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Maternal aggression is impaired by prepartum serotonin-specific lesions of the midbrain dorsal raphe.

Vitale EM, Holschbach MA, Lonstein JS (2016) Maternal aggression is impaired by prepartum serotonin-specific lesions of the midbrain dorsal raphe. Neuroscience 2016 Abstracts 338.01 / SS14. Society for Neuroscience, San Diego, CA.

Summary: The postpartum period in laboratory rats and other animals is characterized by increased maternal responsiveness, decreased anxiety, and increased aggression. Pharmacologically manipulating the serotoninergic system during the postpartum period alters all of these behaviors, and our lab recently found that lesioning serotonergic neurons in the dorsal raphe (DR; primary source of forebrain serotonin) after parturition decreases maternal aggression as well as pup licking in laboratory rats. This demonstrates serotonin’s importance for these behaviors during the postpartum period, but no studies have evaluated the function of serotonin during pregnancy, a highly sensitive period when hormones and peptides alter neurochemistry to initiate maternal responsiveness. Given serotonin’s role in hormone and neuropeptide release, DR serotoninergic activity beginning during pregnancy may be particularly important for the onset of postpartum changes in anxiety, maternal responsiveness, and maternal aggression. To test this hypothesis, we destroyed serotonergic cells with a neurotoxin targeting the serotonin transporter (anti-SERT-saporin; Advanced Targeting Systems) infused into the DR on pregnancy day 15. After parturition, we observed subjects’ maternal caregiving behaviors, maternal motivation during retrieval tests, maternal aggression, and anxiety-like behaviors. We found that DR lesions during pregnancy greatly reduced maternal aggression towards an intruder, and that lesioned mothers also showed increased contact with pups immediately after disruption of the nest site during retrieval tests. Preliminary analysis of serotonin fiber innervation in several forebrain regions indicates tremendous reduction in serotonin fiber density in the amygdala and medial prefrontal cortex of lesioned subjects, but much less so in the medial preoptic area (MPOA). These findings demonstrate that prepartum serotonin-specific lesions of the DR affect particular maternal behaviors, especially aggression, and likely do so by reducing serotonergic innervation of the forebrain in a site-specific manner.

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