A method for determining the position of chronically implanted platinum microwire electrodes.

A histological technique is described for marking the position of the recording tips of platinum microwire electrodes, chronically implanted into the hypothalami of adult rabbits. A small electrolytic lesion was made around the tip of the electrode by passing 100 microA DC for 60 s. The animal was killed 7-10 days later and the brain perfused with formalin-ammonium bromide. Serial sections (20 micrometers thick) were cut on a freezing microtome and stained with Cajal's gold chloride sublimate to highlight the astrocytic reaction which developed in response to the electrolytic lesion. This lesion (60-100 micrometers in diameter) revealed black stained astrocytes around the destroyed tissue. The application of the technique is discussed.