Ephemeral existence of a single catecholamine synthetic enzyme in the olfactory placode and the spinal cord of the embryonic rat

Publisher Website
Google Scholar
Abstract
The distribution of three catecholamine synthetic enzymes (tyrosine hydroxylase, L-aromatic acid decarboxylase and dopamine .beta.-hydroxylase), of the catecholamines themselves (dopamine and noradrenaline) and of a marker for neuronal intermediate filaments (neurofilament) was investigated in the embryonic rat using immunohistochemical and histofluorescence methods. At early stages of gestation (days 11-13), large numbers of tyrosine hydroxylase immunoreactive cells and fibres were apparent in the ventro-lateral spinal cord, and in and around the olfactory placode. In both cases, tyrosine hydroxylase positive fibres coursed between the proliferative layer and the surrounding mesenchyme, indicating the considerable degree of morphological differentiation. The similar disposition of neurofilament-like immunoreactivity in the same regions suggested that the tyrosine hydroxylase containing structures were neuronal. Within 2-3 days of their first manifestation, the tyrosine hydroxylase immunoreactive neurons disappeared. In the spinal cord, this coincided with their migration out of the mantle layer. Over this same period, neither of the other enzymes involved in the synthesis of noradrenaline, namely L-aromatic acid decarboxylase and dopamine .beta.-hydroxylase, nor dopamine and noradrenaline themselves, could be detected. It is concluded that some neurons in the olfactory placodal region and the ventrolateral spinal cord temporarily express a single specifically catecholaminergic enzyme, tyrosine hydroxylase, which is not utilized at that time in catecholamine synthesis. It is suggested that the control of transcription of the gene coding for tyrosine hydroxylase is independent of that for other catecholaminergic synthetic enzymes.