To begin to discern the mechanisms underlying this differential response to chronic morphine in Dcc heterozygous mice, we examined the structural and neurochemical architecture of the dorsal horns of the spinal cords and of dorsal root ganglia (DRG) of wild-type and Dcc heterozygous mice. We analyzed the spinal cords and DRG for peptidergic (CGRP, SP) nerve terminals projecting to lamina I and outer lamina II, as well as non-peptidergic (IB4) nerve terminals projecting to the dorsal border of inner lamina II; and for the levels of DRG expression of selected markers. The normal architecture of these sensory endings in the dorsal spinal cords is preserved in the Dcc heterozygous mice, and the expression of the DRG markers in Dcc heterozygous mice is also unchanged (Figure 5). Thus, the changes in opioid responses observed in Dcc heterozygous mice do not appear to be caused by a gross alteration in spinal cord or DRG architecture.
