White adipose tissue plays an integral role in energy metabolism and is governed 
by endocrine, autocrine, and neural signals. Neural control of adipose 
metabolism is mediated by sympathetic neurons that innervate the tissue. To 
investigate the effects of this innervation, an ex vivo system was developed in 
which 3T3-L1 adipocytes are cocultured with sympathetic neurons isolated from 
the superior cervical ganglia of newborn rats. In coculture, both adipocytes and 
neurons exhibit appropriate morphology, express cell-type-specific markers, and 
modulate key metabolic processes in one another. Lipolysis (stimulated by 
beta-adrenergic agents) and leptin secretion by adipocytes are down-regulated by 
neurons in coculture, effects apparently mediated by neuropeptide Y (NPY). 
Secretion of NPY by neurons is up-regulated dramatically by the presence of 
adipocytes in coculture and appears to be mediated by an adipocyte-derived 
soluble factor. Insulin, an antilipolytic agent, down-regulates NPY secretion. 
Our findings suggest that an adipocyte-derived factor(s) up-regulates the 
secretion of NPY by sympathetic neurons, which, in turn, attenuates lipolytic 
energy mobilization by adipocytes.