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

The dorsal anterior midline thalamus (aMT) consists of several closely packed nuclei that are important for motivated and emotional behavior. Previous work on aMT has focused on cells and synapses in the paraventricular thalamus (PVT), and little is known about the adjacent paratenial thalamus (PT). Here we examine neural circuits involving PT using a combination of molecular profiling, anatomical tracing, electrophysiology, and optogenetics. We first find that Protein Kinase C-delta (PKCd) selectively labels thalamocortical (TC) cells concentrated in PT but largely absent from neighboring PVT. We show that TC cells in PT project to the infralimbic region (IL) of the medial prefrontal cortex (mPFC), where they contact and drive L2/3 pyramidal cells. In return, we find that IL mPFC primarily projects to PT over nearby PVT, making connections onto reciprocally connected TC cells. However, these cortical inputs are even stronger onto thalamostriatal (TS) and thalamoamygdala (TA) cells, allowing the mPFC to broadcast to the subcortex. Together, our findings help to parcellate aMT, highlight PT as a distinct thalamic nucleus, establish reciprocal connectivity between PT and IL mPFC, and show cortico-thalamic throughput to the subcortex.