Figure 2. Microinjection of 5-hydroxytryptamine (5-HT) into T4 IML elicited thermogenic, respiratory and cardiovascular responses.

Microinjection of 5-HT into the right T4 IML (ipsilateral to the recorded nerve) increased brown adipose tissue (BAT) sympathetic nerve activity (SNA; peak: +381% of control), expired CO₂ (peak: +0.2%), and heart rate (HR, peak: +34 beats min⁻¹). Due to the long latency to onset of the 5-HT response and the variability in BAT temperature over long periods of time, responses to microinjection of 5-HT ipsilateral to the BAT from which temperature was recorded were not performed. Vertical scale bar in BAT SNA tracing represents 100 μV.