The researchers studied whether 2 separate motivational systems in the brain underlie the rewarding effects of morphine. The brainstem tegmental pedunculopontine nucleus (TPP) is involved in mediating the motivational effects of opiates in nondeprived (drug-naive) rats, whereas dopamine transmission is necessary in mediating the motivational effects of opiates in deprived rats (opiate withdrawal). The results show that heroin's motivational properties obey the same boundary between a nondeprived and a deprived motivational state. Bilateral ibotenic acid lesions of the TPP blocked the acquisition of a place preference for an environment paired with 0.05 mg/kg heroin (a dose that induces no withdrawal aversion) but had no effect on place preference for an environment paired with 0.5 mg/kg heroin (a dose that does induce withdrawal aversion). Dopamine antagonist pretreatment produced the opposite pattern of results.
No takes yet. Share an insight, caveat, or question.
Nader et al. (1994) studied this question.