Melatonin improves memory acquisition under stress independent of stress hormone release.
BACKGROUND
Animal studies suggest that the pineal hormone melatonin influences basal stress hormone levels and dampens hormone reactivity to stress.


OBJECTIVE
We investigated whether melatonin also has a suppressive effect on stress-induced catecholamine and cortisol release in humans. As stress hormones affect memory processing, we further examined a possible accompanying modulation of memory function.


METHODS
Fifty healthy young men received a single oral dose of either 3 mg melatonin (n = 27) or placebo medication (n = 23). One hour later, they were exposed to a standardized psychosocial laboratory stressor (Trier Social Stress Test). During stress, subjects encoded objects distributed in the test room, for which memory was assessed a day later ("memory encoding under stress"). Fifteen minutes following stress, memory retrieval for words learnt the day before was tested ("memory retrieval after stress"). Plasma epinephrine and norepinephrine levels, salivary free cortisol levels and psychological responses (attention, wakefulness) were repeatedly measured before and after stress exposure.


RESULTS
Melatonin specifically enhanced recognition memory accuracy of objects encoded under stress (p < 0.001). In contrast, 15 min after stress, when cortisol levels were highest, retrieval of memories acquired the day before was not influenced by melatonin. Moreover, melatonin did not influence stress-induced elevation of catecholamine and cortisol levels which in turn did not correlate with the effects of melatonin on memory.


CONCLUSIONS
The findings point to a primary action of melatonin on central nervous stimulus processing under conditions of stress and possibly on memory consolidation and exclude any substantial suppressive action of the substance on hormonal stress responses.
Department of Clinical Psychology and Psychotherapy, Psychological Institute, University of Zürich, Binzmühlestrasse 14, Box 26, CH-8050 Zürich, Switzerland.
Ulrike
U
Rimmele
Maria
M
Spillmann
Carmen
C
Bärtschi
Oliver T
OT
Wolf
Cora S
CS
Weber
Ulrike
U
Ehlert
Petra H
PH
Wirtz
D000328:Adult; D000339:Affect / Q000187:drug effects; D000975:Antioxidants / Q000494:pharmacology*; D001007:Anxiety / Q000523:psychology; D001288:Attention / Q000187:drug effects; D002395:Catecholamines / Q000378:metabolism; D004311:Double-Blind Method; D004837:Epinephrine / Q000097:blood; D005080:Exercise Test; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism; D007858:Learning / Q000187:drug effects*; D008297:Male; D008550:Melatonin / Q000097:blood / Q000494:pharmacology*; D008568:Memory / Q000187:drug effects*; D009638:Norepinephrine / Q000097:blood; D011597:Psychomotor Performance / Q000187:drug effects; D021641:Recognition, Psychology / Q000187:drug effects; D013315:Stress, Psychological / Q000378:metabolism* / Q000523:psychology*; D014851:Wakefulness; D055815:Young Adult
D000975:Antioxidants; D002395:Catecholamines; D008550:Melatonin; D006854:Hydrocortisone; D009638:Norepinephrine; D004837:Epinephrine