Activating M1 muscarinic cholinergic receptors induces destabilization of resistant contextual fear memories in rats.

Destabilization of previously consolidated memories places them in a labile state in which they are open to modification. However, strongly encoded fear memories tend to be destabilization-resistant and the conditions required to destabilize such memories remain poorly understood. Our lab has previously shown that exposure to salient novel contextual cues during memory reactivation can destabilize strongly encoded object location memories and that activity at muscarinic cholinergic receptors is critical for this effect. In the current study, we similarly targeted destabilization-resistant fear memories, hypothesizing that exposure to salient novelty at the time of reactivation would induce destabilization of strongly encoded fear memories in a muscarinic receptor-dependent manner. First, we show that contextual fear memories induced by 3 context-shock pairings readily destabilize upon memory reactivation, and that this destabilization is blocked by systemic (ip) administration of the muscarinic receptor antagonist scopolamine (0.3 mg/kg) in male rats. Following that, we confirm that this effect is dorsal hippocampus (dHPC)-dependent by targeting M1 receptors in the CA1 region with pirenzepine. Next, we show that more strongly encoded fear memories (induced with 5 context-shock pairings) resist destabilization. Consistent with our previous work, however, we report that salient novelty (a change in floor texture) presented during the reactivation session promotes destabilization of resistant contextual fear memories in a muscarinic receptor-dependent manner. Finally, the effect of salient novelty on memory destabilization was mimicked by stimulating muscarinic receptors with the selective M1 agonist CDD-0102A (ip, 0.3 mg/kg). These findings reveal further generalizability of our previous results implicating novel cues and M1 muscarinic signaling in promoting destabilization of resistant memories and suggest possible therapeutic options for disorders characterized by persistent, maladaptive fear memories such as PTSD and phobias.

Age-dependent attenuation of spatial memory deficits by the histone acetyltransferase p300/CBP-associated factor (PCAF) in 3xTG Alzheimer's disease mice.

Histone acetylation, catalyzed by histone acetyltransferases, has emerged as a promising therapeutic strategy in Alzheimer's disease (AD). By longitudinally characterizing spatial memory at 3, 6, and 9 mo of age, we show that acute activation and inhibition of the histone acetyltransferase PCAF remediated memory impairments in 3xTG-AD mice in an age-related bidirectional manner. At 3 and 6 mo of age, PCAF activation ameliorated memory deficits. At 9 mo of age, PCAF activation had no effect on spatial memory, whereas PCAF inhibition improved memory deficits in females. This work reveals a complex potential therapeutic role for PCAF in AD, initially benefitting memory but becoming detrimental as the disease progresses.

Muscarinic (M1 ) cholinergic receptor activation within the dorsal hippocampus promotes destabilization of strongly encoded object location memories.

Following the initial consolidation process, memories can become reactivated by exposure to a reminder of the original learning event. This can lead to the memory becoming destabilized and vulnerable to disruption or other forms of modification. The memory must then undergo the protein-synthesis dependent process of reconsolidation in order to be retained. However, older and/or stronger memories resist destabilization, but can become labile when reactivated in the presence of salient novelty. We have implicated the neurotransmitter acetylcholine, acting at M1 muscarinic cholinergic receptors (mAChRs) within perirhinal cortex (PRh), in novelty-induced destabilization of remote object memories. It remains unclear, however, whether mAChRs are involved in destabilization of other forms of memory. We hypothesized that the role of M1 mAChRs previously demonstrated for PRh-dependent object memory would extend to hippocampus-dependent spatial memory. Using the object location (OL) task, which relies on the dorsal hippocampus (dHPC), we showed that (a) reactivation-dependent reconsolidation of OL memories requires protein synthesis within the dHPC; (b) destabilization of relatively weak OL memories depends on M1 mAChR activation within the dHPC; (c) salient novelty during reactivation promotes destabilization of resistant strongly encoded OL memories; (d) novelty-induced destabilization of strong OL memories requires activation of mAChRs within the dHPC; and (e) M1 mAChR activation within the dHPC in the absence of novelty during memory reactivation mimics the effect of novelty, destabilizing strongly encoded OL memories. These results implicate ACh acting at M1 mAChRs in the destabilization of dHPC-dependent spatial memories, demonstrating generalizability of this cholinergic function beyond memory for object identity. These findings therefore enhance our understanding of the dynamics of long-term memory storage and suggest implications for the treatment of human conditions such as Alzheimer's disease and aging, which are characterized by behavioral and mnemonic inflexibility.

Dissociating the involvement of muscarinic and nicotinic cholinergic receptors in object memory destabilization and reconsolidation.

The content of long-term memory is neither fixed nor permanent. Reminder cues can destabilize consolidated memories, rendering them amenable to change before being reconsolidated. However, not all memories destabilize following reactivation. Characteristics of a memory, such as its age or strength, impose boundaries on destabilization. Previously, we demonstrated that presentation of salient novel information at the time of reactivation can readily destabilize resistant object memories in rats and this form of novelty-induced destabilization is dependent upon acetylcholine (ACh) activity at muscarinic receptors (mAChRs). In the present study, we sought to determine if this same mechanism for initiating destabilization of resistant object memories is present in mice and further expand our understanding of the mechanisms through which ACh modulates object memory destabilization by investigating the role of nicotinic receptors (nAChRs). We provide evidence that in mice mAChRs are necessary for destabilizing object memories that are readily destabilized and those that are resistant to destabilization. Conversely, nAChRs were found to be necessary only when memories are readily destabilized. We then investigated the role of both receptors in the reconsolidation of destabilized object memory traces and determined that nAChRs, but not mAChRs, are necessary for object memory reconsolidation. Together, these results suggest that nAChRs may play a more selective role in the re-storage of object memories following destabilization and that ACh acts through mAChRs to act as an override signal to initiate destabilization of resistant object memories following reactivation with novelty. These findings expand our current understanding of the role of ACh in the dynamic storage of long-term memory.

Fluctuating NMDA Receptor Subunit Levels in Perirhinal Cortex Relate to Their Dynamic Roles in Object Memory Destabilization and Reconsolidation.

Reminder cues can destabilize consolidated memories, rendering them modifiable before they return to a stable state through the process of reconsolidation. Older and stronger memories resist this process and require the presentation of reminders along with salient novel information in order to destabilize. Previously, we demonstrated in rats that novelty-induced object memory destabilization requires acetylcholine (ACh) activity at M1 muscarinic receptors. Other research predominantly has focused on glutamate, which modulates fear memory destabilization and reconsolidation through GluN2B- and GluN2A-containing NMDARs, respectively. In the current study, we demonstrate the same dissociable roles of GluN2B- and N2A-containing NMDARs in perirhinal cortex (PRh) for object memory destabilization and reconsolidation when boundary conditions are absent. However, neither GluN2 receptor subtype was required for novelty-induced destabilization of remote, resistant memories. Furthermore, GluN2B and GluN2A subunit proteins were upregulated selectively in PRh 24 h after learning, but returned to baseline by 48 h, suggesting that NMDARs, unlike muscarinic receptors, have only a temporary role in object memory destabilization. Indeed, activation of M1 receptors in PRh at the time of reactivation effectively destabilized remote memories despite inhibition of GluN2B-containing NMDARs. These findings suggest that cholinergic activity at M1 receptors overrides boundary conditions to destabilize resistant memories when other established mechanisms are insufficient.

Cocaine, nicotine, and their conditioned contexts enhance consolidation of object memory in rats.

To test the hypothesis that drugs of abuse and their conditioned stimuli (CSs) enhance memory consolidation, the effects of post-training exposure to cocaine and nicotine were compared to the effects of post-training exposure to contextual stimuli that were paired with the effects of these drugs. Using the object recognition (OR) task, it was first demonstrated that both 10 and 20 mg/kg cocaine, and 0.2 and 0.4 mg/kg nicotine, enhanced recognition memory when administered immediately after, but not 6 h after the sample phase. To establish the drug CSs, rats were confined for 2 h in a chamber (the CS+) after injections of 20 mg/kg cocaine, or 0.4 mg/kg nicotine, and in another chamber (the CS-) after injections of vehicle. This was repeated over 10 d (5 drug/CS+ and 5 vehicle/CS- pairings in total). At the end of this conditioning period, when tested in a drug-free state, rats displayed conditioned hyperactivity in the CS+ relative to the CS-. More important, immediate, but not delayed, post-sample exposure to the cocaine CS+, or nicotine CS+, enhanced OR memory. Therefore, this study reports for the first time that contextual stimuli paired with cocaine and nicotine, like the drugs themselves, have the ability to enhance memory consolidation.

Involvement of classical neurotransmitter systems in memory reconsolidation: Focus on destabilization.

When consolidated long-term memories are reactivated they can destabilize, rendering the memory labile and vulnerable to modification. This period of lability is followed by reconsolidation, a process that restabilizes the memory trace. Reactivation-induced memory destabilization is the gateway process to reconsolidation, but research in this area has focused primarily on the mechanisms underlying post-reactivation restabilization. As a result, our understanding of processes subserving destabilization have lagged behind those responsible for reconsolidation. Here we review the literature investigating the neural basis of reactivation-induced memory destabilization. We begin by reviewing memory destabilization broadly and the boundary conditions that influence the likelihood of reactivated memories to destabilize. We then discuss the fact that boundary conditions can be overcome in the presence of novelty, providing evidence for the theory that reconsolidation is a mechanism for memory updating. From here, we delve into a detailed review of the role of classical neurotransmitter systems, including dopamine, serotonin, noradrenaline, glutamate, GABA and acetylcholine, in reconsolidation, with a focus on their involvement in destabilization. Many of these neurotransmitters appear capable of promoting memory destabilization, and research investigating the cellular pathways through which they influence destabilization is a growing area. However, gaps remain in our understanding of how these neurotransmitters work in conjunction with one another to support destabilization across different types of memory and in different brain regions. Advances in the coming years within this research field should greatly contribute to our understanding of the neural mechanisms that influence the dynamic process of long-term memory storage and modification, information crucial to the development of potential treatments for disorders characterized by strong, maladaptive memories.

The Dynamic Multisensory Engram: Neural Circuitry Underlying Crossmodal Object Recognition in Rats Changes with the Nature of Object Experience.

Rats, humans, and monkeys demonstrate robust crossmodal object recognition (CMOR), identifying objects across sensory modalities. We have shown that rats' performance of a spontaneous tactile-to-visual CMOR task requires functional integration of perirhinal (PRh) and posterior parietal (PPC) cortices, which seemingly provide visual and tactile object feature processing, respectively. However, research with primates has suggested that PRh is sufficient for multisensory object representation. We tested this hypothesis in rats using a modification of the CMOR task in which multimodal preexposure to the to-be-remembered objects significantly facilitates performance. In the original CMOR task, with no preexposure, reversible lesions of PRh or PPC produced patterns of impairment consistent with modality-specific contributions. Conversely, in the CMOR task with preexposure, PPC lesions had no effect, whereas PRh involvement was robust, proving necessary for phases of the task that did not require PRh activity when rats did not have preexposure; this pattern was supported by results from c-fos imaging. We suggest that multimodal preexposure alters the circuitry responsible for object recognition, in this case obviating the need for PPC contributions and expanding PRh involvement, consistent with the polymodal nature of PRh connections and results from primates indicating a key role for PRh in multisensory object representation. These findings have significant implications for our understanding of multisensory information processing, suggesting that the nature of an individual's past experience with an object strongly determines the brain circuitry involved in representing that object's multisensory features in memory. SIGNIFICANCE STATEMENT: The ability to integrate information from multiple sensory modalities is crucial to the survival of organisms living in complex environments. Appropriate responses to behaviorally relevant objects are informed by integration of multisensory object features. We used crossmodal object recognition tasks in rats to study the neurobiological basis of multisensory object representation. When rats had no prior exposure to the to-be-remembered objects, the spontaneous ability to recognize objects across sensory modalities relied on functional interaction between multiple cortical regions. However, prior multisensory exploration of the task-relevant objects remapped cortical contributions, negating the involvement of one region and significantly expanding the role of another. This finding emphasizes the dynamic nature of cortical representation of objects in relation to past experience.

A Novel Multisensory Integration Task Reveals Robust Deficits in Rodent Models of Schizophrenia: Converging Evidence for Remediation via Nicotinic Receptor Stimulation of Inhibitory Transmission in the Prefrontal Cortex.

Atypical multisensory integration is an understudied cognitive symptom in schizophrenia. Procedures to evaluate multisensory integration in rodent models are lacking. We developed a novel multisensory object oddity (MSO) task to assess multisensory integration in ketamine-treated rats, a well established model of schizophrenia. Ketamine-treated rats displayed a selective MSO task impairment with tactile-visual and olfactory-visual sensory combinations, whereas basic unisensory perception was unaffected. Orbitofrontal cortex (OFC) administration of nicotine or ABT-418, an α4ß2 nicotinic acetylcholine receptor (nAChR) agonist, normalized MSO task performance in ketamine-treated rats and this effect was blocked by GABAA receptor antagonism. GABAergic currents were also decreased in OFC of ketamine-treated rats and were normalized by activation of α4ß2 nAChRs. Furthermore, parvalbumin (PV) immunoreactivity was decreased in the OFC of ketamine-treated rats. Accordingly, silencing of PV interneurons in OFC of PV-Cre mice using DREADDs (Designer Receptors Exclusively Activated by Designer Drugs) selectively impaired MSO task performance and this was reversed by ABT-418. Likewise, clozapine-N-oxide-induced inhibition of PV interneurons in brain slices was reversed by activation of α4ß2 nAChRs. These findings strongly imply a role for prefrontal GABAergic transmission in the integration of multisensory object features, a cognitive process with relevance to schizophrenia. Accordingly, nAChR agonism, which improves various facets of cognition in schizophrenia, reversed the severe MSO task impairment in this study and appears to do so via a GABAergic mechanism. Interactions between GABAergic and nAChR receptor systems warrant further investigation for potential therapeutic applications. The novel behavioral procedure introduced in the current study is acutely sensitive to schizophrenia-relevant cognitive impairment and should prove highly valuable for such research. SIGNIFICANCE STATEMENT: Adaptive behaviors are driven by integration of information from different sensory modalities. Multisensory integration is disrupted in patients with schizophrenia, but little is known about the neural basis of this cognitive symptom. Development and validation of multisensory integration tasks for animal models is essential given the strong link between functional outcome and cognitive impairment in schizophrenia. We present a novel multisensory object oddity procedure that detects selective multisensory integration deficits in a rat model of schizophrenia using various combinations of sensory modalities. Moreover, converging data are consistent with a nicotinic-GABAergic mechanism of multisensory integration in the prefrontal cortex, results with strong clinical relevance to the study of cognitive impairment and treatment in schizophrenia.

Linking muscarinic receptor activation to UPS-mediated object memory destabilization: Implications for long-term memory modification and storage.

Consolidated memories can become destabilized during reactivation, resulting in a transient state of instability, a process that has been hypothesized to underlie long-term memory updating. Consistent with this notion, relatively remote memories, which are resistant to standard destabilization procedures, are reliably destabilized when novel information (i.e., the opportunity for memory updating) is present during reactivation. We have also shown that cholinergic muscarinic receptor (mAChR) activation can similarly destabilize consolidated object memories. Synaptic protein degradation via the ubiquitin proteasome system (UPS) has previously been linked to destabilization of fear and object-location memories. Given the role of calcium in regulating proteasome activity, we hypothesized that activation of cholinergic receptors, specifically M1 mAChRs, stimulates the UPS via inositol triphosphate receptor (IP3R)-mediated release of intracellular calcium stores to facilitate object memory destabilization. We present converging evidence for this hypothesis, which we tested using a modified spontaneous object recognition task for rats and microinfusions into perirhinal cortex (PRh), a brain region strongly implicated in object memory. We extend our previous findings by demonstrating that M1 mAChRs are necessary for novelty-induced object memory destabilization. We also show that proteasome inhibition or IP3R antagonism in PRh prevents object memory destabilization induced by novelty or M1 mAChR stimulation. These results establish an intracellular pathway linking M1 receptors, IP3Rs, and UPS activity to object memory destabilization and suggest a previously unacknowledged role for cholinergic signaling in long-term memory modification and storage.

Postsynaptic nicotinic acetylcholine receptors facilitate excitation of developing CA1 pyramidal neurons.

The hippocampus plays a key role in learning and memory. The normal development and mature function of hippocampal networks supporting these cognitive functions depends on afferent cholinergic neurotransmission mediated by nicotinic acetylcholine receptors. Whereas it is well-established that nicotinic receptors are present on GABAergic interneurons and on glutamatergic presynaptic terminals within the hippocampus, the ability of these receptors to mediate postsynaptic signaling in pyramidal neurons is not well understood. We use whole cell electrophysiology to show that heteromeric nicotinic receptors mediate direct inward currents, depolarization from rest and enhanced excitability in hippocampus CA1 pyramidal neurons of male mice. Measurements made throughout postnatal development provide a thorough developmental profile for these heteromeric nicotinic responses, which are greatest during the first 2 wk of postnatal life and decrease to low adult levels shortly thereafter. Pharmacological experiments show that responses are blocked by a competitive antagonist of α4ß2* nicotinic receptors and augmented by a positive allosteric modulator of α5 subunit-containing receptors, which is consistent with expression studies suggesting the presence of α4ß2 and α4ß2α5 nicotinic receptors within the developing CA1 pyramidal cell layer. These findings demonstrate that functional heteromeric nicotinic receptors are present on CA1 pyramidal neurons during a period of major hippocampal development, placing these receptors in a prime position to play an important role in the establishment of hippocampal cognitive networks.

Cholinergic manipulations bidirectionally regulate object memory destabilization.

Consolidated memories can become destabilized and open to modification upon retrieval. Destabilization is most reliably prompted when novel information is present during memory reactivation. We hypothesized that the neurotransmitter acetylcholine (ACh) plays an important role in novelty-induced memory destabilization because of its established involvement in new learning. Accordingly, we investigated the effects of cholinergic manipulations in rats using an object recognition paradigm that requires reactivation novelty to destabilize object memories. The muscarinic receptor antagonist scopolamine, systemically or infused directly into the perirhinal cortex, blocked this novelty-induced memory destabilization. Conversely, systemic oxotremorine or carbachol, muscarinic receptor agonists, administered systemically or intraperirhinally, respectively, mimicked the destabilizing effect of novel information during reactivation. These bidirectional effects suggest a crucial influence of ACh on memory destabilization and the updating functions of reconsolidation. This is a hitherto unappreciated mnemonic role for ACh with implications for its potential involvement in cognitive flexibility and the dynamic process of long-term memory storage.

Differential contributions of de novo and maintenance DNA methyltransferases to object memory processing in the rat hippocampus and perirhinal cortex--a double dissociation.

Epigenetic mechanisms are increasingly acknowledged as major players in memory formation. Specifically, DNA methylation is necessary for the formation of long-term memory in various brain regions, including the hippocampus (HPC); however, its role in the perirhinal cortex (PRh), a structure critical for object memory, has not been characterized. Moreover, the mnemonic effects of selective DNA methyltransferase (DNMT) inhibition have not yet been investigated systematically, despite distinct roles for de novo (DNMT3a, 3b) and maintenance (DNMT1) methyltransferases. Consequently, we assessed the effects of various DNMT inhibitors within the HPC and PRh of rats using the object-in-place paradigm, which requires both brain regions. The non-nucleoside DNA methyltransferase inhibitor RG-108 impaired long-term object-in-place memory in both regions. Furthermore, intracranial administration of Accell short-interference RNA sequences to inhibit the expression of individual DNMTs implicated DNMT3a and DNMT1 in the HPC and PRh effects, respectively. mRNA expression analyses revealed a complementary pattern of results, as only de novo DNMT3a and DNMT3b mRNA was upregulated in the HPC (dentate gyrus) following object-in-place learning, whereas DNMT1 mRNA was selectively upregulated in the PRh. These results reinforce the established functional double dissociation between the HPC and PRh and imply the operation of different epigenetic mechanisms in brain regions dedicated to long-term memory processing for different types of information.

Evidence for a specific role for muscarinic receptors in crossmodal object recognition in rats.

Acetylcholine (ACh) has been implicated in numerous cognitive functions, including multisensory feature binding. In the present study, we systematically assessed the involvement of cholinergic muscarinic receptors in several variations of an object recognition task for rats. In the standard spontaneous object recognition (SOR) task, tactile and visual properties of objects were freely available throughout the sample and choice phases. In the tactile- and visual-only unimodal SOR tasks, exploration in both phases was restricted to tactile and visual information, respectively. For the basic crossmodal object recognition (CMOR) task, sample object exploration was limited to tactile features, whereas choice objects were available only in the visual domain. In Experiment 1, pre-sample systemic administration of scopolamine (0.2mg/kg) disrupted performance on standard SOR, both unimodal SOR tasks, and basic CMOR, consistent with a role for muscarinic receptors in memory encoding. Conversely, in Experiment 2, pre-choice systemic scopolamine selectively impaired object recognition on the CMOR task. For Experiment 3, the inclusion of multimodal, but not unimodal pre-exposure to the to-be-remembered objects prevented scopolamine from disrupting performance on the CMOR task when given prior to the choice phase. These results suggest that ACh is necessary during the choice phase of the CMOR task to facilitate the binding of object features across sensory modalities, a function that is not required for the other tasks assessed. Multimodal object pre-exposure might preclude the requisite contribution of ACh in the choice phase by allowing rats to bind important visual and tactile object information prior to testing.

Delineating prefrontal cortex region contributions to crossmodal object recognition in rats.

In the present study, we assessed the involvement of the prefrontal cortex (PFC) in the ability of rats to perform crossmodal (tactile-to-visual) object recognition tasks. We tested rats with 3 different types of bilateral excitotoxic lesions: (1) Large PFC lesions, including the medial PFC (mPFC) and ventral and lateral regions of the orbitofrontal cortex (OFC); (2) selective mPFC lesions; and (3) selective OFC lesions. Rats were tested on 2 versions of crossmodal object recognition (CMOR): (1) The original CMOR task, which uses a tactile-only sample phase and a visual-only choice phase; and (2) a "multimodal pre-exposure" version (PE/CMOR), in which simultaneous pre-exposure to the tactile and visual features of an object facilitates CMOR performance over longer memory delays. Inclusive PFC lesions disrupted performance on both versions of CMOR, whereas selective mPFC damage had no effect. Lesions limited to the OFC caused delay-dependent deficits on the CMOR task, but failed to reverse the enhancement produced by multimodal object pre-exposure. This pattern of functional dissociations suggests complex, multidimensional contributions of the PFC and its subregions to crossmodal cognition.

Different roles for M1 and M2 receptors within perirhinal cortex in object recognition and discrimination.

Recognition and discrimination of objects and individuals are critical cognitive faculties in both humans and non-human animals, and cholinergic transmission has been shown to be essential for both of these functions. In the present study we focused on the role of M1 and M2 muscarinic receptors in perirhinal cortex (PRh)-dependent object recognition and discrimination. The selective M1 antagonists pirenzepine and the snake toxin MT-7, and a selective M2 antagonist, AF-DX 116, were infused directly into PRh. Pre-sample infusions of both pirenzepine and AF-DX 116 significantly impaired object recognition memory in a delay-dependent manner. However, pirenzepine and MT-7, but not AF-DX 116, impaired oddity discrimination performance in a perceptual difficulty-dependent manner. The findings indicate distinct functions for M1 and M2 receptors in object recognition and discrimination.

Muscarinic receptor activation promotes destabilization and updating of object location memories in mice.

The storage of long-term memories is a dynamic process. Reminder cues can destabilize previously consolidated memories, rendering them labile and modifiable. However, memories that are strongly encoded or relatively remote at the time of reactivation can resist destabilization only being rendered labile under conditions that favour memory updating. Using the object location recognition task, here we show in male C57BL/6 mice that novelty-induced destabilization of strongly-encoded memories requires muscarinic acetylcholine receptor (mAChR) activation. Furthermore, we use the objects-in-updated locations task to show that updating of object location memories is mAChR-dependent. Thus, mAChR stimulation appears to be critical for spatial memory destabilization and related memory updating. Enhancing our understanding of the role of ACh in memory updating should inform future research into the underlying causes of behavioural disorders that are characterized by persistent maladaptive memories, such as age-related cognitive inflexibility and post-traumatic stress disorder.

Muscarinic receptor activation overrides boundary conditions on memory updating in a calcium/calmodulin-dependent manner.

Long-term memory storage is a dynamic process requiring flexibility to ensure adaptive behavioural responding in changing environments. Indeed, it is well established that memory reactivation can "destabilize" consolidated traces, leading to various forms of updating. However, the neurobiological mechanisms rendering long-term memories labile and modifiable remain poorly described. Moreover, boundary conditions, such as the age or strength of the memory, can reduce the likelihood of this destabilization; yet, intuitively, these most behaviourally influential of memories should also be modifiable under appropriate conditions. Here, we provide evidence that salient novelty at the time of memory reactivation promotes integrative updating of resistant object memories in rats. Furthermore, blockade of muscarinic acetylcholine receptors (mAChRs; with pirenzepine) or disruption of calcium/calmodulin (Ca2+/CaM) with KN-93, a Ca2+/CaM-binding molecule that inhibits calcium/calmodulin-dependent protein kinase II (CaMKII) activation, in perirhinal cortex (PRh) prevented novelty-induced destabilization and updating of resistant object memories. Finally, PRh M1 mAChR activation (with CDD-0102A) was sufficient to destabilize resistant object memories for updating, and this effect was blocked by KN-93, possibly via inhibition of CaMKII activity. Thus, mAChRs and activation of CaMKII appear to interact as part of a mechanism to override boundary conditions on resistant object memories to ensure integrative modification with novel information. These findings therefore have important implications for understanding the dynamic nature of long-term memory storage and potential treatments for conditions characterized by maladaptive and inflexible memories.

Double dissociation of perirhinal nicotinic acetylcholine receptors and dopamine D2 receptors in modulation of object memory consolidation by nicotine, cocaine and their conditioned stimuli.

There are indications that drug conditioned stimuli (CS) may activate neurochemical systems of memory modulation that are activated by the drugs themselves. To directly test this hypothesis, a cholinergic nicotinic receptor antagonist (mecamylamine; MEC: 0, 10 or 30 µg/side) and a dopamine D2 receptor antagonist (l-741,626: 0, 0.63, 2.5 µg/side) were infused in the perirhinal cortex (PRh) to block modulation of object recognition memory consolidation induced by 0.4 mg/kg nicotine, 20 mg/kg cocaine, or their CSs. To establish these CSs, male Sprague-Dawley rats were confined for 2 h in a chamber, the CS+, after injections of 0.4 mg/kg nicotine, or 20 mg/kg cocaine, and in another chamber, the CS-, after injections of vehicle. This was repeated over 10 days (5 drug/CS+ and 5 vehicle/CS- pairings in total). It was found that the memory enhancing action of post-sample nicotine was blocked by intra-PRh infusions of both MEC doses, and 30 µg/side MEC also blocked the memory enhancing action of the nicotine CS. Interestingly, intra-PRh MEC did not block the memory enhancing effect of cocaine, nor that of the cocaine CS. In contrast, the memory enhancing action of post-sample cocaine administration was blocked by both l-741,626 doses, and 2.5 µg/side also blocked the effect of the cocaine CS, but not the memory effects of nicotine or of the nicotine CS. This functional double dissociation strongly indicates that drug CSs modulate memory consolidation by activating neural systems that are activated by the drugs themselves.

CADM2 is implicated in impulsive personality and numerous other traits by genome- and phenome-wide association studies in humans and mice.

Impulsivity is a multidimensional heritable phenotype that broadly refers to the tendency to act prematurely and is associated with multiple forms of psychopathology, including substance use disorders. We performed genome-wide association studies (GWAS) of eight impulsive personality traits from the Barratt Impulsiveness Scale and the short UPPS-P Impulsive Personality Scale (N = 123,509-133,517 23andMe research participants of European ancestry), and a measure of Drug Experimentation (N = 130,684). Because these GWAS implicated the gene CADM2, we next performed single-SNP phenome-wide studies (PheWAS) of several of the implicated variants in CADM2 in a multi-ancestral 23andMe cohort (N = 3,229,317, European; N = 579,623, Latin American; N = 199,663, African American). Finally, we produced Cadm2 mutant mice and used them to perform a Mouse-PheWAS ("MouseWAS") by testing them with a battery of relevant behavioral tasks. In humans, impulsive personality traits showed modest chip-heritability (~6-11%), and moderate genetic correlations (rg = 0.20-0.50) with other personality traits, and various psychiatric and medical traits. We identified significant associations proximal to genes such as TCF4 and PTPRF, and also identified nominal associations proximal to DRD2 and CRHR1. PheWAS for CADM2 variants identified associations with 378 traits in European participants, and 47 traits in Latin American participants, replicating associations with risky behaviors, cognition and BMI, and revealing novel associations including allergies, anxiety, irritable bowel syndrome, and migraine. Our MouseWAS recapitulated some of the associations found in humans, including impulsivity, cognition, and BMI. Our results further delineate the role of CADM2 in impulsivity and numerous other psychiatric and somatic traits across ancestries and species.