ELECTROPHYSIOLOGICAL AND MORPHOLOGICAL CHARACTERIZATION OF PARVALBUMIN POSITIVE INTERNEURONS ALONG THE CA1-SUBICULUM AXIS IN RODENT

The subiculum serves as the main output region of the hippocampus. Recent work has further supported a spatially structured organization along the proximodistal and superficial–deep axes of this region, reflected in the physiological and molecular properties of pyramidal neurons ^{2, 3, 4}, in line with previous connectivity studies¹. However, the organization of GABAergic inhibitory interneurons within this spatial framework remains largely unclear.
In this study, we therefore investigate morpho-electric properties of parvalbumin-positive (PV) interneurons, the most prominent interneuron type in the hippocampus, along the proximodistal axis of the ventral subiculum as well as proximal CA1. Whole-cell patch-clamp recordings were performed in acute horizontal hippocampal slices from VGAT-YFP rats to assess intrinsic and membrane properties. Recorded neurons were filled in parallel with biocytin. Confocal stacks were generated and used for morphometric analysis. Finally, each neuron was mapped onto a linearized representation of the subiculum.
While intrinsic electrophysiological properties of PV interneuron were largely homogenous along the proximo-distal axis of the subiculum, the somato-dendritic morphology displayed a gradual change along the same axis. The bipolar morphology characteristic of CA1 PV basket cell axons and dendrites progressively transitioned into a multipolar, globular configuration toward the distal subiculum in both compartments. These findings suggest that PV+ interneurons exhibit spatially organized structural diversity that may contribute to subregion-specific microcircuit organization within the subiculum.