Neuropeptide Y (NPY) is the most abundant peptide hormone of the central nervous system. It is involved in various processes including stress management, the development of anxiety behaviour and body weight regulation. A collaborative research group including scientists from the Max Planck Institute for Medical Research in Heidelberg has demonstrated using mice that intensive maternal care during infancy promotes the effect of NPY in the brain. As a result of receiving such care, the animals were also less anxious in adulthood and weighed more than their counterparts who had received less affection. The research group was able to show that the effect is explained by the maternal care which stimulated the persistent formation of certain NPY receptors in the forebrain.
Neuropeptide Y (NPY) assumes several key roles in the brain's complex control circuits. The messenger substance not only influences body weight but also controls, among other things, the development of anxiety and stress responses. Hence NPY plays an important role in a series of mental illnesses such as post-traumatic stress disorders and anxiety disorders. NPY takes effect in the brain by binding to different docking sites on the neurons the NPY receptors. In this way, the hormone triggers signal cascades which control the different physical functions.
In a study on mice carried out in Rolf Sprengel from the Max Planck Institute for Medical Research and his colleagues in Italy have shown that the effect of NPY depends on how much care and attention the young animals experienced in the first three weeks of life. Mice who had received little care from their mothers were more anxious adults than their counterparts who had received intensive attention in their early weeks of life. They also remained slimmer throughout their lives. As the researchers discovered, the maternal behaviour influenced the formation of NPY1 receptors in the limbic system the area of the brain responsible for the processing of emotions.
"We were able to show that the expression of the NPY1 receptor in the young animals' limbic system is increased by good maternal care," explains Rolf Sprengel. "This ensures their healthy development in the long term." The positive effects of maternal care and attention were evidenced by the fact that the young animals gained weight faster and showed greater courage in behavioural experiments as adults than rodents which had experienced little warmth and security after birth.
For their study, the scientists had newborn mice, in which the NPY1 receptors had been switched off selectively, raised by mothers who differed in their behaviour towards the young animals. One group belonged to a mouse strain that was exemplary in caring for its young. These females spent a lot of time with their offspring, fed them frequently and, in addition to extensive grooming, also provided intensive physical contact. In young animals which grew up under such conditions, new NPY-1 receptors formed in the brain's limbic system. The second group of females were programmed to take far less care of the young. In this case, the number of NPY1 receptors in the young mice did not increase.
The neuroscientists' findings help us to reach a better understanding of how experience in the early life of an organism can affect it in later life. "The results of the study show how maternal care and attention have a sustained impact on the chemistry of the limbic system," says Rolf Sprengel. Maternal behaviour can influence the emotions and physical constitution into adulthood in this way.
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Ilaria Bertocchi, Alessandra Oberto, Angela Longo, Paolo Mele, Marianna Sabetta, Alessandro Bartolomucci, Paola Palanza, Rolf Sprengel, Carola Eva. Regulatory functions of limbic Y1 receptors in body weight and anxiety uncovered by conditional knockout and maternal care, PNAS, doi: 10.1073/pnas.1109468108