QUANTITATIVE STUDY OF TYROSINE-HYDROXYLASE PROTEIN-LEVELS WITHIN THE SOMATIC AREA OF THE RAT LOCUS-COERULEUS DURING POSTNATAL-DEVELOPMENT

To date only global dosages of tyrosine hydroxylase (TH) protein have been realized in the locus coeruleus (LC) without discriminating the e nzyme contained in the cell body area from the one in the surrounding neuropil. The preceding immunohistochemical study (Bezin et al., 1994) revealed a dramatic plasticity of the cellular expression of TH in th e LC during the postnatal development of the rat. It was therefore nec essary to develop a quantitative biochemical approach, strengthened by a great anatomical resolution, to follow the developmental evolution of TH levels exactly in the space containing the coerulean TH-immunore active perikarya. In the present work two biochemical parameters neces sary for precisely defining the phenotypic characterization of TH expr ession within the rat LC have been established during the postnatal de velopment at six different stages: postnatal day 4 (PND4), PND10, PND1 4, PND21, PND30, and PND42. TH tissue concentration and content were p recisely determined along the caudorostral extent of the LC within the previously (Bezin et al., 1994) defined spaces delimited by the TH-co ntaining perikarya. TH tissue concentration remained quite stable duri ng the postnatal development. TH quantity exhibited few age-related va riations with a transient peak at PND10 and followed the same evolutio n as the volume containing the TH-expressing perikarya. The mean cell contribution to the total quantity of TH measured in the whole LC show ed important age-related fluctuations with a dramatic peak at PND10 fo llowed by a drastic decrease until PND21. Such modifications of the st eady-state levels of TH in the perikarya of coerulean neurons could be related to temporal requirements of this enzyme in their other cellul ar compartments such as dendrites or terminals, and/or alterations of the synthesis of the protein.