Effects of general anesthetics on calcium ion concentration in presynaptic nerve terminals attached to dissociated mammalian neurons

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It is known that general anesthetics affect neurotransmission at lower concentrations than they impair conduction. Accumulating evidence shows that general anesthetics enhance inhibitory transmission carried by GABA or glycine, and that they depress excitatory transmission by Ach or glutamate, with an exception of that by 5HT. Sophisticated experiments on transmission have been performed with post synaptic receptors of dissociated neurons. There is little evidence, however, about the anesthetics effects on the presynaptic processes, which compose an important part of transmission. In the present study, we measure the calcium ion concentration in the presynaptic nerve terminal, attached to mechanically dissociated neurons of rat hippocampus.Wistar rats were decapitated under pentobarbital anesthesia and the brain was removed and sliced. Fire-polished micro glass pipette was attached on the hippocampal region and vibrated at 2Hz for 3min. Dissociated neurons were obtained, with presynapt … More ic terminal (bouton) attached. The boutons were identified with FM1-43 and the intracellular calcium ion concentration [Ca^<2+>]_i was measured with fm-3AM under confocal laser microscope1) High concentration of extracellular K increased the [Ca^<2+>]_i both in neuronal soma and in the bouton This increase was abolished in Ca-free solution, indicating that depolarization induced [Ca^<2+>]_i-increase depends on Ca entry.2) Glutamate (1-300 micro M) increased the [Ca^<2+>]_i both in neuronal soma and in the bouton in a concentration dependent manner. The increases did not occur in the absence of Ca^<2+>.3) CNQX (30 micro M) markedly suppressed the glutamate-induced increases in [Ca^<2+>]_i..4) L-type calcium channel blockers (nimodipine, FS2, calcicludine) inhibited the glutamate-induced increases in [Ca^<2+>]_i. concentration dependently.5) These findings suggest that the glutamate-induced increases in [Ca^<2+>]_i. may be attributed, in part, to opening of L-type calcium channels, which is produced by activation of AMPA/kainate type glutamate receptor.6) Pentobarbital depressed the glutamate-induced increases in [Ca^<2+>]_i. both in soma and in boutons, with greater effects on boutons. This result suggests that pentobarbital modulates neurotransmission via inhibition of calcium channel at the presynaptic nerve terminal. Less