Hypothalamic dopamine signaling regulates brown fat thermogenesis

Dopamine signaling is a crucial part of the brain reward system and can affect feeding behavior. Dopamine receptors are also expressed in the hypothalamus, which is known to control energy metabolism in peripheral tissues. Here we show that pharmacological or chemogenetic stimulation of dopamine receptor 2 (D2R) expressing cells in the lateral hypothalamic area (LHA) and the zona incerta (ZI) decreases body weight and stimulates brown fat activity in rodents in a feeding-independent manner. LHA/ZI D2R stimulation requires an intact sympathetic nervous system and orexin system to exert its action and involves inhibition of PI3K in the LHA/ZI. We further demonstrate that, as early as 3 months after onset of treatment, patients treated with the D2R agonist cabergoline experience an increase in energy expenditure that persists for one year, leading to total body weight and fat loss through a prolactin-independent mechanism. Our results may provide a mechanistic explanation for how clinically used D2R agonists act in the CNS to regulate energy balance.

T1 efficacy of EVP-ABD: a potential manganese-based MR contrast agent for hepatic vascular and tissue phase imaging

PURPOSE

To evaluate the T1 efficacy of EVP-ABD, a new manganese (Mn)-based contrast agent, for vascular and liver tissue enhancement in comparison with currently approved agents.

MATERIALS AND METHODS

Ten Yorkshire pigs (body weight, 26 -46 kg) were used for the efficacy evaluation, nine for kinetic T1 evaluation (three each agent) and one for post EVP-ABD imaging. With a fast imaging scheme to monitor T1 values of blood and liver, 10 micromol/kg EVP-ABD was injected intravenously and compared with gadopentetate dimeglumine (Magnevist, GdDTPA) and mangafodipir trisodium (Teslascan, mangafodipir trisodium) at routine clinical dosages. All were imaged with 3D T1 Gradient Recalled Echo (GRE) sequence (TR/TE/alpha = 3.8/1.6/25 degrees ) prior to and 10 minutes post injection using a 1.5-T whole-body scanner. Additional high-resolution 2D liver images (TR/TE/alpha = 50/4.6/40 degrees ) and arterial phase images of the upper aorta were acquired from the pig for post EVP-ABD imaging.

RESULTS

At 10 micromol/kg, EVP-ABD provided a dramatic decline in blood T1, comparable to 0.1 mmol/kg GdDTPA, followed by a rapid return to blood baseline T1 values. In addition to the blood enhancement phase, EVP-ABD achieved a 70% reduction in liver T1 within 2 minutes postadministration, with an imaging window of at least 2 hours. A substantially improved signal-to-noise ratio (SNR) was observed in both the 2D and 3D liver images postcontrast.

CONCLUSION

EVP-ABD demonstrated peak vascular enhancement similar to GdDTPA and prolonged specific liver enhancement exceeding mangafodipir trisodium. EVP-ABD has favorable T1 enhancing characteristics with the potential to allow for a comprehensive liver evaluation.