Chemical features of monoaminergic and non-monoaminergic neurons in the brain of laboratory shrew (Suncus murinus) are changed by systemic administration of monoamine precursors.

ABSTRACT

5-Hydroxy-L-tryptophan (5-HTP) and L-3,4-dihydroxyphenylalanine (L-DOPA) were injected intraperitoneally (i.p.) into the laboratory shrew (Suncus murinus). Immunocytochemical and immunofluorescence studies were carried out on serial or same sections of the brain, which were reacted with specific antisera to dopamine (DA) or serotonin (5-HT) produced in our laboratory. We observed that cell bodies and nerve terminals of many catecholaminergic (CAnergic) neurons exhibited 5-HTP uptake and conversion of the precursor into 5-HT. However, the locus ceruleus showed scarcely any 5-HT immunoreactivity. This suggests that the precursor uptake mechanism may be different among various CAnergic groups. In contrast to these findings on CAnergic neurons, all serotoninergic (5-HTnergic) neurons after L-DOPA administration showed DA immunopositive reaction in their cell bodies and nerve terminals, suggesting that 5-HTnergic neurons may have the same capacity for precursor uptake. On the other hand, we observed that all aromatic L-amino acid decarboxylase (AADC)-only-positive neuron groups showed both DA and 5-HT immunoreactions after L-DOPA and 5-HTP administration, respectively, in the double-staining immunofluorescence method. From these results, AADC-only-positive neurons may be considered to belong to the amine precursor uptake and decarboxylation (APUD) system.