More recently, a novel area of investigation has emerged with the development of optogenetic approaches to manipulate specific neuronal populations in live animals (Fowler and Kenny, 2012). For example, light-mediated phasic activation of dopaminergic neurons in the VTA produced a place preference in a CPP paradigm (Tsai et al., 2009) and the specific light-activation of cholinergic neurons from nucleus accumbens reduced cocaine reward (Witten et al., 2010). The specific manipulation of mu, delta or kappa receptor expressing neurons will be of great interest towards understanding neuronal connectivity and plasticity while addiction develops. Within this line, non-invasive neuroimaging and functional connectivity techniques, now developed in small rodents, offer promises in translational medicine (Dalley et al., 2009; Jasinska et al., 2013), and neuroimaging of opioid receptor and peptide genetic mutants may provide invaluable information towards understanding the human disease.
