Human threat test: a method to test anxiety-related behavior in a marmoset monkey

S.A.M. van Vliet^1,2, M.J. Jongsma¹, R.A.P. Vanwersch¹ and I.H.C.H.M. Philippens^1,2

¹TNO Defense, security and safety, RG Toxicology and MedicalCounterMeasures, Rijswijk, The Netherlands
²Utrecht University, Dept. of psychopharmacology, Utrecht University, Utrecht, The Netherlands

Defensive responses are components of the daily life of primates. These responses are still present in captivity born animals. Based on this behavior, the human threat test (HTT) is a widely used method in the assessment of anxiety/fear related behavior in a non-human primate. The test is based on findings that non-human primates will exhibit anxiety-related behavior in the presence of a human observer. Retreating to the back of the cage and display of aggressive and anxiety-related postures are the main pronounced reactions.

This study focused on the effects of three psychoactive compounds on the anxiety-related behavior of the marmoset monkey (Callithrix jacchus) measured with the human threat test. First, the sedative compound diazepam, known to decrease anxiety, was applied to validate the HTT on our marmoset colony. Diazepam (0.25 mg/kg, i.m.) decreased the number of characteristic body postures and increased the time spent in the front of the cage. The second compound, modafinil (Modiodal) is a vigilance stimulant used as treatment of narcolepsy. Oral administration of modafinil in a dose varying from 50 mg/kg to 225 mg/kg reduced the anxiety-related behavior. No anxiolytic effects of modafinil were found in earlier studies. The third compound was ?9-tetrahydrocannabinol (?9-THC), the main euphorigenic component of marijuana (Cannabis sativa), was administrated orally in doses of 2, 4 and 8 mg/kg. The display of postures was reduced after all three doses. This anxiolytic effect was found earlier in other anxiety test systems in other species.

In conclusion, this study showed that the human threat test is a sensitive test to measure anxiety-related behavior and can be adapted to other marmoset colonies with different housing situations. It is a good method to distinguish between different effects on anxiety of psychoactive compounds.

Paper presented at Measuring Behavior 2005 , 5^th International Conference on Methods and Techniques in Behavioral Research, 30 August - 2 September 2005, Wageningen, The Netherlands.

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