Dendritic morphology of pyramidal neurons in the chimpanzee neocortex: regional specializations and comparison to humans

Abstract

The primate cerebral cortex is characterized by regional variation in the structure of pyramidal neurons, with more complex dendritic arbors and greater spine density observed in prefrontal compared with sensory and motor cortices. Although there are several investigations in humans and other primates, virtually nothing is known about regional variation in the morphology of pyramidal neurons in the cerebral cortex of great apes, humans' closest living relatives. The current study uses the rapid Golgi stain to quantify the dendritic structure of layer III pyramidal neurons in 4 areas of the chimpanzee cerebral cortex: Primary somatosensory (area 3b), primary motor (area 4), prestriate visual (area 18), and prefrontal (area 10) cortex. Consistent with previous studies in humans and macaque monkeys, pyramidal neurons in the prefrontal cortex of chimpanzees exhibit greater dendritic complexity than those in other cortical regions, suggesting that prefrontal cortical evolution in primates is characterized by increased potential for integrative connectivity. Compared with chimpanzees, the pyramidal neurons of humans had significantly longer and more branched dendritic arbors in all cortical regions.

Keywords: Golgi; area 10; dendrites; evolution; primate cerebral cortex.

Figure 1.

(A–E) Regional differences in TDL (in μm), MSL (in μm), DSC, DSN, and DSD in areas 3b, 4, 18, and 10. (F) Results from a Sholl analysis, reporting the mean number of intersections per 20 μm of dendrite length. Error bars indicate standard deviations.

Figure 2.

(A and B) Photomicrographs of pyramidal neurons in area 10 of chimpanzees; (C) close-up of a basilar dendritic shaft of a pyramidal neuron in area 10. Scale bar in (A and B) = 100 μm and scale bar in (C) = 50 μm.

Figure 3.

Tracings of chimpanzee pyramidal neurons in areas 3b, 4, 18, and 10. Scale bar = 100 μm.

Figure 4.

(A) Photomicrograph of a pyramidal neuron in area 10 of the human prefrontal cortex; (B) close-up of a basilar dendritic branch of a pyramidal neuron in area 10 in the human prefrontal cortex; (C) tracings of human neurons in areas 3b, 4, 18, and 10. Note that only the basilar dendrites were traced in these neurons. Scale bars: (A) = 50 μm; (B) = 50 μm; (C) = 100 μm.