FIG. 2
The effects of b-endorphin or naloxone on measures of masculine sexual behavior. A: Infusions of b-endorphin into the preoptic area virtually abolish mounts and intromissions, but in B: it can be seen that they have no effect on responding for a female under a second-order schedule. C: Neither b-endorphin (b-END) nor naloxone (NAL) when infused into the preoptic area affect a sexually conditioned place preference, however naloxone abolishes such a place preference when given systemically (ip). D: Intra-preoptic b-endorphin abolishes a male's preference for an estrous over an anestrous female, but naloxone given ip or into the preoptic area has no effect on this measure.
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published 2000