The topology of connections between rat prefrontal and temporal cortices

Abstract

Understanding the structural organization of the prefrontal cortex (PFC) is an important step toward determining its functional organization. Here we investigated the organization of PFC using different neuronal tracers. We injected retrograde (Fluoro-Gold, 100 nl) and anterograde [Biotinylated dextran amine (BDA) or Fluoro-Ruby, 100 nl] tracers into sites within PFC subdivisions (prelimbic, ventral orbital, ventrolateral orbital, dorsolateral orbital) along a coronal axis within PFC. At each injection site one injection was made of the anterograde tracer and one injection was made of the retrograde tracer. The projection locations of retrogradely labeled neurons and anterogradely labeled axon terminals were then analyzed in the temporal cortex: area Te, entorhinal and perirhinal cortex. We found evidence for an ordering of both the anterograde (anterior-posterior, dorsal-ventral, and medial-lateral axes: p < 0.001) and retrograde (anterior-posterior, dorsal-ventral, and medial-lateral axes: p < 0.001) connections of PFC. We observed that anterograde and retrograde labeling in ipsilateral temporal cortex (i.e., PFC inputs and outputs) often occurred reciprocally (i.e., the same brain region, such as area 35d in perirhinal cortex, contained anterograde and retrograde labeling). However, often the same specific columnar temporal cortex regions contained only either labeling of retrograde or anterograde tracer, indicating that PFC inputs and outputs are frequently non-matched.

Medial prefrontal-perirhinal cortical communication is necessary for flexible response selection

“…Since inter-region projections are typically more extensive within same hemisphere compared to across hemispheres (Bedwell et al, 2015), this approach blocks communication between inactivated regions while leaving one hemisphere of each brain region intact to support behavior. For the contralateral infusions, MUS or saline was infused simultaneously into the mPFC of one hemisphere and the PER of the contralateral hemisphere.…”

“…After rats acquired the biconditional association, the necessity of mPFC-PER communication was investigated by infusing the GABA A receptor agonist muscimol (MUS) into one hemisphere of the mPFC and the contralateral PER to reversibly disconnect these areas. This approach capitalizes on the fact that the mPFC and PER are densely connected within the same hemisphere, but not across hemispheres (Bedwell, Billett, Crofts, MacDonald, and Tinsley, 2015). Thus, unilateral mPFC and contralateral PER inactivation blocks communication between these areas.…”

Differences in anatomical connections across distinct areas in the rodent prefrontal cortex

“…lateral PFC). This is of interest because it produced a very similar topology and distribution of afferents/efferents to that found following tracer injections into a ‘central’, coronal portion of PFC (Bedwell et al ., ), located at the equivalent coronal level of bregma +4.2 mm (a coronal level half way between the two sections in Fig. of the present study).…”

Prefrontal–hippocampal pathways underlying inhibitory control over memory

“…Although the ACC does not project directly to the hippocampus (Barbas and Blatt, 1995; Cavada et al, 2000; Insausti and Munoz, 2001; Rosene and Van Hoesen, 1977), it does originate parallel projections to a number of memory related structures in the MTL in both the rodent and the primate (Bedwell, Billett, Crofts, MacDonald, and Tinsley, 2015; Delatour and Witter, 2002; Kondo, Saleem, and Price, 2005; Saleem, Kondo, and Price, 2008). 2 The rodent infralimbic cortex originates modest projections to the entorhinal and ectorhinal (analogous to perirhinal area 36 in macaque monkeys) cortices, while pathways originating from PL cortex specifically target the entorhinal cortex (Sesack, Deutch, Roth, and Bunney, 1989; Vertes, 2004).…”