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  • Title: Evidence for a circannual rhythm of reproduction and prolactin secretion in a seasonally breeding macropodid marsupial, the Bennett's wallaby (Macropus rufogriseus rufogriseus).
    Author: Brinklow BR, Loudon AS.
    Journal: J Reprod Fertil; 1993 Jul; 98(2):625-30. PubMed ID: 8410834.
    Abstract:
    Two groups of adult female wallabies were maintained in photoperiod-controlled rooms from June 1987 until August 1988. Group SSH was held on summer solstice photoperiods throughout the experiment; group SN was subjected to weekly stepwise simulated natural changes in photoperiod. Plasma melatonin concentrations reflected photoperiod with high concentrations during the dark phase in both groups. Group SN wallabies commenced oestrous cyclicity on 21 July (+/- 19 days, n = 6) entered reproductive quiescence on 14 February (+/- 10 days, n = 5) and recommenced cycling on 8 June (+/- 3 days, n = 4). Group SSH wallabies began cycling on 27 July (+/- 9 days, n = 7) at a time that was not significantly different from that of group SN. Three out of five of group SSH exhibited a spontaneous period of reproductive quiescence of between 59 and 70 days commencing between 3 December and 25 February. There was a highly significant difference between the transient plasma prolactin response to a dopamine antagonist during cycling and quiescent periods in both groups (P < 0.001) such that the response was increased during periods of quiescence. Our data support the hypothesis that prolactin is involved in the control of seasonal quiescence in the female Bennett's wallaby and demonstrate that spontaneous changes in reproductive state and prolactin can occur when animals are maintained on unchanging long photoperiods.
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