Self-injurious behavior produced in rats by daily caffeine and continuous amphetamine

Self-biting (SB) is an unusual behavioral effect of high doses of certain amphetamine-like drugs in rats. This bizarre behavior has received little attention, perhaps because the high doses of drug required and the dramatic disturbance of the animals' behavioral repertoire have raised the possibility that SB is a high dose phenomenon. However, we have found that continuous administration of very low amounts of amphetamine reliably produces SB in rats, and that this behavioral change can be very selective. We compared SB produced by continuous amphetamine to SB produced by daily caffeine; the latter has been proposed as an animal model for self-injurious behavior (SIB) in the Lesch-Nyhan syndrome. Subcutaneous silicone pellets containing amphetamine base were implanted for 4.5 days; caffeine was administered daily for 10 days. The amphetamine pellets produced the highest rate of SB (75% vs 40%) with the least toxic effects (no deaths vs three deaths). Neither drug produced stereotypy. The dopamine antagonist haloperidol was only marginally effective in controlling SB produced by daily caffeine but the dopamine antagonist pimozide (which has a longer duration of action) prevented SB by amphetamine pellet rats. Continuous release amphetamine pellets may provide an alternative to the caffeine model of SIB in humans, particularly for the Lesch-Nyhan syndrome.