A new device for monitoring concentrations of intracellular Ca2+ in CNS preparations and its application to the frog's spinal cord.

For monitoring the changes in intracellular concentrations of Ca2+ in vertebrate CNS neurones in situ, we devised an assembly of two quartz-made optic fibres enclosed in a glass capillary. Esterified fluorescent Ca2+ indicator (quin2/AM) was injected into the motoneuronal pool of the frog's spinal cord, and about 60 min later, the assembly was inserted directly into the same region. Ultraviolet light for exciting the indicator was transmitted through one optic fibre, while the fluorescence emitted from the cells was guided to a photoelectric converter through the other fibre. Administration of Ringer's solution containing some stimulant (KCl, excitatory amino acids) through arterial perfusion, evoked both an increase of fluorescence intensity under excitation light of 340 nm wavelength and a decrease under 380 nm light. Electrical stimulation delivered to a dorsal root provoked equivalent responses in fluorescence; this response is known to be an indicator of an elevation in intracellular concentrations of Ca2+.