Effects of alpha-chloralose on the activity of the nigrostriatal dopaminergic system in the cat.

The effects of alpha-chloralose anaesthesia were studied in the cat on the release of 3H-dopamine (#H DA) from the caudate nucleus and the substantia nigra using the push-pull cannula method and continuous labelling of the structures with L-3,5-3H-tyrosine. Results were compared to those obtained under the same experimental conditions in both halothane-anaesthetized animals and 'encéphale isolé' preparations. The alpha-chloralose-anaesthetized preparation showed the lowest level of 3H-DA release, both from dopaminergic nerve terminals in the caudate nucleus and from dendrites of dopaminergic neurons in the substantia nigra. Furthermore, the time required to reach a steady-state release of 3H-DA was longer in alpha-chloralose-anaesthetized cats than in animals under halothane. This indicated that the activity of the dopaminergic neurons is depressed under alpha-chloralose anaesthesia. In the second part of the study, we measured the effects of unilateral somatic stimulation on the release of 3H-DA from the caudate nuclei and substantiae nigrae on both sides of the brain. The results show that under alpha-chloralose anaesthesia, the electric stimulation of the paw of the right forelimb does not significantly affect the release of 3H-DA from any of the above four structures. This contrasts with the changes of 3H-DA release seen in the same experimental conditions under halothane anaesthesia.