In this study, we identify and characterize the properties of the BLA-vHPC pathway, which has opposing effects on anxiety-related behaviors compared to the BLA-CeA pathway. These data demonstrate that distinct populations of intermingled neurons in the BLA projecting to different

downstream targets can have unique functional properties. With respect Vemurafenib to the anxiety circuit as a whole, given the evolutionarily adaptive purposes of fear and anxiety for survival, it is likely that anxiety circuits are widely distributed and highly redundant. This may explain why there are a host of parallel circuits in the brain that can contribute to the modulation of anxiety states. While this study represents the identification of a projection that represents an oppositional force to existing circuits in mediating anxiety, much of the anxiety circuit has yet to be carefully characterized on a

circuit and synaptic level. Other circuits to explore in the characterization of critical neural circuit elements of anxiety include the connections of the PFC, the bed nucleus of the stria terminalis, and projections from neuromodulatory regions. All procedures were carried out in accordance with the guidelines from the NIH and with approval of the MIT IACUC and DCM. Dorsomorphin concentration Adult wild-type male C57BL/6J mice (aged 5–6 weeks) were used. Purified AAV5-CaMKIIα-eNpHR3.0-eYFP or eYFP alone was bilaterally injected for mice in Figure 1. AAV5-CaMKIIα-ChR2-eYFP or eYFP alone was unilaterally injected for mice in Figures 2, 3, and 4. To allow for BLA-vHPC terminal photostimulation, mice received chronically tuclazepam implantable optical fibers aimed over the vHPC. For glutamate receptor antagonist (GluR antag) experiments, mice were unilaterally implanted with a guide cannula. Anxiety assays (EPM, OFT, and NSF) were performed 5–8 weeks after surgery. For in vivo pharmacology experiments, a GluR antag cocktail consisting of NBQX and

AP5 dissolved in saline was injected into vHPC 30 min before the behavioral assays and optogenetic manipulations. For mice in Figure 1, ∼10 mW of constant yellow light was bilaterally delivered onto BLA-vHPC terminals. For mice injected with ChR2 or eYFP control in the BLA (Figures 2 and 3), 10–15 mW of light at 20 Hz, 5 ms pulses of blue light was delivered unilaterally onto BLA-vHPC terminals. Mice included in Figure 2 (ChR2 and eYFP) were stimulated with 473 nm laser and perfused 90 min after and the brain was extracted for c-fos expression quantification. Primary antibody (1:500) was incubated for 17–20 hr at 4°C. Sections were then washed with PBS-1X prior to and after incubation with secondary antibody (Alexa Flour 647 1:500) for 2 hr at 25°C.