In vitro autoradiography of [3H]DAMGO binding to the MOPR was examined across a number of brain regions of A/A and G/G mice. The representative pseudo-color auto-radiograms are shown in Fig. 1. Since there is no difference between males and females on the overall anatomical distribution of [3H]DAMGO binding, Fig. 1 shows males AA and GG as representatives. In general, A/A and G/G mice displayed similar regional distribution. Very high levels of MOPR were found in the caudate putamen (CPu), nucleus accumbens (NAc) core and shell, and superficial gray of superior colliculus (SuG) (Table 1). Many other regions exhibited high levels of [3H]DAMGO binding, including thalamus, amygdala, periaqueductal gray (PAG), hypothalamus, ventral tegmental area (VTA), substantial nigra, and cortex (Table 1). This distribution of MOPR in the brain is consistent with previous reports [see (Mansour et al., 1988) for a review]. Quantitation of specific [3H]DAMGO binding was performed by measuring the density of autoradiograms in regions of interest, and calculation was done based on the density of [3H]microscales (Table 1). A/A mice exhibited significantly higher [3H]DAMGO binding than G/G in the
