Researchers from China, France, Italy, and the United Kingdom, have created a model that shows exactly how, when a baby suckles at a mother's breast, it starts a chain of events that leads to a surge of the "trust" hormone oxytocin in their mother's brain.

The study focuses on the role of oxytocin, a hormone recently found be involved in the enhancement of trust and love in humans and animals. Oxytocin has long been known as the trigger that, when released into the blood, causes milk to be let down from the mammary gland. When oxytocin is released within the brain, it strengthens the bond between mother and child. However, to have these effects a very large amount must be released abruptly to cause a wave of the hormone to spread through the brain.

Previous studies on individual neurons have found no obvious way of modifying their behavior to garner the required large, regular pulses of oxytocin.

"For thirty years we have known that these pulses arise because, during suckling, oxytocin neurons fire together in dramatic synchronized bursts, but exactly how these bursts come about has puzzled us so far", said co-author Prof. Jianfeng Feng

Now, this team of experimental neuroscientists and theoreticians have found a likely answer. They show that in response to suckling, oxytocin cells start releasing oxytocin from their "dendrites" as well as from their nerve endings – this was unexpected because dendrites are usually thought of as the part of a neuron that receives, rather than transmits information.

The dendrites usually make up a weak network of connections between neurons. However, the researchers have shown that the release of oxytocin from the dendrites increases the communication between the neurons and triggers a positive-feedback on activity. This coordinates the "swarm" of oxytocin factories, producing massively intense and recurring bursts of release, arising in just the same way as a flock of birds or insects – a closely coordinated action developing without a single leader.

CITATION: Rossoni E, Feng J, Tirozzi B, Brown D, Leng G, et al. (2008) Emergent Synchronous Bursting of Oxytocin Neuronal Network. PLoS Comput Biol 4(7): e1000123. doi:10.1371/journal.pcbi.1000123