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Gamma (gamma) is a recently proposed statistic that quantifies and describes the repetitive patterns of locomotion (locomotor stereotypy) exhibited by amphetamine-treated rats in an open field. The time-course of locomotor stereotypy after 1, 2, 3, and 4 mg/kg amphetamine was investigated in this research. Locomotor stereotypy was often evident during the first observation period after amphetamine. Lower doses of amphetamine produced qualitatively different locomotor stereotypy than higher doses. Rats given higher doses of amphetamine exhibited locomotor stereotypy during the "hyperactivity" phase of the three-phase response produced by higher doses of amphetamine (hyperactivity; absence of locomotions, increased sniffing, biting etc.; hyperactivity). Contrary to expectations, rats injected with 2 mg/kg amphetamine exhibited the highest and most sustained increase in gamma. We conclude that locomotor stereotypy is an important component of the behavioral effects of amphetamine in rats. Whether locomotor stereotypy and focused stereotypy are similar phenomena is still unclear.

Three groups (n = 10) of rat subjects received intraperitoneal injections of Thorazine, Elavil, and isotonic saline, respectively, prior to defensive burying testing. A defensive burying test session consisted of presenting each subject with an aversive stimulus (the discharge of a flashbulb) and recording the time each subject spent in burying behavior and the height of bedding material accumulated around the aversive stimulus during the ensuing 15 min. A retention test was conducted 24 h later. During retention sessions, subjects were simply confined to the testing chamber for 15 min. One half of the subjects in each group received retention testing under the same drug-injection condition used in the original conditioning session. The remaining subjects received retention tests under noninjection conditions. During the initial testing session, Thorazine-injected subjects spent significantly less time engaged in defensive burying and accumulated significantly less bedding material than did the salineinjected subjects. On the other hand, Elavil-injected subjects spent significantly more time burying and accumulated significantly more bedding material than did the saline-injected subjects. No significant differences, either in terms of time spent in burying or height of accumulated bedding material, were observed during retention testing.

Rats were injected with naloxone hydrochloride (3 mg/kg) or saline and subjected to preshock or no preshock prior to receiving a test shock that elicited defensive burying. Preshock was administered in a context different from, or the same as, that in which the test shock was delivered. The combination of naloxone and preshock led to more defensive burying than did saline and preshock. This was the case regardless of preshock context, a result suggesting that fear and/or analgesia may not always be critical ingredients in the preshock-naloxone interaction. Interpretative matters notwithstanding, the pattern of results for defensive burying was in basic agreement with that of other research on naloxone and defensive behavior and represents an extension of the literature to a new species-specific defense reaction.