Sex- and time-dependent changes in neurochemical and hormonal variables induced by predictable and unpredictable...

Previous experiments have revealed sex-dependent effects of inescapable shock in rats. Behavior of male rats was more severely disrupted by inescapable shock than behavior of female rats. These sex differences were found after 1- and 24-hour intervals but not after a 72-hour interval. The present experiment was designed to study various physiological parameters at 1-, 4- and 24-hour intervals after inescapable footshock. The predictability of shock was manipulated by adding a compound light and tone stimulus that preceded shock presentation for one group but was not correlated with shock presentation for another group of subjects. Noradrenaline, dopamine, serotonin, and metabolites of these 3 transmitters were measured in the frontal cortex. Transient shock-induced increments in dopamine and metabolites of dopamine and serotonin were found, but the sex of the animal did not differentially affect this neurotransmitter response. In addition to neurotransmitter concentrations in the frontal cortex, levels of corticosterone were measured in plasma. The pituitary-adrenal axis was activated for a longer period in females than males after shock. The present data do not provide evidence that behavioral sex differences induced by inescapable shock are paralleled by sex differences in neurotransmitter activity. In addition, sex-dependent effects of predictability of shock on neurotransmitter activity were not detected. The relevance of the observed sex-dependent responses in the pituitary-adrenal system is discussed.