Changes in posterior hypothalamic self-stimulation following experimental cerebral infarction in the rat.

Bioplar stimulating electrodes were placed bilaterally in the posterior hypothalamus of rats following which the animals were shaped for intracranial self-stimulation (ICSS). When ICSS rates were stable for 1 wk, the right middle cerebral artery was ligated. During the 25-day postinfarction period, the rate of ICSS at specified current values was compared with preoperative rates. At 2 days after operation, there was a 33% decrease in the maximum frequency of ipsilateral ICSS. However, by 8 days after experimental stroke, there was a 16% increase in the maximal rate of ICSS above the preoperative value, and the rate returned to control levels by 20 days after surgery. The minimum current necessary to elicit the maximal rate of response also changed in a biphasic manner, i.e., the minimum required current was greater than preoperative control levels until 8 days after operation but then dropped below control level until 20 days postoperatively. There were no changes in the current or rate of response in the contralateral electrode. These results are discussed in relation to what may be the underlying neurophysiological changes causing these biphasic alterations in ICSS.