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

We have previously proposed that behavioral alterations induced by salmon c alcitonin in the rat provide an animal model of depression, As depression i s characterized by context-related anxiety, behavioral inhibition and alter ations in memory processing, we tested the effects of microinjections of sa lmon calcitonin into the periaqueductal gray matter (PAG) on contextual fea r conditioning in the rat. In a first experiment, calcitonin or saline were microinjected into the PAG before the training phase and before the testin g phase of a conditional fear testing procedure. In a second experiment, ca lcitonin or saline were injected before and immediately after the training phase. When given before the training phase, calcitonin had no effects on i mmediate postshock freezing but produced significant deficits in contextual freezing (24 h after footshock) in comparison with controls. When given im mediately after the footshocks, calcitonin impaired contextual fear. These results suggest that calcitonin receptor stimulation in the PAG can alter t he acquisition and consolidation of contextual fear behavior processes. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.