THALAMIC RELAY OF PUP SOMATOSENSORY CUES TO THE MEDIAL PREOPTIC AREA PROMOTES MATERNAL BEHAVIOUR

The medial preoptic area (MPOA) is a key hypothalamic hub for maternal behaviour, yet the somatosensory pathways modulating MPOA function remain incompletely defined. Neurons in the posterior intralaminar nucleus (PIL) of the lateral thalamus project to the MPOA and receive somatosensory input during suckling, suggesting a relay for pup-derived touch signals. Here, we examined the role of the PIL→MPOA pathway in maternal care in rat dams. Retrograde tracing from the MPOA revealed that most PIL neurons projecting to the MPOA were activated during maternal interaction, and their majority expressed the maternally-induced neuropeptide parathyroid hormone 2 (PTH2). To address maternal functions, we chemogenetically activated PIL neurons in mother rats whose activation increased pup-directed time, grooming/licking, and nest-building behaviour. In addition, we quantified c-Fos expression in rat dams after pup separation under three conditions: pups returned with free interaction with the mother, pups returned without physical contact, or no pups returned. Triple immunolabelling for PTH2, calbindin (Cb), and c-Fos showed increased c-Fos in Cb+ neurons in both medial and lateral PIL, with maximal activation during unrestricted pup interaction. Nearly all PTH2+ neurons were Cb+ and were activated by unrestrained pup exposure, whereas triple-labelled cells were rare without pups and reduced when touch was prevented. These results support a model in which PTH2-expressing PIL neurons convey pup-related somatosensory tactile information to the MPOA to promote maternal behaviour.
Support: DKOP-23 and Gedeon Richter Excellence PhD Grant for VSz. NKFIH OTKA K146077, NKKP National Research Excellence Program 151425 and MTA NAP2022-I-3/2022(NAP 3) for AD.