ISSN:
1432-1912
Keywords:
DOPA Uptake
;
DOPA Decarboxylation
;
Noradrenaline Receptor Stimulation
;
Capillary Walls
;
Nerve Terminals
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary The uptake and decarboxylation of 3,4-dihydroxyphenylalanine (DOPA) in the central nervous system were studied in spinal rats. The neuronal l-DOPA decarboxylase can be eliminated in the spinal cord caudal to a chronic (9–15 days) transection. The DOPA decarboxylase in the periphery and in the central capillary walls, but not in the central neurons, can be inhibited by l-α-methyl-dopa hydrazine (αMDH, 100 mg/kg i.p.). The DOPA-induced noradrenaline receptor stimulation in the caudal part of the spinal cord was studied by determining increase in hindlimb flexor reflex activity. No marked central accumulation of DOPA was observed after injection of the d-isomer, demonstrating a barrier for the passage of DOPA from the blood. l-DOPA was taken up by a stereoselective mechanism. Pretreatment with αMDH increased the central tissues to plasma ratio of the concentrations of l-DOPA, indicating that there is also an enzymatic barrier for l-DOPA in the capillary walls. After treatment with l-DOPA, no formation of noradrenaline was noted in the spinal cord caudal to a chronic transection because of the disappearance of the noradrenaline nerve terminals with their dopamine-β-hydroxylase activity. The l-DOPA-induced dopamine accumulation in the spinal cord was not reduced caudal to a chronic transection, indicating that most of the l-DOPA entering the central nervous system was decarboxylated in the capillary walls. The dopamine synthesized in the chronically transected cords presumably diffused from the capillary walls to the (probably supersensitive) noradrenaline receptors and produced the same effect as the dopamine and noradrenaline coming from the nerve terminals in the acutely transected cords. In the chronically transected spinal cords, αMDH inhibited the dopamine formation from l-DOPA because of interference with the capillary decarboxylase. In the acutely transected spinal cord, pretreatment with αMDH did not change the amount of dopamine synthesized from l-DOPA, i.e., the decarboxylation occurred in the monoamine nerve terminals instead of in the capillary walls.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00508077
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