Neurochemical characterization and sexual dimorphism of projections from the brain to abdominal and subcutaneous white adipose tissue in the rat.

Retroperitoneal white adipose tissue (rWAT) and subcutaneous (inguinal) white adipose tissue (iWAT) are both innervated and regulated by sympathetic efferents, but the distribution and identity of the cells in the brain that regulate sympathetic outflow are poorly characterized. Our aim was to use two isogenic strains of a neurotropic virus (pseudorabies, Bartha) tagged with either green or red fluorescent reporters to identify cells in the brain that project to rWAT and/or iWAT. These viruses were injected into separate WAT depots in male and female Sprague Dawley rats. Retrogradely labeled neurons in the CNS were characterized by immunohistochemistry and PCR. For the latter, laser capture of individual virally labeled neurons was used. All virally labeled brain regions contained neurons projecting to either and both WAT depots. Neurons to abdominal fat were the most abundant in males, whereas females contained a greater proportion of neurons to subcutaneous via private lines and collateral branches. Retrogradely labeled neurons directed to WAT expressed estrogen receptor-α (ERα), and fewer neurons to subcutaneous WAT expressed ERα in males. Regardless of sex, projections from the arcuate nucleus were predominantly from pro-opiomelanocortin cells, with a notable lack of projections from agouti-related protein-expressing neurons. Within the lateral hypothalamus, neurons directed to rWAT and iWAT expressed orexin and melanin-concentrating hormone (MCH), but male rats had a predominance of MCH directed to iWAT. In conclusion, the neurochemical substrates that project through polysynaptic pathways to iWAT and rWAT are different in male and female rats, suggesting that metabolic regulation of rWAT and iWAT is sexually dimorphic.

A pilot study on lipolytic effect of subcutaneous botulinum toxin injection in rabbits.

OBJECTIVE: To determine whether botulinum toxin type A (BTX-A) exerts a lipolytic effect by interfering with acetylcholine transmission at the cholinergic parasympathetic nerve endings. STUDY DESIGN: Fifteen male rabbits were divided into 3 equal groups: 1 control group (A) and 2 case groups (B and C). The abdomens of all rabbits were divided into a 3 x 3-square grid. The groups received 9 subcutaneous injections of 0.9% normal saline, 1 U BTX-A (group B) and 2 U BTX-A (group C), respectively. Four weeks later the entire grid was excised from the abdominal area. Hematoxylin-eosin-stained tissue was used for stereologic analysis to estimate cell surface and volume in 100 randomly selected cells. RESULTS: Gross thinning of subcutaneous fat and shattering and disappearance of fat globules were seen in both case groups. Fat cell volume was reduced by 65% in group B (p = 0.009) and 77% in group C (p = 0.009) compared to control animals. Fat cell surface also decreased by 51% in group B (p = 0.009) and 63% in group C rabbits (p = 0.009) compared to control animals. CONCLUSION: Our pilot animal study revealed a dose-dependent lipolytic effect of subcutaneous BTX-A injection.