Factors modifying the head-twitch response to 5-hydroxytryptophan

Factors modifying the head twitch response to 5-hydroxy d,l-tryptophan (5-HTP) have been investigated in the mouse. Stage of oestrous cycle and time of day had no effect. Local anaesthesia of the pinna region virtually abolished the response. Painting the pinnae with xylene increased the response and also increased the spontaneous head twitch rate. A concurrent variable frequency sound reduced the head twitch rate as did isolation. These results suggest that sensory input from the pinna is a necessary precondition for the head-twitch response to 5-HTP and demonstrate that the rate of twitching is modified by environmental conditions. The suggestion is made that 5-HTP might allow the perception of previously subliminal stimuli from the pinna region.The authors wish to thank Mr. D. Newton for his able technical assistance during the latter part of this work.