The opioid system modulates several physiological processes, including analgesia, the stress response, the immune response and neuroendocrine function. Pharmacological and molecular cloning studies have identified three opioid-receptor types, delta, kappa and mu, that mediate these diverse effects. Little is known about the ability of the receptors to interact to form new functional structures, the simplest of which would be a dimer. Structural and biochemical studies show that other G-protein-coupled receptors (GPCRs) interact to form homodimers. Moreover, two non-functional receptors heterodimerize to form a functional receptor, suggesting that dimerization is crucial for receptor function. However, heterodimerization between two fully functional receptors has not been documented. Here we provide biochemical and pharmacological evidence for the heterodimerization of two fully functional opioid receptors, kappa and delta. This results in a new receptor that exhibits ligand binding and functional properties that are distinct from those of either receptor. Furthermore, the kappa-delta heterodimer synergistically binds highly selective agonists and potentiates signal transduction. Thus, heterodimerization of these GPCRs represents a novel mechanism that modulates their function.

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The postsynaptic density (PSD) is a cellular structure specialized in receiving and transducing synaptic information. Here we describe the identification of 452 proteins isolated from biochemically purified PSD fractions of rat and mouse brains using nanoflow HPLC coupled to electrospray tandem mass spectrometry (LC-MS/MS). Fluorescence microscopy and Western blotting were used to verify that many of the novel proteins identified exhibit subcellular distributions consistent with those of PSDlocalized proteins. In addition to identifying most previously described PSD components, we also detected proteins involved in signaling to the nucleus as well as regulators of ADP-ribosylation factor signaling, ubiquitination, RNA trafficking, and protein translation. These results suggest new mechanisms by which the PSD helps regulate synaptic strength and transmission. Neurons are highly polarized cells, specializing in the reception of numerous, independent signal inputs and rapid integration of these inputs into an electrochemical response. The major sites of signal input are synapses, which are highly ordered cell junctions formed between two neurons and are typically unidirectional in fast excitatory chemical neurotransmission in the mammalian CNS. The response to neurotransmitter (NT) 1 release at the synapse is provided by a protein matrix of NT receptors and supporting proteins collectively known as the postsynaptic density (PSD) (for review, see Refs. 1-3). The PSD has several proposed functions including: signal amplification, cytoskeletal anchorage, biochemical signaling regulation, and NT receptor clustering (1, 4 -6).Changes in size and composition of the PSD correlate with changes in synaptic strength (7,8), including alterations that are stably maintained such as long-term potentiation (LTP), a physiologically relevant increase in synaptic efficacy and a model for learning and memory (9, 10). Therefore, an understanding of the protein composition of the PSD is a prerequisite for modeling the molecular interactions regulating synaptic strength.The structure of PSDs purified from rodent brains using gradient centrifugation and Triton X-100 extraction has been shown by electron microscopy (EM) to be virtually identical to the "in vivo" PSD structure (4, 11). Gel electrophoresis, enzymatic activity assays, and EM experiments have demonstrated that this procedure yields a highly pure, membranefree PSD fraction (11,12). Recent proteomic studies have investigated the composition of the PSD by SDS-PAGE or two-dimensional gel electrophoresis (2DE) coupled with MS (13-16). Li et al. (16) also performed shotgun proteomics using cysteine-containing peptides selected using ICAT techniques. However, each of these investigations identified less than one-third of previously described and biochemically confirmed PSD components, pointing to limitations in the techniques used. A recent paper by Yoshimura et al. (17) reports the identification by mass spectrometry of 492 proteins in the PSD, which suggests that the PSD is more ...

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Summary Long-term changes of neurotransmitter release are critical for proper brain function. However, the molecular mechanisms underlying these changes are poorly understood. While protein synthesis is crucial for the consolidation of postsynaptic plasticity, whether and how protein synthesis regulates presynaptic plasticity in the mature mammalian brain remains unclear. Here, using paired whole-cell recordings in rodent hippocampal slices, we report that presynaptic protein synthesis is required for long-term, but not short-term, plasticity of GABA release from type-1 cannabinoid receptor (CB1)-expressing axons. This long-term depression of inhibitory transmission (iLTD) involves cap-dependent protein synthesis in presynaptic interneuron axons but not somata. Translation is required during the induction, but not maintenance, of iLTD. Mechanistically, CB1 activation enhances protein synthesis via the mTOR pathway. Furthermore, using super-resolution STORM microscopy, we revealed eukaryotic ribosomes in CB1-expressing axon terminals. These findings suggest that presynaptic local protein synthesis controls neurotransmitter release during long-term plasticity in the mature mammalian brain.