CORTICAL CONTROL OF THE ANTERIOR PARAVENTRICULAR THALAMIC NUCLEUS

The paraventricular thalamic nucleus (PVT) is a critical node in brainstem-cortex communication. The PVT integrates multitudes of stress and arousal related subcortical information, distributes these to widespread forebrain areas. Its main cell type expresses calretinin (CR). PVT/CR+ cells are critical in stress-induced behavioral alterations. How this system is governed by top-down cortical control is presently little understood.
The two main sources of cortical inputs to PVT arise from the medial prefrontal cortex (mPFC), and the ventral subiculum (vSub). To identify connections between the PVT and these cortical regions we used antero-/retrograde viral tracing methods in CR-Cre and vGlut1-Cre mice. For functional relevance we recorded the activity of optogenetically tagged CR+ neurons that project to the vSUB and/or the mPFC.
We found that while the mPFC innervated the entire antero-posterior extent of PVT the vSub axons were restricted to the anterior PVT (aPVT). The distribution of mPFC and vSUB projecting PVT neurons displayed identical patterns. Co-injection of anterograde and retrograde tracers to vSUB demonstrated that the vSUB-aPVT connection is strictly reciprocal. Antidromically activated PVT neurons from the vSUB were localized in the aPVT. Their activity displayed sharp wave ripple (SWR) modulations. Antidromically activated cells from the mPFC were found along the entire antero-posterior extent of PVT but these cells displayed SWR modulation only in they were localized to aPVT.
These data disclose aPVT as a thalamic hot spot that process top-down hippocampal electrical signals and transfers it to mPFC during electrical activity patterns important in memory formation.