Lack of neurotensin type 1 receptor facilitates contextual fear memory depending on the memory strength

Neurotensin is known to have antipsychotic-like behavioral and neurochemical effects, but its participation in fear memory has not been fully elucidated. Here, we report that a lack of type 1 neurotensin receptor (Ntsr1) increases the behavioral fear response elicited by weak fear memory. Adult Ntsr1-knockout (KO) mice and their wild-type (WT) littermates were compared in contextual fear conditioning. The mice were exposed twice for 3 min to the context 24 and 48 h after conditioning (first and second exposure, respectively), and freezing response of mice at the exposure was measured to evaluate fear memory. Ntsr1-KO mice showed a higher freezing rate than WT mice at both first and second exposures under the condition where a relatively weak unconditioned stimulus (footshock) was applied and thus elicited a relatively lower freezing rate. The difference in the first exposure between Ntsr1-KO and WT mice disappeared under the condition where a more intense unconditioned stimulus was used. The enhancement of freezing response in Ntsr1-KO mice at second exposure was abolished by propranolol, a β-adrenergic blocker that suppresses fear memory reconsolidation, and suppressed by MK-801, an NMDA receptor antagonist. These results suggest that Ntsr1 plays inhibitory roles in weak fear memory.     

Neurobehavioral effects of tetrabromobisphenol A,a brominated flame retardant,in mice

Tetrabromobisphenol A (TBBPA) is widely used as a flame retardant and is suspected to be stable in the environment with possible widespread human exposures. In the present study, we investigated the behavioral effects of TBBPA and measured the levels of TBBPA in the brain after oral administration in mice. Acute treatment with TBBPA (5 mg/kg body weight) 3 h before the open-field test induced an increase in the horizontal movement activities. In contextual fear conditioning paradigm, mice treated with TBBPA (0.1 mg/kg or 5 mg/kg body weight) showed more freezing behavior than vehicle-treated mice. In addition, TBBPA (0.1 mg/kg body weight) significantly increased the spontaneous alternation behavior in the Y-maze test. The levels of TBBPA in the brain following TBBPA treatment were determined by using LC/ESI-MS/MS system. In the brain regions examined, high amounts of TBBPA were detected in the striatum after treatment with 0.1 mg/kg or 5 mg/kg body weight TBBPA, whereas non-specific accumulation of TBBPA in the brain was found after treatment with 250 mg/kg body weight TBBPA. These results suggest that TBBPA accumulates in brain regions including the striatum and induces the behavioral alterations. Together, the possibility of widespread human exposure to TBBPA warrants further studies to characterize its neurotoxicity.     

Impaired auditory and contextual fear conditioning in soman-exposed rats

Exposure to soman (GD) can result in prolonged seizures and subsequent neuropathology in a variety of brain regions including the amygdala and hippocampus. Both regions are believed to play important roles in the development and expression of fear conditioning. The purpose of this experiment was to test these conditioning tasks as a possible behavioral correlate of the observed neuropathology. Male rats were exposed to GD (1.0 or 1.2 × LD₅₀) or saline followed with injections of atropine sulfate, the oxime HI-6 and diazepam. Fear conditioning was conducted on post-exposure day (PED) 8 followed by measuring freezing to contextual and auditory conditioned stimuli on PED 9 and 10 respectively. Contextual and auditory fear conditioning was severely impaired in both the 1.0 × LD₅₀ and 1.2 × LD₅₀ GD groups. Both GD groups spent less time freezing than controls when returned to the context in which conditioning occurred. The 1.0 × LD₅₀ and 1.2 × LD₅₀ groups had very low levels of freezing following presentation of the auditory conditioned stimulus. Neuronal fiber degeneration was present in the piriform cortex, thalamus, and amygdala in GD-exposed animals regardless of dose. The present study suggests that contextual and auditory fear conditioning is impaired in GD-exposed rats possibly due to neuropathology observed in the hippocampus, amygdala and thalamus.     

β2 subunit-containing nicotinic receptors mediate the enhancing effect of nicotine on trace cued fear conditioning in C57BL/6 mice

Rationale Previous research indicates that acute nicotine administration enhances the acquisition of contextual fear conditioning and trace cued fear conditioning. Pharmacological inhibition of α4β2 nicotinic acetylcholine receptors (nAChRs), but not α7 nAChRs, blocked the enhancing effect of nicotine on contextual fear conditioning. Similarly, genetic deletion of the β2 nAChR subunit but not the α7 nAChR subunit blocked the enhancing effect of nicotine on contextual fear conditioning. Objectives In the present study, nAChR subunit knockout mice were used to compare the involvement of β2 subunit-containing nAChRs and α7 subunit-containing nAChRs in the effects of nicotine on hippocampus-dependent trace cued fear conditioning and contextual fear conditioning. Methods β2 nAChR subunit knockout mice, α7 nAChR subunit knockout mice, and their wild-type littermates received either nicotine or saline 5 minutes before training and testing. Mice were trained using five conditioned stimulus (CS; 30 s, 85 dB white noise)—trace (30 s)—unconditioned stimulus (US; 2 s footshock) pairings. Freezing to the context and freezing to the CS were assessed 24 h later. Results Both contextual and trace cued fear conditioning were enhanced by nicotine administration in wild-type littermates and in α7 nAChR subunit knockout mice. In contrast, neither contextual fear conditioning nor trace cued fear conditioning was enhanced by nicotine administration in β2 nAChR subunit knockout mice. Conclusions These results suggest that β2 subunit-containing nAChRs but not α7 nAChR subunit-containing nAChRs are critically involved in the enhancing effect of nicotine on contextual and trace cued fear conditioning.     

小鼠条件性恐惧模型的建立和品系敏感性研究

目的在敏感品系上建立稳定可靠的小鼠条件性恐惧模型。方法采用给予30 s声音刺激(85 dB,5000 Hz),后2 s伴随给予不可逃避的足底电击(0.6 mA,持续2 s),声音-电击共配对5次,每次间隔2 min的方法建立小鼠条件性恐惧模型,在ICR、DBA/2(简称DBA)和C57BL/6J(简称C57)3种品系小鼠上评价场景恐惧和声音线索恐惧获得和表达的行为特点,以确定敏感品系鼠;分别于条件性恐惧训练第2,7,14,21和28天对C57小鼠场景恐惧和声音线索恐惧进行检测,以评价该品系小鼠条件性恐惧的自然消退特点;采用30 s声音+30 s间隔+10次消退训练的模式进行声音线索恐惧消退训练,并于24 h后进行消退保持测试,以评价该品系小鼠消退训练和保持的特点。结果声音-电击配对5次可成功诱导C57小鼠形成场景恐惧和声音线索恐惧,DBA小鼠可诱导形成声音线索恐惧但无法形成场景恐惧,ICR小鼠场景恐惧和声音线索恐惧均未诱导成功,确定C57小鼠为敏感品系鼠。C57小鼠呈现时间依赖的恐惧反应自然消退,其中场景恐惧在训练后第7天僵住百分率消退至(25±12)%,声音线索恐惧训练后第28天僵住百分率维持在(48±22)%;C57小鼠经10轮30 s声音消退训练,僵住时间百分率由(55±30)%消退至(32±27)%,但24 h后消退保持测试时僵住时间百分率又回升至(47±35)%。结论以敏感品系C57小鼠为研究对象,建立了恐惧获得、表达、自然消退、消退训练和消退保持各阶段恐惧行为检测的实验方法,成功建立小鼠条件性恐惧模型。     

氯胺酮单次注射对创伤后应激障碍模型动物场景恐惧行为的影响及机制

目的在大、小鼠创伤后应激障碍(PTSD)模型上评价氯胺酮单次预防给药对大、小鼠场景恐惧表达的影响,并基于脑源性神经营养因子(BDNF)表达调节研究其作用机制。方法建立小鼠条件性恐惧和大鼠时间依赖性敏化(TDS)2种PTSD动物模型,在条件性恐惧训练前不同时间点进行不同剂量的单次给药,采用僵住行为测试评价氯胺酮在2个模型上对场景恐惧的影响。在小鼠条件性恐惧模型中,训练前0.5 h单次预防性给予氯胺酮10 mg·kg-1,分别于造模训练后24 h和第14天取脑,采用Western印迹法检测大脑皮质BDNF的表达。结果行为学测试结果表明,在小鼠条件性恐惧模型上,氯胺酮10 mg·kg-1分别在训练前第7天、24 h和0.5 h单次预防给药,训练后24 h场景恐惧测试中各组小鼠僵住时间百分率无明显差异;而训练前0.5 h单次预防性ip氯胺酮10 mg·kg-1,在训练后第14天显著降低小鼠僵住时间百分率(P<0.05);在大鼠TDS模型上,条件性恐惧训练前0.5 h单次ip氯胺酮10 mg·kg-1可显著降低TDS大鼠僵住次数百分率(P<0.05)。Western印迹结果显示,在训练后24 h和第14天,与正常对照组相比,模型组小鼠大脑皮质BDNF表达均显著降低(P<0.05);训练前0.5 h给予氯胺酮10 mg·kg-1组,在训练后24 h和第14天小鼠皮质BDNF的表达较模型组均显著升高(P<0.05)。结论氯胺酮单次预防性给药可减少小鼠场景恐惧的表达,该作用与给药剂量有关,且具有延迟起效的特点,但延迟起效作用与恐惧记忆形成后大脑皮质BDNF表达改变在时间上不具有一致性;氯胺酮单次给药可降低TDS增敏的大鼠场景恐惧的表达,此作用与给药时间点密切相关。     

Increased Contextual Fear Conditioning in iNOS Knockout Mice: Additional Evidence for the Involvement of Nitric Oxide in Stress-Related Disorders and Contribution of the Endocannabinoid System

Background:

Inducible or neuronal nitric oxide synthase gene deletion increases or decreases anxiety-like behavior in mice, respectively. Since nitric oxide and endocannabinoids interact to modulate defensive behavior, the former effect could involve a compensatory increase in basal brain nitric oxide synthase activity and/or changes in the endocannabinoid system. Thus, we investigated the expression and extinction of contextual fear conditioning of inducible nitric oxide knockout mice and possible involvement of endocannabinoids in these responses.

Methods:

We evaluated the effects of a preferential neuronal nitric oxide synthase inhibitor, 7-nitroindazol, nitric oxide synthase activity, and mRNA changes of nitrergic and endocannabinoid systems components in the medial prefrontal cortex and hippocampus of wild-type and knockout mice. The effects of URB597, an inhibitor of the fatty acid amide hydrolase enzyme, which metabolizes the endocannabinoid anandamide, WIN55,212-2, a nonselective cannabinoid agonist, and AM281, a selective CB1 antagonist, on contextual fear conditioning were also evaluated.

Results:

Contextual fear conditioning expression was similar in wild-type and knockout mice, but the latter presented extinction deficits and increased basal nitric oxide synthase activity in the medial prefrontal cortex. 7-Nitroindazol decreased fear expression and facilitated extinction in wild-type and knockout mice. URB597 decreased fear expression in wild-type and facilitated extinction in knockout mice, whereas WIN55,212-2 and AM281 increased it in wild-type mice. Nonconditioned knockout mice showed changes in the mRNA expression of nitrergic and endocannabinoid system components in the medial prefrontal cortex and hippocampus that were modified by fear conditioning.

Conclusion:

These data reinforce the involvement of the nitric oxide and endocannabinoids (anandamide) in stress-related disorders and point to a deregulation of the endocannabinoid system in situations where nitric oxide signaling is increased.     

The CB1 inverse agonist AM251, but not the CB1 antagonist AM4113, enhances retention of contextual fear conditioning in rats

The effects of CB1 antagonist/inverse agonists on the acquisition and consolidation of conditioned fear remain uncertain. Recent studies suggest that the CB1 antagonist/inverse agonist AM251 affects acquisition or consolidation of both contextual and discretely cued fear memories. AM251 is frequently referred to as a CB1 antagonist; however in vitro signal transduction assays indicate that this drug also elicits inverse agonist activity at CB1 receptors. The present studies were undertaken to compare the effects of AM251 on conditioned fear with those produced by AM4113, a novel CB1 antagonist with minimal inverse agonist activity. All drugs were administered prior to conditioning. In retention tests conducted two weeks after conditioning, both AM251 (4.0 mg/kg) and AM4113 (6.0 mg/kg)-treated animals exhibited reduced freezing during a conditioned tone cue played within a novel context. In contextual fear retention tests, animals previously treated with 4.0 or 8.0 mg/kg AM251 exhibited enhanced freezing. By contrast, no dose of AM4113 had any significant effect on contextual fear memory, which is consistent with the lower signal transduction activity of AM4113 at CB1 receptors compared to AM251. These results suggest that CB1 neutral antagonists may be less likely than CB1 inverse agonists to facilitate the acquisition or consolidation of contextual fear that may contribute to some clinical disorders.     

Erk activation in the amygdala and hippocampus induced by fear conditioning in ethanol withdrawn rats: Modulation by mk-801

The extracellular signal-regulated kinase (ERK) pathway, which can be activated by NMDA receptor stimulation, is involved in fear conditioning and drug addiction. We have previously shown that withdrawal from chronic ethanol administration facilitated the formation of contextual fear memory. In order to explore the neural substrates and the potential mechanism involved in this effect, we examined: 1) the ERK1/2 activation in the central (CeA) and basolateral (BLA) nuclei of the amygdala and in the dorsal hippocampus (dHip), 2) the effect of the NMDA receptor antagonist MK-801 on fear conditioning and ERK activation and 3) the effect of the infusion of U0126, a MEK inhibitor, into the BLA on fear memory formation in ethanol withdrawn rats.Rats made dependent via an ethanol-containing liquid diet were subjected to contextual fear conditioning on day 3 of ethanol withdrawal. High basal levels of p-ERK were found in CeA and dHip from ethanol withdrawn rats. ERK activation was significantly increased both in control (60 min) and ethanol withdrawn rats (30 and 60 min) in BLA after fear conditioning. Pre-training administration of MK-801, at a dose that had no effect on control rats, prevented the increase in ERK phosphorylation in BLA and attenuated the freezing response 24 h later in ethanol withdrawn rats. Furthermore, the infusion of U0126 into the BLA, but not the CeA, before fear conditioning disrupted fear memory formation. These results suggest that the increased fear memory can be linked to changes in ERK phosphorylation, probably due to NMDA receptor activation in BLA in ethanol withdrawn rats.     

Early postnatal stress alters the extinction of context-dependent conditioned fear in adult rats

Fear extinction is hypothesized to be a learning process based on a new inhibitory memory. The present study was conducted to elucidate the effect of early postnatal stress on the extinction of context-dependent fear memory in adult rats, with a focus on the serotonergic system. Extinction was estimated by the expression of freezing behavior during repeated extinction trials (i.e., repeated exposure to contextual fear conditioning) on consecutive days. The decrease in fear expression was attenuated in adult rats that had been subjected to footshock (FS) at the third postnatal week (3wFS), but not in those exposed to footshock at the second postnatal week (2wFS). The decreased attenuation of freezing behavior observed in 3wFS was abolished by repeated treatment with the partial N-methyl-D-aspartate receptor agonist D-cycloserine (15 mg/kg, i.p., for 4 days), which has been shown to facilitate cue-dependent extinction. Repeated treatment with the serotonin 5-hydroxytryptamine-1A (5-HT(1A)) receptor agonist tandospirone (1 mg/kg, i.p., for 4 days) prevented the expression of freezing behavior in 3wFS, whereas diazepam treatment (1 mg/kg, i.p., for 4 days) in 3wFS did not. These results suggest that exposure to early postnatal stress at the third week is responsible for attenuating extinction of contextual fear conditioning and is mediated by a serotonergic 5-HT(1A) receptor mechanism. In other words, exposure to traumatic events during the early postnatal period might precipitate long-lasting alterations in synaptic function that underlie extinction processes of context-dependent fear memory.     

The effects of DHBE and MLA on nicotine-induced enhancement of contextual fear conditioning in C57BL/6 mice

Rationale Previous research indicates that nicotine administration enhances hippocampus-dependent forms of learning, including contextual fear conditioning. This effect is blocked by mecamylamine, a noncompetitive, broad-spectrum nicotinic receptor antagonist. Objectives The present study extends previous research by further characterizing the nicotinic acetylcholinergic receptor (nAChR) subtypes through which nicotine acts to enhance contextual fear conditioning. Methods C57BL/6J mice were trained with two conditioned stimulus (CS; 30 s, 85-dB white noise)–unconditioned stimulus (US; 2 s, 0.57-mA foot shock) pairings and tested 24 h later for contextual and cued fear conditioning. The effects of the α7 nAChR antagonist methyllycaconitine (MLA; 1.00, 10.00, and 20.00 mg/kg) and the effects of the α4β2 nAChR antagonist dihydro-beta-erythroidine (DHBE; 1.00, 3.00, and 6.00 mg/kg) on cued and contextual fear conditioning and on the enhancement of contextual fear conditioning by nicotine (0.25 mg/kg) were examined. Results We demonstrate that DHBE (all doses) administration attenuates the enhancing effect of nicotine on contextual fear conditioning, and MLA administration has no significant effect on the enhancement of contextual fear conditioning by nicotine. Conclusions The data suggest that non-α7 nAChRs (most likely α4β2 nAChRs) underlie the enhancement of contextual fear conditioning by nicotine.     

咪喹莫特对尖锐湿疣患者血清干扰素-γ表达的影响

目的研究咪喹莫特对尖锐湿疣患者外周血干扰素γ（IFN-γ）表达的诱导作用。方法利用荧光定量聚合酶链反应法测定22例尖锐湿疣患者治疗前后外周血及20例健康对照者外周血中IFN-γmRNA的定量表达。结果尖锐湿疣患者治疗前外周血中IFN-1mRN的表达水平低于健康对照者（t=-2．87,P=0．0071）,咪喹莫特治疗8周后,皮损消退,外周血中IFN-γmRNA的表达水平高于治疗前的表达水平（t=-2．51,P=0．0159）,但与健康对照者的表达水平差异无统计学意义（t=-1．07,P=0．2922）。结论咪喹莫特可诱导尖锐湿疣患者外周血IFN-γmRNA的表达,这可能是其治疗尖锐湿疣的作用机制之一。     

Role of oxytocin receptors in modulation of fear by social memory

Rationale

Oxytocin receptors (Oxtr) are important mediators of social learning and emotion, with bidirectional effects on fear and anxiety. Contrary to the anxiolytic actions of Oxtr in the amygdala, we recently showed that Oxtr in the lateral septum mediate the enhancement of fear conditioning by social defeat in mice.

Objectives

Using positive social interactions, which impair fear conditioning, here we attempted to delineate whether the role of septal Oxtr in fear regulation depends on the valence of the social memory.

Methods

Pharmacological and genetic manipulations of lateral septal Oxtr were combined with the social buffering of fear paradigm, in which pre-exposure to nonfearful conspecifics reduces subsequent contextual fear conditioning, as revealed by decreased freezing behavior.

Results

Antagonism and down-regulation of Oxtr in the lateral septum abolished, while oxytocin (Oxt) administration before pre-exposure to nonfearful conspecifics facilitated the decrease of freezing behavior.

Conclusions

The septal oxytocin system enhances memory of social interactions regardless of their valence, reducing fear after positive and enhancing fear after negative social encounters. These findings explain, at least in part, the seemingly bidirectional role of Oxt in fear regulation.     

Pharmacological dissociation of moderate and high contextual fear as assessed by freezing behavior and fear-potentiated startle.

The amplitude of the whole-body acoustic startle response is reliably enhanced when elicited in the presence of foreground signals, such as light, previously paired with footshocks. It has been shown that this enhancement is evident by moderate fear levels, but is less affected by high fear levels. Potentiation of the acoustic startle reflex has also been reported in the presence of background cues previously associated with footshocks. However, the effects of anxiolytic drugs on different levels of fear elicited by moderate and intense contextual fear conditioning associated with startle reflex have not been examined yet. To approach this issue, we examined the effects of the anxiolytic, midazolam, on two intensities of contextual fear; freezing behavior and the startle response to loud noise. First, we compared the magnitude of the freezing behavior and the startle amplitude during the testing sessions in groups of rats submitted to fear conditioning using 0.3 and 0.6 mA as unconditioned stimuli (10 stimuli of 1 s each, intertrial interval from 60 to 180 s). Afterwards, the effects of midazolam (0.5 and 1.0 mg/kg) were assessed in these two conditions. Rats showed a potentiated startle reflex and a significant freezing behavior to moderate fear conditioning, which were both attenuated by midazolam. Higher levels of fear conditioning caused more intense freezing behavior without enhancing the startle reflex. Whereas midazolam reduced this freezing response, the startle response was unaffected. These results are indicative that anxiolytic-sensitive freezing and fear-potentiated startle are triggered by moderate contextual fear conditioning, while contextual conditioning with the use of high footshocks causes a distinct pattern of behavioral responses, which is only partially affected by midazolam. Due to the differential sensitivity to midazolam of these two patterns of startle responses generated as a function of the intensity of contextual fear conditioning, it is proposed that they represent moderate and intense aversive states that may be related to anxiety or panic/phobic conditions, respectively.     

The antiviral activity of Toll-like receptor 7 and 7/8 agonists

Imiquimod 5% cream is approved for the topical treatment of external anogenital warts caused by human papillomavirus (HPV) and for the skin cancer conditions superficial basal cell carcinoma and actinic keratosis. This drug is the first approved topically active Toll-like receptor (TLR) 7 agonist. Imiquimod activates innate immune cells to produce interferon-a and other cytokines. The induced cytokine cascade, in combination with effects in enhancing antigen presentation, also promotes an antigen-specific T helper type 1 cell-mediated immune response. This immune-based mechanism provides activity against a number of viruses and other intracellular pathogens. Imiquimod was effective topically in clinical studies for HPV but caused mixed results for Molluscum contagiosum, and herpes simplex virus (HSV). Activity against several other viruses were reported in case reports or patient series involving "off-label" usage of imiquimod, while others were evaluated only in preclinical models. Resiquimod, a more potent investigational analogue of imiquimod with mixed TLR7/8 agonist activity, was evaluated in clinical studies topically for the treatment of HSV and systemically for hepatitis C virus also with mixed success. This review focuses on the mechanism of action and antiviral usage reported for the TLR7 agonist imiquimod, the TLR7/8 agonist resiquimod and related imidazoquinoline analogues.     

Acute ethanol administration affects memory reactivation: a look at the neuronal density and apoptosis in the rat hippocampus

This study is an attempt to examine whether administration of ethanol after memory reactivation will modulate expression of memory in rats or not. We further examined whether this administration alters the number of tunnel positive cells in hippocampus.Adult male Wistar rats were trained in a fear conditioning system using two 1 s , 0.6 mA shock with an interval of 180 s. 24 h later the rats were returned to the chamber for reactivation, and then they were injected with ethanol (0.5, 1, 1.5 mg/kg) or saline, ip. Again, one, seven and fourteen days after reactivation, the rats were returned to the context for 5 min. The freezing time (absence of all movements except respiration) was scored in seconds.In the second experiment, after test 1, the animals were anesthetized and a transcardial perfuse with phosphate buffer and paraformaldehyde 4% was conducted. After post-fixation of brains 5-μm sections were stained with cresyl violet.Finally, paraffin-embedded sections of 10 μm were cut out throughout the tissue and each sample was processed with TUNEL. The number of apoptotic cells in a 130 μm-long segment of the hippocampal CA1 and CA3 fields and dentate gyrus was counted.The data demonstrate that ethanol exposure impairs post retrieval processes. Rats receiving ethanol (1.5 mg/kg) showed lower freezing levels during the first test. Moreover, ethanol decreases the density of CA1, CA3 and DG cells and increases the density of apoptotic cells in all regions of hippocampus. Therefore, ethanol exposure impairs reconsolidation of contextual fear conditioning probably via decreasing the density of CA1, CA3 and DG cells.     

Diazepam-induced increases of synaptic efficacy in the hippocampal-medial prefrontal cortex pathway are associated with its anxiolytic-like effect in rats

The medial prefrontal cortex (mPFC) has recently been shown to be an important brain region for emotional function as well as cognitive ability. In previous experiments, we studied the population spike amplitude (PSA) in the mPFC induced by stimulation of the CA1/subicular region as an index of synaptic efficacy in the hippocampal-mPFC pathway. In the present study, we investigated the relationship between the anxiolytic effect of diazepam and the changes of synaptic efficacy in this pathway. In contextual fear conditioning tests, diazepam (0.1 mg/kg) was not effective for fear-related freezing behavior. At a dose of 0.5 mg/kg, diazepam decreased freezing behavior 20 min after administration, with no discernible effect 30 min after administration. In electrophysiological experiments, 0.1 mg/kg diazepam had no effect on the PSA in the mPFC. In contrast, 0.5 mg/kg diazepam increased the PSA in the mPFC within 30 min of administration; however, this PSA increase was attenuated over the 30-min period. Based on these results, we propose that the diazepam-induced PSA increase in the mPFC is associated with its anxiolytic-like effect.     

Interaction between the Cholecystokinin and Endogenous Cannabinoid Systems in Cued Fear Expression and Extinction Retention

Post-traumatic stress disorder (PTSD) is thought to develop, in part, from improper inhibition of fear. Accordingly, one of the most effective treatment strategies for PTSD is exposure-based psychotherapy. Ideally, neuroscience would inform adjunct therapies that target the neurotransmitter systems involved in extinction processes. Separate studies have implicated the cholecystokinin (CCK) and endocannabinoid systems in fear; however, there is a high degree of anatomical colocalization between the cannabinoid 1 receptor (Cnr1) and CCK in the basolateral amygdala (BLA), a brain region critical for emotion regulation. Although most research has focused on GABA and GABAergic plasticity as the mechanism by which Cnr1 mediates fear inhibition, we hypothesize that a functional interaction between Cnr1 and CCKB receptor (CCKBR) is critical for fear extinction processes. In this study, systemic pharmacological manipulation of the cannabinoid system modulated cued fear expression in C57BL/6J mice after consolidation of auditory fear conditioning. Knockout of the CCKBR, however, had no effect on fear- or anxiety-like behaviors. Nonetheless, administration of a Cnr1 antagonist increased freezing behavior during a cued fear expression test in wild-type subjects, but had no effect on freezing behavior in CCKBR knockout littermates. In addition, we found that Cnr1-positive fibers form perisomatic clusters around CCKBR-positive cell bodies in the BLA. These CCKBR-positive cells comprise a molecularly heterogenous population of excitatory and inhibitory neurons. These findings provide novel evidence that Cnr1 contributes to cued fear expression via an interaction with the CCK system. Dysfunctional Cnr1–CCKBR interactions might contribute to the etiology of, or result from, fear-related psychiatric disease.     

Toluene inhibits hippocampal neurogenesis in adult mice

Toluene, a representative industrial solvent and abused inhalant, decreases neuronal activity in vitro and causes mental depression and cognitive impairment in humans. However, the effects of toluene on brain function and the sites of its action are poorly understood. This study investigated the temporal changes of neurogenesis in the hippocampus of adult C57BL/6 mice after acute administration of toluene using two immunohistochemical markers for neurogenesis, Ki-67 and doublecortin (DCX). In addition, after toluene treatment, depression-like behaviors and learning and memory tasks were examined to assess hippocampal neurogenesis-related behavioral dysfunction. The number of Ki-67- and DCX-positive cells in the dentate gyrus of adult hippocampi declined acutely between 0 h and 24 h after toluene treatment (500 mg/kg, i.p.) and increased gradually from 2 to 8 days post-administration. The level of Ki-67 and DCX immunoreactivity decreased in a dose-dependent manner within the range of toluene administered (0-1000 mg/kg). In tail suspension and forced-swim tests performed at 1 and 4 days after toluene treatment (500 mg/kg), mice showed significant depression-like behaviors compared to the vehicle-treated controls. In the contextual fear conditioning and object recognition memory test, the mice trained at 1 and 4 days after toluene treatment showed significant memory defects compared to the vehicle-treated controls. This study suggests that acute exposure to toluene reduces the rate of adult hippocampal neurogenesis and can cause hippocampal dysfunction such as depression and cognitive impairment.     

Fear conditioning and latent inhibition in mice lacking the high affinity subclass of nicotinic acetylcholine receptors in the brain

Nicotine can enhance performance in several tests of cognition but the specific nicotinic receptor subtypes mediating these effects are largely unknown. Knock out mice lacking the β2 subunit of the nicotinic receptor were evaluated in fear conditioning and latent inhibition tasks to begin to determine which receptor subtypes mediate the cognitive effects of nicotine. Young (2–4 months) knock out and wild type mice did not differ in either contextual or tone-conditioned fear, but aged (9–20 months) knock out males were impaired in freezing to both context and tone compared to aged wild type males. No differences in fear conditioning were observed between aged knock out and wild type females. Latent inhibition of fear to a pre-exposed tone, as measured by behavioral freezing, was also assessed. Both knock out and wild type mice displayed similar levels of latent inhibition, although overall levels of freezing were lower in knock out mice. These results support a previous study showing spatial learning deficits in aged β2 subunit knock out mice [EMBO J. 18 (1999) 1235] and suggest that performance of other cognitive tasks may not be influenced by absence of β2 subunit-containing receptors.