Studies on catecholamine-synthesizing enzymes

Postnatal development and laminar distribution of noradrenergic fibers in cat visual cortex

Previous studies have indicated that adrenergic receptors show significant changes either in laminar distribution or in number during the critical period of kitten visual cortex development. In order to further investigate the postnatal development of this neurotransmitter system, especially in relation to the critical period, we used a polyclonal antibody against dopamine-beta-hydroxylase to localize noradrenaline-containing afferents in visual cortex of kittens of various ages from birth to adulthood. In young kittens, less than 2 weeks of age, noradrenergic fibers were sparse, short and randomly oriented, and were concentrated in layer I and in deep cortical layers V and VI. By postnatal day 40, the fibers were present throughout all cortical layers and exhibited higher densities in layers I, II, III, V and VI, with a band of lower staining in layer IV. While tangential fibers predominated in layers I, V and VI, relatively straight radial fibers traversed layers II and III. After postnatal day 40, we did not find major changes in the laminar distribution of adrenergic fibers. This developmental laminar distribution pattern of adrenergic fibers resembles that of the beta-adrenergic receptors that we and others have studied in kitten visual cortex, but differs from that of alpha-adrenergic receptors.

Evidence for cyclic AMP-mediated increase of aromatic L-amino acid decarboxylase activity in the striatum and midbrain

Aromatic L-amino acid decarboxylase (AAAD) activity of mouse striatum and midbrain increased after an intracerebroventricular injection of either forskolin or 8-bromo-cyclic AMP. The increase was transient, peaking between 15 and 30 min and returning to baseline by approximately 90 min. The increase of AAAD activity after forskolin was not affected by pretreatment with cycloheximide. Kinetic studies indicated an apparent increase of Vmax with little change of the Km for L-DOPA or pyridoxal 5'-phosphate. We conclude that AAAD activity of striatum and midbrain can be modulated by a cyclic AMP-dependent process.

Aromatic L-amino acid decarboxylase activity of mouse striatum is modulated via dopamine receptors

Aromatic L-amino acid decarboxylase (AAAD) activity is enhanced in the striatum of control and MPTP-treated mice after administration of a single dose of the dopamine receptor antagonists haloperidol, sulpiride, and SCH 23390. MPTP-treated mice appear more sensitive to the antagonists, i.e., respond earlier and to lower doses of antagonists than control mice. The rise of AAAD activity induced by the antagonists is prevented by pretreatment with cycloheximide. The apparent Km values for L-3,4-dihydroxyphenylalanine (L-DOPA) and pyridoxal 5-phosphate appear unchanged after treatment with the antagonists. Increased AAAD activity was observed also after subchronic administration of dopamine receptor antagonists or treatment with reserpine. A single dose of a selective dopamine receptor agonists had no effect on AAAD activity. In contrast, administration of L-DOPA, quinpirole, or SKF 23390 for 7 days lowers AAAD activity in the striatum. We conclude that AAAD is modulated in striatum via dopaminergic receptors.