Parvalbumin expression in the claustrum of the adult dog. An immunohistochemical and topographical study with comparative notes on the structure of the nucleus

Although the detailed structure and function of the claustrum remain enigmatic, its extensive reciprocal connection with the cortex suggests a role in the integration of multisensory information. Claustrum samples, obtained from necropsy of four dogs, were formalin fixed for paraffin embedding. Sections were either stained for morpho-histological analysis or immunostained for parvalbumin (PV). We focused on PV because in cortical and hippocampal areas it is a marker of the fast-spiking interneurons which have an important role in the information transmission and processing. Soma area, perimeter and circularity were considered as morphological parameters to quantitatively group the PV positive somata by k-means clustering. The histological investigation revealed a superior pyramidoid puddle and a posterior puddle characterized by a "cloud" of neurons in its dorso-lateral part. Immunostaining showed positive somata and fibers throughout the rostro-caudal extent of the dog claustrum, localized principally in the dorsal region. k-Means clustering analysis enabled neuron classification according to size, identifying respectively big (radius=11.42±1.99μm) and small (radius=6.33±1.08μm) cells. No statistical differences in soma shape were observed. The topographical distribution of PV immunoreactivity suggests that the dog dorsal claustrum might be functionally related to the processing of visual inputs. Taken together our findings may help in the understanding the physiology of claustrum when compared with anatomical and functional data obtained in other species.