Structural, functional and behavioral impact of allergic rhinitis on olfactory pathway and prefrontal cortex.

Background: Allergic rhinitis (AR) has been identified as a cause of olfactory dysfunction. Beyond the classic symptoms, AR has been associated with altered sleep patterns, a decline in cognitive performance and higher likelihood of depression and anxiety. The olfactory pathway has been postulated to be a possible link between nasal inflammation and central nervous system (CNS) modifications. Thus, we aimed to investigate the structural, functional and behavioral changes in the olfactory pathway and related areas in an animal model of AR.

Methods: AR was induced in adult Wistar rats by ovalbumin sensitization and challenge. Following olfactory and behavioral tests we investigated the synaptic structure of the olfactory bulb (OB), anterior olfactory nuclei (AON), piriform cortex and prefrontal cortex (PFC), by immunofluorescence detection of synaptophysin (Syn) and glutamatergic, GABAergic and dopaminergic neuronal markers.

Results: We detected a significant decrease in Syn in the glomerular layer (GL) of OB and in the PFC of the AR group. Additionally, the optical density of GAD67 and VGLUT2 was reduced in the OB, AON and PFC, compared to controls. The behavioral tests demonstrated olfactory dysfunction and reduced male aggressiveness in AR rats, but we did not find any difference in the cognition and anxiety-like behavior.

Conclusions: We confirmed olfactory dysfunction in a rat model of AR and we identified modifications in synaptic activity by reduction of Syn optical density in the GL of the OB and in the PFC. This was accompanied by structural changes in glutamatergic and GABAergic activity in essential components of the olfactory pathway and PFC.