TRANSIENT NEURONAL POPULATION OF THE INTERNAL CAPSULE IN THE DEVELOPING HUMAN CEREBRUM

THE present study reveals the presence of a distinct group of cells, r esembling reticular thalamic neurones, in the internal capsule during fetal development. This cell population rapidly decreases in size duri ng early infancy and few cells are apparent in the 1-year-old infant. Internal capsule cells are well differentiated, multipolar or polymorp hous, AChE (acetylcholinesterase)-reactive neurones. The following spe cific molecular markers were demonstrated in the neurones of the inter nal capsule: MAP2 (microtubule-associated protein 2), somatostatin, ca lbindin-D-28K and p75 low-affinity NGF (nerve growth factor) receptor. A group of neurones described here corresponds to the perireticular t halamic nucleus found in certain mammalian species, hitherto unidentif ied in the primate brain, which may play an important role during deve lopment.