Vestibular-induced behaviour of rats born and raised in hypergravity

One group of rats were bred and kept under hypergravity (HG) conditions (2.5 g) in a centrifuge, Another group were bred and kept under normal gravity conditions (1 g), Rats from both groups were dropped from a supine position into a water basin under infrared illumination leaving only gravity (1 g for both groups) for orientation, The airrighting reflex and reappearance at the water surface were examined, The success rate for airrighting of HG rats is 47% versus 45% for controls, and is performed about equally fast by both groups. The success rate of HG and control hamsters is less than or equal to 25% and greater than or equal to 80%, respectively [22]. This interspecific difference does not appear to support the conjecture that altered behaviour is caused by a structural change of vestibular end organs during ontogenetic development under HG. The success rate for surfacing of control rats is 100%, Surfacing of young HG rats is less successful (36% at age 6 weeks) and requires more time, On average, surfacing of adult rats of both groups is about the same. Apparently, the repeated stay of centrifuge-bred rats at 1 g for experiments and daily care suffices to recalibrate and improve their orientation, which is essential for surfacing. (C) 2000 Elsevier Science Inc.