Contextual Fear Retrieval Research Articles

The interaction between hippocampal cholinergic and nitrergic neurotransmission coordinates NMDA-dependent behavior and autonomic changes induced by contextual fear retrieval.

Re-exposing an animal to an environment previously paired with an aversive stimulus evokes large alterations in behavioral and cardiovascular parameters. Dorsal hippocampus (dHC) receives important cholinergic inputs from the basal forebrain, and respective acetylcholine (ACh) levels are described to influence defensive behavior. Activation of muscarinic M1 and M3 receptors facilitates autonomic and behavioral responses along threats. Evidence show activation of cholinergic receptors promoting formation of nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) in dHC. Altogether, the action of ACh and NO on conditioned responses appears to converge within dHC. As answer about how ACh and NO interact to modulate defensive responses has so far been barely addressed, we aimed to shed additional light on this topic. Male Wistar rats had guide cannula implanted into the dHC before being submitted to the contextual fear conditioning (3footshocks/085mA/2s). A catheter was implanted in the femoral artery the next day for cardiovascular recordings. Drugs were delivered into dHC 10min before contextual re-exposure, which occurred 48h after the conditioning procedure. Neostigmine (Neo) amplified the retrieval of conditioned responses. Neo effects (1nmol) were prevented by the prior infusion of a M1-M3 antagonist (fumarate), a neuronal nitric oxide synthase inhibitor (NPLA), a NO scavenger (cPTIO), a guanylyl cyclase inhibitor (ODQ), and a NMDA antagonist (AP-7). Pretreatment with a selective M1 antagonist (pirenzepine) only prevented the increase in autonomic responses induced by Neo. The results show that modulation in the retrieval of contextual fear responses involves coordination of the dHC M1-M3/NO/cGMP/NMDA pathway.

Dorsal hippocampal muscarinic cholinergic receptors orchestrate behavioral and autonomic changes induced by contextual fear retrieval

Re-exposure of rats to a previously fear-conditioned environment arouses great alterations in behavioral and cardiovascular parameters. Pieces of works provide putative evidence for the contribution of the dorsal hippocampus (dHC) to contextual conditioning. dHC gathers massive cholinergic inputs from the basal forebrain, and dHC acetylcholine (ACh) is often described as triggering the retrieval of defensive behavior. ACh acts partially through muscarinic receptors (mAChRs) M1R and M3R subtypes. Hence, activation of mAChRs facilitates autonomic and behavioral responses associated with threats and dangers. Therefore, this study explored the likely involvement of M1R and M3R in rat dHC to establish the behavioral and autonomic changes associated with contextual fear retrieval. Male Wistar rats had stainless steel guide cannula implanted into the dHC before being submitted to contextual fear conditioning (6 footshocks, 1.5 mA, 3 s). A catheter placed within the femoral artery allowed autonomic recordings. A variety of drugs were delivered into the dHC 10 min before contextual re-exposure. The choline reuptake inhibitor hemicholinium induced a decrease of the fear conditioned responses, while did not modify it in non-conditioned animals. The non-selective mAChR antagonist atropine also reduced the fear-conditioned responses, as did the selective M1/M3 mAChRs antagonist fumarate. On the other hand, the M1 selective mAChR antagonist pirenzepine inhibited all the autonomic fear responses without affecting animal freezing. These findings support that cholinergic neurotransmission present in the dHC acts through mAChRs to coordinate the expression of fear evoked by contextual conditioning.

Patterns of Cellular Overlap in Expression of c‐Fos and Arc Activity‐Regulated Genes in the Mouse Brain Regions During Acquisition and Retrieval of Contextual Conditioned Fear

Consolidation of long-term memory requires expression of immediate early genes (IEGs) encoding regulatory and effector proteins, such as inducible transcription factor c-Fos and activity-regulated cytoskeleton-associated protein Arc/Arg3.1. Since these IEGs are involved in various forms of behavioral and stimulus-induced plasticity, their products are often used to label active neurons, and their promoters are employed to tag and manipulate active engram cells. However, little is still known as to whether c-Fos and Arc proteins are induced identically and in the same neurons of different brain structures under various behavioral conditions. In the present work we compared expression patterns of c-Fos and Arc proteins in the mouse brain after acquisition and retrieval of contextual fear and analyzed cellular overlap of their expression in both conditions. Our hypothesis was that the activity patterns of two genes would not be identical though would substantially overlap according to similarities and differences in signaling cascades driving their expression. Both cohorts of mice were subjected to standard contextual fear conditioning with an electric footshock. One group of animals was sacrificed 90 minutes after the training session and the other was tested for retrieval of contextual memory on the next day and sacrificed 90 minutes later. The percentage of freezing in the conditioning context was measured as an index of memory. Brain sections were collected from hippocampus, amygdala and associative cortices of experimental mice, active control mice and home cage control mice. Double immunohistochemical staining with anti-Fos and anti-Arc antibodies was performed, and stained sections were scanned with a confocal microscope. The cell count showed behavioral induction of both c-Fos and Arc in all the examined brain structures. However, there was only a partial overlap of about 30% between the two labelled cell populations. Arc-positive cells predominated over c-Fos-positive cells in the hippocampus regardless of cognitive task, and in cingulate and parietal cortex Arc prevalence was stronger in after memory retrieval compared to learning. Moreover, within the above structures localization of c-Fos- and Arc-positive cells had different distribution across cortical layers and hippocampal subfields. Our results indicate that c-Fos and Arc proteins are not equivalent markers of stimulus-induced neural activity, as they are expressed in cell populations that differ by more than 60%. This data imposes a significant restraint on the use of these IEGs as interchangeable markers of neuronal activity/plasticity and calls for a further study of the differences in their regulation during behavior and learning.

Experience-dependent resonance in amygdalo-cortical circuits supports fear memory retrieval following extinction

Learned fear and safety are associated with distinct oscillatory states in the basolateral amygdala (BLA) and medial prefrontal cortex (mPFC). To determine if and how these network states support the retrieval of competing memories, we mimicked endogenous oscillatory activity through optogenetic stimulation of parvalbumin-expressing interneurons in mice during retrieval of contextual fear and extinction memories. We found that exogenously induced 4 Hz and 8 Hz oscillatory activity in the BLA exerts bi-directional control over conditioned freezing behavior in an experience- and context-specific manner, and that these oscillations have an experience-dependent ability to recruit distinct functional neuronal ensembles. At the network level we demonstrate, via simultaneous manipulation of BLA and mPFC, that experience-dependent 4 Hz resonance across BLA-mPFC circuitry supports post-extinction fear memory retrieval. Our findings reveal that post-extinction fear memory retrieval is supported by local and interregional experience-dependent resonance, and suggest novel approaches for interrogation and therapeutic manipulation of acquired fear circuitry.

Anterior Cingulate Cortex to Ventral Hippocampus Circuit Mediates Contextual Fear Generalization.

Contextual fear memory becomes less context-specific over time, a phenomenon referred to as contextual fear generalization. Overgeneralization of contextual fear memory is a core symptom of post-traumatic stress disorder (PTSD), but circuit mechanisms underlying the generalization remain unclear. We show here that neural projections from the anterior cingulate cortex (ACC) to ventral hippocampus (vHPC) mediate contextual fear generalization in male mice. Retrieval of contextual fear in a novel context at a remote time point activated cells in the ACC and vHPC, as indicated by significantly increased C-fos+ cells. Using chemogenetic or photogenetic manipulations, we observed that silencing the activity of ACC or vHPC neurons reduced contextual fear generalization at the remote time point, whereas stimulating the activity of ACC or vHPC neurons facilitated contextual fear generalization at a recent time point. We found that ACC neurons projected to the vHPC unidirectionally, and importantly, silencing the activity of projection fibers from the ACC to vHPC inhibited contextual fear generalization at the remote time point. Together, our findings reveal an ACC to vHPC circuit that controls expression of fear generalization and may offer new strategies to prevent or reverse contextual fear generalization in subjects with anxiety disorders, especially in PTSD.SIGNIFICANCE STATEMENT Overgeneralization of contextual fear memory is a cardinal feature of PTSD, but circuit mechanisms underlying it remain unclear. Our study indicates that neural projections from the anterior cingulate cortex to ventral hippocampus control the expression of contextual fear generalization. Thus, manipulating the circuit may prevent or reverse fear overgeneralization in subjects with PTSD.

Uncoupling nNOS-PSD-95 in the ACC can inhibit contextual fear generalization

A typical feature of the contextual fear memory is increased fear generalization with time. Though much attention has been given to the neural structures that underlie the long-term consolidation of a contextual fear memory, the molecular mechanisms regulating fear generalization remain unclear. We observed that retrieval of contextual fear in a novel context at a remote time point increased coupling of neuronal nitric oxide synthase (nNOS) with postsynaptic density-95 (PSD-95) and c-Fos expression in the anterior cingulate cortex (ACC). Disrupting nNOS-PSD-95 coupling in the ACC decreased the expression of Histone deacetylase 2 (HDAC2), and inhibited contextual fear generalization at a remote time point. Together, our findings reveal nNOS-PSD-95 interaction in the ACC could be a promising target to prevent or reverse contextual fear generalization.

Dopamine D1-like receptors in the dorsomedial prefrontal cortex regulate contextual fear conditioning

RationaleDopamine D1 receptor (D1R) signalling is involved in contextual fear conditioning. The D1R antagonist SCH23390 impairs the acquisition of contextual fear when administered systemically or infused locally into the dorsal hippocampus or basolateral amygdala.ObjectivesWe determined if state dependency may account for the impairment in contextual fear conditioning caused by systemic SCH23390 administration. We also examined if the dorsomedial prefrontal cortex (dmPFC), nucleus accumbens (NAc), and ventral hippocampus (VH) are involved in mediating the effect of systemic SCH23390 treatment on contextual fear conditioning.MethodsIn experiment 1, SCH23390 (0.1 mg/kg) or vehicle was given before contextual fear conditioning and/or retrieval. In experiment 2, SCH23390 (2.5 μg/0.5 uL) or vehicle was infused locally into dmPFC, NAc, or VH before contextual fear conditioning, and retrieval was tested drug-free. Freezing was quantified as a measure of contextual fear.ResultsIn experiment 1, SCH23390 given before conditioning or before both conditioning and retrieval decreased freezing at retrieval, whereas SCH23390 given only before retrieval had no effect. In experiment 2, SCH23390 infused into dmPFC before conditioning decreased freezing at retrieval, while infusion of SCH23390 into NAc or VH had no effect.ConclusionsThe results of experiment 1 confirm those of previous studies indicating that D1Rs are required for the acquisition but not retrieval of contextual fear and rule out state dependency as an explanation for these findings. Moreover, the results of experiment 2 provide evidence that dmPFC is also part of the neural circuitry through which D1R signalling regulates contextual fear conditioning.

Dissociations across the dorsal–ventral axis of CA3 and CA1 for encoding and retrieval of contextual and auditory-cued fear

The present study was designed to dissociate the roles of dorsal CA3, dorsal CA1, ventral CA3, and ventral CA1 in contextual and auditory-cued classical fear conditioning. Rats received excitotoxic lesions of dorsal CA3, dorsal CA1, ventral CA3, or ventral CA3 prior to acquisition of classical fear conditioning. Dorsal CA3 and dorsal CA1, but not ventral CA3 or ventral CA1, lesions caused a deficit for the acquisition of contextual fear. Dorsal CA1, ventral CA3, and ventral CA1, but not dorsal CA3, lesions caused deficits for the retrieval/expression of contextual fear when tested either 24 or 48 h after encoding. Ventral CA3, but not dorsal CA3, dorsal CA1, or ventral CA1, lesions caused a deficit for retrieval of auditory-cued fear when tested either 24 or 48 h after encoding. The data suggest that dorsal CA3 mediates encoding of contextual fear, whereas ventral CA3 mediates retrieval of contextual fear. The data also suggest that dorsal CA1 mediates encoding and retrieval of contextual fear, whereas ventral CA1 mediates only the retrieval of contextual fear.