Neural influences on trophic changes in brown adipose tissue during cold acclimation

Area of Science:

• Physiology
• Endocrinology
• Metabolism

Background:

• Brown adipose tissue (BAT) plays a key role in thermogenesis and energy expenditure.
• Cold exposure stimulates BAT growth and metabolic activity, involving complex regulatory mechanisms.

Purpose of the Study:

• To investigate the role of sympathetic innervation in the development and maintenance of cold-induced changes in BAT.
• To determine the specific involvement of sympathetic nerves in regulating uncoupling protein (UCP) and thyroxine 5 -deiodinase (TD) in BAT.

Main Methods:

• Unilateral and bilateral denervation of interscapular BAT in rats before or after cold acclimation (4°C).
• Measurement of BAT norepinephrine levels, total protein, mitochondrial GDP binding, UCP concentration, and TD activity.
• Assessment of changes following denervation during cold exposure.

Main Results:

• Denervation significantly reduced BAT norepinephrine levels.
• Cold-induced increases in total protein, mitochondrial GDP binding, and UCP concentration were slowed but not prevented by denervation.
• TD activity in denervated BAT remained very low (<10% of intact tissue) during cold acclimation.
• Denervation after cold acclimation led to rapid loss of TD activity and slower loss of UCP and protein.

Conclusions:

• Sympathetic innervation is essential for optimal cold-induced growth and maintenance of BAT hypertrophy.
• While other factors contribute, sympathetic nerves are required for the induction and sustained activity of TD in BAT.
• Sympathetic nerves play a critical role in regulating UCP levels and overall BAT function during cold adaptation.