Organization of anterior cingulate and frontal cortical projections to the retrosplenial cortex in the rat

Abstract

The retrosplenial cortex (areas 29a-d), which plays an important role in spatial memory and navigation, is known to provide massive projections to frontal association and motor cortices, which are also essential for spatial behavior. The reciprocal projections originating from these frontal cortices to areas 29a-d, however, have been analyzed to only a limited extent. Here, we report an analysis of the anatomical organization of projections from anterior cingulate area 24 and motor and prefrontal cortices to areas 29a-d in the rat, using the axonal transport of cholera toxin B subunit and biotinylated dextran amine. Area 29a receives projections from rostral area 24a, area 24b, the ventral orbital area, and the caudal secondary motor area. Rostral area 29b receives projections from caudal area 24a, whereas caudal area 29b receives projections from rostral area 24a. Area 29b also receives projections from area 24b and the ventral orbital area. Areas 29c and 29d receive projections from areas 24a and 24b and the secondary motor area in a topographic manner such that the rostrocaudal axis of areas 29c and 29d corresponds to the caudorostral axis of areas 24a and 24b and the secondary motor area. Rostral areas 29c and 29d also receive projections from the caudal primary motor area, and area 29d receives projections from the ventral, lateral, and medial orbital areas. These differential frontal cortical projections to each area of the retrosplenial cortex suggest that each area may contribute to different aspects of retrosplenial cortical function such as spatial memory and behavior.

Brain-wide map of efferent projections from rat barrel cortex

“…In the cases injected in the S1 barrel cortex a modest amount of labeling was also seen in the ipsilateral retrosplenial cortex. Our observations confirm earlier reports of moderate or weak projections from S1 to the anterior cingulate cortex (Reep et al, 1990; Van Eden et al, 1992; Condé et al, 1995) and retrosplenial cortex (Shibata and Naito, 2008). …”

Distinct patterns of neuronal inputs and outputs of the juxtaparaventricular and suprafornical regions of the lateral hypothalamic area in the male rat

“…Major projections from the medial prefrontal cortex that relate directly to the interconnections of the LHAjp (in addition to the direct LHAjp projection already described) include pathways from the anterior cingulate area to the retrosplenial area (van Groen and Wyss, 1992; Risold and Swanson, 1995; Shibata and Naito, 2008) and anteromedial and lateral dorsal thalamic nuclei (Shibata and Naito, 2005) -- relating strongly, as discussed, to aspects of attention (especially visual), learning, and memory. Similarly, major projections from the prelimbic and infralimbic areas include those to the thalamic paratenial and reuniens nuclei -- the paratenial nucleus and rostral division of the nucleus reuniens receive a substantial projection from the LHAjp.…”

Organization of intrinsic connections of the retrosplenial cortex in the rat

“…The locations of the injection site and labeled cells or labeled fibers/terminals in selected frontal sections were plotted with the aid of camera lucida for demonstration purposes. To compare more readily the distribution of labeling among cases, we mapped the location of the injection site and the relative density of labeled cells or terminals onto a two-dimensional flattened cortical map (Shibata and Naito 2008).…”

“…Although the contributions of each area to such functions are not exactly known, area 29d has been suggested to be important for visual information processing involved in allocentric spatial learning tasks (Vann and Aggleton 2005), and even area 29c alone may contribute to spatial working memory processing (Van Groen et al 2004). These presumably different functional contributions of each area are substantiated by anatomical studies, which have demonstrated that areas 29a-d have different connections with various cortical and subcortical regions, such as the frontal, anterior cingulate, visual, and retrohippocampal cortices, and anterior and laterodorsal thalamus (Van Groen and Wyss 1990Shibata 1993Shibata , 1994Shibata , 1998Shibata , 2000Van Groen et al 1993;Shibata et al 2004;Shibata and Naito 2008). In addition to demonstrating these extrinsic connections, some of these and other anatomical studies have also demonstrated that areas 29a-d have unique and complex interconnections, although the descriptions of these connections are incomplete and partially contradictory.…”