EFFECTS OF BARBITURATES AND A TETRAHYDROCANNABINOL DERIVATIVE ON RECOVERY CYCLES OF MEDIAL LEMNISCUS, THALAMUS AND RETICULAR FORMATION IN THE CAT

¹ Department of Pharmacology, The University of Rochester, Rochester, New York

The effects of pentobarbital (2 mg/kg), a synthetic dimethylheptyl analog (DMHP) of one of the active constituents of marihuana (0.2 mg/kg) and thiopental (2 mg/kg) upon the recovery cycles, latencies to peak of response and amplitudes of responses in the medial lemniscus, the mesencephalic reticular formation and the ventrobasal complex of the thalamus (VBC) were investigated. Responses were generated by stimulation of the radial nerve. A computer averaging technique was used to increase the accuracy of the measurements and to detect small drug effects. The recovery cycles measured in the medial lemniscus were relatively fast with an average of 50% recovery in 10 msec. Recovery cycles in VBC were slower and more irregular with only about 20% recovery in 10 msec. Recovery cycles in the reticular formation were very variable, both in rate of recovery and degree of regularity. There were no marked or consistent differences between the effects of the barbiturates and those of DMHP. In the medial lemniscus, the drugs frequently caused an increased or decreased recovery at one or more points in the recovery cycle but had no effect on latencies or amplitudes of responses to conditioning stimuli. In VBC, effects on the recovery cycle were more frequent and more pronounced, with a decrease in recovery being the predominant effect. The drugs did not affect latencies in VBC but did produce some changes in response amplitudes, with a decreased amplitude being the predominant effect. Drug effects in the reticular formation were similar to those in VBC, except that they were still more pronounced and there were changes, in either direction, in latencies, as well as changes in recovery cycles and amplitudes of responses. It is concluded that the sedative actions of the drugs under investigation may be primarily due either to a depression of some system in the reticular formation or to a more generalized depression of the reticular formation, the primary sensory pathways and possibly other systems as well.