Differential Actions of Volatile Anaesthetics and a Systemic Barbiturate on Strongly Electrically Coupled Neurons

The actions of clinical concentrations of volatile anaesthetic halothane and isoflurane were compared with those of pentobarbitone on identified neurons of the pond snail Lymnaea stagnalis. Application of halothane and isoflurane (1% v/v and 2% v/v), to the CNS of Lymnaea caused the strongly electrically coupled neurons VD1 and RPD2 to become quiescent, with a significant increase in membrane potential and a significant reduction in their coupling coefficient. These results clearly demonstrate that the volatile anaesthetics and barbiturates have different mechanisms of action at electrical synapses. The effects of volatile anaesthetics were dose dependent, and the actions of halothane were more rapid than those of isoflurane, reflecting their different anaesthetic potencies. Sodium-pentobarbitone had markedly different effects from the volatile anaesthetics. Clinical concentrations of pentobarbitone (100 ± M) caused VD1 and RPD2 to become quiescent with no significant change in either their resting membrane potential or the coupling coefficient between them. Higher concentrations of pentobarbitone (0.5 and 2.0 mM), caused VD1 and RPD2 to fire in doublets and triplets until their hyper-activity increased leading to paroxysmal depolarising shifts (PDS) (phase I). Following this the cells became quiescent and hyperpolarised (phase II). During phase I, the VD1-RPD2 coupling coefficient increased significantly, but during phase II the coupling coefficient returned to control values. There was no dose dependency in the effects of pentobarbitone at high concentrations. Citation: Munir M Qazzaz and William Winlow. “Differential Actions of Volatile Anaesthetics and a Systemic Barbiturate on Strongly Electrically Coupled Neurons”. EC Neurology 2.4 (2015): 188-204.