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Abstract
Recent reports have suggested that various general anesthetics affect presynaptic processes in the central nervous system. However, characterizations of the influence of intravenous anesthetics on neurotransmitter release from presynaptic nerve terminals (boutons) are insufficient. Because the presynaptic calcium concentration ([Ca2+]pre) regulates neurotransmitter release, we investigate the effects of the intravenous anesthetic propofol on neurotransmitter release by measuring [Ca2+]pre in the presynaptic boutons of individual dissociated hippocampal neurons. Brain slices were prepared from Sprague–Dawley rats (10 - 14 days of age). The hippocampal CA1 area was isolated with a fire-polished glass pipette, which vibrated horizontally to dissociate hippocampal CA1 neurons along with their attached presynaptic boutons. Presynaptic boutons were visualized under a confocal laser scanning microscope after staining with FM1-43 dye, and [Ca2+]pre was measured using fluo-3 AM dye. Glutamate (3 – 100 μM) administration increased [Ca2+]pre in Ca2+- containing external solution in a concentration-dependent manner. Propofol (3 – 30 μM) dose-dependently suppressed this glutamate (30 μM)-induced increase in [Ca2+]pre in boutons attached to dendrites, but not to the soma or base of the dendritic tree. The large majority of excitatory synapses on CA1 neurons are located on dendritic spines; therefore, propofol may affect glutamate-induced Ca2+ mobilization in excitatory, but not inhibitory, presynaptic boutons. Propofol may possibly have some effect on glutamate-regulated neurotransmitter release from excitatory presynaptic nerve terminals through inhibiting the increase in [Ca2+]pre induced by glutamate.
Highlights
The intravenous anesthetic propofol is frequently used in general anesthesia and intravenous sedation
We investigated the effects of the intravenous anesthetic propofol on glutamate-regulated neurotransmitter release by measuring [Ca2+]pre in the presynaptic boutons of hippocampal neurons
Identification of Presynaptic Boutons Single presynaptic boutons on a hippocampal CA1 pyramidal neuron were stained with FM1-43 after Ca2+ measurement so that the green fluorescence emitted by FM1-43 would not affect the measurement of fluo-3 fluorescence intensity changes
Summary
The intravenous anesthetic propofol is frequently used in general anesthesia and intravenous sedation. It is typically thought that propofol mainly affects γ-aminobutyric acid type A (GABAA) receptors on the postsynaptic membrane of neurons in the central nervous system [1]-[7]. There has been great interest in the effects of propofol on presynaptic events, as several reports have suggested that propofol regulates neurotransmitter release from presynaptic nerve terminals (boutons) [8]-[11]. Metabotropic glutamate receptors mediate presynaptic processes [15] [16]. It is unclear if and how general anesthetics, including propofol, affect glutamate-regulated neurotransmitter release from presynaptic boutons
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