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Abstract: Visceral sensory pathways mediate homeostatic reflexes, the dysfunction of which leads to many neurological disorders1. The Bezold–Jarisch reflex (BJR), first described2,3 in 1867, is a cardioinhibitory reflex that is speculated to be mediated by vagal sensory neurons (VSNs) that also triggers syncope. However, the molecular identity, anatomical organization, physiological characteristics and behavioural influence of cardiac VSNs remain mostly unknown. Here we leveraged single-cell RNA-sequencing data and HYBRiD tissue clearing4 to show that VSNs that express neuropeptide Y receptor Y2 (NPY2R) predominately connect the heart ventricular wall to the area postrema. Optogenetic activation of NPY2R VSNs elicits the classic triad of BJR responses—hypotension, bradycardia and suppressed respiration—and causes an animal to faint. Photostimulation during high-resolution echocardiography and laser Doppler flowmetry with behavioural observation revealed a range of phenotypes reflected in clinical syncope, including reduced cardiac output, cerebral hypoperfusion, pupil dilation and eye-roll. Large-scale Neuropixels brain recordings and machine-learning-based modelling showed that this manipulation causes the suppression of activity across a large distributed neuronal population that is not explained by changes in spontaneous behavioural movements. Additionally, bidirectional manipulation of the periventricular zone had a push–pull effect, with inhibition leading to longer syncope periods and activation inducing arousal. Finally, ablating NPY2R VSNs specifically abolished the BJR. Combined, these results demonstrate a genetically defined cardiac reflex that recapitulates characteristics of human syncope at physiological, behavioural and neural network levels.

Loss-of-function variants in SYNGAP1 cause a developmental encephalopathy defined by cognitive impairment, autistic features, and epilepsy. SYNGAP1 splicing leads to expression of distinct functional protein isoforms. Splicing imparts multiple cellular functions of SynGAP proteins through coding of distinct C-terminal motifs. However, it remains unknown how these different splice sequences function in vivo to regulate neuronal function and behavior. Reduced expression of SynGAP-α1/2 C-terminal splice variants in mice caused severe phenotypes, including reduced survival, impaired learning, and reduced seizure latency. In contrast, upregulation of α1/2 expression improved learning and increased seizure latency. Mice expressing α1-specific mutations, which disrupted SynGAP cellular functions without altering protein expression, promoted seizure, disrupted synapse plasticity, and impaired learning. These findings demonstrate that endogenous SynGAP isoforms with α1/2 spliced sequences promote cognitive function and impart seizure protection. Regulation of SynGAP-αexpression or function may be a viable therapeutic strategy to broadly improve cognitive function and mitigate seizure.

The RASopathies are a group of genetic disorders that result from germline pathogenic variants affecting RAS-mitogen activated protein kinase (MAPK) pathway genes. RASopathies share RAS/MAPK pathway dysregulation and share phenotypic manifestations affecting numerous organ systems, causing lifelong and at times life-limiting medical complications. RASopathies may benefit from precision medicine approaches. For this reason, the Sixth International RASopathies Symposium focused on exploring precision medicine. This meeting brought together basic science researchers, clinicians, clinician scientists, patient advocates, and representatives from pharmaceutical companies and the National Institutes of Health. Novel RASopathy genes, variants, and animal models were discussed in the context of medication trials and drug development. Attempts to define and measure meaningful endpoints for treatment trials were discussed, as was drug availability to patients after trial completion.

Endocannabinoids (ECBs) depress transmitter release at sites throughout the brain. Here, we describe another form of ECB signaling that triggers a novel form of long-term potentiation (LTP) localized to the lateral perforant path (LPP) which conveys semantic information from cortex to hippocampus. Two cannabinoid CB1 receptor (CB1R) signaling cascades were identified in hippocampus. The first is pregnenolone sensitive, targets vesicular protein Munc18-1 and depresses transmitter release; this cascade is engaged by CB1Rs in Schaffer-Commissural afferents to CA1 but not in the LPP, and it does not contribute to LTP. The second cascade is pregnenolone insensitive and LPP specific; it entails co-operative CB1R/β1-integrin signaling to effect synaptic potentiation via stable enhancement of transmitter release. The latter cascade is engaged during LPP-dependent learning. These results link atypical ECB signaling to the encoding of a fundamental component of episodic memory and suggest a novel route whereby endogenous and exogenous cannabinoids affect cognition.

microRNAs (miRNAs) have emerged as potent regulators of learning, recent memory, and extinction. However, our understanding of miRNAs directly involved in regulating complex psychiatric conditions perpetuated by aberrant memory, such as in posttraumatic stress disorder (PTSD), remains limited. To begin to address the role of miRNAs in persistent memories, we performed small-RNA sequencing on basolateral amygdala (BLA) tissue and identified miRNAs altered by auditory fear conditioning (FC) one month after training. mir-598-3p, a highly conserved miRNA previously unstudied in the brain, was down-regulated in the BLA. Further decreasing BLA mir-598-3p levels did not increase strength of the remote fear memory. Given that stress is a critical component in PTSD, we next assessed the impact of stress and stress-enhanced fear learning (SEFL) on mir-598-3p levels, finding the miRNA is elevated in the BLA of male, but not female, mice susceptible to the effects of stress in SEFL. Accordingly, intra-BLA inhibition of mir-598-3p interfered with expression and extinction of the remote fear memory in male, but not female, mice. This effect could not be attributed to an anxiolytic effect of miRNA inhibition. Finally, bioinformatic analysis following quantitative proteomics on BLA tissue collected 30 d post-SEFL training identified putative mir-598-3p targets and related pathways mediating the differential susceptibility, with evidence for regulation of the actin cytoskeleton, the core mediator of structural plasticity. Taken together, the results suggest BLA mir-598-3p may be recruited by stress to mediate a critical switch from a salient remote fear memory to one that is enhanced and extinction-resistant.

Using pharmacologic and genetic approaches targeting actin or the actin-driving molecular motor, nonmuscle myosin II (NMII), we previously discovered an immediate, retrieval-independent, and long-lasting disruption of methamphetamine- (METH-) and amphetamine-associated memories. A single intrabasolateral amygdala complex infusion or systemic administration of the NMII inhibitor Blebbistatin (Blebb) is sufficient to produce this disruption, which is selective, having no retrieval-independent effect on memories for fear, food reward, cocaine, or morphine. However, it was unclear if Blebb treatment would disrupt memories of other stimulants and amphetamine class drugs, such as nicotine (NIC) or mephedrone (MEPH; bath salts). Moreover, many individuals abuse multiple drugs, but it was unknown if Blebb could disrupt polydrug memories, or if the inclusion of another substance would render Blebb no longer able to disrupt METH-associated memories. Therefore, the present study had two primary goals: (1) to determine the ability of Blebb to disrupt NIC- or MEPH-associated memories, and (2) to determine the ability of METH to modify other unconditioned stimulus (US) associations' susceptibility to Blebb. To this end, using the conditional place preference model, mice were conditioned to NIC and MEPH alone or METH in combination with NIC, morphine, or foot shock. We report that, unlike METH, there was no retrieval-independent effect of Blebb on NIC- or MEPH-associated memories. However, similar to cocaine, reconsolidation of the memory for both drugs was disrupted. Further, when combined with METH administration, NIC- and morphine-, but not fear-, associated memories were rendered susceptible to disruption by Blebb. Given the high rate of polydrug use and the resurgence of METH use, these results have important implications for the treatment of substance use disorder.

Syngap1 haploinsufficiency is a common cause of sporadic intellectual disability. Syngap1 mutations disrupt developing pyramidal neurons, although it remains unclear if this process contributes to cognitive abnormalities. Here, we found that haploinsufficiency restricted to forebrain glutamatergic neurons was sufficient to disrupt cognition and removing mutations from this population prevented cognitive abnormalities. In contrast, manipulating Syngap1 function in GABAergic neurons had no effect on cognition, excitability, or neurotransmission, highlighting the specificity of Syngap1 mutations within forebrain excitatory neurons. Interestingly, cognitive abnormalities were reliably predicted by the emergence of enhanced excitatory synaptic function in mature superficial cortical pyramidal cells, which was a neurophysiological disruption caused by Syngap1 dysfunction in developing, but not adult, forebrain neurons. We conclude that reduced cognition in Syngap1 mutants is caused by isolated damage to developing forebrain glutamatergic neurons. This damage triggers secondary disruptions to synaptic homeostasis in mature cortical pyramidal cells, which perpetuates brain dysfunction into adulthood.

Depolymerizing actin in the amygdala through nonmuscle myosin II inhibition (NMIIi) produces a selective, lasting, and retrieval-independent disruption of the storage of methamphetamine-associated memories. Here we report a similar disruption of memories associated with amphetamine, but not cocaine or morphine, by NMIIi. Reconsolidation appeared to be disrupted with cocaine. Unlike in the amygdala, methamphetamine-associated memory storage was not disrupted by NMIIi in the hippocampus, nucleus accumbens, or orbitofrontal cortex. NMIIi in the hippocampus did appear to disrupt reconsolidation. Identification of the unique mechanisms responsible for NMII-mediated, amygdala-dependent disruption of memory storage associated with the amphetamine class may enable induction of retrieval-independent vulnerability to other pathological memories.

Extracellular signal-regulated kinase (ERK) signaling is important for neuronal synaptic plasticity. We report here that the protein kinase ribosomal S6 kinase (RSK)2, a downstream target of ERK, uses a C-terminal motif to bind several PDZ domain proteins in heterologous systems and in vivo. Different RSK isoforms display distinct specificities in their interactions with PDZ domain proteins. Mutation of the RSK2 PDZ ligand does not inhibit RSK2 activation in intact cells or phosphorylation of peptide substrates by RSK2 in vitro but greatly reduces RSK2 phosphorylation of PDZ domain proteins of the Shank family in heterologous cells. In primary neurons, NMDA receptor (NMDA-R) activation leads to ERK and RSK2 activation and RSK-dependent phosphorylation of transfected Shank3. RSK2-PDZ domain interactions are functionally important for synaptic transmission because neurons expressing kinase-dead RSK2 display a dramatic reduction in frequency of AMPA-type glutamate receptor-mediated miniature excitatory postsynaptic currents, an effect dependent on the PDZ ligand. These results suggest that binding of RSK2 to PDZ domain proteins and phosphorylation of these proteins or their binding partners regulates excitatory synaptic transmission. extracellular signal-regulated kinase | glutamate receptors | RAS | synaptic plasticity