Kaoru Komori

Transient tyrosine hydroxylase-immunoreactive neurons in the region of the anterior olfactory nucleus of pre- and postnatal mice do not contain dopamine

The transient appearance of tyrosine hydroxylase (TH)-immunoreactive (IR) neurons in the anterior olfactory nuclear region of mice was investigated using TH-immunocytochemistry. In this region, a new cell group composed of a small number of neurons immunoreactive to TH was demonstrated for the first time from the embryonic stages of E16-E18. These cells were not shown using antisera against aromatic L-amino acid decarboxylase, dopamine-beta-hydroxylase, phenylethanolamine-N-methyl-transferase, dopamine or serotonin. TH-IR cells progressively increased in number until birth. After birth the numbers reached maximum at postnatal days 9-12 and decreased until 4 weeks old, and then mostly disappeared at 6 weeks. Only single TH-IR cells were occasionally observed in this brain area of adult mice. Ultrastructurally some of these TH-IR neurons had immature Golgi apparatus, only a few mitochondria and deformed nuclei along with thin cytoplasma. Some other TH-IR cells, however, had mature Golgi apparatus, many mitochondria and a round nucleus more closely resembling mature cells. These neurons do not belong to the dopaminergic neuron system, because they lack dopamine production, and may be tentatively involved in early limbic circuits.

Identification of L-DOPA immunoreactivity in some neurons in the human mesencephalic region : a novel DOPA neuron group ?

The presence of L-3,4-dihydroxyphenylalanine (L-DOPA) immunoreactivity is reported for the first time in some neurons in the human mesencephalic region, using an immunohistochemical method with a newly raised, highly specific anti-L-DOPA antiserum. We have found many L-DOPA-positive/dopamine (DA)-positive and a few L-DOPA-positive/DA-negative cell bodies in dopaminergic regions in the midbrain. The present results suggest the existence of more than one neuronal group of L-DOPA in the human mesencephalon. L-DOPA in one group is an intermediate metabolite for decarboxylation to DA and in another group may exist as an end-product. L-DOPA in the latter neurons could be a neuromodulator and/or neurotransmitter. Thus, we suggest that L-DOPA plays an important role besides being an intermediate of DA in the human mesencephalon.

Antibodies raised against different oligopeptide segments of human dopamine-β-hydroxylase

We raised antibodies against 3 oligopeptide segments of human dopamine-beta-hydroxylase (hDBH) corresponding to the N-terminal (hDBH-N), the intermediate (hDBH-I), and the C-terminal (hDBH-C) amino acid sequences (residues 26-43, 452-468, and 582-598), respectively. We characterized the antibodies in terms of specificity by means of Western blotting and immunohistochemistry. Anti-hDBH-N antiserum recognized DBH in the brain (noradrenergic neurons in the pons and medulla oblongata) and adrenal medulla, not only of human but also of mouse, rat and house shrew. In contrast, anti-hDBH-C antiserum recognized only human DBH. These observations suggest that the antibody raised against the hDBH-C terminal peptide may specifically recognize only human DBH.

Semiquantitative analysis of immunoreactivities of tyrosine hydroxylase and aromatic l-amino acid decarboxylase in the locus coeruleus of desipramine-treated mice

The influence of antidepressant drugs on catecholaminergic neuron groups of the mouse brain was studied immunohistochemically, using a microphotometric semiquantitative method. The immunoreactive level of tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC) in the locus coeruleus (LC) was significantly decreased after 2 weeks of antidepressant administration. Our results suggest that long-term exposure to an antidepressant drug, desipramine, significantly affects intracellular catecholamine-synthesizing enzymes. These results may suggest some significant roles of the catecholaminergic neuronal groups to the action of the tricyclic antidepressant drugs.

Studies on the effect of L-threo-DOPS as a catecholamine precursor in the mouse brain

Recently, we investigated the changes in immunohistochemical features of monoaminerglc and nonmonoaminergic neurons in the laboratory shrew brain following the administration of monoamine precursors (Karasawa et al., 1994,1995). One of the monoamine precursors, L-threo-3,4-dihydroxyphelserine (L-threo-DOPS) is directly converted into noradrenaline by Laromatic amino acid decarboxylase (AADC). Previous biochemical studies have shown that monoamine content m the brain is increased following the administration of L-three-DOPS. However, based on immunohistochemical studies, little is precisely known. In the present study, we demonstrated the influence of L-threo-DOPS on monoaminergic and nonmonoaminergic neuronal groups of the mouse brain. The results showed that noradrenergic-immunoreactivity was distinctly identified in not only the primarily noradrenergic neurons but also in some dopaminergic neurons and nonmonoaminergic neurons (AADC-only postttve neurons). This suggests that amine precursors are taken up and decarboxylated in these neurons.

Detection of the Transient Expression of Monoamine Synthesizing Enzyme Immunoreactivity in Some Neurons: A Novel Neuron Group?

Recently, a transient expression of monoaminesynthesizing enzymes in several parts of the mammalian brain during preand postnatal development has been reported by several investigators. In this study, we reveal immunocytochemical evidence of “only-tyrosine hydroxylase (TH)”-and “only-aromatic L-amino acid decarboxylase (AADC)”-like immunoreactive neurons in the mouse brain by light and electron microscopy. The apparent lack of other monoamine-synthesizing enzymes would suggest that each of these neurons might contain L-DOPA or trace monoamines as an end product but were probably unable to synthesize monoamines. Both L-DOPA and tracemonoamines may be considered as new neurotransmitter candidates.