Phorbol ester-induced changes in rat hippocampal glycoprotein fucosylation

Identification of fucose alpha(1-2) galactose epitope-containing glycoproteins from rat hippocampus

Fucosylation of terminal galactose residues of brain glycoproteins in the alpha(1-2) position has been shown to be crucial for neuronal plasticity, including phenomena such as long-term potentiation and long-term memory formation. We raised antibodies against the plasticity-relevant fucalpha(1-2)gal epitope and used them to determine the distribution of the epitope in adult rat hippocampus. To identify proteins bearing fucalpha(1-2)gal glycostructures antibodies against known synaptic fucoglycoproteins were used in combination with the fucalpha(1-2)gal antibodies. The NMDA receptor subunit NR1 and fractions of gp65 and cadherin were found to carry the epitope, while fucosylation of NCAM180 and NCAM140 obviously occurs via different linkages to the glycan chains.

Influence of dopaminergic agonists/antagonists on fucose metabolism in the rat brain

Valid indications of a key role for dopaminergic drugs in glycoprotein fucosylation in neuronal tissue in vitro led us to investigate whether the administration of dopaminergic agonists/antagonists influences fucose metabolism in the rat brain in vivo. Three test groups were set up. Group 1 was given L-DOPA (210 mg/l), Group 2 haloperidol (10.5 mg/l) in drinking water, Group 3 served as control. The rats were sacrificed after 8 weeks and enzyme activities in 5 different brain areas were determined concerning the enzymes of the anabolic fucose metabolism: fucokinase, fucose-1-phosphate pyrophosphorylase and fucosyltransferase 1 and 2. Only the specific activity of fucokinase was affected by haloperidol or L-DOPA administration. In the olfactory bulbus, thalamus and cortex, haloperidol decreased fucokinase activity by 21%, 37%, and 39%, respectively (p < 0.05 in each case). No changes were observed in the cerebellum and striatum. Surprisingly, fucokinase activity in the cortex was decreased by L-DOPA (31%, p < 0.05).

CONCLUSIONS

Cerebral fucokinase activity is influenced in vivo by dopaminergic drugs in well circumscribed brain areas. Other enzymes of the anabolic fucose metabolism showed no change in activity. It is, therefore, conceivable that these drugs, apart from known mechanisms, exert part of their pharmacological action via a modulation of fucose metabolism.