An examination of intolerance of uncertainty effects on subjective, psychophysiological, and neural markers during uninstructed and instructed threat acquisition and extinction training

Individuals who score high in self-reported Intolerance of Uncertainty (IU) tend to find uncertainty aversive. Prior research has demonstrated that under uncertainty individuals with high IU display difficulties in updating learned threat associations to safety associations. Importantly, recent research has shown that providing contingency instructions about threat and safety contingencies (i.e. reducing uncertainty) to individuals with high IU promotes the updating of learned threat associations to safety associations. Here we aimed to conceptually replicate IU and contingency instruction-based effects by conducting a secondary analysis of self-reported IU, ratings, skin conductance, and functional magnetic resonance imaging (fMRI) data recorded during uninstructed/instructed blocks of threat acquisition and threat extinction training (n = 48). Self-reported IU was not associated with differential responding to learned threat and safety cues for any measure during uninstructed/instructed blocks of threat acquisition and threat extinction training. There was some tentative evidence that higher IU was associated with greater ratings of unpleasantness and arousal to the safety cue after the experiment and greater skin conductance response to the safety cue during extinction generally. Potential explanations for these null effects and directions for future research are discussed.

Effects of intolerance of uncertainty on subjective and psychophysiological measures during fear acquisition and delayed extinction

Individuals who score high in self-reported Intolerance of Uncertainty (IU) tend to find uncertainty unacceptable and aversive. In recent years, research has shed light on the role of IU in modulating subjective (i.e. expectancy ratings) and psychophysiological responses (i.e. skin conductance) across different classical fear conditioning procedures, particularly that of immediate extinction. However, there remain gaps in understanding how IU, in comparison to other negative emotionality traits (STAI-T), impact different types of subjective and psychophysiological measures during different classical fear conditioning procedures. Here, we analyzed IU, STAI-T, subjective (i.e. fear ratings) and psychophysiological (i.e. skin conductance, auditory startle blink) data recorded during fear acquisition training and 24h-delayed extinction training (n = 66). Higher IU, over STAI-T, was: (1) significantly associated with greater fear ratings to the learned fear cue during fear acquisition training, and (2) at trend associated with greater fear ratings to the learned fear versus safe cue during delayed extinction training. Both IU and STAI-T were not related to skin conductance or auditory startle blink during fear acquisition training and delayed extinction training. These results add to and extend our current understanding of the role of IU on subjective and physiological measures during different fear conditioning procedures, particularly that of delayed extinction training. Implications of these findings and future directions are discussed.

Glucagon-Like Peptide-1 Agonist Exendin-4 Facilitates the Extinction of Cocaine-Induced Condition Place Preference

Accumulating studies suggest that the glucagon-like peptide-1 receptor agonist exendin-4 (Ex4) and toll-like receptor 4 (TLR4) play a pivotal role in the maladaptive behavior of cocaine. However, few studies have assessed whether Ex4 can facilitate the extinction of drug-associated behavior and attenuate the reinstatement of cocaine-induced condition place preference (CPP) in mice. The main objective of the present study was to evaluate Ex4’s ability to regulate the extinction and reinstatement of cocaine-induced CPP. C57BL/6 mice were conditioned to either cocaine (20 mg/kg) or an equivalent volume of saline to establish a cocaine-mediated CPP paradigm. To investigate the potential effects of Ex4 on extinction, animals received an intraperitoneal injection of Ex4 either immediately or 6 h after each extinction or only on the test day. The persistence of extinction was measured using the reinstatement paradigm evoked by 10 mg/kg of cocaine. To explore the possible impacts of Ex4 and neuroinflammation on cocaine, the expression levels of TLR4 within the hippocampus was detected using western blotting. As a result, we found that systemic administration of Ex4 immediately after each extinction training, instead of 6 h after each extinction and on the day of extinction test, was capable of facilitating extinction in the confined or non-confined CPP extinction paradigms and blocking the cocaine-primed reinstatement of cocaine-induced CPP. Additionally, we also observed that Ex4 was competent to alleviate TLR4 signaling that has been up-regulated by cocaine. Altogether, our findings indicated that the combination of Ex4 with daily extinction training was sufficient to facilitate extinction of the conditioned behavior, attenuate reinstatement of cocaine-induced CPP and inhibit TLR4 signaling. Thus, Ex4 deserves further investigation as a potential intervention for the treatment of cocaine use disorder.

Sleep and conditioning of the siphon withdrawal reflex in Aplysia

Sleep is essential for memory consolidation after learning as shown in mammals and invertebrates such as bees and flies. Aplysia californica displays sleep and sleep in this mollusk was also found to support memory for an operant conditioning task. Here, we investigated whether sleep in Aplysia is also required for memory consolidation in a simpler type of learning, i.e., the conditioning of the siphon withdrawal reflex. Two groups of animals (Wake, Sleep, each n=11) were conditioned on the siphon withdrawal reflex with the training following a classical conditioning procedure where an electrical tail shock served as unconditioned stimulus (US) and a tactile stimulus to the siphon as conditioned stimulus (CS). Responses to the CS were tested before (Pre-test), 24 and 48 hours after training. While Wake animals remained awake for 6 hours after training, Sleep animals had undisturbed sleep. The 24h-test in both groups was combined with extinction training, i.e., the extended presentation of the CS alone over two blocks. At the 24h-test, siphon withdrawal durations to the CS were distinctly enhanced in both Sleep and Wake groups with no significant difference between groups, consistent with the view that consolidation of a simple conditioned reflex response does not require post-training sleep. Surprisingly, extinction training did not reverse the enhancement of responses to the CS. On the contrary, at the 48h-test, withdrawal durations to the CS were even further enhanced across both groups. This suggests that processes of sensitization, an even simpler non-associative type of learning, contributed to the withdrawal responses. Our study provides evidence for the hypothesis that sleep preferentially benefits consolidation of more complex learning paradigms than conditioning of simple reflexes.

Expression patterns of Arc mRNA after renewal of appetitive behavior in female rats.

Renewal of appetitive behavior depends on the gonadal hormonal state of the female rat. In this experiment the effect of female rat estrous cycle stage on renewal of appetitive behaviors is replicated and extended upon to understand how endogenous hormonal states around the estrous cycle drive renewal at the neuronal population level. Estrous cycle stage (i.e., proestrus (P, high hormone) or metestrus/diestrus (M/D, low hormone)) was considered during two important learning and behavioral expression windows: at extinction training and during LTM/renewal testing. First, rats in P during context-dependent extinction training but in some other stage of the estrous cycle during long-term memory and renewal testing (Different) were shown to exhibit more renewal of conditioned foodcup (but not conditioned orienting) behavior compared to rats in other estrous cycle groups. Next, cellular compartment analysis of temporal activity using fluorescence in situ hybridization (catFISH) was used to examine immediate early gene activity of Arc mRNA in neuronal populations after distinct context-stimulus exposures (i.e., extinction and acquisition test contexts). Arc mRNA expression patterns were examined in the prefrontal cortex (PFC), amygdala, hippocampus (HPC), and paraventricular nucleus of the thalamus. P-different rats showed differential neuronal population activity in the infralimbic cortex of the PFC, the lateral amygdaloid nucleus, and both CA1 and CA3 regions of the dorsal HPC. In each region P-different rats exhibited more co-expression and less specificity of Arc mRNA compared to other hormonal groups, indicating that renewal of appetitive foodcup behavior induces Arc mRNA in overlapping neuronal populations in female rats.

Role of Amygdala-Infralimbic Cortex Circuitry in Glucocorticoid-Induced Facilitation of Auditory Fear Memory Extinction

Purpose: The basolateral amygdala (BLA) and infralimbic area (IL) of medial prefrontal cortex (mPFC) are two inter-connected brain structures that mediate both fear memory expression and extinction. Besides the well-known role of the BLA in the acquisition and expression of fear memory, projections from IL to BLA inhibit fear expression and have a critical role in fear extinction. However, the details of IL-BLA interaction remain unclear. Here, we aimed to investigate the role of functional reciprocal interactions between BLA and IL in mediating fear memory extinction. Methods: Using lidocaine (LID), male rats underwent unilateral or bilateral inactivation of the BLA and then unilateral intra-IL infusion of CORT, prior to extinction training of auditory fear conditioning paradigm. Freezing behavior was reported as an index for the measurement of conditioned fear. Infusions were performed before the extinction training, allowing to examine the effects on fear expression and also further extinction memory. Experiments 1-3 investigated the effects of left or right infusion of CORT into IL, and LID unilaterally into BLA on fear memory extinction. Results: Results showed that intra-IL infusion of CORT in the right hemisphere reduced freezing behavior when administrated before the extinction training. Auditory fear memory extinction was impaired by asymmetric inactivation of BLA and CORT infusion in the right IL; however, the same effect was not observed with symmetric inactivation of BLA. Conclusion: It is concluded that that the IL-BLA neural circuit may provide additional evidence to contribution of this circuit in auditory fear extinction. This study demonstrate dissociable roles for right or left BLA in subserving the auditory fear extinction. Our finding also raise the possibility that left BLA-IL circuitry may contribute in mediating auditory fear memory extinction via underlying mechanisms, however further research is required.

Extinction vs. Abstinence: A Review of the Molecular and Circuit Consequences of Different Post-Cocaine Experiences

The intravenous cocaine self-administration model is widely used to characterize the neurobiology of cocaine seeking. When studies are aimed at understanding relapse to cocaine-seeking, a post-cocaine abstinence period is imposed, followed by “relapse” tests to assess the ability of drug-related stimuli (“primes”) to evoke the resumption of the instrumental response previously made to obtain cocaine. Here, we review the literature on the impact of post-cocaine abstinence procedures on neurobiology, finding that the prelimbic and infralimbic regions of the prefrontal cortex are recruited by extinction training, and are not part of the relapse circuitry when extinction training does not occur. Pairing cocaine infusions with discrete cues recruits the involvement of the NA, which together with the dorsal striatum, is a key part of the relapse circuit regardless of abstinence procedures. Differences in molecular adaptations in the NA core include increased expression of GluN1 and glutamate receptor signaling partners after extinction training. AMPA receptors and glutamate transporters are similarly affected by abstinence and extinction. Glutamate receptor antagonists show efficacy at reducing relapse following extinction and abstinence, with a modest increase in efficacy of compounds that restore glutamate homeostasis after extinction training. Imaging studies in humans reveal cocaine-induced adaptations that are similar to those produced after extinction training. Thus, while instrumental extinction training does not have face validity, its use does not produce adaptations distinct from human cocaine users.

Elevated activity in the dorsal dentate gyrus reduces expression of fear memory after fear extinction training

Background: Effectively reducing the expression of certain aversive memories (fear or trauma memories) with extinction training is generally viewed to be therapeutically important. A deeper understanding of the biological basis for a more effective extinction process is also of high scientific importance. Methods: Our study involved intraventricular injection or local injection into the dorsal dentate gyrus of anti-neuregulin 1 antibodies (anti-NRG1) before fear extinction training, followed by testing the expression of fear memory 24 hours afterward or 9 days later. We used local injection of chemogenetic or optogenetic viruses into the dorsal dentate gyrus to manipulate the activity of the dorsal dentate gyrus and test the expression of fear memory. We also examined the effect of deep brain stimulation in the dorsal dentate gyrus on the expression of fear memory. Results: Mice that received intraventricular injection with anti-NRG1 antibodies exhibited lower expression of fear memory and increased density of activated excitatory neurons in the dorsal dentate gyrus. Injection of anti-NRG1 antibodies directly into the dorsal dentate gyrus also led to lower expression of fear memory and more activated neurons in the dorsal dentate gyrus. Inhibiting the activity of dorsal dentate gyrus excitatory neurons using an inhibitory designer receptor exclusively activated by designer drugs (DREADD) eliminated the effects of the anti-NRG1 antibodies. Enhancing the activity of the dorsal dentate gyrus with an excitatory DREADD or optogenetic stimulation resulted in lower expression of fear memory in mice that did not receive infusion of anti-NRG1 antibodies. Deep brain stimulation in the dorsal dentate gyrus effectively suppressed expression of fear memory, both during and after fear extinction training. Limitations: The mechanism for the contribution of the dorsal dentate gyrus to the expression of fear memory needs further exploration. Conclusion: Activation of the dorsal dentate gyrus may play an important role in modulating the expression of fear memory; its potential use in fear memory extinction is worthy of further exploration.