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

In the cattle tick Boophilus 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 enshealth 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 studied, the gap junctions appear to be typical of arthropids 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.