The development of glutamatergic synapses involves changes in the number and type of receptors present at the postsynaptic density. To elucidate molecular mechanisms underlying these changes, we combine in utero electroporation of constructs that alter the molecular composition of developing synapses with dual whole-cell electrophysiology to examine synaptic transmission during two distinct developmental stages. We find that SAP102 mediates synaptic trafficking of AMPA and NMDA receptors during synaptogenesis. Surprisingly, after synaptogenesis, PSD-95 assumes the functions of SAP102 and is necessary for two aspects of synapse maturation: the developmental increase in AMPA receptor transmission and replacement of NR2B-NMDARs with NR2A-NMDARs. In PSD-95/PSD-93 double-KO mice, the maturational replacement of NR2B-with NR2A-NMDARs fails to occur, and PSD-95 expression fully rescues this deficit. This study demonstrates that SAP102 and PSD-95 regulate the synaptic trafficking of distinct glutamate receptor subtypes at different developmental stages, thereby playing necessary roles in excitatory synapse development.AMPAR and NMDAR trafficking ͉ membrane-associated guanylate kinase ͉ synaptogenesis ͉ postsynaptic density ͉ synaptic transmission A fundamental goal of developmental neurobiology is to identify the sequence of molecular events underlying excitatory synapse development, a process that can be divided into two distinct stages: synaptogenesis and synapse maturation. Synaptogenesis follows the specification of cell-to-cell contacts mediated by cell adhesion molecules (1, 2) and involves the initiation of chemical communication through the recruitment of pre-and postsynaptic proteins necessary for fast synaptic transmission (3, 4), such as AMPA receptors (AMPARs) and NMDA receptors (NMDARs). Synapse maturation is characterized by two functional events: an increase in the strength of AMPAR-mediated transmission (5, 6) and a switch in the subunit composition of synaptic NMDARs (7). NMDARs are composed of two obligatory NR1 subunits and two NR2 subunits, of which there are four members (NR2A-D) (8). NR2B-NMDARs are expressed during synaptogenesis and are replaced by NR2A-NMDARs during synapse maturation (9-11), a replacement that accounts for the developmental decrease in the NMDAR excitatory postsynaptic current (EPSC) decay time (12, 13) and the loss of sensitivity to the NR2B antagonist ifenprodil (14). The precise molecular mechanisms underlying the differential synaptic trafficking of AMPAR and NMDAR during developmental synaptogenesis and maturation remain largely unknown.PSD-95 is a member of a family of proteins collectively known as membrane-associated guanylate kinases (MAGUKs) (15-17). The PSD-95-like subfamily of neuronal MAGUKs (PSD-MAGUKs) includes PSD-93, SAP102, and SAP97 (15-17). Comparative studies emphasize the remarkable similarities among PSD-MAGUKs in terms of protein-protein interactions (18,19) and overlapping functions in synaptic trafficking of AMPARs at mature synapses (20-24). On the ot...

Spatial and temporal features of synaptic inputs engage integration mechanisms on multiple scales, including presynaptic release sites, postsynaptic dendrites, and networks of inhibitory interneurons. Here we investigate how these mechanisms cooperate to filter synaptic input in hippocampal area CA1. Dendritic recordings from CA1 pyramidal neurons reveal that proximal inputs from CA3 as well as distal inputs from entorhinal cortex layer III (ECIII) sum sublinearly or linearly at low firing rates due to feedforward inhibition, but sum supralinearly at high firing rates due to synaptic facilitation, producing a high-pass filter. However, during ECIII and CA3 input comparison, supralinear dendritic integration is dynamically balanced by feedforward and feedback inhibition, resulting in suppression of dendritic complex spiking. We find that a particular subpopulation of CA1 interneurons expressing neuropeptide Y (NPY) contributes prominently to this dynamic filter by integrating both ECIII and CA3 input pathways and potently inhibiting CA1 pyramidal neuron dendrites.

Behavior has molecular, cellular, and circuit determinants. However, because many proteins are broadly expressed, their acute manipulation within defined cells has been difficult. Here, we combined the speed and molecular specificity of pharmacology with the cell type specificity of genetic tools. DART (drugs acutely restricted by tethering) is a technique that rapidly localizes drugs to the surface of defined cells, without prior modification of the native target. We first developed an AMPAR antagonist DART, with validation in cultured neuronal assays, in slices of mouse dorsal striatum, and in behaving mice. In parkinsonian animals, motor deficits were causally attributed to AMPARs in indirect spiny projection neurons (iSPNs) and to excess phasic firing of tonically active interneurons (TANs). Together, iSPNs and TANs (i.e., D2 cells) drove akinesia, whereas movement execution deficits reflected the ratio of AMPARs in D2 versus D1 cells. Finally, we designed a muscarinic antagonist DART in one iteration, demonstrating applicability of the method to diverse targets.