A conditioned anti-parkinsonian drug effect in the hemi-parkinsonian rat.

In two separate experiments contralateral rotation was classically conditioned in hemi-Parkinsonian rats. In the first experiment, ten rats with unilateral 6-hydroxydopamine lesions of the substantia nigra, which produced ipsiversive circling, were given five daily injections of the dopamine receptor agonist apomorphine (0.5 mg/kg) to induce circling contralateral to the lesion hemisphere. One half of the rats (the conditioning group) were placed in a novel environment for 15 min during each apomorphine treatment. Subsequently, when placed into this environment 3, 10, 17, and 24 days after the final apomorphine injection, the conditioning group spontaneously rotated contralateral to the lesion hemisphere, whereas a similarly drug-treated non-conditioned group spontaneously rotated ipsilateral to the lesion hemisphere. On day 26, all rats were given a 2.0 mg/kg injection of d-amphetamine, which generated ipsilateral rotation in all rats in their home environment, but when placed in the conditioning environment, the conditioned group rotated contralateral whereas the non-conditioned group rotated ipsilateral. In the second experiment, eight rats with unilateral destruction of dopamine neurons were given differential conditioning in two novel environments. In every case, environments associated with 0.5 mg/kg apomorphine treatment induced contralateral rotation when the rats were tested without drug but ipsilateral rotation in environments not associated with apomorphine. These findings suggest a role for respondent or Pavlovian conditioning in the pharmacological management of Parkinsonism.