Distribution of parvalbumin immunoreactivity in the rat septal area.

The distribution of parvalbumin (PV)-containing neurons and processes in the septal area of the rat brain was studied using a monoclonal antibody and the avidin-biotin immunoperoxidase method. PV-immunoreactive neurons were mainly located in the medial septum/diagonal band complex and in the horizontal limb of the diagonal band of Broca, showing a high density of heavily immunostained neurons and fibers. Nonimmunoreactive cells surrounded by PV-positive cells and processes were observed in the same region, but no pericellular basket-like arrangements were found. On the contrary, the dorsal, intermediate, and ventral nuclei of the lateral septum were practically devoid of PV-positive neurons and processes. Thus, in these nuclei only a very low density of isolated neurons was labeled; these were specially scattered in the ventrolateral septal nucleus and in the dorsolateral septal nucleus just below the corpus callosum. Delicate PV-positive axonal plexuses were also observed in the dorsal and intermediate nuclei of the lateral septum. The immunopositive neurons displayed very different sizes and morphologies among the various septal nuclei and inside each of them, indicating that they do not belong to a single morphological class of neurons. Finally, the distribution of PV in the rat septal area is not directly related to cholinergic and GABAergic septal neurons.