Does increasing stress change the behavioral action of mescaline from disruption to facilitation?

This experiment is related to the hypothesis of Bridger and of Wray that hallucinogens have facilitatory effects on animal behavior when stress is part of the experiment and have disruptive effects otherwise. Male Long-Evans rats were trained to high (above 89%), stable base line rates of shuttlebox avoidance, then given each of four treatments at 6-day intervals after returning to base line avoidance rates: 1. saline (1 ml i.p.), 2. saline+stressor, 3. mescaline hydrochloride (36.6 mg/kg i.p.), 4. mescaline (39.6 mg/kg i.p.)+stressor. Stress treatment was 1.0 mA footshock (1 sec duration) every 20-30 sec for 15 min between injection and session. Sessions (100 trials) began 20 min after injection. Treatments 1 and 2 had no effect on avoidance rate. Treatments 3 and 4 significantly decreased avoidance rate, with the latter causing significantly more decrease than the former. None of the treatments affected presession (5 min adaptation period) or intertrial crossings of the shuttlebox or latency on escape trials. These results suggest that exposure to a stressor, per se, is not the crucial factor causing hallucinogens to have facilitatory effects on animal behavior.