Figure 6. Hypothalamus-pituitary-adrenal (HPA) axis activation during morphine withdrawal is attenuated by α₁- but not β-adrenoceptor blockade.

Placebo and morphine-dependent rats were pretreated with prazosin or propranolol and plasma levels of corticosterone (a marker of HPA axis activity) were determined 60 min after naloxone injection. Praz: prazosin; prop; propranolol; sal: saline; nx: naloxone. Each bar represents mean ± SEM. Post hoc analysis revealed a significant increase in plasma corticosterone concentration after naloxone-induced morphine withdrawal, which was attenuated in prazosin- but not in propranolol-pretreated rats. ***p<0.001 versus placebo+naloxone; ⁺⁺⁺p<0.001 versus morphine+saline; ^&&&p<0.001 versus placebo+prazosin+naloxone; ^$$$p<0.001 versus morphine+prazosin+saline; ^##p<0.01 versus morphine+naloxone; @@@p<0.001 versus placebo+propranolol+naloxone; ^%%%p<0.001 versus morphine+propranolol+saline.