Brown adipose tissue temperature responses following electrical stimulation of ventromedial hypothalamic and lateral preoptic areas or after norepinephrine infusion to long evans or sprague-dawley rats

Abstract

Thermoregulatory (brown adipose tissue temperature) experiments were conducted in age-matched anesthetized, male Sprague-Dawley andLong Evans rats kept at 37°C given unilateral electrical stimulation of the ventromedial hypothalamic nucleus or the lateral preoptic area or after intravenous infusion of norepinephrine HCl (50 μg/kg total dose). Unilateral electrical stimulation (0.5 ms pulses of 250 μA at 50 Hz for 30 s) of the ventromedial nucleus or lateral preoptic area caused significant rises (>0.6°C) of intrascapular brown adipose tissue temperature in the Long Evans group only. Norepinephrine infusion (0.1 ml/min for 10 min), or intravenous bolus injection of propranolol HCl (2.5 mg/kg) caused significant yet similar increases (>1.0°C) and decreases (>−0.3°C), respectively, of intrascapular brown adipose tissue temperature from pre-administration control temperatures in both Long Evans and Sprague-Dawley groups. The results demonstrate that intrascapular brown adipose tissue sensitivity towards exogenous norepinephrine or propranolol administration is similar between Sprague-Dawley and Long Evans rats acclimated to 21°C as determined by increases in temperature in the intrascapular brown adipose tissue pad. However, intrascapular brown adipose tissue thermogenesis of 21°C-acclimated Long Evans rats is also activated after CNS electrical stimulation of the ventromedial nucleus or lateral preoptic area, an activation not seen in Sprague-Dawley rats suggestive that the latter group has some inhibition of neural pathways that activate brown adipose tissue tissue thermogenesis.