Difference in brown adipose tissue effector response and associated thermoresponsiveness of ventromedial hypothalamic (VMH) neurons of 21 degrees C vs. 4 degrees C acclimatized rats to scrotal thermal stimulation

Abstract

The present study was designed (1) to determine if scrotal thermal stimulation would activate brown adipose tissue (BAT) thermogenesis, indicated by increases in interscapular BAT temperature (TIBAT) of cold acclimatized (CA, kept at 4 degrees C for 4 weeks) and room temperature acclimatized rats (RA, kept at 21 degrees C for 4 weeks) and (2) to compare the thermoresponsiveness of VMH neurons of both groups to scrotal heating and cooling. VMH extracellular activity was recorded in male RA and CA Sprague-Dawley rats when scrotal temperatures (Tsc) were changed between 5-40 degrees C via localized thermode (3 mm2) along with measurements of TscS and TIBATS. The CA-group showed significant increases in TIBATS during scrotal cooling compared to respective TIBATS of the RA-group. The ratio of VMH warm responsive (WRN), cold responsive (CRN) and temperature non-responsive (TNRN) neurons in the CA-group changed compared to that in the RA-group as a greater percentage of CRNs occurred in the CA-group. Also, the thermoresponsiveness of individual VMH CRNs of the CA rats was significantly increased compared to VMH CRNs of the RA-group. The results indicated that localized scrotal cooling of CA-rats (not RA-rats) can activate BAT thermogenesis. Furthermore, VMH CRNs increased their thermoresponsiveness with chronic cold exposure which may be an important neuronal adaptive response for the subsequent enhanced BAT thermogenic effector response seen in that group.