Nitric oxide (NO) in the PAG is involved in anxiety like behaviors. NO scavengers and antagonists of neuronal nitric oxide synthase (Nos1) injected into the PAG have been shown to reduce anxiogenic effects of alcohol withdrawal in rats (Bonassoli et al., 2012). Nos1 increased 1.75 fold in the PAG. Nitric oxide works by increasing the production of the second messenger cGMP (Meyer and Queszner, 2013). Phosphodiesterase 5A (Pde5a), which breaks down cGMP, was up 1.75 fold. The drug sildenafil, a Pde5a inhibitor (Table 5), could reverse some of the effects.
