Inhibition of fatty acid binding protein-5 in the basolateral amygdala induces anxiolytic effects and accelerates fear memory extinction

RATIONALE

The endocannabinoid (eCB) system critically controls anxiety and fear-related behaviours. Anandamide (AEA), a prominent eCB ligand, is a hydrophobic lipid that requires chaperone proteins such as Fatty Acid Binding Proteins (FABPs) for intracellular transport. Intracellular AEA transport is necessary for degradation, so blocking FABP activity increases AEA neurotransmission.

OBJECTIVE

To investigate the effects of a novel FABP5 inhibitor (SBFI-103) in the basolateral amygdala (BLA) on anxiety and fear memory.

METHODS

We infused SBFI-103 (0.5 μg-5 μg) to the BLA of adult male Sprague Dawley rats and ran various anxiety and fear memory behavioural assays, neurophysiological recordings, and localized molecular signaling analyses. We also co-infused SBFI-103 with the AEA inhibitor, LEI-401 (3 μg and 10 μg) to investigate the potential role of AEA in these phenomena.

RESULTS

Acute intra-BLA administration of SBFI-103 produced strong anxiolytic effects across multiple behavioural tests. Furthermore, animals exhibited acute and long-term accelerated associative fear memory extinction following intra-BLA FABP5 inhibition. In addition, BLA FABP5 inhibition induced strong modulatory effects on putative PFC pyramidal neurons along with significantly increased gamma oscillation power. Finally, we observed local BLA changes in the phosphorylation activity of various anxiety- and fear memory-related molecular biomarkers in the PI3K/Akt and MAPK/Erk signaling pathways. At all three levels of analyses, we found the functional effects of SBFI-103 depend on availability of the AEA ligand.

CONCLUSIONS

These findings demonstrate a novel intra-BLA FABP5 signaling mechanism regulating anxiety and fear memory behaviours, neuronal activity states, local anxiety-related molecular pathways, and functional AEA modulation.

Recreational drug use and prospective memory

Prospective memory (PM) impairment in recreational drug users has been documented in recent years. However, most studies on the effects of drugs on PM contain several methodological challenges, such as small sample size (< 100 participants), unrepresentative sample type (e.g., student or patient), short abstinence period (< 7 days), and lack of control of potential confounds (e.g., sleep and IQ). The present study investigated the possible consequences of recreational drug use on prospective memory, using self-report and lab-based prospective memory measures while overcoming the methodological challenges. The sample was composed of 47 non-users (27 females, age range from 18 to 50 +) and 53 drug users (21 females, age range from 18 to 50 +). Recreational drug users reported significantly more deficits in the long-term episodic, short-term habitual, and internally cued PM failures subscales of the Prospective Memory Questionnaire. However, these deficits were eliminated after controlling for covariates (e.g., age, sleep quality, general health, alcohol usage). Recreational drug users also performed worse than non-users in the short-term, long-term, event-based, and time-based PM subscales of the Royal Prince Alfred Prospective Memory Test. These results remained significant after controlling for the covariates. Drug users demonstrated greater impairments on time-based and long-term PM tasks thought to be linked with executive functioning. Taken together, the present study provides further support for recreational drug-related deficits in PM and highlights a dissociation between self-report and lab-based PM measures.

MP1104, a mixed kappa-delta opioid receptor agonist has anti-cocaine properties with reduced side-effects in rats

Kappa opioid receptor (KOPr) agonists have preclinical anti-cocaine and antinociceptive effects. However, adverse effects including dysphoria, aversion, sedation, anxiety and depression limit their clinical development. MP1104, an analogue of 3-iodobenzoyl naltrexamine, is a potent dual agonist at KOPr and delta opioid receptor (DOPr), with full agonist efficacy at both these receptors. In this study, we evaluate the ability of MP1104 to modulate cocaine-induced behaviors and side-effects preclinically. In male Sprague-Dawley rats trained to self-administer cocaine, MP1104 (0.3 and 1 mg/kg) reduced cocaine-primed reinstatement of drug-seeking behavior and caused significant downward shift of the dose-response curve in cocaine self-administration tests (0.3 and 0.6 mg/kg). The anti-cocaine effects exerted by MP1104 are in part due to increased dopamine (DA) uptake by the dopamine transporter (DAT) in the dorsal striatum (dStr) and nucleus accumbens (NAc). MP1104 (0.3 and 0.6 mg/kg) showed no significant anxiogenic effects in the elevated plus maze, pro-depressive effects in the forced swim test, or conditioned place aversion. Furthermore, pre-treatment with a DOPr antagonist, led to MP1104 producing aversive effects. This data suggests that the DOPr agonist actions of MP1104 attenuate the KOPr-mediated aversive effects of MP1104. The overall results from this study show that MP1104, modulates DA uptake in the dStr and NAc, and exerts potent anti-cocaine properties in self-administration tests with reduced side-effects compared to pure KOPr agonists. This data supports the therapeutic development of dual KOPr/DOPr agonists to reduce the side-effects of selective KOPr agonists. This article is part of the Special Issue entitled 'Opioid Neuropharmacology: Advances in treating pain and opioid addiction'.

Whole tobacco smoke extracts to model tobacco dependence in animals

Smoking tobacco is highly addictive and a leading preventable cause of death. The main addictive constituent is nicotine; consequently it has been administered to laboratory animals to model tobacco dependence. Despite extensive use, this model might not best reflect the powerful nature of tobacco dependence because nicotine is a weak reinforcer, the pharmacology of smoke is complex and non-pharmacological factors have a critical role. These limitations have led researchers to expose animals to smoke via the inhalative route, or to administer aqueous smoke extracts to produce more representative models. The aim was to review the findings from molecular/behavioural studies comparing the effects of nicotine to tobacco/smoke extracts to determine whether the extracts produce a distinct model. Indeed, nicotine and tobacco extracts yielded differential effects, supporting the initiative to use extracts as a complement to nicotine. Of the behavioural tests, intravenous self-administration experiments most clearly revealed behavioural differences between nicotine and extracts. Thus, future applications for use of this behavioural model were proposed that could offer new insights into tobacco dependence.