A novel, fully automated rotometer for the study of turning behavior. Comparison of results under different experimental conditions.

The turning or circling activity of the rat is a very useful experimental model for the study of dopaminergic cerebral pathways. Quantification of turning makes it applicable to follow changes of pattern evolution in the same subject or for comparison between animals under different experimental conditions. Automated quantitative evaluation of turning has the advantage of its reliability, eliminates subjective inaccuracies and allows longer periods of observation. Therefore a fully automated rotometer aimed to accomplish these objectives was developed. It consists of a sensor box to transduce the circling movement of animals into computed information to be processed by a microprocessor and a printer for recording of results. The sensor was designed with a 16 holes perforated disc and two infrared receiver/emitter units. Pulses generated in the sensor box are computed and stored by the microprocessor. Reading of results may be made in manual or automated mode from the display or listed through the printer connected on-line. The reliability and validity of the rotometer were tested in animals submitted to different experimental conditions. Rats with unilateral chemical lesions (6-hydroxy-dopamine or kainic acid) of substantia nigra pars compacta rotated vigorously contraversive to lesion side after apomorphine injection (0.5 and 1 mg/kg, s.c.). Electrolytic lesion of the same nucleus made animals rotate ipsiversive to the lesion after apomorphine. To attain significant level of circling activity, the electrolytic lesion should be placed in the external boundaries of substantia nigra (265.8 +/- 53.4 turns/60 min for group with external placed lesion; (n = 5); 97.3 +/- 19.5 for group with internal placed lesion (n = 3); t = 2.31; p less than 0.05). Unilateral striatal lesion with ibotenic acid made animals rotate ipsilaterally with apomorphine as well as with the selective D-2 agonist bromocriptine (10 and 30 mg/kg, i.p.). Qualiquantitative differences in circling were observed between these two dopaminergic agonists. Comparison of circling activity on semispherical and flat surfaces showed a non significant trend to rotate more intensively on spherical surfaces but only in those animals turning greater than or equal to 3 turns/min. The results obtained with the automated rotometer herein described agree with those currently reported in the literature about the subject. They demonstrate also that this apparatus is adequate and reliable for the study of turning behavior under different experimental conditions. Interestingly enough, our observation on the specificity of electrolytic lesions placed in the lateral boundaries of substantia nigra to induce rotation is worth further investigation.