Project 17

Sexually stimulated neurogenesis in sheep; fact or fantasy?

It has long been assumed that the mammalian brain completes cell division during early life, but we now know that it continues in several regions, especially the olfactory system. New neurons originate from proliferating cells in the subventricular zone then migrate rostrally along a pathway known as the rostral migratory stream towards the main olfactory bulb. On arrival, they differentiate into local interneurons and functionally integrate into circuits.

The introduction of rams to anoestrous (seasonally reproductively inactive) ewes stimulates an almost instantaneous increase in luteinizing hormone, which under certain physiological conditions and in certain breeds of sheep is sufficient to reinstate reproductive activity. The neurological mechanism controlling this phenomenon, termed the ‘ram effect’, is currently unknown. However as exposure to male pheromones stimulates neurogenesis in female prarie voles (Fowler et al., 2002) it is likely that neurogenesis is also involved in this phenomenon. Furthermore the occurrence and magnitude of neurogenesis may be a key determinant of whether ewes ovulate or not in response to the ram effect.