Parvalbumin‐producing cortical interneurons receive inhibitory inputs on proximal portions and cortical excitatory inputs on distal dendrites

Abstract

To examine inputs to parvalbumin (PV)-producing interneurons, we generated transgenic mice expressing somatodendritic membrane-targeted green fluorescent protein specifically in the interneurons, and completely visualized their dendrites and somata. Using immunolabeling for vesicular glutamate transporter (VGluT)1, VGluT2, and vesicular GABA transporter, we found that VGluT1-positive terminals made contacts 4- and 3.1-fold more frequently with PV-producing interneurons than VGluT2-positive and GABAergic terminals, respectively, in the primary somatosensory cortex. Even in layer 4, where VGluT2-positive terminals were most densely distributed, VGluT1-positive inputs to PV-producing interneurons were 2.4-fold more frequent than VGluT2-positive inputs. Furthermore, although GABAergic inputs to PV-producing interneurons were as numerous as VGluT2-positive inputs in most cortical layers, GABAergic inputs clearly preferred the proximal dendrites and somata of the interneurons, indicating that the sites of GABAergic inputs were more optimized than those of VGluT2-positive inputs. Simulation analysis with a PV-producing interneuron model compatible with the present morphological data revealed a plausible reason for this observation, by showing that GABAergic and glutamatergic postsynaptic potentials evoked by inputs to distal dendrites were attenuated to 60 and 87%, respectively, of those evoked by somatic inputs. As VGluT1-positive and VGluT2-positive axon terminals were presumed to be cortical and thalamic glutamatergic inputs, respectively, cortical excitatory inputs to PV-producing interneurons outnumbered the thalamic excitatory and intrinsic inhibitory inputs more than two-fold in any cortical layer. Although thalamic inputs are known to evoke about two-fold larger unitary excitatory postsynaptic potentials than cortical ones, the present results suggest that cortical inputs control PV-producing interneurons at least as strongly as thalamic inputs.

Lack of Cdkl5 Disrupts the Organization of Excitatory and Inhibitory Synapses and Parvalbumin Interneurons in the Primary Visual Cortex

“…Importantly, the adjustment of the strength of synapses made by PV + INs is needed for equalizing E/I ratio of pyramidal cells following increased activity (Xue et al, 2014). Moreover, pyramidal neurons targeting PV + dendrites represent critical regulators of PV + cell activity (Kameda et al, 2012), and their excitatory synapses can undergo activity-dependent plastic modifications that may be required for rebalancing dynamic changes in network E/I ratio (Chang et al, 2010; Nissen et al, 2010; Le Roux et al, 2013). The hyperconnectivity of pyramidal neurons with PV + cells observed in V1 of Cdkl5 KOs is, therefore, expected to cause a major perturbation of cortical activity, resulting in hypoactivation of projection neurons.…”

Differential Inputs to the Perisomatic and Distal-Dendritic Compartments of VIP-Positive Neurons in Layer 2/3 of the Mouse Barrel Cortex

“…Both the myristoylation/palmitoylation site of the Fyn N-terminus (myr) and the C-terminus of the low-density lipoprotein receptor (LDLRct) were added to green fluorescent protein (GFP), referred to as FGL. FGL was previously reported to be distributed specifically on the somatodendritic membranes of neurons (Kameda et al, 2008, 2012). (C–E) Specific labeling of somatodendritic membranes of VIP+ neurons.…”

“…myrGFP-LDLRct, referred to as FGL in the present study, was previously developed for specific labeling of the somatodendritic plasma membranes of neurons. FGL was composed of the myristoylation/palmitoylation site of Fyn N-terminus, GFP and the C-terminus of low density lipoprotein receptor (Kameda et al, 2008, 2012). The sequence of the flip-excision (FLEX) switch (Schnütgen et al, 2003) consisted of two pairs of loxP and lox2272 sites in opposite orientations, and the FGL sequence was introduced between these pairs in the antisense orientation.…”

3D Clustering of GABAergic Neurons Enhances Inhibitory Actions on Excitatory Neurons in the Mouse Visual Cortex

“…Among these subtypes, the principal groups in the rodent neocortex are interneurons, which express PV or SOM, although other subtypes of interneurons such as those expressing 5-hydroxytryptamine 3A receptors (5HT3aR) and vasoactive intestinal polypeptide (VIP) exist abundantly in superficial layers of the mouse neocortex . To see how those two subtypes of interneurons are distributed in the 3D space of the visual cortex, we used PV/myristoylationGFP-low-density lipoprotein receptor C-terminal BAC transgenic mice (PV/ myrGFP-LDLRct mice), which express somatodendritic-membrane-targeted EGFP (myrGFP-LDLRct) in PV neurons (Kameda et al, 2012). In these mice, SOM neurons were identified with immunohistochemistry after the recording experiments ( Figures 6A-6C), and visually responsive neurons of this type were incorporated into the 3D cube of visual cortex together with PV neurons and the other visually responsive neurons ( Figure 6D).…”