title: Corrigendum
abstract: In a previous manuscript the staining pattern of a monoclonal antibody generated to the N-terminal sequence of the ORL-1 receptor was described in the rat CNS (Anton et al., 1996). Subsequently, this antibody was used in double-label confocal experiments to map mu opioid and ORL-1 receptors in areas of brain associated with pain processing (Monteillet-Agius et al., 1998). In order to stain sections in mice, the monoclonal antibody was biotinylated, and as one of the specificity controls, brain sections from mutant mice lacking the ORL-1 receptor were stained. Mice null for both exon 2 and 3 of the ORL-1 receptor (generated by Zhenping Chen in John Pintar's laboratory, UMDNJ-Robert Wood Johnson Medical School, unpublished) as well as exon 1 knockout mice, which eliminates the epitope to which the antibody was raised, (Nishi et al., 1997) were tested and the same results obtained. The biotinylated antibody showed a staining pattern in the ORL-1 knockout mice indistinguishable from wild-type mice and similar to the pattern found in rat brain. Although the CNS staining pattern in rat was consistent with the distribution of mRNA for the receptor, the retained staining pattern in ORL-1 null mice demonstrates that the monoclonal antibody is recognizing a protein distinct from the ORL-1 receptor.