Effects of biogenic amines and intravenous anesthetics on the activity of rat locus coeruleus neurons in vitro.

To examine the effects of biogenic amines and clinically relevant concentrations of intravenous anesthetics on neuronal activities, the authors analyzed both spontaneous and evoked activities of neurons in the nucleus locus coeruleus (LC)in vitro using a single unit recording technique. Spontaneous firing was observed in 37% (14/38) of LC neurons, andN-methyl-D-aspartate (NMDA, 50 μM), glutamate (250 μM), and carbachol (1-2 mM) elicited firing in 100% (38/38), 63% (12/19), and 58% (7/12) of silent LC neurons respectively. Noradrenaline (50 μM) and serotonin (5-HT) (1-5 μM) suppressed spontaneous and drug-induced activities in 47% (15/32) and 23% (8/35) of LC neurons, respectively. Pentobarbital (100 μM) inhibited 50% (5/10) of LC neurons. All neurons activated by NMDA (n=8) and glutamate (n-3) were suppressed by ketamine (40 μM), but fentanyl (1 μM) only suppressed 60% (3/5) of spontaneously active and 75% (3/4) of glutamate-activated neurons. Identical LC neurons were inhibited by various combinations of noradrenaline, 5-HT, pentobarbital, ketamine, and fentanyl. The results suggest that clinically relevant concentrations of anesthetics and opioids modulate the activity of LC neurons induced by biogenic amines, excitatory amino acids, and acetylcholine.