Evaluation of efficiency omega 3 fatty acid improves the behavioural phenotype and protects against oxidative stress against MPP+ induces Parkinson's disease in mice.

This experiment proposed to study the efficiency omega 3 fatty acid on behavioural phenotype of Parkinson's disease (PD) in mice. Totally 7 groups (each group 6 mice) were used in this assessment, each groups were treated with saline (control), MPP+, L-DOPA, Omega 3 oil, Omega 3 oil (three different concentrations) +MPP+ separately. The behavioral assessments such as bar test, open field test, maze test, hang test were noted on 7th, 14th, 21st and 28th day. After the examination period, the tested animals' midbrains and frontal cortex were dissected to analyze TBARS, GSH, Catalase, Superoxide Dismutase and Glutathione Peroxidase assay. In the bar test, 500mg omega 3 fatty acid administrated mice showed a high cataleptic scores. In open field Test, significant reductions in behavior analysis were observed from the tested mice group. Maze test and hang test doesn't show much difference. In biochemical test, tested groups showed promising results compared to control group. The result strongly proved that the omega 3 fatty acid has remarkable abilities to control the neurodegenerative diseases.

Functional organization of the midbrain periaqueductal gray for regulating aversive memory formation.

Innately aversive experiences produce rapid defensive responses and powerful emotional memories. The midbrain periaqueductal gray (PAG) drives defensive behaviors through projections to brainstem motor control centers, but the PAG has also been implicated in aversive learning, receives information from aversive-signaling sensory systems and sends ascending projections to the thalamus as well as other forebrain structures which could control learning and memory. Here we sought to identify PAG subregions and cell types which instruct memory formation in response to aversive events. We found that optogenetic inhibition of neurons in the dorsolateral subregion of the PAG (dlPAG), but not the ventrolateral PAG (vlPAG), during an aversive event reduced memory formation. Furthermore, inhibition of a specific population of thalamus projecting dlPAG neurons projecting to the anterior paraventricular thalamus (aPVT) reduced aversive learning, but had no effect on the expression of previously learned defensive behaviors. By contrast, inactivation of dlPAG neurons which project to the posterior PVT (pPVT) or centromedial intralaminar thalamic nucleus (CM) had no effect on learning. These results reveal specific subregions and cell types within PAG responsible for its learning related functions.

Ninjinyoeito improves anxiety behavior in neuropeptide Y deficient zebrafish.

Anxiety induced by excess mental or physical stress is deeply involved in the onset of human psychiatric diseases such as depression, bipolar disorder, and panic disorder. Recently, Kampo medicines have received focus as antidepressant drugs for clinical use because of their synergistic and additive effects. Thus, we evaluated the anxiolytic activity of Ninjinyoeito (NYT) using neuropeptide Y-knockout (NPY-KO) zebrafish that exhibit severe anxiety responses to acute stress. Adult NPY-KO zebrafish were fed either a 3% NYT-supplemented or normal diet (i.e., the control diet) for four days and were then examined via behavioral tests. After short-term cold stress (10 °C, 2 s) was applied, control-fed NPY-KO zebrafish exhibited anxiety behaviors such as freezing, erratic movement, and increased swimming time along the tank wall. On the other hand, NYT-fed NPY-KO zebrafish significantly suppressed these anxiety behaviors, accompanied by a downregulation of tyrosine hydroxylase levels and phosphorylation of extracellular signal-regulated kinases in the brain. To understand the responsible component(s) in NYT, twelve kinds of herbal medicines that composed NYT were tested in behavioral trials with the zebrafish. Among them, nine significantly reduced freezing behavior in NPY-KO zebrafish. In particular, Schisandra fruit induced the most potent effect on abnormal zebrafish behavior, even in the lower amount (0.3% equivalent to NYT), followed by Atractylodes rhizome and Cinnamon bark. Subsequently, four lignans uniquely found in Schisandra fruit (i.e., gomisin A, gomisin N, schizandrin, and schizandrin B) were investigated for their anxiolytic activity in NPY-KO zebrafish. As a result, schizandrin was identified as a responsible compound in the anxiolytic effect of NYT. These results suggest that NYT has a positive effect on mental stress-induced anxiety and may be a promising therapeutic for psychiatric diseases.

Inhaled Lavandula angustifolia essential oil enhances extinction learning and inhibits memory updating in mice submitted to the contextual fear conditioning.

ETHNOPHARMACOLOGICAL RELEVANCE: Lavender (Lavandula angustifolia) essential oil (EO) has a long history of use in emotional illness, including anxiety disorders. Cognitive mechanisms of learning and memory play a pivotal role in the etiology and maintenance of anxiety since exposure to cues related to aversive situations induces high arousal and anticipatory anxiety. Memory become labile after its reactivation and can be modulated by reconsolidation or extinction. Inhibition of memory reconsolidation or facilitation of memory extinction may be effective in preventing or minimizing the effect of contextual cues on anticipatory anxiety. AIM OF THE STUDY: We investigated the effect of Lavandula angustifolia EO in the memory updating of conditioned contextual fear. MATERIALS AND METHODS: Adult male C57Bl6 mice were submitted to fear conditioning. Two days after conditioning the mice underwent a reactivation session in a hybrid context and were then immediately exposed to vaporized water or essential oil at concentrations of 1%, 2.5% or 5% for 3 h. Two days later, the mice were tested in the original or an altered context and their freezing behavior was measured. In addition, mice were subjected to a fear memory recovery protocol followed by a reinstatement session. RESULTS: In the contextual fear test, 1% essential oil, but not 2.5% or 5%, reduced the freezing behavior response, whereas after a reinstatement session, exposure to 1% essential oil increased the freezing behavior response. CONCLUSIONS: These results suggest that Lavandula angustifolia essential oil enhances memory extinction and, consequently, inhibits memory updating.

Investigating the role of the amygdala orexin receptor 1 in memory acquisition and extinction in a rat model of PTSD.

Understanding the mechanisms underlying memory is essential for the treatment of post-traumatic stress disorder (PTSD). Orexin, as a lateral hypothalamic (LH) neuropeptide, interferes with the stages of memory, primarily through the orexin receptor1 (Orx1R). The aim of this study was to evaluate the effects of amygdala Orx1R in the acquisition and extinction processes of PTSD modeled in animals. In three experiments, rats were divided into three groups: control (Naïve), shock (receiving a foot shock), and PTSD (experiencing Single prolonged stress (SPS) method). The first experiment aimed to evaluate LH activity in PTSD modeled rats. The second and third experiments aimed to evaluate the effects of Orx1R in the acquisition and extinction of fear memory in PTSD modeled animals. SB334867 (SB) or its solvent was microinjected into the amygdala and the rats were subjected to conditioning thereafter. In the second group, we used a single injection after conditioning. In the third group, we used three consecutive injections (one after each memory test). Some behaviors and Orx1R expression were evaluated. The freezing response was significantly longer in the PTSD group than on the control. Similarly, anxiety and sensitized fear were also intensified. CFos expression levels in LH was higher in the PTSD group. Inhibition of Orx1R in the amygdala significantly decreased memory acquisition, diminished anxiety, and decreased the sensitized fear in the SB group. Applying SB to the amygdala after each fear memory test significantly decreased freezing. Expression of Orx1R was significantly higher following fear conditioning. These results indicate a likely involvement of the orexin and amygdalar Orx1R in memory acquisition and in extinction of PTSD.

Defensive behaviors and brain regional activation changes in rats confronting a snake.

In the present study, we examined behavioral and brain regional activation changes of rats). To a nonmammalian predator, a wild rattler snake (Crotalus durissus terrificus). Accordingly, during snake threat, rat subjects showed a striking and highly significant behavioral response of freezing, stretch attend, and, especially, spatial avoidance of this threat. The brain regional activation patterns for these rats were in broad outline similar to those of rats encountering other predator threats, showing Fos activation of sites in the amygdala, hypothalamus, and periaqueductal gray matter. In the amygdala, only the lateral nucleus showed significant activation, although the medial nucleus, highly responsive to olfaction, also showed higher activation. Importantly, the hypothalamus, in particular, was somewhat different, with significant Fos increases in the anterior and central parts of the ventromedial hypothalamic nucleus (VMH), in contrast to patterns of enhanced Fos expression in the dorsomedial VMH to cat predators, and in the ventrolateral VMH to an attacking conspecific. In addition, the juxtodorsalmedial region of the lateral hypothalamus showed enhanced Fos activation, where inputs from the septo-hippocampal system may suggest the potential involvement of hippocampal boundary cells in the very strong spatial avoidance of the snake and the area it occupied. Notably, these two hypothalamic paths appear to merge into the dorsomedial part of the dorsal premammillary nucleus and dorsomedial and lateral parts of the periaqueductal gray, all of which present significant increases in Fos expression and are likely to be critical for the expression of defensive behaviors in responses to the snake threat.

Projection from the Anterior Cingulate Cortex to the Lateral Part of Mediodorsal Thalamus Modulates Vicarious Freezing Behavior.

Emotional contagion, a primary form of empathy, is present in rodents. Among emotional contagion behaviors, social transmission of fear is the most studied. Here, we modified a paradigm used in previous studies to more robustly assess the social transmission of fear in rats that experienced foot-shock. We used resting-state functional magnetic resonance imaging to show that foot-shock experience enhances the regional connectivity of the anterior cingulate cortex (ACC). We found that lesioning the ACC specifically attenuated the vicarious freezing behavior of foot-shock-experienced observer rats. Furthermore, ablation of projections from the ACC to the mediodorsal thalamus (MDL) bilaterally delayed the vicarious freezing responses, and activation of these projections decreased the vicarious freezing responses. Overall, our results demonstrate that, in rats, the ACC modulates vicarious freezing behavior via a projection to the MDL and provide clues to understanding the mechanisms underlying empathic behavior in humans.

Effect of Paeonia lactiflora, a traditional Chinese herb, on migraines based on clinical application and animal behavior analyses.

BACKGROUND: Paeonia lactiflora (PL) was widely used for pain relief, but its effects on migraine headaches remain unclear. PURPOSE: The aim of the present study was to investigate the effects of PL on migraine headaches. METHODS: First, we found that PL was frequently used in Taiwan for headache treatment based on data from Taiwan's National Health Insurance Research Database. Migraine was induced through the intraperitoneal injection (i.p.) of nitroglycerin (NTG, 10 mg/kg) in rats. Pretreatment with PL was administered orally 30 min prior to the NTG i.p. Migraine headache behavior was observed by video-recordings. Finally, the rats were sacrificed and brain was removed for immunohistochemistry staining analysis. RESULTS: The frequency and total time spent rearing up and sniffing in exploratory behavior, and walking in locomotor behavior, were reduced in the NTG group compared with the control group (all p <  0.001). This reduction could be ameliorated by pretreatment with PL 1.0 g/kg (all p <  0.05). Total time spent in the light chamber was lower in the NTG group compared with the control group (p <  0.05); this could be ameliorated by pretreatment with 1.0 g/kg PL (p <  0.05). The rats in the NTG group spent longer time on the smooth surface than those in the control group (p <  0.001); this could be shortened by pretreatment with 0.5 and 1.0 g/kg PL (both p <  0.01). The traveling distance of rats in the NTG group was shorter than in the control group (p <  0.001); rats given 1.0 g/kg PL had a longer traveling distance than those in the NTG group (p <  0.01). Both c-fos and CGRP immunoreactive cells increased in the TNC in the NTG group compared with that of the control group (both p <  0.001); this increased could be reduced by pretreatment with PL 0.5 and 1.0 g/kg (both p <  0.05). CONCLUSION: Pretreatment with PL ameliorated migraine headache behaviors in the NTG-induced migraine rat model, suggesting pretreatment with PL is beneficial for migraine headache treatment. This effect of PL is related to the decrease of c-fos and CGRP in the TNC. However, still there are too many methodological limitations which need to be overcome in further experiments to support the data.

A Fear Memory Engram and Its Plasticity in the Hypothalamic Oxytocin System.

Oxytocin (OT) release by axonal terminals onto the central nucleus of the amygdala exerts anxiolysis. To investigate which subpopulation of OT neurons contributes to this effect, we developed a novel method: virus-delivered genetic activity-induced tagging of cell ensembles (vGATE). With the vGATE method, we identified and permanently tagged a small subpopulation of OT cells, which, by optogenetic stimulation, strongly attenuated contextual fear-induced freezing, and pharmacogenetic silencing of tagged OT neurons impaired context-specific fear extinction, demonstrating that the tagged OT neurons are sufficient and necessary, respectively, to control contextual fear. Intriguingly, OT cell terminals of fear-experienced rats displayed enhanced glutamate release in the amygdala. Furthermore, rats exposed to another round of fear conditioning displayed 5-fold more activated magnocellular OT neurons in a novel environment than a familiar one, possibly for a generalized fear response. Thus, our results provide first evidence that hypothalamic OT neurons represent a fear memory engram.

Conditioned stimulus presentations alter anxiety level in fear-conditioned mice.

It is generally believed that fear is rapidly triggered by a distinct cue while anxiety onset is less precise and not associated with a distinct cue. Although it has been claimed that both processes can be measured with certain independence of each other, it is unclear how exactly they differ. In this study, we measured anxiety in mice that received discriminative fear conditioning using behavioral, heart rate and calcium (Ca2+) responses in the ventral hippocampal CA1 (vCA1) neurons. We found that the occurrence of fear significantly interfered with anxiety measurements under various conditions. Diazepam reduced basal anxiety level but had no effect during the presentation of conditioned stimulus (CS). Injection of an inhibitory peptide of PKMzeta (ZIP) into the basolateral amygdala almost entirely abolished CS-triggered fear expression and reduced anxiety to basal level. Heart rate measures suggested a small reduction in anxiety during CS-. Calcium responses in the lateral hypothalamus-projecting vCA1 neurons showed a steady decay during CS suggesting a reduced anxiety. Thus, under our experimental conditions, CS presentations likely reduce anxiety level in the fear-conditioned mice.

Posttraumatic stress disorder-type behaviors in streptozotocin-induced diabetic rats can be prevented by prolonged treatment with vitamin E.

Anxiety and stress disorders, such as posttraumatic stress disorder (PTSD) have been described as debilitating comorbidities of diabetes. In the present study, we aimed to investigate anxiety-like behavior and the extinction and generalization of aversive memories in fear conditioning using a streptozotocin-induced model of diabetes (DBT). Moreover, considering that DBT animals present increased oxidative stress in brain areas related to anxiety and memory, we aimed to evaluate the effect of prolonged treatment with antioxidant vitamin E on behavioral parameters of anxiety and fear memory and on the diabetic condition. It was observed that DBT animals showed a deficiency in extinguishing the aversive memory in a fear conditioning test, along with a generalization of the fear memory. They also present a more pronounced anxiety-like behavior in the elevated plus maze test. VIT E treatment (300 mg/kg, p.o.) was not able to reduce hyperglycemia; however, it was able to block the anxiogenic-like behavior, also improving the deficit in the extinction of the aversive memory as well as blocking the generalization of such memory in a different context. Taken together, our data suggest that DBT animals are prone to extinction deficits and generalization of fear memories, behaviors which are observed in models of PTSD. Lastly, prolonged VIT E supplementation may be effective in the treatment of anxiety, extinction deficit and generalization of fear memories induced by the diabetic condition.

Electrolytic post-training lesions of the bed nucleus of the stria terminalis block startle potentiation in a cued fear conditioning procedure.

Existing neuroanatomical models argue that the bed nucleus of the stria terminalis (BST) principally mediates sustained, long-lasting fear or anxiety responses, but not shorter, phasic fear responses, although recent studies paint a more complex picture. In the current study, we evaluated the effect of post-training electrolytic BST lesions in a cued fear conditioning protocol with relatively short (10 s) tones. We hypothesized that the BST would not play a crucial role in the expression of fear upon re-exposure to the conditioned tones. Tone fear memory was primarily assessed through fear-potentiated startle. In addition, freezing measurements were obtained throughout the test sessions. In a series of three experiments, we explored the effects of BST lesions, taking into consideration contextual influences on cued fear expression (using (dis)similar training and test contexts) and temporal involvement of the BST in the consolidation of fear learning (lesion induction 3 or 27 h after fear conditioning). In all three experiments, we found that post-training electrolytic lesions of the BST significantly reduced fear-potentiated startle, implying a deficit in differentiation between tone and context. These results are surprising and challenge the general consensus on the lack of BST involvement in cued fear. We discuss several alternative explanations that may account for these unexpected findings.

Response-specific sex difference in the retention of fear extinction.

Fear conditioning studies in rodents allow us to assess vulnerability factors which might underlie fear-based psychopathology such as post-traumatic stress disorder (PTSD). Despite PTSD being more prevalent in females than males, very few fear conditioning studies in rodents have tested females. Our study assessed fear conditioning and extinction in male and female rats using both fear-potentiated startle and freezing behavior as measures. Rats were trained to fear cues that predicted the occurrence of shock and then subsequently exposed to an extinction training procedure where the cue was presented repeatedly in the absence of shock. Retention of the extinction memory was assessed the next day. Our results showed that females exhibited less retention of fear extinction, but only when measured by fear-potentiated startle. Our results highlight the importance of using multiple indices of fear behavior, particularly when comparing sexes on measures of extinction learning.

Auditory conditioned stimulus presentation during NREM sleep impairs fear memory in mice.

Externally manipulating memories by presenting conditioned stimuli (CS) during sleep is a new approach to investigating memory processing during sleep. However, whether presenting a CS during REM or NREM sleep enhances or extinguishes fear memory has not been clearly delineated. In this study, mice underwent trace fear conditioning consisting of an auditory CS paired with a foot shock, and the auditory CS was re-presented during subsequent REM or NREM sleep. Mice that received auditory cueing during NREM but not REM sleep showed impaired fear memory upon later presentation of the auditory CS. These findings have implications for the use of cueing during sleep and advance our understanding of the role of REM and NREM sleep in memory consolidation.

Histaminergic Neurotransmission as a Gateway for the Cognitive Effect of Oleoylethanolamide in Contextual Fear Conditioning.

Background: The integrity of the brain histaminergic system is necessary for the unfolding of homeostatic and cognitive processes through the recruitment of alternative circuits with distinct temporal patterns. We recently demonstrated that the fat-sensing lipid mediator oleoylethanolamide indirectly activates histaminergic neurons to exerts its hypophagic effects. The present experiments investigated whether histaminergic neurotransmission is necessary also for the modulation of emotional memory induced by oleoylethanolamide in a contextual fear conditioning paradigm. Methods: We examined the acute effect of i.p. administration of oleoylethanolamide immediately posttraining in the contextual fear conditioning test. Retention test was performed 72 hours after training. To test the participation of the brain histaminergic system in the cognitive effect of oleoylethanolamide, we depleted rats of brain histamine with an i.c.v. injection of alpha-fluoromethylhistidine (a suicide inhibitor of histidine decarboxylase) or bilateral intra-amygdala infusions of histamine H1 or H2 receptor antagonists. We also examined the effect of oleoylethanolamide on histamine release in the amygdala using in vivo microdialysis. Results: Posttraining administration of oleoylethanolamide enhanced freezing time at retention. This effect was blocked by both i.c.v. infusions of alpha-fluoromethylhistidine or by intra-amygdala infusions of either pyrilamine or zolantidine (H1 and H2 receptor antagonists, respectively). Microdialysis experiments showed that oleoylethanolamide increased histamine release from the amygdala of freely moving rats. Conclusions: Our results suggest that activation of the histaminergic system in the amygdala has a "permissive" role on the memory-enhancing effects of oleoylethanolamide. Hence, targeting the H1 and H2 receptors may modify the expression of emotional memory and reduce dysfunctional aversive memories as found in phobias and posttraumatic stress disorder.

Acoustic startle response in rats predicts inter-individual variation in fear extinction.

Although a large portion of the population is exposed to a traumatic event at some point, only a small percentage of the population develops post-traumatic stress disorder (PTSD), suggesting the presence of predisposing factors. Abnormal acoustic startle response (ASR) has been shown to be associated with PTSD, implicating it as a potential predictor of the development of PTSD-like behavior. Since poor extinction and retention of extinction learning are characteristic of PTSD patients, it is of interest to determine if abnormal ASR is predictive of development of such deficits. To determine whether baseline ASR has utility in predicting the development of PTSD-like behavior, the relationship between baseline ASR and freezing behavior following Pavlovian fear conditioning was examined in a group of adult, male Sprague-Dawley rats. Baseline acoustic startle response (ASR) was assessed preceding exposure to a Pavlovian fear conditioning paradigm where freezing behavior was measured during fear conditioning, extinction training, and extinction testing. Although there was no relationship between baseline ASR and fear memory following conditioning, rats with low baseline ASR had significantly lower magnitude of retention of the extinction memory than rats with high baseline ASR. The results suggest that baseline ASR has value as a predictive index of the development of a PTSD-like phenotype.

Social buffering enhances extinction of conditioned fear responses in male rats.

In social species, the phenomenon in which the presence of conspecific animals mitigates stress responses is called social buffering. We previously reported that social buffering in male rats ameliorated behavioral fear responses, as well as hypothalamic-pituitary-adrenal axis activation, elicited by an auditory conditioned stimulus (CS). However, after social buffering, it is not clear whether rats exhibit fear responses when they are re-exposed to the same CS in the absence of another rat. In the present study, we addressed this issue using an experimental model of extinction. High stress levels during extinction training impaired extinction, suggesting that extinction is enhanced when stress levels during extinction training are low. Therefore, we hypothesized that rats that had received social buffering during extinction training would not show fear responses to a CS, even in the absence of another rat, because social buffering had enhanced the extinction of conditioned fear responses. To test this, we subjected male fear-conditioned rats to extinction training either alone or with a non-conditioned male rat. The subjects were then individually re-exposed to the CS in a recall test. When the subjects individually underwent extinction training, no responses were suppressed in the recall test. Conversely, when the subjects received social buffering during extinction training, freezing and Fos expression in the paraventricular nucleus of the hypothalamus and lateral amygdala were suppressed. Additionally, the effects of social buffering were absent when the recall test was conducted in a different context from the extinction training. The present results suggest that social buffering enhances extinction of conditioned fear responses.

Secondary task performance during challenging walking tasks and freezing episodes in Parkinson's disease.

Parkinson's disease (PD) patients likely use attentional strategies to compensate for their gait deficits, which increases the cognitive challenge of walking. The interplay between cognitive functions and gait can be investigated by evaluating the subject's attendance to a secondary task during walking. We hypothesized that the ability to attend to a secondary task decreases during challenging walking conditions in PD, particularly during freezing of gait (FOG)-episodes. Twenty-nine PD patients and 14 age-matched controls performed a simple reaction task that involved squeezing a ball as fast as possible in response to an auditory stimulus. Participants performed this reaction task during four conditions: (1) walking at preferred speed; (2) walking with short steps at preferred speed; (3) walking with short steps, as rapidly as possible; (4) making rapid full turns. We used surface electromyography to determine reaction times, and a pressure sensor located within the ball to determine movement onset. Reaction times of PD patients were slower (on average by 42 ms) compared to controls, regardless of the walking task. In both groups, reaction times were significantly longer during the turning condition compared to all other conditions. FOG-episodes were most often seen during the turning condition. In PD patients, reaction times were significantly longer during FOG-episodes compared to trials without FOG. Our results suggest that turning requires more attentional resources than other walking tasks. The observation of delayed reaction times during FOG-episodes compared to trials without FOG suggests that freezers use additional resources to overcome their FOG-episodes.

Salidroside, a Bioactive Compound of Rhodiola Rosea, Ameliorates Memory and Emotional Behavior in Adult Mice.

Rhodiola Rosea (R. Rosea) is a plant used in traditional popular medicine to enhance cognition and physical performance. R. Rosea medicinal properties have been related to its capability to act as an adaptogen, i.e., a substance able to increase the organism's resistance to a variety of chemical, biological, and physical stressors in a non-specific way. These adaptogen properties have been mainly attributed to the glycoside salidroside, one of the bioactive compounds present in the standardized extracts of R. Rosea. Here, we aimed to investigate whether a single dose of salidroside is able to affect memory and emotional behavior in wild type adult mice. We performed fear conditioning to assess cued and contextual memory, elevated plus maze and open field to evaluate anxiety, and tail suspension test to evaluate depression. Our results showed that a single i.p. administration of salidroside was able to enhance fear memory and exerted an anxiolytic and antidepressant effect. These data confirmed the adaptogenic effect of R. Rosea bioactive compounds in animal models and suggest that salidroside might represent an interesting pharmacological tool to ameliorate cognition and counteract mood disorders.

Anti-stress effects of ONO-2952, a novel translocator protein 18 kDa antagonist, in rats.

Accumulating evidence has shown the pathophysiological significance of the translocator protein 18 kDa (TSPO) in the central nervous system. In this study, we evaluated the beneficial effects of ONO-2952, a novel TSPO antagonist in rat stress models. ONO-2952 potently bound both rat and human TSPO (Ki=0.330-9.30 nmol/L) with high selectivity over other receptors, transporters, ion channels and enzymes. ONO-2952 inhibited both neurosteroid accumulation and noradrenaline release in the brain of rats exposed to acute stress. The inhibitory effect of ONO-2952 on stress-induced noradrenaline release was attenuated by co-treatment with the TSPO agonist CB34 in a dose-dependent manner. ONO-2952, at 0.3 mg/kg or higher, dose-dependently suppressed restraint stress-induced defecation in rats with brain TSPO occupancy of more than 50%. In addition, ONO-2952, at 1 mg/kg or higher, suppressed conditioned fear stress-induced freezing behavior in rats with an efficacy equivalent to that of diazepam, given orally at 3 mg/kg. Results of the passive avoidance learning test revealed that ONO-2952, unlike diazepam, did not affect learning and memory even at doses 10 times higher than its effective doses in the stress models. The present findings indicate that ONO-2952 is a promising candidate for the treatment of stress-related disorders.