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.

Thermoregulatory (brown adipose tissue temperature) experiments were conducted in age-matched anesthetized, male Sprague-Dawley and Long Evans rats kept at 37 degrees C given unilateral electrical stimulation of the ventromedial hypothalamic nucleus or the lateral preoptic area or after intravenous infusion of norepinephrine HCl (50 micrograms/kg total dose). Unilateral electrical stimulation (0.5 ms pulses of 250 microA at 50 Hz for 30 s) of the ventromedial nucleus or lateral preoptic area caused significant rises (greater than 0.6 degrees 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 (greater than 1.0 degrees C) and decreases (greater than -0.3 degrees 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 degrees C as determined by increases in temperature in the intrascapular brown adipose tissue pad. However, intrascapular brown adipose tissue thermogenesis of 21 degrees 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 thermogenesis.