Previous Stress Attenuates the Susceptibility to Midazolam's Disruptive Effect on Fear Memory Reconsolidation: Influence of Pre-Reactivation D-Cycloserine Administration

It is well known that, under certain boundary conditions, the retrieval of a stable consolidated memory results into a labile one. During this unstable phase, memory can be vulnerable to interference by a number of pharmacological agents, including benzodiazepines. One of the goals of this study was to evaluate the vulnerability to midazolam (MDZ) after reactivation of recent and remote contextual fear memories in animals that experienced a stressful situation before learning. Animals were subjected to a restraint session and trained in a contextual fear paradigm the following day; consolidated memories were reactivated at different times after learning and different MDZ doses (1.5, 3.0 mg/kg) were administered to rats after reactivation. Our results show that MDZ did not affect memory reconsolidation in older-than-one-day memories of stressed animals, even after the administration of a higher MDZ dose and a longer reactivation session (5 min). In contrast, MDZ was effective in blocking reconsolidation at all memory ages in unstressed animals. In addition, the current research investigated whether activating NMDA sites before reactivation promotes the destabilization of resistant memories such as those of stressed animals. We tested the influence of pre-reactivation D-cycloserine (DCS), a partial NMDA agonist, on MDZ''s effect on fear memory reconsolidation in stressed animals. Our findings indicate that DCS before reactivation promotes retrieval-induced lability in resistant memory traces, as MDZ-induced memory impairment in stressed rats became evident with pre-reactivation DCS but not after pre-reactivation sterile isotonic saline.     

On Disruption of Fear Memory by Reconsolidation Blockade: Evidence from Cannabidiol Treatment

The search for reconsolidation blockers may uncover clinically relevant drugs for disrupting memories of significant stressful life experiences, such as those underlying the posttraumatic stress disorder. Considering the safety of systemically administered cannabidiol (CBD), the major non-psychotomimetic component of Cannabis sativa, to animals and humans, the present study sought to investigate whether and how this phytocannabinoid (3–30 mg/kg intraperitoneally; i.p.) could mitigate an established memory, by blockade of its reconsolidation, evaluated in a contextual fear-conditioning paradigm in rats. We report that CBD is able to disrupt 1- and 7-days-old memories when administered immediately, but not 6 h, after their retrieval for 3 min, with the dose of 10 mg/kg being the most effective. This effect persists in either case for at least 1 week, but is prevented when memory reactivation was omitted, or when the cannabinoid type-1 receptors were antagonized selectively with AM251 (1.0 mg/kg). Pretreatment with the serotonin type-1A receptor antagonist WAY100635, however, failed to block CBD effects. These results highlight that recent and older fear memories are equally vulnerable to disruption induced by CBD through reconsolidation blockade, with a consequent long-lasting relief in contextual fear-induced freezing. Importantly, this CBD effect is dependent on memory reactivation, restricted to time window of <6 h, and is possibly dependent on cannabinoid type-1 receptor-mediated signaling mechanisms. We also observed that the fear memories disrupted by CBD treatment do not show reinstatement or spontaneous recovery over 22 days. These findings support the view that reconsolidation blockade, rather than facilitated extinction, accounts for the aforementioned CBD results in our experimental conditions.     

Effect of Intensity of Unconditional Stimulus on Reconsolidation of Contextual Fear Memory

Memory reconsolidation is ubiquitous across species and various memory tasks. It is a dynamic process in which memory is modified and/or updated. In experimental conditions, memory reconsolidation is usually characterized by the fact that the consolidated memory is disrupted by a combination of memory reactivation and inhibition of protein synthesis. However, under some experimental conditions, the reactivated memory is not disrupted by inhibition of protein synthesis. This so called "boundary condition" of reconsolidation may be related to memory strength. In Pavlovian fear conditioning, the intensity of unconditional stimulus (US) determines the strength of the fear memory. In this study, we examined the effect of the intensity of US on the reconsolidation of contextual fear memory. Strong contextual fear memory, which is conditioned with strong US, is not disrupted by inhibition of protein synthesis after its reactivation; however, a weak fear memory is often disrupted. This suggests that a US of strong intensity can inhibit reconsolidation of contextual fear memory.     

Stimulation of the Noradrenergic System during Memory Formation Impairs Extinction Learning but not the Disruption of Reconsolidation

The noradrenergic system plays a critical role in the ‘consolidation'' of emotional memory. If we are to target ‘reconsolidation'' in patients with anxiety disorders, the noradrenergic strengthening of fear memory should not impair the disruption of reconsolidation. In Experiment I, we addressed this issue using a differential fear conditioning procedure allowing selective reactivation of one of two fear associations. First, we strengthened fear memory by administering an α₂-adrenergic receptor antagonist (ie, yohimbine HCl; double-blind placebo-controlled study) 30 min before acquisition (time for peak value yohimbine HCl <1 h). Next, the reconsolidation of one of the fear associations was manipulated by administering a β-adrenergic receptor antagonist (ie, propranolol HCl) 90 min before its selective reactivation (time for peak value propranolol HCl <2 h). In Experiment II, we administered propranolol HCl after reactivation of the memory to rule out a possible effect of the pharmacological manipulation on the memory retrieval itself. The excessive release of noradrenaline during memory formation not only delayed the process of extinction 48 h later, but also triggered broader fear generalization. Yet, the β-adrenergic receptor blocker during reconsolidation selectively ‘neutralized'' the fear-arousing aspects of the noradrenergic-strengthened memory and undermined the generalization of fear. We observed a similar reduction in fear responding when propranolol HCl was administered after reactivation of the memory. The present findings demonstrate the involvement of noradrenergic modulation in the formation as well as generalization of human fear memory. Given that the noradrenergic strengthening of fear memory impaired extinction learning but not the disruption of reconsolidation, our findings may have implications for the treatment of anxiety disorders.     

The Effect of Propranolol on the Electroencephalogram in Normal and Ethanol Dependent Rats

Abstract: Electroencephalograms were recorded from scalp electrodes placed over the cerebral hemispheres of rats withdrawing from ethanol. The purpose was to investigate whether administration of the β-adrenergic receptor blocker propranolol changed the EEG during that condition. The animals were artificially ventilated with an air mixture of 70% N₂O:30% O₂ and PaO₂ PaCO₂ and mean arterial blood pressure were kept constant. There were no significant differences in EEG frequencies or amplitudes between abstinent animals and controls neither before nor 20 min. after intravenous administration of propranolol 2 mg/kg body weight. Similarly, there was no EEG changes during 3 min. of photic stimulation. It has been reported that electrophysiological abnormalities during physical ethanol dependence are generated in subcortical brain structures but the 4 day intoxication period used in the present study seems too short to involve the cerebral cortex.     

Extracellular Signal-Regulated Kinase in the Basolateral Amygdala,but not the Nucleus Accumbens Core,is Critical for Context-Response-Cocaine Memory Reconsolidation in Rats

The reconsolidation of cocaine memories following retrieval is necessary for the sustained ability of a cocaine-paired environmental context to elicit cocaine seeking. Extracellular signal-regulated kinase (ERK) is an intracellular signaling molecule involved in nucleus accumbens core (NACc)-mediated reconsolidation of Pavlovian cocaine memories. Here, we used a rodent model of drug context-elicited relapse to test the hypothesis that ERK would be similarly required for the reconsolidation of context-response-cocaine memories that underlie drug context-induced reinstatement of instrumental cocaine-seeking behavior, with a focus on the NACc and on the basolateral amygdala (BLA), another important locus for the reconsolidation of cocaine memories. We show that the mitogen-activated protein kinase (MEK)/ERK1/2 inhibitor, U0126 (1.0 μg/0.5 μl/hemisphere), microinfused bilaterally into the BLA—but not the NACc—immediately after brief re-exposure to a previously cocaine-paired context (that is, cocaine-memory reactivation), significantly attenuated subsequent drug context-induced cocaine seeking relative to vehicle (VEH). This effect in the BLA was associated with a transient inhibition of ERK1/2 phosphorylation, and it depended on memory reactivation given that U0126 administered following exposure to a novel context did not alter subsequent cocaine seeking. Furthermore, similar to U0126, baclofen+muscimol-induced (B+M; 106.8/5.7 ng/0.5 μl/hemisphere) neural inactivation of the NACc, following cocaine-memory reactivation, failed to alter subsequent cocaine seeking. These findings demonstrate that ERK activation in the BLA, but not the NACc, is required for the reconsolidation of context-response-cocaine associative memories. Together with prior research, these results suggest that contextual drug-memory reconsolidation in Pavlovian and instrumental settings involves distinct neuroanatomical mechanisms.     

Impaired Extinction Retention in Adolescent Rats: Effects of D-Cycloserine

The developmental trajectory of the prefrontal cortex (PFC) in both rats and humans is nonlinear, with a notable decline in synaptic density during adolescence, potentially creating a ‘natural lesion'' preparation at this age. Given that the PFC is critically involved in retention of extinction of learned fear in adult humans and rodents, the present study examined whether adolescent rats exhibit impaired extinction retention. The results of experiment 1 showed that adolescent rats were impaired in extinction retention, compared with both younger and older rats. The partial NMDA receptor agonist D-cycloserine (DCS) improved extinction retention in adolescent rats (experiment 2), but only if administered immediately after extinction training (experiment 3). In addition, providing extended extinction training improved extinction retention in adolescent rats in a manner similar to that of DCS (experiment 4). The results of this study show that adolescent rats exhibit impaired extinction retention, and that this can be reduced through either DCS or extended extinction training. These novel findings have potential implications for clinical treatments of fear and anxiety disorders in adolescent patients.     

Long-Lasting Increase of Corticosterone After Fear Memory Reactivation: Anxiolytic Effects and Network Activity Modulation in the Ventral Hippocampus

Pathological fear and anxiety can be studied, in rodents, with fear conditioning and exposure to reminder cues. These paradigms are thought to critically involve the ventral hippocampus, which also serves as key site of glucocorticoid action in the brain. Here, we demonstrate a long-lasting reduction of kainate-induced gamma oscillations in slice preparations of the ventral hippocampal area CA3, 30 days after a single fear conditioning training. Reduction of gamma power was sensitive to corticosterone application and associated with a decrease in glucocorticoid and mineralocorticoid receptor mRNA expression across strata of the ventral hippocampal CA3. A fear reactivation session 24 h after the initial conditioning normalized receptor expression levels and attenuated the corticosterone-mediated recovery of gamma oscillations. It moreover increased both baseline and stimulus-induced corticosterone plasma levels and evoked a generalization of fear memory to the background context. Reduced ventral hippocampal gamma oscillation in both fear reactivated and non-reactivated mice were associated with a decrease of anxiety-like behavior in an elevated plus maze. Taking advantage of the circadian fluctuation in corticosterone, we demonstrated the association of high endogenous basal corticosterone plasma concentrations during morning hours with reduced anxiety-like behavior in fear reactivated mice. The anxiolytic effect of the hormone was verified with local applications to the ventral hippocampus. Our data suggest that corticosterone acting on ventral hippocampal network activity has anxiolytic-like effects following fear exposure, highlighting its potential therapeutic value for anxiety disorders.     

The Influence of Prazosin and Propranolol on Serum Lipids and Atherosclerosis in Standard Fed Pigs

Abstract: The influence of prazosin and propranolol on serum lipids and atherosclerosis was evaluated in standard fed pigs during a nine months experimental period. The incidence and severity of atherosclerotic lesions was very low, and no difference could be observed neither between the two drugs nor between the drug groups and the placebo group. Prazosin and propranolol induced no marked change in the serum lipid profile. The results could be explained by the very low fat content, 3.6 per cent, in the present standard diet.     

丙泊酚与咪达唑仑合用对小鼠学习记忆的影响

目的:观察咪达唑仑和丙泊酚合用对小鼠学习记忆的影响。方法:小鼠分为5组(n=10):生理盐水(NS,皮下注射)组、10%脂肪乳(LM,腹腔注射)组、咪达唑仑(MZ,皮下注射1mg·kg-1)组、丙泊酚(PP,腹腔注射20mg·kg-1)组及咪达唑仑与丙泊酚合用(MP,0.5mg·kg-1+10mg·kg-1)组。用跳台和避暗实验分别观察各组不同时间相应的潜伏期、错误次数,以其评估对小鼠学习记忆的影响。结果:用药后第1、2天,MP、PP和MZ组与对照组(NS和LM)比较,跳台和避暗实验中错误次数、潜伏期均有显著性差异(P<0.01);用药后第3、4天,各组间比较各指标无显著性差异(P>0.05)。用药后第2天,与MZ组比较,MP和PP组跳台和避暗实验的错误次数减少、潜伏期延长(P<0.01),MP与PP组间比较无显著性差异(P>0.05)。结论:咪达唑仑和丙泊酚减半合用与两药单用同样可致小鼠学习记忆功能减退,二者具有协同作用。     

Aquaporin-4 Deficiency Impairs Synaptic Plasticity and Associative Fear Memory in the Lateral Amygdala: Involvement of Downregulation of Glutamate Transporter-1 Expression

Astrocytes are implicated in information processing, signal transmission, and regulation of synaptic plasticity. Aquaporin-4 (AQP4) is the major water channel in adult brain and is primarily expressed in astrocytes. A growing body of evidence indicates that AQP4 is a potential molecular target for the regulation of astrocytic function. However, little is known about the role of AQP4 in synaptic plasticity in the amygdala. Therefore, we evaluated long-term potentiation (LTP) in the lateral amygdala (LA) and associative fear memory of AQP4 knockout (KO) and wild-type mice. We found that AQP4 deficiency impaired LTP in the thalamo-LA pathway and associative fear memory. Furthermore, AQP4 deficiency significantly downregulated glutamate transporter-1 (GLT-1) expression and selectively increased NMDA receptor (NMDAR)-mediated EPSCs in the LA. However, low concentration of NMDAR antagonist reversed the impairment of LTP in KO mice. Upregulating GLT-1 expression by chronic treatment with ceftriaxone also reversed the impairment of LTP and fear memory in KO mice. These findings imply a role for AQP4 in synaptic plasticity and associative fear memory in the amygdala by regulating GLT-1 expression.     

Effect of Propranolol and Related Drugs on Transmembraneous pH Differences in Liposomes

Abstract Propranolol (1-isopropylamino-3-(1-naphtoloxy)-propan-2-ol) a β-adren-ergic receptor blocking agent was found to cause changes of transmembraneous pH in liposomes prepared from Soy-lecithin and cardiolipin. When the external pH was neutral and the internum of the liposomes acidic, the drug decreased the pH gradient. When the externum was acidic and the internum neutral, the gradient was increased by the drug. The effect of butacaine was similar to that of propranolol, while procaine, timolol and practolol were ineffective. It is suggested that the charged form of propranolol is bound to the membrane and dislocates protons from binding sites in the membrane and that the uncharged form of propranolol penetrates the membrane. After penetration it could associate with protons in the intraliposomal compartment and hence increase the pH of the interior. Depending on the direction of the pre-existing proton gradient propranolol would thus be able to increase or decrease the pH difference across the liposomal membrane.     

Selective Effect of Adjuvant Arthritis on the Disposition of Propranolol Enantiomers in Rats Detected Using a Stereospecific HPLC Assay

Nonstereospecific studies have indicated that the pharmacokinetics of propranolol (PR) are altered in inflammatory conditions such as arthritis. However, as the kinetics and dynamics of PR are stereoselective, we examined the effect of adjuvant arthritis (AA) on the disposition of the individual enantiomers. A novel normal-phase stereospecific HPLC assay for PR was developed involving chiral derivatization with S-(naphthyl)ethyl isocyanate and fluorescence detection. Oral and iv doses of racemic PR were administered to control and AA rats (n = 6). AA had no significant effect on either clearance or S:R ratio after iv doses. On the other hand, after oral doses, clearance was significantly decreased in AA. Although significant for both enantiomers, this effect was more pronounced on the less active R-enantiomer. The AUC R:S ratio was, therefore, significantly altered (AA, 14 ± 3.0; control, 4.3 ± 1.2). Increased total (S + R) plasma concentrations of PR in AA, possibly due to a reduced intrinsic clearance, therefore, reflect mainly increased concentrations of the less active R-enantiomer.     

Differential Recruitment of the Infralimbic Cortex in Recent and Remote Retrieval and Extinction of Aversive Memory in Post-Weanling Rats

BackgroundWe previously showed that the infralimbic medial prefrontal cortex (IL-mPFC) plays an important role in recent and remote memory retrieval and extinction of conditioned odor aversion (COA) and contextual fear conditioning (CFC) in adult rats. Because the mPFC undergoes maturation during post-weaning, here, we aimed to explore (1) whether post-weanling rats can form recent and remote COA and CFC memory, and (2) the role of the IL-mPFC in mediating these processes.MethodsTo investigate the retrieval process, we transiently inactivated the IL-mPFC with lidocaine prior to the retrieval test at either recent or remote time points. To target the consolidation process, we applied the protein synthesis inhibitor after the retrieval at recent or remote time points.ResultsOur results show that the post-weanling animals were able to develop both recent and remote memory of both COA and CFC. IL-mPFC manipulations had no effect on retrieval or extinction of recent and remote COA memory, suggesting that the IL has no effect in COA at this developmental stage. In contrast, the IL-mPFC played a role in (1) the extinction of recent, but not remote, CFC memory, and (2) the retrieval of remote, but not recent, CFC memory. Moreover, remote, but not recent, CFC retrieval enhanced c-Fos protein expression in the IL-mPFC.ConclusionsAltogether, these results point to a differential role of the IL-mPFC in recent and remote CFC memory retrieval and extinction and further confirm the differences in the role of IL-mPFC in these processes in post-weanling and adult animals.     

Absence of an Effect of Naloxone on Ethanol Intoxication and Withdrawal Reactions

Abstract Experimental and clinical results suggest a relationship between the action of ethanol and opiates. Therefore, we have tested whether the specific morphine antagonist naloxone (2 mg/kg intraperitoneally every six hours) affects signs of severe ethanol intoxication or modifies the withdrawal syndrome following chronic ethanol intoxication in rats. Using a double blind technique, we did not find any difference between saline treated and naloxone treated animals with respect to level of intoxication and severity of withdrawal symptoms. We must therefore conclude that naloxone does not modify signs of severe ethanol intoxication or change the ethanol withdrawal syndrome in the rat. These findings do not rule out that there might be a biochemical link between actions of ethanol and opiates, but this link is probably not localized at the level of specific drug receptor interaction.     

The Serotonergic Projection from the Median Raphe Nucleus to the Ventral Hippocampus is Involved in the Retrieval of Fear Memory Through the Corticotropin-Releasing Factor Type 2 Receptor

Several different studies have separately established that serotonin, corticotropin-releasing factor (CRF) receptors, and the hippocampus are involved in fear memory retrieval. The main aim of this study is to connect these separate studies. To assess the levels of anxiety/fear, we used the contextual fear-conditioning test and the elevated plus maze test as memory-dependent and memory-independent tasks, respectively. We injected CRF receptor antagonists or vehicle into the median raphe nucleus (MRN) 10 min before behavioral tests. As a result, 1000 ng of astressin 2B (CRF₂ receptor antagonist), but not 250 ng of antalarmin (CRF₁ receptor antagonist), significantly suppressed the expression rate of freezing behavior in the contextual fear-conditioning test. However, in the elevated plus maze test, there was no difference between astressin 2B-injected rats and saline-injected rats in the time spent in open arms. Neither the amount of exploratory behavior nor the moving distance in the EPM of astressin 2B-injected rats differed from that of vehicle-injected rats. Moreover, when we assessed the extracellular serotonin release in the ventral hippocampus in freely moving rats through in vivo microdialysis, it was shown that the blockade of the CRF₂ receptor in the MRN suppressed serotonin release in the ventral hippocampus during fear memory retrieval. These results indicated that endogenous CRF and/or related ligands that were released in the MRN could activate the CRF₂ receptor and stimulate serotonin release in the ventral hippocampus, thereby inducing fear memory retrieval.     

健脑生智口服液对老年痴呆大鼠的学习记忆功能的影响

目的：研究健脑生智口服液对老年痴呆模型大鼠学习记忆功能的影响。方法：大鼠60只,采用腹腔注射东莨菪碱法和AlCl3法复制老年痴呆模型,随机分为正常对照组、模型组、阳性脑复康组（0．301g·kg^-1）、健脑生智口服液高剂量组（16．8g·kg^-1）、中剂量组（8．4g·kg^-1）、低剂量组（4．2g·kg^-1）,测定脑组织中SOD、MDA、Na^＋ -K^＋-ATP酶活性及血清、脑组织中AchE活性、脑蛋白含量。结果：健脑生智口服液能升高脑组织SOD活性、降低MDA活性,提高Na^＋-K^＋-ATP酶活性,降低脑、血清中AchE活性,增加脑蛋白含量。结论：健脑生智口服液能增强老年痴呆大鼠的学习记忆能力。     

蜕皮甾酮对小鼠学习记忆的促进作用

采用一次性训练被动回避性条件反应方法———跳台法,观察了蜕皮甾酮（Ｅｃｄｙｓｔｅｒｏｎｅ）对小鼠学习记忆功能的影响．结果表明,蜕皮甾酮可拮抗东莨菪碱造成的记忆获得障碍,改善环己酰亚胺造成的记忆巩固不良和３０％乙醇造成的记忆再现缺失．蜕皮甾酮还具有抗急性脑缺氧作用,提示蜕皮甾酮可改善记忆障碍,具有较高的药用价值．     

Influence of Anesthetic Regimens on Intestinal Absorption in Rats

We compared the influence of anesthetic regimens using urethane (U), pentobarbital (P), ether (E), and ketamine/midazolam (K) on the intestinal absorption of several probes using a single-pass per-fusion technique in rats. The selected probes were D-glucose (1 mM) for the resistance of the unstirred water layer (UWL), D-glucose (100 mM) for the capacity of carrier-mediated D-glucose transport, L-glucose, and urea for membrane-limited passive transport, and tritiated water (³H₂O) for blood flow at the absorption site. The absorbed fraction of D-glucose (1 mM) was the smallest for U and the largest for P, suggesting that the resistance of UWL is the largest for U and the smallest for P. The absorbed fraction of D-glucose (100 mM) was the largest for P (U = E = K < P), suggesting a higher capacity of carrier-mediated D-glucose transport for P. The absorbed fraction of urea was similar for all anesthetics, while that of L-glucose was the smallest for K (U = P = E > K). Although the results for these two markers of membrane-limited passive transport were inconsistent, the passive permeability of the intestinal membrane may be lower when treating with K. The intestinal absorptions of D-glucose (1 and 100 mM), L-glucose, and urea were, in general, lower with any of the anesthetics than under nonanesthesia (N), suggesting increased resistance of UWL and decreased intestinal membrane permeability by carrier-mediated and passive transport under anesthesia. The only exception was the absorption of D-glucose (100 mM) under P, which was comparable to that under N. The results were similar when considering the membrane permeability clearance estimated by correcting for the resistance of UWL. The blood flow at the absorption site, estimated from the absorption of ³H₂O, was decreased under U, compared with N, and increased under K(U

in vivo.