Topographic organization of orbitofrontal projections to the parahippocampal region in rats

• Published in: Journal of comparative neurology (1911) 2014-03, Vol.522 (4), p.772-793
• Main Authors: Kondo, Hideki, Witter, Menno P.
• Format: Article
• Language: English
• Subjects: Animals; anterograde tracing; Axons; Biotin - analogs & derivatives; Biotin - metabolism; Brain Mapping; Dextrans - metabolism; Efferent Pathways - physiology; entorhinal cortex; Female; Iontophoresis; Male; Neurofilament Proteins - metabolism; orbitofrontal cortex; Parahippocampal Gyrus - cytology; perirhinal cortex; Phaseolus; Phytohemagglutinins - metabolism; postrhinal cortex; Prefrontal Cortex - cytology; presubiculum; Rats; Rats, Sprague-Dawley
• ISSN: 0021-9967; 1096-9861
• DOI: 10.1002/cne.23442

ABSTRACT The parahippocampal region, which comprises the perirhinal, postrhinal, and entorhinal cortices, as well as the pre‐ and parasubiculum, receives inputs from several association cortices and provides the major cortical input to the hippocampus. This study examined the topographic organization of projections from the orbitofrontal cortex (OFC) to the parahippocampal region in rats by injecting anterograde tracers, biotinylated dextran amine (BDA) and Phaseolus vulgaris‐leucoagglutinin (PHA‐L), into four subdivisions of OFC. The rostral portion of the perirhinal cortex receives strong projections from the medial (MO), ventral (VO), and ventrolateral (VLO) orbitofrontal areas and the caudal portion of lateral orbitofrontal area (LO). These projections terminate in the dorsal bank and fundus of the rhinal sulcus. In contrast, the postrhinal cortex receives a strong projection specifically from VO. All four subdivisions of OFC give rise to projections to the dorsolateral parts of the lateral entorhinal cortex (LEC), preferentially distributing to more caudal levels of LEC. The medial entorhinal cortex (MEC) receives moderate input from VO and weak projections from MO, VLO, and LO. The presubiculum receives strong projections from caudal VO but only weak projections from other OFC regions. As for the laminar distribution of projections, axons originating from OFC terminate more densely in upper layers (layers I–III) than in deep layers in the parahippocampal region. These results thus show a striking topographic organization of OFC‐to‐parahippocampal connectivity. Whereas LO, VLO, VO, and MO interact with perirhinal–LEC circuits, the interactions with postrhinal cortex, presubiculum, and MEC are mediated predominantly through the projections of VO. J. Comp. Neurol. 522:772–793, 2014. © 2013 Wiley Periodicals, Inc. We examined the topographic organization of orbitofrontal projections to the parahippocampal region in rats with the use of anterograde tracing and visualization. Our findings show that the perirhinal cortex and the lateral entorhinal cortex receive inputs from all subdivisions of the orbitofrontal cortex, whereas the postrhinal cortex and the presubiculum receive inputs mainly from the ventral orbitofrontal area, and the rostral perirhinal cortex receives more substantial orbitofrontal projections than the more caudally located perirhinal cortex.