TOPOGRAPHY OF CHOLINERGIC AFFERENTS FROM THE NUCLEUS BASALIS OF MEYNERT TO REPRESENTATIONAL AREAS OF SENSORIMOTOR CORTICES IN THE RAT

We investigated (1) the topography of projection neurons in the nucleu s basalis of Meynert (NBM) with efferents to restricted regions of the primary somatosensory (SI), the second somatosensory (SII), and the p rimary motor (MI) cortices in the rat; (2) the percentage of these NBM projection neurons that were cholinergic; and (3) the collateralizati on, if any, of single NBM neurons to different subdivisions within SI, to homotopic areas of SI and SII, and to homotopic areas of SI and MI . Retrograde single- and double-labeling techniques were used to study NBM projections to electrophysiologically identified subdivisions of SI and to homotopic representational areas of SI and SII, and of SI an d MI. Choline acetyltransferase immunocytochemistry was done to identi fy cholinergic NBM neurons. Of the retrogradely labeled NBM neurons th at projected to selective subdivisions of SI, SII, and MI, 89%, 87%, a nd 88%, respectively, were cholinergic. We found a rostral-to-caudal p rogression of retrogradely labeled NBM neurons following a medial-to-l ateral sequence of injections into subdivisions of SI. Overlapping gro ups of single-labeled NBM neurons were observed after injections of di fferent tracers into adjacent subdivisions within SI or homotopic area s of SI and SII, and of SI and MI. We conclude that NBM innervation to SI, SII, and MI is mostly cholinergic in the rat, that each cortical area receives cholinergic afferents from neurons widely distributed wi thin the NBM, and that each NBM neuron projects to a restricted cortic al area without significant collateralization to adjacent subdivisions within SI or to homotopic areas of SI and SII, or SI and MI. (C) 1993 Wiley-Liss, Inc.