Injections of an opioid antagonist into the locus coeruleus and periaqueductal gray but not the amygdala precipitates morphine withdrawal in the 7-day-old rat

Opiate withdrawal behaviors in the infant differ from those of the adult. T he neural circuitry underlying opioid withdrawal in the adult rat is well d efined and includes the locus coeruleus (LC) and periaqueductal gray (PAG), with a minor role of the amygdala. Because the different behaviors that co nstitute the infant syndrome may be mediated by different neural circuits, we tested the hypothesis that these three sites are involved in opiate with drawal. Pups were injected with morphine from day 1-6 after birth (b.i.d.) and on the morning of the seventh day. Withdrawal was then elicited by loca l injection of the opioid antagonist methylnaloxonium into the LC, PAG, or amygdala. Withdrawal signs were precipitated in a dose-dependent manner fol lowing injection into the LC or PAG, but not the amygdala. The withdrawal b ehaviors elicited from the LC and PAG included both the same and different behaviors. The results support the hypothesis that the neural circuitry med iating opiate withdrawal behaviors is similar in infant and adult animals, but the behaviors expressed are age-specific. (C) 2001 Wiley-Liss, Inc.