SYNAPTIC TARGETS OF CHOLINERGIC TERMINALS IN THE PULVINAR NUCLEUS OF THE CAT

We compared the cholinergic innervation of the pulvinar nucleus, a tha lamic association nucleus, to previous studies of the cholinergic inne rvation of the dorsal lateral geniculate nucleus (dLGN), a thalamic re lay nucleus. Both nuclei receive a dense innervation from cholinergic cells of the brainstem parabrachial region (PER). In the dLGN, PER ter minals are located in close proximity to retinal terminals. Our goal w as to determine whether PER terminals in the pulvinar nucleus are loca ted in close proximity to corticothalamic terminals. We identified PER terminals with a monoclonal antibody directed against choline acetylt ransferase (ChAT). Cholinergic terminals contacted dendrites (142 of 1 60, or 89%) or vesicle-filled profiles (18 of 160, or 11%). A subset o f 55 terminals was stained for gamma-aminobutyric acid (GABA) to deter mine whether profiles postsynaptic to cholinergic terminals originate from thalamocortical cells (GABA-) or interneurons (GABA+). The majori ty (44 of 55, or 80%) of postsynaptic profiles were GABA-dendrites. Th e minority (11 of 55, or 20%) were GABA+ dendrites with vesicles. This distribution of contacts is very similar to that seen in the dLGN. Ho wever, the most significant finding was that most cholinergic contacts (121 of 160, or 76%) were located within complex clusters identified as glomeruli. This is the primary site of contacts made by corticothal amic terminals originating from layer V cells. These results suggest t hat while the PER enhances retinal signals in the dLGN, it may also en hance cortical signals in the pulvinar nucleus. Thus, activity in the PER may stimulate both an increased flow of retinal information to vis ual cortex, as well as an increased flow of information between differ ent visuomotor areas of cortex. (C) 1997 Wiley-Liss, Inc.