Activity and spatial distribution of synaptic vesicles at inhibitory and excitatory synapses in chronically epileptic mice

Abstract

The brain is a highly regulated and organised structure. It is composed of neuronal networks that integrate signals and generate responses through neuron-to-neuron communication. The brain is covered by the cerebral cortex where the neocortex makes its largest part. The neocortex is divided into six cortical layers (1-6) and it is topologically classified to four lobes. One of the lobes is the occipital lobe, which has the visual cortex. Here we used Tetanus neurotoxin in the visual cortex of mouse models to induce chronic focal epilepsy and examine synaptic neuronal excitability. Epilepsy is a neurological disorder that causes signalling disturbance and uncontrolled neurotransmitter release. This paper examines and compares synaptic vesicles in epileptic and healthy mice where neurons are observed by electron microscopy. The procedure includes FM1-43 dye injection, brain slicing, vesicle photoconversion with DAB and serial sectioning in preparation for electron microscopy. The aim is to obtain ultrastructural readouts of photoconverted (activated) and clear (non- activated) vesicles within synapses. This technique is used to test whether there is a difference in the number and position of activated vesicles in epileptic mice compared to healthy ones. Our findings indicate a significant difference in the organisation of photoconverted vesicles, particularly to the active zone. Our approach also revealed a significant difference in the GABAergic and glutamatergic synapses within both groups.