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SEASONALITY AND NEUROENDOCRINOLOGYSEASONALITY AND NEUROENDOCRINOLOGYADVANCING A SHORT NIGHT SIGNAL DOES NOT NECESSARILY STOP OVARIANACTIVITY EARLIER IN THE EWE.Michael Guerin, Jim Deed and Colin MatthewsDepartment ofObstetrics and Gynaecology, The University ofAdelaide, Adelaide South Australia 5000AIMSWe have proposed that the signal for the cessation ofovarian activity in seasonal breeding ewes is light coincident with an.afternoon-located sensitive phase ofthe circadian pacemaker. In earlier studies when similar 8-week treatments. o~ short mghts(which advance the afternoon portion ofthe pacemaker into the light) have been utilised.we have rep~rted CO~ICtingresultson the timing ofoestrus offset (1 )(2). In this study we have provided 8 weeks ofshort mghts at tw~ different ~es, ~n~commencing four weeks earlier than the other, to examine for any effect on the timing ofthe cessanon ofovanan actiVIty.METHODSThree groups of6 mature Romney Marsh ewes were established at the Waite Campus ofthe ~niversi~ ofAdelaide in early1998. Group 1 remained outside under natural conditions throughout. Group 2 was br~ught mto envrronment c?ntrolledrooms and subjected to eight weeks ofshort night photoperiod (10D:14L) from 21 Apni. Group 3 was brou~ht m andsubjected to eight weeks ofshort night photoperiod (10D:14L) from 21 May. At the end ofeach 8-week penod Groups 2 & 3were subjected to long night photoperiods (14D:lOL) until 21 December 1998 when both groups were paddocked.All ewes were blood sampled twice a week for progesterone determinations to monitor ovarian activity throughout. ?n twooccasions during short night treatments and three during long night treatments all ewes were blood sampled over 2 mghts. Thefirst night under treatment conditions to monitor endogenous melatonin elevation and the second night under acutely extendeddarkness where melatonin acts as a marker for pacemaker activity.RESULTSThere were no differences between the groups in the timing ofthe mid-year cessation ofovarian activity (see Figure 1). Thetiming ofthe onsets and offsets ofinduced ovarian activity for Groups 2 &3 were not different. The measure~ents ofendogenous melatonin demonstrated that all animals in Groups 2 & 3 correctly perceived the short and long mght treatments.The marker ofpacemaker activity indicated that the short night treatments advanced the afternoon portion ofthe pacemakerinto the light.OutsideControlGroupNATURAL PHOTOPERIOD: 1 I•AIMSORAL MELATONIN ADMINISTERED TO CYCLING MARES IN AUTUMN DOES NOTADVANCE ANOESTRUS.METHODSM Guerin, J Deed, R Woodward*, D Washington* and C MatthewsDepartment ofObstetrics and Gynaecology, *Department ofAnimal ScienceThe University ofAdelaide, Adelaide South Australia 5000We have proposed that the timing for seasonal breeding is dependent on the correct sequence oflight anddark/melatonin signals to the endogenous circadian pacemaker. Studies in the ewe indicate there is an aftemoonlocatedsensitive phase ofthe pacemaker that sets up the reproductive system when light is coincident withitin theshort days ofspring/summer. The same sensitive phase then directly signals the onset ofoestrus when it iscoincident with darkness/melatonin in the lengthening days ofautumn (1). Exogenous melatonin in the afternoon,not the morning, will mimic long nights to maintain existing ovarian activity (2) and will initiate new ovarianactivity in ewes already primed with short nights (3).Exogenous melatonin, in the afternoon not the morning, has been shown to inhibit the effect ofadditional artificiallight that normally advances the time ofseasonal breeding in the horse mare (4). From studies ofmelatonin as amarker for the endogenous circadian pacemaker we have proposed that the mare may use a similar basicmechanism to time seasonal breeding as the ewe (5). Since the mare is considered to be a "long day" breeder, theadministration ofexogenous melatonin should be inhibitory to ovarian activity. In this study we administered oralmelatonin, in the afternoon or morning, to mares during the autumn to see ifeither treatment could mimic darknessand advance anoestrus.In late March 1999 three groups offive Standardbred mares were established at the Roseworthy Campus ofTheUniversity ofAdelaide (latitude 35°S). All mares were confirmed in oestrus, and ovulating, by ultrasound scanningand blood progesterones. Commencing on 30 March two groups were orally administered a daily 12 mgm dose ofmelatonin, in a 1 ml solution, given at either 30 mins prior to sunrise or 4 hrs prior to sunset. The dose given hadpreviously been shown to elevate plasma melatonin in the horse to normal nighttime levels, or greater, for at least 5hours. All mares were blood sampled twice weekly throughout and progesterone determinations were performed tomonitor ovarian activity. Anoestrus was taken as the date ofthe last confirmed ovulation for the season.; SHORT NIGHTS ~LONG NIGHTSNATURALRESULTSGrouplGroup 3: SHORT NIGHTS:: I I :LONG NIGHTSNATURAL____L~~ MA~_l!~ i JULY i AUG 1 SEPT I ocr I NOV I DEC I JAN !Figure 1. The ovarian activityfor the three groups during the course ofthe experiment. The shaded blocksillustrate the periods ofextended cyclic pattern as determined by twice-weekly plasma progesterone.CONCLUSIONSA short night signal (light on the afternoon portion ofthe pacemaker) four weeks earlier than natural oestrus cessation time didnot alter the timing, however it still provided the priming signal for induced ovarian activity in subsequent long nights. Thecircadian mechanism that times the offset ofovarian activity requires further investigation.Guerin MV & Matthews CD. (1998) 1. BioI. Rhytluns 13,60-69Guerin MV, Deed JR & Matthews CD. (1998) Proc. Aust. Soc. Reprod. BioI. 29,36(Acknowledgment. This research was supported by a Large ARC Grant to Matthews and Guerin)There were no differences in the timing ofanoestrus between the 3 groups. The Control Group ceased ovarianactivity on 18 May (2:19.5 days), the Morning Melatonin Group on 24 May (±19.6 days) and the AfternoonMelatonin Group on 15 June (± 38.4 days).CONCLUSIONSAlthough oral melatonin in the afternoon has been shown to block light advancing the onset ofoestrus (4), in thisstudy it has failed to act as darkness to advance anoestrus. It is possible that the signal to cease ovarian activity wasperceived before treatments began and the treatments were insufficient to alter the outcome. Alternatively, with themare's and the ewe's natural ovarian responses to increasing darkness different (the mare is normally anoestrousover winter and the ewe oestrous) it may be that melatonin has a different role in the timing events ofseasonaloestrus between the two species. .REFERENCES(1) Matthews CD, Guerin MV and Napier AJ (1995) 1. BioI. Rhythms 10,308-318(2) Guerin MV, Deed JR & Matthews CD. (1998) Proc. Aust. Soc. Reprod. BioI. 29, 36(3) Guerin MV, Deed JR & Matthews CD. (2000) Proc. Aust. Soc. Reprod. BioI. 31,(4) Palmer E and Guillaume D (1992) Anim. Reprod. Sci. 28, 21-30(5) Guerin MV, Deed JR, Kennaway DJ and Matthews CD (1995) 1. Pineal Res. 19,7-1526 27