DECIPHERING INTERNEURON DISTRIBUTIONS IN THE MEDIAL ENTORHINAL CORTEX

GABAergic interneurons (INs) are highly heterogenous, exhibiting diverse morphological, physiological, and molecular properties. They are commonly classified into three major groups based on largely non-overlapping molecular markers: parvalbumin (PV), somatostatin (SST), and serotonin-receptor 5HT3A. Their relative proportions vary across brain regions, with PV INs being predominant in most neocortical primary sensory cortices and SST INs being more prominent in association cortices.
Despite its role in learning and memory, and its involvement in neurodevelopmental disorders, IN distributions in the medial entorhinal cortex (MEC), an associative cortex, remain understudied.
Here we aim to decipher IN subtype distribution in the MEC and investigate how it arises during postnatal development. By immunohistochemically staining GAD67-EGFP mouse tissue at P90, we confirmed the previously reported dorsoventral (DV) gradient of PV INs. We further unveiled distributions of other IN subtypes, including SST, calretinin, vasoactive intestinal peptide (VIP), and reelin. The total MEC IN population does not display a DV gradient, despite the PV gradient. Stainings for MGE-derived INs, a group comprised of PV and SST INs, with the MGE marker Lhx6 revealed an increase in MGE INs ventrally. However, SST INs do not present a higher density ventrally, despite constituting the largest MEC IN group.
To further elucidate this discrepancy, explore IN heterogeneity in greater detail, and uncover potential developmental mechanisms underlying these distributions, we performed spatial transcriptomics on MEC tissue from WT mice at P4, P7, P15, and P90. Current analyses focus on identifying spatial patterns of MEC IN subtypes and exploring their postnatal developmental dynamics.