Projection from nucleus reuniens thalami to piriform cortex: A tracing study in the rat

To study the cells of origin and area of termination of the projection from the nucleus reuniens thalami (NRe) to the piriform cortex (PC) we used anterograde and retrograde tracing with the B subunit of the cholera toxin. Tracer injections in the NRe resulted in anterogradely labeled fibers in the dorsolateral part of the PC layers I and III. Following injections in the PC, retrogradely labeled cells were observed primarily in the dorsal subdivision of the NRe. Moreover, a topographical organization was observed in this subdivision: its anterior part projects to the posterior part of the PC, whereas its middle part projects to the anterior part of the PC. The present findings suggest that the NRe may exert different modulatory influences on the dorsolateral part of both anterior and posterior PC areas. The possible role of the NRe in the olfactory information processing is discussed.