PsychopharmacoIogia (Berl.) 8, 290--294 (1965) The Effect of Strychnine Sulphate on Learning as a Function of Time of Administration By WILLIAM T. GREENOUGH and JAMES L. ~ICGAUGH (Received .February18, 1965) A number of recent experiments indicate that rats' performance on a learning task can be facilitated by injections of CNS stimulants. Post- trial facilitation has been demonstrated with strychnine, picrotoxin, diphenyldiazadamantol, physostigmine, and caffeine (McGAvG~ and PnT~INOWC~ 1959; McGAvG~ et al. 1962a; McGAvG~ eta]. 1962b; PS~T~I~OVIC~ 1963 ; B R n ~ and MCGAVGH1961 ; STriATiON and Ps, T~I~o- wc~ 1963; PA~ 1961). Evidence of learning facilitation has been found when rats are injected either shortly before or shortly after training trials (e. g. McGAvG~ et al. 1962a). These findings have generally been interpreted as evidence that the drugs enhance learning by facilitating memory trace consolidation (McGA~G~ and P~TnI~ovIc~ 1965). Recently CooPv,~ and X~Ass (1963) proposed an alternate inter~ pretation of the findings. They suggested that the posttrial facilitation might be due to some direct residual effect of the drug on subsequent learning or performance trials. CooPeR and KaAss reported that the learning of female rats given 1.25 mg/kg of strychnine sulphate either 72 or 24 hours before maze training was superior to that of non-injected controls. These results are, however, inconsistent with the findings of previous studies (e. g. PA~ 1961; MCGAVGH et al. 1962a). McGAuG~ et al. (1962a) found that the learning of rats injected 90 min after each trial was significantly poorer than of rats injected within 15 rain after each trial, even though the delayed injections were closer in time to each subsequent day's test. The present study was designed to examine these conflicting results. Rats were given two training trials in a maze followed by five retention trials one week later. Strychnine injections were given either two days before the training trials, immediately after the training trials, or two days prior to the retention trials. According to the interpretation offered by Coor~ and K~ASS, the performance of animals injected two days prior to the training or retention trials should be superior to that of the animals injected immediately after the training trials. The consolidation interpretation predicts that rats injected immediately after training would be superior in the retention task.