A novel automated apomorphine climbing test

W.H.I.M. Drinkenburg1, P. Vijn1, M.G. Martorana1, M. Dickson1 and W. van Schaijk2

1Organon Laboratories Ltd., R & D, Newhouse, Lanarkshire, United Kingdom
2ERG, NICI, University of Nijmegen, Nijmegen, The Netherlands

Apomorphine-induced climbing behaviour in mice is used by the pharmaceutical industry for selecting compounds, which interact in vivo with dopaminergic neurotransmission [1,4,5]. Classically, climbing is determined visually using various climbing scores: climbing/not-climbing [6], duration of climbing [1], or rank scales [2,4]. These methods require a well-trained observer, while observational bias may result in differences between two experimenters. An automated scoring system would minimise differences and improve reproducibility and efficiency. The validation of a novel, automated climbing system that detects the climbing activity of mice by means of electrical conductivity and infrared beam breaks is presented.

Figure 1. The novel automated system as in use at Organon Newhouse, Scotland (built at ERG/MID departments, University of Nijmegen, The Netherlands

Test compound or vehicle is administered subcutaneously (SC) 30 minutes before apomorphine HCl (0.75 mg.kg-1, SC). Mice are then placed individually in metal mesh cylinders (diameter 12 cm, height 14 cm, Figure 1) where they stay for 30 minutes during which climbing behaviour is monitored. The system samples continuously and outputs the data as either climbing scores or duration of climbing. The climbing scores and ED50 values for inhibiting apomorphine-induced climbing for five psychoactive compounds (Table 1) produced by the automated climbing system were compared to those obtained by visual rank scoring [4].

Average climbing scores per animal were determined by three methods:

  1. The average of two visual scores taken at 10 and 20 minutes post apomorphine.
  2. The average of the automatic scores in the 10-11 and 20-21 minute periods post apomorphine.
  3. The average of the automatic scores in the 10-21 period post apomorphine.

A climbing score is determined by averaging the individual scores in each treatment group and each run. Fifteen climbing scores are thus determined per experiment.

Table 1. ED50 values together with their 95% confidence limits for the inhibition of apomorphine-induced climbing by various psychoactive compounds.
Coumpound Visual 10, 20 Automated 10, 20 Automated 10-21
Clozapine 4.52 (3.19-6.40) 4.06 (2.57-6.42) 4.54 (2.87-7.19)
Diazepam No Fit No Fit No Fit
Mirtazapine 15.5 (8.8-27.4) 15.4 (6.1-39.0) 16.0 (5.3-48.3)
Chlorpromazine 0.29 (0.19-0.45) 0.30 (0.18-0.49) 0.30 (0.19-0.47)
Haloperidol 0.023 (0.016-0.033) 0.017 (0.012-0.026) 0.018 (0.013-0.023)

 

For the coumpounds tested, 75 visual climbing scores were plotted against 75 automatic climbing scores, and a regression line was fitted. . Results obtained showed a good correlation between visual and automated climbing scores (r = 0.94, Figure 2) and calculated ED50'S (Table 1).

Figure 2. Plot and the linear regression between the automatic scores and the visual scores.

Automatically scoring climbing is not a new approach, a mechanical system using the force applied to a transducer by a mouse climbing a cage, was described as early as 1977 [3]. However, mechanical systems require calibration and are more prone to failure. Our automated climbing system not only correctly identified active test compounds, but also generated climbing scores and ED50 values similar to those obtained by visual scoring. This novel climbing system is an efficient and validated instrument for drug discovery and development.

References

  1. Costall, B.; Naylor, R.J.; Nohria, V. (1978). Climbing behaviour induced by apomorphine in mice: a potential model for the detection of neuroleptic activity. European Journal of Pharmacology, 50, 39-50.
  2. Costentin, J.; Protais, P.; Schwartz, J.C. (1975). Rapid and dissociated changes in sensitivities of different dopamine receptors in mouse brain. Nature, 257, 405-407.
  3. Farrant, G.; Thompson, S.E.; Schnieden, H. (1977). Quantitative assessment of climbing behaviour in mice. British Journal of Pharmacolology, 61, 495P.
  4. Protais, P.; Costentin, J.; Schwartz, J.C. (1976). Climbing behaviour induced by apomorphine in mice: a simple test for the study of dopamine receptors in striatum. Psychopharmacology, 50, 1-6.
  5. Vasse, M..; Chagraoui, A.; Protais, P. (1988). Climbing and stereotyped behaviours in mice require the stimulation of D-1 dopamine receptors. European Journal of Pharmacology, 148, 221-229.
  6. Von Voigtlander, P.F.; Losey, E.G.; Triezenberg, H.J. (1975). Increased sensitivity to dopaminergic agents after chronic neuroleptic treatment. Journal of Pharmacology and Experimental Therapeutics, 193, 88-94.

Poster presented at Measuring Behavior 2000, 3rd International Conference on Methods and Techniques in Behavioral Research, 15-18 August 2000, Nijmegen, The Netherlands

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