The hypothesis that brain rewarding and pain modulating systems could involve a common
opiate system, identically blocked by naloxone, has been tested in three experiments. The
preferences or aversions for sapid solutions in rats have been employed as reliable
measures of responses to rewarding or nociceptive stimulations. In the first experiment, it
was shown that the spontaneous aversion to a quinine HCl solution was enhanced when
rats were offered the solution 30 min after naloxone at a dose of 1 mg/kg. The same�…