the memory trace is sufficiently changed as to make the familiar
male that mated be now treated as strange (Kaba et al., 1988).
If the female is allowed to remain pregnant (21 days) the memory
duration is foreshortened and its circuitry made available to
new memory formation at post-partum oestrous. This foreshortening
of recognition memory by pregnancy may be duplicated
by administering the hormones of pregnancy (Kaba et al., 1988).
Since pregnancy increases nerve growth factors in saliva, which
enters the VNO during licking and grooming, this may account
for the increased neurogenesis observed in the VNO. Pregnancy
is also a period when female mouse urine contains high levels
of MUPs (lipocalins), which promote generation of vomeronasal
(V2R) stem cells, and accelerate their turnover. This provides an
example of how neural pheromone memory is adapted to ensuring
reproductive success of the female by enhancing receptor turnover
and providing a new template for re-establishment of recognition
memory according to female endocrine state.