Subcellular distribution of δ-opioid receptors in the rat spinal cord: an approach using a three-dimensional reconstruction of confocal series of immunolabelled neurons

Using a specific rat monoclonal anti-idiotypic antibody we have examined the subcellular distribution of δ-opioid receptors in various neuronal subtypes of the rat spinal cord. The immunofluorescence was detected with a confocal microscope and in some cases serial images were processed for a three-dimensional (3-D) reconstruction of the neurons. Immunolabelling was found to be distributed throughout the spinal cord grey matter specially in the most superficial layers of the dorsal horn, around the central canal and in the region of motoneurons of the ventral horn. The 3-D reconstruction made on large neurons of lamina IX in the ventral horn and on neurons of lamina X around the central canal allowed the visualization of δ-opioid receptors in the cytoplasm of the soma and proximal neurites of immunofluorescent neurons. Some immunolabelled receptors were also detected at the level of the plasma membrane of the cell bodies and in the nuclear matrix. Interestingly, a particular arrangement of δ-opioid receptors organized along parallel alignments was observed on the plasma membrane of some neurons. This study emphasizes the potential usefulness of a 3-D reconstruction in the study of the spatial arrangement of cellular components.