Effects of cortical ablation on apomorphine- and scopolamine-induced changes in dopamine turnover and ascorbic acid catabolism in the rat striatum.
Levels of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), ascorbic acid and dehydroascorbic acid (DHAA) were measured by HPLC in the striatum of rats whose fronto-parietal cortex had been unilaterally ablated after a single injection of apomorphine (1 mg/kg s.c.), scopolamine (0.6 mg/kg s.c.) or L-glutamate (500 mg/kg i.p.). Unilateral cortical ablation decreased striatal levels of glutamate in both striata ipsilateral (35%) and contralateral (17-25%) to the lesion. Apomorphine and scopolamine significantly increased (+94 and +122%, respectively) the DHAA/ascorbic acid ratio in the striata ipsilateral to the lesion in unoperated and sham-operated rats (+72 and +34%, respectively), but both drugs failed to increase it in ablated rats. L-Glutamate significantly increased the DHAA/ascorbic acid ratio in unoperated (+53%) and ablated rats (+37%). The increase in sham-operated rats (+34%) did not reach statistical significance. Apomorphine and scopolamine significantly decreased the DOPAC/DA ratio in the striata ipsilateral to the lesion of unoperated, sham-operated and ablated rats. The decrease in the DOPAC/DA ratio induced by apomorphine and scopolamine was greater in ablated rats than in sham-operated rats. L-Glutamate induced only minor changes in striatal DA and DOPAC levels. We conclude that the apomorphine- and scopolamine-induced increase in ascorbic acid oxidation in the striatum requires intact cortico-striatal glutamatergic pathways. Cortical ablation potentiates the apomorphine- and scopolamine-induced inhibition of striatal DA turnover.
Desole
M S
MS
Institute of Pharmacology, University of Sassari, Italy.
Miele
M
M
Enrico
P
P
Esposito
G
G
Fresu
L
L
De Natale
G
G
Miele
E
E
D015102:3,4-Dihydroxyphenylacetic Acid / Q000032:analysis; D000818:Animals; D001058:Apomorphine / Q000494:pharmacology*; D001205:Ascorbic Acid / Q000032:analysis / Q000378:metabolism*; D002540:Cerebral Cortex / Q000502:physiology*; D003342:Corpus Striatum / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism*; D005971:Glutamates / Q000032:analysis / Q000494:pharmacology; D018698:Glutamic Acid; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012601:Scopolamine / Q000494:pharmacology*
D005971:Glutamates; D015102:3,4-Dihydroxyphenylacetic Acid; D018698:Glutamic Acid; D012601:Scopolamine; D001058:Apomorphine; D001205:Ascorbic Acid; D004298:Dopamine