Connections of the retrosplenial granular b cortex in the rat

Abstract

Although the retrosplenial granular b cortex (Rgb) is situated in a critical position between the hippocampal formation and the neocortex, surprisingly few studies have examined its connections carefully. The present experiments use both anterograde and retrograde tracing techniques to characterize the connections of Rgb. The main cortical projections from Rgb are to the caudal part of the anterior cingulate cortex, area 18b, retrosplenial granular a cortex (Rga), and postsubiculum, and less dense terminal fields are present in the prelimbic and caudal occipital cortices. The major subcortical projections are to the anterior thalamic nuclei and the rostral pontine nuclei, and very small terminal fields are present in the caudal dorsomedial part of the striatum, the reuniens and reticular nuclei of the thalamus, and the mammillary bodies. Contralaterally, Rgb primarily projects to itself, i.e., homotypically, and more sparsely projects to Rga and postsubiculum. In general, the axons from Rgb terminate ipsilaterally in cortical layers I and III-V and contralaterally in layer V, with a smaller number of terminals in layers I and VI. Thalamic projections from Rgb target the anteroventral and laterodorsal nuclei of the thalamus, with only a few axons terminating in the anterodorsal nucleus, the reticular nucleus, and the nucleus reuniens of the thalamus. Rgb is innervated by the anterior cingulate cortex, precentral agranular cortex, cortical area 18b, dorsal subiculum, and postsubiculum. Subcortical projections to Rgb originate mainly in the claustrum, the horizontal limb of the diagonal band of Broca, and the anterior thalamic nuclei. These data demonstrate that, in the rat, Rgb is a major nodal point for the integration and subsequent distribution of information to and from the hippocampal formation, the midline limbic and visual cortices, and the thalamus. Thus, similarly to the entorhinal cortex, Rgb in the rat is a prominent gateway for information exchange between the hippocampal formation and other limbic areas of the brain.

Hippocampal Network Connectivity and Activation Differentiates Post-Traumatic Stress Disorder From Generalized Anxiety Disorder

“…Lu et al (2012) demonstrated in rats that the default-mode network not only exists but also includes homologues of key structures noted in our work and that of others (Poppenk and Moscovitch, 2011) (eg, anterior cingulate cortex, retrosplenial cortex, and the dorsal hippocampus), which further strengthens the basis for parcellating hippocampus along its longitudinal axis. As such, converging evidence from noninvasive neuroimaging methods, along with those based on comparative anatomy techniques (ie, tract tracing) in rats (Van Groen and Wyss, 2003) and monkeys (Aggleton et al, 2012;Roberts et al, 2007), together provide support for the homology of hippocampal subdivisions that are the basis for this study (dorsal/ventral and posterior/anterior, respectively).…”

Distinct Functional Properties of Primary and Posteromedial Visual Area of Mouse Neocortex

“…A simpler patchwork model is based on the evolutionary addition of visual areas depending on the species' visual ability (de Haan and Cowey, 2011). The rodent area PM, located between V1 and the retrosplenial cortex, has been shown to mediate visually evoked activity between these areas (Van Groen and Wyss, 2003;Xu et al, 2007). The retrosplenial complex receives projections from medial visual areas, further projects to the hippocampus (Wyss and Van Groen, 1992), and is involved in observing familiar environments (Vann et al, 2009).…”

“…The visual information required for navigation is projected from visual cortex via retrosplenial cortex to the hippocampus (Wyss and Van Groen, 1992;Vann et al, 2009). In rodents, the retrosplenial cortex receives this information from the medial secondary visual area (Van Groen and Wyss, 2003), which has been described to be identical to the location of PM (Wang and Burkhalter, 2007). In addition, voltage-sensitive dye imaging has shown that visual stimulation evokes activity waves originating in V1 and traveling toward PM from where feedback waves are returned (Xu et al, 2007).…”

Acute phencyclidine administration induces c-Fos-immunoreactivity in interneurons in cortical and subcortical regions

“…Both regions are thought to be affected in schizophrenia (Morris et al 2005;Bluhm et al 2009) and connected to the PFC (Van Groen and Wyss, 2003;Price, 2007). Previous studies have shown that PCP administration increases the c-Fos mRNA expression in both glutamatergic and GAD67 positive neurons in the RS and in GAD67 positive neurons in the CA1 (Kargieman et al 2007;Santana et al 2011).…”