Ionic Mechanisms Underlying Depolarizing Responses of an Identified Insect Motor Neuron to Short Periods of Hypoxia

• Published in: Journal of neurophysiology 1999-01, Vol.81 (1), p.307-318
• Main Authors: Le Corronc, Herve, Hue, Bernard, Pitman, Robert M
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphate - physiology; Animals; Blattidae; Calcium - physiology; Calcium Channel Blockers - pharmacology; Electrophysiology; Enzyme Inhibitors - pharmacology; Ganglia, Invertebrate - cytology; Ganglia, Invertebrate - drug effects; Hypoxia - physiopathology; In Vitro Techniques; Ion Channels - physiology; Male; Membrane Potentials - physiology; Motor Neurons - physiology; Ouabain - pharmacology; Patch-Clamp Techniques; Periplaneta - physiology; Periplaneta americana; Potassium Channel Blockers; Potassium Channels - metabolism; Sodium - physiology; Tetrodotoxin - pharmacology
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.1999.81.1.307

Hervé Le Corronc 1 , Bernard Hue 1 , and Robert M. Pitman 2 1  Laboratory of Neurophysiology, University of Angers, F-49045 Angers Cedex, France; and 2  School of Biomedical Sciences, Gatty Marine Laboratory, University of St. Andrews, Fife KY16 8LB, Scotland Le Corronc, Hervé, Bernard Hue, and Robert M. Pitman. Ionic mechanisms underlying depolarizing responses of an identified insect motor neuron to short periods of hypoxia. J. Neurophysiol. 81: 307-318, 1999. Hypoxia can dramatically disrupt neural processing because energy-dependent homeostatic mechanisms are necessary to support normal neuronal function. In a human context, the long-term effects of such disruption may become all too apparent after a "stroke," in which blood-flow to part of the brain is compromised. We used an insect preparation to investigate the effects of hypoxia on neuron membrane properties. The preparation is particularly suitable for such studies because insects respond rapidly to hypoxia, but can recover when they are restored to normoxic conditions, whereas many of their neurons are large, identifiable, and robust. Experiments were performed on the "fast" coxal depressor motoneuron (D f ) of cockroach ( Periplaneta americana ). Five-minute periods of hypoxia caused reversible multiphasic depolarizations (10-25 mV; n  = 88), consisting of an initial transient depolarization followed by a partial repolarization and then a slower phase of further depolarization. During the initial depolarizing phase, spontaneous plateau potentials normally occurred, and inhibitory postsynaptic potential frequency increased considerably; 2-3 min after the onset of hypoxia all electrical activity ceased and membrane resistance was depressed. On reoxygenation, the membrane potential began to repolarize almost immediately, becoming briefly more negative than the normal resting potential. All phases of the hypoxia response declined with repeated periods of hypoxia. Blockade of ATP-dependent Na/K pump by 30 µM ouabain suppressed only the initial transient depolarization and the reoxygenation-induced hyperpolarization. Reduction of aerobic metabolism between hypoxic periods (produced by bubbling air through the chamber instead of oxygen) had a similar effect to that of ouabain. Although the depolarization seen during hypoxia was not reduced by tetrodotoxin (TTX; 2 µM), lowering extracellular Na + concentration or addition of 500 µM Cd 2+ greatly reduced all phases of the hypoxia-induced response, sugges