The use of the elevated plus maze as an assay of anxiety-related behavior in rodents

Chronic gestational stress leads to depressive-like behavior and compromises medial prefrontal cortex structure and function during the postpartum period

Postpartum depression, which affects approximately 15% of new mothers, is associated with impaired mother-infant interactions and deficits in cognitive function. Exposure to stress during pregnancy is a major risk factor for postpartum depression. However, little is known about the neural consequences of gestational stress. The medial prefrontal cortex (mPFC) is a brain region that has been linked to stress, cognition, maternal care, and mood disorders including postpartum depression. Here we examined the effects of chronic gestational stress on mPFC function and whether these effects might be linked to structural modifications in the mPFC. We found that in postpartum rats, chronic gestational stress resulted in maternal care deficits, increased depressive-like behavior, and impaired performance on an attentional set shifting task that relies on the mPFC. Furthermore, exposure to chronic stress during pregnancy reduced dendritic spine density on mPFC pyramidal neurons and altered spine morphology. Taken together, these findings suggest that pregnancy stress may contribute to postpartum mental illness and its associated symptoms by compromising structural plasticity in the mPFC.

Communal nesting increases pup growth but has limited effects on adult behavior and neurophysiology in inbred mice

Laboratory mice preferentially rear their offspring in communal nests (CN), with all mothers contributing to maternal care and feeding of all the pups. Previous studies using primarily outbred mice have shown that offspring reared under CN conditions may display increased preweaning growth rates and differences in adult behavior and neurobiology compared with mice reared under single-nesting (SN; one dam with her litter) conditions. Here we compared pup mortality; weaning and adult body weights; adult behavior; and gene expression in the hippocampus and frontal cortex between C57BL/6J, DBA/2J and 129x1/SvJ mice reared by using CN (3 dams and their litters sharing a single nest) or SN. Male and female pups of all 3 strains reared in CN cages showed higher body weight at weaning than did SN pups of the same strain, with no significant difference in pup mortality between groups. Adult male offspring reared in CN showed no differences in any behavioral test when compared with SN offspring. Combining CN dams and litters after parturition revealed greater cortical brain-derived neurotropic factor expression in adult male C57BL/6J offspring and cortical glucocorticoid receptor expression in adult male C57BL/6J and 129x1/SvJ offspring as compared with SN offspring of the same strain. Communal rearing can enhance juvenile growth rates but does not change adult behavior in inbred mouse strains, although potential effects on adult neurophysiology are possible.

TBI and sex: crucial role of progesterone protecting the brain in an omega-3 deficient condition

We assessed whether the protective action of progesterone on traumatic brain injury (TBI) could be influenced by the consumption of omega-3 fatty acids during early life. Pregnant Sprague-Dawley rats were fed on omega-3 adequate or deficient diet from 3rd day of pregnancy and their female offspring were kept on the same diets up to the age of 15 weeks. Ovariectomy was performed at the age of 12 weeks to deprive animals from endogenous steroids until the time of a fluid percussion injury (FPI). Dietary n-3 fatty acid deficiency increased anxiety in sham animals and TBI aggravated the effects of the deficiency. Progesterone replacement counteracted the effects of TBI on the animals reared under n-3 deficiency. A similar pattern was observed for markers of membrane homeostasis such as 4-Hydroxynonenal (HNE) and secreted phospholipases A2 (sPLA2), synaptic plasticity such as brain derived neurotrophic factor (BDNF), syntaxin (STX)-3 and growth associated protein (GAP)-43, and for growth inhibitory molecules such as myelin-associated glycoprotein (MAG) and Nogo-A. Results that progesterone had no effects on sham n-3 deficient animals suggest that the availability of progesterone is essential under injury conditions. Progesterone treatment counteracted several parameters related to synaptic plasticity and membrane stability reduced by FPI and n-3 deficiency suggest potential targets for therapeutic applications. These results reveal the importance of n-3 preconditioning during early life and the efficacy of progesterone therapy during adulthood to counteract weaknesses in neuronal and behavioral plasticity.

Repeated transcranial direct current stimulation prevents abnormal behaviors associated with abstinence from chronic nicotine consumption

Successful available treatments to quit smoking remain scarce. Recently, the potential of transcranial direct current stimulation (tDCS) as a tool to reduce craving for nicotine has gained interest. However, there is no documented animal model to assess the neurobiological mechanisms of tDCS on addiction-related behaviors. To address this topic, we have developed a model of repeated tDCS in mice and used it to validate its effectiveness in relieving nicotine addiction. Anodal repeated tDCS was applied over the frontal cortex of Swiss female mice. The stimulation electrode (anode) was fixed directly onto the cranium, and the reference electrode was placed onto the ventral thorax. A 2 × 20 min/day stimulation paradigm for five consecutive days was used (0.2 mA). In the first study, we screened for behaviors altered by the stimulation. Second, we tested whether tDCS could alleviate abnormal behaviors associated with abstinence from nicotine consumption. In naive animals, repeated tDCS had antidepressant-like properties 3 weeks after the last stimulation, improved working memory, and decreased conditioned place preference for nicotine without affecting locomotor activity and anxiety-related behavior. Importantly, abnormal behaviors associated with chronic nicotine exposure (ie, depression-like behavior, increase in nicotine-induced place preference) were normalized by repeated tDCS. Our data show for the first time in an animal model that repeated tDCS is a promising, non-expensive clinical tool that could be used to reduce smoking craving and facilitate smoking cessation. Our animal model will be useful to investigate the mechanisms underlying the effects of tDCS on addiction and other psychiatric disorders.

The orexin-1 receptor antagonist SB-334867 attenuates anxiety in rats exposed to cat odor but not the elevated plus maze: an investigation of Trial 1 and Trial 2 effects

The orexins are hypothalamic neuropeptides most well known for their roles in regulating feeding and sleeping behaviors. Recent findings suggest that orexin-A may also modulate anxiety, although how and when the orexin system is involved remains unclear. To address this, we investigated the dose-dependent effects of the orexin-1 receptor antagonist SB-334867 in two rodent models of anxiety: the cat odor avoidance model and the elevated plus maze. In both models we tested the effects of SB-334867 when anxiety is novel (Trial 1) and familiar (Trial 2). In the first experiment, Wistar rats were treated with vehicle or SB-334867 (5, 10 or 20mg/kg, i.p.) prior to their first or second exposure to cat odor. During Trial 1, rats treated with 10mg/kg of SB-334867 approached the cat odor stimulus more than vehicle-treated rats. During Trial 2 the effects were more marked, with 10mg/kg of SB-334867 increasing approach times, increasing the number of times rats exited the hide box to engage in exploratory behavior, and decreasing overall hide times. In addition, the 20mg/kg dose decreased general activity during Trial 2. In the second experiment, the effects of SB-334867 (10 and 20mg/kg) were tested in the elevated plus maze. There were no significant differences produced by drug treatment during either Trial 1 or Trial 2. Results suggest that SB-334867 decreases anxiety induced by some, but not all, stressors.

Early enriched environment induces an increased conversion of proBDNF to BDNF in the adult rat's hippocampus

An enriched environment has been shown to influence brain plasticity and function by involving the action of brain-derived neurotrophic factor (BDNF). BDNF, which is synthesized as a precursor molecule (proBDNF) that undergoes proteolytic cleavage, plays an important role in synaptic plasticity and contributes to several brain functions such as memory, learning, and behavior. The neurotrophins and proneurotrophins often play opposite roles in the brain, suggesting that proteolytic cleavage of proneurotrophins controls the action of neurotrophins. However, few studies have focused on the expression and cleavage of proBDNF after exposure to an enriched environment. Our study aimed to explore the effects of an early-enriched environment on the conversion of proBDNF to BDNF in the adult rats' hippocampus. We found that there was no difference in the expression of proBDNF in the hippocampus between the SE (standard environment) and EE (enriched environment) rats, but a significantly increased BDNF protein level was found in the EE rats. Thus, a remarkably enhanced ratio of BDNF to proBDNF (BDNF/proBDNF) was observed in the EE rats. In addition, the EE resulted in a remarkably up-regulated matrix metalloproteinase-9 (MMP-9) in the hippocampus, which played a key role in converting proBDNF to BDNF in the extracellular space. Furthermore, the expression of synapse-related proteins (NR1 and NR2A) was analyzed, and the results indicated that EE could significantly increase the expression of NR1 and NR2A in the hippocampus. In addition, the behavioral results showed that EE reduced anxiety-like behavior in the elevated-plus maze test and reduced immobility time in the forced swimming test. Moreover, the EE resulted in an increased preference for sucrose compared to the SE. These results suggested that the EE up-regulated MMP-9 levels within the hippocampus, which might facilitate the conversion of proBDNF to BDNF, thereby contributing to the long lasting alterations of synaptic plasticity and behavior.

Ingestion of Lactobacillus strain reduces anxiety and improves cognitive function in the hyperammonemia rat

Evidence suggests that the hyperammonemia (HA)-induced neuroinflammation and alterations in the serotonin (5-HT) system may contribute to cognitive decline and anxiety disorder during hepatic encephalopathy (HE). Probiotics that maintain immune system homeostasis and regulate the 5-HT system may be potential treatment for HA-mediated neurological disorders in HE. In this study, we tested the efficacy of probiotic Lactobacillus helveticus strain NS8 in preventing cognitive decline and anxiety-like behavior in HA rats. Chronic HA was induced by intraperitoneal injection of ammonium acetate for four weeks in male Sprague-Dawley rats. HA rats were then given Lactobacillus helveticus strain NS8 (10(9) CFU mL(-1)) in drinking water as a daily supplementation. The Morris water maze task assessed cognitive function, and the elevated plus maze test evaluated anxiety-like behavior. Neuroinflammation was assessed by measuring the inflammatory markers: inducible nitric oxide synthase, prostaglandin E2, and interleukin-1 β in the brain. 5-HT system activity was evaluated by measuring 5-HT and its metabolite, 5-HIAA, and the 5-HT precursor, tryptophan. Probiotic treatment of HA rats significantly reduced the level of inflammatory markers, decreased 5-HT metabolism, restored cognitive function and improved anxiety-like behavior. These results indicate that probiotic L. helveticus strain NS8 is beneficial for the treatment of cognitive decline and anxiety-like behavior in HA rats.

Chronic cerebral hypoperfusion causes decrease of O-GlcNAcylation, hyperphosphorylation of tau and behavioral deficits in mice

Chronic cerebral hypoperfusion (CCH) is one of the causes of vascular dementia (VaD) and is also an etiological factor for Alzheimer’s disease (AD). However, how CCH causes cognitive impairment and contributes to Alzheimer’s pathology is poorly understood. Here we produced a mouse model of CCH by unilateral common carotid artery occlusion (UCCAO) and studied the behavioral changes and brain abnormalities in mice 2.5 months after UCCAO. We found that CCH caused significant short-term memory deficits and mild long-term spatial memory impairment, as well as decreased level of protein O-GlcNAcylation, increased level of tau phosphorylation, dysregulated synaptic proteins and insulin signaling, and selective neurodegeneration in the brain. These findings provide mechanistic insight into the effects of CCH on memory and cognition and the likely link between AD and VaD.

Vitamin A status regulates glucocorticoid availability in Wistar rats: consequences on cognitive functions and hippocampal neurogenesis?

A disruption of the vitamin A signaling pathway has been involved in age-related memory decline and hippocampal plasticity alterations. Using vitamin A deficiency (VAD), a nutritional model leading to a hyposignaling of the retinoid pathway, we have recently demonstrated that retinoic acid (RA), the active metabolite of vitamin A, is efficient to reverse VAD-induced spatial memory deficits and adult hippocampal neurogenesis alterations. Besides, excess of glucocorticoids (GCs) occurring with aging is known to strongly inhibit hippocampal plasticity and functions and few studies report on the counteracting effects of RA signaling pathway on GCs action. Here, we have addressed whether the modulation of brain GCs availability could be one of the biological mechanisms involved in the effects of vitamin A status on hippocampal plasticity and functions. Thus, we have studied the effects of a vitamin A-free diet for 14 weeks and a 4-week vitamin A supplementation on plasma and hippocampal corticosterone (CORT) levels in Wistar rats. We have also investigated corticosteroid binding globulin (CBG) binding capacity and 11beta-Hydrosteroid Dehydrogenase type 1 (11β-HSD1) activity, both important modulators of CORT availability at the peripheral and hippocampal levels respectively. Interestingly, we show that the vitamin A status regulates levels of free plasma CORT and hippocampal CORT levels, by acting through a regulation of CBG binding capacity and 11β-HSD1 activity. Moreover, our results suggest that increased CORT levels in VAD rats could have some deleterious consequences on spatial memory, anxiety-like behavior and adult hippocampal neurogenesis whereas these effects could be corrected by a vitamin A supplementation. Thus, the modulation of GCs availability by vitamin A status is an important biological mechanism that should be taken into account in order to prevent age-related cognitive decline and hippocampal plasticity alterations.

Assessment of an experimental rodent model of pediatric mild traumatic brain injury

Childhood is one the highest risk periods for experiencing a mild traumatic brain injury (mTBI) from sports-related concussions, motor vehicle accidents, and falls. In addition, many children experience lingering symptomology (post-concussion syndrome) from these closed head injuries. Although the negative sequel of mTBI has been described, a clinically reliable animal model of mild pediatric brain injury has not. The purpose of this study was to examine the validity of a modified weight-drop technique as a model for the induction of mTBI/concussion in juvenile rats following a single impact. Male and female rats (P30) were exposed to a single mTBI or a sham injury followed by a behavioral test battery. Juvenile rats who experienced a single mTBI displayed significant motor/balance impairments when tested on the beam walking task and in the open field, as well as deficits of executive functioning as measured with the novel context mismatch task and the probe trial of the Morris water task. In addition, both male and female rats showed depression-like behavior in the forced swim task, with male rats also exhibiting decreased anxiety-related behaviors in the elevated plus maze. The results from this study suggest that the modified weight-drop technique induces a clinically relevant behavioral phenotype in juvenile rats, and may provide researchers with a reliable animal model of mTBI/concussion from which clinical therapeutic strategies could be developed.

Paternal ethanol exposure and behavioral abnormities in offspring: associated alterations in imprinted gene methylation

Research confirms that maternal ethanol (EtOH) exposure can induce physical and mental disorders in offspring, yet the effect of paternal ethanol exposure on offspring is unclear. Methylation alterations in imprinted genes may be related to the well-documented teratogenic effects of ethanol. Here, we report that ethanol (0, 1.1, 3.3 g/kg) was administered intragastrically to male mice and a behavioral study was performed on their F1 generation. Data show that F1 mice with fathers exposed to the highest dose of ethanol had delayed cognitive performance and increased anxiety and depression. A specific circling behavior was observed in the offspring of the paternally ethanol-exposed group. The degree of methylation and mRNA expression of H19, Peg3, Ndn and Snrpn were assessed in paternal sperm and in the cerebral cortices of each offspring. It did affect methylation in paternal sperm (H19 and Peg3) and in the offspring's cerebral cortices (CpG7 and CpG11 in Peg3 and Snrpn), but the level of mRNA expression has not changed. In the circling mice, the highest ethanol exposure increase in methylation (CpG 1, 2, 7 and 11) and decreases in mRNA of Peg3.Thus, chronic paternal ethanol exposure can affect the methylation of imprinted genes in sire sperm that may be passed on to offspring, giving rise to mental deficits.

Long-term behavioral effects of neonatal blockade of gastrin-releasing peptide receptors in rats: similarities to autism spectrum disorders

Gastrin releasing peptide, the mammalian counterpart of the amphibian peptide, bombesin, has been increasingly implicated in regulating normal brain function as well as in the pathogenesis of psychiatric and/or neurodevelopmental disorders. We have previously shown that the neonatal blockade of the gastrin-releasing peptide receptor (GRPr) in rats produces long-lasting consequences during central nervous system development that are commonly observed in neurodevelopmental disorders such as autism spectrum disorders. The present investigation assessed in further detail, long-term behavioral effects of neonatal GRPr blockade. During postnatal days 1-10, male Wistar rat pups (n=5-10/litter) were injected (subcutaneously) with the GRPr antagonist, RC-3095 (1 mg/kg), or a vehicle (control), twice daily. Following the drug treatment regimen, several behaviors were assessed (starting on postnatal day 14) including specific social behaviors (namely, group huddling characteristics, social interaction, and social approach), restrictive/repetitive and stereotyped behaviors (y-maze, repetitive novel object contact task, observation for stereotypies) and anxiety/fear-related responses (open field, elevated plus maze and contextual fear conditioning). Rats treated neonatally with RC-3095 showed reduced sociability, restrictive interests, motor stereotypies and enhanced learned fear response compared to the controls (vehicle-treated rats). These behavioral abnormalities are consistent with those observed in autism spectrum disorders and provide further evidence that neonatal blockade of GRPr could potentially serve as a useful model to gain a better understanding of the underlying neurodevelopmental disruptions contributing to the expression of autism-relevant phenotypes.

Moderate Alcohol Exposure during the Rat Equivalent to the Third Trimester of Human Pregnancy Alters Regulation of GABAA Receptor-Mediated Synaptic Transmission by Dopamine in the Basolateral Amygdala

Fetal ethanol (EtOH) exposure leads to a range of neurobehavioral alterations, including deficits in emotional processing. The basolateral amygdala (BLA) plays a critical role in modulating emotional processing, in part, via dopamine (DA) regulation of GABA transmission. This BLA modulatory system is acquired during the first 2 weeks of postnatal life in rodents (equivalent to the third trimester of human pregnancy) and we hypothesized that it could be altered by EtOH exposure during this period. We found that exposure of rats to moderate levels of EtOH vapor during the third trimester-equivalent [postnatal days (P) 2-12] alters DA modulation of GABAergic transmission in BLA pyramidal neurons during periadolescence. Specifically, D1R-mediated potentiation of spontaneous inhibitory postsynaptic currents (IPSCs) was significantly attenuated in EtOH-exposed animals. However, this was associated with a compensatory decrease in D3R-mediated suppression of miniature IPSCs. Western blot analysis revealed that these effects were not a result of altered D1R or D3R levels. BLA samples from EtOH-exposed animals also had significantly lower levels of the DA precursor (L-3,4-dihydroxyphenylalanine) but DA levels were not affected. This is likely a consequence of reduced catabolism of DA, as indicated by reduced levels of 3,4-dihydroxyphenylacetic acid and homovanillic acid in the BLA samples. Anxiety-like behavior was not altered in EtOH-exposed animals. This is the first study to demonstrate that the modulatory actions of DA in the BLA are altered by developmental EtOH exposure. Although compensatory adaptations were engaged in our moderate EtOH exposure paradigm, it is possible that these are not able to restore homeostasis and correct anxiety-like behaviors under conditions of heavier EtOH exposure. Therefore, future studies should investigate the potential role of alterations in the modulatory actions of DA in the pathophysiology of fetal alcohol spectrum disorders.

Quercetin improves behavioral deficiencies, restores astrocytes and microglia, and reduces serotonin metabolism in 3-nitropropionic acid-induced rat model of Huntington's Disease

AIM

Huntington's disease (HD) is an autosomal dominant disorder, for which clinically available drugs offer only symptomatic relief. These prescription drugs are not free of side effects, and the patients usually suffer from anxiety and depression. We investigated quercetin, a dietary flavonoid with free radical scavenging properties, for its beneficial potential if any, in 3-nitropropionic acid (3-NP)-induced HD in rats where both drugs were administered simultaneously.

METHODS

Performance of rats on beam balancing, elevated plus maze and gait traits were investigated following 3-NP and/or quercetin treatments for 4 days. Striatal biogenic amine levels and monoamine oxidase activity were assayed. Striatal sections were examined for Cd11B and glial fibrillary acidic protein immunoreactivity, and for evidences of neuronal lesion.

RESULTS

Quercetin significantly attenuated 3-NP-induced anxiety, motor coordination deficits, and gait despair. While the dopaminergic hyper-metabolism was unaffected, quercetin provided a significant reduction of 3-NP mediated increase in serotonin metabolism. Quercetin failed to affect 3-NP-induced striatal neuronal lesion, but decreased microglial proliferation, and increased astrocyte numbers in the lesion core.

CONCLUSION

These results taken together suggest that quercetin could be of potential use not only for correcting movement disturbances and anxiety in HD, but also for addressing inflammatory damages.

Enkephalin downregulation in the nucleus accumbens underlies chronic stress-induced anhedonia

Restraint and immobilization have been extensively used to study habituation of the neuroendocrine response to a repeated stressor, but behavioral consequences of this stress regimen remain largely uncharacterized. In this study, we used sucrose preference and the elevated-plus maze to probe behavioral alterations resulting from 14 days of restraint in rats. We observed a decrease in sucrose preference in stressed animals, particularly in a subgroup of individuals, but no alteration in anxiety behaviors (as measured in the elevated-plus maze) four days following the last restraint. In these low-sucrose preference animals, we observed a downregulation of the expression of preproenkephalin mRNA in the nucleus accumbens. Furthermore, we observed a strong correlation between enkephalin expression and sucrose preference in the shell part of the nucleus accumbens, with a lower level of enkephalin expression being associated with lower sucrose preference. Interestingly, quantification of the corticosterone response revealed a delayed habituation to restraint in the low-sucrose preference population, which suggests that vulnerability to stress-induced deficits might be associated with prolonged exposure to glucocorticoids. The induction of ΔFosB is also reduced in the nucleus accumbens shell of the low-sucrose preference population and this transcription factor is expressed in enkephalin neurons. Taken together, these results suggest that a ΔFosB-mediated downregulation of enkephalin in the nucleus accumbens might underlie the susceptibility to chronic stress. Further experiments will be needed to determine causality between these two phenomena.

Anxiogenic Effects of Acute Injection of Sesame oil May be Mediated by β-1 Adrenoceptors in the Basolateral Amygdala

PURPOSE

A few studies have indicates that the sesame oil influences anxiety, but many reports show that β-1 adrenoceptors (ARs) of the basolateral amygdala (BLA) plays a pivotal role in this regard. Therefore, in this study the effect of acute injection of sesame oil on anxiety-like behavior in the presence and absence of the BLA β-1 ARs in the male Wistar rats were investigated.

METHODS

Guide cannulas, for seven groups of rats, were implanted bilaterally into the BLA. Two weeks after the stereotaxic surgery, anxiety-like behaviors (the OAT%, OAE % and locomotor activity) were evaluated by Elevated Plus-Maze (EPM) for all groups. 3 groups received different volumes of sesame oil (i.p.) and they were compared with control group (received saline via i.p.), and the anxiogenic volume of sesame oil (1.5ml/kg) was determined. Then, 3 other groups received constant effective volume of sesame oil (1.5ml/kg) along with 3 different doses of betaxolol, selective β-1 ARs antagonist, intra BLA microinjection in order to be compared with sesame oil group (1.5 ml/kg).

RESULTS

The acute injection of sesame oil with the volume dependent manner showed an anxiogenic effect with reduction of the OAT% and OAE% which the maximum effect of sesame oil was observed in the dose of 1.5mg/kg. Also, betaxolol with dose dependent manner attenuated the anxiogenic effects of sesame oil (1.5mg/kg), but this reduction could not remove the anxiety effects completely.

CONCLUSION

It seems that the sesame oil acute (i.p.) injection induces anxiety, and this effect is attenuated by inhibition of β-1ARs in the BLA.

Nonsteroidal selective androgen receptor modulators and selective estrogen receptor β agonists moderate cognitive deficits and amyloid-β levels in a mouse model of Alzheimer's disease

Decreases of the sex steroids, testosterone and estrogen, are associated with increased risk of Alzheimer's disease. Testosterone and estrogen supplementation improves cognitive deficits in animal models of Alzheimer's disease. Sex hormones play a role in the regulation of amyloid-β via induction of the amyloid-β degrading enzymes neprilysin and insulin-degrading enzyme. To mimic the effect of dihydrotestosterone (DHT), we administered a selective androgen receptor agonist, ACP-105, alone and in combination with the selective estrogen receptor β (ERβ) agonist AC-186 to male gonadectomized triple transgenic mice. We assessed long-term spatial memory in the Morris water maze, spontaneous locomotion, and anxiety-like behavior in the open field and in the elevated plus maze. We found that ACP-105 given alone decreases anxiety-like behavior. Furthermore, when ACP-105 is administered in combination with AC-186, they increase the amyloid-β degrading enzymes neprilysin and insulin-degrading enzyme and decrease amyloid-β levels in the brain as well as improve cognition. Interestingly, the androgen receptor level in the brain was increased by chronic treatment with the same combination treatment, ACP-105 and AC-186, not seen with DHT or ACP-105 alone. Based on these results, the beneficial effect of the selective ERβ agonist as a potential therapeutic for Alzheimer's disease warrants further investigation.

Experimental gastritis leads to anxiety- and depression-like behaviors in female but not male rats

Human and animals studies support the idea that there is a gender-related co-morbidity of pain-related and inflammatory gastrointestinal (GI) diseases with psychological disorders. This co-morbidity is the evidence for the existence of GI-brain axis which consists of immune (cytokines), neural (vagus nerve) and neuroendocrine (HPA axis) pathways. Psychological stress causes disturbances in GI physiology, such as altered GI barrier function, changes in motility and secretion, development of visceral hypersensitivity, and dysfunction of inflammatory responses. Whether GI inflammation would exert impact on psychological behavior is not well established. We examined the effect of experimental gastritis on anxiety- and depression-like behaviors in male and female Sprague-Dawley rats, and evaluated potential mechanisms of action. Gastritis was induced by adding 0.1% (w/v) iodoacetamide (IAA) to the sterile drinking water for 7 days. Sucrose preference test assessed the depression-like behavior, open field test and elevated plus maze evaluated the anxiety-like behavior. IAA treatment induced gastric inflammation in rats of either gender. No behavioral abnormality or dysfunction of GI-brain axis was observed in male rats with IAA-induced gastritis. Anxiety- and depression-like behaviors were apparent and the HPA axis was hyperactive in female rats with IAA-induced gastritis. Our results show that gastric inflammation leads to anxiety- and depression-like behaviors in female but not male rats via the neuroendocrine (HPA axis) pathway, suggesting that the GI inflammation can impair normal brain function and induce changes in psychological behavior in a gender-related manner through the GI-to-brain signaling.

The 5-HT3A receptor is essential for fear extinction

The 5-HT3 receptor, the only ionotropic 5-HT receptor, is expressed in limbic regions, including the hippocampus, amygdala, and cortex. However, it is not known whether it has a role in fear memory processes. Analysis of 5-HT3A receptor knockout mice in fear conditioning paradigms revealed that the 5-HT3A receptor is not required for the acquisition or retention of fear memory but is essential for the extinction of contextual and tone-cued fear. Our data suggest that the 5-HT3A receptor could be a key molecule regulating fear memory processes and a potential therapeutic target for fear disorders.

Bisphenol A does not affect memory performance in adult male rats

Bisphenol A (BPA) is an estrogenic endocrine disruptor used for producing polycarbonate plastics and epoxy resins. This study investigated the effects of oral BPA administration on memory performance, general activity, and emotionality in adult male Sprague Dawley rats using a battery of behavioral tests, including an appetite-motivated maze test (MAZE test) used to assess spatial memory performance. In addition, in order to confirm the effects of BPA on spatial memory performance, we examined whether intrahippocampal injection of BPA affects spatial memory consolidation. In the MAZE test, although oral BPA administration at 10 mg/kg significantly altered the number of entries into the incorrect area compared to those of vehicle-treated rats, male rats given BPA through either oral administration or intrahippocampal injection failed to show significant differences in latencies to reach the reward. Also, oral BPA administration did not affect fear-motivated memory performance in the step-through passive avoidance test. Oral BPA administration at 0.05 mg/kg, the lowest dose used in this study, was correlated with a decrease in locomotor activity in the open-field test, whereas oral administration at 10 mg/kg, the highest dose used in this study, was correlated with a light anxiolytic effect in the elevated plus-maze test. The present study suggests that BPA in adulthood has little effect on spatial memory performance in male rats.

All-trans retinoic acid-induced hypothalamus-pituitary-adrenal hyperactivity involves glucocorticoid receptor dysregulation

Clinical reports have highlighted a role for retinoids in the etiology of mood disorders. Although we had shown that recruitment of the nuclear receptor retinoic acid receptor-α (RAR-α) to corticotropin-releasing hormone (CRH) promoter is implicated in activation of the hypothalamus-pituitary-adrenal (HPA) axis, further insight into how retinoids modulate HPA axis activity is lacking. Here we show that all-trans retinoic acid (RA)-induced HPA activation involves impairments in glucocorticoid receptor (GR) negative feedback. RA was applied to rats chronically through intracerebroventricular injection. A 19-day RA exposure induced potent HPA axis activation and typical depression-like behavior. Dexamethasone failed to suppress basal corticosterone (CORT) secretion, which is indicative of a disturbed GR negative feedback. In the hypothalamic paraventricular nucleus, increased CRH⁺ and c-fos⁺ cells were found while a negative R-2⁺/ER⁺ correlation was present between the number of RAR-α⁺ and GR⁺ cells. This was paralleled by increased RAR-α and decreased GR protein expression in the hypothalamus. Additional in vitro studies confirmed that RA abolished GR-mediated glucocorticoid-induced suppression of CRH expression, indicating a negative cross-talk between RAR-α and GR signaling pathways. Finally, the above changes could be rapidly normalized by treatment with GR antagonist mifepristone. We conclude that in addition to the 'classic' RAR-α-mediated transcriptional control of CRH expression, disturbances in GR negative feedback constitute a novel pathway that underlies RA-induced HPA axis hyperactivity. The rapid normalization by mifepristone may be of potential clinical interest in this respect.

Natural variation in maternal care shapes adult social behavior in rats

Features of the early postnatal environment profoundly shape later physical and behavioral phenotypes. The amount of licking/grooming that rat dams direct towards their offspring has durable consequences, including behavioral and physiological dimensions of stress reactivity, cognition, and reproductive behavior. We examined how natural variation in maternal care alters social behavior in adult offspring and how this relates to anxiety behavior and oxytocin receptor density. Male and female offspring of mothers who received high levels of licking spent significantly more time in social contact with unfamiliar individuals than did offspring whose dams provided less grooming. Reduced anxiety behavior was associated with greater social interaction. No differences in oxytocin receptor binding assessed by (125) I-OVTA autoradiography were detected between groups. The present investigation characterizes a novel impact of maternal care on adult social interaction behavior, replicates anxiety behavior differences, and illustrates connections between social behavior and anxiety in adulthood across maternal treatment groups.

Object recognition test in mice

The object recognition test is now among the most commonly used behavioral tests for mice. A mouse is presented with two similar objects during the first session, and then one of the two objects is replaced by a new object during a second session. The amount of time taken to explore the new object provides an index of recognition memory. As more groups have used the protocol, the variability of the procedures used in the object recognition test has increased steadily. This protocol provides a necessary standardization of the procedure. This protocol reduces inter-individual variability with the use of a selection criterion based on a minimal time of exploration for both objects during each session. In this protocol, we describe the three most commonly used variants, containing long (3 d), short (1 d) or no habituation phases. Thus, with a short intersession interval (e.g., 6 h), this procedure can be performed in 4, 2 or 1 d, respectively, according to the duration of the habituation phase. This protocol should allow for the comparison of results from different studies, while permitting adaption of the protocol to the constraints of the experimenter.

Androgen insensitive male rats display increased anxiety-like behavior on the elevated plus maze

Male rats carrying the testicular feminization mutation (Tfm-affected males) are insensitive to androgens, resulting in a female-typical peripheral phenotype despite possession of inguinal testes that are androgen secretory. Androgen-dependent neural and behavioral processes may likewise show atypical sexual differentiation. Interestingly, these mutant rats display elevated serum corticosterone, suggesting a chronic anxiety phenotype and dysregulated hypothalamic-pituitary-adrenal axis. In order to understand if elevated anxiety-like behavior is a possible mediating variable affecting the display of certain androgen-dependent behaviors, we compared the performance of Tfm-affected males to wild type males and females in the elevated plus maze (EPM). Two well-established indicators of anxiety-like behavior in the EPM were analyzed: total percentage of time spent on the open arms, and the percentage of open arm entries. We also analyzed the total number of open arm entries. Interestingly, Tfm-affected males spent less percentage of time on the open arms than both males and females, suggesting increased anxiety-like behavior. Percentage of open arm entries and the total number of arm entries was comparable between the groups, indicating that the observed decrease in the percentage of time spent on the open arms was not due to a global reduction in exploratory behavior. These data, in contrast to earlier reports, thus implicate androgen receptor-mediated functions in the expression of anxiety behaviors in male rats. Given that anxiety is widely reported as a precipitating factor in depression, studying the role of the androgen receptor in anxiety may give insights into the pathogenesis of major depressive disorder.

Hypnotic, anticonvulsant and anxiolytic effects of 1-nitro-2-phenylethane isolated from the essential oil of Dennettia tripetala in mice

This study investigated the hypnotic, anti-convulsant and anxiolytic effects of 1-nitro-2-phenylethane (BPNE) obtained from the oil of Dennettia tripetala G. Baker (Annonaceae) and established its mechanism of action. The essential oil (EO) from the leaf, fruit and seed was obtained by hydrodistillation, followed by isolation of BPNE purified to 99.2% by accelerated gradient chromatography on silica, and identified by NMR and GC-MS. The pure BPNE and EO of the dried seed (93.6%) were comparatively evaluated for hypnotic, anticonvulsant and anxiolytic effects in mice. The acute toxicity of BPNE was determined and the LD50 was 490 mg/kg, intrapritonealy. The hypnotic activities of the EO and BPNE (50-400 mg/kg, i.p.) were assessed by loss of righting reflex, while sodium pentobarbitone (PBS) and diazepam (DZM) were used as positive controls. The anticonvulsant and anxiolytic effects of the EO and BPNE were evaluated in mice. Both BPNE and EO at doses ≥100 mg/kg induced spontaneous hypnosis with loss of righting reflex, significantly decreased sleep latency (SL) and also increased total sleeping time (TST) dose-dependently. They had comparable activity with NAP in TST. The BPNE exhibited higher hypnotic potency than EO at the same dose levels. The EO and BPNE offered comparable dose-related protections against PTZ- and strychnine-induced convulsions. Flumazenil (2 mg/kg) blocked the hypnotic and anticonvulsant (PTZ-convulsions) effects of both EO and BPNE. The essential oil at 5-20 mg/kg dose levels significantly (p<0.05) increased the percentage time spent and number of entries into the open arms. While at the same dose range BPNE significantly (p<0.05) increased the percentage time spent and the number of entries into the open arms respectively. The study concluded that 1-nitro-2-phenylethane exhibited dose dependent significant hypnotic, anticonvulsant and anxiolytic effects and it is the compound largely responsible for the neuropharmacological effects of the oil.

Endogenous IL-1 in cognitive function and anxiety: a study in IL-1RI-/- mice

Interleukin-1 (IL-1) is a key pro-inflammatory cytokine, produced predominantly by peripheral immune cells but also by glia and some neuronal populations within the brain. Its signalling is mediated via the binding of IL-1α or IL-1β to the interleukin-1 type one receptor (IL-1RI). IL-1 plays a key role in inflammation-induced sickness behaviour, resulting in depressed locomotor activity, decreased exploration, reduced food and water intake and acute cognitive deficits. Conversely, IL-1 has also been suggested to facilitate hippocampal-dependent learning and memory: IL-1RI^−/− mice have been reported to show deficits on tasks of visuospatial learning and memory. We sought to investigate whether there is a generalised hippocampal deficit in IL-1RI^−/− animals. Therefore, in the current study we compared wildtype (WT) mice to IL-1RI^−/− mice using a variety of hippocampal-dependent learning and memory tasks, as well as tests of anxiety and locomotor activity. We found no difference in performance of the IL-1RI^−/− mice compared to WT mice in a T-maze working memory task. In addition, the IL-1RI^−/− mice showed normal learning in various spatial reference memory tasks including the Y-maze and Morris mater maze, although there was a subtle deficit in choice behaviour in a spatial discrimination, beacon watermaze task. IL-1RI^−/− mice also showed normal memory for visuospatial context in the contextual fear conditioning paradigm. In the open field, IL-1RI^−/− mice showed a significant increase in distance travelled and rearing behaviour compared to the WT mice and in the elevated plus-maze spent more time in the open arms than did the WT animals. The data suggest that, contrary to prior studies, IL-1RI^−/− mice are not robustly impaired on hippocampal-dependent memory and learning but do display open field hyperactivity and decreased anxiety compared to WT mice. The results argue for a careful evaluation of the roles of endogenous IL-1 in hippocampal and limbic system function.

Developmental changes in structural and functional properties of hippocampal AMPARs parallels the emergence of deliberative spatial navigation in juvenile rats

The neural mechanisms that support the late postnatal development of spatial navigation are currently unknown. We investigated this in rats and found that an increase in the duration of AMPAR-mediated synaptic responses in the hippocampus was related to the emergence of spatial navigation. More specifically, spontaneous alternation rate, a behavioral indicator of hippocampal integrity, increased at the end of the third postnatal week in association with increases in AMPAR response duration at SC-CA1 synapses and synaptically driven postsynaptic discharge of CA1 pyramidal neurons. Pharmacological prolongation of glutamatergic synaptic transmission in juveniles increased the spontaneous alternation rate and CA1 postsynaptic discharge and reduced the threshold for the induction of activity-dependent synaptic plasticity at SC-CA1 synapses. A decrease in GluA1 and increases in GluA3 subunit and transmembrane AMPAR regulatory protein (TARP) expression at the end of the third postnatal week provide a molecular explanation for the increase in AMPAR response duration and reduced efficacy of AMPAR modulators with increasing age. A shift in the composition of AMPARs and increased association with AMPAR protein complex accessory proteins at the end of the third postnatal week likely "turns on" the hippocampus by increasing AMPAR response duration and postsynaptic excitability and reducing the threshold for activity-dependent synaptic potentiation.

Neuropeptide S: a novel regulator of pain-related amygdala plasticity and behaviors

Amygdala plasticity is an important contributor to the emotional-affective dimension of pain. Recently discovered neuropeptide S (NPS) has anxiolytic properties through actions in the amygdala. Behavioral data also suggest antinociceptive effects of centrally acting NPS, but site and mechanism of action remain to be determined. This is the first electrophysiological analysis of pain-related NPS effects in the brain. We combined whole cell patch-clamp recordings in brain slices and behavioral assays to test the hypothesis that NPS activates synaptic inhibition of amygdala output to suppress pain behavior in an arthritis pain model. Recordings of neurons in the laterocapsular division of the central nucleus (CeLC), which serves pain-related amygdala output functions, show that NPS inhibited the enhanced excitatory drive [monosynaptic excitatory postsynaptic currents (EPSCs)] from the basolateral amygdala (BLA) in the pain state. As shown by miniature EPSC analysis, the inhibitory effect of NPS did not involve direct postsynaptic action on CeLC neurons but rather a presynaptic, action potential-dependent network mechanism. Indeed, NPS increased external capsule (EC)-driven synaptic inhibition of CeLC neurons through PKA-dependent facilitatory postsynaptic action on a cluster of inhibitory intercalated (ITC) cells. NPS had no effect on BLA neurons. High-frequency stimulation (HFS) of excitatory EC inputs to ITC cells also inhibited synaptic activation of CeLC neurons, providing further evidence that ITC activation can control amygdala output. The cellular mechanisms by which EC-driven synaptic inhibition controls CeLC output remain to be determined. Administration of NPS into ITC, but not CeLC, also inhibited vocalizations and anxiety-like behavior in arthritic rats. A selective NPS receptor antagonist ([d-Cys(tBu)(5)]NPS) blocked electrophysiological and behavioral effects of NPS. Thus NPS is a novel tool to control amygdala output and pain-related affective behaviors through a direct action on inhibitory ITC cells.

Basal blood corticosterone level is correlated with susceptibility to chronic restraint stress in mice

Corticosterone is released in response to stress and manifests as various bodily stress responses in rodents. While corticosterone reflects acute adaptive responses, how the basal steady-state corticosterone level relates to the subsequent stress response is largely unknown. Here, we investigated how basal corticosterone levels can affect the susceptibility to chronic restraint stress in mice. We designed a longitudinal experiment, enabling us to compare the basal corticosterone level and the subsequent response to repeated restraint stress within the same animal. We found that the mice had differential changes in plasma corticosterone levels, which either increased or decreased, with exposure to chronic stress. These differential changes reflected the differential stress susceptibility of the mice, as evaluated by changes in body weight. The extent of the changes in corticosterone level during chronic stress exposure was predicted by the basal corticosterone level. In addition, the behavioral consequence of chronic stress was also correlated with the basal corticosterone level prior to chronic stress experience. These data reveal that the basal steady-state corticosterone level is a predictor of stress susceptibility or resilience to subsequent stress exposures.

Participation of GABAA chloride channels in the anxiolytic-like effects of a fatty acid mixture

Human amniotic fluid and a mixture of eight fatty acids (FAT-M) identified in this maternal fluid (C12:0, lauric acid, 0.9 μg%; C14:0, myristic acid, 6.9 μg%; C16:0, palmitic acid, 35.3 μg%; C16:1, palmitoleic acid, 16.4 μg%; C18:0, stearic acid, 8.5 μg%; C18:1cis, oleic acid, 18.4 μg%; C18:1trans, elaidic acid, 3.5 μg%; C18:2, linoleic acid, 10.1 μg%) produce anxiolytic-like effects that are comparable to diazepam in Wistar rats, suggesting the involvement of γ-aminobutyric acid-A (GABA_A) receptors, a possibility not yet explored. Wistar rats were subjected to the defensive burying test, elevated plus maze, and open field test. In different groups, three GABA_A receptor antagonists were administered 30 min before FAT-M administration, including the competitive GABA binding antagonist bicuculline (1 mg/kg), GABA_A benzodiazepine antagonist flumazenil (5 mg/kg), and noncompetitive GABA_A chloride channel antagonist picrotoxin (1 mg/kg). The FAT-M exerted anxiolytic-like effects in the defensive burying test and elevated plus maze, without affecting locomotor activity in the open field test. The GABA_A antagonists alone did not produce significant changes in the behavioral tests. Picrotoxin but not bicuculline or flumazenil blocked the anxiolytic-like effect of the FAT-M. Based on the specific blocking action of picrotoxin on the effects of the FAT-M, we conclude that the FAT-M exerted its anxiolytic-like effects through GABA_A receptor chloride channels.

Anxiolytic-like effects of carvacryl acetate, a derivative of carvacrol, in mice

Studies showing anxiolytic-like properties of natural products have grown. This paper evaluated if carvacryl acetate (CA) could be studied as an alternative drug to treat anxiety disorders. Elevated plus maze (EPM) tests , light-dark box (LDB) tests, and marble-burying tests (MBTs) were performed on mice. In the first protocol, the anxiolytic-like activities of CA 25, 50, 75 and 100mg/kg at single doses were compared to those of the vehicle, buspirone 5mg/kg (BUSP) and diazepam 1mg/kg (DZP). In the second protocol, the anxiolytic-like actions of CA were tested for GABAergic and serotonergic systems. The time spent in the open arms (TSOA) and the number of open arms entries (NOAE) were measured in EPM; the time spent in the light box (TSLB) and the number of entries to light box (NELB) were measured in LDB; and the number of marbles buried (NMB) were measured in MBT. CA increased TSOA and NOAE in the EPM, as well as TSLB and NELB in the LDB and the NMB in the MBT. The anxiolytic-like activity of CA 25; 50; 75 and 100mg/kg was not associated with psychomotor retardation in the open field test and in the Rota rod test, contrarily with what happened with DZP. In the second protocol, to suggest the mechanism of action of CA, flumazenil 25mg/kg ip (FLU) and WAY 100,635 10mg/kg ip (WAY-5-HT1A antagonist) were also used. FLU+CA100 reduced TSOA in the EPM when compared to CA100 but WAY+CA100 did not. In LDB, FLU+CA100 reduced the TSLB when compared to CA100 but WAY+CA100 did not. In the MBT, FLU+CA100 inhibited the effect of CA100 on the NMB but WAY+CA100 did not. In conclusion, CA seems to have an anxiolytic-like effect, probably due to GABAergic agonist action, without psychomotor side effects.

Anxiolytic-Like Effects of Chrysanthemum indicum Aqueous Extract in Mice: Possible Involvement of GABAA Receptors and 5-HT1A Receptors

Chrysanthemum indicum Linne is an ancient herbal medicine used to treat bone and muscle deterioration, ocular infl ammation, headache, and anxiety in Korea, China, and Japan. Furthermore, tea derived from Chrysanthemum indicum Linne has been used to treat anxiety by facilitating relaxation and curing insomnia. However, no reports exist on the anxiolytic-like effects of Chrysanthemum indicum Linne water extract (CWE) in mice. In the present study, we investigated the anxiolytic-like effects of CWE using the elevated plus-maze (EPM) test in mice. CWE, at a dose of 500 mg/kg (p.o.), signifi cantly increased the time spent in the open arms of the EPM compared to a vehicle-injected control group. Moreover, the effect of CWE (500 mg/kg) was blocked by bicuculline (a selective GABA_A receptor antagonist) and WAY 100635 (a selective 5-HT_1A receptor antagonist). Taken together, these fi ndings suggest that the anxiolytic-like effects of CWE might be mediated by the GABA_A receptor and the 5-HT_1A receptor.

Cannabinoid CB1 receptor in dorsal telencephalic glutamatergic neurons: distinctive sufficiency for hippocampus-dependent and amygdala-dependent synaptic and behavioral functions

A major goal in current neuroscience is to understand the causal links connecting protein functions, neural activity, and behavior. The cannabinoid CB1 receptor is expressed in different neuronal subpopulations, and is engaged in fine-tuning excitatory and inhibitory neurotransmission. Studies using conditional knock-out mice revealed necessary roles of CB1 receptor expressed in dorsal telencephalic glutamatergic neurons in synaptic plasticity and behavior, but whether this expression is also sufficient for brain functions is still to be determined. We applied a genetic strategy to reconstitute full wild-type CB1 receptor functions exclusively in dorsal telencephalic glutamatergic neurons and investigated endocannabinoid-dependent synaptic processes and behavior. Using this approach, we partly restored the phenotype of global CB1 receptor deletion in anxiety-like behaviors and fully restored hippocampus-dependent neuroprotection from chemically induced epileptiform seizures. These features coincided with a rescued hippocampal depolarization-induced suppression of excitation (DSE), a CB1 receptor-dependent form of synaptic plasticity at glutamatergic neurons. By comparison, the rescue of the CB1 receptor on dorsal telencephalic glutamatergic neurons prolonged the time course of DSE in the amygdala, and impaired fear extinction in auditory fear conditioning. These data reveal that CB1 receptor in dorsal telencephalic glutamatergic neurons plays a sufficient role to control neuronal functions that are in large part hippocampus-dependent, while it is insufficient for proper amygdala functions, suggesting an unexpectedly complex circuit regulation by endocannabinoid signaling in the amygdala. Our data pave the way to a better understanding of neuronal networks in the context of behavior, by fine-tuned interference with synaptic transmission processes.

5-HT2CR blockade in the amygdala conveys analgesic efficacy to SSRIs in a rat model of arthritis pain

BACKGROUND

Pain, including arthritic pain, has a negative affective component and is often associated with anxiety and depression. However, selective serotonin reuptake inhibitor antidepressants (SSRIs) show limited effectiveness in pain. The amygdala plays a key role in the emotional-affective component of pain, pain modulation and affective disorders. Neuroplasticity in the basolateral and central amygdala (BLA and CeA, respectively) correlate positively with pain behaviors. Evidence suggests that serotonin receptor subtype 5-HT2CR in the amygdala contributes critically to anxiogenic behavior and anxiety disorders. In this study, we tested the hypothesis that 5-HT2CR in the amygdala accounts for the limited effectiveness of SSRIs in reducing pain behaviors and that 5-HT2CR blockade in the amygdala renders SSRIs effective.

RESULTS

Nocifensive reflexes, vocalizations and anxiety-like behavior were measured in adult male Sprague-Dawley rats. Behavioral experiments were done in sham controls and in rats with arthritis induced by kaolin/carrageenan injections into one knee joint. Rats received a systemic (i.p.) administration of an SSRI (fluvoxamine, 30 mg/kg) or vehicle (sterile saline) and stereotaxic application of a selective 5-HT2CR antagonist (SB242084, 10 μM) or vehicle (ACSF) into BLA or CeA by microdialysis. Compared to shams, arthritic rats showed decreased hindlimb withdrawal thresholds (increased reflexes), increased duration of audible and ultrasonic vocalizations, and decreased open-arm choices in the elevated plus maze test suggesting anxiety-like behavior. Fluvoxamine (i.p.) or SB242084 (intra-BLA) alone had no significant effect, but their combination inhibited the pain-related increase of vocalizations and anxiety-like behavior without affecting spinal reflexes. SB242084 applied into the CeA in combination with systemic fluvoxamine had no effect on vocalizations and spinal reflexes.

CONCLUSIONS

The data suggest that 5-HT2CR in the amygdala, especially in the BLA, limits the effectiveness of SSRIs to inhibit pain-related emotional-affective behaviors.

Membrane progestin receptors in the midbrain ventral tegmental area are required for progesterone-facilitated lordosis of rats

Progesterone (P₄) and its metabolites, rapidly facilitate lordosis of rats partly through actions in the ventral tegmental area (VTA). The study of membrane progestin receptors (mPRs), of the Progestin and AdipoQ Receptor (PAQR) superfamily, has been limited to expression and regulation, instead of function. We hypothesized that if mPRs are required for progestin-facilitated lordosis in the VTA, then mPRs will be expressed in this region and knockdown will attenuate lordosis. First, expression of mPR was examined by reverse-transcriptase polymerase chain reaction (RT-PCR) in brain and peripheral tissues of proestrous Long-Evans rats. Expression of mPRα (paqr7) was observed in peripheral tissues and brain areas, including hypothalamus and midbrain. Expression of mPRβ (paqr8) was observed in brain tissues and was abundant in the midbrain and hypothalamus. Second, ovariectomized rats were estrogen (E₂; 0.09 mg/kg, SC), and P₄ (4 mg/kg, SC) or vehicle-primed, and infused with antisense oligodeoxynucleotides (AS-ODNs) targeted against mPRα and/or mPRβ intracerebroventricularly or to the VTA. Rats were assessed for motor (open field), anxiety (elevated plus maze), social (social interaction), and sexual (lordosis) behavior. P₄-facilitated lordosis was significantly reduced with administration of AS-ODNs for mPRα, mPRβ, or co-administration of mPRα and mPRβ to the lateral ventricle, compared to vehicle. P₄-facilitated lordosis was reduced, compared to vehicle, by administration of mPRβ AS-ODNs, or co-administration of mPRα and mPRβ AS-ODNs, but not mPRα AS-ODNs alone, to the VTA. No differences were observed for motor, anxiety, or social behaviors. Thus, mPRs in the VTA are targets of progestin-facilitated lordosis of rats.

Iron deficiency with or without anemia impairs prepulse inhibition of the startle reflex

Iron deficiency (ID) during early life causes long-lasting detrimental cognitive sequelae, many of which are linked to alterations in hippocampus function, dopamine synthesis, and the modulation of dopaminergic circuitry by the hippocampus. These same features have been implicated in the origins of schizophrenia, a neuropsychiatric disorder with significant cognitive impairments. Deficits in sensorimotor gating represent a reliable endophenotype of schizophrenia that can be measured by prepulse inhibition (PPI) of the acoustic startle reflex. Using two rodent model systems, we investigated the influence of early-life ID on PPI in adulthood. To isolate the role of hippocampal iron in PPI, our mouse model utilized a timed (embryonic day 18.5), hippocampus-specific knockout of Slc11a2, a gene coding an important regulator of cellular iron uptake, the divalent metal transport type 1 protein (DMT-1). Our second model used a classic rat dietary-based global ID during gestation, a condition that closely mimics human gestational ID anemia (IDA). Both models exhibited impaired PPI in adulthood. Furthermore, our DMT-1 knockout model displayed reduced long-term potentiation (LTP) and elevated paired-pulse facilitation (PPF), electrophysiological results consistent with previous findings in the IDA rat model. These results, in combination with previous findings demonstrating impaired hippocampus functioning and altered dopaminergic and glutamatergic neurotransmission, suggest that iron availability within the hippocampus is critical for the neurodevelopmental processes underlying sensorimotor gating. Ultimately, evidence of reduced PPI in both of our models may offer insights into the roles of fetal ID and the hippocampus in the pathophysiology of schizophrenia.

Physical exercise prevents stress-induced activation of granule neurons and enhances local inhibitory mechanisms in the dentate gyrus

Physical exercise is known to reduce anxiety. The ventral hippocampus has been linked to anxiety regulation but the effects of running on this subregion of the hippocampus have been incompletely explored. Here, we investigated the effects of cold water stress on the hippocampus of sedentary and runner mice and found that while stress increases expression of the protein products of the immediate early genes c-fos and arc in new and mature granule neurons in sedentary mice, it has no such effect in runners. We further showed that running enhances local inhibitory mechanisms in the hippocampus, including increases in stress-induced activation of hippocampal interneurons, expression of vesicular GABA transporter (vGAT), and extracellular GABA release during cold water swim stress. Finally, blocking GABAA receptors in the ventral hippocampus, but not the dorsal hippocampus, with the antagonist bicuculline, reverses the anxiolytic effect of running. Together, these results suggest that running improves anxiety regulation by engaging local inhibitory mechanisms in the ventral hippocampus.

Reducing mouse anxiety during handling: effect of experience with handling tunnels

Handling stress is a well-recognised source of variation in animal studies that can also compromise the welfare of research animals. To reduce background variation and maximise welfare, methods that minimise handling stress should be developed and used wherever possible. Recent evidence has shown that handling mice by a familiar tunnel that is present in their home cage can minimise anxiety compared with standard tail handling. As yet, it is unclear whether a tunnel is required in each home cage to improve response to handling. We investigated the influence of prior experience with home tunnels among two common strains of laboratory mice: ICR(CD-1) and C57BL/6. We compared willingness to approach the handler and anxiety in an elevated plus maze test among mice picked up by the tail, by a home cage tunnel or by an external tunnel shared between cages. Willingness to interact with the handler was much greater for mice handled by a tunnel, even when this was unfamiliar, compared to mice picked up by the tail. Once habituated to handling, C57BL/6 mice were most interactive towards a familiar home tunnel, whereas the ICR strain showed strong interaction with all tunnel handling regardless of any experience of a home cage tunnel. Mice handled by a home cage or external tunnel showed less anxiety in an elevated plus maze than those picked up by the tail. This study shows that using a tunnel for routine handling reduces anxiety among mice compared to tail handling regardless of prior familiarity with tunnels. However, as home cage tunnels can further improve response to handling in some mice, we recommend that mice are handled with a tunnel provided in their home cage where possible as a simple practical method to minimise handling stress.

The successive alleys test of anxiety in mice and rats

The plus-maze was derived from the early work of Montgomery. He observed that rats tended to avoid the open arms of a maze, preferring the enclosed ones. Handley, Mithani and File et al. performed the first studies on the plus-maze design we use today, and in 1987 Lister published a design for use with mice. Time spent on, and entries into, the open arms are an index of anxiety; the lower these indices, the more anxious the mouse is. Alternatively, a mouse that spends most of its time in the closed arms is classed as anxious. One of the problems of the plus-maze is that, while time spent on, and entries into, the open arms is a fairly unambiguous measure of anxiety, time in the central area is more difficult to interpret, although time spent here has been classified as “decision making”. In many tests central area time is a considerable part of the total test time. Shepherd et al. produced an ingenious design to eliminate the central area, which they called the “zero maze”. However, although used by several groups, it has never been as widely adopted as the plus-maze. In the present article I describe a modification of the plus-maze design that not only eliminates the central area but also incorporates elements from other anxiety tests, such as the light-dark box and emergence tests. It is a linear series of four alleys, each having increasing anxiogenic properties. It has given similar results to the plus-maze in general. Although it may not be more sensitive than the plus-maze (more data is needed before a firm conclusion can be reached on this point), it provides a useful confirmation of plus-maze results which would be useful when, for example, only a single example of a mutant mouse was available, as, for example, in ENU-based mutagenesis programs.

Mood and memory function in ovariectomised rats exposed to social instability stress

This study aims to compare the effects of social instability stress on memory and anxiety- and depressive-like behaviour between sham-operated controls and ovariectomised (OVX) rats. Forty adult female Sprague-Dawley rats (8 weeks old) were randomly divided into four groups, (n = 10 per group). These were non-stressed sham-operated control rats, stressed sham-operated control rats, non-stressed OVX rats, and stressed OVX rats. The rats were subjected to social instability stress procedure for 15 days. Novel object recognition, open field, and forced swim tests were conducted after the stress procedure. Serum estradiol, ACTH and corticosterone levels were measured using commercially available ELISA kits. Lower serum estradiol level and uterine weight with higher weight gain were observed in OVX rats compared to sham-operated controls. Serum ACTH, and corticosterone levels were higher in stressed compared to non-stressed groups. Memory deficit and anxiety- and depressive-like behaviour were significantly increased in stressed compared to non-stressed OVX rats but these changes were not seen in sham-operated controls. These results suggest that the high circulating corticosterone acts synergistically with low circulating estradiol to exert negative effects on mood and memory function.

Heterozygosity for nuclear factor one x affects hippocampal-dependent behaviour in mice

Identification of the genes that regulate the development and subsequent functioning of the hippocampus is pivotal to understanding the role of this cortical structure in learning and memory. One group of genes that has been shown to be critical for the early development of the hippocampus is the Nuclear factor one (Nfi) family, which encodes four site-specific transcription factors, NFIA, NFIB, NFIC and NFIX. In mice lacking Nfia, Nfib or Nfix, aspects of early hippocampal development, including neurogenesis within the dentate gyrus, are delayed. However, due to the perinatal lethality of these mice, it is not clear whether this hippocampal phenotype persists to adulthood and affects hippocampal-dependent behaviour. To address this we examined the hippocampal phenotype of mice heterozygous for Nfix (Nfix (+/-)), which survive to adulthood. We found that Nfix (+/-) mice had reduced expression of NFIX throughout the brain, including the hippocampus, and that early hippocampal development in these mice was disrupted, producing a phenotype intermediate to that of wild-type mice and Nfix(-/-) mice. The abnormal hippocampal morphology of Nfix (+/-) mice persisted to adulthood, and these mice displayed a specific performance deficit in the Morris water maze learning and memory task. These findings demonstrate that the level of Nfix expression during development and within the adult is essential for the function of the hippocampus during learning and memory.