PRESENCE OF TONE IN THE DENERVATED AND IN THE DECENTRALIZED NICTITATING MEMBRANE OF THE SPINAL CAT AND ITS INFLUENCE ON DETERMINATIONS OF SUPERSENSITIVITY

¹ Department of Pharmacology, Harvard Medical School, Boston, Massachusetts

The presence of tone has been demonstrated in the denervated and in the decentralized nictitating membrane of the cat. The magnitude of tone is more pronounced in the spinal cat (set up under ether) than in the cat anesthetized with sodium pentobarbital. The presence and the magnitude of tone were determined by the following procedures: difference in the maximal responses of the nictitating membrane of the normal and of the operated side; phentolamine (3 mg/kg i.v.); isoproterenol (10 pg/kg i.v.); or hexamethonium (5 mg/kg i.v.). The magnitude of tone was determined at different time intervals after decentralization and after denervation of the nictitating membrane. There was a steady increase in tone with increasing time after decentralization. After denervation there was a sharp rise in the magnitude of tone on the second postoperative day; thereafter the tone increased gradually. The magnitude of tone continued to increase up to 28 days after decentralization and after denervation. Tone in the denervated and in the decentralized nictitating membrane of the spinal cat is due to an increase in circulating catecholamines because it was reduced or abolished after either bilateral adrenalectomy, reserpine pretreatment or administration of phentolamine. The time course of development of corrected supersensitivity to synephrine was qualitatively and quantitatively similar to that of the magnitude of tone. Corrected values show that denervation supersensitivity to synephrine is greater than previously reported, and that the magnitude of decentralization and of denervation supersensitivity to synephrine continued to increase up to 28 days after the operation.