Abstract
Rhode Island Red chicks were hatched either in isolation or in pairs. On the second day after hatching they were injected with either 0, 0.5, 1.5, 4.5, or 13.5 mg of testosterone. Two days later their emotional response to a novel environment was determined by counting the cheeping rate. It was found that, while low doses of testosterone elevated cheeping, the highest doses caused a depression back to, or below, control levels. The rearing environment also had an effect in that the isolated chicks cheeped more than their social counterparts for every dose except the 0.5-mg dose. It was concluded that testosterone can influence behavioral arousal in chicks but that the effect is dependent upon both dose and previous environmental experience.
Highlights
Rhode Island Red chicks were hatched either in isolation or in pairs
Contrast markedly with the probable endogenous levels since plasma testosterone has been assayed at 0.12 pg/lOO ml in S-mo-old cocks; this value rising to only 0.24 ~8/100 ml in sexually mature birds (Schrocksnadel, Bator and Frick, 1971)
A dose X intervals analysis of variance (ANOVA) between the 0.5 and 0 dose showed a main effect for dose in the SC group (F(1,34) = 3.888; P < 0.06) and a dose X intervals interaction in the IC (F(9,252) = 2.233; P< 0.02) indicating that irrespective of environment or sex the 0.5mg dose of testosterone stimulated cheeping, The significant environmental effect is apparent from Fig. 1
Summary
Rhode Island Red chicks were hatched either in isolation or in pairs. On the second day after hatching they were injected with either 0, 0.5, 1.5, 4.5, or 13.5 mg of testosterone. Observedbehavioral changeshave included the following: an increased persistencewith which chicks organize their search pattern for a preferred food type (Andrew and Rogers, 1972), a decreased frequency of cheeping(peeping) in both familiar and unfamiliar environments (Andrew, 1963, 1969), a depressionof carbachol-inducedincreasesin locomotion (Andrew, 1969), and there hasbeen a suggestionthat testosterone-treated chicks show a decreasedemotional responseto a novel environment (Archer, 1973) These results suggestthat testosterone can act as a central nervous system depressant,a rather surprising conclusion considering the hormone’s importance in the arousalof male sexual and aggressivebehaviors. Contrast markedly with the probable endogenous levels since plasma testosterone has been assayed at 0.12 pg/lOO ml in S-mo-old cocks; this value rising to only 0.24 ~8/100 ml in sexually mature birds (Schrocksnadel, Bator and Frick, 1971) This suggested to us the possibility that the testosterone-induced depression might be a pharmacological effect and that the expected increase in behavioral arousal might accompany smaller doses. Cheeping rate was used as the dependent variable for the following reasons: first because it has been used previously in this context (Archer, 1973), second because, from our observations, it seemed to represent the most obvious response to the novel environment, and third because cheeping represents a highly reliable form of behavioral quantification
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