The influence of the ketogenic diet on insulin receptor expression in the caudal hippocampus

The ketogenic diet (KD) has long been used to treat intractable epilepsy when pharmacological methods proved ineffective. It is a high fat, low carbohydrate, calorie restricted diet that induces a metabolic state of ketosis in patients. Although it is common, the mechanism of action is not well understood and understanding it would likely inform diet administration to sustainability. We have identified the insulin signaling pathway as a possible candidate for this function of the KD because of its unique roles in the brain, including learning and memory, neuronal excitability, and reward pathways. Previous work in this lab has suggested that there is decreased expression of insulin receptors (IR) in several parts of the brain, specifically the hypothalamus, entorhinal cortex, and dentate gyrus, after administration of the KD. To add to research done in this lab, we localized and quantified IR expression using immunohistochemistry, microscopy, and digital image analysis in the caudal CA3 of the hippocampus, the medial habenula (MHb) and the periventricular (PV) nuclei of the thalamus in rats fed the KD compared to the control diet. After assessing several quantification measures, we used a color deconvolution and subtraction method of analysis on ImageJ to assess both the intensity and area of the diaminobenzidine (DAB) stain. The changes we noted between control and KD animals in the CA3, MHb, and PV were regionally distinct, but not significant. However, we did find a trend of decreased IR expression in animals fed the KD that was unique to the caudal region of the hippocampus. This trend, together with previous findings, suggest that IR expression and the insulin signaling pathway may be influenced by the KD during treatment for intractable epilepsy. This warrants further exploration to determine if insulin is an important aspect of the KD efficacy or if it is involved in the mechanism of action of the KD.