Poster Presentation The International Congress of Neuroendocrinology 2014

The “ram effect”: a model for new insights into how the activity of the gonadotropic axis can be modulated by socio-sexual interactions. (#275)

Claude FABRE-NYS 1 , Rex Scaramuzzi 2 , Claude Fabre-Nys 1
  1. INRA Centre Val de Loire, NOUZILLY, France
  2. 2Department of Comparative Biological Sciences, Royal Veterinary College, South Mimms, UK


The introduction of a sexually active ram to a group of sexually inactive ewes stimulates ovarian activity, a phenomenon known as the "ram effect" discovered in Australia in 1944 (1). A similar “male effect” exists in a number of domestic and wild ungulates and is probably an adaptation to predation. In this presentation I will review recent progress on the understanding of central mechanism involved in the “ram effect”. The effect of a ram can be partly mimicked by its odour and is due to the immediate stimulation of the secretion of LH and oestradiol that eventually induce an LH surge (2). Mean plasma concentrations of oestradiol are elevated (> 2pg/mL) for 14.5 ± 0.86h before the LH surge. An exception is a minority of ewes that have a precocious LH surge (within 4h) and no increase in oestradiol just before. The main olfactory system and the cortical nucleus of the amygdala are critical brain structures and their inactivation by lesion or local lidocaine inhibits the stimulatory effect of ram odour (3). Sexual experience has a role because cFos immunoreactivity after exposure to a ram or ram odour is lower in sexually naïve ewes (4) compared to experienced ewes (5) and their GnRH and tyrosine hydroxylase neurons remain inactive. In adult ewes kisspeptin neurons from the arcuate and preoptic regions are involved because both populations contain a significantly higher proportion of neurons immuno-reactive for both kisspeptin and cFos two hours after exposure to a ram (6). In adult ewes, the male and to a lesser extent its odour induce an increase in noradrenaline in the posterior preoptic area (7) and pharmacological modulation of this system modifies LH secretion in response to the male or male odour. This noradrenergic activation could be responsible for the precocious LH response.

  1. 1 Underwood E et al 1944, Journal of Agriculture of Western Australia 11, 135–143.
  2. 2 Poindron P et al 1980 Physiology and Behavior 25, 227–236.
  3. 3 Gelez H, Fabre-Nys C. 2004, Horm Behav;46:257–71.
  4. 4 Chanvallon A , Fabre-Nys C. 2009 , Behav Brain Res 205, 272-279.
  5. 5 Gelez H, Fabre-Nys C. Neuroscience 2006;140:791–800
  6. 6 Ghenim et al 2012 2nd World Conference on Kisspeptin Signaling in the Brain P 41
  7. 7 Fabre-Nys C et al 2005, Horm Behav, 48, 99.