Amylin, a peptide previously known to be released from the pancreas, was found to be expressed in the preoptic area of mother rats in our recent microarray study. Here, we report that amylin is not expressed in the brain during pregnancy but a significant increase in amylin expression is found immediately after parturition in the preoptic area, a region whose lesion abolishes maternal behaviors. We also showed that amylin mRNA level remained elevated as long as the pups were not removed from the dams. Amylin expression was also induced in maternally behaving (sensitized) non-lactating virgin rats but not in non-sensitized virgin females, or in females that did not become maternal despite the sensitization procedure. Immunohistochemistry an increased amylin peptide expression was verified in maternally behaving rats, and demonstrated the same expression pattern of amylin in dams, as in situ hybridization histochemistry. Ovariectomy had no effect on the activation of amylin neurons suggesting the case of sexual steroid independent mechanisms. In subsequent experiments, mothers were separated from their pups for 22 hours. Upon returning the pups, neuronal activation was found in the mothers´ preoptic area with a distribution pattern similar to amylin-expressing neurons in the medial preoptic nucleus, some parts of the medial preotic area, and the ventral part of the bed nucleus of the stria terminalis. Double labeling revealed that 86–93% of amylin neurons were activated by pup exposure. The results implicate that amylin is a novel neuropeptide with specific maternal functions that may exert its actions on maternal behaviors via amylin receptors present in brain regions, one of the brain areas with projection of preoptic neurons.

Support: Bolyai János Fellowship of the HAS, OTKA NNF2 85612 and K100319 research grants.