The connectome of the parahippocampal cortex - mice studies.

An important function of the brain is to store acquired information, experience, for later use. These so-called memory processes are mediated by widespread networks including the parahippocampal-hippocampal network that is assumed to be essential to conscious memory. Within the parahippocampal-hippocampal network different subunits have been identified, each of which contributes in a unique though complementary way to learning and memory. The goal of this study is to understand the functional architecture of the entorhinal cortex in relation to main input and output structures, which are key elements of this memory network. We will use a combination of anatomical and electrophysiological approaches in mice. This protocol is paralleled with a comparable protocol for rats. Certain non-toxic vital dyes will be injected in the brain to visualize circuitry. We will further use an optogenetic approach in which we will express light-sensitive channels into cells of origin of input pathways to the entorhinal cortex, using viral transfer techniques. Using comparable viral approaches, we will add a pharmacogenetic component to the optogenetic component. This allows us to manipulate activity in specific input pathways in vivo, in addition to selectively manipulate synaptic transmission in in vitro brain slice preparations. Analysis will be carried out at different levels of resolution, from network to single cells using qualitative and (semi)quantitative morphological methods at light, confocal and electronmicroscopical level, in tissue sections obtained from the brain after euthanasia. In a number of experiments these approaches will be combined with electrophysiological and optical recordings in living brain slices and subsequent analyses after these slices are fixed for further use. We estimate to use a maximum of 1370 wildtype and transgenic mice of either sex and we will pay close attention to reduce the number of animals used, if at all possible. We consider reduction possible when we have obtained the required statistical valid data to publish our results. We make use of methods that are continuously monitored and updated by our animal staff and veterinarian and we evaluate the impact on the animals as moderate, since the animals show complete recovery within two days after surgery. Animals will be group housed prior to the experiment in cages with enriched environment. Before the experiment starts, the animals are given 7 days to acclimate to their new environment. All members who are involved in surgeries and perfusions are trained and licensed. Moreover, regular training updates are required. The study of brain functions, as yet, cannot be done using computational models or cell cultures, since those model systems do not allow an appropriate detailed level of assessment of the complexity of brain networks. The obtained information will be instrumental, not only within the context of many of the functional studies carried out in our centre but also to understand the critical changes in the system in the early stages of Alzheimer’s disease.