Effects of aggressive encounters on pineal melatonin formation in male gerbils (Meriones unguiculatus, Cricetidae)

Abstract

Pineal N-acetyl-transferase activity and radioimmunoassayable melatonin levels were determined in adult male gerbils subjected to aggressive encounters using the intruder-model. In the first experiment, a single encounter of 3 min was applied in the afternoon to intact and to animals with sympathetically denervated pineal organs. Compared with controls, both stressed groups demonstrated a drastic decrease in N-acetyl-transferase activity followed by a slow recovery. In both groups there also occurred a marked change in pineal melatonin content: in intact animals pineal melatonin levels were elevated immediately after the encounter; thereafter, melatonin values decreased. In animals bearing denervated pineal organs melatonin levels fell as a consequence of the encounter. In a second experiment, intact gerbils experienced four daily encounters of 1 min for one week. Thereafter the nocturnal formation of melatonin was studied. In comparison with untreated controls, the repeatedly stressed animals demonstrated a temporal delay in the rise of both N-acetyl-transferase activity and melatonin. Since the pineal organ is able to transduce events of the social environment into an endocrine message--as set forth by both our experiments--the pineal organ might play an important role within central processing of social stress.

Melatonin and aggressive behavior: A systematic review of the literature on preclinical and clinical evidence

“…An interesting experiment by Heinzeller et al 37 examined the effects of single and repeated aggressive encounters on the synthesis of MLT in the pineal gland. The authors found an elevation of MLT immediately at the end of the encounter, followed by a decline in the levels of the neurohormone.…”

The origin of REM sleep: A hypothesis.

“…Melatonin, a hormone produced by the pineal gland, is a substance that seems to have a special relationship to tonic immobility. Thus, as mentioned above, exposure to stress (e.g., aggression, temperature changes) increases melatonin production in a number of species (Heinzeller et al, 1988; Lynch & Deng, 1986). Moreover, the duration of tonic immobility correlates positively with the cycle of melatonin release in many species; these species are more susceptible to tonic immobility during the night (Hennig & Dunlap, 1977a, 1977b).…”

“…Melatonin is also implicated in the tonic immobility reaction. It has been found that exposure to aggression and stress increases melatonin production in a number of species (Heinzeller, Joshi, Nürnberber, & Reiter, 1988; Lynch & Deng, 1986). Similarly, melatonin injections directly potentiate the tonic immobility reaction (Hennig et al, 1979; Hennig, Harston, & Dunlap, 1980).…”

Melatonin in the Control of the Estrous Cycle of the Indian Desert Gerbil <i>(Meriones hurrianae: </i>Jerdon)

“…The unique social behavior and the ecological niche the species occupies may be other reasons for the varied results. In Mongolian gerbils the aggressive encounters are known to affect pineal biosyn thesis of melatonin [27]. The Indian desert gerbil too exhibits aggressive and conflict be havior [28].…”