Postnatal development of retrosplenial projections to the parahippocampal region of the rat

Abstract

The rat parahippocampal region (PHR) and retrosplenial cortex (RSC) are cortical areas important for spatial cognition. In PHR, head-direction cells are present before eye-opening, earliest detected in postnatal day (P)11 animals. Border cells have been recorded around eye-opening (P16), while grid cells do not obtain adult-like features until the fourth postnatal week. In view of these developmental time-lines, we aimed to explore when afferents originating in RSC arrive in PHR. To this end, we injected rats aged P0-P28 with anterograde tracers into RSC. First, we characterized the organization of RSC-PHR projections in postnatal rats and compared these results with data obtained in the adult. Second, we described the morphological development of axonal plexus in PHR. We conclude that the first arriving RSC-axons in PHR, present from P1 onwards, already show a topographical organization similar to that seen in adults, although the labeled plexus does not obtain adult-like densities until P12.DOI: http://dx.doi.org/10.7554/eLife.13925.001

Parahippocampal and retrosplenial connections of rat posterior parietal cortex

“…These observations thus corroborate the finding that PPC only sparsely projects to MEC. It is noteworthy that the retrograde rabies tracing showed substantial labeling in dorsal PrS, caudal PaS, POR, and RSC already after 2 days (not shown), corroborating that these areas provide major inputs to MEC (Caballero-Bleda and Witter, 1993Witter, , 1994van Haeften et al, 1997;Burwell and Amaral, 1998a,b;Jones and Witter, 2007;Canto et al, 2012;Kononenko and Witter, 2012;Czajkowski et al, 2013;Koganezawa et al, 2015;Sugar and Witter, 2016). In view of the observed labeling in all of these areas following anterograde tracer injections in PPC, we infer that PPC might influence MEC most likely by way of these four areas.…”

“…RSC is another candidate structure to mediate PPC interactions with the parahippocampal‐hippocampal system as has been suggested by others (Save and Poucet, ; Whitlock et al, ; Whitlock, ; Wilber et al, ), since it has direct projections to MEC (Burwell and Amaral, ; Jones and Witter, ; Czajkowski et al, ; Sugar and Witter, ). However, some observations from our data in combination with previous studies suggest that this may be an inefficient route to the hippocampal‐projecting cells of MEC.…”

“…However, some observations from our data in combination with previous studies suggest that this may be an inefficient route to the hippocampal-projecting cells of MEC. First, PPC projects preferentially to rostral RSC, while it is the caudal RSC that originates the heaviest input to MEC (Jones and Witter, 2007;Sugar and Witter, 2016). Second, RSC projections mainly terminates in layer V of MEC (Burwell and Amaral, 1998a;Jones and Witter, 2007;Czajkowski et al, 2013;Sugar and Witter, 2016) where the receiving neurons relay to superficial layers (Czajkowski et al, 2013).…”

Laminar Localization and Projection-Specific Properties of Presubicular Neurons Targeting the Lateral Mammillary Nucleus, Thalamus, or Medial Entorhinal Cortex

“…Visual cortex sends direct projections to the superficial layers of PrS (Vogt and Miller, 1983) and also indirectly via the retrosplenial cortex (Sugar and Witter, 2016). Presubicular layer IV pyramidal neurons could receive these inputs directly, given their prominent dendritic arborization that extends in superficial layers (Yoder and Taube, 2011; Simonnet et al, 2013).…”

The marked diversity of unique cortical enhancers enables neuron-specific tools by Enhancer-Driven Gene Expression

“…The brains were removed and horizontal or coronal 500 µm sections were cut on a Leica VT 1000 S microtome and kept at 4 °C until dissection. Bilateral dissection was performed, while watching the tissue through a dissection microscope with transmitted and reflected white light (Zeiss Discovery V8 stereomicroscope) applying architectonic criteria (Boccara et al, 2015;Jones and Witter, 2007;O'Reilly et al, 2015;Sugar and Witter, 2016;Witter, 2011) to unstained tissue. The tissue samples were snap-frozen in liquid nitrogen, kept at -80 0 C and shipped on dry ice.…”