Dose-related effects of pentobarbital on the genetic differences seen between paired, Roman high- or low-avoidance rats in a shuttle box.

The effects of low doses of pentobarbital (PB) were measured on the activity levels, shock-induced fighting and avoidance or escape behavior of paired rats of two psychogenetically-selected lines, in multiple shuttle box sessions, following shock-induced fighting or two-way avoidance training. Each pair served as its own control, by receiving drug injections only every second week. Independent of training conditions, the RLA/Verh pairs showed about 90% freezing behavior and no fighting, whereas all RHA/Verh pairs preferred avoidance or escape behavior to fighting. Although their intertrial (shuttling) responses (ITRs) were reduced at the higher doses of PB used, RHA/Verh rats were still capable of most behavioral responses even at 24 mg/kg, whereas all RLA/Verh rats slept at that dose. On the other hand, the ITRs and avoidance responses of the (less active) RLA/Verh rats were increased by injections of 8 and 16 mg/kg PB. The results, especially those pertaining to freezing behavior and changes in activity levels, were discussed in comparison to other selected rat strains which have shown certain similarities to the Roman lines in regard to "emotionality" and associated neurochemical status.