The lateral septum (LS) demonstrates activation in response to pup exposure in rat mothers, and its lesions eliminate maternal behaviors suggesting its involvement in maternal brain circuitry. This study shows that the density of pup-activated neurons in the ventral subdivision of the LS (LSv) is nearly equivalent to that in the medial preoptic area (MPOA), the major regulatory site of maternal behavior. When somatosensory inputs including suckling are not allowed, pup-induced activation was markedly reduced in the LSv. Retrograde tract tracing identified various brain regions potentially influencing LSv neuronal activation. Anterograde studies confirmed that the posterior intralaminar thalamic nucleus (PIL), implicated in processing touch-related stimuli, targets the pup-activated region of the LSv. Moreover, nerve terminals containing the maternally induced PIL neuropeptide parathyroid hormone 2 (PTH2), were found to synapse on the c-Fos activated LSv neurons by electron microscopy. Confirmation of PTH2+ PIL fibers projecting to LSv was achieved by retrograde tracing. Furthermore, double retrograde injections revealed that neurons within the PIL can project to both LSv and MPOA, suggesting their simultaneous regulation by PIL input. We also established that maternally activated septal neurons are GABAergic and send inhibitory projections to the MPOA. This implies that the LSv and MPOA form an interconnected subcircuit in the maternal brain network, which is primarily driven by somatosensory input from the pups via the PIL PTH2+ neurons. Acknowledgement: Strategic research fund of the University of Veterinary Medicine Budapest (Grant No. SRF-001.), ÚNKP-23-3, NKFIH OTKA K134221 and K146077, and MTA NAP2022-I-4/2022(NAP 3).