| dc.description.abstract | The entorhinal cortex (EC) is the major input and output structure between the hippocampal formation (HF) and the rest of the brain. Here, as is the case in the rest of the cortex, there are 2 main types of cortical neurons: excitatory or principal neurons which account for 80-90% of the neuronal population and the remaining 10-20% are inhibitory interneurons. PV+ and SOM+ interneurons account for ~70% of the interneurons in the cortex, while the last 30% belongs to the 5HT3aR+ group of which approximately 40% express vasoactive intestinal peptide (VIP). This interneuron type has been less studied, but they are known to target primarily other interneuron types suggesting a role in top-down modulation and gain control. The EC receives input from the HF as well as several cortical and subcortical areas. Both PV+ and SOM+ interneurons in the EC receive local and long-range inputs from most areas that provide general inputs to the EC. Understanding how specific groups of neurons are connected to each other is critical to understand how cortical networks function. Since VIP+ interneurons in the EC have not been studied to any great extent, characterizing them, and describing their monosynaptic inputs across the brain will provide a deeper insight into the EC microcircuit. To achieve this, I performed monosynaptic rabies virus retrograde tracing in combination with immunohistochemistry. I found out that VIP+ interneurons in the EC are a morphologically heterogenous population that receives local input as well as input from multiple cortical and subcortical areas, and these inputs are considerably similar to the inputs to the general population of the EC and the inputs to PV+ and SOM+ interneurons. This suggest VIP+ interneurons in the EC could be part of predominantly feedforward inhibition networks where the end result could be disinhibition of principal cells. The results in this thesis provide a basis for further studies into the functional role of VIP+ interneurons in the entorhinal-hippocampal system. | |