DIFFERENTIAL-EFFECTS OF NEUROKININ-1 RECEPTOR ACTIVATION IN SUBREGIONS OF THE PERIAQUEDUCTAL GRAY-MATTER ON CONDITIONAL AND UNCONDITIONAL FEAR BEHAVIORS IN RATS

Central neurokinin-1 (NK-1) receptors are thought to modulate aversion , whereas the periaqueductal gray matter (PAG) is a common pathway for the integration of fear behaviors. The authors determined whether inj ection of an NK-1 agonist (GR73632) into subregions of the PAC would a lter fear-related behaviors. Behavioral inactivity was increased by GR 73632 injected into the caudodorsal FAG or the dorsal raphe. Flight be havior induced by stimulation of the dorsal FAG or by a footshock was decreased after injection of GR73632 into the dorsal FAG. Rats that ha d 6 pairings of a tone with a footshock after injection of GR73632 int o the dorsal FAG displayed more freezing behavior than controls at the beginning of the session. However, there was no change in the shock- or the tone-induced freezing because some GR73632-treated rats, but no controls, froze during the baseline period. It is concluded that NK-1 receptors in the dorsal FAG modulate the unconditional but not the mn emonic aspects of fear behaviors.