A Comparative Study of Cell Specific Effects of Systemic and Volatile Anesthetics on Identified Motor Neurons and Interneurons of Lymnaea stagnalis (L.), Both in the Isolated Brain and in Single Cell Culture.

Hadi Fathi Moghadam,Talay Yar,William Winlow,Ibrahim Abdelrazig Ahmed,Munir M Qazzaz

doi:10.3389/fphys.2019.00583

Abstract

1. A comparative descriptive analysis of systemic (sodium pentobarbital, sodium thiopentone, ketamine) and volatile (halothane, isoflurane, enflurane) general anesthetics revealed important differences in the neuronal responses of identified motor neurons and interneurons in the isolated central nervous system (CNS) and cultured identified neurons in single cell culture of Lymnaea stagnalis (L.).2. At high enough concentrations all anesthetics eventually caused cessation of spontaneous or evoked action potentials, but volatile anesthetics were much faster acting. Halothane at low concentrations caused excitation, thought to be equivalent to the early excitatory phase of anesthesia. Strong synaptic inputs were not always abolished by pentobarbital.3. There were cell specific concentration-dependent responses to halothane and pentobarbital in terms of membrane potential, action potential characteristics, the after hyperpolarization and patterned activity. Individual neurons generated specific responses to the applied anesthetics.4. The inhalation anesthetics, enflurane, and isoflurane, showed little concentration dependence of effect, in contrast to results obtained with halothane. Enflurane was faster acting than halothane and isoflurane was particularly different, producing quiescence in all cells types studied at all concentrations studied.5. Halothane, enflurane, the barbiturate general anesthetics, pentobarbital, and sodium thiopentone and the dissociative anesthetic ketamine, produced two distinctly different effects which could be correlated with cell type and their location in the isolated brain: either a decline in spontaneous and evoked activity prior to quiescence in interneurons or paroxysmal depolarizing shifts (PDS) in motor neurons, again prior to quiescence, which were reversed when the anesthetic was eliminated from the bath. In the strongly electrically coupled motor neurons, VD1 and RPD2, both types of response were observed, depending on the anesthetic used. Thus, with the exception isoflurane, all the motor neurons subjected to the anesthetic agents studied here were capable of generating PDS in situ, but the interneurons did not do so.6. The effects of halothane on isolated cultured neurons indicates that PDS can be generated by single identified neurons in the absence of synaptic inputs. Further, many instances of PDS in neurons that do not generate it in situ have been found in cultured neurons. The nature of PDS is discussed.

Highlights

In a recent review (Winlow et al, 2018) we suggested that clues to the likely effects of anesthetics on cephalopods such as Octopus vulgaris might be gained from related studies on gastropod molluscs such as Lymnaea stagnalis which has proved to be an excellent model system for studies of the cellular actions of general anesthetics on individual identified neurons (e.g., McCrohan et al, 1987; Winlow et al, 1987, 1995; Franks and Lieb, 1988; McKenzie et al, 1995; Spencer et al, 1995, 1996) many of which have known functions
The utility of such a preparation is that it allows us to study of the modes of action of general anesthetics, since behavioral, cell physiological, and biophysical experiments can all be performed on this preparation (e.g., McCrohan et al, 1987; Girdlestone et al, 1989a,b; Winlow et al, 2018) at clinical concentrations (Girdlestone et al, 1989c; Yar and Winlow, 2016b)
All the neurons tested with the various anesthetics used in this study eventually became quiescent if an adequate concentration of anesthetic was applied to the brain or to isolated, cultured, identified neurons for an appropriate length time, which varies from one cell type to another

Summary

Introduction

In a recent review (Winlow et al, 2018) we suggested that clues to the likely effects of anesthetics on cephalopods such as Octopus vulgaris might be gained from related studies on gastropod molluscs such as Lymnaea stagnalis which has proved to be an excellent model system for studies of the cellular actions of general anesthetics on individual identified neurons (e.g., McCrohan et al, 1987; Winlow et al, 1987, 1995; Franks and Lieb, 1988; McKenzie et al, 1995; Spencer et al, 1995, 1996) many of which have known functions The utility of such a preparation is that it allows us to study of the modes of action of general anesthetics, since behavioral, cell physiological, and biophysical experiments can all be performed on this preparation (e.g., McCrohan et al, 1987; Girdlestone et al, 1989a,b; Winlow et al, 2018) at clinical concentrations (Girdlestone et al, 1989c; Yar and Winlow, 2016b). Neurons have very diverse morphologies, physiologies, biochemical, and pharmacological properties so they might be expected to have differing responses to applied agents and this is the case in relation to anesthetic substances applied to identified neurons of the pond snail Lymnaea stagnalis (L.) (Winlow et al, 1991, 1992, 1995, 2018; Qazzaz and Winlow, 2015, 2017)

Methods

Results

Discussion

Conclusion