S. Vanhatalo et S. Soinila, SUPERFLUOUS EXPRESSION OF TRYPTOPHAN-HYDROXYLASE IN THE ZONA INCERTA DOPAMINERGIC-NEURONS, NeuroReport, 7(18), 1996, pp. 2889-2892
WE studied by double labelling the relationship between tryptophan hyd
roxylase-immunoreactive (TpOH-IR) neurones and A13 dopaminergic neuron
es in the zona incerta (ZH). TpOH-IR in the ZI was dramatically increa
sed after colchicine treatment. While all of the TpOH-IR neurones exhi
bited also tyrosine hydroxylase-immunoreactivity (TH-IR), a marker of
dopaminergic neurones, less than half (46%; n = 794) of the A13 TH-IR
neurones in the ZI showed TpOH-IR. None of these neurones were immunor
eactive, however, for serotonin either in intact animals or in animals
pretreated with serotonin precursor L-tryptophan and the monoamine ox
idase inhibitor pargyline. Thus, the neurones of the A13 dopaminergic
group in the ZI expressing TpOH are unable to synthesize serotonin. Th
ese findings support the idea that neurones may superfluously express
nonfunctional transmitter synthesizing enzymes, in this case TpOH, and
suggest that expression of an enzyme synthesizing a certain transmitt
er does not necessarily confirm the corresponding transmitter phenotyp
e.