Maternal behaviour itself can trigger the development of new neurons in the brain independent of whether the female was pregnant or has nursed, says a new study on adult, virgin rats.
In the study, virgin, or nulliparous, rats were exposed to foster pups each day until they began to exhibit maternal behaviour, including crouching over the young, grouping them, or retrieving them back to the nest.
Data from the study by researchers at Tufts University's Cummings School of Veterinary Medicine showed that the nulliparous rats exposed to pups have increased numbers of new neurons.
Previous research has found that exposure to young can stimulate maternal behaviour not only in rats, but also mice, hamsters, monkeys, and even humans.
Increased creation of new neurons, or neurogenesis, has also been shown during pregnancy and lactation in rodents and associated with maternal behaviour, but studies analyzing neurogenesis in nulliparous animals exhibiting maternal behaviour had not been done.
The area of the brain that was the focus of the present study was the subventricular region- a region involved in the production of cells that affect odor recognition and possibly recognition of young.
The researchers found increased numbers of new neurons in the subventricular zone in adult, nulliparous rats that behaved maternally compared with numbers in subjects that either were not exposed to young or exposed to young, but did not behave maternally.
What stimulates increased new neuron production in the nulliparous mothers is not known. One possibility is that the hormone prolactin, which stimulates both the onset of maternal behaviour as well as production of neurons during pregnancy, may play a role in the production of new neurons in nulliparous females exhibiting maternal behaviour.
However, this possibility remains to be investigated. A second possibility is that stimulation received from the young themselves may, in fact, play a crucial role in stimulating maternal neuron production.
The study was published in Brain Research Bulletin.