The TRN nucleus and some of its neurochemical features. Brightfield photomicrographs of coronal sections from rostral (top) to caudal (bottom) levels of the rhesus monkey thalamus showing the TRN in sections treated for: Column A, acetylcholinesterase (AChE) histochemistry, showing TRN as it enveils the dorsal thalamus. Column B, High magnification of sections at the same rostrocaudal levels as in column A, immunohistochemically labeled with PV, showing that the majority of TRN neurons are PV+. Black and white arrows indicate the borders of TRN. Scale bars A, 5 mm; B, 500 μm.