TYROSINE-HYDROXYLASE EXPRESSION WITHIN BALB C AND C57BLACK/6 MOUSE LOCUS-COERULEUS .1. TOPOLOGICAL ORGANIZATION AND PHENOTYPIC PLASTICITY OF THE ENZYME-CONTAINING CELL-POPULATION/

Tyrosine hydroxylase phenotype expression was investigated in the cate cholaminergic population of the locus coeruleus neurons of two pure in bred mouse strains, Balb/C and C57Black/6. Therefore, we have characte rized the precise organization of tyrosine hydroxylase-expressing peri karya population, in control animals and following RU24722 treatment, which is known to induce tyrosine hydroxylase expression. Serial coron al sections were selected along the caudo-rostral extent of the struct ure and were processed for tyrosine hydroxylase immunocytochemistry. T hree days after the treatment, an increase in the number of cells whic h expressed tyrosine hydroxylase was observed all along the locus coer uleus in the Balb/C strain only. This increase equalized the catechola minergic neuron populations of the two strains. In the caudal subdivis ion of the structure, these newly detected perikarya were intermingled with the perikarya which expressed tyrosine hydroxylase in control co nditions. In the rostral half, the additional immunoreactive perikarya enlarged the mean coerulean space, defined as the area delimited by t he tyrosine hydroxylase-containing perikarya. These results demonstrat e a plasticity of the tyrosine hydroxylase phenotype expression, topol ogically organized and specific to the Balb/C strain.