Retrieval of fear extinction memory is associated with increased firing of neurons in the medial prefrontal cortex (mPFC). It is unknown, however, how extinction learning-induced changes in mPFC activity are relayed to target structures in the amygdala, resulting in diminished fear responses. Here, we show that fear extinction decreases the efficacy of excitatory synaptic transmission in projections from the mPFC to the basolateral nucleus of the amygdala (BLA), whereas inhibitory responses are not altered. In contrast,synaptic strength at direct mPFC inputs to intercalated neurons remains unchanged following extinction. Moreover, priming stimulation of mPFC projections induced heterosynaptic inhibition in auditory cortical inputs to the BLA. These synaptic mechanisms could contribute to the encoding of extinction memory by diminishing the ability of projections from the mPFC to drive BLA activity while retaining the ability of intercalated neurons to inhibit the output nuclei of the amygdala.

Summary Seizure disorders debilitate more than 65,000,000 people worldwide, with temporal lobe epilepsy (TLE) being the most common form. Previous studies have shown that transplantation of GABA-releasing cells results in suppression of seizures in epileptic mice. Derivation of interneurons from human PSC has been reported, pointing to clinical translation of quality-controlled human cell sources that can enhance inhibitory drive and restore host circuitry. In this study, we demonstrate that human PSC-derived maturing GABAergic interneurons (mGIN) migrate extensively and integrate into dysfunctional circuitry of the epileptic mouse brain. Using optogenetic approaches, we find that grafted mGINs generate inhibitory postsynaptic responses in host hippocampal neurons. Importantly, even before acquiring full electrophysiological maturation, grafted neurons were capable of suppressing seizures and ameliorating behavioral abnormalities such as cognitive deficits, aggressiveness and hyperactivity. These results provide support for the potential of human PSC-derived mGIN for restorative cell therapy for epilepsy.

In contextual fear conditioning, experimental subjects learn to associate a neutral context with an aversive stimulus and display fear responses to a context that predicts danger. Although the hippocampal-amygdala pathway has been implicated in the retrieval of contextual fear memory, the mechanism by which fear memory is encoded in this circuit has not been investigated. Here, we show that activity in the ventral CA1 (vCA1) hippocampal projections to the basal amygdala (BA), paired with aversive stimuli, contributes to encoding conditioned fear memory. Contextual fear conditioning induced selective strengthening of a subset of vCA1-BA synapses, which was prevented under anisomycin-induced retrograde amnesia. Moreover, a subpopulation of BA neurons receives stronger monosynaptic inputs from context-responding vCA1 neurons, whose activity was required for contextual fear learning and synaptic potentiation in the vCA1-BA pathway. Our study suggests that synaptic strengthening of vCA1 inputs conveying contextual information to a subset of BA neurons contributes to encoding adaptive fear memory for the threat-predictive context.

SUMMARYIn auditory fear conditioning, experimental subjects learn to associate an auditory conditioned stimulus (CS) with an aversive unconditioned stimulus. With sufficient training, animals fear conditioned to an auditory CS show fear response to the CS, but not to irrelevant auditory stimuli. Although long-term potentiation (LTP) in the lateral amygdala (LA) plays an essential role in auditory fear conditioning, it is unknown whether LTP is induced selectively in the neural pathways conveying specific CS information to the LA in discriminative fear learning. Here, we show that postsynaptically expressed LTP is induced selectively in the CS-specific auditory pathways to the LA in a mouse model of auditory discriminative fear conditioning. Moreover, optogenetically induced depotentiation of the CS-specific auditory pathways to the LA suppressed conditioned fear responses to the CS. Our results suggest that input-specific LTP in the LA contributes to fear memory specificity, enabling adaptive fear responses only to the relevant sensory cue.

GABAergic interneurons regulate cortical neural networks by providing inhibitory inputs, and their malfunction, resulting in failure to intricately regulate neural circuit balance, is implicated in brain diseases such as Schizophrenia, Autism and Epilepsy. During early development, GABAergic interneuron progenitors arise from the ventral telencephalic area such as Medial Ganglionic Eminence (MGE) and caudal ganglionic eminence (CGE) by the actions of secreted signaling molecules from nearby organizers, and migrate to their target sites where they form local synaptic connections. In this study, using combinatorial and temporal modulation of developmentally relevant dorsoventral and rostrocaudal signaling pathways (SHH, Wnt and FGF8), we efficiently generated MGE cells from multiple human pluripotent stem cells. Especially, modulation of FGF8/FGF19 signaling efficiently modultated MGE vs CGE differentiation. Human MGE cells spontaneously differentiated into Lhx6-expressing GABAergic interneurons and showed migratory properties. These human MGE-derived neurons generated GABA, fired action potential and displayed robust GABAergic postsynaptic activity. Transplantation into rodent brains results in well-contained neural grafts enriched with GABAergic interneurons that migrate in the host and mature to express somatostatin or parvalbumin. Thus, we propose that signaling modulation recapitulating normal developmental patterns efficiently generates human GABAergic interneurons. This strategy represents a novel tool in regenerative medicine, developmental studies, disease modeling, bioassay, and drug screening.

The acquisition and retrieval of contextual fear memory requires coordinated neural activity in the hippocampus, medial prefrontal cortex (mPFC), and amygdala. The contextual information encoded in the hippocampus is conveyed to the mPFC and amygdala for contextual fear conditioning. Previous studies have suggested that a CA1 neuronal population in the ventral hippocampus (VH) projects to both the mPFC and amygdala and is recruited in context-dependent control of conditioned fear. However, how double-projecting ventral CA1 hippocampal (vCA1) neurons modulate the activity of the mPFC and amygdala at the synaptic level has not been determined previously. Here, we show that the optogenetic silencing of the VH prevented the recall of contextual fear memory in mice, indicating its role in contextual fear expression. In dual retrograde viral tracing and c-Fos immunostaining experiments, we found that a proportion of vCA1 neurons projected to both the mPFC and amygdala and were recruited preferentially during context exposure, suggesting their role in encoding context representations. Moreover, optogenetic stimulation of axon collaterals of double-projecting vCA1 neurons induced monosynaptic excitatory responses in both the mPFC and basal amygdala, indicating that they could convey contextual information through the VH-mPFC and VH-amygdala pathways. The activation of double-projecting vCA1 neurons also induced action potential firings in the mPFC neurons that project to the amygdala, suggesting that they can also activate the VH-mPFC-amygdala pathway. With these synaptic mechanisms, double-projecting vCA1 neurons could induce synchronized neural activity in the mPFC and amygdala and convey contextual information efficiently to the basal amygdala for contextual fear conditioning. This work demonstrates that ventral CA1 hippocampal (vCA1) neurons projecting to both the medial prefrontal cortex (mPFC) and amygdala are activated preferentially when contextual information is processed in the ventral hippocampus, which is required for contextual fear expression. Our electrophysiological experiments reveal that the activation of double-projecting vCA1 neurons induces excitatory synaptic activity in both the mPFC and amygdala. These results suggest that double-projecting vCA1 neurons could contribute to contextual fear responses by inducing synchronized activity in the mPFC and amygdala and conveying contextual information to the basal amygdala more efficiently than vCA1 neurons projecting to either the mPFC or amygdala alone. These findings provide important insights into the mechanisms of the acquisition and retrieval of contextual fear memory.

We generated cortical interneurons (cINs) from iPSCs derived from14 healthy controls (HC cINs) and 14 patients with schizophrenia (SCZ cINs). Both HC cINs and SCZ cINs were authentic, fired spontaneously, received functional excitatory inputs from host neurons, and induced GABA-mediated inhibition in host neurons in vivo . However, SCZ cINs had dysregulated expression of protocadherin genes, which lie within documented SCZ loci. Mice lacking protocadherin α showed defective arborization and synaptic density of prefrontal cortex cINs and behavioral abnormalities. SCZ cINs similarly showed defects in synaptic density and arborization, which were reversed by inhibitors of Protein Kinase C, a downstream kinase in the protocadherin pathway. These findings reveal an intrinsic abnormality in SCZ cINs in the absence of any circuit-driven pathology. They also demonstrate the utility of homogenous and functional populations of a relevant neuronal subtype for probing pathogenesis mechanisms during development.

Synaptic rules that may determine the interaction between coexisting forms of long-term potentiation (LTP) at glutamatergic central synapses remain unknown. Here, we show that two mechanistically distinct forms of LTP could be induced in thalamic input to the lateral nucleus of the amygdala (LA) with an identical presynaptic stimulation protocol, depending on the level of postsynaptic membrane polarization. One form of LTP, resulting from pairing of postsynaptic depolarization and low-frequency presynaptic stimulation, was both induced and expressed postsynaptically ("post-LTP"). The same stimulation in the absence of postsynaptic depolarization led to LTP, which was induced and expressed presynaptically ("pre-LTP"). The inducibility of coexisting pre-and postsynaptic forms of LTP at synapses in thalamic input followed a well-defined hierarchical order, such that pre-LTP was suppressed when post-LTP was induced. This interaction was mediated by activation of cannabinoid type 1 receptors by endogenous cannabinoids released in the lateral nucleus of the amygdala in response to activation of the type 1 metabotropic glutamate receptor. These results suggest a previously unknown mechanism by which the hierarchy of coexisting forms of long-term synaptic plasticity in the neural circuits of learned fear could be established, possibly reflecting the hierarchy of memories for the previously experienced fearful events according to their aversiveness level.synaptic transmission | glutamate | plasticity | endocannabinoids F ear conditioning is one of the best experimental models of associative learning, which results from memorizing the temporal association between biologically neutral conditioned stimuli (CS) and aversive unconditioned stimuli (US) during behavioral training (1, 2). In the course of auditory fear conditioning, signals produced by the acoustic conditioned stimulus enter the lateral nucleus of the amygdala (LA) through projections originating in the auditory thalamus (thalamic input) and indirect projections from the auditory cortex (cortical input) (3). The acquisition of fear memory to auditory stimulation is mediated by long-term potentiation (LTP)-like synaptic enhancements in the CS pathways, including both cortical and thalamic inputs to the LA (4-9). Different forms of LTP could be observed, however, at synapses in the amygdala (7,8,(10)(11)(12) as well as in other regions of the brain (13, 14), depending on the presynaptic activity levels and degree of postsynaptic depolarization. Thus, conventional pairing-induced LTP and spike timing-dependent LTP in thalamic projections to the LA are expressed postsynaptically and may implicate trafficking of AMPA receptors at stimulated synapses ("post-LTP") (8, 15), whereas LTP in cortical input to the LA is expressed presynaptically, resulting from an increase in the probability of neurotransmitter release ("pre-LTP") (7). Little is known, however, about whether the coexisting forms of LTP at glutamatergic synapses interact with each other during the induction ...