The distribution of presumptive glutamatergic and/or aspartatergic neurons retrogradely labeled following injections of [3H]-D-aspartate into the magnocellular basal forebrain of the rat was compared with the distribution of neurons labeled by comparable injections of the nonspecific retrograde axonal tracer wheat germ agglutinin conjugated to horseradish peroxidase. Cells retrogradely labeled by wheat germ agglutinin-horseradish peroxidase were found in a wide range of limbic and limbic-related structures in the forebrain and brainstem. In the telencephalon, labeled neurons were seen in the orbital, medial prefrontal, and agranular insular cortical areas, the amygdaloid complex, and the hippocampal formation. Labeled cells were also seen in the olfactory cortex, the lateral septum, the ventral striatopallidal region, and the magnocellular basal forebrain itself. In the diencephalon, neurons were labeled in the midline nuclear complex of the thalamus, the lateral habenular nucleus, and the hypothalamus. In the brainstem, labeled cells were found bilaterally in the ventral midbrain, the central gray, the reticular formation, the parabrachial nuclei, the raphe nuclei, the laterodorsal tegmental nucleus, and the locus coeruleus. A significant fraction of the afferents to the magnocellular basal forebrain appear to be glutamatergic and/or aspartatergic. Only a few of the regions labeled with wheat germ agglutinin-horseradish peroxidase were not also labeled with [3H]-D-aspartate in the comparable experiments. Most prominent among the non-glutamatergic/aspartatergic projections were those from fields CA1 and CA3 of the hippocampus, the hilus of the dentate gyrus, the dorsal subiculum, the tuberomammillary nucleus, and the ventral pallidum. In addition, most of the lateral hypothalamic and brainstem projections to the magnocellular basal forebrain were not significantly labeled with [3H]-D-aspartate. In addition to these inputs, a commissural projection from the region of the contralateral nucleus of the horizontal limb of the diagonal band was confirmed with both wheat germ agglutinin-horseradish peroxidase and the anterograde axonal tracer Phaseolus vulgaris leucoagglutinin. This projection did not label with [3H]-D-aspartate or [3H]-GABA, suggesting that it is not glutamatergic/aspartatergic or GABAergic. Furthermore, double labeling experiments with the fluorescent retrograde tracer True Blue and antibodies against choline acetyltransferase indicate that the projection is not cholinergic.

INSTRUCTIONS 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...

We have traced the postnatal development of axons and cells in kitten striate cortex that contain acetylcholinesterase (AChE) by using a modification of Koelle's histochemical method. The maturation of AChE-positive axons was not found to be fully complete until at least 3 months of age, and was characterized by several distinct developmental trends. AChE-positive fibers in layers IVc-VI proliferate rapidly after birth until, by 4 weeks postnatal, they appear to exceed the adult density. They remain at this level as late as 8 weeks and then decrease to the adult density by 13 weeks. In contrast, the AChE-positive fibers in layer I do not show a substantial increase in density until 6 weeks of age and the adult level is not achieved before 3 months postnatal. Finally, the density of AChE-positive fibers in layers II and III appears to increase gradually from birth until the mature pattern is reached at about 6 weeks. AChE could also be localized histochemically to cell bodies whose position and appearance depended on postnatal age. Stained cells first appeared in the white matter subjacent to layer VI shortly after birth. By 2 weeks of age, most cells in layer VI were also AChE positive. The staining of these cells gradually disappears over the next 2 months until, at 3 months of age, there are no AChE-positive cells in cat striate cortex. However, a subpopulation of stained neurons appears in layer V by 1 year of age that persists throughout adulthood. The possible contributions of acetylcholine and AChE to the postnatal development of kitten striate cortex are discussed.