TDK conference 2015

Lactation is a special physiological state with peculiar behavioral, endocrine and neuronal adaptations. Prolactin produced by the lactotroph cells in the anterior lobe of the pituitary gland has a central role in the regulation of lactation. The receptor of prolactin belongs to the family of cytokine receptors. Its signal transduction is mediated by STAT5, which is phosphorylated by JAK2 adaptor proteins following the binding of prolactin to its receptor. Subsequently, phosphorylated STAT5 (pSTAT5) is translocated to the nucleus where it promotes the transcription of a specific gene set.

During the period of lactation, neurons in maternal brain centers are activated, which is maintained by both neural and hormonal mechanisms. These processes are influenced by the offspring, e.g. by the sucking stimulus. Sucking activates an ascending pathway, which is relayed to forebrain maternal centers through the tuberoinfundibular peptide 39 (TIP39)-containing the posterior intralaminal thalamic complex (PIL), as our research group previously established.

In the present study, we mapped the location of prolactin and neurally activated neurons in suckling mother rats so that we can compare the networks they affect. In order to detect hormonal and neural activity by immunohistochemistry, we used pSTAT5 and c-Fos protein markers, respectively. The temporal dynamics of these activation patterns were established in 3 treatment groups containing mother rats with different suckling times (30 mins, 2- and 6 hours) following 20 hours long period of mother-litter separation to eliminate basal activations of mother brain. At the end of the experimental suckling period, the mother rats were perfused and the immunohistochemical treatment was evaluated by flourescent and confocal microscopic techniques.

We revealed that some brain areas contained neurons activated by both hormonal (pSTAT-positive) and neuronal (c-FOS-positive) activity at the same time, which means that these neurons were responsive to maternal prolactin level and also to neural stimuli from offspring. Besides, there were brain regions where only one of these two effects manifested. In summary, we found that the prolactin effect can be described by a complex spatiotemporal activation pattern, partly overlapping with neuronal activation paths.