Dopamine D2 receptor agonists protect against ischaemia-induced hippocampal neurodegeneration in global cerebral ischaemia

To characterise the role played by dopamine receptors in ischaemic brain damage, we have evaluated the effects of pergolide, bromocriptine and lisuride (dopamine D-2 receptor agonists), haloperidol(a dopamine D-2 receptor antagonist), 2,3,4,5-tetrahydro-7,8,dihydroxy-1-phenyl-1H-3-benzazepine (SKF 38393; a dopamine D-1 receptor agonist) and (R)-(+)-8-chloro 2,3,4,5-tetra-hydro-3-methyl-5-phenyl-1 H-3-benzazepin-7-ol (SCH 23390; a dopamine D-1 receptor antagonist) in the gerbil model of global cerebral ischaemia. Ischaemia was induced by 5 min of bilateral carotid artery occlusion under halothane anaesthesia. Sham operated animals were used as controls. Pergolide (0.5 or 1.0 mg/kg i.p), bromocriptine (0.5 or 1.0 mg/kg i.p.), lisuride (0.5 or 1.0 mg/kg i.p.), SCH 23390 (0.1 or 1.0 mg/kg i.p.), haloperidol (0.5, 1.0 or 2 mg/kg i.p.) and SKF 38393 (1.0 or 2 mg/kg i.p.) were administered 1 h before occlusion. Five-minute-occluded animals had extensive damage in the CAI region of the hippocampus 5 days after surgery. Pergolide 0.5 and 1.0 mg/kg i.p. provided significant (P < 0.05 and P < 0.01, respectively) neuroprotection against the ischaemia-induced hippocampal damage. Bromocriptine and lisuride also provided significant (P < 0.05) neuroprotection, but only at the higher 1.0 mg/kg dose. In contrast, the dopamine D-2 receptor antagonist (haloperidol), the dopamine D-1 receptor agonist (SKF 38393) and the dopamine D-1 receptor antagonist (SCH 23390) failed to provide any neuroprotection in the model. These results support studies indicating that dopamine is important in ischaemic situations. The results also indicate that dopamine D-2 receptor agonists are neuroprotective against ischaemia-induced brain injury and may play a role in neurodegenerative disorders. (C) 1998 Elsevier Science B.V. All rights reserved.