The in situ perfused spinal cord of the rat: Applicability of drugs and chemicals, sodium-lithium exchange, and calcium reduction to functional intact central nervous system tissue

A new forequarters preparation, the in situ perfused cervical spinal cord of the adult rat, is described with respect to its suitability for pharmacological and toxicological investigations. The dose-dependent actions of strychnine, p-chloromercuriphenylsulfonate, ouabain, dinitrophenol, bicuculline, and (−)-nipecotic acid ethyl ester on mass reflex discharges were studied. The study was extended to sodium-lithium exchange and calcium reduction in the perfusion medium. With the intent to discriminate between primary central actions of substances and ion changes and their secondary metabolic effects, the flow rate, the sodium and potassium concentrations, the pH, the pO 2 and the pCO 2 of the perfusion medium were measured. The new perfused forequarters preparation, including the intact cervical spinal cord, has a number of advantages over an experimental design using an intact animal dependent on its physiological circulation. These advantages are: 1) the composition of fluids supplying the preparation is under control; 2) the oxygen supply to the cord is no longer dependent on the cardiovascular function, which may be impaired by the substance under study; 3) a complete dose-response curve may be obtained from each animal; 4) washout experiments may be performed; 5) the action of substances can be studied in the presence of extreme concentrations of drugs, ions, etc.