Paratenial thalamus engages in reciprocal and broadcast circuits with the prefrontal cortex

The dorsal anterior midline thalamus (aMT) consists of two adjacent nuclei important for motivated and emotional behavior. Previous work focused on the paraventricular thalamus (PVT), with little known about the adjacent paratenial thalamus (PT). We examine neural circuits involving the PT using molecular profiling, anatomical tracing, electrophysiology, and optogenetics. We find that protein kinase C-delta (PKCd) selectively labels thalamocortical (TC) cells in the PT but is sparse in the PVT. We show that TC cells in the PT project to the infralimbic region (IL) of the medial prefrontal cortex (mPFC), where they engage L2/3 pyramidal cells. We find that mPFC primarily projects to the PT over PVT, making connections onto reciprocally connected TC cells. However, these cortical inputs are even stronger onto thalamostriatal (TS) and thalamoamygdala (TA) cells in the PT, allowing the mPFC to broadcast to the subcortex. These findings help parcellate aMT, highlight PT as a distinct nucleus, establish reciprocal connectivity with the mPFC, and show corticothalamic throughput to the subcortex.