Perineurial and glial cells in the tickBoophilus microplus (Acarina: Ixodidae): freeze-fracture and tracer studies

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Abstract
In the cattle tickBoophilus microplus, the cells of the perineurium are characterized by accumulations of glycogen which increase dramatically after feeding. Gap junctions couple both these perineurial cells which ensheath the C.N.S. and the underlying glial cells. No tight junctions have been found between perineurial cells and there is in consequence no blood-brain barrier. Using ionic lanthanum as a tracer the extensive gap junctions are shown to have no occluding effect and lanthanum penetrates through the perineurium and glial layers to the level of the axonal surfaces. By colloidal lanthanum impregnation and freeze-fracture studies, the gap junctions appear to be typical of arthropods in that their particles show a characteristic diameter (13 nm in freeze-fracture), are distributed relatively loosely within the junctional plaques and fracture onto the E face of the junctional membranes. Semi-ordered particle arrays are found on E face membranes of adjacent axons and glia which may represent axoglial junctions.