Investigation of the neuronal activity in the different functional columns of periaqueductal gray matter in response to a predatory threat and a predatory context

Abstract

Periaqueductal gray matter (PAG) is involved in behavioral responses related to innate and learned fear. These involvements were verified by several methods, among them, indirect markers for neural activity, lesions, inactivations through specific receptor antagonists, activations of different modalities, and through the recording of neuronal activity by chronic implantation for extracellular registration. However, there are few studies of extracellular activity in animals experiencing fear. In one study, the flight and risk assessment behavior were related to an increased electrical activity of the dorsal PAG in the mice. In another, in rats, it was shown an increase in electrical activity in about half of the cells in dorsal and ventral PAG during exposure to predator odor, albeit PAGvl cells activity increase was lower and shorter in duration. In none of these studies were a natural predator used to evoke fear reactions as strong as a cat evokes in a rat. In addition, PAG functional columns have not been systematically described nor their neuronal activities compared between experimental conditions (i.e., safe environment, cat exposure and predatory context). This work aims to relate the neuronal activities of PAG functional columns with the above-mentioned experimental conditions and with the behavioral aspects of the anti-predatory response (eg, freezing and risk assessment). In addition, we will try to verify possible differences in the pattern of cellular activity between the columns along its rostral-caudal axis. Preliminary results of this project indicate the existence of 4 types of behaviors in dorsal PAG cells: cells that increase activity during predator exposure, cells that increase activity during predatory conditions, cells that increase activity in both conditions, and one group of neurons that are indifferent to the experimental condition. (AU)