The β3-Adrenoceptor is insensitive to the commonly used ß-antagonists and has often been referred to as the 'atypical' ß-Adrenoceptor. Mouse β3-Adrenoceptor has two known splice variants, isoforms β3a-Adrenoceptor and β3b-Adrenoceptor. Both isoforms are expressed in white and brown adipose tissues.3 The β3b-Adrenoceptor is highly exspressed in brain.The β3- Adrenoceptor has been found to play a key role in the lipolytic action of catecholamines.