Chronic administration of ketamine ameliorates the anxiety- and aggressive-like behavior in adolescent mice induced by neonatal maternal separation

Boosting decision-making in rat models of early-life adversity with environmental enrichment and intranasal oxytocin

Impaired decision-making constitutes a fundamental issue in numerous psychiatric disorders. Extensive research has established that early life adversity (ELA) increases vulnerability to psychiatric disorders later in life. ELA in human neonates is associated with changes in cognitive, emotional, as well as reward-related processing. Maternal separation (MS) is an established animal model of ELA and has been shown to be associated with decision-making deficits. On the other hand, enriched environment (EE) and intranasal oxytocin (OT) administration have been demonstrated to have beneficial effects on decision-making in humans or animals. Given these considerations, our investigation sought to explore the impact of brief exposure to EE and intranasal OT administration on the decision-making abilities of adolescent rats that had experienced MS during infancy. The experimental protocol involved subjecting rat pups to the MS regimen for 180 min per day from postnatal day (PND) 1 to PND 21. Then, from PND 22 to PND 34, the rats were exposed to EE and/or received intranasal OT (2 μg/μl) for seven days. The assessment of decision-making abilities, using a rat gambling task (RGT), commenced during adolescence. Our findings revealed that MS led to impaired decision-making and a decreased percentage of advantageous choices. However, exposure to brief EE or intranasal OT administration mitigated the deficits induced by MS and improved the decision-making skills of maternally-separated rats. Furthermore, combination of these treatments did not yield additional benefits. These results suggest that EE and OT may hold promise as therapeutic interventions to enhance certain aspects of cognitive performance.

Maternal separation stress through triggering of the neuro-immune response in the hippocampus induces autistic-like behaviors in male mice

Autism spectrum disorder (ASD) is the fastest-growing neurodevelopmental disease throughout the world. Neuro-immune responses from prenatal to adulthood stages of life induce developmental defects in synaptic signaling, neurotransmitter imbalance, and even structural changes in the brain. In this study, we aimed to focus on the possible role of neuroinflammatory response in the hippocampus in development of the autistic-like behaviors following maternal separation (MS) stress in mice. To do this, mice neonates daily separated from their mothers from postnatal day (PND) 2 to PND 14 for 3 h. During PND45-60, behavioral tests related to autistic-like behaviors including three-chamber sociability, Morris water maze (MWM), shuttle box, resident-intruder, and marble burying tests were performed. Then, hippocampi were dissected out, and the gene expression of inflammatory mediators including TNF-α, IL-1β, TLR4, HMGB1, and NLRP3 was assessed in the hippocampus using RT-PCR. Results showed that MS mice exerted impaired sociability preference, repetitive behaviors, impaired passive avoidance, and spatial memories. The gene expression of inflammatory mediators significantly increased in the hippocampi of MS mice. We concluded that MS stress probably via activating of the HMGB1/TLR4 signaling cascade in the hippocampus induced autistic-like behaviors in mice.

[Ketamine and suicidal behavior: Contribution of animal models of aggression-impulsivity to understanding its mechanism of action]

More than two-thirds of suicides occur during a major depressive episode. Acting out prevention measures and therapeutic options to manage the suicidal crisis are limited. The impulsive-aggressive dimensions are vulnerability factors associated with suicide in patients suffering from a characterized depressive episode: this can be a dimension involved in animals. Impulsive and aggressive rodent models can help analyze, at least in part, the neurobiology of suicide and the beneficial effects of treatments. Ketamine, a glutamatergic antagonist, by rapidly improving the symptoms of depressive episodes, would help reduce suicidal thoughts in the short term. Animal models share with humans impulsive and aggressive endophenotypes modulated by the serotonergic system (5-HTB receptor, MAO-A enzyme), neuroinflammation or the hypothalamic-pituitary-adrenal axis and stress. Significant effects of ketamine on these endophenotypes remain to be demonstrated.

Maternal separation early in life induces excessive activity of the central amygdala related to abnormal aggression

Epidemiological studies have indicated that child maltreatment, such as neglect, is a risk factor of escalated aggression, potentially leading to delinquency and violent crime in the future. However, little is known about the mechanisms by which an early adverse environment may later cause violent behavior. In this study, we aimed to thoroughly examine the association between aggression against conspecific animals and the activity of amygdala subnuclei using the maternal separation (MS) model, which is a common model of early life stress. In the MS group, pups of Sprague-Dawley rats were separated from their dam during postnatal days 2-20 (twice a day, 3 h each). We only included 9-week-old male offspring for each analysis and compared the MS group with the mother-reared control group; both groups were raised by the same dam during postnatal days 2-20. The results revealed that the MS group exhibited higher aggression and excessive activity of only the central amygdala (CeA) among the amygdala subnuclei during the aggressive behavior test. Moreover, a significant positive correlation was observed between higher aggression and CeA activation. While CeA activity is known to be involved in hunting behavior for prey, some previous studies have also indicated a relationship between CeA and intraspecific aggression. It remains unclear, however, whether excessive CeA activity directly induces intraspecific aggression. Therefore, we stimulated the CeA using optogenetics with 8-week-old rats to clarify the relationship between intraspecific aggression and CeA activity. Notably, CeA activation resulted in higher aggression, even when the opponent was a conspecific animal. In particular, bilateral CeA activation resulted in more severe displays of aggressive behavior than necessary, such as biting a surrendered opponent. These findings suggest that an adverse environment during early development intensifies aggression through excessive CeA activation, which can increase the risk of escalating to violent behavior in the future.

A single dose of ketamine enhances early life stress-induced aggression with no effect on fear memory, anxiety-like behavior, or depression-like behavior in mice

Ketamine is a dissociative anesthetic that has been shown to have antidepressant effects in humans and has been proposed as a potential treatment for mood disorders such as posttraumatic stress disorder and aggression. However, previous studies from our lab and others have demonstrated that ketamine's effects are highly context- and dose-dependent. In a recent study, we found that 10 mg/kg ketamine could exacerbate the effects of early life stress on excessive aggression in mice. To further investigate, the effect of ketamine on moods, such as fear, anxiety, depression, and aggression, we used a mouse model of early life stress, involving chronic social isolation followed by acute traumatic stress in the form of noncontingent, unpredictable foot shock during adolescence. We find this is necessary to induce long-lasting excessive aggression in a novel environment. Seven- to eight-week-old socially isolated mice were given IP injections of 10 mg/kg ketamine 30 min before being subjected to foot shock and then assessed 7 days later for changes in sociability, aggression, mobility, anxiety-like behavior, and depression-like behavior. The results show that ketamine selectively increases long-lasting aggression in mice exposed to foot shock, but does not affect mood-related behaviors or locomotion. These findings suggest that during early life stress, ketamine may exert its effects by specifically targeting aggression brain circuitry that is distinct from brain circuits responsible for nonaggressive social or emotional behaviors. Therefore, while ketamine may be a promising treatment for various mood disorders, caution should be exercised when using ketamine to treat disorders associated with early life stress. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Ketamine Use in Child and Adolescent Psychiatry: Emerging Data in Treatment-Resistant Depression, Insights from Adults, and Future Directions

PURPOSE OF REVIEW

The following review will explore ketamine's antidepressant and antisuicidal properties in adults, review of what is known about ketamine's safety in children, and summarize the limited information we have on ketamine's role in treating depression and suicidal ideation in adolescents with depression. Future directions for ketamine's role in child psychiatry based on animal and adult studies will also be explored.

RECENT FINDINGS

Over the past 20 years, ketamine has emerged as a novel treatment for depression and suicidal ideation in adults. In recent years, these studies have been extended to adolescents. In 2021, the first placebo-controlled trial examining ketamine's antidepressant potential in adolescents was performed, demonstrating superior efficacy over midazolam. Initial studies suggest that ketamine functions as a rapidly acting antidepressant in adolescents. Case reports suggest that ketamine may also reduce suicidal ideation in this population. However, existing studies are small, and more research is needed to solidify these findings and inform clinical practice.

The impact of environmental factors during maternal separation on the behaviors of adolescent C57BL/6 mice

Neonatal maternal separation is a widely used method to construct an early-life stress model in rodents. In this method, pups are separated from their mothers for several hours every day during the first 2 weeks of life, which results in adverse early-life events. It is a known fact that maternal separation can exert a significant impact on the behavior and psychological health, such as anxiety and depression, in adolescent offspring. However, environmental conditions during maternal separation can differ such as the presence of other animals or by placing pups in a different dam. To investigate the differential effects of various conditions of maternal separation on the behavior of adolescent mice, we created the following groups: (1) iMS group: pups were moved to an isolated room with no other adult mice in a nearby cage, (2) eDam group: the pups randomly exchanged their dams, (3) OF group: pups were shifted to another cage with the bedding material containing maternal odor (olfactory stimulation), and (4) MS group: pups were shifted to another vivarium. From postnatal day (PND) 2-20 (i.e., 19 consecutive days), pups were separated from the dam daily for 4 h and exposed to various environments (MS, iMS, eDam, and OF) or were left undisturbed [control (CON) group]. A series of behavioral assessments were conducted to evaluate locomotion, anxiety, recognition, learning, and memory in adolescent offspring. The results showed that neonatal maternal separation led to impaired recognition memory, motor coordination, and motor skill learning across all groups. However, the iMS group exhibited anxiety-like behavior in the elevated plus maze test and enhanced the extinction of fear memory in the auditory fear conditioning test. The OF and eDam groups displayed partially recovered short-term working memory in the Y-maze test but exhibited opposite exploratory behaviors. The OF group spent more time in the center, while the eDam group spent less time. These findings demonstrated that exposure to different environmental conditions during maternal separation causes behavioral alterations in adolescent offspring, providing a potential explanation for the variation in behavioral phenotypes observed in the early-life stress models.

Neurobiology of Aggression-Review of Recent Findings and Relationship with Alcohol and Trauma

Aggression can be conceptualized as any behavior, physical or verbal, that involves attacking another person or animal with the intent of causing harm, pain or injury. Because of its high prevalence worldwide, aggression has remained a central clinical and public safety issue. Aggression can be caused by several risk factors, including biological and psychological, such as genetics and mental health disorders, and socioeconomic such as education, employment, financial status, and neighborhood. Research over the past few decades has also proposed a link between alcohol consumption and aggressive behaviors. Alcohol consumption can escalate aggressive behavior in humans, often leading to domestic violence or serious crimes. Converging lines of evidence have also shown that trauma and posttraumatic stress disorder (PTSD) could have a tremendous impact on behavior associated with both alcohol use problems and violence. However, although the link between trauma, alcohol, and aggression is well documented, the underlying neurobiological mechanisms and their impact on behavior have not been properly discussed. This article provides an overview of recent advances in understanding the translational neurobiological basis of aggression and its intricate links to alcoholism and trauma, focusing on behavior. It does so by shedding light from several perspectives, including in vivo imaging, genes, receptors, and neurotransmitters and their influence on human and animal behavior.

Effects of the Recurrent and Different Doses of Ketamine Exposure on Anxiety-like Behaviors and Locomotor Activity in Juvenile Rats

BACKGROUND

Ketamine is a widely used anesthetic agent. Although the potential adverse effects of ketamine use in juvenile age are uncertain, certain studies reported that children exposed to recurrent anesthesia could face an increased risk of neurodevelopmental deficits in motor function and behavioral risks. We aimed to investigate the long-term effects of repeated exposure to various ketamine doses on anxious behavior and locomotor activity in juvenile rats.

OBJECTIVE

We aimed to investigate the long-term effects of repeated exposure to various ketamine doses on anxious behavior and locomotor activity in juvenile rats.

METHODS

Thirty-two Wistar Albino juvenile male rats were randomized into 5 mg/kg, 20 mg/kg, and 50 mg/kg ketamine (KET) and saline (Group C) Groups and KET was administered for 3 consecutive days at 3-hour intervals in 3 doses. Ten days after the last KET dose, behavioral parameters were analyzed with an open field test (OFT), elevated plus maze (EPM), and light-dark box (LDB). Satistical analysis was conducted with Kruskall-Wallis test followed by Dunn's Multiple Comparison Test.

RESULTS

Unsupported rearing behavior decreased in 50 mg/kg KET Groups when compared to Group C. Incorrect transition time, total grooming time, and transfer latency time increased significantly in the 50 mg/kg KET Group when compared to Group C.

CONCLUSION

These results suggested that 50 mg/kg KET led to anxiety-like behavior and destroyed memory and spatial navigation. Ketamine doses were associated with late effects of ketamine on anxiety- like behavior in juvenile rats. Further studies are needed to determine the mechanisms that play a role in the different effects of ketamine doses on anxiety and memory.

The Effects of Acute and Repeated Administration of Ketamine on Memory, Behavior, and Plasma Corticosterone Levels in Female Mice

Ketamine is an anesthetic drug that has recently been approved for the treatment of treatment-resistant depression. Females are diagnosed with Major Depressive Disorder at higher rates than males, yet most of the pre-clinical research on ketamine has been conducted in male subjects. Additionally, the literature on the acute and long-term behavioral and cognitive effects of ketamine shows conflicting results. It is important to examine the acute and long-term cognitive and behavioral effects of ketamine exposure at lower sub-anesthetic doses, as the recreational use of the drug at higher doses is associated with cognitive and memory impairments. The current study examined the effects of acute and repeated ketamine exposure on anxiety-like behavior, novel object recognition memory, depression-like behavior, and plasma corticosterone levels in 20 adult female C57BL/6J mice. Mice were exposed acutely or repeatedly for 10 consecutive days to saline or 15 mg/kg ketamine and behavior was measured in the open field test, novel object recognition test, and the Porsolt forced swim test. Plasma corticosterone levels were measured following behavioral testing. Acute ketamine exposure decreased locomotor activity and increased anxiety-like behavior in the open field test compared to controls, while repeated ketamine exposure impaired memory in the novel object recognition test. There were no effects of acute or repeated ketamine exposure on depression-like behavior in the Porsolt forced swim test or on plasma corticosterone levels. These findings suggest that a subanesthetic dose of ketamine alters behavior and cognition in female mice and the effects are dependent on the duration of exposure.

Neural mechanism underlying depressive-like state associated with social status loss

Downward social mobility is a well-known mental risk factor for depression, but its neural mechanism remains elusive. Here, by forcing mice to lose against their subordinates in a non-violent social contest, we lower their social ranks stably and induce depressive-like behaviors. These rank-decline-associated depressive-like behaviors can be reversed by regaining social status. In vivo fiber photometry and single-unit electrophysiological recording show that forced loss, but not natural loss, generates negative reward prediction error (RPE). Through the lateral hypothalamus, the RPE strongly activates the brain's anti-reward center, the lateral habenula (LHb). LHb activation inhibits the medial prefrontal cortex (mPFC) that controls social competitiveness and reinforces retreats in contests. These results reveal the core neural mechanisms mutually promoting social status loss and depressive behaviors. The intertwined neuronal signaling controlling mPFC and LHb activities provides a mechanistic foundation for the crosstalk between social mobility and psychological disorder, unveiling a promising target for intervention.

Maternal separation in mice leads to anxiety-like/aggressive behavior and increases immunoreactivity for glutamic acid decarboxylase and parvalbumin in the adolescence ventral hippocampus

It has been reported that stressful events in early life influence behavior in adulthood and are associated with different psychiatric disorders, such as major depression, post-traumatic stress disorder, bipolar disorder, and anxiety disorder. Maternal separation (MS) is a representative animal model for reproducing childhood stress. It is used as an animal model for depression, and has well-known effects, such as increasing anxiety behavior and causing abnormalities in the hypothalamic-pituitary-adrenal (HPA) axis. This study investigated the effect of MS on anxiety or aggression-like behavior and the number of GABAergic neurons in the hippocampus. Mice were separated from their dams for four hours per day for 19 d from postnatal day two. Elevated plus maze (EPM) test, resident-intruder (RI) test, and counted glutamic acid decarboxylase 67 (GAD67) or parvalbumin (PV) positive cells in the hippocampus were executed using immunohistochemistry. The maternal segregation group exhibited increased anxiety and aggression in the EPM test and the RI test. GAD67-positive neurons were increased in the hippocampal regions we observed: dentate gyrus (DG), CA3, CA1, subiculum, presubiculum, and parasubiculum. PV-positive neurons were increased in the DG, CA3, presubiculum, and parasubiculum. Consistent with behavioral changes, corticosterone was increased in the MS group, suggesting that the behavioral changes induced by MS were expressed through the effect on the HPA axis. Altogether, MS alters anxiety and aggression levels, possibly through alteration of cytoarchitecture and output of the ventral hippocampus that induces the dysfunction of the HPA axis.

Neurobiological, behavioral, and cognitive effects of ketamine in adolescents: A review of human and pre-clinical research

S-ketamine is approved for treatment-resistant patients with depression and adult patients with suicide behavior. While ketamine is therapeutically beneficial in adults, there is a dearth of research on the effects of ketamine on adolescent brain function and behavior. In this review we summarize the current literature on the neurobiological and behavioral effects of adolescent ketamine exposure in preclinical animal models and humans. A search of PubMed was conducted using pre-defined criteria, resulting in the evaluation of 406 articles. A total of 39 animal studies and 7 human studies met the selection criteria. The included studies examined the effects of ketamine exposure during adolescence and excluded studies on ketamine use for pain or anesthesia and ketamine as a model of schizophrenia. Pre-clinical animal models of adolescent ketamine exposure show ketamine-induced neurotoxicity and apoptosis, and changes in locomotor activity, social behaviors, anxiety- and depression-like behaviors, and memory. There is variability in the results, and differences in ketamine dose and length of exposure appears to influence the results. Ketamine reduces symptoms of depression and anxiety and improves mood in human adolescents. Much of the literature on adolescent ketamine exposure examines the effects in males, with more limited research in females. Relatively little research has focused on adolescent ketamine exposure. Despite its effectiveness for mitigating symptoms of depression, adolescent ketamine exposure can disrupt memory and other behaviors and have deleterious effects on brain function. Further research is warranted to better define doses and dosing paradigms that are beneficial without unintended side effects in adolescence.

Promises and Pitfalls of NMDA Receptor Antagonists in Treating Violent Aggression

Treatment options for chronically aggressive individuals remain limited despite recent medical advances. Traditional pharmacological agents used to treat aggression, such as atypical antipsychotics, have limited efficacy and are often replete with dangerous side effects. The non-competitive NMDAR antagonists ketamine and memantine are promising alternatives, but their effects appear to be highly dependent on dosage, context, and personal experience. Importantly, these drugs can increase aggression when combined with substances of abuse or during periods of heightened stress. This is likely due to mechanistic differences operating at specific synapses under different contexts. Previous findings from our lab and others have shown that early life stress, substance abuse, and attack experience promote aggression through NMDAR-dependent synaptic plasticity within aggression-related brain circuits. Ketamine and memantine affect these types of aggression in opposite ways. This has led us to propose that ketamine and memantine oppositely affect aggression brought on by early life stress, substance abuse, or attack experience through opposite effects on NMDAR-dependent synaptic plasticity. This would account for the persistent effects of these drugs on aggression and suggest they could be leveraged as a more long-lasting treatment option. However, a more thorough examination of the effects of ketamine and memantine on cellular and synaptic function will be necessary for responsible administration. Additionally, because the effects of ketamine and memantine are highly dependent on prior drug use, traumatic stress, or a history of aggressive behavior, we propose a more thorough medical evaluation and psychiatric assessment will be necessary to avoid possible adverse interactions with these drugs.

Opposing effects of NMDA receptor antagonists on early life stress-induced aggression in mice

Rates of childhood trauma are high amongst violent offenders who frequently recidivate. Few clinical options are available to treat excessive and recurring violent aggression associated with childhood trauma. Those that do exist are largely ineffective and often replete with side effects. One promising pharmacological target is the glutamate binding N-methyl- d-aspartate receptor (NMDAR). Clinically available NMDAR antagonists have proven successful in mitigating violent and aggressive behavior associated with a host of psychiatric diseases and have both immediate and long-term effects on nervous system function and behavior. This study examined the impact of three NMDAR antagonists on long-lasting aggression brought on by early-life stress: MK-801, memantine, and ketamine. We find that social isolation early in adolescence followed by acute traumatic stress in the form of noncontingent foot shock (FS) late in adolescence works in tandem to promote long-lasting excessive aggression in mice when measured 1 week later. Systemic injections of MK-801 and memantine 30 min before FS suppressed the long-lasting attack behavior induced by our early life stress induction protocol. Systemic injections of ketamine, on the other hand, significantly enhanced the long-lasting attack behavior when injected before FS. These findings indicate that MK-801, memantine, and ketamine have distinct and opposing effects on early life stress-induced aggression, suggesting these drugs may be mechanistically distinct. This study identifies memantine as a promising pharmacological treatment for aggressive behavior associated with early life stress and demonstrates the need for greater care when using glutamate receptor antagonists to treat aggression.

Acute (R,S)-Ketamine Administration Induces Sex-Specific Behavioral Effects in Adolescent but Not Aged Mice

(R,S)-ketamine is an N-methyl-D-aspartate (NMDA) receptor antagonist that was originally developed as an anesthetic. Most recently, (R,S)-ketamine has been used as a rapid-acting antidepressant, and we have reported that (R,S)-ketamine can also be a prophylactic against stress in adult mice. However, most pre-clinical studies have been performed in adult mice. It is still unknown how an acute (R,S)-ketamine injection influences behavior across the lifespan (e.g., to adolescent or aged populations). Here, we administered saline or (R,S)-ketamine at varying doses to adolescent (5-week-old) and aged (24-month-old) 129S6/SvEv mice of both sexes. One hour later, behavioral despair, avoidance, locomotion, perseverative behavior, or contextual fear discrimination (CFD) was assessed. A separate cohort of mice was sacrificed 1 h following saline or (R,S)-ketamine administration. Brains were processed to quantify the marker of inflammation Cyclooxygenase 2 (Cox-2) expression to determine whether the acute effects of (R,S)-ketamine were partially mediated by changes in brain inflammation. Our findings show that (R,S)-ketamine reduced behavioral despair and perseverative behavior in adolescent female, but not male, mice and facilitated CFD in both sexes at specific doses. (R,S)-ketamine reduced Cox-2 expression specifically in ventral CA3 (vCA3) of male mice. Notably, (R,S)-ketamine was not effective in aged mice. These results underscore the need for sex- and age-specific approaches to test (R,S)-ketamine efficacy across the lifespan.

Effects of short environmental enrichment on early-life adversity induced cognitive alternations in adolescent rats

Early-life experiences, including parental care, affect cognitive performance later in life. Being exposed to early-life maternal separation (MS) increases susceptibility to stress-related psychopathology. Previous studies suggest that MS could induce learning and memory impairments. Since enriched environment (EE) provides more opportunities for exploration and social interaction, in the present study we evaluated the effects of a short EE paradigm with a duration of 13 days on cognitive abilities of maternally separated rats (MS; 180 min/day, postnatal day (PND) 1-21) during adolescence in four experimental groups: Control, Control+EE, MS, and MS+EE. Plasma corticosterone (CORT) and brain-derived neurotrophic factor (BDNF) levels were also measured in experimental animals. We also studied the induction of long-term potentiation (LTP) in the slices of hippocampal CA1 area. The behavioral and electrophysiological assessments were started at PND 35. MS caused higher basal CORT levels in plasma and impaired spatial learning, memory, and social interaction. LTP induction was also impaired in MS rats and plasma BDNF levels were reduced in these animals. MS also induced more anxiety-like behavior. Short EE reduced plasma CORT levels had the potential to improve locomotor activity and anxiety-like behavior in MS+EE rats and reversed MS-induced impairments of spatial learning, memory, and social behavior. LTP induction and plasma BDNF levels were also enhanced in MS+EE rats. We concluded that short EE might be considered as a therapeutic strategy for promoting cognition.

Anger management: Mechanisms of glutamate receptor-mediated synaptic plasticity underlying animal aggression

Excessive and recurring violent aggression is a serious concern for society and a symptom of many psychiatric diseases. Substance abuse, attack experience, and social and traumatic stress increase vulnerability to developing this type of aggression. Glutamate receptors are an intriguing target for long-term treatment. This review will assess the importance of glutamate receptors and glutamatergic pathways in aggression, focusing on the role of glutamate receptor-mediated synaptic plasticity in experience-dependent long-lasting aggression. By synthesizing what is known about glutamatergic systems in aggression, it is hoped more effective treatments can be developed.

Context-Specific Tolerance and Pharmacological Changes in the Infralimbic Cortex-Nucleus Accumbens Shell Pathway Evoked by Ketamine

Like other drugs, ketamine is abused due to its ability to act as a positive reinforcer in the control of behavior, just as natural reinforcers do. Besides, through Pavlovian conditioning, tolerance to drug effects can become conditioned to specific contextual cues showing that environmental stimuli can act as powerful mediators of craving and relapse. In the present study, we shall investigate the effects of long-term ketamine administration and withdrawal on behavioral measures and emotionality, the drug-context-specific influence on the tolerance to the sedative effects of an anesthetic dose of ketamine, and the neuropharmacological events underlying this phenomenon, in rats conditioned with 10 mg/kg of ketamine and later challenged with a dose of ketamine of 80 mg/kg in a familiar and non-familiar environment. Variations in dopamine and serotonin efflux in the infralimbic cortex-nucleus accumbens shell circuitry (IL-NAcSh) was further recorded in the same conditions. Our results highlight that besides its well-known reinforcing properties, ketamine also shares the ability to induce behavioral and pharmacological conditioned tolerance, associated with increases in cortical (IL), and decreases in striatal (NAcSh) dopamine release. To our knowledge, we are presenting the first set of behavioral and neurochemical data showing that, like other drugs of abuse, ketamine can induce learned context-specific tolerance.

Intranasal oxytocin administration facilitates the induction of long-term potentiation and promotes cognitive performance of maternally separated rats

Maternal separation (MS) is known to induce permanent changes in the central nervous system and is associated with increased levels of anxiety and cognitive impairments. The neuropeptide oxytocin (OT) has been implicated in a broad spectrum of social and nonsocial and behaviors. Since it plays a significant role in learning and memory and enhances synaptic plasticity, we hypothesized that OT may affect MS-induced changes in synaptic plasticity and cognitive performance. Rat pups underwent MS protocol for 180 min/day from postnatal day (PND) 1-21. OT was administered intranasally (2 μg/μl, 7 days) to control and MS groups from PND 22-34. Plasma corticosterone (CORT) levels, anxiety-like behavior, sociability, learning and memory were measured in adolescent rats. In addition, extracellular evoked field excitatory postsynaptic potentials (fEPSP) were also recorded from hippocampal slices. MS induced higher plasma CORT levels and impaired social interaction, learning and memory. Moreover, MS reduced locomotor activity and increased anxiety-like behavior. Intranasal OT could overcome MS-induced deficits and promoted sociability, learning and memory of MS rats. OT also enhanced locomotor activity in the open field and decreased anxiety-like behavior. Obtained results showed that long term potentiation (LTP) was not induced in MS animals. However, OT injection overcame the MS-induced impairment in LTP generation in CA1 area of the hippocampus.

Possible involvement of NMDA receptor in the anxiolytic-like effect of caffeic acid in mice model of maternal separation stress

Background and aim

Anxiety disorders are one of the most common psychiatric disorders worldwide. Common anti-anxiety medications are associated with several side effects. Caffeic acid (CA) is a phenolic compound with several pharmacological effects. The aim of this study was to investigate the anxiolytic-like effect of CA in maternally separated (MS) mice focusing on the possible involvement of the NMDA receptor.

Materials and methods

In this study, we used the MS paradigm (as a valid animal model of anxiety) in male mice and examined their anxiety-like behavior in postnatal day (PND) 45. The animals were divided into 12 experimental groups. Mice treated with CA alone and in combination with the NMDA receptor agonist/antagonist and then using open field (OFT) and elevated plus maze (EPM) anxiety-like behavior was assessed. Finally, the expression of NMDA receptor subtypes was assessed in the hippocampus using RT- PCR.

Results

Finding showed that CA exerted anxiolytic –like effects in the OFT and EPM tests. We showed that administration of effective dose of NMDA significantly reversed the anxiolytic-like effect of effective dose of CA and co-administration of ketamine (a NMDA receptor antagonist) significantly potentiated the effect of sub-effective dose of CA. Furthermore, ketamine enhanced the CA-reducing effect on NMDA receptors in the MS mice.

Conclusion

Our finding demonstrated that, probably at least, NMDA receptors are involved in the anxiety-like properties of CA in MS mice.

Maternal separation plus social isolation during adolescence reprogram brain dopamine and endocannabinoid systems and facilitate alcohol intake in rats

Adverse early life experiences, i.e. abusive parenting, during postnatal development, induce long-lasting effects on the stress response systems and behavior. Such changes persist throughout an individual's life, making him/her vulnerable to suffer psychiatric disorders, including anxiety disorders and drug addiction. Rat pup maternal separation (MS) is a widely used rodent early-life stress model. MS induces changes in the dopamine and endocannabinoid systems in the nucleus accumbens (NAcc) that facilitate alcohol consumption. In this study, our endeavor was to determine if social isolation during adolescence (aSI) was as efficient as MS to facilitate alcohol intake; and moreover, if their combination (MS + aSI) induces even higher alcohol intake and exacerbates anxiety-like behaviors. Also, we evaluated dopamine and endocannabinoid receptors in the NAcc to describe potential changes caused by MS, aSI or both. Wistar rats were reared under 4 different conditions: non-MS + social housing (SH), MS + SH, non-MS + aSI and MS + aSI. Once these rats became adults they were submitted to a voluntary alcohol intake protocol for 10 days. Similar groups of rats with no exposure to alcohol whatsoever, were sacrificed to dissect out the NAcc to analyze the expression of cannabinoid (CB1R and CB2R) and dopamine (D2R and D3R) receptors. Results showed that MS, aSI and MS + aSI increase both CB1R, D2R and D3R expression in the NAcc and also increase alcohol intake and anxiety. These results suggest that early life adverse experiences induce a reprogramming of the brain's dopamine and endocannabinoid systems which increases subject's vulnerability to develop anxiety, alcohol abuse and dependence.

Effect of early life stress on anxiety and depressive behaviors in adolescent mice

INTRODUCTION

Adolescence is a critical period for physical and mental development. The effect of early life stress on mood disorders has been intensively studied in adults using rodent models, but it has been less studied in adolescents. The present study aimed to examine the effect of early life stress on anxiety-related and depression-like behaviors in adolescent C57BL/6 mice and the sex difference.

METHODS

C57BL/6 mice of both sexes were used, and early life stressors included maternal separation (MS, P2-12, 4 hr per day), restraint stress (RS, P33 to 39, 4 hr per day), and their combination (MRS). Open field test, elevated plus maze, and forced swimming test were performed at different time points during adolescence and adulthood.

RESULTS

It was found that MS did not affect the anxiety-related behaviors of both males and females tested on P30-31 and P41-42. RS decreased the anxiety level in adolescent males but did not affect it in the females. MS, RS, and MRS all significantly increased the depression-like behavior in adolescent males, but only MRS increased the depression-like behavior in adolescent females. All effects on adolescent males and females did not persist into adulthood.

CONCLUSION

The present results showed that early life stress affected anxiety-related and depression-like behavior in adolescent mice in manners depending on the nature of stress, the developmental period, and sex.

Early Celastrol Administration Prevents Ketamine-Induced Psychotic-Like Behavioral Dysfunctions, Oxidative Stress and IL-10 Reduction in The Cerebellum of Adult Mice

Administration of subanesthetic doses of ketamine during brain maturation represents a tool to mimic an early insult to the central nervous system (CNS). The cerebellum is a key player in psychosis pathogenesis, to which oxidative stress also contributes. Here, we investigated the impact of early celastrol administration on behavioral dysfunctions in adult mice that had received ketamine (30 mg/kg i.p.) at postnatal days (PNDs) 7, 9, and 11. Cerebellar levels of 8-hydroxydeoxyguanosine (8-OHdG), NADPH oxidase (NOX) 1 and NOX2, as well as of the calcium-binding protein parvalbumin (PV), were also assessed. Furthermore, celastrol effects on ketamine-induced alterations of proinflammatory (TNF-α, IL-6 and IL-1β) and anti-inflammatory (IL-10) cytokines in this brain region were evaluated. Early celastrol administration prevented ketamine-induced discrimination index decrease at adulthood. The same was found for locomotor activity elevations and increased close following and allogrooming, whereas no beneficial effects on sniffing impairment were detected. Ketamine increased 8-OHdG in the cerebellum of adult mice, which was also prevented by early celastrol injection. Cerebellar NOX1 levels were enhanced at adulthood following postnatal ketamine exposure. Celastrol per se induced NOX1 decrease in the cerebellum. This effect was more significant in animals that were early administered with ketamine. NOX2 levels did not change. Ketamine administration did not affect PV amount in the cerebellum. TNF-α levels were enhanced in ketamine-treated animals; however, this was not prevented by early celastrol administration. While no changes were observed for IL-6 and IL-1β levels, ketamine determined a reduction of cerebellar IL-10 expression, which was prevented by early celastrol treatment. Our results suggest that NOX inhibition during brain maturation prevents the development of psychotic-like behavioral dysfunctions, as well as the increased cerebellar oxidative stress and the reduction of IL-10 in the same brain region following ketamine exposure in postnatal life. This opens novel neuroprotective opportunities against early detrimental insults occurring during brain development.