In conjunction with the characterization of physiological responses, neuronal activities stimulated by central CART has been investigated by structural studies for the purpose of identifying brain areas potentially crucial for CART-induced anorectic effects. Following i.c.v. CART administration, temporal expression patterns of the immediate early gene c-Fos (Dragunow and Faull, 1989; VanElzakker et al., 2008), which has been adopted to depict neuronal firing of actions potentials (Dragunow and Faull, 1989; VanElzakker et al., 2008), were found to concentrate in the hypothalamic and brainstem structures implicated in the central regulation of feeding (Vrang et al., 1999b; Zheng et al., 2002). In the hypothalamus in particular, high density of Fos expression was located in the PVN and the posterior DMH, while considerable Fos-IR cells were also identified in the Arc and SO. In the brainstem, Fos-positive cell nuclei were also concentrated in the PBN and, more importantly, in the NTS, which serves a key sensory relay nucleus with reciprocal connections with numerous forebrain and brainstem structures (Vrang et al., 1999b). Such CART-induced Fos activation in the NTS has been indicated independent from possible secondary effects triggered by chemo-activation at the area postrema (AP) directed to the NTS, as the chemosensitive neurons in the AP were devoid of Fos-IR cells (Vrang et al., 1999b). Moderately high Fos expression was also detected in cerebral nuclei associated with autonomic functions and energy balance (Smith and DeVito, 1984; Vrang et al., 1999b), including the central nucleus of the amygdala, where neuronal projections also reciprocally link with the PVN of the hypothalamus and the PBN and NTS of the hindbrain (Hopkins and Holstege, 1978; Holstege et al., 1985). The widespread Fos expression pattern elicited by forebrain i.c.v. CART has been demonstrated to encompass an anatomical continuum of neuronal activations across the cerebrum, hypothalamus and brainstem (Vrang et al., 1999b). The paralleled effects on appetite inhibition and metabolic regulation are believed to portray an integrated outcome of the interactions between central CART-interfered pathways residing primarily within the hypothalamic and brainstem neurons. For instance, as aforementioned, the administration of CART combined with other neuromodulatory such as CCK in mice generated synergistic effects on food intake and locomotion, while displaying concomitant enhancement in the number of Fos-positive neurons compared to injecting each peptide alone (Maletinska et al., 2008; Pirnik et al., 2010). The additive effect on Fos immunoreactivity was especially notable in the target areas common to both peptides, namely the hypothalamic PVN, DMH, VMH and Arc, as well as NTS at the brainstem (Maletinska et al., 2008; Pirnik et al., 2010), wherein the CCK-related satiety signals transmitted to the hindbrain were suggested to be further regulated by leptin action integrated in the Arc as well as neuronal signals from both PVN and LHA (Broberger, 2005; Morton et al., 2005; Maletinska et al., 2008).