Topographic organization of the basal forebrain projections to the perirhinal, postrhinal, and entorhinal cortex in rats

• Published in: Journal of comparative neurology (1911) Vol. 524; no. 12; pp. 2503 - 2515
• Main Authors: Kondo, Hideki, Zaborszky, Laszlo
• Format: Journal Article
• Language: English
• Published: United States Blackwell Publishing Ltd 15-08-2016; Wiley Subscription Services, Inc
• Subjects: Animals; Basal Forebrain - cytology; Basal Forebrain - physiology; Brain Mapping - methods; cholinergic and noncholinergic neurons; Entorhinal Cortex - cytology; Entorhinal Cortex - physiology; globus pallidus; Humans; Male; medial septum; Neural Pathways - cytology; Neural Pathways - physiology; parahippocampal region; Perirhinal Cortex - cytology; Perirhinal Cortex - physiology; Rats; Rats, Sprague-Dawley; retrograde tracing; substantia innominata; vertical and horizontal limbs of diagonal band; parahippocampal region; cholinergic and noncholinergic neurons; substantia innominata; medial septum; globus pallidus; vertical and horizontal limbs of diagonal band; retrograde tracing
• ISSN: 0021-9967; 1096-9861
• DOI: 10.1002/cne.23967

ABSTRACT
Previous studies have shown that the basal forebrain (BF) modulates cortical activation via its projections to the entire cortical mantle. However, the organization of these projections is only partially understood or, for certain areas, unknown. In this study, we examined the topographic organization of cholinergic and noncholinergic projections from the BF to the perirhinal, postrhinal, and entorhinal cortex by using retrograde tracing combined with choline acetyltransferase (ChAT) immunohistochemistry in rats. The perirhinal and postrhinal cortex receives major cholinergic and noncholinergic input from the caudal BF, including the caudal globus pallidus and substantia innominata and moderate input from the horizontal limb of the diagonal band, whereas the entorhinal cortex receives major input from the rostral BF, including the medial septum and the vertical and horizontal limbs of the diagonal band. In the perirhinal cases, cholinergic projection neurons are distributed more caudally in the caudal globus pallidus than noncholinergic projection neurons. Compared with the perirhinal cases, the distribution of cholinergic and noncholinergic neurons projecting to the postrhinal cortex shifts slightly caudally in the caudal globus pallidus. The distribution of cholinergic and noncholinergic neurons projecting to the lateral entorhinal cortex extends more caudally in the BF than to the medial entorhinal cortex. The ratio of ChAT‐positive projection neurons to total projection neurons is higher in the perirhinal/postrhinal cases (26–48%) than in the entorhinal cases (13–30%). These results indicate that the organization of cholinergic and noncholinergic projections from the BF to the parahippocampal cortex is more complex than previously described. J. Comp. Neurol. 524:2503–2515, 2016. © 2016 Wiley Periodicals, Inc.
Using retrograde tracing combined with ChAT immunohistochemistry, we show that the perirhinal and postrhinal cortices receive cholinergic and noncholinergic projections mainly from the caudal part of the basal forebrain, whereas the entorhinal cortex receives projections mainly from the rostral part of the basal forebrain in rats.