Dihydroergocristine and memory alterations of aged male rats.

The ergot alkaloid derivative dihydroergocristine (DHECS) was injected acutely or subchronically to aged male rats of the Sprague-Dawley strain, 26 months old, at the dose of 0.05 or 0.1 mg/kg. Learning and memory ability of the animals were studied with tests of avoidance behavior. The acquisition of active avoidance behavior was studied with the shuttle-box and pole-jumping tasks. In the latter, the extinction of active avoidance behavior was also studied. A step-through type of passive avoidance task was used to examine the retention of passive avoidance responses. The acquisition of the active avoidance behavior and the retention of the passive avoidance response were reduced in aged animals as compared to those of young animals. Acute treatment of old rats with DHECS was followed by a facilitation of acquisition of active avoidance behavior in the shuttle box and of retention of passive avoidance responses in the dark box. The effect on the acquisition and extinction of pole-jumping behavior after a single injection of DHECS at the beginning of the acquisition session was restricted to the first acquisition trial. A more potent effect on the acquisition of the shuttle-box behavior and on the retention of passive avoidance reaction was found in animals treated subchronically with the ergot derivative (0.05 and 0.1 mg/kg for 10 days). These rats also showed a facilitation of acquisition and an inhibition of extinction of pole jumping behavior.