Computer analysis and quantification of periaqueductal grey-induced defence behaviour.

The pharmacological study of midbrain-evoked aversive behaviours is commonly measured in terms of electrical escape thresholds, although studies which examine the actual expression of the behaviour are being introduced. A computer-driven automated tracking system has been developed to record and analyse the very rapid locomotor activity produced by the defence response. Stimulation of the midbrain periaqueductal grey (PAG) matter in rats with the excitatory amino acid D,L-homocysteic acid (DLH) produced very rapid and short-lasting escape behaviour which was tracked by computer. The system, VideoTrack, determines the speed and distance travelled by the animal and stores and statistically analyses the data. VideoTrack was able to detect a pharmacological modifications of the response; anti-aversive effects produced by intra-PAG pretreatment with the 5-HT1A agonist 8-hydroxy 2-(di-n-propylamino)tetralin (8-OHDPAT) and its reversal by peripheral pretreatment with the 5-HT1A antagonist N-[2-[-(2-methoxyphenyl)-1-piperazinyl]ethyl-N- (pyridinyl)cyclohexanecarboxanide (WAY 100635).