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The decision to either approach or avoid a potentially threatening environment is thought to rely upon the coordinated activity of heterogeneous neural populations in the hippocampus and prefrontal cortex (PFC). However, how this circuitry is organized to flexibly promote both approach or avoidance at different times has remained elusive. Here, we show that the hippocampal projection to PFC is composed of two parallel circuits located in the superficial or deep pyramidal layers of the CA1/subiculum border. These circuits have unique upstream and downstream connectivity, and are differentially active during approach and avoidance behaviour. The superficial population is preferentially connected to widespread PFC inhibitory interneurons, and its activation promotes exploration; while the deep circuit is connected to PFC pyramidal neurons and fast spiking interneurons, and its activation promotes avoidance. Together this provides a mechanism for regulation of behaviour during approach avoidance conflict: through two specialized, parallel circuits that allow bidirectional hippocampal control of PFC. The authors reveal a mechanism for regulation of behaviour during approach avoidance conflicts that relies on two specialized, parallel circuits that allow bidirectional hippocampal control of the prefrontal cortex. [ABSTRACT FROM AUTHOR]

Summary Correct mitochondrial distribution is critical for satisfying local energy demands and calcium buffering requirements and supporting key cellular processes. The mitochondrially targeted proteins Miro1 and Miro2 are important components of the mitochondrial transport machinery, but their specific roles in neuronal development, maintenance, and survival remain poorly understood. Using mouse knockout strategies, we demonstrate that Miro1, as opposed to Miro2, is the primary regulator of mitochondrial transport in both axons and dendrites. Miro1 deletion leads to depletion of mitochondria from distal dendrites but not axons, accompanied by a marked reduction in dendritic complexity. Disrupting postnatal mitochondrial distribution in vivo by deleting Miro1 in mature neurons causes a progressive loss of distal dendrites and compromises neuronal survival. Thus, the local availability of mitochondrial mass is critical for generating and sustaining dendritic arbors, and disruption of mitochondrial distribution in mature neurons is associated with neurodegeneration. [ABSTRACT FROM AUTHOR]

Repeated exposure to cocaine alters the structural and functional properties of medium spiny neurons (MSNs) in the nucleus accumbens (NAc). These changes suggest a rewiring of the NAc circuit, with an enhancement of excitatory synaptic connections onto MSNs. However, it is unknown how drug exposure alters the balance of long-range afferents onto different cell types in the NAc. Here we used whole-cell recordings, two-photon microscopy, optogenetics and pharmacogenetics to show how repeated cocaine exposure alters connectivity in the mouse NAc medial shell. Cocaine selectively enhanced amygdala innervation of MSNs expressing D1 dopamine receptors (D1-MSNs) relative to D2-MSNs. We also found that amygdala activity was required for cocaine-induced changes to behavior and connectivity. Finally, we established how heightened amygdala innervation can explain the structural and functional changes evoked by cocaine. Our findings reveal how exposure to drugs of abuse fundamentally reorganizes cell type- and input-specific connectivity in the NAc. [ABSTRACT FROM AUTHOR]

Autism spectrum disorders (ASDs) are an early onset, heterogeneous group of heritable neuropsychiatric disorders with symptoms that include deficits in social interaction skills, impaired communication abilities, and ritualistic-like repetitive behaviours. One of the hypotheses for a common molecular mechanism underlying ASDs is altered translational control resulting in exaggerated protein synthesis. Genetic variants in chromosome 4q, which contains the EIF4E locus, have been described in patients with autism. Importantly, a rare single nucleotide polymorphism has been identified in autism that is associated with increased promoter activity in the EIF4E gene. Here we show that genetically increasing the levels of eukaryotic translation initiation factor 4E (eIF4E) in mice results in exaggerated cap-dependent translation and aberrant behaviours reminiscent of autism, including repetitive and perseverative behaviours and social interaction deficits. Moreover, these autistic-like behaviours are accompanied by synaptic pathophysiology in the medial prefrontal cortex, striatum and hippocampus. The autistic-like behaviours displayed by the eIF4E-transgenic mice are corrected by intracerebroventricular infusions of the cap-dependent translation inhibitor 4EGI-1. Our findings demonstrate a causal relationship between exaggerated cap-dependent translation, synaptic dysfunction and aberrant behaviours associated with autism. [ABSTRACT FROM AUTHOR]

Modification of the number of GABAA receptors (GABAARS) clustered at inhibitory synapses can regulate inhibitory synapse strength with important implications for information processing and nervous system plasticity and pathology. Currently, however, the mechanisms that regulate the number of GABAARS at synapses remain poorly understood. By imaging superecliptic pHluonn tagged GABAAR subunits we show that synaptic GABAAR clusters are normally stable, but that increased neuronal activity upon glutamate receptor (GIuR) activation results in their rapid and reversible dispersal. This dispersal correlates with increases in the mobility of single GABAARs within the clusters as determined using singleparticle tracking of GABAARs labeled with quantum dots. GluRdependent dispersal of GABAAR clusters requires Ca2+ influx via NMDA receptors (NMDARs) and activation of the phosphatase calcineurin. Moreover, the dispersal of GABAAR clusters and increased mobility of individual GABAARs are dependent on serine 327 within the intracellular loop of the GABAAR γ2 subunit Thus, NMDAR signaling, via calcineunn and a key GABAAR phosphorylation site, controls the stability of synaptic GABAARS, with important implications for activity dependent control of synaptic inhibition and neuronal plasticity. [ABSTRACT FROM AUTHOR]

Neuronal postsynaptic currents consume most of the brain's energy supply. Delineating how neurons control the distribution, morphology and function of the energy-producing mitochondria that fuel synaptic communication is therefore important for our understanding of nervous system function and pathology. Here we review recent insights into the molecular mechanisms that control activity-dependent regulation of mitochondrial trafficking, morphology and activity at excitatory synapses. We also consider some implications of this regulation for synaptic function and plasticity and discuss how this may contribute to synaptic dysfunction and signalling in neurological disease, with a focus on Alzheimer's disease. [ABSTRACT FROM AUTHOR]

We found that medium spiny neurons (MSNs) in both the direct and indirect pathways of the mouse nucleus accumbens (NAc) receive inputs from the cortex, thalamus and hippocampus. However, hippocampal inputs were much weaker onto indirect MSNs, where they contacted small spines located in the distal dendrites. This selective targeting means that these inputs must be gated by subthreshold depolarization to trigger action potentials and influence NAc output. [ABSTRACT FROM AUTHOR]