Opiate receptor autoradiography in fasting rats

: The discovery of opiate receptors and endogenous opiates within the brain has led to a variety of speculations concerning the physiological significance of these peptides. Opioid receptor antagonists, such as naloxone and naltrexone, have been shown consistently to reduce the consumption of food in many situations in different animal species. This study was undertaken to examine the modification of opiate receptors in hypothalamus and in medulla oblongata of fasted rats (72 h). In this condition, in which several authors observed an activation of opiate system, we describe a decrease in the number of 3H-naloxone binding sites that could indicate an homeostatic receptor down-regulation.