Results of studies of "transfer of learning" effects by brain ribonucleic acid (RNA) extraction from trained rats and its injection into naive rats have been apparently conflicting. In a recent study by Luttges, Johnson, Buck, Holland, & McGaugh (I %6) no difference was found in task performance between naive rats injected with RNA from trained rats and naive rats injected with RNA from naive rats. On the other hand, Babich, Jacobson, Bubash, & Jacobson (1965) found the task performance of naive rats injected with RNA from trained rats to be superior to that of naive rats injected with RNA from naive rats.Studies supporting RNA "transfer of learning" effects have tested recipient rats I to 3 h after injection, whereas, studies disproving this transfer effect have tested the rats 18 to 24 h after RNA injection. In the present study, time between RNA injection and performance testing of recipient rats was varied in an attempt to verify "transfer of learning" effects and determine the optimal transfer retention interval for a passive-avoidance task requiring light-dark discrimination. METHOD The Ss were 80 naive, male, Sprague-Dawley rats, approximately 55 days old at the beginning of the study.A Miller-Mowrer box (24 x 5 x 15 in.) was divided into a black and a white section of equal size by a guillotine door (5 x 15 in.). A 25-W light was placed directly above the white section and a shock source of 2.4 mA was wired to the grid of the black section. Electric clocks with photoelectric relays measured time (to the nearest .1 sec) spent in each section.Previous work has demonstrated that rats showadefinite preference for the darkest areas in a maze when permitted to explore freely (Gay & Rapheison, 1967). Avoidance training for this preference was carried out on 20 rats. These 20 rats and 20 others were decapitated and brain RNA extracted and injected into 40 rats. The recipients were tested for light-dark preference 1,2,8, or 16 h after injection.On a 3-min preference trial all 80 rats showed the expected preference for the black compartment and were randomly divided into four groups of 20: Learned-Donor, ControlDonor, Learned-Recipient, and Control-Recipient. Each Leamed-Donor rat was confined in the black compartment and administered a 2.4-mA shock for 5 sec, after which time the dOOf was raised 3 in. and Spermitted to escape to the white compartment. Three such shock trials per day for five consecutive days was sufficient for the Ss to exhibit an inhibition of their original preference for the black compartment. 1 During these sessions the Donor-Control Ss were administered an equal amount and dura ti on of shock in a neutral environment. Two hours after the last training session both Donor groups were decapitated.Within each group the Donor brains were pooled and processed together according to the following procedure: 2
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