Stressor-induced changes in open-field behavior of Japanese quail selected for contrasting adrenocortical responsiveness to immobilization

The effect of no treatment (undisturbed controls; CON) or 5 min exposure to immobilization stress (STR) before assessment of open-field behavior in Japanese quail lines selected for high (high stress; HS) or low (low stress; LS) plasma corticosterone (B) response to a similar immobilization stress was examined. During a 5-min test period in an open field, the following behavioral measurements were made: the latency to ambulate (LAMB), the number of open-field floor sectors entered (SECTORS), and freezing behavior (total time spent in complete silence and inactivity, apart from slight movements associated with respiration; FREEZE). A further measure of ambulation across time (ambulation rate; ARATE) was calculated using the formula: ARATE = (SECTORS/[(300 s test ceiling)--LAMB)]. The LS-quail showed higher (P < 0.04) ARATE and lower (P < 0.05) FREEZE behavior than did their HS counterparts. When compared with the CON, quail exposed to STR showed decreased ARATE (P < 0.02) and numbers of open-field SECTORS entered (P < 0.04). More importantly, the LS-CON exhibited a higher (P < 0.05) mean ARATE, less FREEZE behavior, and increased numbers of SECTORS entered than did the other 3 treatment groups (LS-STR, HS-CON, and HS-STR), all of which showed similar responses for these variables. The LS-CON vs. HS-CON findings support our contention that selection for reduced adrenocortical responsiveness has been accompanied by a concomitant decrease in underlying fearfulness (exemplified herein by heightened activity in the open field in LS-CON). We further show here that this relationship was eliminated by application of an acute stressor before open-field testing of LS quail, wherein a reduction in activity similar to that found in both HS quail treatment groups was evident in comparison to the LS-CON.