Neurophysiologic Effects of Chemical Agent Hydrolysis Products on Cortical Neurons In Vitro

• Published in: Neurotoxicology (Park Forest South) 2001-06, Vol.22 (3), p.393-400
• Main Authors: Pancrazio, Joseph J., Keefer, Edward W., Ma, Wu, Stenger, David A., Gross, Guenter W.
• Format: Article
• Language: English
• Subjects: Action Potentials - drug effects; Action Potentials - physiology; Animals; Biological and medical sciences; Cerebral Cortex - cytology; Cerebral Cortex - drug effects; Chemical and industrial products toxicology. Toxic occupational diseases; Chemical Warfare Agents - metabolism; Chemical Warfare Agents - pharmacology; Cortical neurons; Embryo, Mammalian; Extracellular recording; Female; Hydrolysis; Medical sciences; Microelectrodes; Multielectrode array; Nerve Net - drug effects; Nerve Net - physiology; Neurons - drug effects; Organ Culture Techniques; Patch clamp; Patch-Clamp Techniques; pinacolyl methylphosphonic acid; Pregnancy; Rats; Sarin; Soman; Toxicology; Various organic compounds
• ISSN: 0161-813X; 1872-9711
• DOI: 10.1016/S0161-813X(01)00028-6

The neurophysiologic effects of chemical agent hydrolysis products were examined on cultured cortical neurons using multielectrode array (MEA) recording and the whole-cell patch clamp technique. Measurement of neuronal network extracellular potentials showed that the primary hydrolysis product of soman, pinacolyl methylphosphonic acid (PMPA), inhibited network mean burst and spike rates with an EC 50 of approximately 2 mM. In contrast, the degradation product of sarin, isopropyl methylphosphonic acid (IMPA), and the final common hydrolysis product of both soman and sarin, methylphosphonic acid (MPA), failed to affect neuronal network behavior at concentrations reaching 5 mM. Closer examination of the effects of PMPA (2 mM) on discriminated extracellular units revealed that mean spike amplitude was slightly diminished to 95 ± 1% (mean ± S.E.M., n = 6, P < 0.01) of control. Whole-cell patch clamp records under current clamp mode also showed a PMPA-induced depression of the firing rate of spontaneous action potentials (APs) to 36 ± 6% (n = 5, P < 0.001) of control. In addition, a minor depression with exposure to PMPA was observed in spontaneous and evoked AP amplitude to 93 ± 3% (n = 5, P < 0.05) of control with no change in either the baseline membrane potential or input resistance. Preliminary voltage clamp recordings indicated a reduction in the occurrence of spontaneous inward currents with application of PMPA. These findings suggest that PMPA, unlike MPA or IMPA, may more readily interfere with one or more aspects of excitatory synaptic transmission. Furthermore, the data demonstrate that the combination of extracellular microelectrode array and patch clamp recording techniques facilitates analysis of compounds with neuropharmacologic effects.