Characterization of inhibitory and projection specific neurons of the presubiculum

The presubiculum (PrS) is a transitional cortical area of the parahippocampal formation in the temporal lobe, close to hippocampus and entorhinal cortex. PrS is involved in spatial navigation processing by encoding an animal’s head direction. The HD signal is most likely generated in lateral mammillary nucleus (LMN) and relayed in anterodorsal thalamus (ADN) before being processed in the PrS. PrS is thought to be crucial for updating the HD signal with visual landmark information as it receives direct projections of visual cortex and projects back to downstream ADN and LMN. The aim of my work has been twofold. First, I examined the GABAergic neurons of the PrS. GABAergic interneurons are at the source of inhibitory activity that is essential for local signal generation. I quantified the total number of presubicular interneurons in the GAD67-GFP transgenic mouse and investigated morphological properties and layer specific distribution of interneuron subtypes. The proportion of interneurons in the PrS was 11% of all neurons. To identify neurochemical subpopulations, I performed double immunolabeling with combinations of Parvalbumin (PV), Calretinin (CR), Calbindin (CB), Somatostatin (SOM), Vasointestinal Peptide (VIP) and Neuropeptide Y (NPY). Largest population of presubicular interneurons was PV+ (36%). CR, CB and SOM interneurons contributed evenly to the population (~18%), while there were less VIP+ interneurons (9%). Double labeling experiments revealed a small subpopulation of presubicular interneurons positive for PV and SOM, a co- expression pattern seen in the hippocampal formation but usually absent in neocortical regions. Indeed, the PrS displays a unique expression pattern of inhibitory cells, and their functional role within the presubicular microcircuit will have to be investigated in future studies. The second part of my work focused on projection-specific neurons of the PrS targeting LMN and ADN. To reveal their morphological and electrophysiological identity, I injected retrogradely migrating fluorescent beads into LMN or ADN which allowed assessing the laminar origin of projection neurons. While LMN projecting neurons were exclusively seen in layer IV, ADN projecting neurons were restricted to deep layers. Patch clamp recordings of bead-containing presubicular neurons indicated a relatively homogenous population of LMN projecting neurons, displaying an intrinsic bursting behavior which matches their presumed role of operating fast visual update. ADN projecting neurons were mostly regular spiking with otherwise heterogeneous intrinsic properties. Both populations had dendrites extending up to superficial layers, making them well suited to receiving visual input and updating subcortical HD-signal with landmark information. Future work should shed light on recruitment of neuronal subpopulations by specific afferent inputs for a better understanding of information processing in the PrS.

Author dc:creator

• Lofredi, Roxanne

• presubiculum
• interneurons
• head direction circuit

Licence dc:rights.uri

• http://www.fu-berlin.de/sites/refubium/rechtliches/Nutzungsbedingungen

Language dc:language

eng

Identifier URI

http://dx.doi.org/10.17169/refubium-17159

OAI record oai:identifier

https://refubium.fu-berlin.de/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Arefubium.fu-berlin.de%3Afub188%2F12961