The capacity of the spinal cord of the rat to synthesize and metabolize
catecholamines from injected
L-DOPA, was tested
at 10 and 100 days after a middle thoracic transection of the cord. There was no indication of even a minimal recovery of the capacity to synthesize
noradrenaline in the caudal region of the transected cord.
At 10 days after transection, the lumbar cord could synthesize 50% of the
dopamine formed in the intact cord. At 100 days after transection the synthesis of
dopamine in the transected cord was equal to that in the intact control animal. At both 10 and 100 days after transection, the
dopamine synthesized from
L-DOPA was efficiently metabolized to dihydroxyphenylacetic
acid (
DOPAC) and
homovanillic acid (HVA). As judged from the levels of
gamma-aminobutyric acid (
GABA) and
glutamic acid (
glutamate) present in the transected cord, no major metabolic derangement of the spinal cord tissue seemed to have been present at the times the experiments were done. It is concluded that
dopamine can be efficiently synthesized and metabolized from its immediate precursor,
L-DOPA, even in the absence of monoaminergic nerves. The results are discussed with reference to two main themes. The first, is the likelihood that in the
therapeutic use of
L-DOPA in states of chronic dopaminergic
nerve degeneration (e.g.
Parkinson's disease), the synthesis and metabolism of
dopamine probably occurs throughout the entire central nervous system. The second, is the possible usefulness of
L-DOPA to test for the relative intactness of spinal reflex circuities in the chronically spinalized animal.