The memory of fear extinction is context dependent: fear that is suppressed in one context readily renews in another. Understanding of the underlying neuronal circuits is, therefore, of considerable clinical relevance for anxiety disorders. Prefrontal cortical and hippocampal inputs to the amygdala have recently been shown to regulate the retrieval of fear memories, but the cellular organization of these projections remains unclear. By using anterograde tracing in a transgenic rat in which neurons express a dendriticallytargeted PSD-95:Venus fusion protein under the control of a c-fos promoter, we found that, during the retrieval of extinction memory, the dominant input to active neurons in the lateral amygdala was from the infralimbic cortex, whereas the retrieval of fear memory was associated with greater hippocampal and prelimbic inputs. This pattern of retrieval-related afferent input was absent in the central nucleus of the amygdala. Our data show functional anatomy of neural circuits regulating fear and extinction, providing a framework for therapeutic manipulations of these circuits.gene expression | hippocampus | prefrontal cortex | learning and memory T here is an increasing interest in the neural mechanisms underlying extinction of learned fear, in part because fear extinction is a useful model for exposure-based therapies for the treatment of human anxiety disorders, such as phobias and posttraumatic stress disorder (1). During fear extinction, a previously conditioned stimulus (CS) is repeatedly presented in the absence of the unconditioned stimulus (US), a procedure that induces a progressive decrease in the magnitude and probability of learned fear responses, including freezing behavior. However, extinction does not erase the original fear memory; rather, it promotes the formation of a new inhibitory memory that reduces fear to the CS (2). Extinguished fear is highly context dependent, insofar as CS presentation outside the extinction context results in the recovery of the previously conditioned fear response, a phenomenon known as fear renewal (3). The return of fear after extinction is a considerable challenge for the efficacy of exposure-based therapies (4). Therefore, identification of brain structures and neuronal circuits selectively implicated in extinction vs. renewal of fear is of great importance.Owing to substantial progress toward understanding the neural mechanisms underlying the context specificity of fear extinction, there is now a general consensus that, for auditory fear conditioning, extinction involves three main structures: the amygdala, hippocampus (HIPP), and prefrontal cortex (PFC) (2, 5-8). However, the neuronal interactions between these structures that underlie contextual retrieval of fear memory after extinction remain to be elucidated. This problem is further complicated by the fact that neither the amygdala nor the PFC is a homogeneous structure. Among the substructures of the amygdala, the central, basal, and lateral nuclei (Ce, Ba, and La, respectively) have been impl...

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Summary Ras GTPase-activating protein-binding proteins 1 and 2 (G3BP1 and G3BP2, respectively) are widely recognized as core components of stress granules (SGs). We report that G3BPs reside at the cytoplasmic surface of lysosomes. They act in a non-redundant manner to anchor the tuberous sclerosis complex (TSC) protein complex to lysosomes and suppress activation of the metabolic master regulator mechanistic target of rapamycin complex 1 (mTORC1) by amino acids and insulin. Like the TSC complex, G3BP1 deficiency elicits phenotypes related to mTORC1 hyperactivity. In the context of tumors, low G3BP1 levels enhance mTORC1-driven breast cancer cell motility and correlate with adverse outcomes in patients. Furthermore, G3bp1 inhibition in zebrafish disturbs neuronal development and function, leading to white matter heterotopia and neuronal hyperactivity. Thus, G3BPs are not only core components of SGs but also a key element of lysosomal TSC-mTORC1 signaling.