Behavioral assay procedures for transfer of learned behavior by brain extracts.

Abstract

In Part I of this paper,' we presented details of the first seven of a series of ten experiments, aimed at finding a suitable behavioral assay procedure for studies of transfer of learned behavior by means of brain extracts. In continuing this presentation, we shall be chiefly concerned with experiments 8, 9, and 10, which made use of reinforced test procedures in a pair of left-right discrimination tasks in a Y-maze and a two-lever Skinner box. Methods.-The equipment used in these experiments was discussed in Part I, and is shown in Figure 1 of that paper. Extraction procedures, injection techniques, and methods of analysis were also discussed in Part I, and the same notation and conventions will be used here. Each of the following three experiments used intravenous injections, through the external jugular vein. Expeimnent 8 and following experiments made use of reinforced tests in place of the previous method of extinction testing. This experiment used 15 leftand 15 righttrained donors (10 sessions, 15 min each). Recipients were given two unreinforced sessions in the Y-maze (Fig. IF in Part I) followed by three 15-min training sessions in the shuttle box (Part I, Fig. IE) prior to injection, and were given a minimal cage diet during this time. Test sessions, in which the rats were fed regardless of which way they chose to turn, lasted 10 min each. In this and the following experiments, volume reduction in extract preparation was done by lyophilization. Further details can be found in Table 1. Experiment 9 repeated the design of experiment 8, with 24 left and 24 right donors. Three sessions of pretraining of the recipients in the shuttle box were followed by two 5-min unreinforced sessions in the Y-maze before injection, and tests were reduced to 5 min each. Experimnent 10 used 20 left and 20 right donors trained in the two-lever box (Part I, Fig. ID) for 10 days, and recipients received 5 days of pretraining in the one-lever box (Fig. IC) with minimal feeding before injection. Water and sucrose homogenates were prepared, half of the donors being used for each, and were centrifuged immediately after homogenization, at 100,000 g. Triton extracts of the particle fractions were precipitated with ethanol and a water wash of the precipitate divided into two portions (extract E and F), half injected without further treatment and half treated with TCA, the precipitate being discarded. All test sessions lasted 5 min. Results.--As in the previous experiments, the measure of transfer is given by A, which is equal to L R, where L is the mean percentage of left responses made by rats receiving extract from left-trained donors, and R is the mean percentage of left responses made by rats receiving extracts from right-trained donors. A positive A indicates that the left-injected rats were biased more strongly to the left than the right group, while a negative A indicates an inversion of the expected bias. In the unreinforced test procedures, which allow the rats to extinguish relatively quickly, the value of A is rarely very large. In the reinforced test procedures, the