Identifying Parvalbumin-positive Interneurons in the Mouse Amygdala Based on Unique Marker Combinations

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Supervisor:
Dr. Jobbágy Ákos Andor
Department of Measurement and Information Systems

The amygdala is an almond-shaped region located in the temporal lobes of the brain. It’s primary roles are the processing of negative emotions and fear, and to create and store fear-associated memories. The primary cells, similarly to the neocortex, are pyramid cells, but the local interneurons are not so well known, and we are not yet able to categorize them based on neuromarkers, targets and firing properties. Typical types are parvalbumin-, or cholecystokinin-expressing interneurons. They are also routinely separated based on targeting axon initial segments, dendrites, or the perisomatic region of principal cells.

The long-term goal of the project is to identify the different cell types in the basolateral amygdala, and to explore how the different types build up the neural network of this region. To this end, we need to find marker combinations that can uniquely label the different neuron types, and determine the synaptic target distribution of local inhibitory interneurons. This thesis describes a small part of this project: parvalbumin-expressing, fast spiking interneurons in the amygdala mainly consist of axo-axonic, and basket cells. My goal was to determine the synaptic target distribution of the basket cells identified in my previous experiments.

I performed patch clamp experiments on brain slices obtained from transgenic mice, in which parvalbumin-expressing cells were fluorescently labeled. During the patch clamp experiments I filled these cells with biocytin, then through multiple immunostaining I determined, whether they express calbindin, and whether they are axo-axonic or basket cells. Here, I performed immunohistochemistry on the slices containing basket cells, labeling the Kv2.1 proteins.

Subsequently I obtained high resolution image stacks using confocal miscroscopy, and determinded the synaptic target distribution of the basket cells, which were found to be expressing calbindin.

I also performed paired recordings on cholecystokinin expressing amygdalar interneurons and their postsynaptic partners. I found, that PV immunopositíve (+), CCK+ and principal cells can be distinguished based on their firing properties. CCK+ interneurons form a tightly coupled network, and innervate local interneurons and principal cells.

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