Naloxone increases ketamine-induced hyperactivity in the open field in female rats.

In considering possible effects of ketamine, and its interactions with drugs that might be administered following ketamine abuse, researchers investigated the effects of administering combinations of saline, naloxone, and/or ketamine on open-field activity levels and frequencies of turning, reverse locomotion, head weaving, and rearing in 50-day-old rats. Female subjects having received ketamine combined with saline showed significant increases in open-field activity as compared with male subjects and subjects having received combinations of saline and/or naloxone. When combined with ketamine, naloxone caused an increase in the aforementioned ketamine-induced hyperactivity in female rats. In addition, ketamine caused increases in turning in female rats and increases in reverse locomotion and head weaving in male and female rats. Decreases in rearing were reported in both males and females with administration of ketamine. In general, naloxone had little, if any, effect on these behaviors. Thus, the primary effect of administration of naloxone reported in this study is an exacerbation of ketamine-induced open-field hyperactivity. The authors discuss the results with respect to indirect effects of ketamine on endogenous opiate and dopamine systems on the aforementioned behaviors. The researchers also consider sex differences and possible precautions when dealing with individuals having ingested psychedelic anesthetics.