Calcitonin microinjection into the periaqueductal gray impairs contextual fear conditioning in the rat

We have previously proposed that behavioral alterations induced by salmon calcitonin in the rat provide an animal model of depression. As depression is characterized by context-related anxiety, behavioral inhibition and alterations in memory processing, we tested the effects of microinjections of salmon calcitonin into the periaqueductal gray matter (PAG) on contextual fear conditioning in the rat. In a first experiment, calcitonin or saline were microinjected into the PAG before the training phase and before the testing phase of a conditional fear testing procedure. In a second experiment, calcitonin or saline were injected before and immediately after the training phase. When given before the training phase, calcitonin had no effects on immediate postshock freezing but produced significant deficits in contextual freezing (24 h after footshock) in comparison with controls. When given immediately after the footshocks, calcitonin impaired contextual fear. These results suggest that calcitonin receptor stimulation in the PAG can alter the acquisition and consolidation of contextual fear behavior processes.