CHOLINERGIC PROPERTIES OF THE RELAY JUNCTIONS OF THE PRIMARY AFFERENT PATHWAY

¹ Department of Physiology and Biophysics, University of Kentucky College of Medicine, Lexington, Kentucky

The effect of the anticholinesterases, diisopropyl fluorophosphate (DFP) and eserine, on evoked slow potentials of somesthetic cortical, thalamic and cuneate neurons was studied in the cat. The responses were evoked by stimulation of the superficial radial nerve and, in the case of the thalamus and cortex, by direct monosynaptic excitation. The routes of infusion were chosen so as to deliver as high a concentration of the drugs as possible to the area under study. The evoked slow potentials in all three areas were sensitive to the anticholinesterases, the cortex and thalamus being much more sensitive than the cuneate. DFP was the more potent inhibitor of the recorded potentials, usually depressing the response within 30 sec after infusion. Eserine, on the other hand, was slower in action, usually producing a potentiation of the slow response followed by a depression. The effects of DFP and eserine on the three relay junctions could be reversed or prevented by the administration of atropine. The results of these experiments are consistent with the presence of cholinergic fibers in all relay junctions of the primary afferent pathway.