Behavioral effects induced by intracisternally injected ACTH and MSH.

TLDR: This report deals with the efforts to identify the optimal amino acid sequence that evokes a complex behavioral syndrome and with the preliminary attempts to localize the site of action of these polypeptides.

Abstract: Our experiments began several years ago as a by-product of studies on the mechanism of the eosinopenic action of ACTH. The results of previous experiments convinced us that the eosinopenia caused by ACTH stemmed from its action on hypothalamic structures which had been shown to control the blood eosinophils.l-O To test this working hypothesis we injected dogs intracisternally (i.c.) with a commercial preparation of ACTH. We not only found that the eosinopenic action of ACTH was more pronounced after intracisternal than after intravenous injection,'O but we were fortunate to observe a complex behavioral syndrome, unfamiliar to us, which warranted further investigation." Most of the dogs given ACTH i.c. exhibit apparently normal behavior for about half an hour. Thereafter all animals become apathetic and exhibit diffuse muscular tremors which, a t this time, are more marked in the limbs. The rhythm of respiratory activity assumes a peculiar characteristic which will be described in more detail. The dogs are drowsy, yawn frequently and after about one hour they start to stretch in the way they usually do when they awake from physiological sleep (FIGURE 1). The intervals between successive stretching acts become shorter and shorter until a stretching act begins immediately after the preceding one (stretching crisis). Despite this peculiar behavior the dogs seem to remain in contact with the environment, as they are responsive to calls and perform normal activities without fear or aggressiveness. Occasionally some animals exhibit sialorrhea. The stretching activity persists approximately 24 to 72 hours according to the amovnt of ACTH injected and terminates with complete reintegration of normal behavior. Even when given chronically i.c., crude ACTH preparations are devoid of toxicity and on successive administrations they maintain the same degree of activity. This report deals with our efforts to identify the optimal amino acid sequence that evokes such a syndrome and with our preliminary attempts to localize the site of action of these polypeptides.