Olfactory bulbectomy induces neuronal rearrangement in the entorhinal cortex in the rat.

In humans, depression has been associated with disturbances in olfactory circuitry. Symptoms of depression can be mimicked in animals after olfactory bulbectomy (OBX). Animal models of depression-like behavior produce similar neuronal rearrangements in various brain regions as seen in patients affected by depression. We have recently observed that OBX produces neuronal hypotrophy in the piriform cortex (PirC) and CA1 hippocampus as well as decreased adult cell proliferation in the dentate gyrus (DG) of hippocampus. Thus we further evaluated the effects of OBX in neuronal arborization and spine density in brain regions involved in the control of circadian circle, emotion and memory processing such as the prefrontal cortex (PFC), nucleus accumbens (NAcc), infralimbic cortex (ILC), orbitolateral cortex (OLC) and entorhinal cortex (EC). Our present results show that along with severe behavioral deficits observed in these animals, OBX considerably decreased dendritic branching and the total dendritic length in the EC, a major interface of the hippocampus and neocortical regions. The remaining cortices and NAcc were not affected by OBX. Thus, we propose that the lack of input from the olfactory bulbs resulted in serial neuronal rearrangements in the PirC, EC, and hippocampus leading, at least partially, to behavioral deficits in emotion and memory processes.