COMPARISON OF THE RAT DORSAL AND VENTRAL STRIATOPALLIDAL SYSTEM - A STUDY USING THE GABA(A)-RECEPTOR ALPHA(1)-SUBUNIT AND PARVALBUMIN IMMUNOLABELING

The ventral striatum is more closely related to limbic brain regions t han the dorsal striatum in spite of the remarkable similarities in the structural organization between these two brain regions. The present study is focused on the comparison of ventral striatopallidal territor ies and the dorsal striatopallidal system regarding the GABAA-receptor alpha(1)-subunit and parvalbumin immunoreactivity, as these markers s howed specific distribution patterns and coexpression sites in the mor e intensely studied dorsal regions. Our investigations revealed that: (1) Parvalbumin single-labeled cells and a moderate number of neurons single-labeled with the GABA(A)-receptor subunit exist not only in the dorsal but also in the ventral striatum, including the striatal cell bridges. In addition, morphologically similar neurons positive for the alpha(1)-subunit were also found in the corpus callosum and anterior commissure. (2) A small number of double-labeled neurons was seen not only in dorsal but also in ventral striatal regions. Such cells were m ainly located near the border with the globus pallidus and ventral pal lidum. They are likely to represent a further type of striatal neuron. (3) The vast majority of neurons in the entopeduncular nucleus, the h omologue of the primate internal globus pallidus segment, coexpressed alpha(1)-subunit and parvalbumin immunoreactivity, as reported previou sly for the other pallidal compartments. (4) The islands of Calleja ad joining the ventral pallidal extensions in the olfactory tubercle exhi bited a strong al-subunit immunoreactivity in the neuropil as well as somata single- or double-labeled for both markers. Our findings indica te that the dorsal and ventral striatopallidal compartments are simila rly organized in general with respect to the occurrence and distributi on of single- and double-labeled parvalbumin-immunoreactive and GABA(A )-receptor alpha(1)-subunit-immunoreactive neurons.