The autonomic nervous system regulates fuel availability and energy storage in the liver, adipose tissue, and other organs; however, the molecular components of this neural circuit are poorly understood. We sought to identify neural populations that project from the CNS indirectly through multisynaptic pathways to liver and epididymal white fat in mice using pseudorabies virus strains expressing different reporters together with BAC transgenesis and immunohistochemistry. Neurons common to both circuits were identified in subpopulations of the paraventricular nucleus of the hypothalamus (PVH) by double labeling with markers expressed in viruses injected in both sites. The lateral hypothalamus and arcuate nucleus of the hypothalamus and brainstem regions (nucleus of the solitary tract and A5 region) also project to both tissues but are labeled at later times. Connections from these same sites to the PVH were evident after direct injection of virus into the PVH, suggesting that these regions lie upstream of the PVH in a common pathway to liver and adipose tissue (two metabolically active organs). These common populations of brainstem and hypothalamic neurons express neuropeptide Y and proopiomelanocortin in the arcuate nucleus, melanin-concentrating hormone, and orexin in the lateral hypothalamus and in the corticotrophin-releasing hormone and oxytocin in the PVH. The delineation of this circuitry will facilitate a functional analysis of the possible role of these potential commandlike neurons to modulate autonomic outflow and coordinate metabolic responses in liver and adipose tissue.autonomic nervous system | neuronal tracing | pseudorabies virus T he autonomic nervous system plays a prominent role in modulating carbohydrate and lipid metabolism. The original theories of sympathetic activation (1) proposed a body-wide increase in sympathetic outflow. However, later studies suggested differential sympathetic activation on specific organs through distinct autonomic projections, which permits more finely tuned control of metabolism (2, 3).The liver and adipose tissue play important roles in fuel storage and release. These organs respond to altered energy availability with a set of homeostatic responses mediated by humoral factors and autonomic outflow. For example, activation of hepatic sympathetic aminergic and peptidergic innervation increases glucose output and modulates fatty acid transport. Conversely, parasympathetic activity decreases hepatic glucose output and increases carbohydrate storage (4). Likewise, the sympathetic innervation of white adipose tissue induces lipolysis (5) and alters glucose uptake. Thus, in general, parasympathetic activity favors fuel storage, whereas sympathetic activity increases the fuel available for immediate use.Many CNS regions regulate autonomic outflow to hepatic or adipose tissue to influence peripheral energy homeostasis. In particular, the ventromedial hypothalamus (VMH), dorsomedial hypothalamus (DMH), lateral hypothalamus (LH), and nucleus of the solitary tract (NTS) (6)...