Table 3. Studies reporting myelination of parvalbumin-expressing interneurons.

Study	Species	Brain region	Technique	Conclusion
Micheva et al.125	Mouse	Somatosensory cortex	Array tomography; electron microscopy; immunofluorescence	~25–50% of myelinated axons in the neocortex are GABAergic, of which nearly all are PV+
McGee et al.97	Mouse	Visual cortex	Immunofluorescence	~One-third of myelinated axons are PV+
Somogyi et al.98	Cat	Visual cortex	Electron microscopy	Presence of several myelinated basket cells
Somogyi et al.99	Cat	Visual cortex	Electron microscopy	Presence of two myelinated basket cells
Chung et al.101	Human	Frontal cortex	Immunofluorescence (CLARITYa)	Single figure of myelinated PV axons
Seress et al.103	Human	Hippocampus	Electron microscopy	Presence of a few myelinated PV axons
Hinova-Palova et al.104	Human	Claustrum	Electron microscopy; Immunofluorescence	Presence of several myelinated PV axons
Peters et al.112	Rat	Visual cortex	Electron microscopy	Presence of several myelinated basket cells
Wouterlood et al.119	Rat	Entorhinal cortex	Electron microscopy	Extensive presence of myelinated PV axons throughout all cortical layers
Gartner et al.115, 116;Brauer et al.124	Rat	Hippocampus	Immunofluorescence; electron microscopy	Majority of septohippocampal PV fibers show myelination, but not cholinergic ones
Kita et al.123	Rat	Neostriatum	Electron microscopy; light microscopy	Presence of several myelinated PV neurons
Freeman et al.117	Rat	Hippocampus (in vitro)	Hippocampal cultures; immunofluorescence	Myelination of PV neurons in vitro
Katsumaru et al.122	Rat	Hippocampus	Electron microscopy	Presence of myelinated PV neurons
Hu et al.151	Rat	Hippocampal dentate gyrus	Immunofluorescence	No myelinated PV fibers present

Abbreviations: GABA, gamma-aminobutyric acid; PV, parvalbumin.

^aCLARITY (Chung et al.¹⁰⁰) is a recently developed technique which enables immunofluorescence-based labeling and imaging of large volumes of structurally intact, optically transparent tissue.