Synthesis of catecholamines in the developing spinal cord of the rat

Using mass fragmentographic techniques, the synthesis of dopamine (DA) and norepinephrine (NE) was studied in five functional regions in the spinal cord of the developing rat. Norepinephrine was first detectable in the whole cord on fetal day (FD) 16. Thereafter, there was a rapid increase in synthesis. The fastest rate occurred in the ventral horn. The peak concentration was recorded in the latter half of neonatal life, followed by a decline back to the levels found in the adult cord. The capacity of the developing cord to synthesize NE from injected L-dihydroxyphenylalanine (L-DOPA) increased in concert with its normal synthetic capacity. There was no clear consistent pattern in the development of DA synthesis, with two exceptions: (1) in the cervical dorsal horn (CDH), cervical ventral horn ( CVH ), and thoracic zona intermedia ( TZI ), there was a peak of DA on the day of birth; (2) in all regions there was a peak of DA on neonatal day (ND) 20. At FD 16 (the earliest time studied) the developing cord was capable of considerable synthesis (6.0 nmol/g) of DA from injected L-DOPA. This synthetic capacity developed rapidly, peaked at ND 4, and declined back to the adult levels by ND 20. Control experiments indicate that only about 10% (at best) of the DA synthesized from injected L-DOPA occurs in monoaminergic nerve terminals. Norepinephrine is synthesized exclusively in noradrenergic nerve terminals. The newly synthesized DA and NE are both extensively metabolized in the cord. The results are discussed in relationship to current attempts to understand the functional importance of spinal monoaminergic nerves.(ABSTRACT TRUNCATED AT 250 WORDS)