Inhibitory actions of general anesthetics on hippocampal CA1 neurons modified by activation of amygdala circuitry are demonstrated on the novel amygdala-hippocampal slice preparation

In order to examine effects of general anesthetics on hippocampal synaptic transmission in the absence and presence of amygdala circuitry activation, we have developed a unique amygdala-hippocampal slice preparation in which projections between amygdala and hippocampal CA1 are conserved. Stimulating electrodes were placed in radiatum stratum (Rad) to stimulate CA1, and in amygdala-hippocampal area (AH) to simulate amygdala inputs to hippocampus. Two sets of extracellular recording microelectrodes were positioned in cell bodies and dendrites of CA1 to record population spikes (PSs) and excitatory post-synaptic potentials (EPSPs), respectively. Intravenous anesthetics did not elicit consistent effects on PS and EPSP following a test stimulus on Rad. A pre-pulse of AH in addition to a test-pulse on Rad produced significant reduction of PS amplitude without a change in EPSP. Pre-treatment with tetanus-pulse on AH reversed the anesthetic-induced reduction of PS. The results suggest that inhibitory actions of general anesthetics in CA1 can be modified by activation of amygdala, suggesting that preoperative anxiety and fear could modify anesthetic actions. The modification was more prominent in the presence of intravenous anesthetics than with volatile agents.