Perirhinal and postrhinal cortices of the rat: Interconnectivity and connections with the entorhinal cortex

Abstract

The cortical regions dorsally adjacent to the posterior rhinal sulcus in the rat can be divided into a rostral region, the perirhinal cortex, which shares features of the monkey perirhinal cortex, and a caudal region, the postrhinal cortex, which has connectional attributes similar to the monkey parahippocampal cortex. We examined the connectivity among the rat perirhinal (areas 35 and 36), postrhinal, and entorhinal cortices by placing anterograde and retrograde tracers in all three regions. There is a dorsal-to-ventral cascade of connections in the perirhinal and entorhinal cortices. Dorsal area 36 projects strongly to ventral area 36, and ventral area 36 projects strongly to area 35. The return projections are substantially weaker. The cascade continues with the perirhinal to entorhinal connections. Area 35 is more strongly interconnected with the entorhinal cortex, ventral area 36 somewhat less strongly, and dorsal area 36 projects only weakly to the entorhinal cortex. The postrhinal-to-perirhinal connections also follow this general pattern. The postrhinal cortex is more heavily connected with dorsal area 36 than with ventral area 36 and is more heavily connected with area 36 than with area 35. The rostral portion of the postrhinal cortex has the strongest connections with the perirhinal cortex. Like in the monkey, the perirhinal and postrhinal cortices have different patterns of projections to the entorhinal cortex. The perirhinal cortex is preferentially connected with the rostrolateral portion of the entorhinal cortex. The postrhinal cortex projects to a part of this same region but is also connected to caudal and redial portions of the entorhinal cortex. The perirhinal and postrhinal projections to the entorhinal cortex originate in layers III and V and terminate preferentially in layers II and III.

The rat perirhinal cortex: A review of anatomy, physiology, plasticity, and function

“…The lateral entorhinal cortex projection to the perirhinal cortex originates in all layers of the lateral entorhinal cortex but laminar distribution changes depending on location within the entorhinal cortex (Insausti et al, 1997) which supports later findings that suggest the projection originates in layers III and V of the lateral entorhinal cortex (Burwell and Amaral, 1998a). In any case, the lateral entorhinal cortex projects more heavily to area 35 than area 36 (Insausti et al, 1997;Burwell and Amaral, 1998a). These projections terminated across all layers of area 35 (albeit with heavier staining present in layers I and V comparatively) and a similar story is seen for area 36 (Burwell and Amaral, 1998a).…”

“…Area 36 projects laterally into area 35 with the majority of connections originating in the ventral region of area 36 in layers II, V and VI and terminating in layers I and V of area 35 (Burwell and Amaral, 1998a). Burwell and Amaral (1998a) also show that area 35 of the perirhinal cortex projects into area 36 (to a lesser degree than the 36 into 35 projections) and forms a feedback pathway with most projections originating in layers II and III and terminating in all layers.…”

“…Lateral entorhinal projections project more to area 35 than 36 with rostral lateral entorhinal projections terminating in rostral regions of the perirhinal cortex and caudal lateral entorhinal projections terminating across the perirhinal cortex (Burwell and Amaral, 1998a). The lateral entorhinal cortex projection to the perirhinal cortex originates in all layers of the lateral entorhinal cortex but laminar distribution changes depending on location within the entorhinal cortex (Insausti et al, 1997) which supports later findings that suggest the projection originates in layers III and V of the lateral entorhinal cortex (Burwell and Amaral, 1998a). In any case, the lateral entorhinal cortex projects more heavily to area 35 than area 36 (Insausti et al, 1997;Burwell and Amaral, 1998a).…”

“…Unlike the afferent projections of the perirhinal cortex, its efferents all involve both areas 35 and 36, albeit with some weighting towards one or the other in some cases (Burwell and Amaral, 1998a;McIntyre et al, 1996;Delatour and Witter, 2002;Agster and Burwell, 2009).…”

“…The most prominent of all afferent cortical projections to the perirhinal cortex is the one originating in the entorhinal cortex (Wyss, 1981;Kosel et al, 1982;Kö hler, 1988;Insausti et al, 1997;Burwell and Amaral, 1998a;Canto et al, 2008). Lateral entorhinal projections project more to area 35 than 36 with rostral lateral entorhinal projections terminating in rostral regions of the perirhinal cortex and caudal lateral entorhinal projections terminating across the perirhinal cortex (Burwell and Amaral, 1998a).…”