Terminal Schwann‐like cells interconnecting between the axon terminal and capillaries or fine varicose fibers in the skin mechanoreceptors

Abstract

Mechanoreceptors are important sensory endings derived from large caliber myelinated nerve (Aβ‐) fibers in the mammalian skin tissue. Their structure is complex, but recently, our three‐dimensional confocal studies of the cat or the rat vibrissal follicles and of the hairy skin of the cat paws have revealed that they consisted of one or several branched and thickened axon terminals (AT) surrounded by terminal Schwann cell (TSC) sheaths. The cell bodies of the TSC exist in the interstitium far from the axon terminals. By using confocal analyses followed by transmission electron microscopic observations on the same sections, we demonstrated that S100β protein (S100β) positive TSC‐like cells were interconnected between the AT and the capillaries or unmyelinated varicose nerve fibers closely surrounding the Merkel endings in the touch domes or the lanceolate endings in the vibrissae. Nerve elements were mainly immunocytochemically stained by anti‐protein gene product 9.5 (PGP9.5) and anti‐S100β antiserum, and capillaries were stained by using tomato‐lectin. These TSC‐like cells showed different appearances from normal TSCs in that some had a large number of dendrites and others had a few. Some had long dendrites, but others had short. A few of those were distributed around degenerating or regenerating nerve fibers. Those findings strongly suggest existence of a glial cell system totally independent from the conventional Schwann cells in the peripheral nervous system. The functions may be similar to the astroglia and the microglia in the central nervous system.