DRUG MODIFICATION OF THE SCHIFF-SHERRINGTON PHENOMENON

¹ Department of Pharmacology, University of California Medical Center, San Francisco, California

A study of the effects of various drugs on the Schiff-Sherrington phenomenon (SSP) was carried out in an attempt to understand better how these agents modify spinal cord activity. The SSP manifests itself as an increase in forelimb extensor tone due to removal of ascending lumbosacral inhibitory impulses by thoracic spinal transection. A reversible transection of the cord was achieved by passing 0°C brine through a copper tube at T₁₀ and the resulting increase in forelimb rigidity was recorded electromyographically. The results of cumulative i.v. injections of the drugs fall into three categories. 1) Atropine (12 mg/kg) was without effect. 2) Phenoxybenzamine (0.4-0.6 mg/kg) was the most potent suppressive agent while chlorpromazine (up to 38.0 mg/kg) required higher doses. The SSP was not present in seven of nine animals pretreated for 24 hr with 1 mg/kg of reserpine and in six of these same animals decerebrate rigidity was also absent. The influences involved in the SSP would be lost in an anesthetized preparation since pentobarbital abolished the reaction at low doses (6.3-9.5 mg/kg). 3) Amphetamine would either enhance the SSP or cause the reaction to appear in some animals where it was not initially present. Picrotoxin was without effect. These results tend to indicate that an adrenergic facilitatory influence is involved in the SSP. The drugs modifying the SSP can be acting on intraspinal or supraspinal influences.