Abstract
Orphenadrine has been reported to cause a decrease in the flexor reflex of thalamic cats. In contrast, it had no effect on the flexor reflex of decerebrate cats(l). The technique of decerebration, whether by brainstem section or by ligation of the basilar artery, employed in the cited study was not specified. Certain drugs, such as chlorpromazine(2), have a much more profound effect on the rigidity following intercollicular section than on the “alpha” rigidity produced by ligation of the basilar artery. This differential action on Sherringtonian decerebrate preparations can be correlated with depression of gamma (fusi-motor) neuron activity.
The observation that scopolamine produces significant, but limited, relaxation of the decerebrate rigidity following intercollicular section (3) prompted the investigation of 2 other tertiary anticholinergic compounds, diphen-hydramine, and its o-methyl analog, orphenadrine, for their effects on decerebrate rigidity.
Methods. Ten adult cats of both sexes were decerebrated in the intercollicular plane by electro-coagulation under pentobarbital anesthesia (30 mg/kg intraperitoneally) one or two days prior to assessment of drug action according to the method of Smith et al(4).
The force developed by the ankle extensor muscles of the decerebrate cat opposing forced flexion of the foot through an angle of 20° was measured using a force-displacement transducer and polygraph. The flexion was maintained for 10 seconds and repeated every 30 seconds. The magnitude of the phasic and tonic components of the reflex was assessed(3). Aqueous solutions of orphenadrine citrate∗ or diphenhydramine hy-drochloride were administered intravenously using a timed interrupted infusion (i.e., each dose increment was injected slowly over a period of one minute, a dose calculated to double the total previously administered given 5 minutes later, etc.). The complete or 100% depression of the reflex response was taken as that response observed after administering ether to the point of respiratory arrest.
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