Recall rendered dependent on an opiate state

Remembering may require that the organism be in a state that is similar to that in which the event was initially experienced (state dependence [StD]). We determined whether morphine induces StD and whether this StD is conceiv ably involved in the analgesic effects that opiates produce. Rats trained w hile treated with morphine recalled the learned response when tested with t his opiate but not when in their nondrugged state, and vice versa. Furtherm ore, morphine analgesia occurred in a manner that was similar to StD in ter ms of both dose and time. In as much as responses to nociceptive stimulatio n are learned during the course of ontogeny, StD may constitute the psychop hysiological mechanism whereby opiates produce their character istic analge sic effects.