The correlation between hypothalamic and midbrain biogenic amine content and the intensity of the emotional-defensive arousal in cats

Changes in levels of noradrenaline (NA), dopamine (DA), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in the medial hypothalamus and the midbrain central grey matter were determined and correlated with various levels of an emotional-defensive arousal in cats, evoked by an intrahypothalamic injection of carbachol. At the initial stage of excitation, 3 min after the injection of carbachol, the levels of NA, DA, and 5-HIAA in the medial hypothalamus increased, whereas in the central grey matter only the 5-HIAA level was elevated. During the maximum excitation (when the vocalization attained the peak level) the level of amines and 5-HIAA decreased in the medial hypothalamus; in the central grey matter only the levels of 5-HT and 5-HIAA declined. In the final phase of response, 5 min after the disappearance of vocalization, the 5-HT level in both structures increased. These results confirm the notion that the noradrenergic, dopaminergic and serotonergic systems participate in the central regulation of the emotional-defensive behavior, and show that the hypothalamus and midbrain play different roles in this regulation. The results also indicate that neurochemical mechanisms are similar in different types of emotional-defensive behavior. It seems that catecholaminergic systems play a stimulating role, while the serotonergic system inhibits the carbachol-induced defensive response.