Astrocytic IGF-IRs induce adenosine-mediated inhibitory downregulation and improve sensory discrimination

Insulin-like growth factor-I (IGF-I) signaling plays a key role in learning and memory processes. While the effects of IGF-I on neurons have been studied extensively, the involvement of astrocytes in IGF-I signaling and the consequences on synaptic plasticity and animal behavior remain unknown. We have found that IGF-I induces long-term potentiation (LTP) of the postsynaptic potentials that is caused by a long-term depression of inhibitory synaptic transmission in mice. We have demonstrated that this long-lasting decrease in the inhibitory synaptic transmission is evoked by astrocytic activation through its IGF-I receptors (IGF-IRs). We show that LTP not only increases the output of pyramidal neurons, but also favors the NMDAR-dependent LTP, resulting in the crucial information processing at the barrel cortex since specific deletion of IGF-IR in cortical astrocytes impairs the whisker discrimination task. Our work reveals a novel mechanism and functional consequences of IGF-I signaling on cortical inhibitory synaptic plasticity and animal behavior, revealing that astrocytes are key elements in these processes.This work was supported by Grants BFU2016-80802-P from Agencia Estatal de Investigación Spain/Fondo Europeo de Desarrollo Regional, and from the European Union [Ministerio de Economía y Competitividad (MINECO)] to D.F.d.S.; Grants R01-NS-097312 and R01-DA-048822 from National Institutes of Health/National Institute of Neurological Disorders and Stroke to A.A.; and grants from Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED) and Grant SAF2016-76462-C2-1-P from MINECO to I.T.-A. J.A.Z.-V. was supported by the National Council of Science, Technology and Technological Innovation (CONCYTEC, Perú) through the National Fund for Scientific and Technological Development (FONDECYT, Perú). J.F. received a postdoctoral fellowship from Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP; Grants #2017/14742-0 and #2019/03368-5). We thank the University of Minnesota Viral Vector and Cloning Core for production of some of the viral vectors used in this study; and Dr. G. Perea and Dr. Washington Buño for helpful comments