A subpopulation of cortical VIP-expressing interneurons with highly dynamic spines

Abstract

Structural synaptic plasticity may underlie experience and learning-dependent changes in cortical circuits. In contrast to excitatory pyramidal neurons, insight into the structural plasticity of inhibitory neurons remains limited. Interneurons are divided into various subclasses, each with specialized functions in cortical circuits. Further knowledge of subclass-specific structural plasticity of interneurons is crucial to gaining a complete mechanistic understanding of their contribution to cortical plasticity overall. Here, we describe a subpopulation of superficial cortical multipolar interneurons expressing vasoactive intestinal peptide (VIP) with high spine densities on their dendrites located in layer (L) 1, and with the electrophysiological characteristics of bursting cells. Using longitudinal imaging in vivo, we found that the majority of the spines are highly dynamic, displaying lifetimes considerably shorter than that of spines on pyramidal neurons. Using correlative light and electron microscopy, we confirmed that these VIP spines are sites of excitatory synaptic contacts, and are morphologically distinct from other spines in L1.

Perisomatic Features Enable Efficient and Dataset Wide Cell-Type Classifications Across Large-Scale Electron Microscopy Volumes

“…Because they are similar in shape, this analysis groups these inhibitory "thorn" like protrusions with the smaller stubby spines found on excitatory cells. 23 Consistent with that, the bipolar example shown here contains an elevated number of such small protrusions, 26 including in the somatic region, whereas the smoother dendritic shafts of this basket cell example contain virtually no counts in these bins. (Fig.…”

“…This suggests that NP cells might be an intriguing target to understand the role of spine shape in cortical computation. [38][39][40] Our observation that spine shapes vary systematically across cell types could relate to differences in the average age or nature of spines across those types, 41 as at least VIP dendrites have been shown to have much more motile spines than other interneurons, 26 and some spiny SST+ interneurons have highly multi-synaptic spine like protrusions. 23 We observed some clear but previously unquantified differences in features of different inhibitory sub-classes in cortex.…”

“…The local somatic region contains both somatic membrane and proximal dendritic shafts thereby enabling the examination of properties like the size and distribution of spines. 4,26…”

“…The local somatic region contains both somatic membrane and proximal dendritic shafts thereby enabling the examination of properties like the size and distribution of spines. 4,26 Here we report the first large scale survey of somatic properties of cells as measured with EM across the cortical depth. From the analysis of these properties we describe some novel structural patterns of cortical organization.…”

Spine dynamics of dentate gyrus parvalbumin-positive interneurons are defined by network activity and experience

“…Moreover, the volume of spine heads linearly increased with the area of postsynaptic densities (PSDs; P=2.47x10 -6 ; 21 spines; Fig. 2a; Methods), suggesting that similar to observations in PCs, spine head volume may correlate with their synaptic input area and strength [31][32][33][34][35] .…”