Activation of nitric oxide-synthesizing neurones during precipitated morphine withdrawal.

Activation of nitric oxide (NO)-synthesizing neurones in the hypothalamus and brain stem was studied during naloxone-precipitated morphine withdrawal in rats. In animals that underwent behavioural changes consistent with withdrawal, Fos and nicotinamide dinucleotide phosphate-diaphorase (NADPH-D)-positive neurones were identified within the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei as well as the brain stem nucleus tractus solitarius (NTS). A larger proportion of NADPH-D-positive neurones were activated in the PVN than in the NTS. While NO has been implicated in the genesis of opioid withdrawal, the present data provide evidence for the activation of select populations of NO-synthesizing neurones during the opiate withdrawal syndrome.