The spike-timing-dependent plasticity of VIP interneurons in motor cortex

Front Cell Neurosci. 2024 Apr 19:18:1389094. doi: 10.3389/fncel.2024.1389094. eCollection 2024.


The plasticity of inhibitory interneurons (INs) plays an important role in the organization and maintenance of cortical microcircuits. Given the many different IN types, there is an even greater diversity in synapse-type-specific plasticity learning rules at excitatory to excitatory (E→I), I→E, and I→I synapses. I→I synapses play a key disinhibitory role in cortical circuits. Because they typically target other INs, vasoactive intestinal peptide (VIP) INs are often featured in I→I→E disinhibition, which upregulates activity in nearby excitatory neurons. VIP IN dysregulation may thus lead to neuropathologies such as epilepsy. In spite of the important activity regulatory role of VIP INs, their long-term plasticity has not been described. Therefore, we characterized the phenomenology of spike-timing-dependent plasticity (STDP) at inputs and outputs of genetically defined VIP INs. Using a combination of whole-cell recording, 2-photon microscopy, and optogenetics, we explored I→I STDP at layer 2/3 (L2/3) VIP IN outputs onto L5 Martinotti cells (MCs) and basket cells (BCs). We found that VIP IN→MC synapses underwent causal long-term depression (LTD) that was presynaptically expressed. VIP IN→BC connections, however, did not undergo any detectable plasticity. Conversely, using extracellular stimulation, we explored E→I STDP at inputs to VIP INs which revealed long-term potentiation (LTP) for both causal and acausal timings. Taken together, our results demonstrate that VIP INs possess synapse-type-specific learning rules at their inputs and outputs. This suggests the possibility of harnessing VIP IN long-term plasticity to control activity-related neuropathologies such as epilepsy.

Keywords: VIP; inhibitory interneurons; motor cortex; plasticity; spike-timing-dependent plasticity.

Grants and funding

The author(s) declare that financial support was received for the research, authorship, and/or publication of this article. ARM was supported by doctoral awards from FRQS (287520) and HBHL. CG won NSERC USRA, FRQNT BPC, and RI-MUHC studentships. TAL was funded by an NSERC USRA award. PJS acknowledges funding from CFI LOF 28331, CIHR PG 156223, FRSQ CB 254033, and NSERC DG/DAS 2017-04730 as well as 2017-507818. The Montreal General Hospital Foundation kindly funded the Chameleon ULTRA II laser.