27 June 2000

Who Did You Sleep With Last Night?

Love is chemical and so, it seems, is remembering it - at least if you're a mouse according to a report out in 'Nature' magazine today. Male mice missing certain brain proteins cannot recall which females they have had sex with. A certain missing gene means their ‘social’ memory fails them. Mice meetings are dominated by smell. Females release pheromones that males use to tell their friends from their mates but in order to turn these smells into memory they need the presence of the neurochemical 'oxytocin'. Researchers at Emory University, Georgia, USA, experimenting on mice have shown that without oxytocin male mice cannot even recognise females they met a few minutes earlier. But in all other aspects their memories are intact. If these mice were men, they would be able to recite your telephone number but would not remember if they had slept with you. Normal male mice gradually lose interest in a female that rejects their advances, only perking up when one smelling different comes along. But male mice unable to produce oxytocin could not take the hint: they were just as eager every time they were introduced. Oxytocin injections seemed to restore memory, they then quickly learn to ignore females who have previously refused them. This particular study analysed brief encounters between males and females brought out of individual cages and then separated again after a few minutes. But James Winslow leading the research says other, unpublished, work shows that the social amnesia in oxytocin knockout mice also extends to long-term partners. "They behave as if they have never seen each other before," he remarks. Related Sites: www.nature.com