M1-muscarinic receptors promote fear memory consolidation via phospholipase C and the M-current.

Neuromodulators released during and after a fearful experience promote the consolidation of long-term memory for that experience. Because overconsolidation may contribute to the recurrent and intrusive memories of post-traumatic stress disorder, neuromodulatory receptors provide a potential pharmacological target for prevention. Stimulation of muscarinic receptors promotes memory consolidation in several conditioning paradigms, an effect primarily associated with the M1 receptor (M1R). However, neither inhibiting nor genetically disrupting M1R impairs the consolidation of cued fear memory. Using the M1R agonist cevimeline and antagonist telenzepine, as well as M1R knock-out mice, we show here that M1R, along with ß2-adrenergic (ß2AR) and D5-dopaminergic (D5R) receptors, regulates the consolidation of cued fear memory by redundantly activating phospholipase C (PLC) in the basolateral amygdala (BLA). We also demonstrate that fear memory consolidation in the BLA is mediated in part by neuromodulatory inhibition of the M-current, which is conducted by KCNQ channels and is known to be inhibited by muscarinic receptors. Manipulating the M-current by administering the KCNQ channel blocker XE991 or the KCNQ channel opener retigabine reverses the effects on consolidation caused by manipulating ß2AR, D5R, M1R, and PLC. Finally, we show that cAMP and protein kinase A (cAMP/PKA) signaling relevant to this stage of consolidation is upstream of these neuromodulators and PLC, suggesting an important presynaptic role for cAMP/PKA in consolidation. These results support the idea that neuromodulatory regulation of ion channel activity and neuronal excitability is a critical mechanism for promoting consolidation well after acquisition has occurred.

Positional cloning of Sorcs1, a type 2 diabetes quantitative trait locus.

We previously mapped the type 2 diabetes mellitus-2 locus (T2dm2), which affects fasting insulin levels, to distal chromosome 19 in a leptin-deficient obese F2 intercross derived from C57BL/6 (B6) and BTBR T+ tf/J (BTBR) mice. Introgression of a 7-Mb segment of the B6 chromosome 19 into the BTBR background (strain 1339A) replicated the reduced insulin linked to T2dm2. The 1339A mice have markedly impaired insulin secretion in vivo and disrupted islet morphology. We used subcongenic strains derived from 1339A to localize the T2dm2 quantitative trait locus (QTL) to a 242-kb segment comprising the promoter, first exon and most of the first intron of the Sorcs1 gene. This was the only gene in the 1339A strain for which we detected amino acid substitutions and expression level differences between mice carrying B6 and BTBR alleles of this insert, thereby identifying variation within the Sorcs1 gene as underlying the phenotype associated with the T2dm2 locus. SorCS1 binds platelet-derived growth factor, a growth factor crucial for pericyte recruitment to the microvasculature, and may thus have a role in expanding or maintaining the islet vasculature. Our identification of the Sorcs1 gene provides insight into the pathway underlying the pathophysiology of obesity-induced type 2 diabetes mellitus.

Redundant catecholamine signaling consolidates fear memory via phospholipase C.

Memories for emotionally arousing experiences are typically vivid and persistent. The recurrent, intrusive memories of traumatic events in post-traumatic stress disorder (PTSD) are an extreme example. Stress-responsive neurotransmitters released during emotional arousal are proposed to enhance the consolidation of fear memory. These transmitters may include norepinephrine and epinephrine (NE/E) because stimulating ß-adrenergic receptors shortly after training can enhance memory consolidation. However, mice lacking NE/E acquire and consolidate fear memory normally. Here, we show by using pharmacologic and genetic manipulations in mice and rats that NE/E are not essential for classical fear memory consolidation because signaling by the ß(2)-adrenergic receptor is redundant with signaling by dopamine at the D(5)-dopaminergic receptor. The intracellular signaling that is stimulated by these receptors to promote consolidation uses distinct G proteins to redundantly activate phospholipase C. The results support recent evidence indicating that blocking ß-adrenergic receptors alone shortly after trauma may not be sufficient to prevent PTSD.

Single-dose psilocybin for a treatment-resistant episode of major depression: Impact on patient-reported depression severity, anxiety, function, and quality of life.

BACKGROUND: COMP360 is a proprietary, synthetic formulation of psilocybin being developed for treatment-resistant depression (TRD), a burdensome, life-threatening illness with high global impact. Here, we expand upon the previous report of primary outcomes from a phase 2 study of COMP360 in individuals with TRD-the largest randomised controlled clinical trial of psilocybin-to discuss findings of the exploratory efficacy endpoints. METHODS: In this phase 2, double-blind trial, 233 participants with TRD were randomised to receive a single dose of psilocybin 25 mg, 10 mg, or 1 mg (control), administered alongside psychological support from trained therapists. Efficacy measures assessed patient-reported depression severity, anxiety, positive and negative affect, functioning and associated disability, quality of life, and cognitive function. RESULTS: At Week 3, psilocybin 25 mg, compared with 1 mg, was associated with greater improvements from Baseline total scores in all measures. The 10 mg dose produced smaller effects across these measures. LIMITATIONS: Interpretation of this trial is limited by the absence of an active comparator and the possibility of functional unblinding in participants who received a low dose of psilocybin. CONCLUSIONS: Three weeks after dosing, psilocybin 25 mg and, to a lesser degree, 10 mg improved measures of patient-reported depression severity, anxiety, affect, and functioning. These results extend the primary findings from the largest randomised clinical trial of psilocybin for TRD to examine other outcomes that are of importance to patients.

Separating the agony from ecstasy: R(-)-3,4-methylenedioxymethamphetamine has prosocial and therapeutic-like effects without signs of neurotoxicity in mice.

S,R(+/-)-3,4-methylenedioxymethamphetamine (SR-MDMA) is an amphetamine derivative with prosocial and putative therapeutic effects. Ongoing clinical trials are investigating it as a treatment for post-traumatic stress disorder (PTSD) and other conditions. However, its potential for adverse effects such as hyperthermia and neurotoxicity may limit its clinical viability. We investigated the hypothesis that one of the two enantiomers of SR-MDMA, R-MDMA, would retain the prosocial and therapeutic effects but with fewer adverse effects. Using male Swiss Webster and C57BL/6 mice, the prosocial effects of R-MDMA were measured using a social interaction test, and the therapeutic-like effects were assessed using a Pavlovian fear conditioning and extinction paradigm relevant to PTSD. Locomotor activity and body temperature were tracked after administration, and neurotoxicity was evaluated post-mortem. R-MDMA significantly increased murine social interaction and facilitated extinction of conditioned freezing. Yet, unlike racemic MDMA, it did not increase locomotor activity, produce signs of neurotoxicity, or increase body temperature. A key pharmacological difference between R-MDMA and racemic MDMA is that R-MDMA has much lower potency as a dopamine releaser. Pretreatment with a selective dopamine D1 receptor antagonist prevented SR-MDMA-induced hyperthermia, suggesting that differential dopamine signaling may explain some of the observed differences between the treatments. Together, these results indicate that the prosocial and therapeutic effects of SR-MDMA may be separable from the stimulant, thermogenic, and potential neurotoxic effects. To what extent these findings translate to humans will require further investigation, but these data suggest that R-MDMA could be a more viable therapeutic option for the treatment of PTSD and other disorders for which SR-MDMA is currently being investigated.

(±)-MDMA and its enantiomers: potential therapeutic advantages of R(-)-MDMA.

The use of (±)-3,4-methylenedioxymethamphetamine ((±)-MDMA) as an adjunct to psychotherapy in the treatment of psychiatric and behavioral disorders dates back over 50 years. Only in recent years have controlled and peer-reviewed preclinical and clinical studies lent support to (±)-MDMA's hypothesized clinical utility. However, the clinical utility of (±)-MDMA is potentially mitigated by a range of demonstrated adverse effects. One potential solution could lie in the individual S(+) and R(-) enantiomers that comprise (±)-MDMA. Individual enantiomers of racemic compounds have been employed in psychiatry to improve a drug's therapeutic index. Although no research has explored the individual effects of either S(+)-MDMA or R(-)-MDMA in humans in a controlled manner, preclinical research has examined similarities and differences between the two molecules and the racemic compound. This review addresses information related to the pharmacodynamics, neurotoxicity, physiological effects, and behavioral effects of S(+)-MDMA and R(-)-MDMA that might guide preclinical and clinical research. The current preclinical evidence suggests that R(-)-MDMA may provide an improved therapeutic index, maintaining the therapeutic effects of (±)-MDMA with a reduced side effect profile, and that future investigations should investigate the therapeutic potential of R(-)-MDMA.

A peripheral immune response to remembering trauma contributes to the maintenance of fear memory in mice.

Alterations in peripheral immune markers are observed in individuals with post-traumatic stress disorder (PTSD). PTSD is characterized in part by impaired extinction of fear memory for a traumatic experience. We hypothesized that fear memory extinction is regulated by immune signaling stimulated when fear memory is retrieved. The relationship between fear memory and the peripheral immune response was tested using auditory Pavlovian fear conditioning in mice. Memory for the association was quantified by the amount of conditioned freezing exhibited in response to the conditioned stimulus (CS), extinction and time-dependent changes in circulating inflammatory cytokines. Brief extinction training with 12 CS rapidly and acutely increased circulating levels of the cytokine interleukin-6 (IL-6), downstream IL-6 signaling, other IL-6 related pro-inflammatory cytokines. Transgenic manipulations or neutralizing antibodies that inhibit IL-6 activity did not affect conditioned freezing during the acquisition of fear conditioning or extinction but significantly reduced conditioned freezing 24 h after extinction training with 12 CS. Conversely, conditioned freezing after extinction training was unchanged by IL-6 inhibition when 40 CS were used during the extinction training session. In addition to effectively diminishing conditioned freezing, extinction training with 40 CS also diminished the subsequent IL-6 response to the CS. These data demonstrate that IL-6 released following fear memory retrieval contributes to the maintenance of that fear memory and that this effect is extinction dependent. These findings extend the current understanding for the role of the immune system in PTSD and suggest that IL-6 and other IL-6 related pro-inflammatory cytokines may contribute to the persistence of fear memory in PTSD where fear memory extinction is impaired.

Inhibition of serotonin transporters disrupts the enhancement of fear memory extinction by 3,4-methylenedioxymethamphetamine (MDMA).

RATIONALE: 3,4-Methylenedioxymethamphetamine (MDMA) persistently improves symptoms of post-traumatic stress disorder (PTSD) when combined with psychotherapy. Studies in rodents suggest that these effects can be attributed to enhancement of fear memory extinction. Therefore, MDMA may improve the effects of exposure-based therapy for PTSD, particularly in treatment-resistant patients. However, given MDMA's broad pharmacological profile, further investigation is warranted before moving to a complex clinical population. OBJECTIVES: We aimed to inform clinical research by providing a translational model of MDMA's effect, and elucidating monoaminergic mechanisms through which MDMA enhances fear extinction. METHODS: We explored the importance of monoamine transporters targeted by MDMA to fear memory extinction, as measured by reductions in conditioned freezing and fear-potentiated startle (FPS) in mice. Mice were treated with selective inhibitors of individual monoamine transporters prior to combined MDMA treatment and fear extinction training. RESULTS: MDMA enhanced the lasting extinction of FPS. Acute and chronic treatment with a 5-HT transporter (5-HTT) inhibitor blocked MDMA's effect on fear memory extinction. Acute inhibition of dopamine (DA) and norepinephrine (NE) transporters had no effect. 5-HT release alone did not enhance extinction. Blockade of MDMA's effect by 5-HTT inhibition also downregulated 5-HT2A-mediated behavior, and 5-HT2A antagonism disrupted MDMA's effect on extinction. CONCLUSIONS: We validate enhancement of fear memory extinction by MDMA in a translational behavioral model, and reveal the importance of 5-HTT and 5-HT2A receptors to this effect. These observations support future clinical research of MDMA as an adjunct to exposure therapy, and provide important pharmacological considerations for clinical use in a population frequently treated with 5-HTT inhibitors.