Epinephrine Released During Traumatic Events May Strengthen Contextual Fear Memory Through Increased Hippocampus mRNA Expression of Nr4a Transcription Factors

Hippocampus muscarinic M4 receptor mRNA expression may influence central cholinergic activity, causing fear memory strengthening by peripheral adrenaline

Adrenaline (Ad) strengthens contextual fear memory by increasing blood glucose, possibly enhancing hippocampus acetylcholine synthesis. Nevertheless, it is unclear if peripheral Ad influences the cholinergic system, contributing to contextual fear memory strengthening. We aimed to evaluate whether peripheral Ad alters muscarinic receptor expression and if the cholinergic system is involved in peripheral Ad contextual fear memory strengthening effect. Wild-type (WT) and Ad-deficient male mice (129 × 1/SvJ) underwent a fear conditioning procedure followed by intraperitoneal pre-training and pre-context administration of Ad (0.1 mg/kg), atropine (10 mg/kg), methylatropine (0.5 mg/kg), Ad (0.1 mg/kg) plus atropine (10 mg/kg) or vehicle (NaCl, 0.9%). Shock responsiveness and freezing behaviour were accessed. Hippocampal M1, M2, and M4 mRNA expression were evaluated. Ad-deficient mice presented decreased hippocampal muscarinic M4 subtype receptor mRNA expression compared to WT mice. In Ad-administered Ad-deficient mice, hippocampal muscarinic M4 subtype receptor mRNA expression increased compared with vehicle-administered Ad-deficient mice. On the context day, atropine-administered WT mice presented decreased freezing behaviour compared to vehicle or methylatropine-administered WT mice. Moreover, Ad plus atropine-administered Ad-deficient mice led to decreased freezing behaviour compared to Ad-administered Ad-deficient mice. In conclusion, Ad-deficient mice's contextual fear memory impairment was associated with hippocampal muscarinic M4 subtype receptor down expression, which was reversed by Ad. This may be related to contextual fear memory consolidation or retrieval induced by peripheral Ad. Furthermore, the effect of Ad contextual fear memory might be due to increased hippocampus muscarinic subtype M4 expression, which may contribute to increased cholinergic activity in the central nervous system.

Cannabidiol inhibits transient receptor potential canonical 4 and modulates excitability of pyramidal neurons in mPFC

Cannabidiol (CBD), a non-psychoactive compound derived from the cannabis plant, has been extensively studied for its potential therapeutic effects on various central nervous system (CNS) disorders, including epilepsy, chronic pain, Parkinson's disease, and stress-related neuropsychiatric disorders. However, the pharmacological mechanisms of CBD have not been fully elucidated due to the complexity of their targets. In this study, we reported that the transient receptor potential canonical 4 (TRPC4) channel, a calcium-permeable, non-selective cation channel, could be inhibited by CBD. TRPC4 is highly abundant in the central nervous system and plays a critical role in regulating axonal regeneration, neurotransmitter release, and neuronal network activity. Here, we used whole-cell electrophysiology and intracellular calcium measurements to identify the inhibitory effects of CBD on TRPC4, in which CBD was found to inhibit TRPC4 channel with an IC50 value of 1.52 μM TRPC4 channels function as receptor-operated channels (ROC) and could be activated by epinephrine (EP) via G proteins. We show that CBD can inhibit EP-evoked TRPC4 current in vitro and EP-evoked neuronal excitability in the medial prefrontal cortex (mPFC). These results are consistent with the action of TRPC4-specific inhibitor Pico145, suggesting that TRPC4 works as a functional ionotropic receptor of CBD. This study identified TRPC4 as a novel target for CBD in the CNS and suggested that CBD could reduce the pyramidal neuron excitability by inhibiting TRPC4-containing channels in the mPFC.

Glucose may Contribute to Retrieval and Reconsolidation of Contextual Fear Memory Through Hippocampal Nr4a3 and Bdnf mRNA Expression and May Act Synergically with Adrenaline

Adrenaline (Ad) and glucose released into the bloodstream during stress may strengthen contextual fear memory. However, no previous studies have detached the effects of glucose from Ad in this paradigm. Using Ad-deficient mice, we aimed to evaluate the effect of glucose on contextual fear memory when endogenous Ad is absent. Fear conditioning was performed in wild-type (WT) and Ad-deficient mice (129 × 1/SvJ) administered with glucose (30 or 10 mg/kg; i.p.) or/and Ad (0.01 mg/kg; i.p.) or vehicle (0.9% NaCl; i.p.). Catecholamines were quantified using HPLC-ED. Real-time qPCR was used to assess mRNA expression of hippocampal genes. WT and Ad-deficient mice display increased contextual fear memory when administered with glucose both in acquisition and context days when compared to vehicle. Also, Nr4a3 and Bdnf mRNA expression increased in glucose-administered Ad-deficient mice. Sub-effective doses of glucose plus Ad administered simultaneously to Ad-deficient mice increased contextual fear memory, contrary to independent sub-effective doses. Concluding, glucose may be an important part of the peripheral to central pathway involved in the retrieval and reconsolidation of fear contextual memories independently of Ad, possibly due to increased hippocampal Nr4a3 and Bdnf gene expression. Furthermore, Ad and glucose may act synergically to strengthen contextual fear memory.

Synaptically-targeted long non-coding RNA SLAMR promotes structural plasticity by increasing translation and CaMKII activity

Long noncoding RNAs (lncRNAs) play crucial roles in maintaining cell homeostasis and function. However, it remains largely unknown whether and how neuronal activity impacts the transcriptional regulation of lncRNAs, or if this leads to synapse-related changes and contributes to the formation of long-term memories. Here, we report the identification of a lncRNA, SLAMR, which becomes enriched in CA1-hippocampal neurons upon contextual fear conditioning but not in CA3 neurons. SLAMR is transported along dendrites via the molecular motor KIF5C and is recruited to the synapse upon stimulation. Loss of function of SLAMR reduces dendritic complexity and impairs activity-dependent changes in spine structural plasticity and translation. Gain of function of SLAMR, in contrast, enhances dendritic complexity, spine density, and translation. Analyses of the SLAMR interactome reveal its association with CaMKIIα protein through a 220-nucleotide element also involved in SLAMR transport. A CaMKII reporter reveals a basal reduction in CaMKII activity with SLAMR loss-of-function. Furthermore, the selective loss of SLAMR function in CA1 disrupts the consolidation of fear memory in male mice, without affecting their acquisition, recall, or extinction, or spatial memory. Together, these results provide new molecular and functional insight into activity-dependent changes at the synapse and consolidation of contextual fear.

Epinephrine injected into the basolateral amygdala affects anxiety-like behavior and memory performance in stressed rats

The amygdala is known to mediate in moderating the impacts of emotional arousal and stress on memory. According to a growing body of research, the basolateral amygdala (BLA) is an important locus for integrating neuromodulator influences coordinating the retrieval of different types of memory and anxiety. This study aimed to investigate how the epinephrine in the BLA affects hippocampal fear memory, anxiety, and plasticity in control and stressed rats. For four days, male Wistar rats were exposed to electrical foot-shock stress. Animals received bilateral micro-injections of either vehicle or epinephrine (1 µg/side) into the BLA over four days (5 min before foot-shock stress). Behavioral characteristics (fear memory and anxiety-like behavior), histological features and electrophysiological parameters were investigated. Epinephrine injection into BLA resulted in a considerable impairment of fear memory in stressed rats. On the other hand, epinephrine effectively affected fear memory in control rats. Under stress conditions, epinephrine in the BLA is thought to increase anxiety-like behaviors. Treatment with epinephrine significantly increases the slope of fEPSP in the CA1 region of the hippocampus in the control and stress rats. In different groups, foot-shock stress had no effect on the apical and basal dendritic length in the CA1 region of the hippocampus. These results indicate that activating adrenergic receptors diminish fear memory and anxiety-like behaviors in the foot-shock stress, which this impact is independent of CA1 long-term potentiation induction.

Molecular pathways underlying sympathetic autonomic overshooting leading to fear and traumatic memories: looking for alternative therapeutic options for post-traumatic stress disorder

The sympathoadrenal medullary system and the hypothalamic-pituitary-adrenal axis are both activated upon stressful events. The release of catecholamines, such as dopamine, norepinephrine (NE), and epinephrine (EPI), from sympathetic autonomic nerves participate in the adaptive responses to acute stress. Most theories suggest that activation of peripheral β-adrenoceptors (β-ARs) mediates catecholamines-induced memory enhancement. These include direct activation of β-ARs in the vagus nerve, as well as indirect responses to catecholamine-induced glucose changes in the brain. Excessive sympathetic activity is deeply associated with memories experienced during strong emotional stressful conditions, with catecholamines playing relevant roles in fear and traumatic memories consolidation. Recent findings suggest that EPI is implicated in fear and traumatic contextual memories associated with post-traumatic stress disorder (PTSD) by increasing hippocampal gene transcription (e.g., Nr4a) downstream to cAMP response-element protein activation (CREB). Herein, we reviewed the literature focusing on the molecular mechanisms underlying the pathophysiology of memories associated with fear and traumatic experiences to pave new avenues for the treatment of stress and anxiety conditions, such as PTSD.

Cell-Effective Transition-State Analogue of Phenylethanolamine N-Methyltransferase

Phenylethanolamine N-methyltransferase (PNMT) catalyzes the S-adenosyl-l-methionine (SAM)-dependent methylation of norepinephrine to form epinephrine. Epinephrine is implicated in the regulation of blood pressure, respiration, Alzheimer's disease, and post-traumatic stress disorder (PTSD). Transition-state (TS) analogues bind their target enzymes orders of magnitude more tightly than their substrates. A synthetic strategy for first-generation TS analogues of human PNMT (hPNMT) permitted structural analysis of hPNMT and revealed potential for second-generation inhibitors [Mahmoodi, N.; J. Am. Chem. Soc. 2020, 142, 14222-14233]. A second-generation TS analogue inhibitor of PNMT was designed, synthesized, and characterized to yield a Ki value of 1.2 nM. PNMT isothermal titration calorimetry (ITC) measurements of inhibitor 4 indicated a negative cooperative binding mechanism driven by large favorable entropic contributions and smaller enthalpic contributions. Cell-based assays with HEK293T cells expressing PNMT revealed a cell permeable, intracellular PNMT inhibitor with an IC50 value of 81 nM. Structural analysis demonstrated inhibitor 4 filling catalytic site regions to recapitulate both norepinephrine and SAM interactions. Conformation of the second-generation inhibitor in the catalytic site of PNMT improves contacts relative to those from the first-generation inhibitors. Inhibitor 4 demonstrates up to 51,000-fold specificity for PNMT relative to DNA and protein methyltransferases. Inhibitor 4 also exhibits a 12,000-fold specificity for PNMT over the α2-adrenoceptor.

Insulin enhances contextual fear memory independently of its effect in increasing plasma adrenaline

AIMS

Adrenaline enhances contextual fear memory consolidation possibly by activating liver β₂-adrenoceptors causing transient hyperglycaemia. Contrastingly, insulin-induced hypoglycaemia may culminate in blood adrenaline increment, hidering the separation of each hormone's action in contextual fear memory. Therefore, an Ad-deficient mouse model was used aiming to investigate if contextual fear memory consolidation following insulin administration requires or not subsequent increases in plasma adrenaline, which occurs in response to insulin-induced hypoglycemia.

MAIN METHODS

Fear conditioning was performed in wild-type (WT) and adrenaline-deficient (Pnmt-KO) male mice (129 × 1/SvJ) treated with insulin (2 U/kg, intraperitoneal (i.p.)) or vehicle (0.9 % NaCl (i.p.)). Blood glucose was quantified. Catecholamines were quantified using HPLC with electrochemical detection. Quantitative real-time polymerase chain reaction was used to assess mRNA expression of hippocampal Nr4a1, Nr4a2, Nr4a3, and Bdnf genes.

KEY FINDINGS

Insulin-treated WT mice showed increased freezing behaviour when compared to vehicle-treated WT mice. Also, plasma dopamine, noradrenaline, and adrenaline increased in this group. Insulin-treated Pnmt-KO animals showed increased freezing behaviour when compared with respective vehicle. However, no changes in plasma or tissue catecholamines were identified in insulin-treated Pnmt-KO mice when compared with respective vehicle. Furthermore, insulin-treated Pnmt-KO mice presented increased Bdnf mRNA expression when compared to vehicle-treated Pnmt-KO mice.

SIGNIFICANCE

Concluding, enhanced freezing behaviour after insulin treatment, even in adrenaline absence, may indicate a key role of insulin in contextual fear memory. Insulin may cause central molecular changes promoting contextual fear memory formation and/or retrieval. This work may indicate a further role of insulin in the process of contextual fear memory modulation.

New Concepts on the Pathophysiology of Acute Coronary Syndrome

Acute coronary syndrome (ACS) is the most severe form of ischemic heart disease. Although it is caused by atherosclerotic plaque thrombosis or nonatherosclerotic causes, its pathophysiological mechanism of ACS is not fully understood, and its concept is constantly updated and developed. At present, the main pathophysiological mechanisms include plaque rupture, plaque erosion, calcified nodules (CN) and non-atherosclerotic causes such as coronary vasospasm and myocardial bridging (MB). These mechanisms may overlap and coexist in some ACS patients. Therefore, the pathophysiological mechanism of ACS is complex, and is of great significance for the diagnosis and treatment of ACS. This review will discuss the pathophysiological mechanisms of ACS to provide new thoughts on the pathogenesis, diagnosis and treatment of ACS.

SLAMR, a synaptically targeted lncRNA, facilitates the consolidation of contextual fear memory

LncRNAs are involved in critical processes for cell homeostasis and function. However, it remains largely unknown whether and how the transcriptional regulation of long noncoding RNAs results in activity-dependent changes at the synapse and facilitate formation of long-term memories. Here, we report the identification of a novel lncRNA, SLAMR, that becomes enriched in CA1- but not in CA3-hippocampal neurons upon contextual fear conditioning. SLAMR is transported to dendrites via the molecular motor KIF5C and recruited to the synapse in response to stimulation. Loss of function of SLAMR reduced dendritic complexity and impaired activity dependent changes in spine structural plasticity. Interestingly, gain of function of SLAMR enhanced dendritic complexity, and spine density through enhanced translation. Analyses of the SLAMR interactome revealed its association with CaMKIIα protein through a 220-nucleotide element and its modulation of CaMKIIα activity. Furthermore, loss-of-function of SLAMR in CA1 selectively impairs consolidation but neither acquisition, recall, nor extinction of fear memory and spatial memory. Together, these results establish a new mechanism for activity dependent changes at the synapse and consolidation of contextual fear.

The glucose tolerance test in mice: Sex, drugs and protocol

AIM

To establish the impact of sex, dosing route, fasting duration and acute habituation stress on glucose tolerance test (GTT) measurements used in the preclinical evaluation of potential glucose-modulating therapeutics.

METHODS

Adult male and female C57Bl/6J mice, implanted with HD-XG glucose telemetry devices, were fasted for 16 hours or 6 hours following acute habituation stress due to whole cage change, cage change with retention of used bedding or no cage change prior to intraperitoneal (IP) GTTs. To evaluate protocol refinement and sex on the ability of the GTT to detect drug effects, we administered 250 mg/kg oral metformin or 10 nmol/kg IP exendin-4 using optimized protocols.

RESULTS

Female mice were less sensitive to human intervention when initiating fasting. Following a 6-hour fast, retention of bedding whilst changing the cage base promotes quicker stabilization of basal blood glucose in both sexes. Prolonged fasting for 16 hours resulted in an exaggerated GTT response but induced pronounced basal hypoglycaemia. Following GTT protocol optimization the effect of exendin-4 and metformin was equivalent in both sexes, with females showing a more modest but more reproducible GTT response.

CONCLUSIONS

Variations in GTT protocol have profound effects on glucose homeostasis. Protocol refinement and/or the use of females still allows for detection of drug effects, providing evidence that more severe phenotypes are not an essential prerequisite when characterizing/validating new drugs.

Comprehensive insights into the function and molecular and pharmacological regulation of neuron-derived orphan receptor 1, an orphan receptor

Neuron-derived orphan receptor 1 (NOR1), also called nuclear receptor subfamily 4 group A member 3 (NR4A3), is a nuclear receptor belonging to the NR4A family. Since no endogenous ligand has been identified to date, NOR1 is also referred to as an orphan receptor. NOR1 is expressed in a variety of cells and tissues, including neurons, vascular smooth muscle cells, T lymphocytes, dendritic cells, tumor cells, heart, liver, and pancreas. Because NOR1 was first identified in apoptotic neurons, it is functionally associated with the regulation of cell migration and the growth of neuronal synapses. In-depth studies have shown that NOR1 can be edited by the immediate early gene and functions as a transcription factor. NOR1 has been shown to be rapidly induced by a number of stimulants including growth factors, fatty acids, and neurotransmitters. Elevated NOR1 levels may be involved in a number of pathophysiological processes. These include regulation of cellular apoptosis and regeneration, neuron formation, contextual fearing memory, inflammation, vascular smooth muscle proliferation, insulin secretion, and tumor development, whereby NOR1 mediates the pathogenesis of numerous diseases such as cerebral ischemia, depression, post-traumatic stress disorder, atherosclerosis, abdominal aortic aneurysm, cardiac hypertrophy, diabetes, osteoarthritis, rheumatoid arthritis, and cancer. However, to date, comprehensive insights into the function of NOR1 are not available in sources published online. In this review, we provide a brief overview of the function and molecular and pharmacological regulation of NOR1 in various pathological or physiological conditions to advance the development of NOR1 as a novel target for disease treatment.

Sotalol Treatment may Interfere With Retrieval, Expression, and/or Reconsolidation Processes Thus Disrupting Traumatic Memories in a Post-Traumatic Stress Disorder Mice Model

The processes by which fear memory is encoded, consolidated, and re-consolidated are extremely complex and appear to require the release of stress hormones, especially adrenaline (AD). AD improves contextual fear memory, acting specifically on peripheral β2-adrenoceptors. Propranolol (peripheral and central β-adrenoceptor antagonist) treatment was shown to prevent post-traumatic stress disorder (PTSD) development and reduce its symptoms. However, propranolol has several side effects. Thus, we aimed to evaluate if sotalol (a peripheral β-adrenoceptor antagonist) treatment interferes with retrieval, expression, and/or reconsolidation of traumatic memories in a validated mice model that mimics the signs/symptoms of PTSD, thus intending to decrease them. Female mice were induced with PTSD following an established protocol. Sotalol (2.0 mg/kg) or vehicle were administered on days 2, 7, and 14. The percentage of freezing was calculated, and behavioral tests were carried out. Catecholamines in plasma were quantified by HPLC with electrochemical detection. Quantitative real-time polymerase chain reaction (qPCR) was used to evaluate mRNA expression of NR4A family genes in hippocampus. Following the submission of the animals to the same aversive context on days 2, 7, and 14, sotalol-treated mice exhibited significant less freezing behavior. In the elevated plus-maze test, the time spent and number of entries in the open arms, and total arm entries were increased in sotalol-treated mice. Also, the light-dark transition test revealed higher time spent, number of transitions to the light, and total number of transitions in sotalol-treated mice. Moreover, plasma AD was significantly decreased in sotalol-treated mice. On day 14, sotalol-treated mice exhibited a decrease in mRNA expression of Nr4a1 in the hippocampus. In conclusion, in PTSD mice model, sotalol appears to decrease traumatic memories and anxiety-like behavior, probably due to a decrease in peripheral adrenergic activity, which influences traumatic memories. The effects of sotalol upon re-exposure to the traumatic context may be consistent with interference in the retrieval, expression, and/or reconsolidation processes of contextual traumatic memory, resulting in a long-term reduction of PTSD symptoms and signs. The decreased Nr4a1 mRNA expression in the hippocampal formation may be crucial for these mice to develop diminished traumatic contextual memories after sotalol therapy in PTSD.

Nr4a2 Transcription Factor in Hippocampal Synaptic Plasticity, Memory and Cognitive Dysfunction: A Perspective Review

Long-lasting changes of synaptic efficacy are largely mediated by activity-induced gene transcription and are essential for neuronal plasticity and memory. In this scenario, transcription factors have emerged as pivotal players underlying synaptic plasticity and the modification of neural networks required for memory formation and consolidation. Hippocampal synaptic dysfunction is widely accepted to underlie the cognitive decline observed in some neurodegenerative disorders including Alzheimer’s disease. Therefore, understanding the molecular pathways regulating gene expression profiles may help to identify new synaptic therapeutic targets. The nuclear receptor 4A subfamily (Nr4a) of transcription factors has been involved in a variety of physiological processes within the hippocampus, ranging from inflammation to neuroprotection. Recent studies have also pointed out a role for the activity-dependent nuclear receptor subfamily 4, group A, member 2 (Nr4a2/Nurr1) in hippocampal synaptic plasticity and cognitive functions, although the underlying molecular mechanisms are still poorly understood. In this review, we highlight the specific effects of Nr4a2 in hippocampal synaptic plasticity and memory formation and we discuss whether the dysregulation of this transcription factor could contribute to hippocampal synaptic dysfunction, altogether suggesting the possibility that Nr4a2 may emerge as a novel synaptic therapeutic target in brain pathologies associated to cognitive dysfunctions.

Treatment With Nepicastat Decreases Contextual Traumatic Memories Persistence in Post-traumatic Stress Disorder

Post-traumatic stress disorder (PTSD) is a common anxiety mental disorder and can be manifested after exposure to a real or perceived life-threatening event. Increased noradrenaline and adrenaline in plasma and urine have been documented in PTSD. Dopamine-β-hydroxylase (DBH) catalyzes the conversion of dopamine to noradrenaline and consequently, DBH inhibition reduces catecholamines. Our aim was to evaluate if nepicastat treatment decreases PTSD signs in an animal model. Wild-type (129x1/SvJ) female mice were submitted to PTSD induction protocol. DBH-inhibitor nepicastat (30 mg/kg) or vehicle (0.2% HPMC) were administered once daily since day 0 until day 7 or 12. The percentage of freezing was calculated on days 0, 1, 2, and 7, and behavioral tests were performed. Quantification of nepicastat in plasma and DBH activity in the adrenal gland was evaluated. Catecholamines were quantified by HPLC with electrochemical detection. mRNA expression of Npas4 and Bdnf in hippocampus was evaluated by qPCR.Mice in the PTSD-group and treated with nepicastat showed a decrease in freezing, and an increase in the time spent and entries in open arms in elevated plus maze test. In mice treated with nepicastat, adrenal gland DBH activity was decreased, and catecholamines were also decreased in plasma and tissues. On day 7, in mice treated with nepicastat, there was an increase of Npas4 and Bdnf mRNA expression in the hippocampus.In conclusion, DBH inhibitor nepicastat has an effect consistent with a decrease in the persistence of traumatic memories and anxiety-like behavior in this PTSD mice model. The disruption of traumatic memories through interference with the formation, consolidation, retrieval, and/or expression processes may be important to decrease PTSD symptoms and signs. The increase in Npas4 and Bdnf mRNA expression in the hippocampus may be important to develop a weaker traumatic contextual memory after nepicastat treatment.

Interactions of Noradrenergic, Glucocorticoid and Endocannabinoid Systems Intensify and Generalize Fear Memory Traces

Systemic administration of drugs that activate the noradrenergic or glucocorticoid system potentiates aversive memory consolidation and reconsolidation. The opposite happens with the stimulation of endocannabinoid signaling under certain conditions. An unbalance of these interacting neurotransmitters can lead to the formation and maintenance of traumatic memories, whose strength and specificity attributes are often maladaptive. Here we aimed to investigate whether originally low-intensity and precise contextual fear memories would turn similar to traumatic ones in rats systemically administered with adrenaline, corticosterone, and/or the cannabinoid type-1 receptor antagonist/inverse agonist AM251 during consolidation or reconsolidation. The high dose of each pharmacological agent evaluated significantly increased freezing times at test in the conditioning context one and nine days later when given alone post-acquisition or post-retrieval. Their respective low dose produced no relative changes when given separately, but co-treatment of adrenaline with corticosterone or AM251 and the three drugs combined, but not corticosterone with AM251, produced results equivalent to those mentioned initially. Neither the high nor the low dose of adrenaline, corticosterone, or AM251 altered freezing times at test in a novel, neutral context two and ten days later. In contrast, animals receiving the association of their low dose exhibited significantly higher freezing times than controls. Together, the results indicate that newly acquired and destabilized threat memory traces become more intense and generalized after a combined interference acting synergistically and mimicking that reported in patients presenting stress-related psychiatric conditions.

Micro-injection of propranolol within basolateral amygdala impaired fear and spatial memory and dysregulated evoked responses of CA1 neurons following foot shock stress in rats

The basolateral nucleus of the amygdala (BLA) is responsible for memory retrieval after stress. It regulates hippocampal long-term potentiation (LTP) during stress. Although β-adrenoceptors of the BLA have a critical role in memory, few studies have addressed this question in the BLA, and the results still have been contradictory. The present study was designed to investigate the involvement of β-adrenoceptors of the BLA on hippocampus memory, anxiety, and plasticity in intact and stressed rats. Male Wistar rats were submitted to the electrical foot-shock stress for four consecutive days. Over four consecutive days, animals received bilateral micro-injections of either vehicle or propranolol (4 µg in 1 µl/side) into the BLA (5 min before foot-shock stress). Behavioral (memory, as well as anxiety-like behaviors), electrophysiological, and histological (neural arborization in the hippocampal CA1 pyramidal neurons) studies were performed. Results showed that inhibition of β-adrenoceptors of BLA by propranolol significantly further impaired fear and spatial memory in stressed rats. Similarly, propranolol effectively impaired both memories in the intact animals. Propranolol significantly amplified the slope and amplitude of fEPSP in the CA1 area of the hippocampus only in stressed rats. Foot-shock stress significantly increased the number of dendritic branches in the hippocampus, and propranolol suppressed this effect of stress. It is suggested that β-adrenoceptors in the BLA promote memory and reduce anxiety-like behaviors under tonic and stress conditions. Propranolol dysregulated LTP parameters and reduced dendritic branches, resulting in memory impairment. Probably β-adrenoceptors of BLA regulate evoked responses of CA1 neurons only in stress- and not the tonic condition.

Epinephrine May Contribute to the Persistence of Traumatic Memories in a Post-traumatic Stress Disorder Animal Model

The importance of catecholamines in post-traumatic stress disorder (PTSD) still needs to be explored. We aimed to evaluate epinephrine’s (EPI) causal role and molecular mechanism for the persistence of PTSD traumatic memories. Wild-type (WT) and EPI-deficient mice (phenylethanolamine-N-methyltransferase-knockout mice, Pnmt-KO) were induced with PTSD and behavioral tests were performed. Some Pnmt-KO mice were administered with EPI or vehicle. Catecholamines were quantified by HPLC-ED. Nr4a1, Nr4a2, and Nr4a3 mRNA expression were evaluated by real-time PCR in hippocampus samples. It was observed an increase in EPI and freezing behavior, and a decrease in open arm entries in the elevated plus-maze test and time spent in the light in the light–dark test in WT mice in the PTSD-induction group compared to control. After induction of PTSD, Pnmt-KO mice showed a decrease in freezing, as well as an increase in open arm entries and transitions between compartments compared to WT. After PTSD induction, Pnmt-KO mice administered with EPI showed an increase in freezing compared with the vehicle. On day 0 of PTSD induction, it was observed an increase in mRNA expression of Nr4a2 and Nr4a3 genes in the hippocampus of WT mice compared to control, contrary to Pnmt-KO mice. In conclusion, our data suggest that EPI may be involved in the persistence of traumatic memories in PTSD, possibly through enhancement of the expression of Nr4a2 and Nr4a3 genes in the hippocampus. Peripheral administration of EPI restored contextual traumatic memories in Pnmt-KO mice, which suggests a causal role for EPI. The persistence of contextual traumatic memories may contribute to anxiety-like behavior and resistance of traumatic memory extinction in this PTSD mice model.

Interactions of Aβ1-42 Peptide and Its Three Fragments (Aβ8-12, Aβ8-13, and Aβ5-16) with Selected Nonsteroidal Drugs and Compounds of Natural Origin

In the following paper, we present the results of our studies on the interactions of the Aβ1-42 peptide and its three short fragments, namely Aβ5-16 (RHDSGYEVHHQK; HZ1), Aβ8-13 (SGYEVH; HZ2), and Aβ8-12 (SGYEV; HZ3) with selected painkillers (ibuprofen and aspirin) and compounds of natural origin (anabasine and epinephrine). Steady-state fluorescence spectroscopy was used to study the binding properties of the selected systems. Additionally, based on molecular dynamics (MD) calculations supported by NMR-derived restrains, we have proposed the most likely area of the interactions of Aβ1-42 and Aβ5-16 peptides with the investigated compounds. The influence of symmetrically oriented side chains of amino acid residues present in the first part of the Aβ1-42 sequence on the stability of the resulting complexes has been discussed. Finally, the changes in the peptide structures on account of complex formation were analyzed.