Handling alters habituation and response to stimulus change in the holeboard.

The responses of rats that had been extensively handled for 18 days were compared in the holeboard with those of rats that had received handling for only 4 days before the test. The extensively handled group showed slower between-day habituation of exploratory head-dipping. They did not differ in the number of head-dips, but spent longer head-dipping, at holes with objects than at those without. The less-handled group did not differ in the time spent head-dipping, but made more head-dips at empty holes. Both groups reacted similarly to the removal of the objects on day 4. However, the extensively handled rats showed a greater response of increased head-dipping when a novel object was introduced on day 5. The groups did not differ in their locomotor activity, but the extensively handled group made more rears. The results are discussed with respect to the neurochemical changes that have been found after repeated handling.