CATECHOLAMINE INNERVATION OF THE PIRIFORM CORTEX - A TRACING AND IMMUNOHISTOCHEMICAL STUDY IN THE RAT

In order to determine the origin of the catecholamine innervation of t he rat piriform cortex (PC), we combined retrograde transport of the B subunit of the cholera toxin (CTb) with tyrosine hydroxylase (TH) imm unohistochemistry. A substantial number of CTb retrogradely labeled ce lls was found in the parabrachial pigmented, paranigral and interfasci cular nuclei of the ventral tegmental area and the dorsal part of the locus coeruleus, whereas nearly no labeling was noted in the substanti a nigra. Following TH immunohistochemistry on the same sections, most if not all of the CTb labeled cells were also Tn immunoreactive. Occas ional double-labeled cells were also observed in the anterior part of the raphe dorsal nucleus. As visualized with dopamine beta-hydroxylase , dopamine or TH immunohistochemistry, the noradrenaline fibers were h omogeneously distributed whereas the dopamine fibers showed rostro-cau dal and latero-medial differences. The distribution of TH fibers overl apped both patterns. Our report suggests that the heterogeneous distri bution of the DA fibers could support a differential centrifugal modul ation of the olfactory information processing throughout the PC.