Proteins were separated on Novex Tris-Glycine 16% or NuPage Bis-Tris 4C12% protein gels (Invitrogen) in SDS jogging buffer and were transferred to PVDF membranes (BioRad). GABAergic interneurons change in the postnatal brain. How and whether mTORC1 signaling affects PV cell development is unknown. Here, we show that Tsc1 haploinsufficiency causes a premature increase in terminal axonal branching and bouton density formed by mutant PV cells, followed by a loss of perisomatic innervation in adult mice. PV cell-restricted Tsc1 haploinsufficient and knockout mice show deficits in social behavior. Finally, we identify a sensitive period during the third postnatal week during which treatment with the mTOR inhibitor Rapamycin rescues deficits in both PV cell innervation and social behavior in adult conditional haploinsufficient mice. Our findings reveal a role of mTORC1 signaling in the regulation of the developmental time course and maintenance of cortical PV Ramelteon (TAK-375) cell connectivity and support a mechanistic Ramelteon (TAK-375) basis for the targeted rescue of autism-related behaviors in disorders associated with deregulated mTORC1 signaling. or cause tuberous sclerosis complex (TSC), an autosomal dominant disease associated with high occurrence of epilepsy, intellectual disabilities, and autistic traits4. Extensive studies on TSC mutations have set the paradigm for monogenic mTORpathies, to understand how mTOR dysregulation affects different processes of brain development3 and how these may ultimately lead to cognitive and neurological deficits. The theory of an increased excitation/inhibition (E/I) ratio as an underlying cause of network hyper-excitability and reduced signal-to-noise in the cortex was initially proposed by Rubenstein and Merzenich as a framework for understanding the pathophysiology of autism5. Over the past 15 years, numerous studies have provided evidence that alterations in E/I balance may be involved in many Ramelteon (TAK-375) mouse models of monogenetic autism, however the nature of the underlying mechanisms are heterogeneous thus highlighting that it is critical to understand what sort of circuit alterations are caused by specific genetic mutations6. While numerous studies have focussed on the effects of deletion, and mTOR dysregulation, on cortical and hippocampal excitatory cells7C10, only few studies have addressed whether and how deletion affects cortical GABAergic circuit development11C15. In particular, whether it plays different roles in specific GABAergic populations is not known. The neocortex is comprised of a diverse group of inhibitory neurons, which differ in morphology, intrinsic physiological properties, and connectivity16. Among them, parvalbumin (PV) expressing cells, which represent the largest class of cortical interneurons, specifically target the soma and proximal dendrites of pyramidal cells, and have been implicated in synchronizing the firing of neuronal populations to generate gamma oscillation17C19, which in turn allows the cortex to perform precise computational tasks underlying perception, selective attention, working memory, and cognitive flexibility in humans and rodents20C23. The development of PV cell circuit connectivity is a prolonged process, terminating around the end of adolescence in rodents and primates24C28. PV cells dysfunction has been found in several mouse models of autism29C33. Conversely, stimulating PV cells has been shown to be sufficient to ameliorate social behavior29,34,35. Since mutations in Tsc1 give rise to autistic traits, we questioned whether and how deletion FANCH selectively in PV cells affects their connectivity, and whether and to what extent these alterations in cortical PV cell circuits might be contributing to changes in social behavior downstream of altered mTOR signaling. Here, we used a combination of single-cell genetics in cortical organotypic cultures, conditional mutant mice, and high-resolution imaging to investigate the effects of TSC-mTORC1 pathway on the development of PV cell connectivity. We found that mutant PV cells (both heterozygous and homozygous) showed a premature increase of their axonal arbor complexity and bouton density in the first three postnatal weeks, followed by a striking loss of connectivity by adulthood. The effect of Tsc1 haploinsufficiency or deletion on PV cell connectivity was cell-autonomous. Further, conditional mutant mice showed social behavior deficits. Strikingly, both PV cell connectivity and social behavior in adult mice were rescued by a short treatment with the mTORC1 inhibitor rapamycin during the third postnatal week, suggesting that inhibiting the premature maturation of PV cell innervations was sufficient to ameliorate the long-term neurological outcomes of the mutation. Results TSC1 haploinsufficiency in postnatal PV cells reduced PV cell connectivity and altered social behavior in adulthood The maturation of PV cell innervation is a prolonged process that plateaus at the end of the first postnatal month in mouse cortex24. To Ramelteon (TAK-375) investigate whether mTORC1 activation plays a role in this process, we first analyzed the time course of pS6 expression, one of the direct downstream effectors of mTORC1, in PV cells identified by PV immunolabeling (Fig.?1a). We found that both the proportion of PV cells.