The Pia-Arachnoid as a Barrier in Experimental Poliomyelitis. ∗

Abstract

The occasional demonstration of poliomyelitis virus in the cerebrospinal fluid of experimental animals has given rise to a series of experiments and speculations regarding the rôle of this body liquid in the dissemination of the disease through the central nervous system. Such investigations as those of Clark and Amoss 1 and Hurst 2 who produced experimental poliomyelitis regularly by intra-cisternal and intrathecal inoculation have led to the assumption recently made articulate by Schaeffer and Muckenfuss 3 that intracerebral inocula may be effective at sites far distant from the point of introduction. In previous observations the permeability of the ependyma and the possibility of injury to the pia-arachnoid are factors which have not been properly controlled. The following experiments indicate that under ordinary conditions the leptomeninges constitute an effective barrier—so effective that large amounts of active virus may be present in the cerebrospinal fluid without any clinical indication of poliomyelitis.

These experiments fall into 3 groups: (a) virus dripped over an exposed cortical surface with intact pia; (b) virus introduced into the lumbar cistern with intact pia; (c) virus introduced at either of the above sites after deliberate pial injury.

Fifteen animals were used in the first group. The cerebral cortex was exposed by opening an oval dural flap 3 cm by 2 cm which was centered over the paracentral lobule with the long axis in a rostro-caudal direction. Great care was taken to avoid injury to the pia, although the arachnoid was undoubtedly torn in places. One-quarter to three-quarters cc of 20% MV virus in salt solution was then dripped over the exposed cortical surface, the edges of the dural flap being elevated to insure as wide dissemination as possible. The dura was then carefully sutured and the incision closed.