CENTRAL NERVOUS SYSTEM EFFECTS OF HYOSCINE IN MAN

¹ Departments of Preventive Medicine and Pharmacology, University of Illinois College of Medicine, Chicago, Illinois

Hyoscine, in doses of 0.15 to 0.8 mg, was injected subcutaneously in 54 subjects to determine its effects on salivary functioning, the spontaneous EEG, the electroencephalographic "arousal" response to photostimulation, motor behavior, mood, and the ability to focus and maintain attention.

Hyoscine induced a moderate bradycardia and a marked decrease in salivation and in the duration of the EEG "arousal" response. These effects were maximal at 1 to 2 hours after administration of hyoscine but were no longer present at 4 hours.

Consistent behavioral effects of hyoscine in the EEG experiments were a decrease in spontaneous speech and movement and a significant decrease in the "Energetic" Scale of the Clyde Mood Scale. The spontaneous EEG exhibited a consistent shift toward lower amplitude of 5 to 8 cycles per second activity. The alpha index significantly decreased. The effects on these behaviors and the spontaneous EEG differed from those noted in2) above in that they were maximal at 3 to 4 hours after hyoscine administration and persisted for at least 4 to 7 hours.

We suggest that the depression of the EEG "arousal" response may be attributed to an action of hyoscine on the ascending reticular activating system, which occurs independently of the action on the spontaneous EEG rhythm.

In comparing the effects of two dose levels of hyoscine, larger doses were associated with a decrease in performance on behavioral tests involving the ability to maintain an attentive set. However, differential doses of arecoline and methacholine did not exert differential effects on these same measures. In doses which antagonized the effects of hyoscine on salivation, arecoline and methacholine did not antagonize the effects of hyoscine on these behaviors.

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