Synthesis and functional integration of a neurotransmitter receptor in isolated invertebrate axons

Neurotransmitter receptors are considered an important class of membrane pr oteins that are involved in plasticity-induced changes underlying learning and memory. Recent studies, which demonstrated that the mRNAs encoding for various receptor proteins are localized to specific dendritic domains, allu de toward the possibility that these membrane bound molecules may be synthe sized locally. However, direct evidence for the local axonal or dendritic s ynthesis and functional integration of receptor proteins in either vertebra tes or invertebrates is still lacking. In this study, using an invertebrate model system we provide the first direct evidence that isolated axons (in the absence of the soma) can intrinsically synthesize and functionally inte grate a membrane-bound receptor protein from an axonally injected mRNA. Sur gically isolated axons from identified neurons mere injected with mRNA enco ding a G-protein-coupled conopressin receptor. Immunocytochemical and elect rophysiological techniques were used to demonstrate functional integration of the receptor protein into the membrane of the isolated axon. Ultrastruct ural analysis of axonal compartments revealed polyribosomes, suggesting tha t some components of the protein synthesizing machinery are indeed present in these extrasomal compartments. Such axonal propensity to locally synthes ize and functionally insert transmitter receptors may be instrumental in pl asticity induced changes, for instance those that underlie learning and mem ory. (C) 2000 John Wiley & Sons, Inc.