramine (CMI) administered directly into the LS. In addition, spironolactone and CMI actions were studied in animals with serotonergic depletion induced by dl-p-chlorophenylalanine (pCPA). Finally, adrenalectomized and Sham-operated rats were subjected to the FST to determine MR- and GR-mRNA expression in the LS at different post-FST intervals. The results showed that intraseptal injection of spironolactone, but not mifepristone induced antidepressant-like actions in the FST; this effect was blocked by pCPA treatment. CMI and spironolactone increased 5-HT concentrations in the LS of rats subjected to the FST. Increases in corticosterone release, induced by the FST, correlated with a decrease in MR-mRNA expression in the LS; no correlation was found with GR-mRNA expression. In conclusion, MRs in the lateral septum, but not GRs, participate in the regulation of depressive-like behavior of animals subjected to the FST. Both serotonin and corticosterone play an important role in MR actions in the LS.

Progesterone reduces depressive behavior of young ovariectomized, aged progestin receptor knockout, and aged wild type mice in the tail suspension test

Progestins may have effects to reduce depressive behavior, in part through actions of its metabolite, 5α-pregnan-3α-ol-20-one (3α,5α-THP) at GABA(A) receptors, rather than through intracellular progestin receptors. In this study, we examined the effects of progesterone (10 mg/kg, subcutaneous injection) versus vehicle control (propylene glycol) on the depressive behavior of young and aged mice in the tail suspension test. In Experiment 1, we first characterized progesterone's anti-depressant effects by utilizing young (4-6-month-old) intact or ovariectomized female, and intact or gonadectomized male, C57BL/6 mice. Young female mice showed more depressive behavior than the young male mice. Compared with vehicle administration, progesterone reduced depressive behavior of ovariectomized female, but not male or intact female mice. In Experiment 2, mice were aged (20-24-month-old) intact wild type or progestin receptor knockout mice. Progestin receptor knockout mice showed less depressive behavior than wild type mice. Administration of progesterone to wild type and progestin receptor knockout mice reduced depressive behavior. Together, these data suggest that progesterone can decrease depressive behavior of young adult ovariectomized female, aged wild type and progestin receptor knockout mice. Thus, progesterone's effect to reduce depressive behavior of aged mice may not require actions at the intracellular progestin receptors.

Beyond the HPA Axis: Progesterone-Derived Neuroactive Steroids in Human Stress and Emotion

Stress and social isolation are well-known risk factors for psychopathology. However, more research is needed as to the physiological mechanisms by which social support buffers the impacts of stress. Research in animal models suggests important roles for progesterone (P) and its product, the neuroactive steroid allopregnanolone (ALLO), in stress and psychopathology. These hormones are produced in brain and periphery during stress in rodents, and down-regulate anxiety behavior and hypothalamic-pituitary-adrenal axis activity. Human clinical populations, including depressed patients, have alterations in ALLO levels, but it is unclear whether these basal hormone level differences have clinical import. To begin to address this question, this review examines the role of P and ALLO in stress physiology, and the impact of these hormones on mood, in healthy humans. Evidence largely supports that P and ALLO increase during stress in humans. However, P/ALLO administration appears to cause only mild effects on mood and subjective anxiety, while exerting effects consistent with gamma-aminobutyric acid receptor modulation. Additionally, P is linked to motivation for affiliation/social contact; P (and ALLO) release may be especially responsive to social rejection. These observations lead to the novel hypothesis that stress-related P/ALLO production functions not only to down-regulate stress and anxiety, but also to promote social contact as a long-term coping strategy. Malfunctioning of the P/ALLO system could therefore underlie depression partly by decreasing propensity to affiliate with others.

Chronic creatine supplementation alters depression-like behavior in rodents in a sex-dependent manner

Impairments in bioenergetic function, cellular resiliency, and structural plasticity are associated with the pathogenesis of mood disorders. Preliminary evidence suggests that creatine, an ergogenic compound known to promote cell survival and influence the production and usage of energy in the brain, can improve mood in treatment-resistant patients. This study examined the effects of chronic creatine supplementation using the forced swim test (FST), an animal model selectively sensitive to antidepressants with clinical efficacy in human beings. Thirty male (experiment 1) and 36 female (experiment 2) Sprague-Dawley rats were maintained on either chow alone or chow blended with either 2% w/w creatine monohydrate or 4% w/w creatine monohydrate for 5 weeks before the FST. Open field exploration and wire suspension tests were used to rule out general psychostimulant effects. Male rats maintained on 4% creatine displayed increased immobility in the FST as compared with controls with no differences by diet in the open field test, whereas female rats maintained on 4% creatine displayed decreased immobility in the FST and less anxiety in the open field test compared with controls. Open field and wire suspension tests confirmed that creatine supplementation did not produce differences in physical ability or motor function. The present findings suggest that creatine supplementation alters depression-like behavior in the FST in a sex-dependent manner in rodents, with female rats displaying an antidepressant-like response. Although the mechanisms of action are unclear, sex differences in creatine metabolism and the hormonal milieu are likely involved.

Acute restraint stress produces behavioral despair in weanling rats in the forced swim test

Stressful experiences in the rat during early life increase the vulnerability to later signs of behavioral despair in adulthood, reflected in increased immobility in the forced swim test (FST). However, the possible immediate effects of stress in weanling rats have only been partially described. The present study tested whether a single session of mild restraint stress modifies immobility in the FST in 21-day-old Wistar rats. After evaluating any possible changes in locomotion using the open field test (OFT), the latency and total duration of immobility were assessed in a single FST session. Regardless of gender, mild restraint stress significantly reduced crossings in the OFT, shortened the latency to the first period of immobility, and increased immobility in the FST compared with a control group devoid of stress. We conclude that a single mild physical stress session, as early as postnatal day 21, produces signs of behavioral despair.

Toluene has antidepressant-like actions in two animal models used for the screening of antidepressant drugs

RATIONALE

Many abused solvents share a profile of effects with classical antidepressants. For example, toluene, which is a representative and widely abused solvent, has been reported to increase both serotonin and noradrenaline levels in several brain areas after an acute exposure and to act as a noncompetitive antagonist of the glutamatergic N-methyl-D-aspartic acid (NMDA) receptor subtype. Therefore, it is possible that toluene could possess antidepressant-like actions.

OBJECTIVE

To provide an initial screening of toluene's antidepressant-like actions in the forced swimming test (FST) and the tail suspension test (TST) in mice and to analyze its possible mechanism of action.

MATERIALS AND METHODS

Two series of experiments were performed. In the first one, male animals were exposed to toluene (0, 500, 1,000, 2,000, or 4,000 ppm) in a static exposure chamber for 30 min, and immediately after, evaluated for antidepressant-like effects. The results were compared with those obtained from mice treated with the serotonergic antidepressant clomipramine (CMI), the noradrenergic antidepressant desipramine (DMI), and the glutamatergic antidepressants, ketamine and MK-801. In the second part, we analyzed the effect of a combined administration of a subeffective concentration of toluene with a suboptimal dose of the various antidepressants acting at different neurotransmitter systems.

RESULTS

Toluene produced a concentration-dependent antidepressant-like action in the FST and TST and facilitated both MK-801 and ketamine antidepressant-like effects, but not those of DMI or CMI.

CONCLUSIONS

Toluene has antidepressant-like effects that are synergized with NMDA receptor antagonists.

Progesterone reduces depression-like behavior in a murine model of Alzheimer's Disease

Although anxiety and depression are not the core symptoms of Alzheimer's Disease (AD), there are changes observed in mood in those with AD, as well as in the aging population. Anxiety and depression may be influenced by progesterone P(4) and/or its neuroactive metabolites, dihydroprogesterone (DHP) and 5 alpha-pregnan-3 alpha-ol-20-one (3 alpha,5 alpha-THP). To begin to investigate progestogens' role in AD, a double transgenic mouse model of early-onset familial AD that co-overexpresses mutant forms of amyloid precursor protein (APPswe) and presenilin 1 Delta exon 9 mutation was utilized. As such, the effects of long-term (from 6 to 12 months of age) administration of P(4) to ovariectomized (ovx) wildtype and APPswe+PSEN1 Delta e9 mice for changes in affective behavior was investigated. APPswe+PSEN1 Delta 9 mutant mice had increased anxiety-like (i.e., increased emergence latencies, decreased time spent on the open quadrants of the elevated zero maze) and increased depressive-like behavior (i.e., increased time spent immobile) than did wildtype mice. Compared to vehicle-administration, P(4) administration (which produced physiological circulating P(4), DHP, and 3 alpha,5 alpha-THP levels, particularly in the wildtype mice) decreased depressant-like behavior in the forced swim test. These effects occurred independent of changes in general motor behavior/coordination, pain threshold, and plasma corticosterone levels. Thus, the APPswe+PSEN1 Delta 9 mutation alters affective behavior, and P(4) treatment reversed depressive-like behavior.

Antidepressant effect and changes of GABAA receptor gamma2 subunit mRNA after hippocampal administration of allopregnanolone in rats

The present study aimed to verify the effect of bilateral intra-hippocampus administration of the neurosteroid allopregnanolone (3alpha-hydroxy-5alpha-pregnan-20-one; 3alpha, 5alpha-THP) in the forced swimming test (FST) and in the alpha4 and gamma2 GABA(A) receptor subunits gene expression. Results showed that bilateral intra-hippocampal allopregnanolone administration of 2.5 microg/rat ( P<0.05) reduced immobile behavior and increased climbing behavior in the FST. Overall, for all doses of allopregnanolone tested (1.25, 2.5, 5.0 microg/rat), an increase of gamma2 (P<0.05) GABA(A) subunit mRNA was observed. There was a higher increase in the gamma2 gene expression in the right hemisphere than in the left hemisphere (P<0.01) after allopregnanolone treatment. Intra-hippocampal allopregnanolone did not change the expression of the alpha4 subunits. In conclusion, intra-hippocampal administration of allopregnanolone produces an antidepressant-like effect in the FST at an intermediate dose, confirming the potential of neurosteroids as a new class of antidepressant drugs. Our findings suggest that the gamma2, but not the alpha4 GABA(A) subunit, needs further evaluation to be involved in the antidepressant effect of allopregnanolone in the hippocampus and that there is a hemispheric diversity in the biochemical effect of the drug.

Inhibition of progesterone metabolism mimics the effect of progesterone withdrawal on forced swim test immobility

Withdrawal from high levels of progesterone in rodents has been proposed as a model for premenstrual syndrome or postpartum depression. Forced swim test (FST) immobility, used to model depression, was assessed in intact female DBA/2J mice following progesterone withdrawal (PWD) or treatment with the 5alpha-reductase inhibitor finasteride. Following 5 daily progesterone injections (5 mg/kg IP) FST immobility increased only in mice withdrawn for 3 days (p<.05). In another experiment, 3 days of PWD significantly decreased levels of progesterone compared to 0 days of withdrawal, but progesterone levels at 3 days of PWD did not differ from vehicle-treated controls. In a final study, mice received daily injections of progesterone (5 mg/kg IP) for 8 days, with 0 mg/kg, 50 mg/kg, or 100 mg/kg finasteride co-administered for the last three days. Mice that received 100 mg/kg finasteride, but not 50 mg/kg finasteride, displayed increased FST immobility. PWD and finasteride treatment, both of which reduce allopregnanolone levels, were associated with increased FST immobility in female DBA/2J mice. These findings suggest that decreased levels of the GABAergic neurosteroid allopregnanolone contribute to symptoms of PWD. Future studies of PWD may provide information about human conditions that are associated with hormone changes such as premenstrual syndrome or postpartum depression.