PDE1 is significantly expressed in neurons of the hippocampus and cortex (Lugnier, selleck chemical 2006), which suggests that this enzyme may control cAMP levels in areas that are markedly affected by ethanol exposure during the brain growth spurt (Gil-Mohapel et al., 2010 and Olney et al., 2002a). Considering that the cAMP/PKA signaling system is involved in the control of a variety of cellular processes related with metabolism, gene transcription

and neurotransmission, it is difficult to clearly identify the mechanism(s) through which the cAMP/PKA cascade and the ethanol-induced hyperactivity are linked. One possibility is related to the fact that cAMP is a critical second messenger involved in catecholaminergic transmission and exerts its effects mainly through the PKA (Missale et al., 1998). Of note, PKA plays a key role in the control

of the catalytic activity of tyrosine hydroxylase find more (TH), the rate-limiting enzyme in the catecholamine biosynthesis. PKA acts by phosphorylating TH (Zigmond et al., 1989) or CREB, which is the major transcript factor for TH gene (Lewis-Tuffin et al., 2004). In the rat brain, the inhibition of PDE stimulates TH activity (Kehr et al., 1985) and increases the release of noradrenaline and dopamine in vitro (Schoffelmeer et al., 1985 and Yamashita et al., 1997). In addition, in spontaneously hypertensive rats (SHR), a widely studied model for ADHD has demonstrated a reduced expression of TH (King et al., 2000 and Wu et al., 2010). Based on this evidence, it is possible that the impairment in the cAMP/PKA cascade contributes to the reduction in the catecholaminergic function that, in turn, is strongly associated

with the hyperactivity phenotype (O’Malley and Nanson, 2002). In not addition to the well-documented role of catecholaminergic dysfunction, other factors such as a deficient ATP production may play role in the pathophysiology of hyperactivity (Russell et al., 2006). Interestingly, the administration of vinpocetine increases ATP levels in the rat’s cortex (Rosdy et al., 1976) and in astrocyte cultures (Gabryel et al., 2002). Finally, PDE1 inhibition caused by vinpocetine has also been reported to promote elevation of cGMP levels, which activates the cGMP-dependent protein kinase G (PKG) (Medina, 2011b). Although there are no studies associating cGMP levels and hyperactivity, it is not possible to discard that increased cGMP level significantly contributes to the vinpocetine-mediated amelioration of hyperactivity in ethanol-treated animals. Some studies have proposed the use of PDE inhibitors as neuronal plasticity enhancers (Medina, 2011b, Navakkode et al., 2004 and Puzzo et al., 2008). Neuronal plasticity entails functional changes in the efficacy of excitatory and inhibitory connections (e.g., synaptic strength), structural changes in the shape and size of synapses and in the physical connectivity of networks.