ABSTRACT
Here we describe a novel mechanism for plasma membrane insertion of the delta opioid receptor (DOR). In small dorsal root ganglion neurons, only low levels of DORs are present on the cell surface, in contrast to high levels of intracellular DORs mainly associated with vesicles containing calcitonin gene-related peptide (CGRP). Activation of surface DORs caused Ca(2+) release from IP(3)-sensitive stores and Ca(2+) entry, resulting in a slow and long-lasting exocytosis, DOR insertion, and CGRP release. In contrast, membrane depolarization or activation of vanilloid and P2Y(1) receptors induced a rapid DOR insertion. Thus, DOR activation induces a Ca(2+)-dependent insertion of DORs that is coupled to a release of excitatory neuropeptides, suggesting that treatment of inflammatory pain should include blockade of DORs.
Subject(s)
Cell Membrane/metabolism , Exocytosis/physiology , Ganglia, Spinal/metabolism , Neurons, Afferent/metabolism , Nociceptors/metabolism , Receptors, Opioid, delta/metabolism , Animals , Calcitonin Gene-Related Peptide/metabolism , Calcium/metabolism , Calcium Signaling/drug effects , Calcium Signaling/physiology , Cell Membrane/drug effects , Cell Membrane/ultrastructure , Exocytosis/drug effects , Fluorescent Antibody Technique , Ganglia, Spinal/drug effects , Ganglia, Spinal/ultrastructure , Male , Membrane Potentials/drug effects , Membrane Potentials/physiology , Mice , Mice, Inbred C57BL , Microscopy, Electron , Neurons, Afferent/drug effects , Neurons, Afferent/ultrastructure , Neuropeptides/metabolism , Nociceptors/drug effects , Nociceptors/ultrastructure , PC12 Cells , Pain/metabolism , Pain/physiopathology , Rats , Receptors, Drug/drug effects , Receptors, Drug/metabolism , Receptors, Neurotransmitter/drug effects , Receptors, Neurotransmitter/metabolism , Receptors, Opioid, delta/drug effects , Receptors, Purinergic P2/drug effects , Receptors, Purinergic P2/metabolism , Receptors, Purinergic P2Y1 , Secretory Vesicles/metabolism , Secretory Vesicles/ultrastructureABSTRACT
Galanin overexpressing transgenic mice (GAL-tg) were generated on two different promoters. Both lines of GAL-tg displayed high levels of galanin in the hippocampus and reduced sensitivity to seizures, as compared to their respective wildtype littermate controls (WT). Performance deficits on learning and memory tasks, impaired long-term potentiation, reduced hippocampal excitability, lower evoked glutamate release, and reduced numbers of choline acetyltransferase immunoreactive neurons in the horizontal limb of the diagonal band were detected in GAL-tg as compared to WT. Changes in sensitivity to nociceptive stimuli were demonstrated in one line. GAL-tg represent a new model for investigating the biological actions of endogenous galanin, and for testing novel therapeutics based on galanin receptor ligands.
