Effects of organophosphates on rabbit pyramidal cells firing pattern and hippocampal theta rhythm

• Published in: Brain research bulletin Vol. 33; no. 3; pp. 241 - 248
• Main Authors: Nio, Jacques, Breton, Patrick
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 1994; Elsevier Science
• Subjects: Animals; Biological and medical sciences; Carotid Arteries; Chemical and industrial products toxicology. Toxic occupational diseases; Electroencephalography; Extracellular recording; Female; Hippocampus; Hippocampus - drug effects; Hippocampus - physiology; Injections, Intra-Arterial; Iontophoresis; Male; Medical sciences; Organophosphates; Organophosphorus Compounds - pharmacology; Paraoxon - pharmacology; Physostigmine; Physostigmine - pharmacology; Pyramidal cells; Pyramidal Cells - drug effects; Pyramidal Cells - physiology; Rabbits; Theta Rhythm - drug effects; Toxicology; Various organic compounds; Physostigmine; Extracellular recording; Pyramidal cells; Hippocampus; Organophosphates; Toxicity; Central nervous system; Discharge pattern; Rabbit; Lagomorpha; Cholinergic pathway; Vertebrata; Mammalia; Animal; Acetylcholine; Organophosphorus compounds; Anticholinesterase agent; Pyramidal neuron; θ-Rhythm; Brain (vertebrata)
• ISSN: 0361-9230; 1873-2747
• DOI: 10.1016/0361-9230(94)90190-2

The effects of the irreversible acetylcholinesterase (AChE) antagonist paraoxon (Px) on hippocampal neurophysiology were investigated and compared to those of physostigmine in urethane-anaesthetized rabbits. Hippocampal CA1 EEG signals were analyzed by power spectra. Following intracarotid administration, the two drugs induced a similar fundamental low-frequency theta power peak while the appearance of a second theta harmonic was commonly found under Px. Again, inhibition of CA1 pyramidal cells firing was significantly more pronounced after Px injection than after physostigmine. A potent inhibitory action was also described following local Px iontophoretic application. However, a discrepancy appeared between the effects of Px and the classical cholinergic drugs (acetylcholine, physostigmine). The results indicate that Px and physostigmine have a rather similar influence on the septo-hippocampal pathway and support suggestions that Px could act within local hippocampal circuitry through other systems than the cholinergic system exclusively.