Role of Midbrain Central Gray in Pain-Induced Defensive Boxing of Rats
Method Page 3

Title/Summary Page

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Behavioral Testing

Lesioned animals were tested pre-operatively for boxing, and one week post-operatively for open field behavior, boxing, flinch, and escape in that order. Control animals were tested for open field behavior, boxing, flinch, and escape in that order and then retested one week later. Five lesioned animals were maintained for more than one week and given repeated weekly tests to ascertain recovery of function.

Boxing tests. A threshold procedure was used in boxing tests because previous research had found it to be a sensitive measure of the effect of brain lesions [2]. Pairs of rats were given 20 trials of 20 shocks per trial (0.5 sec on, 0.5 sec off) with a 30 sec rest between trials. Shock intensity for each trial was determined by a titration procedure; i.e., raised if boxing had not occurred, lowered if it had occurred on the previous trial. Intensities were 0.05, 0.10, 0.30, 0.50, 1.00 and 1.50 mA. Threshold (50% level) of boxing was determined by extrapolation from graphed data, and data were also recorded on the overall percentage of shocks on which boxing occurred. If boxing did not occur, then ascending and descending series of shock intensities were alternated.

Post-operative boxing tests were conducted first between the original partners. If there was less boxing than in pre-operative tests, each lesioned animal was then tested with a normal control, and the data from this latter test were used in the final results. This procedure was necessitated by findings that a lowered rate of fighting by one rat results in a lower fighting rate by its opponent [24].

Open field tests. Individual animals were placed in the open field for 4 min, and the number of intersections crossed by both hindlegs was scored. Freezing postures and other behaviors were noted. After each test the floors and walls were scrubbed clean.

Flinch tests. As a control for pain perception, flinch thresholds were determined for individual animals using a procedure similar to that of the boxing tests. Each animal received 20 trials of 10 shocks each (0.5 sec on, 0.5 sec off) with a 30 sec rest between trials. The intensity for each trial was varied in alternating ascending and descending series of 0.03, 0.05, 0.1 and 0.3 mA. The flinch threshold refers to the shock intensity at which the rat flinched during 50% of the shocks as extrapolated from graphed data.

Escape tests. For escape testing, individual rats were placed in the shock-box with the wooden platform elevated and accessible, and they were given 25 trials of 20 shocks each with a 30 sec rest between trials. A titration schedule was used similar to that of boxing tests (intensities of 0.1, 0.3, 0.5 and 1.0 mA). If the rat did not escape on an ascending series, then descending and ascending series were alternated until escape did occur.

Criterion for escape performance was three consecutive platform mounts at or above a given intensity, each with a latency of 5 sec or less. If no mounting of the platform occurred after 10 trials, learning was facilitated by alternating trials of escape with trials of passive avoidance in which the rat was placed on the platform and shocked whenever it descended.

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