Triple retrograde tracing of retrosplenial efferents

Abstract

We injected three retrograde tracers, Fast Blue, Diamidino Yellow (FB)and Cholera toxin subunit B conjugated to Alexa Fluor 488 or 594 (CTB-488/-594), into medial entorhinal cortex (MEC), presubiculum (PrS) and postrhinal cortex (POR) and looked at the distribution of retrogradely labeled cells in the retrosplenial cortex (RSC). In one out of a total of six cases we had successful injections of CTB-594 and DY in MEC and PrS, respectively, a partially successful injection of FB in POR. In this case we saw extensive areal overlap of CTB-594 positive and DY-positive neurons in RSC, and also observed some cases of neurons positive for both of those tracers in RSC area 29ab. Meager overlap between all three kinds of labeled neurons was seen in area 30 of RSC. These findings might shed new light on the position of the RSC in the network dealing with spatial navigation and memory.