Fig. 16.

Simplified diagram of endogenous pain control circuitry in the rat brain. The diagram emphasizes centers that contribute to the antinociceptive effect of systemically administered morphine, including two novel forebrain contributors, the amygdala and the posterior hypothalamic area (PHA; Manning et al., 1994; Manning and Franklin, 1998). The amygdala is interconnected with the PAG and PHA (see references in Manning and Franklin, 1998).A, amygdala; PAG, midbrain periaqueductal gray matter; RVM, rostral ventromedial medulla.