Effects of propofol and pentobarbital on calcium concentration in presynaptic boutons on a rat hippocampal neuron

Purpose: Numerous reports suggest that intravenously administered (IV) anesthetics affect postsynaptic events in the central nervous system. However, there is little evidence about how general anesthetics influence the presynaptic processes. The level of presynaptic calcium (Ca²⁺) concentration ([Ca²⁺]_pre) regulates neurotransmitter release. In this study, we investigated the effects of anesthetic propofol IV and the barbiturate pentobarbital on neurotransmitter release by measuring [Ca²⁺] _pre in the presynaptic nerve terminals (boutons) on a dissociated single hippocampal rat neuron. Methods: Sprague-Dawley rats 10-14 days old were decapitated under pentobarbital anesthesia, and brain slices were prepared. The hippocampal CA1 area was touched with a fire-polished glass pipette, which vibrated horizontally, and neurons were dissociated, along with the attached presynaptic boutons. The presynaptic boutons were visualized under a confocal laser-scanning microscope after staining with FM1-43 dye, and [Ca ²⁺]_pre was measured with acetoxymethyl ester of fluo-3 (fluo-3 AM). Results: High potassium (K⁺) (15-90 mM) increased the [Ca²⁺]_pre in the Ca²⁺-containing solution in a concentration-dependent manner. Whereas propofol (10 μM) and pentobarbital (300 μM) suppressed the high K⁺ (60 mM)-induced increase in [Ca²⁺]_pre in the boutons attached to the dendrite, they did not affect [Ca²⁺]_pre in the boutons attached to the soma or dendrite base. As a large majority of excitatory synapses are located on dendritic spines, these agents may affect Ca²⁺ mobilization in the excitatory presynaptic boutons. Conclusions: Propofol and pentobarbital may affect neurotransmitter release from the excitatory presynaptic nerve terminals due to inhibition of increase in [Ca²⁺]_pre.