Hormonas

Professor Barry Keverne
|Sub-Department of Animal Behaviour, Department of Zoology, University of Cambridge. |
|The information humans receive from their nose is rarely of vital significance and although perfumers and masters of wine have developed a large vocabulary of |
|descriptors, most of us categorise odoursinto pleasant or unpleasant. Not surprisingly therefore, most of our olfactory receptor genes are non-functional |
|pseudogenes. Rodents, on the other hand, not only have a vast repertoire of olfactory genes (1000-1500) but also possess two additional sets of receptors in the |
|vomeronasal organ that is specialised for pheromone reception.|
|Strange males |
|The reproductive biology of rodents is strongly influenced by chemical cues, both in the context of behaviour (signalling pheromones) and reproductive |
|endocrinology(primer pheromones). An important effect of primer pheromones, observed in the female, is the control of oestrus. This occurs in a number of |
|species by invoking the onset of puberty and the onset of oestrus after a period without ovarian cycles. |
|A special case of oestrus control which occurs in the mouse and a few other rodentspecies, is the olfactory block to pregnancy. This was first described by |
|Hilda Bruce in 1959 who found that newly mated female mice returned to oestrus if they were exposed to strange males within 72h of the initial mating. The fact |
|that pregnancy block cannot occur after implantation of the embryo suggests that the effect of male primer pheromones is on the pre-implantation hormonalstatus.|
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|In both the block to pregnancy and the induction of oestrus, the primary endocrine change is a fall in serum prolactin. Evidence that prolactin is the hormone |
|mainly responsible for pregnancy block comes from experimentswhich show that restricted exposure of female mice to primer pheromones coincident with prolactin |
|surges, following mating, blocks pregnancy. |
|Where do pheromones act?|
|In parallel to the common neuroendocrine mechanisms for oestrous induction, all of the pheromone effects involve the vomeronasal organ (VNO), an accessory |
|structure in the nose. Damage of the vomeronasal organ or to its neural processing centre, the accessory olfactory bulb (AOB), prevents female odours from |
|inducing anoestrus and male odoursfrom inducing oestrus, accelerating puberty onset, and blocking pregnancy. These pheromones are non-volatile peptides, hence |
|females must make contact with male urine to stimulate the sensory receptors in the VNO. Pheromone information received in the AOB is relayed to a group of nerve|
|cells in the arcuate nucleus of the hypothalamus, at the base of the brain, which secrete dopamine; apowerful regulator of the production of prolactin from the |
|pituitary gland. |
|Why not all? |
|The...