Eur J Anat, 3 (2): 101-109 (1999)

Morphology and laminar distribution of cortico-claustral neurons in different areas of the rabbit cerebral cortex

Gutierrez-Ibarluzea I., Acera-Osa A., Mendizabal-Zubiaga J.L., Arana-Arri E., Bueno-Lopez J.L., Reblet C.

Dpto. de Neurociencias, Facultad de Medicina y Odontologia, Universidad del Pais Vasco, E-48940 Leioa, Vizcaya, Spain

ABSTRACT This study examines the morphology and laminar distribution of cortico- claustral neurons that were retrogradely labelled after single injections of biotinylated dextran amine in the caudal two thirds of the rabbit insular claustrum. Labelled neurons were studied in neocortical areas 17, 18, and A2, insular cortex and cingulate areas 24a,b and 29b,c,d. Most of the labelled neurons lay in layer VI for area 17 and in layer V for the remaining areas. Most of the labelled neurons were either normally oriented pyramidal cells or inverted neurons (spiny neurons with their major dendritic shaft oriented towards the white matter). Labelled inverted neurons were 85% for area 17 and under 30% for other isocortical areas. For the allocortex, they were less than 20%. For all areas, labelled inverted neurons lay chiefly in layer VI and normally oriented pyramidal neurons in layer V. The findings show that while neurons with inverted morphology are a minor but consistent source for axonal projections from the cortex to the claustrum, they are paramount in area 17. The findings also show that the laminar distribution of cortico- claustral cells is also area-specific.

Keywords: animal tissue, article, brain cortex, brain region, cell labeling, cellular distribution, claustrum, morphology, nonhuman, pyramidal nerve cell, rabbit