Long-term labeling of microelectrode tracks with fluorescent latex microspheres

After physiological recordings are performed in behaving animals, it is valuable to identify microelectrode tracks in histological sections so that neuronal responses can be correlated with brain anatomy. However, no good method currently exists for long-term labeling, so that microelectrode tracks can be recovered months or even years after recording sessions.

Penetrations were made into the brains of mice with microelectrodes coated with fluorescent dyes packaged into 0.2 μm polystyrene microspheres, followed by survival periods of 3 days, 2, 4, or 6 months. Sections were examined by fluorescence microscopy before and after cytochrome oxidase histochemistry to identify microelectrode tracks.

After all 4 survival periods, 0.2 μm fluorescent microspheres clearly marked the tracks of microelectrode penetrations.

Fluorescent microspheres label microelectrode penetrations for longer than do fluorescent lipophilic dyes, such as FM 1-43FX. The label appears punctate, and resistant to degradation, because it is protected by the barrier of the polystyrene micro-container.

Coating of microelectrodes with fluorescent microspheres allows one to identify the penetration track in histological sections half a year later. This technique may be useful when electrophysiological recording sessions are being carried out in behaving animals, with plans to identify electrode tracks in histological sections many months later.