INTRODUCTION: There are two main types of neuronal inhibition: phasic and tonic one. Recent findings show that N-methyl-D-aspartic acid (NMDA) treatment induces plastic changes in tonic inhibition in hippocampal interneurons including somatostatin-expressing (SST+) cells which, through interactions with other neurons, play a crucial role in regulating the hippocampal neuronal network (Wyroślak et al., 2023).

AIM(S): Herein, we investigated the influence of heterosynaptic inhibitory long-term potentiation (iLTP) induction via transient NMDA applications on tonic current density in subtypes of SST+ cells.

METHOD(S): Experiments were conducted on brain slices (hippocampal CA1 region) from SST-Cre x Ai14 mice. Tonic currents were measured using patch-clamp and pharmacology. Cells were filled with biocytin and imaged using confocal microscopy.

RESULTS: Our data allowed us to divide SST+ cells into two subgroups: oriens-lacunosum/moleculare (OLM) and non-OLM cells. OLM cells showed a higher tonic current density (0.78 ± 0.40 pA/pF, p < 0.05) in the control group than non-OLM cells (0.21 ± 0.02 pA/pF, p < 0.05). Induction of plasticity with NMDA caused an increase in tonic current density in OLM cells (0.92 ± 0.48 pA/pF, p > 0.05) but in non-OLM cells we observed a decrease in tonic inhibition (0.13 ± 0.01 pA/pF, p < 0.05).

CONCLUSIONS: We conclude that distinct subgroups of SST+ cells show differences in tonic inhibition and NMDA treatment causes the opposite plastic effect on tonic currents in OLM cells and other SST+ cells. These differences indicate functional heterogeneity of SST+ neurons and their distinct roles in local network regulation.

FINANCIAL SUPPORT: Supported by Polish National Science Centre grant OPUS 2021/43/B/NZ4/01675