Abstract

Dopaminergic innervation of the entorhinal cortex may contribute to the integration and encoding of sensory information. The primary olfactory cortex (piriform cortex) projects to the superficial layers of the entorhinal cortex, and converging dopaminergic inputs from the ventral tegmental area may modulate processes in the entorhinal cortex related to the salience of olfactory stimuli. In the current study, food-restricted rats were trained to dig in cups filled with scented sand and to discriminate between two different odours to obtain a buried food-reward which was always associated with one odour (CS+). Upon reaching criterion performance on this task, animals underwent sham surgery or 6-hydroxydopamine lesions of the entorhinal cortex. After retraining on the original discrimination rule, olfactory sensitivity was tested using cups containing decreasing amounts of the original CS+ odour. Animals showed graded decrements in response accuracy as the concentration of odorant was reduced, but no significant differences were observed between control and lesioned animals. In addition, lesioned animals did not differ in their ability to learn to perform the discrimination task with a new odour pair at low concentrations, and did not show differences in their ability to respond accurately to either the initial or novel odour pair after a delay of two weeks. These findings show that scented sand can be used as an effective stimulus to assess the sensitivity to olfactory stimuli in the rat, but do not provide evidence for deficits in olfactory sensitivity or memory performance in animals with 6-OHDA lesions of the entorhinal cortex.