Dorsal peduncular cortex activity modulates affective behavior and fear extinction in mice

The medial prefrontal cortex (mPFC) is critical to cognitive and emotional function and underlies many neuropsychiatric disorders, including mood, fear and anxiety disorders. In rodents, disruption of mPFC activity affects anxiety- and depression-like behavior, with specialized contributions from its subdivisions. The rodent mPFC is divided into the dorsomedial prefrontal cortex (dmPFC), spanning the anterior cingulate cortex (ACC) and dorsal prelimbic cortex (PL), and the ventromedial prefrontal cortex (vmPFC), which includes the ventral PL, infralimbic cortex (IL), and in some studies the dorsal peduncular cortex (DP) and dorsal tenia tecta (DTT). The DP/DTT have recently been implicated in the regulation of stress-induced sympathetic responses via projections to the hypothalamus. While many studies implicate the PL and IL in anxiety-, depression-like and fear behavior, the contribution of the DP/DTT to affective and emotional behavior remains unknown. Here, we used chemogenetics and optogenetics to bidirectionally modulate DP/DTT activity and examine its effects on affective behaviors, fear and stress responses in C57BL/6J mice. Acute chemogenetic activation of DP/DTT significantly increased anxiety-like behavior in the open field and elevated plus maze tests, as well as passive coping in the tail suspension test. DP/DTT activation also led to an increase in serum corticosterone levels and facilitated auditory fear extinction learning and retrieval. Activation of DP/DTT projections to the dorsomedial hypothalamus (DMH) acutely decreased freezing at baseline and during extinction learning, but did not alter affective behavior. These findings point to the DP/DTT as a new regulator of affective behavior and fear extinction in mice.

Behavioral effects of chronic stress in Carioca high- and low-conditioned freezing rats

Chronic unpredictable mild stress (CUMS) is a widely used model to study stress-coping strategies in rodents. Different factors have been shown to influence whether animals adopt passive or active coping responses to CUMS. Individual adaptation and susceptibility to the environment seem to play a critical role in this process. To further investigate this relationship, we examined the effects of CUMS on Carioca high- and low-conditioned freezing rats (CHF and CLF, respectively), bidirectional lines of animals selected for high and low freezing in response to contextual cues that were previously associated with footshocks. For this purpose, the behavior of CHF and CLF animals was evaluated in the contextual fear conditioning, open field, elevated T maze, and forced swimming tests before and after 21 days of CUMS. For all tests, CHF rats were more susceptible to the effects of CUMS compared to CLF. CHF animals exposed to CUMS displayed a reduction in freezing behavior, decreased number of entries and time spent in the center of the open field, greater latencies to become immobile, and increased avoidance and escaping behaviors in the elevated T maze. Overall, these findings support the hypothesis that a heightened susceptibility to the environment exerts a strong influence on coping responses to chronic stress.

Glial-Specific Deletion of Med12 Results in Rapid Hearing Loss via Degradation of the Stria Vascularis

Mediator protein complex subunit 12 (Med12) is a core component of the basal transcriptional apparatus and plays a critical role in the development of many tissues. Mutations in Med12 are associated with X-linked intellectual disability syndromes and hearing loss; however, its role in nervous system function remains undefined. Here, we show that temporal conditional deletion of Med12 in astrocytes in the adult CNS results in region-specific alterations in astrocyte morphology. Surprisingly, behavioral studies revealed rapid hearing loss after adult deletion of Med12 that was confirmed by a complete abrogation of auditory brainstem responses. Cellular analysis of the cochlea revealed degeneration of the stria vascularis, in conjunction with disorganization of basal cells adjacent to the spiral ligament and downregulation of key cell adhesion proteins. Physiologic analysis revealed early changes in endocochlear potential, consistent with strial-specific defects. Together, our studies reveal that Med12 regulates auditory function in the adult by preserving the structural integrity of the stria vascularis.SIGNIFICANCE STATEMENT Mutations in Mediator protein complex subunit 12 (Med12) are associated with X-linked intellectual disability syndromes and hearing loss. Using temporal-conditional genetic approaches in CNS glia, we found that loss of Med12 results in severe hearing loss in adult animals through rapid degeneration of the stria vascularis. Our study describes the first animal model that recapitulates hearing loss identified in Med12-related disorders and provides a new system in which to examine the underlying cellular and molecular mechanisms of Med12 function in the adult nervous system.

PIEZO2 mediates ultrasonic hearing via cochlear outer hair cells in mice

Ultrasonic hearing and vocalization are the physiological mechanisms controlling echolocation used in hunting and navigation by microbats and bottleneck dolphins and for social communication by mice and rats. The molecular and cellular basis for ultrasonic hearing is as yet unknown. Here, we show that knockout of the mechanosensitive ion channel PIEZO2 in cochlea disrupts ultrasonic- but not low-frequency hearing in mice, as shown by audiometry and acoustically associative freezing behavior. Deletion of Piezo2 in outer hair cells (OHCs) specifically abolishes associative learning in mice during hearing exposure at ultrasonic frequencies. Ex vivo cochlear Ca2+ imaging has revealed that ultrasonic transduction requires both PIEZO2 and the hair-cell mechanotransduction channel. The present study demonstrates that OHCs serve as effector cells, combining with PIEZO2 as an essential molecule for ultrasonic hearing in mice.

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.

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.

Impaired pattern separation in Tg2576 mice is associated with hyperexcitable dentate gyrus caused by Kv4.1 downregulation

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that causes memory loss. Most AD researches have focused on neurodegeneration mechanisms. Considering that neurodegenerative changes are not reversible, understanding early functional changes before neurodegeneration is critical to develop new strategies for early detection and treatment of AD. We found that Tg2576 mice exhibited impaired pattern separation at the early preclinical stage. Based on previous studies suggesting a critical role of dentate gyrus (DG) in pattern separation, we investigated functional changes in DG of Tg2576 mice. We found that granule cells in DG (DG-GCs) in Tg2576 mice showed increased action potential firing in response to long depolarizations and reduced 4-AP sensitive K+-currents compared to DG-GCs in wild-type (WT) mice. Among Kv4 family channels, Kv4.1 mRNA expression in DG was significantly lower in Tg2576 mice. We confirmed that Kv4.1 protein expression was reduced in Tg2576, and this reduction was restored by antioxidant treatment. Hyperexcitable DG and impaired pattern separation in Tg2576 mice were also recovered by antioxidant treatment. These results highlight the hyperexcitability of DG-GCs as a pathophysiologic mechanism underlying early cognitive deficits in AD and Kv4.1 as a new target for AD pathogenesis in relation to increased oxidative stress.

Physiological response to the odorant TMT in fully fed and calorically restricted laboratory mice

2,3,5-trimethyl-3-thiazoline (TMT) is a chemical compound that is extracted from red fox urine and can be used to artificially simulate the presence of a predator. The purpose of this study was to test the hypothesis that TMT would block entry into torpor in the calorically restricted C57Bl/6 mouse. We first demonstrated that TMT induced fear in the mouse. Exposure to TMT induced an acute freeze response (67.2 ± 6.7% of time), as compared to 6.7 ± 1.7% when exposed to water. Further, exposure to TMT for 30 min led to elevated circulating corticosterone levels, 377 ± 33 ng/ml, as compared to 29 ± 4 ng/ml when exposed to water. When mice were exposed to TMT during the dark or light phase, body temperature (T_b) dropped by 1.7 ± 0.9 °C and 0.7 ± 1.1 °C, respectively, over the first 110 min after exposure. To determine whether TMT influences daily torpor, mice were calorically restricted and exposed to either water or TMT. Mice were exposed 30 min before the start of torpor, determined by the bout of the previous day. Exposure to TMT significantly (p < 0.01) blunted the fall in the minimum T_b from 28.8 ± 0.3 °C (water) to 30.1 ± 0.6 °C (TMT) and significantly (p < 0.05) decreased the amount of time T_b was under 32 °C, from 431 ± 48 min (water) to 292 ± 78 min (TMT). These results establish that mice perceived the scent of TMT as a physiologically stressful stimulus and that T_b response is modestly blunted in the presence of that stressor. Our experiment highlights the intricate interplay between predation risk and energy conservation.

c-Fos expression following context conditioning and deep brain stimulation in the bed nucleus of the stria terminalis in rats

Deep brain stimulation (DBS) in the bed nucleus of the stria terminalis (BST), a region implicated in the expression of anxiety, shows promise in psychiatric patients, but its effects throughout the limbic system are largely unknown. In male Wistar rats, we first evaluated the neural signature of contextual fear (N = 16) and next, of the anxiolytic effects of high-frequency electrical stimulation in the BST (N = 31), by means of c-Fos protein expression. In non-operated animals, we found that the left medial anterior BST displayed increased c-Fos expression in anxious (i.e., context-conditioned) versus control subjects. Moreover, control rats showed asymmetric expression in the basolateral amygdala (BLA) (i.e., higher intensities in the right hemisphere), which was absent in anxious animals. The predominant finding in rats receiving bilateral BST stimulation was a striking increase in c-Fos expression throughout much of the left hemisphere, which was not confined to the predefined regions of interest. To conclude, we found evidence for lateralized c-Fos expression during the expression of contextual fear and anxiolytic high-frequency electrical stimulation of the BST, particularly in the medial anterior BST and BLA. In addition, we observed an extensive and unexpected left-sided c-Fos spread following bilateral stimulation in the BST.

Cerebellar modulation of synaptic input to freezing-related neurons in the periaqueductal gray

Innate defensive behaviors, such as freezing, are adaptive for avoiding predation. Freezing-related midbrain regions project to the cerebellum, which is known to regulate rapid sensorimotor integration, raising the question of cerebellar contributions to freezing. Here, we find that neurons of the mouse medial (fastigial) cerebellar nuclei (mCbN), which fire spontaneously with wide dynamic ranges, send glutamatergic projections to the ventrolateral periaqueductal gray (vlPAG), which contains diverse cell types. In freely moving mice, optogenetically stimulating glutamatergic vlPAG neurons that express Chx10 reliably induces freezing. In vlPAG slices, mCbN terminals excite ~20% of neurons positive for Chx10 or GAD2 and ~70% of dopaminergic TH-positive neurons. Stimulating either mCbN afferents or TH neurons augments IPSCs and suppresses EPSCs in Chx10 neurons by activating postsynaptic D2 receptors. The results suggest that mCbN activity regulates dopaminergic modulation of the vlPAG, favoring inhibition of Chx10 neurons. Suppression of cerebellar output may therefore facilitate freezing.

Event boundaries do not cause the immediate extinction deficit after Pavlovian fear conditioning in rats

Recent work reveals that the extinction of conditioned fear depends upon the interval between conditioning and extinction. Extinction training that takes place within minutes to hours after fear conditioning fails to produce a long-term extinction memory, a phenomenon known as the immediate extinction deficit (IED). Neurobiological evidence suggests that the IED results from stress-induced dysregulation of prefrontal cortical circuits involved in extinction learning. However, a recent study in humans suggests that an "event boundary" between fear conditioning and extinction protects the conditioning memory from interference by the extinction memory, resulting in high levels of fear during a retrieval test. Here, we contrast these hypotheses in rats by arranging extinction trials to follow conditioning trials with or without an event boundary; in both cases, extinction trials are delivered in proximity to shock-elicited stress. After fear conditioning, rats either received extinction trials 60-sec after the last conditioning trial (continuous, no event boundary) or 15-minutes after conditioning (segmented, a standard "immediate" extinction procedure associated with an event boundary). Both groups of animals showed decreases in conditional freezing to the auditory conditioned stimulus (CS) during extinction and exhibited an equivalent IED relative to non-extinguished controls when tested 48 hours later. Thus, eliminating the event boundary between conditioning and extinction with the continuous extinction procedure did not prevent the IED. These data suggest that the IED is the result of shock-induced stress, rather than boundary-induced reductions in memory interference.

The serial blocking effect: a testbed for the neural mechanisms of temporal-difference learning

Temporal-difference (TD) learning models afford the neuroscientist a theory-driven roadmap in the quest for the neural mechanisms of reinforcement learning. The application of these models to understanding the role of phasic midbrain dopaminergic responses in reward prediction learning constitutes one of the greatest success stories in behavioural and cognitive neuroscience. Critically, the classic learning paradigms associated with TD are poorly suited to cast light on its neural implementation, thus hampering progress. Here, we present a serial blocking paradigm in rodents that overcomes these limitations and allows for the simultaneous investigation of two cardinal TD tenets; namely, that learning depends on the computation of a prediction error, and that reinforcing value, whether intrinsic or acquired, propagates back to the onset of the earliest reliable predictor. The implications of this paradigm for the neural exploration of TD mechanisms are highlighted.

Predicting extinction phenotype to optimize fear reduction

Fear conditioning is widely employed to study dysregulations of the fear system. The repeated presentation of a conditioned stimulus in the absence of a reinforcer leads to a decrease in fear responding-a phenomenon known as extinction. From a translational perspective, identifying whether an individual might respond well to extinction prior to intervention could prove important to treatment outcomes. Here, we test the hypothesis that CO₂ reactivity predicts extinction phenotype in rats, and that variability in CO₂ reactivity as well as extinction long-term memory (LTM) significantly predicts orexin activity in the lateral hypothalamus (LH). Our results validate a rat model of CO₂ reactivity and show that subcomponents of behavioral reactivity following acute CO₂ exposure explain a significant portion of the variance in extinction LTM. Furthermore, we show evidence that variability in CO₂ reactivity is also significantly predictive of orexin activity in the LH, and that orexin activity, in turn, significantly accounts for LTM variance. Our findings open the possibility that we may be able to use CO₂ reactivity as a screening tool to determine if individuals are good candidates for an extinction/exposure-based approach.

The Basolateral Amygdala Is Essential for Rapid Escape: A Human and Rodent Study

Rodent research delineates how the basolateral amygdala (BLA) and central amygdala (CeA) control defensive behaviors, but translation of these findings to humans is needed. Here, we compare humans with natural-selective bilateral BLA lesions to rats with a chemogenetically silenced BLA. We find, across species, an essential role for the BLA in the selection of active escape over passive freezing during exposure to imminent yet escapable threat (Timm). In response to Timm, BLA-damaged humans showed increased startle potentiation and BLA-silenced rats demonstrated increased startle potentiation, freezing, and reduced escape behavior as compared to controls. Neuroimaging in humans suggested that the BLA reduces passive defensive responses by inhibiting the brainstem via the CeA. Indeed, Timm conditioning potentiated BLA projections onto an inhibitory CeA pathway, and pharmacological activation of this pathway rescued deficient Timm responses in BLA-silenced rats. Our data reveal how the BLA, via the CeA, adaptively regulates escape behavior from imminent threat and that this mechanism is evolutionary conserved across rodents and humans.

A Patient Suffering From Neurodegenerative Disease May Have a Strengthened Fractal Gait Rhythm

Scale invariance in stride series, namely, the series shows similar patterns across multiple time scales, is used widely as a non-invasive identifier of health assessment. Detailed calculations in the literature with standard tools, such as de-trended fluctuation analysis and wavelet transform modulus maxima seem to lead a conclusion that patients suffering from neurodegenerative diseases have weakened fractal gait rhythm compared with healthy persons. These variance-based methods are dynamical mechanism dependent, namely, for some dynamical process the scale invariance cannot be detected qualitatively, while for some others the scale invariance can be detected correctly, but the estimated value of scaling exponent is not correct. Generally, we have limited knowledge on the dynamical mechanism. What is more, the stride series for the patients have a typical finite length of ~300, which may lead to unreasonable statistical fluctuations to the evaluation procedure. Hence, how a neurodegenerative disorder disease affects the scale invariance is still an open problem. In this paper the balanced estimation of diffusion entropy (cBEDE) is used to overcome the limitations. The volunteers include healthy individuals and patients with/without freezing of gait (FOG). It is found that scale invariance exists widely in the gait time series for all the individuals. The average of scaling exponents for patients suffering from FOG is similar with or larger than that for healthy individuals, and similar with that for patients without FOG. The patients not suffering from FOG have an average of scaling exponent significantly larger than that for healthy people. From the results estimated by cBEDE, we can conclude that a patient may have an increased scaling exponent, which is contradictory qualitatively with that in the literatures.

Ongoing neurogenesis in the adult dentate gyrus mediates behavioral responses to ambiguous threat cues

Fear learning is highly adaptive if utilized in appropriate situations but can lead to generalized anxiety if applied too widely. A role of predictive cues in inhibiting fear generalization has been suggested by stress and fear learning studies, but the effects of partially predictive cues (ambiguous cues) and the neuronal populations responsible for linking the predictive ability of cues and generalization of fear responses are unknown. Here, we show that inhibition of adult neurogenesis in the mouse dentate gyrus decreases hippocampal network activation and reduces defensive behavior to ambiguous threat cues but has neither of these effects if the same negative experience is reliably predicted. Additionally, we find that this ambiguity related to negative events determines their effect on fear generalization, that is, how the events affect future behavior under novel conditions. Both new neurons and glucocorticoid hormones are required for the enhancement of fear generalization following an unpredictably cued threat. Thus, adult neurogenesis plays a central role in the adaptive changes resulting from experience involving unpredictable or ambiguous threat cues, optimizing behavior in novel and uncertain situations.

The ability to predict whether an experience will end favorably is critical for well-being. Cues associated with specific outcomes can aid in prediction, enabling adaptive behaviors, but cue-outcome relationships are often difficult to learn or inherently ambiguous. Human studies have suggested that the hippocampus, a brain region involved in learning and memory, is also important for predicting outcomes and mediating behavior in situations of uncertainty and conflict. We tested the role of a subtype of hippocampal neurons born in adulthood in responding to ambiguously cued shock. We found that mice without these young neurons show less defensive behavior than normal mice when they hear an ambiguous cue, paired with shock in 50% of trials, but react normally when the cue perfectly predicts the shock. In a novel situation, normal mice behave defensively after ambiguously cued shocks but show very little anxiety-like (defensive) behavior if shocks were predictable. Mice without new neurons fail to make this adaptive change, showing moderate levels of anxiety-like behavior regardless of the predictability of earlier threats. Our findings suggest that an important role for the continued neurogenesis in the hippocampus is to enable adaptive changes to future behavior depending upon predictability of prior threats.

Body length rather than routine metabolic rate and body condition correlates with activity and risk-taking in juvenile zebrafish Danio rerio

In this study, the following hypotheses were explored using zebrafish Danio rerio: (1) individuals from the same cohort differ consistently in activity and risk-taking and (2) variation in activity and risk-taking is linked to individual differences in metabolic rate, body length and body condition. To examine these hypotheses, juvenile D. rerio were tested for routine metabolic rate and subsequently exposed to an open field test. Strong evidence was found for consistent among-individual differences in activity and risk-taking, which were overall negatively correlated with body length, i.e. larger D. rerio were found to be less active in a potentially dangerous open field and a similar trend was found with respect to a more direct measure of their risk-taking tendency. In contrast, routine metabolic rate and body condition were uncorrelated with both activity and risk-taking of juvenile D. rerio. These findings suggest that body length is associated with risk-related behaviours in juvenile D. rerio for which larger, rather than smaller, individuals may have a higher risk of predation, while the role for routine metabolic rate is relatively limited or non-existent, at least under the conditions of the present study.

[CHRONIC UNPREDICTABLE STRESS OF PREGNANT RATS AND HEALTH OUTCOMES OF THEIR OFFSPRING]

It was established that chronic unpredictable stress, which was reproduced by repeated exposure of adverse factors on the pregnant rats (food deprivations during one day, immobilization in the water of room temperature and contact with Felis excrements) results in the stable and sex-specific offspring's behavioural changes in the «open field» test, disorders of motor and coordinator functions and the increased sensitivity to pain at the age of both 1 and 3 months. Male and female rats, which were exposed to the prenatal stress, demonstrate elevated blood pressure. Enhanced lipoperoxidation in the blood serum of male rats after prenatal stress was indicated. Thus, prenatal stress leads to the stable alteration of the reactivity, which may favour persistent social maladjustment and the development of different pathologies.

Role played by periaqueductal gray neurons in parasympathetically mediated fear bradycardia in conscious rats

Freezing, a characteristic pattern of defensive behavior elicited by fear, is associated with a decrease in the heart rate. Central mechanisms underlying fear bradycardia are poorly understood. The periaqueductal gray (PAG) in the midbrain is known to contribute to autonomic cardiovascular adjustments associated with various emotional behaviors observed during active or passive defense reactions. The purpose of this study was to elucidate the role played by PAG neurons in eliciting fear bradycardia. White noise sound (WNS) exposure at 90 dB induced freezing behavior and elicited bradycardia in conscious rats. The WNS exposure-elicited bradycardia was mediated parasympathetically because intravenous administration of atropine abolished the bradycardia (P < 0.05). Moreover, WNS exposure-elicited bradycardia was mediated by neuronal activation of the lateral/ventrolateral PAG (l/vlPAG) because bilateral microinjection of muscimol, a GABAA agonist, into the l/vlPAG significantly suppressed the bradycardia. It is noted that muscimol microinjected bilaterally into the dorsolateral PAG had no effect on WNS exposure-elicited bradycardia. Furthermore, retrograde neuronal tracing experiments combined with immunohistochemistry demonstrated that a number of l/vlPAG neurons that send direct projections to the nucleus ambiguus (NA) in the medulla, a major origin of parasympathetic preganglionic neurons to the heart, were activated by WNS exposure. Based on these findings, we propose that the l/vlPAG-NA monosynaptic pathway transmits fear-driven central signals, which elicit bradycardia through parasympathetic outflow.

Repeated Witnessing of Conspecifics in Pain: Effects on Emotional Contagion

Witnessing of conspecifics in pain has been shown to elicit socially triggered freezing in rodents. It is unknown how robust this response is to repeated exposure to a cage-mate experiencing painful stimulation. To address this question, shock-experienced Observer rats repeatedly witnessed familiar Demonstrators receive painful footshocks (six sessions). Results confirm that Observers freeze during the first testing session. The occurrence of this behaviour however gradually diminished as the experimental sessions progressed, reaching minimal freezing levels by the end of the experiments. In contrast, the appearance and continuous increase in the frequency of yawning, a behavior that was inhibited by metyrapone (i.e,. a glucocorticoid synthesis blocker), might represent an alternative coping strategy, suggesting that the observer’s reduced freezing does not necessarily indicate a disappearance in the affective response to the Demonstrator’s distress.

[SOUND SIGNALS OF DANGER ACTIVATE THE NITRERGIC SYSTEM OF THE MEDIAL PREFRONTAL CORTEX]

In Sprague-Dawley rats by means of in vivo microdialysis, we have shown that presentation to rats-during conditioned fear expression of a sound conditioned stimulus previously paired with footshock (CS+) produces an increase in extracellular levels of citrulline (an NO co-product) in the medial prefrontal cortex. Presentation to the same rats of a different sound stimulus (not associated with footshock) (CS-) causes a very small increase in extracellular citrulline level. CS+ induced citrulline increase is prevented by infusions into the medial prefrontal cortex of Nomega-propyl-L-arginine (1 mM), a neuronal NO synthase inhibitor and it is not observed in control rats (same procedure, no footshock). These data indicate for the first time that sound signals of danger, but not safety signals activate nitrergic system of the medial prefrontal cortex.

Distinct Hippocampal Expression Profiles of lncRNAs in Rats Exhibiting a PTSD-like Syndrome

Posttraumatic stress disorder (PTSD) refers to a series of clinical syndromes, including symptoms such as nightmares, hallucinations, severe anxiety, fear, and trauma related to the environment. These symptoms tend to occur after intense psychological trauma or physiological stress. Long non-coding RNAs (lncRNAs) have been shown to play key roles in various biological processes, although it is unknown whether they have important functions in PTSD. Here, we present the first study exploring the connection between lncRNAs and a PTSD-like syndrome in rats. We find distinct expression profiles of lncRNAs between PTSD-like syndrome rats and a control group, which provides information for further research on the differentiation of PTSD and transdifferentiation between the PTSD-like syndrome and the control group. This information will be helpful for finding new therapeutic targets for the treatment of PTSD.

Effect of cardiac arrest on cognitive impairment and hippocampal plasticity in middle-aged rats

Cardiopulmonary arrest is a leading cause of death and disability in the United States that usually occurs in the aged population. Cardiac arrest (CA) induces global ischemia, disrupting global cerebral circulation that results in ischemic brain injury and leads to cognitive impairments in survivors. Ischemia-induced neuronal damage in the hippocampus following CA can result in the impairment of cognitive function including spatial memory. In the present study, we used a model of asphyxial CA (ACA) in nine month old male Fischer 344 rats to investigate cognitive and synaptic deficits following mild global cerebral ischemia. These experiments were performed with the goals of 1) establishing a model of CA in nine month old middle-aged rats; and 2) to test the hypothesis that learning and memory deficits develop following mild global cerebral ischemia in middle-aged rats. To test this hypothesis, spatial memory assays (Barnes circular platform maze and contextual fear conditioning) and field recordings (long-term potentiation and paired-pulse facilitation) were performed. We show that following ACA in nine month old middle-aged rats, there is significant impairment in spatial memory formation, paired-pulse facilitation n dysfunction, and a reduction in the number of non-compromised hippocampal Cornu Ammonis 1 and subiculum neurons. In conclusion, nine month old animals undergoing cardiac arrest have impaired survival, deficits in spatial memory formation, and synaptic dysfunction.

Neonatal phencyclidine administration and post-weaning social isolation as a dual-hit model of 'schizophrenia-like' behaviour in the rat

RATIONALE

Schizophrenia is a debilitating disorder comprising positive, negative and cognitive deficits with a poorly defined neurobiological aetiology; therefore, animal models with greater translational reliability are essential to develop improved therapies.

OBJECTIVES

This study combines two developmental challenges in rats, neonatal phencyclidine (PCP) injection and subsequent rearing in social isolation from weaning, to attempt to produce more robust behavioural deficits with greater translational relevance to schizophrenia than either challenge alone.

METHODS

Forty-two male Lister-hooded rat pups received the N-methyl-D-aspartate (NMDA) receptor antagonist, phencyclidine (PCP, 10 mg/kg, s.c.), or vehicle on post-natal day (PND) 7, 9 and 11 and were weaned on PND 23 into group housing (saline-treated n = 11 or PCP-treated n = 10) or isolation (saline n = 10 or PCP n = 11). Six weeks post-weaning, novelty- and PCP-induced (3.2 mg/kg) locomotor activity, novel object discrimination, prepulse inhibition of acoustic startle and contextual memory in a conditioned emotion response (CER) were recorded.

RESULTS

Isolation rearing alone significantly elevated baseline locomotor activity and induced visual recognition memory impairment in novel object discrimination. Neonatal PCP treatment did not induce locomotor sensitisation to a subsequent acute PCP injection, but it impaired prepulse inhibition when combined with isolation rearing. CER freezing behaviour was significantly reduced by isolation rearing but an even greater effect occurred when combined with neonatal PCP treatment.

CONCLUSIONS

Neonatal PCP and isolation rearing both produce behavioural deficits in adult rats, but combined treatment caused a wider range of more severe cognitive impairments, providing a more comprehensive preclinical model to determine the neurobiological aetiology of schizophrenia than either treatment alone.

Detection of freezing of gait in Parkinson disease: preliminary results

Freezing of gait (FOG) is a common symptom in Parkinsonism, which affects the gait pattern and is associated to a fall risk. Automatized FOG episode detection would allow systematic assessment of patient state and objective evaluation of the clinical effects of treatments. Techniques have been proposed in the literature to identify FOG episodes based on the frequency properties of inertial sensor signals. Our objective here is to adapt and extend these FOG detectors in order to include other associated gait pattern changes, like festination. The proposed approach is based on a single wireless inertial sensor placed on the patient's lower limbs. The preliminary experimental results show that existing frequency-based freezing detectors are not sufficient to detect all FOG and festination episodes and that the observation of some gait parameters such as stride length and cadence are valuable inputs to anticipate the occurrence of upcoming FOG events.

The effect of brief neonatal cryoanesthesia on physical development and adult cognitive function in mice

Deep hypothermia (cryoanesthesia) is often used as general anesthesia during surgery in neonatal rodents. Neonatal cryoanesthesia has been used recently to generate somatic brain transgenic (SBT) mouse models via intracerebral ventricular injection of rAAV vectors into both non-transgenic mice and numerous transgenic mouse models. Since, the evaluation of cognition is one of the main experimental endpoints in many of these studies, we examined the consequences of brief neonatal cryoanesthesia on the physical development and mnemonic function of adult mice. Two groups of 129FVBF1 pups from reciprocal breeding crosses underwent cryoanesthesia for 6 min (Cryo6) or 12 min (Cryo12), respectively, within the first hours (<12h) of postnatal life. A group of pups separated from the nest and kept in ambient temperature of 33 °C for 6 min served as a control. Our results revealed that lowering the temperature of pups to ~8 °C (Cryo6) or ~5 °C (Cryo12) did not affect their body weight at pre-weaning stage and in the adulthood. The evaluation of cognitive function in adult mice revealed strong and comparable to control spatial reference, and context and tone fear memories of neonatally cryoanesthetized mice. Also, the experimental and control groups had comparable brain weight at the end of the study. Our results demonstrate that neonatal cryoanesthesia, lasting up to 12 min, has no adverse effects on the body weight of mice during development, and on their cognition in the adulthood.

Age and adolescent social stress effects on fear extinction in female rats

We previously observed that social instability stress (SS: daily 1 h isolation and change of cage partners for 16 days) in adolescence, but not in adulthood, decreased context and cue memory after fear conditioning in male rats. Effects of stress are typically sex-specific, and so here we investigated adolescent and adult SS effects in females on the strength of acquired contextual and cued fear conditioning, as well as extinction learning, beginning either the day after the stress procedure or four weeks later. For SS in adolescence, SS females spent more time freezing (fear measure) during extinction than did controls, whereas SS in adulthood had no effect on any measure of fear conditioning. The results also indicated an effect of age: females in late adolescence show more rapid extinction of cue and better memory of extinction of context compared to adult females, which may indicate resilience to acute footshock in adolescence. Thus fear circuitry continues to mature into late adolescence, which may underlie the heightened plasticity in response to chronic stressors of adolescents compared to adults.

Empathic fear responses in mice are triggered by recognition of a shared experience

Empathy is an important psychological capacity that involves the ability to recognize and share emotions with others. In humans, empathy for others is facilitated by having had a similar prior experience. It increases with the intensity of distress that observers believe is occurring to others, and is associated with acute emotional responses to witnessing others’ distress. We sought to develop a relatively simple and fast mouse model of human empathy that resembled these characteristics. We modeled empathy by measuring the freezing of observer mice to observing the footshock of a subject mouse. Observer mice froze to subject footshocks only when they had a similar shock experience 24 hours earlier. Moreover, this freezing increased with the number of footshocks given to the subject and it was accentuated within seconds after footshock delivery. Freezing was not seen in naïve observers or in experienced observers that observed a subject who was spared footshock. Observers did not freeze to a subject’s footshock when they had experienced a swim stress 24 hours prior, demonstrating a specific effect for shared experience, as opposed to a generalized stressor in eliciting observer mouse freezing. We propose that this two-day experimental protocol resembles many aspects of human empathy in a mouse model that is amenable to transgenic analysis of neural substrates for empathy and its impairment in certain clinical disorders.

[Il6st gene mRNA and gp130 protein distribution in the brain structures in mice differing in exagerrated freezing reaction (catalepsy)]

Glycoprotein gp130 is involved in the intracellular transduction of signals from receptors ofinterleukin-6--related cytokines. The linkage between Il6st gene encoding gp130 and predisposition to excessive freezing (catalepsy) in mice was shown. The aim of present study was to investigate the Il6st mRNA concentration, the level and the rate of glycosilation of gp130 in five brain structures in catalepsy-resistant AKR/J mice strain and in catalepsy-prone CBA/LacJ, AKR.CBA-D13Mit76 with the CBA-derived Il6st gene variant in the AKR/J genome, and ASC created by selection of back-crosses between CBA and AKR strains on catalepsy. Highest concentrations of the nonglycosilated and the glycosilated gp130 protein levels were detected in the midbrain. High levels of Il6st mRNA were discovered in the midbrain, the striatum and the hypothalamus in all mouse strains. The level of Il6st mRNA in the striatum of AKR.CBA-D13Mit76 mice was significantly higher compared with AKR/J. An association between hereditary catalepsy and Il6st expression in the striatum in mice was suggested.

The effect of visual cues on the number and duration of freezing episodes in Parkinson's patients

Freezing of gait is a phenomenon common in Parkinson's patients and significantly affects quality of life. Sensory cues have been known to improve walking performance and reduce freezing of gait. Visual cues are reported to be particularly effective for this purpose. So far, sensory cues have generally been provided continuously, even when currently not needed. However, a recent approach suggests the provision of cues just in the case that freezing actually occurs. The arguments in favor of this "on-demand" cueing are reduced intrusiveness and reduced habituation to cues. Here, we analyzed the effect of visual cues on the number and duration of freezing episodes when activated either just "on-demand" or continuously and compare it to the baseline condition where no cue is provided. For this purpose, 7 Parkinson's patients regularly suffering from freezing of gait repeatedly walked a pre-defined course and their reaction to parallel laser lines projected in front of them on the floor was analyzed. The results show that, in comparison to the baseline condition, the mean duration of freezing was reduced by 51% in continuous cueing and by 69% in "on-demand" cueing. Concerning the number of freezing episodes, 43% fewer episodes were observed for continuous cueing and 9% less episodes for "on-demand" cueing.

Bi-parental care contributes to sexually dimorphic neural cell genesis in the adult mammalian brain

Early life events can modulate brain development to produce persistent physiological and behavioural phenotypes that are transmissible across generations. However, whether neural precursor cells are altered by early life events, to produce persistent and transmissible behavioural changes, is unknown. Here, we show that bi-parental care, in early life, increases neural cell genesis in the adult rodent brain in a sexually dimorphic manner. Bi-parentally raised male mice display enhanced adult dentate gyrus neurogenesis, which improves hippocampal neurogenesis-dependent learning and memory. Female mice display enhanced adult white matter oligodendrocyte production, which increases proficiency in bilateral motor coordination and preference for social investigation. Surprisingly, single parent-raised male and female offspring, whose fathers and mothers received bi-parental care, respectively, display a similar enhancement in adult neural cell genesis and phenotypic behaviour. Therefore, neural plasticity and behavioural effects due to bi-parental care persist throughout life and are transmitted to the next generation.

[Influence of maternal factor on motor behavior and lipid turnover in rats exposed to severe psychoemotional stress]

Adverse condition of rat development during the prenatal period (rearing by mother survived brain injury) or during the early post-natal period (cross fostering), causes impairment of motor behavior and a lipid turnover in adult rats. Such rats under severe stress showed decrease of adaptation (as expressed or low indexes of motor impellent behavior and lipid metabolism) in comparison with rats that were grown up by own mother. The psychoemotional stress caused the most expressed deficient behavior in males that were grown up by mothers with brain injury (decrease in serum level of HC and HDL and depressively - similar behavior).

Enhanced hippocampal long-term potentiation and fear memory in Btbd9 mutant mice

Polymorphisms in BTBD9 have recently been associated with higher risk of restless legs syndrome (RLS), a neurological disorder characterized by uncomfortable sensations in the legs at rest that are relieved by movement. The BTBD9 protein contains a BTB/POZ domain and a BACK domain, but its function is unknown. To elucidate its function and potential role in the pathophysiology of RLS, we generated a line of mutant Btbd9 mice derived from a commercial gene-trap embryonic stem cell clone. Btbd9 is the mouse homolog of the human BTBD9. Proteins that contain a BTB/POZ domain have been reported to be associated with synaptic transmission and plasticity. We found that Btbd9 is naturally expressed in the hippocampus of our mutant mice, a region critical for learning and memory. As electrophysiological characteristics of CA3-CA1 synapses of the hippocampus are well characterized, we performed electrophysiological recordings in this region. The mutant mice showed normal input-output relationship, a significant impairment in pre-synaptic activity, and an enhanced long-term potentiation. We further performed an analysis of fear memory and found the mutant mice had an enhanced cued and contextual fear memory. To elucidate a possible molecular basis for these enhancements, we analyzed proteins that have been associated with synaptic plasticity. We found an elevated level of dynamin 1, an enzyme associated with endocytosis, in the mutant mice. These results suggest the first identified function of Btbd9 as being involved in regulating synaptic plasticity and memory. Recent studies have suggested that enhanced synaptic plasticity, analogous to what we have observed, in other regions of the brain could enhance sensory perception similar to what is seen in RLS patients. Further analyses of the mutant mice will help shine light on the function of BTBD9 and its role in RLS.

Dietary n-3 polyunsaturated fatty acid deprivation together with early maternal separation increases anxiety and vulnerability to stress in adult rats

Low concentrations of n-3 polyunsaturated fatty acid (PUFA) and chronic stress are implicated in susceptibility to mood disorders. We have investigated the combined effects of chronic n-3 PUFA dietary deficiency and early maternal separation (MS) stress on the reactivity to stressful situations of rats as adults. Pups fed a control or an n-3 PUFA deficient diet were daily separated for two weeks before weaning They were all tested at 3 month-old to determine their anxiety, and their ability to learn two aversive tasks differing in the control they could exert on the situation: auditory fear conditioning and brightness avoidance discrimination. Neither the n-3 PUFA-deficient diet nor MS alone significantly affected behavior. But n-3 PUFA-deficient rats that had been separated were more anxious and fearful in inescapable situations, while their ability to cope with an aversive avoidance task remained unaffected. These results support the notion that PUFA-unbalanced diet, together with stress, may be a determinant risk factor in emotional disorders.

Paternal experience and stress responses in California mice (Peromyscus californicus)

Paternal behavior greatly affects the survival, social development, and cognitive development of infants. Nevertheless, little research has been done to assess how paternal experience modifies the behavioral characteristics of fathers, including fear and stress responses to a novel environment. We investigated long-term behavioral and physiologic effects of parental experience in mice (Peromyscus californicus) and how this response activates the hypothalamic-pituitary-adrenal axis (as measured by corticosterone and dehydroepiandrosterone [DHEA] levels) and interacts with anxiety-related behaviors. Three groups of adult males were tested--fathers exposed to pups, virgins exposed to pups, and virgins never exposed to pups--in 2 environments designed to elicit anxiety response: an open field with a novel object placed in the center and a closed cage containing a sample of a component of fox feces. Behavioral responses were measured by using traditional methods (duration and frequency) and behavioral-chain sequences. Results indicated that paternal experience significantly modifies a male mouse's behavioral and physiologic responses to stress-provoking stimuli. Compared with inexperienced male mice, experienced male mice had a significant decrease in the occurrence of incomplete behavioral chains during the exposure to the novel object, an index of reduced stress. Further, even moderate pup exposure induced behavioral modifications in virgin male mice. These behavioral responses were correlated with changes in corticosterone and DHEA levels. Together, these data provide evidence that interactions between male mice and offspring may have mutually beneficial long-term behavioral and physiologic effects.

Maternal separation modulates short-term behavioral and physiological indices of the stress response

Early-life stress produces an anxiogenic profile in adulthood, presumably by activating the otherwise quiescent hypothalamic-pituitary-adrenal (HPA) axis during the vulnerable 'stress hyporesponsive period'. While the long-term effects of such early-life manipulations have been extensively characterized, little is known of the short-term effects. Here, we compared the short-term effects of two durations of maternal separation stress and one unseparated group (US) on behavioral and physiological indices of the stress response in rat pups. Separations included 3h on each of 12days, from postnatal day (PND) 2 to 13 (MS2-13) and 3days of daily, 6-h separation from PND11-13 (MS11-13). On PND14 (Experiment 1), both MS2-13 and MS11-13 produced marked reductions in freezing toward an adult male conspecific along with reduced levels of glucocorticoid type 2 (GR) and CRF type-1 (CRF(1)) receptor mRNA in the hippocampus. Group MS2-13 but not MS11-13 produced deficits in stressor-induced corticosterone secretion, accompanied by reductions in body weight. Our results suggest that GR and/or CRF(1) levels, not solely the magnitude of corticosterone secretion, may be involved in the modulation of freezing. In a second experiment, we aimed to extend these findings by testing male and female separated and unseparated pups' unconditioned defensive behaviors to cat odor on PND26, and subsequent cue+context conditioning and extinction throughout postnatal days 27-32. Our results show that maternal separation produced reductions in unconditioned freezing on PND26, with MS2-13 showing stronger deficits than MS11-13. However, separation did not affect any other defensive behaviors. Furthermore, separated rats failed to show conditioned freezing, although they did avoid the no-odor block conditioned cue. There were no sex differences other than weight. We suggest that maternal separation may have produced these changes by disrupting normal development of hippocampal regions involved in olfactory-mediated freezing, not in mechanisms of learning and memory per se. These findings may have direct relevance for understanding the mechanisms by which early-life adverse experiences produce short-term and lasting psychopathologies.

Updating contextual information during consolidation as result of a new memory trace

Reconsolidation studies have led to the hypothesis that memory, when labile, would be modified in order to incorporate new information. This view has reinstated original propositions suggesting that short-term memory provides the organism with an opportunity to evaluate and rearrange information before storing it, since it is concurrent with the labile state of consolidation. The Chasmagnathus associative memory model is used here to test whether during consolidation it is possible to change some attribute of recently acquired memories. In addition, it is tested whether these changes in behavioral memory features can be explained as modifications on the consolidating memory trace or as a consequence of a new memory trace. We show that short-term memory is, unlike long-term memory, not context specific. During this short period after learning, behavioral memory can be updated in order to incorporate new contextual information. We found that, during this period, the cycloheximide retrograde amnesic effect can be reverted by a single trial in a new context. Finally, by means of memory sensitivity to cycloheximide during consolidation and reconsolidation, we show that the learning of a new context (CS) during this short-term memory period builds up a new memory trace that sustains the behavioral memory update.

Protein kinase Mzeta maintains fear memory in the amygdala but not in the hippocampus

Recent work on the long-term stability of memory and synaptic plasticity has identified a potentially critical role for protein kinase Mzeta (PKMzeta). PKMzeta is a constitutively active, atypical isoform of protein kinase C that is believed to maintain long term potentiation at hippocampal synapses in vitro. In behaving animals, local inhibition of PKMzeta disrupts spatial memory in the hippocampus and conditioned taste aversion memory in the insular cortex. The role of PKMzeta in context fear memory is less clear. This study examined the role of PKMzeta in amygdala and hippocampal neurons following a standard fear conditioning protocol. The results indicate that PKMzeta inhibition in the amygdala, but not in the hippocampus, can disrupt fear memory. This suggests that PKMzeta may only maintain select forms of memory in specific brain structures and does not participate in a universal memory storage mechanism.

Mineralocorticoid receptors in control of emotional arousal and fear memory

The stress hormone corticosterone acts via two receptor types in the brain: the mineralocorticoid (MR) and the glucocorticoid receptor (GR). Both receptors are involved in processing of stressful events. A disbalance of MR:GR functions is thought to promote stress-related disorders. Here we studied the effect of stress on emotional and cognitive behaviors in mice with forebrain-specific inactivation of the MR gene (MR(CaMKCre), 4 months old; and control littermates). MR(CaMKCre) mice responded to prior stress (5 min of restraint) with higher arousal and less locomotor activity in an exploration task. A fear conditioning paradigm allowed assessing in one experimental procedure both context- and cue-related fear. During conditioning, MR(CaMKCre) mice expressed more cue-related freezing. During memory test, contextual freezing remained potentiated, while control mice distinguished between cue (more freezing) and context episodes (less freezing) in the second memory test. At this time, plasma corticosterone levels of MR(CaMKCre) mice were 40% higher than in controls. We conclude that control of emotional arousal and adaptive behaviors is lost in the absence of forebrain MR, and thus, anxiety-related responses are and remain augmented. We propose that such a disbalance in MR:GR functions in MR(CaMKCre) mice provides the conditions for an animal model for anxiety-related disorders.

Female fear: influence of estrus cycle on behavioral response and neuronal activation

Our observation that male rat's innate fear response differed with hormonal status, as well as the higher prevalence of fear and anxiety disorders in human females led to the current investigation of the impact of phases of the estrus cycle on innate fear responding. Female rats in different phases of the cycle were exposed to an innate fear-inducing stimulus (2,5-dihydro-2,4,5-trimethylthiazoline, TMT odor) and monitored for changes in behavior and brain activation. Behavioral data showed freezing responses to TMT were significantly enhanced during estrus as compared to other phases of the cycle. This data was supported by significant increases in pixel intensity in cortical and sub-cortical regions in estrus compared to proestrus and diestrus. Imaging results demonstrated significant increases in brain activation in the somatosensory and insular cortices when comparing estrus to diestrus. There were significant increases in neural activity in the bed nucleus of the stria terminals (BNST) and septum in estrus as compared to proestrus. Additionally, the hippocampus, hypothalamus, olfactory system, and cingulate cortex show significant increases in the estrus phase when compared to both diestrus and proestrus. Taken together, these results suggest that the female's hormonal status may be correlated with alterations in both neuronal and behavioral indices of fear.

Neonatal acute stress by novelty in the absence of social isolation decreases fearfulness in young chicks

Two hours after hatching (Day 0), groups of chicks from both sexes were housed either individually (IND) or socially in pairs (SOC) for 24 h. On Day 1, for each of the two conditions, half of the chicks were individually exposed to early novelty for 10 min, which comprised being placed in a novel-cage with small pebbles glued to the floor. The other half (controls) remained in the home-cage (IND-C and SOC-C). Thus, the IND-N group was exposed to early novelty, and the SOC-N+I group was exposed to early novelty and social isolation. Subsequently, all groups were mixed and socially reared until reaching 15 days of age. At this time, chicks were exposed to open field (OF) and tonic immobility (TI) tests. The IND-N group showed a shorter latency to ambulate in the OF test, shorter immobility duration in the TI test, a reduced plasma corticosterone concentration and increased flunitrazepam sensitive-GABA(A) receptor basal forebrain density compared with other groups, indicating that a neonatal novelty induced lower fearfulness in young chicks. In contrast, the effect of neonatal novelty was abolished by a simultaneous effect of social isolation in the SOC-N+I group. Thus, early post-hatch life events such as early novelty could improve a bird's later ability to cope with new stressful events. In addition, it is possible that both novelty and social isolation act on different neurobiological processes.

Adult rats exposed to early-life social isolation exhibit increased anxiety and conditioned fear behavior, and altered hormonal stress responses

Social isolation of rodents during development is thought to be a relevant model of early-life chronic stress. We investigated the effects of early-life social isolation on later adult fear and anxiety behavior, and on corticosterone stress responses, in male rats. On postnatal day 21, male rats were either housed in isolation or in groups of 3 for a 3 week period, after which, all rats were group-reared for an additional 2 weeks. After the 5-week treatment, adult rats were examined for conditioned fear, open field anxiety-like behavior, social interaction behavior and corticosterone responses to restraint stress. Isolates exhibited increased anxiety-like behaviors in a brightly-lit open field during the first 10 min of the test period compared to group-reared rats. Isolation-reared rats also showed increased fear behavior and reduced social contact in a social interaction test, and a transient increase in fear behavior to a conditioned stimulus that predicted foot-shock. Isolation-reared rats showed similar restraint-induced increases in plasma corticosterone as group-reared controls, but plasma corticosterone levels 2 h after restraint were significantly lower than pre-stress levels in isolates. Overall, this study shows that isolation restricted to an early part of development increases anxiety-like and fear behaviors in adulthood, and also results in depressed levels of plasma corticosterone following restraint stress.

Inverse temporal contributions of the dorsal hippocampus and medial prefrontal cortex to the expression of long-term fear memories

Retrograde amnesia following disruptions of hippocampal function is often temporally graded, with recent memories being more impaired. Evidence supports the existence of one or more neocortical long-term memory storage/retrieval site(s). Neurotoxic lesions of the medial prefrontal cortex (mPFC) or the dorsal hippocampus (DH) were made 1 day or 200 days following trace fear conditioning. Recently encoded trace fear memories were most disrupted by DH lesions, while remotely encoded trace and contextual memories were most disrupted by mPFC lesions. These data strongly support the consolidation theory of hippocampus function and implicate the mPFC as a site of long-term memory storage/retrieval.

Genetic architecture of fear conditioning in chromosome substitution strains: relationship to measures of innate (unlearned) anxiety-like behavior

We measured fear conditioning (FC) in a panel of chromosome substitution strains (CSS) created using the C57BL/6J (B6) and A/J (AJ) inbred strains. Mice were trained to associate a specific context and tone with a foot shock. FC was measured by observing freezing behavior during re-exposure to the context and tone. Freezing to context was more than twofold greater in the AJ strain relative to the B6 strain. Among the CSS we identified four strains with higher (CSS-6, -10, -11, and -18) and two strains with lower (CSS-7 and -14) freezing to context. CSS-10 and -18 also showed higher freezing to tone, while CSS-12 showed less freezing to tone. CSS-1 has been implicated in open-field (OF) and light-dark box (LDB); we observed significant activity differences prior to training but no differences in FC. Chromosomes 6 and 10 have been associated with differences in anxiety-like behaviors, suggesting the existence of pleiotropic alleles that influence both learned and innate fear. By utilizing a genetic reference population, we have identified chromosomes that pleiotropically influence multiple phenotypes hypothesized to reflect a common ethologic construct that has been termed emotionality. The CSS provide a straightforward means of isolating the underlying genetic factors.

Dissociated theta phase synchronization in amygdalo- hippocampal circuits during various stages of fear memory

The amygdala and the hippocampus are critically involved in the formation and retention of fear memories. However, their precise contribution to, and their interplay during, fear memory formation are not fully understood. In the present study we investigated network activities in the amygdalo-hippocampal system of freely behaving mice at different stages of fear memory consolidation and retention. Our data show enhanced theta phase synchronization in this pathway during the retrieval of fear memory at long-term (24 h post-training), but not short-term (2 min, 30 min and 2 h post-training) stages, following both contextual and auditory cued conditioning. However, retrieval of remotely conditioned fear (30 days post-training) failed to induce an increase in synchronization despite there still being memory retention. Thus, our data indicate that the amygdalo-hippocampal interaction reflects a dynamic interaction of ensemble activities related to various stages of fear memory consolidation and/or retention, and support the notion that recent and remote memories are organized through different network principles.

5-HT2 receptor mechanisms of the dorsal periaqueductal gray in the conditioned and unconditioned fear in rats

RATIONALE

It is well known that 5-HT(2) mechanisms modulate the defensive behavior produced by the stimulation of the dorsal periaqueductal gray (dPAG). However, in spite of the notion that past stressful experiences play a role in certain types of anxiety, only studies with the stimulation of the dPAG of rats without previous aversive experience have been conducted so far.

OBJECTIVES

We investigated the mediation of 5-HT(2) receptors of the dPAG in rats previously submitted to contextual fear conditioning (CFC). Defensive behaviors induced by the activation of the dPAG were assessed by measuring the lowest intensity of electric current applied to this structure (threshold) able to produce freezing and escape responses during the testing sessions of CFC in which animals were placed in a context previously paired to footshocks. The 5-HT(2) function of the dPAG in this condition was evaluated by local injections of alpha-methyl-5-HT (20 nmol/0.2 mul) and ketanserin (5 and 10 nmol/0.2 mul), selective agonist and antagonist of 5-HT(2) receptors, respectively.

RESULTS

In accordance with previous studies, alpha-methyl-5-HT increased the aversive thresholds (antiaversive effects) in naive rats, and injection of ketanserin into the dPAG did not produce significant effects. On the other hand, ketanserin decreased in a dose-dependent manner the freezing threshold (proaversive effect) determined by the dPAG electrical stimulation, whereas alpha-methyl-5-HT continued to show antiaversive effects in animals under CFC.

CONCLUSIONS

The present results suggest that past stressful experience can produce changes in the synaptic function of 5-HT(2) receptors within the dPAG with important impact on the expression of defensive behaviors.

The disruptive effects of the CB1 receptor antagonist rimonabant on extinction learning in mice are task-specific

RATIONALE

Disruption of CB(1) receptor signaling through the use of CB(1) (-/-) mice or the CB(1) receptor antagonist rimonabant (SR141716) has been demonstrated to impair extinction of learned responses in conditioned fear and Morris water maze tasks. In contrast, CB(1) (-/-) mice exhibited normal extinction rates in an appetitively motivated operant conditioning task.

OBJECTIVES

The purpose of this study was to test whether rimonabant would differentially disrupt extinction learning between fear-motivated and food-motivated tasks.

MATERIALS AND METHODS

Separate groups of C57BL/6J mice were trained in two aversively motivated tasks, conditioned freezing and passive avoidance, and an appetitively motivated operant conditioning task at a fixed ratio (FR-5) schedule of food reinforcement. After acquisition, the respective reinforcers in each task were withheld, and an intraperitoneal injection of vehicle or rimonabant was given 30 min before each extinction session.

RESULTS

Rimonabant (3 mg/kg) treatment significantly disrupted extinction in both the conditioned freezing and passive avoidance tasks but failed to affect extinction rates in the operant conditioning task, whether using daily or weekly extinction sessions. Interestingly, rimonabant (3 mg/kg) prevented the significant increases in lever pressing (i.e., extinction burst) that occurred during the first extinction session of the operant conditioning task.

CONCLUSIONS

These results support the hypothesis that the CB(1) receptor plays a vital role in the extinction of aversive memories but is not essential for extinction of learned responses in appetitively motivated tasks.

Oral vaccination with a viral vector containing Abeta cDNA attenuates age-related Abeta accumulation and memory deficits without causing inflammation in a mouse Alzheimer model

Immunotherapy with Abeta is expected to bring great improvement for Alzheimer disease (AD). However, clinical trials have been suspended because of meningoencephalitics, which accompanied lymphocytic infiltration. We have developed an oral vaccine for AD with a recombinant adeno-associated viral vector carrying Abeta cDNA (AAV/Abeta). The vaccine reduces the amount of Abeta deposited without lymphocytic infiltration in APP transgenic (Tg2576) mice. In the present study, Tg2576 mice showed progressive cognitive impairments in the novel object recognition test, Y-maze test, water maze test, and contextual conditioned fear learning test. A single oral administration of AAV/Abeta to Tg2576 mice at the age of 10 months alleviated progressive cognitive impairment with decreased Abeta deposition, insoluble Abeta, soluble Abeta oligomer (Abeta*56), microglial attraction, and synaptic degeneration induced in the brain regions at the age of 13 months. A histological analysis with hematoxylin and eosin and an immunohistochemical analysis with antibodies against CD3, CD4, CD8, and CD19 suggested there was no lymphocytic infiltration or microhemorrhage in the brain of AAV/Abeta-vaccinated Tg2576 mice at 13 months of age. Taken together, these results suggest that immunotherapy with AAV/Abeta is a safe and effective treatment for AD.

Predator threat induces behavioral inhibition, pituitary-adrenal activation and changes in amygdala CRF-binding protein gene expression

Behavioral inhibition (BI) is an adaptive defensive response to threat; however, extreme BI is associated with anxiety-related psychopathology. When rats are exposed to a natural predator they display stress- and anxiety-related behavioral alterations and physiological activation. To develop a preclinical rodent model to study mechanisms underlying human BI and anxiety, we examined the extent to which ferret exposure elicits anxiety-related BI and HPA and amygdala activation of the CRF system. In the first experiment, BI and other behaviors were assessed in the presence or absence of a ferret. In the second experiment, ferret-induced corticosterone release and changes in brain c-fos expression were assessed. In the final experiment, gene chip and quantitative real time-PCR analyses were performed on amygdala tissue from control and ferret-exposed rats. Ferret exposure increased BI and submissive posturing, as well as plasma corticosterone and the number of Fos-positive cells in several brain regions including the amygdala. Gene expression analysis revealed increased amygdalar mRNA for CRF-binding protein, but not the CRF1 receptor, CRF2 receptor or CRF. In rodents, ferret exposure can be used to elicit anxiety-related BI, which is associated with HPA and amygdala activation. Since the amygdala and the CRF system have been implicated in adaptive and maladaptive anxiety responses in humans, these data support use of our rodent model to further investigate mechanisms underlying anxiety-related psychopathology in humans.