Effects of Acth, Dexamethasone and Deoxycorticosterone on Aversive Threshold of Rats

The present study explored the effects of ACTH (4, 12, 24 units), dexamerhasone (.10, .50, 1.0 mg/kg) and deoxycorticosterone (.5, 1.0, 2.0 mg/kg) upon the aversive threshold of the rat using the spatial preference technique. Both ACTH and dexamethasone reduced the mean aversive threshold during the initial presentation of the compound, but only dexamethasone produced decrements that were statistically reliable. Subsequent administration of these two substances, however, produced no reliable effects upon the aversive threshold. The various doses of deoxycorticosterone produced no consistent changes in the threshold to electric shock. None of the substances were able to reliably alter motor activity on this test. These results were interpreted to suggest that the above acute changes in adrenocortical activity have little prolonged effects upon the aversive threshold to grid shock in the rat.

Agonistic Postures Elicited by Subdermal Shock in Sprague-Dawley and Long-Evans Rats

Different agonistic postures were elicited by subdermal shock in Long-Evans and Sprague-Dawley rats. 0-, 1-, 2-, and 3-mA shocks were used. All postures were reliably identified by independent observers at greater than chance levels, although absolute agreement between observers was relatively poor for several postures. Long-Evans rats engaged in more aggressive postures than Sprague-Dawley animals. Agonistic postures were more frequent with 2-mA shocks in Long-Evans rats, while 3-mA shocks elicited more agonistic postures in Sprague-Dawley rats. Subdermal shock appeared to produce less variability than has been reported in previous studies where grid shock was used.

Effects of Tone Cessation and Warning Signal Duration on Temporal Responding in an Avoidance Procedure

Six albino rats responded by lever-pressing to avoid grid shock in a free-operant, signaled avoidance situation. Tone cessation was the warning signal for 3 Ss while tone onset was the warning signal for a fourth S. The distribution of avoidance responses during successive reductions of the response-to-warning signal interval indicated a temporal discrimination during the warning signal. Immediate stimulus control, i.e., occurrence of the greatest amount of avoidance responses immediately following the occurrence of the warning signal, was not observed.