Submedius thalamic inputs shape the presynaptic architecture of layer 5 orbitofrontal cortex in mice

The orbitofrontal cortex (OFC) is central to cognitive and social functions, yet its presynaptic partners remain incompletely defined. In female mice, the OFC modulates infant-directed caregiving behaviors in an experience-dependent manner. Here, we identify the submedius thalamus (SMT) as a major presynaptic partner of the OFC. <i>Trans</i>-synaptic tracing revealed intensive inputs from both the SMT and mediodorsal thalamus (MD) to OFC layer 5 excitatory neurons. We generated a <i>Tnnt1-Cre</i> mouse line that enables selective targeting of these higher-order thalamic nuclei. Axonal tracing demonstrated complementary projection patterns of the SMT and MD across prefrontal regions. Microendoscopic Ca²⁺ imaging demonstrated pup retrieval-related activity in both SMT and MD, with SMT exhibiting learning-related plasticity. Projection-specific chemogenetic silencing demonstrated that SMT modulates OFC activity during pup retrieval, although its behavioral relevance appeared limited. Collectively, our study provides a presynaptic map of OFC layer 5 neurons and a proof of concept for selective manipulation of the SMT as a previously understudied thalamic input to the OFC.