CELLULAR QUANTIFICATION OF TYROSINE-HYDROXYLASE IN THE RAT-BRAIN BY IMMUNOAUTORADIOGRAPHY

We developed a rapid and sensitive radioimmunohistochemical method for the quantification of tyrosine hydroxylase (TH) at both the anatomica l and cellular level. Coronal tissue sections from fresh-frozen rat br ains were incubated in the presence of a TH monoclonal antibody. The r eaction was revealed with a S-35-labeled secondary antibody. TH conten t was quantified in catecholaminergic brain areas by measuring optical density on autoradiographic films or silver grain density on autoradi ographic emulsion-coated sections. Regional TH concentrations determin ed in the locus ceruleus (LC), substantia nigra pars compacta (SNC), a nd ventral tegmental area (VTA) were significantly increased by 45% af ter reserpine treatment in the LC but unchanged in the SNC and VTA. Mi croscopic examination of TH radioimmunolabeling showed a heavy accumul ation of silver grains over catecholaminergic cell bodies. In the LC, grain density per cell was heterogeneous and higher in the ventral tha n in the dorsal part of the structure. After reserpine treatment, TH l evels were significantly increased (57%) in the neurons of the LC but not in those of the SNC or VTA. The data support the validity of this radioimmunohistochemical method as a tool for quantifying TH protein a t the cellular level and they confirm that TH protein content is diffe rentially regulated in noradrenergic and dopaminergic neurons in respo nse to reserpine.