Effects of both a melatonin agonist and antagonist on seasonal changes in body mass and energy intake in the garden dormouse.
BACKGROUND
Many physiological functions including nycthemeral rhythm, reproductive cycles, body temperature and body mass are controlled by photoperiodic changes in different species. In the hibernating garden dormouse, both energy intake and body mass increase with the duration of the night. This seasonal mass gain is spontaneous and reversible.


OBJECTIVE
We have studied the occurrence of the increase of body mass by taking into account the endogenous variations of melatonin due to changing photoperiod or to pharmacological treatment.


RESULTS
A single daily administration of either a melatonin agonist or antagonist just before night mimics the short day and long day effects, respectively. Compared to the control animals (natural photoperiod), the mass gain was greater and occurred earlier in animals under short days (6 h light (L)/18 h dark (D)) and in those receiving the melatonin agonist (S 20304). The animals treated with the antagonist (S 20928) during the same period exhibited no mass gain and their response was similar to that of the long-day group (16L/8D). Solely agonist treatment acted on metabolic rate.


CONCLUSIONS
These results demonstrate that the duration of melatonin-receptor exposure per day determines the onset of seasonal obesity in garden dormice and, on the other hand, that restriction of melatonin-receptor exposure by pharmacological treatment prevents it.
Le Gouic
S
S
URA CNRS 1937, UPS, CHU Rangueil, Toulouse, France.
Delagrange
P
P
Atgié
C
C
Nibbelink
M
M
Hanoun
N
N
Casteilla
L
L
Renard
P
P
Lesieur
D
D
Guardiola-Lemaitre
B
B
Ambid
L
L
D000818:Animals; D001835:Body Weight; D002940:Circadian Rhythm; D002149:Energy Intake; D004734:Energy Metabolism; D008297:Male; D008550:Melatonin / Q000819:agonists* / Q000037:antagonists & inhibitors* / Q000502:physiology; D009043:Motor Activity; D009765:Obesity; D010101:Oxygen Consumption; D017440:Photoperiod; D012377:Rodentia / Q000502:physiology*; D012621:Seasons
D008550:Melatonin