The expression levels of several additional genes were measured as a specificity control in C57BL/6J and 129/SvlmJ mice. There were no interstrain differences after chronic morphine treatment in the brain levels of expression of Kcnj6, C3ar1, C5ar1 or Htr3b mRNA between these two strains (Fig. 7). Importantly, the Htr3b gene is located adjacent to Htr3a on chromosome 9, and encodes a protein that forms heteromultimeric 5-HT3 receptors, with biophysical properties that are distinct from Htr3a homomultimers [42].
