Identification and electrophysiological investigations of embryonic mammalian motoneurones in culture

The retrograde transport of fluorochromes from muscle was used to label embryonic rat motoneurones in vivo. The fluorescent motoneurones were subsequently detected in cultures of dissociated spinal cord neurones using an image-intensification video camera, the images from which allowed identification of the motoneurones under phase-contrast microscopy. Such motoneurones were mostly phase dark, often with a multipolar appearance and were detectable for up to 4 days in culture. Whole-cell patch-clamp recordings from these motoneurones demonstrated mean input resistances of 635 MΩ and resting membrane potentials of −65 mV; action potentials could be evoked and, under voltage-clamp, inward and outward currents were present.