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REPOT DCUMNTATON AGEBEFORECOMPLETING. ,h , -in c , I lcho l n t e ra ,-( H iSto- Iicor'anization of cholinergic inputs to cat striate cortex (area 17)1 was studied using a histochemical stain for acetvcholinesterase (AChE).Axons were labelled in all layers of striate cortex, with distinct plexuses occurring in layer 1, lower layer 1II, layer IVc and layer VI. 1striate cortex, indicating that this innervation arises entirel; from an extrinsic source in the cat. To identify this source, cell groups projecting to area 17 were retrogradelv labelled with horseradish peroxidase (HRP). HRP-labelled cell groups that were also intenselvtAChE-pogitive were considere( as possible candidates for providing the cholinergic input to striate cortex. Th'lese included the basal forebrain, several intralaminar nuclIei and the lateral geniculate nucleus. Kainate lesions were then made in each of these structures to assess their individual contributions to the cortical AChE pattern.-) Cortical AChE was depleted only after lesions of the basal forebrain suggesting that this is the sole source of AChE-positive ixons in area17-- 3 To whom correspondence should be addressed.-1.
ABSTRACTThe organization of cholinergic inputs to cat striate cortex (area 17) was studied using a hi.tochemical stain for acetylcholinesterase (AChE). Axons were labelled in all layers of striate cortex, with distinct plexuses occurring in layer I, lower layer Ill, layer IVc and layer VI. In addition to the stained axons, a population of layer V pyramidal cells was intensely AChE-positive.Surgical undercutting eliminated virtually all of the AChE-positive axons in striate cortex, indicating that this innervation arises entirely from an extrinsic source in the cat.To identify this source, cell groups projecting to area 17 were retrogradely labelled with horseradish peroxidase (HRP). HRP-labelled cell groups that were also intensely AChEpositive were considered as possible candidates for providing the cholinergic input to striate cortex. These included the basal forebrain, several intralaminar nuclei and the lateral geniculate nucleus. Kainate lesions were then made in each of these structures to assess their individual contributions to the cortical AChE pattern. Cortical AChE was depleted only after lesions of the basal forebrain, suggesting that this is the sole source of AChEpositive axons in area 17. Because the cortically-projecting cells in this region have been shown to contain choline acetyltransferase in a number of species, we postulate that the AChE-positive fibers we describe in cat striate cortex are in fact cholinergic.-2.
INTRODUCTIONIn 1967 Shute and Lewis mapped the central cholinergic pathways using a histocherpical stain for acetylcholinesterase (AChE). The AChE-containing pathways of the forebrain seemed to be derived largely from cells in the reticular formation of the brainstem and included cell groups in the intralaminar thalamus and basal telencephalon. They called this the "ascending cholinergic reticular activating system" be...