Three experiments are reported in which rats first received 50 escapable or inescapable signaled-shock trials. Experiment 1 (n = 22) employed an acquired-drive paradigm and found inescapable shock subjects learned a hurdle-jump response to escape the signal less rapidly than did escapable-shock subjects. Experiment 2 (n = 24) employed a conditioned emotional response paradigm and found inescapable-shock subjects suppressed more when the signal was introduced in the appetitive bar-pressing task. Both experiments measured spontaneous activity immediately following conditioning and found no group differences. Experiment 3 (n = 39) employed the same activity task and found no difference between escapable- and inescapable-shock groups when the signal was introduced into the activity task. Both groups displayed less activity than a nonshock control group during the signal. The results suggest that lack of control over the shock in the conditioning phase did not result in an increase of conditioned fear. The results are discussed in terms of a learned active-inactive predisposition to respond.

The present study was designed to assess the role of stimulus and response factors in the context-dependency of behavioral sensitization to the direct dopamine agonist apomorphine. In two experiments, male Wistar rats were given repeated injections of the direct dopamine agonist, apomorphine (5 mg/kg, s.c.), or vehicle at 24- to 72-h intervals and tested for locomotor activity for 30 min in either an openfield activity drum or a running wheel. In experiment 1, after eight activity sessions in either the activity drum or running wheel, one-half of the rats in each drug condition (apomorphine or vehicle) were tested in the alternate activity test environment. In both activity test environments, apomorphine produced progressively greater levels of locomotor activity with repeated treatment (i.e., sensitization). Moreover, sensitization to apomorphine transferred completely across test environments. That is, rats given apomorphine associated with one test environment (e.g., wheel) displayed equivalent sensitization when tested in the alternate environment (e.g., drum). Thus, changing external stimulus cues associated with repeated drug exposure did not affect the expression of sensitization. In experiment 2, rats were given either apomorphine or vehicle daily and tested for activity in a running wheel. For one-half the rats in each drug condition, the running wheel was free to move, but for the remainder the wheel was immobilized. After nine training sessions, all rats were given an apomorphine challenge injection and tested in a mobile wheel. After the challenge injection of apomorphine, rats previously treated with apomorphine and trained in the mobile wheel were significantly more active than rats previously treated with vehicle. In contrast, rats given equivalent apomorphine treatments and trained in the immobile wheel did not differ in activity from rats previously given only vehicle. Since the external stimulus cues associated with drug exposure for the mobile and immobile wheel groups were the same, this finding suggests that environmental factors affecting response expression are critical to the development of behavioral sensitization to apomorphine.

2 experiments investigated the relative effects of critical signal rate, normal noncntical signal rate, and critical signal probability on detection in a visual vigilance task In all conditions Ss had to monitor a clock display for a period of 54 min The results of both experiments suggested that normal signal rate may be of greater importance in a vigilance situation than either critical signal rate or critical signal probability In general, both percentage of detections and percentage of stimuli falsely responded to were in\ersel\ related to normal signal presentation.

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