AXONAL EXPRESSION SITES OF TYROSINE-HYDROXYLASE, CALRETININ-IMMUNOREACTIVITY AND CALBINDIN-IMMUNOREACTIVITY IN STRIATOPALLIDAL AND SEPTAL NUCLEI OF THE RAT-BRAIN - A DOUBLE-IMMUNOLABELING STUDY

Besides the dopaminergic afferent projection system, calbindin (CALB)- and calretinin (CR)-immunoreactive fibres of intrinsic and extrinsic origin represent the most abundant axonal categories in the rat striat al and lateral septal areas. The question arises whether or not they m ay represent separate populations, or whether they form subgroups whic h co-express more than one of these antigens. Therefore, the present s tudy is focused on the distribution patterns of the axons single-immun olabelled by the catecholaminergic marker tyrosine hydroxylase (TH), a nd on TH-immunoreactive axons displaying also CR- and/or CALB-immunore activity in double-immunostained sections. Striking differences were f ound between the patch and matrix compartments of the caudate-putamen (CP). Whereas the vast majority of TH-immunoreactive fibres in the pat ches and a patch-associated subcallosal layer co-expressed CR but not CALB, fibres mono-labelled by the TH-immunoreactivity were predominant in the matrix. The matrix-like regions of the core of nucleus accumbe ns (CACC), fundus striati (FS), the striatal cell bridges (CB) and the striatal part of olfactory tubercle (OTU) coincided in this respect w ith the matrix in CP. The absence of CR-immunoreactivity was also char acteristic of the TH-immunoreactive fibres in the patch-like areas of the accumbal core, although a high number of separate CR-immunoreactiv e axons were present. In the shell of nucleus accumbens (SACC) which r eceives a rich catecholaminergic innervation, fibres co-expressing eit her one of the calcium-binding proteins were absent. The islands of Ca lleja (Cn) displaying a strongly TH-immunoreactive centre and a periph ery of lower staining intensity, showed only a low number of TH-immuno reactive fibres co-expressing CR or CALB. The broad shell-like band of TH-immunoreactive axons between medial and lateral part of the septum was single-stained with the TH-immunoreactivity. In contrast, the TH- positive fibres forming basket-like arrangements around some neurons i n the dorsal lateral septal nucleus co-expressed also CR, but not CALB . The results are discussed in view of the recent concepts of basal fo rebrain organization and the cytochemical characteristics of mesenceph alic dopaminergic nuclei giving rise to the vast majority of the stria tal and septal TH-immunoreactive fibre supply, in order to correlate t he known projection patterns with the content of calcium-binding prote ins in TH-immunolabelled fibres and presumed cells of origin. The TH-i mmunoreactive fibres in the striatal patches displaying CR- but not CA LB-immunoreactivity may originate mainly from neurons in the ventral t ier of pars compacta (SNC) and from the pars reticulata of substantia nigra (SNR) which show identical cytochemical properties. Axons in the matrix of CP and the accumbal core as well as in the islands of Calle ja single-labelled by the TH-immunoreactivity or additionally containi ng CALB and CR may originate from neurons in the dorsal tier of mesenc ephalic nuclei like SN, pars compacta and ventral tegmental area. CR-c ontaining TH-immunoreactive basket-like axon terminations in the dorsa l lateral septal nucleus are likely to originate either from mesenceph alic nuclei or from the supramammillary region. (C) 1998 Elsevier Scie nce B,V. All rights reserved.