Experimental Disruption of the Blood-Brain Barrier System in an Insect (Periplaneta Americana)

1. The effects of hypertonic urea and hypertonic glucose solutions upon the ‘blood-brain barrier’ in the isolated abdominal nerve cord of the cockroach have been studied. 2. Electrophysiological studies showed that a hypertonic solution of urea, but not of glucose, was effective in reducing the barrier to the entry of potassium and the loss of sodium. 3. Electron-microscopic studies revealed no significant ultrastructural changes, and no disruption of the perineurial barrier to the entry of ionic lanthanum, following comparable exposure to the hypertonic solutions. 4. It is suggested that this alteration of the blood-brain barrier may result from a selective change in permeability of the perineurial membranes or tight junctions.