On the possible involvement of glutamate receptors in conditioning of behavioural effects of apomorphine.

It was shown previously that behavioural effects of apomorphine (locomotor activation and stereotyped behaviour) can be conditioned when they are associated with well-defined environmental stimuli. In the present study, the hypothesis was tested that glutamatergic mechanisms play an important role either in formation of conditioned responses to apomorphine or in the expression of previously established conditioned responses. For this purpose, two blockers of glutamate receptors were applied, either MK-801 (dizocilpine), a non-competitive, but selective blocker of NMDA-type receptors or MLV-6976, a non-selective blocker of glutamate receptors. MK-801 produced some locomotor activation by itself in a dose-dependent way (0.125-0.50 mg/kg ip). The locomotor activation produced by 0.25 mg/kg could not be conditioned. When rats were conditioned 9 times with 2 mg/kg apomorphine after pretreatment with 0.25 mg/kg of MK-801, this pretreatment did not prevent the development of apomorphine-conditioned locomotor activity or stereotypies which appeared when the rats were treated with saline in presence of the conditioned stimuli. Similar results were obtained when rats were conditioned 7 times with the same dose of apomorphine after pretreatment with 20 mg/kg ip MLV-6976, which drug did not induce any visible alterations in motility by itself. When rats were conditioned 7 times with 2 mg/kg apomorphine alone and tested with MK-801 (0.25 mg/kg) in the presence of the conditioned stimuli, neither locomotor activity nor stereotypies appeared as conditioned responses. When rats were conditioned with the same dose of apomorphine alone and tested with MLV-6976 (20 mg/kg ip), stereotypies did not appear as conditioned responses, but some locomotor activity occurred.(ABSTRACT TRUNCATED AT 250 WORDS)