DIVERSITY OF FAST-SPIKING PARVALBUMIN-CONTAINING INTERNEURONS IN THE DENTATE GYRUS

GABAergic interneurons (INs) account for a small percentage of cortical neuronal populations (10-20%), but are vastly heterogeneous in their morphological, intrinsic and synaptic properties. A major class of cortical INs which provides perisomatic inhibition is characterized by parvalbumin (PV) expression and fast-spiking discharge. These INs include at least two types: basket cells (BCs) and axo-axonic interneurons (AACs). While their existence in the DG has been documented, the two types have not been systematically compared. To address this lack of information, we have collected a larger sample of BCs and AACs to assess the physiological and morphological differences between them. We performed whole-cell patch-clamp recordings from DG PV-INs and recorded their intrinsic and active properties in acute slices of the rat hippocampus. We have subsequently visualized and imaged the recorded cells, and reconstructed them for morphological analysis. Our results show that BCs and AACs share similarities in their intrinsic properties (RMP, input resistance, membrane time constant, capacitance) but some of their active properties diverge (firing frequency, sag, mAHP). Morphologically, BCs have more complex apical dendritic branching patterns, a higher soma volume and differential laminar distribution of the axon in comparison to AACs. Additionally, only a minority of BCs have an axon originating from the soma, whilst in AACs most axons originate somatically. Our findings contribute to a more detailed account of the distinct morphological and physiological properties between BCs and AACs that support their unique roles.