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Tyrosine hydroxylase, aromatic L-amino-acid decarboxylase, and dopamine beta-hydroxylase activities were studied in the developing fetal rat brain. A delay of 2-3 days between the detection of the tyrosine hydroxylase and the aromatic L-amino-acid decarboxylase and dopamine beta-hydroxylase activities was observed. For this reason, the expression of tyrosine hydroxylase mRNA was studied. Tyrosine hydroxylase mRNA was visualized in the whole brain from 13 days of gestation, but the largest increase of the expression was observed in the hypothalamus. These results are discussed in terms of the relative gene expressions of the three enzymes involved in the biosynthesis of catecholamines and phenolamines in nervous tissues.

Summary. Unexpectedly, the administration of L-dopa, alone or after reserpine depletion of octopamine, results in an increase of octopamine in the cephalic ganglions of Locusta migratoria L. This increase is exclusively due to m-octopamine and is correlated to dopamine and m-tyramine enhancement. This observation agrees with the basic idea of different biosynthetic pathways for p-and m-octopamine and indicates that unlike p-octopamine, m-octopamine synthesis is related to catecholic amine pathways.In the Insecta nervous system, the direct incorporation of lac-tyrosine into octopamine, as well as the presence of dopamine hydroxylase, indicates that p-octopamine is biosynthesized from p-tyramine resulting from the decarboxylation of p-tyrosine 3-6. Moreover, this route appears to be quantitatively important since in Schistocerca, the incorporation of 14C-tyrosine is 10-fold higher in p-octopamine than in dopamine 3. Yet the meta-isomer of octopamine has not been detected in the cerebral ganglions of either Schistocerca gregaria 3 or Locusta migratoria 7. In order to study the interrelations of the different monoaminergic neurotransmitters in vivo and the importance of the tyrosine-octopamine pathway, we have examined the effects on octopamine synthesis of a treatment with precursors of this amine either associated or not with reserpine depletion 8.Materials and methods. 1-day-old 4th stage larvae of both sexes and 7-day-old male adults of the gregarious Locusta migratoria L. were used in these experiments. 15 lag and 45 lag of reserpine (Serpasil, Ciba-Geigy Lab.) and/or 5 lag and 15 lag of L-dopa (ICN Pharmaceutical, free of precursor contaminants as checked according to different chromatographic procedures 9m) were given every 2 days to the larvae and the adults respectively. 2% acetic acid or 5% HC1 N (solvents of reserpine and L-dopa respectively) were given to the controls. The larvae were treated during 4 or 6 days and the adults during 4 days. 2 h after the last injection, the animals were decapitated and the brain plus the optic and suboesophageal ganglions were rapidly dissected, frozen in liquid nitrogen and kept at -40 ~ until used.Octopamine with no separation of the m-and p-isomers was determined by the method of Molinoff et al. 12. The dansylation of the methylated amines allowed the identification and separation of m-and p-octopamine 1~ Dopamine and noradrenaline were determined as described by Dymond and Evans 15. m-tyramine was assayed according to Tallman et a1.16; the extracts were prepared as for octopamine assays and the hydroxylated and N-methylated products were isolated as described for octopamine 1~Results and discussion. As shown in table 1, reserpine treatment results in a large depletion of octopamine in the L.migratoria cephalic ganglions, whereas unexpectedly, treatment with L-dopa, either alone or after reserpine depletion, produces a slight increase or a partial replenishment of the octopamine stores. Moreover the octopamine content increases with age in the cephalic ganglions of ani...