Conditioned locomotion induced by unilateral intrastriatal administration of apomorphine: D(2) receptor activation is critical but not the expression of the unconditioned response.
The present study examined the role of D(1) and D(2) receptors in the conditioning of apomorphine-induced locomotor behavior. A Pavlovian conditioning protocol was used in which rats received 5 daily intrastriatal apomorphine treatments paired or unpaired to an open-field environment followed, 2 days later, by a saline test for conditioning. In the conditioning induction phase, the intrastriatal apomorphine treatment increased locomotor activity expressed as an increased number of sectional crossings and rearings. In the conditioning test, the apomorphine-paired group had significantly higher locomotor activity than the unpaired and vehicle groups, consistent with the development of a conditioned locomotor response. The concomitant blockade of D(1) and D(2) receptors with D(1) (SCH23390) and D(2) (sulpiride) antagonists prevented the apomorphine-induced behavioral response during the induction phase and in the conditioning test. Pretreatment with the D(1) antagonist SCH 23390 also blocked the apomorphine-induced behavioral response during the induction phase but did not block the apomorphine conditioned response. Pretreatment with the selective D(2) antagonist sulpiride blocked the apomorphine behavioral response during the induction phase and in the conditioning test. Altogether, these results indicate that antagonism of either the D(1) or D(2) receptors in the dorsal striatum can block apomorphine-induced locomotor activation but that D(2) but not D(1) antagonism can prevent the development of the apomorphine conditioned response. Altogether, these findings indicate a key role for the D(2) receptor site in the mediation of apomorphine conditioned behavior; and, in addition, that apomorphine conditioned locomotor response can develop without the expression of the locomotor stimulant response during the induction phase of conditioning.
Dias
Flávia Regina Cruz
FR
Behavioral Pharmacology Group, Laboratory of Animal Health, State University of North Fluminense, Avenida Alberto Lamego 2000, Campos dos Goytacazes, 28013-600 RJ, Brazil.
Carey
Robert J
RJ
Carrera
Marinete Pinheiro
MP
D000818:Animals; D001058:Apomorphine / Q000494:pharmacology*; D001552:Benzazepines / Q000494:pharmacology; D003213:Conditioning, Psychological / Q000187:drug effects* / Q000502:physiology; D003342:Corpus Striatum / Q000187:drug effects* / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism; D018491:Dopamine Agonists / Q000494:pharmacology*; D018492:Dopamine Antagonists / Q000494:pharmacology; D065127:Dopamine D2 Receptor Antagonists; D004333:Drug Administration Routes; D004347:Drug Interactions / Q000502:physiology; D007839:Functional Laterality / Q000187:drug effects; D008297:Male; D009043:Motor Activity / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D017447:Receptors, Dopamine D1 / Q000037:antagonists & inhibitors / Q000187:drug effects; D017448:Receptors, Dopamine D2 / Q000819:agonists / Q000187:drug effects*; D013469:Sulpiride / Q000494:pharmacology
D001552:Benzazepines; D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D065127:Dopamine D2 Receptor Antagonists; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; D013469:Sulpiride; D001058:Apomorphine; D004298:Dopamine