R. Hudson et al., EFFECT OF PHOTOPERIOD AND EXOGENOUS MELATONIN ON CORRELATES OF ESTRUSIN THE DOMESTIC RABBIT, Journal of comparative physiology. A, Sensory, neural, and behavioral physiology, 175(5), 1994, pp. 573-579
It was the purpose of this study to test whether inhibition of estrus
in the rabbit by short photoperiod could be simulated by subcutaneous
implants of the pineal hormone melatonin. By measuring two non-invasiv
e and readily quantifiable correlates of estrus, emission of the so-ca
lled nipple-search pheromone and scent-marking behavior (chinning), it
was found that: 1. In intact does kept in stimulatory long photoperio
d, melatonin suppressed chinning but had no effect on emission of nipp
le-search pheromone. 2. In intact, melatonin-treated does which were r
eturned from inhibitory short day to stimulatory long day, chinning re
mained suppressed, whereas pheromone emission increased as for the veh
icle-treated, control does. 3. In ovariectomized does, estradiol admin
istration stimulated both pheromone emission and chinning whereas mela
tonin failed to suppress these effects. Thus, although the administrat
ion of melatonin had an inhibitory effect on chinning it failed to sup
press emission of the nipple-search pheromone and therefore failed to
fully simulate the effect of short photoperiod on these two correlates
of estrus. Several explanations for this discrepancy are considered,
including the possibility that melatonin is not the sole mediary of th
e photoperiodic response, and that at least in female rabbits, other p
ineal products may also play a significant role.