ELECTRON-MICROSCOPIC EVIDENCE THAT CORTICAL TERMINALS MAKE DIRECT-CONTACT ONTO CELLS OF THE THALAMIC RETICULAR NUCLEUS IN THE MONKEY

Injections of WGA-HRP were made into somatosensory cortex to determine whether or not the cortex makes monosynaptic connections with neurons of the thalamic reticular nucleus. Two classes of synaptic profiles m aking asymmetric contacts onto small dendrites were labeled. The first class was small, and contained densely packed vesicles and few mitoch ondria. The second, larger class contained loosely packed vesicles, se veral mitochondria, and accounted for approximately one-third of label ed contacts.