NMDA receptor antagonists ameliorate the stepping deficits produced by unilateral medial forebrain bundle injections of 6-OHDA in rats.
OBJECTIVE
To test the hypothesis that excess glutamatergic transmission at NMDA receptors may contribute to the pathogenesis of Parkinson's disease (PD), we examined the effects of various NMDA receptor antagonists on a recently developed rat model of PD.


METHODS
Following unilateral injections of 12 microg 6-OHDA into the medial forebrain bundle of male Long Evans rats, stepping with both front paws was measured separately as the paws were dragged backwards and laterally. The effects of i.p. injections of varying doses of L-dopa, the non-competitive NMDA receptor antagonist dizocilpine [(+)-MK-801], the competitive NMDA receptor antagonist CPP, and combinations of L-dopa and NMDA receptor antagonists were then examined on stepping in three separate groups of rats.


RESULTS
The lesioned rats stepped less often with their contralateral paw than with their ipsilateral paw, and the magnitude of this stepping deficit was positively correlated with the amount of DA depletion in the ipsilateral dorsal striatum. L-dopa (1-25 mg/kg) dose dependently enhanced stepping with the contralateral paw, and 0.15-0.3 mg/kg dizocilpine and 1.5-6.25 mg/kg CPP enhanced stepping with the contralateral paw as much as did 8 mg/kg L-dopa. The combinations of L-dopa and each of the NMDA receptor antagonists did not significantly improve stepping more than either drug alone. Moreover, none of the drugs completely eliminated the stepping deficits, and high doses began to impair stepping with the ipsilateral paw by inducing turning.


CONCLUSIONS
These data indicate that deficits in contralateral stepping are a reliable and sensitive measure of akinesia in unilateral 6-OHDA-lesioned rats, and they support the hypothesis that excess glutamatergic transmission at NMDA receptors may play a role in the expression of PD symptomology.
Department of Psychology, Bates College, Lewiston, ME 04240, USA. jkelsey@bates.edu
John E
JE
Kelsey
Stephen D
SD
Mague
Reyna S
RS
Pijanowski
Ryan C
RC
Harris
Nancy W
NW
Kleckner
Russell T
RT
Matthews
D018663:Adrenergic Agents / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000187:drug effects*; D016291:Dizocilpine Maleate / Q000494:pharmacology; D015259:Dopamine Agents / Q000627:therapeutic use*; D004347:Drug Interactions; D005684:Gait / Q000187:drug effects*; D007980:Levodopa / Q000627:therapeutic use*; D008297:Male; D018696:Neuroprotective Agents / Q000494:pharmacology; D016627:Oxidopamine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D010300:Parkinson Disease / Q000517:prevention & control; D051381:Rats; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors*
D018663:Adrenergic Agents; D015259:Dopamine Agents; D018696:Neuroprotective Agents; D016194:Receptors, N-Methyl-D-Aspartate; D007980:Levodopa; D016291:Dizocilpine Maleate; D016627:Oxidopamine