Anaesthetic modulation of synaptic transmission in the mammalian CNS C.D. Richards  British Journal of Anaesthesia  Volume 89, Issue 1, Pages 79-90 (July 2002) DOI: 10.1093/bja/aef162 Copyright © 2002 British Journal of Anaesthesia Terms and Conditions

Fig 1 Diagrammatic representation of a typical CNS synapse showing the main ultrastructural characteristics. This type of synapse is called an en passage synapse and an axon makes many such contacts as it courses through the cerebral cortex. Note the presence of endoplasmic reticulum in the boutons and dendritic spines, which appears to act as an intracellular calcium store. British Journal of Anaesthesia 2002 89, 79-90DOI: (10.1093/bja/aef162) Copyright © 2002 British Journal of Anaesthesia Terms and Conditions

Fig 2 Flow chart illustrating the principal stages of synaptic transmission in the CNS. Although anaesthetics affect many aspects of cell function, only those that appear to be of most importance in modulating synaptic transmission are indicated here. British Journal of Anaesthesia 2002 89, 79-90DOI: (10.1093/bja/aef162) Copyright © 2002 British Journal of Anaesthesia Terms and Conditions

Fig 3 Evidence that pentobarbital has no effect on action potential invasion of axon branches. To visualize the invasion of an axon and its collateral branch by an action potential, the parent neurone was loaded with a calcium-sensing dye (Oregon green BAPTA-1), which then diffused into the dendrites, axon and axon collaterals. The passage of the action potential led to a transient increase in intracellular calcium concentration, which is revealed as a change in the fluorescence intensity of the calcium indicator. Calcium transients are seen in both axon branches, showing that both are invaded by the action potential. ΔF/F is the relative change in the fluorescent signal, which is roughly proportional to the increase in calcium concentration.5a British Journal of Anaesthesia 2002 89, 79-90DOI: (10.1093/bja/aef162) Copyright © 2002 British Journal of Anaesthesia Terms and Conditions

Fig 4 Effects of three anaesthetics on catecholamine secretion by electropermeabilized adrenal chromaffin cells. Catecholamine secretion was stimulated by increasing concentrations of calcium. For each anaesthetic, the left column shows the control condition ([Ca2+] 10−8 M), the centre column shows the secretion elicited by [Ca2+] 10−6 M (around threshold for activation of secretion) and the right column shows maximal secretion (obtained in response to [Ca2+] 10−4 M). The concentrations of all three anaesthetics would be sufficient to inhibit depolarization-induced secretion by 30–50%. These data show that anaesthetics do not increase the basal leakage of transmitter (in this case epinephrine and norepinephrine) and do not alter significantly the threshold or the maximal secretion that can be attained. From Pocock and Richards70 71 and the same authors’ unpublished experiments. British Journal of Anaesthesia 2002 89, 79-90DOI: (10.1093/bja/aef162) Copyright © 2002 British Journal of Anaesthesia Terms and Conditions