Estrous cycle variation in anxiolytic-like effects of topiramate in Wistar rats in two animal models of anxiety-like behavior

Reproductive experience alters the effects of diazepam and fluoxetine on anxiety-like behaviour, fear extinction, and corticosterone levels in female rats

OVERVIEW

Reproductive experience (pregnancy and motherhood) leads to long-term changes in the neurobiological and hormonal features of anxiety in rats and humans. The aim of this study was to examine whether reproductive experience alters the effects of two pharmacological treatments for anxiety, a benzodiazepine (diazepam) and a selective serotonin reuptake inhibitor (fluoxetine), on animal models of anxiety.

METHODS

In Experiment 1, virgin (n = 47) and age-matched mother (n = 50) rats at 1-month post-weaning were injected with diazepam (1.3 mg/kg or 1.7 mg/kg, i.p.) or vehicle, in the proestrus (high estradiol/progesterone/allopregnanolone) or metestrus (low estradiol/progesterone/allopregnanolone) phase of the estrous cycle 30 min prior to the elevated plus maze (EPM). In Experiment 2, virgin (n = 25) and mother rats (n = 20) were administered fluoxetine (10 mg/kg) or vehicle for 2 weeks prior to being tested on a Pavlovian fear conditioning and extinction protocol, and the EPM.

RESULTS

Replicating past research, in virgin rats, the low dose of diazepam produced anxiolytic-like effects in proestrus, but only the high dose was anxiolytic-like in metestrus. In contrast, in mother rats, both doses of diazepam were anxiolytic-like irrespective of estrous phase. Fluoxetine produced anxiogenic-like effects in virgin rats during fear extinction and the EPM, but had no behavioural effects in mothers. In contrast, fluoxetine increased plasma corticosterone levels measured 30-min post-EPM in mothers, but not virgin rats.

CONCLUSIONS

Reproductive experience alters the dose responsivity and efficacy of common anti-anxiety medications in female rats. These findings highlight the importance of considering reproductive status in studies on anxiety and its treatment.

The anticonvulsant effect of chronic treatment with topiramate after pilocarpine-induced status epilepticus is accompanied by a suppression of comorbid behavioral impairments and robust neuroprotection in limbic regions in rats

Epilepsy is a widespread neurological disorder frequently associated with a lot of comorbidities. The present study aimed to evaluate the effects of the antiseizure medication topiramate (TPM) on spontaneous motor seizures, the pathogenesis of comorbid mood and cognitive impairments, hippocampal neuronal loss, and oxidative stress and inflammation in a rat model of temporal lobe epilepsy (TLE). Vehicle/TPM treatment (80 mg/kg, p.o.) was administered 3 h after the pilocarpine (pilo)-induced status epilepticus (SE) and continued for up to 12 weeks in Wistar rats. The chronic TPM treatment caused side effects in naïve rats, including memory disturbance, anxiety, and depressive-like responses. However, the anticonvulsant effect of this drug, administered during epileptogenesis, was accompanied by beneficial activity against comorbid behavioral impairments. The drug treatment suppressed the SE-induced neuronal damage in limbic structures, including the dorsal (CA1 and CA2 subfield), the ventral (CA1, CA2 and CA3) hippocampus, the basolateral amygdala, and the piriform cortex, while was ineffective against the surge in the oxidative stress and inflammation. Our results suggest that neuroprotection is an essential mechanism of TPM against spontaneous generalized seizures and concomitant emotional and cognitive impairments.

What Pre-clinical Rat Models Can Tell Us About Anxiety Across the Menstrual Cycle in Healthy and Clinically Anxious Humans

PURPOSE OF REVIEW

Anxiety symptoms increase during the peri-menstrual phase of the menstrual cycle in people with anxiety disorders. Whether this reflects a heightened variant of normal menstrual-related changes in psychological states experienced by healthy (i.e. non-anxious) people is unknown. Moreover, menstrual-related change in anxiety symptoms is a poorly understood phenomenon, highlighting a need for pre-clinical models to aid mechanistic discovery. Here, we review recent evidence for menstrual effects on anxiety-like features in healthy humans as a counterpart to recent reviews that have focused on clinically anxious populations. We appraise the utility of rodent models to identify mechanisms of menstrual effects on anxiety and offer suggestions to harmonise methodological practices across species to advance knowledge in this field.

RECENT FINDINGS

Consistent with reports in clinical populations, some evidence indicates anxiety symptoms increase during the peri-menstrual period in healthy people, although null results have been reported, and these effects are heterogeneous across studies and individuals. Studies in rats show robust increases in anxiety during analogous phases of the oestrous cycle. Studies in female rats are useful to identify the evolutionarily conserved biological mechanisms of menstrual-related changes in anxiety. Future experimental approaches in rats should model the heterogeneity observed in human studies to increase alignment across species and advance understanding of the individual factors that increase the propensity to experience menstrual-related changes in anxiety.

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

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

Effects of new antiseizure drugs on seizure activity and anxiety-like behavior in adult zebrafish

Several studies with larvae and adult zebrafish have shown that old and new antiseizure drugs (ASDs) produce discrepant results in seizure tests, locomotor activity or anxiety models. In this study, the pentylenetetrazole seizure test (PTZ) was performed to assess the effectiveness of four new ASDs: lamotrigine (LTG), topiramate (TPM), felbamate (FBM), and levetiracetam (LEV) in the subsequent stages of seizures in adult fish. All ASDs were administered intraperitoneally (i.p.). The time of maximal anticonvulsant effect and the dose-response relationship of the drugs were assessed. The effects of studied ASDs on the locomotor activity and the anxiety-like behavior in the color preference test were also investigated. Furthermore, drug concentrations in zebrafish homogenates were determined. LTG, TPM, and LEV significantly increased the seizure latency at three subsequent stages of seizures (SI-SIII), while FBM was effective only at SI. Locomotor activity decreased after TPM treatment. TPM and FBM exhibited a strong anxiolytic-like effect in the color preference test. LEV at the highest dose tested had a weak anxiolytic-like effect. The HPLC analysis showed average concentrations of the studied ASDs in the fish body during their maximum anticonvulsant activity. The present study shows that FBM cannot inhibit all subsequent PTZ seizure stages in the adult fish. Except for LTG, the studied drugs affected the anxiety-like behavior of treated animals. Furthermore, only TPM significantly changed locomotion parameters. Our findings support the need to accurately characterize the efficacy of new ASDs at different stages of the PTZ-induced seizures in adult zebrafish.

Topiramate inhibits offensive aggression through targeting ventrolateral periaqueductal gray

Topiramate is an approved antiepileptic drug clinically used to treat epilepsy and prevent migraines. Currently, topiramate has been found to be effective in treating aggressive symptoms in neuropsychiatric patients. In preclinical studies, however, the effects and mechanisms of topiramate on offensive aggression are still largely uninvestigated. Our previous studies indicated that glutamatergic transmission in the ventrolateral periaqueductal gray (vlPAG) plays a crucial role in regulating elements of offensive aggressive behaviors. In the present work, we investigated the actions of topiramate on vlPAG glutamatergic transmission and aggressive behaviors in group-housed (GH) and socially isolated (SI) rats. The results suggested that a single injection of topiramate systemically and dose-dependently inhibited elements of offensive aggressive behaviors of both GH and SI rats in the resident-intruder test (RIT), with long-lasting effective time profiles in SI rats. Moreover, systemic single administration of topiramate reduced the frequency and amplitude of miniature excitatory postsynaptic currents (mEPSCs) in the vlPAG. Bath perfusion of topiramate directly decreased the frequency and amplitude of mEPSCs and shortened the amplitude of evoked excitatory postsynaptic currents (EPSCs) in the vlPAG. Furthermore, intra-vlPAG single microinjection of topiramate dose-dependently inhibited offensive aggressive behaviors in GH and SI rats in a time-dependent manner. Additionally, both systemic and local topiramate inhibited offensive aggressive behaviors in a (2R,6R)-hydroxynorketamine (HNK)-dependent rat model. In conclusion, the present results suggest that topiramate exerts anti-aggressive roles through its inhibitory actions on glutamatergic activities in the vlPAG. These preclinical results support topiramate as a candidate drug to treat patients with heightened offensive aggression.

Chrysin reduces anxiety-like behavior through actions on GABAA receptors during metestrus-diestrus in the rat

Low concentrations of ovarian hormones, among other factors, are associated with greater vulnerability to negative effects of environmental stressors and may trigger anxiety symptoms in females. The flavonoid chrysin (5,7-dihydroxyflavone) exerts anxiolytic-like effects in male and ovariectomized female rats, but it is unknown if chrysin could reduce anxiety-like behavior that naturally occurs through the ovarian cycle phases. The present study evaluated the effect of chrysin on anxiety-like behavior associated with the ovarian cycle phases in rats and the participation of γ-aminobutyric acid-A (GABA_A) receptors in these actions. The acute effects of chrysin (2 mg/kg) were investigated in female cycling Wistar rats in the elevated plus maze, locomotor activity test, and light/dark test. Diazepam (2 mg/kg) was used as reference anxiolytic drug. The participation of GABA_A receptor in the anxiolytic actions of chrysin was explored by pretreating the rats with the noncompetitive GABA_A chloride ion channel antagonist picrotoxin (1 mg/kg). Chrysin and diazepam prevented anxiety-like behavior that was associated with the metestrus-diestrus phase in both the elevated plus maze and light/dark test, and these effects were reversed by picrotoxin, with no significant changes in spontaneous locomotor activity. No significant motor effects of chrysin were detected in either behavioral test during proestrus-estrus or metestrus-diestrus phases, whereas diazepam produced motor hypoactivity in the locomotor activity test during proestrus-estrus phase. These results indicate that the flavonoid chrysin prevents anxiety-like behavior that naturally occurs during metestrus-diestrus in two unconditioned models that are used to evaluate anxiety-like behavior, and these effects were mediated by actions on GABA_A receptors.

Anxiolytic- and anxiogenic-like effects of Montanoa tomentosa (Asteraceae): Dependence on the endocrine condition

ETHNOPHARMACOLOGICAL RELEVANCE

Montanoa tomentosa Cerv. (MT) is a native plant from Mexico used in traditional medicine as a remedy for reproductive impairments and relaxing effects. In previous studies, it has been shown that the endocrine state could modify the antianxiety-like actions of anxiolytic compounds. Although women are the primary user of MT, no studies have evaluated the potential impact of the endocrine milieu on its anti-anxiety actions.

AIMS OF THE STUDY

Ascertain the antianxiety effects of M. tomentosa in rats with different hormonal conditions, and to analyze the participation of the GABA_A receptor in ovariectomized rats treated with MT.

MATERIALS AND METHODS

The animal model of anxiety used was the elevated plus-maze (EPM). Rats' endocrine conditions were: a) Low hormone levels (rats in diestrus I and II phases); b) High hormone levels (proestrus/estrus phases); c) No hormones (ovariectomized rats); and d) Rats under progesterone withdrawal (PW). To evaluate the participation of the GABA_A receptor in the anxiolytic-like action of MT the antagonist picrotoxin was used.

RESULTS

Results showed that MT induced dose-dependent anxiolytic-like actions in rats with low hormone level conditions. Also, MT reduced anxiety-like behavior in female rats under PW, in contrast to diazepam which was ineffective. MT's anxiolytic-like effect was blocked by picrotoxin, suggesting the participation of the GABA_A receptor complex. However, increased anxiety-like behavior was observed in rats with a high hormone level condition and low doses of MT.

CONCLUSIONS

Beneficial anxiolytic-like actions of MT are observed under low hormone conditions, particularly in the PW challenge (a condition that can be related to a premenstrual period). Furthermore, the participation of the GABA_A receptor is evidenced. However, hormonal variations could induce the opposite effects, hence women should be cautious.

Possible involvement of CREB/BDNF signaling pathway in neuroprotective effects of topiramate against methylphenidate induced apoptosis, oxidative stress and inflammation in isolated hippocampus of rats: Molecular, biochemical and histological evidences

Chronic abuse of methylphenidate (MPH) can cause serious neurotoxicity. The neuroprotective effects of topiramate (TPM) were approved, but its putative mechanism remains unclear. In current study the role of CREB/BDNF signaling pathway in TPM protection against methylphenidate-induced neurotoxicity in rat hippocampus was evaluated. 60 adult male rats were divided randomly into six groups. Groups received MPH (10mg/kg) only and concurrently with TPM (50mg/kg and 100mg/kg) and TPM (50 and 100mg/kg) only for 14 days. Open field test (OFT) was used to investigate motor activity. Some biomarkers of apoptotic, anti-apoptotic, oxidative, antioxidant and inflammatory factors were also measured in hippocampus. Expression of total (inactive) and phosphorylated (active) CREB and BDNF were also measured in gene and protein levels in dentate gyrus (DG) and CA1 areas of hippocampus. MPH caused significant decreases in motor activity in OFT while TPM (50 and 100mg/kg) inhibited MPH-induced decreases in motor activity. On the other hand, MPH caused remarkable increases in Bax protein level, lipid peroxidation, catalase activity, IL-1β and TNF-α levels in hippocampal tissue. MPH also caused significant decreases of superoxide dismutase, activity and also decreased CREB, in both forms, BDNF and Bcl-2 protein levels. TPM, by the mentioned doses, attenuated these effects and increased superoxide dismutase, glutathione peroxidase and glutathione reductase activities and also increased CREB, in both forms, BDNF and Bcl-2 protein levels and inhibited MPH induced increase in Bax protein level, lipid peroxidation, catalase activity, IL-1β and TNF-α levels. TPM also inhibited MPH induced decreases in cell number and changes in cell shapes in DG and CA1 areas. TPM can probably act as a neuroprotective agent against MPH induced neurotoxicity and this might have been mediated by CREB/BDNF signaling pathway.

Sex and estrous cycle influence diazepam effects on anxiety and memory: Possible role of progesterone

Studies with rodents and humans show the relationship between female sex hormones and cognitive/emotional tasks. However, despite the greater incidence of anxiety disorders in women, the data are still inconclusive regarding the mechanisms related to this phenomenon. We evaluated the effects of a classical anxiolytic/amnestic drug (diazepam; DZP) on female (at different estrous cycle phases) and male rats tested in the plus-maze discriminative avoidance task (PMDAT), that allows the concomitant evaluation of memory and anxiety-like behavior. Further, in order to investigate the role of progesterone and its metabolites in the effects of DZP in the PMDAT, female rats were pre-treated with the progesterone receptor antagonist mifepristone or the 5-alpha-reductase inhibitor finasteride. The main findings were: (1) DZP caused memory impairment and anxiolysis in both sexes, but only the highest dose induced the anxiolytic effect in females; (2) females in proestrus did not present the amnestic and anxiolytic effects of DZP (at 2.0 and 4.0mg/kg, respectively) and (3) the co-administration of mifepristone reestablished both amnestic and anxiolytic effects of DZP, while finasteride reinstated the amnestic effect in proestrus female rats. These results suggest that changes in the endogenous levels of progesterone and its metabolites are important in the modulation of emotional/cognitive behavior in female rats. Based on the influence on different aspects of DZP action, the mechanisms related to this modulation are probably linked to GABAergic transmission, but this point remains to be investigated. Further, the variation in therapeutic and adverse effects of DZP depending on sex and hormonal state is of great relevance considering the higher prevalence of anxiety disorders in women.

Short term, low dose fluoxetine blocks estrous cycle-linked changes in responsiveness to diazepam in female rats

Anxiety behavior in female Wistar rats was assessed at different stages of the estrous cycle using the elevated plus maze (EPM). No differences were observed at any cycle stage. Pretreatment with diazepam (1 mg kg(-1) intraperitoneal (i.p.)) 30 min before testing produced an anxiolytic effect (significant increase in percentage of time in the open arms compared to control group in the same cycle phase) in animals in proestrus, estrus, and early diestrus but had no effect in rats in late diestrus. Locomotor activity (total arm entries) was unchanged at any cycle phase. When rats in the late diestrus phase were pretreated with the selective serotonin reuptake inhibitor fluoxetine (1.75 mg kg(-1) i.p. on the afternoon of early diestrus and again in the morning of late diestrus) diazepam produced an anxiolytic effect (increase percentage time in the open arms). This dose is sufficient to raise brain allopregnanolone concentration without affecting 5-hydroxytryptamine (5-HT) systems. We propose that insensitivity to diazepam in late diestrus is due to increased expression of benzodiazepine insensitive α4 subunit-containing gamma-aminobutyric acid A (GABAA) receptors triggered by a sharp decrease in brain allopregnanolone concentration. Pretreatment with fluoxetine to raise brain allopregnanolone concentration during late diestrus prevents the withdrawal effect.

Gender Differences in the Neurobiology of Anxiety: Focus on Adult Hippocampal Neurogenesis

Although the literature reports a higher incidence of anxiety disorders in women, the majority of basic research has focused on male rodents, thus resulting in a lack of knowledge on the neurobiology of anxiety in females. Bridging this gap is crucial for the design of effective translational interventions in women. One of the key brain mechanisms likely to regulate anxious behavior is adult hippocampal neurogenesis (AHN). This review paper aims to discuss the evidence on the differences between male and female rodents with regard to anxiety-related behavior and physiology, with a special focus on AHN. The differences between male and female physiologies are greatly influenced by hormonal differences. Gonadal hormones and their fluctuations during the estrous cycle have often been identified as agents responsible for sexual dimorphism in behavior and AHN. During sexual maturity, hormone levels fluctuate cyclically in females more than in males, increasing the stress response and the susceptibility to anxiety. It is therefore of great importance that future research investigates anxiety and other neurophysiological aspects in the female model, so that results can be more accurately applicable to the female population.