Receptor-mediated internalization of [3H]-neurotensin in synaptosomal preparations from rat neostriatum.
Following its binding to somatodendritic receptors, the neuropeptide neurotensin (NT) internalizes via a clathrin-mediated process. In the present study, we investigated whether NT also internalizes presynaptically using synaptosomes from rat neostriatum, a region in which NT1 receptors are virtually all presynaptic. Binding of [(3)H]-NT to striatal synaptosomes in the presence of levocabastine to block NT2 receptors is specific, saturable, and has NT1 binding properties. A significant fraction of the bound radioactivity is resistant to hypertonic acid wash indicating that it is internalized. Internalization of [(3)H]-NT, like that of [(125)I]-transferrin, is blocked by sucrose and low temperature, consistent with endocytosis occurring via a clathrin-dependent pathway. However, contrary to what was reported at the somatodendritic level, neither [(3)H]-NT nor [(125)I]-transferrin internalization in synaptosomes is sensitive to the endocytosis inhibitor phenylarsine oxide. Moreover, treatment of synaptosomes with monensin, which prevents internalized receptors from recycling to the plasma membrane, reduces [(3)H]-NT binding and internalization, suggesting that presynaptic NT1 receptors, in contrast to somatodendritic ones, are recycled back to the plasma membrane. Taken together, these results suggest that NT internalizes in nerve terminals via an endocytic pathway that is related to, but is mechanistically distinct from that responsible for NT internalization in nerve cell bodies.
Department of Neurology and Neurosurgery, Montreal Neurological Institute, 3801 University St., McGill University, Montreal, Quebec, Canada H3A 2B4.
Ha Minh Ky
HM
Nguyen
Catherine M
CM
Cahill
Peter S
PS
McPherson
Alain
A
Beaudet
D000818:Animals; D004705:Endocytosis / Q000502:physiology*; D008297:Male; D017072:Neostriatum / Q000378:metabolism* / Q000648:ultrastructure; D009496:Neurotensin / Q000378:metabolism*; D017729:Presynaptic Terminals / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018028:Receptors, Neurotensin / Q000502:physiology* / Q000648:ultrastructure; D015398:Signal Transduction / Q000502:physiology*; D013574:Synaptosomes / Q000378:metabolism* / Q000648:ultrastructure; D014316:Tritium
D018028:Receptors, Neurotensin; D014316:Tritium; D009496:Neurotensin