Pial Vascular Responses in the Rat

To the Editor: Morii, Ngai, and Winn (1986) are to be congratulated on their careful analysis of pial vascular responses in the rat. However there are several points that require clarification. Contrary to the impression given in the author's discussion, an "open" window need not result in a change in local pH. If the craniotomy is small, for example when mice are used, the pH shift is avoided by contin uously superfusing the craniotomy site at high rate offlow, with an artificial CSF at correct pH. This is readily done in mice and could probably be done in rats. Since the authors indicate awareness of my own work with the mouse, they should have cited the many papers in which I carefully control local pH by using such a suffusate. Moreover in my studies of mice, contrary to their experience with