Callosal neurons in the cingulate cortical plate and subplate of human fetuses

Abstract

Given the scarcity of data on the development of the cerebral cortex and its connections in man, four brains of human fetuses at 25, 26, 30, and 32 weeks postovulation were used to investigate the following: 1) the radial distribution of callosal neurons in the cingulate cortex at the immediate postmigratory period; 2) the existence of callosally projecting neurons in the cortical subplate; and 3) the dendritic morphology of developing callosal neurons. The carbocyanine dye (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate) (DiI) was used as a fluorescent postmortem tracer for the identification and morphological description of callosal neurons, 4-6 months after the insertion of DiI crystals at the callosal midplane. Sixty-one completely labeled neurons were selected for microscopical analysis, drawn by use of a camera lucida and photographed. The main findings were the following: 1) the human cingulate cortex at 25-32 weeks postovulation contains callosally projecting neurons both in the cortical plate and in the subplate; 2) callosal cells in the plate are mostly spiny pyramids with somata distributed uniformly throughout the depth of the plate, irrespective of rostrocaudal position. They have well-differentiated basal dendrites and apical dendrites that consistently ramify within layer 1; 3) subplate callosal cells are smooth neurons of diverse dendritic morphology, distributed widely throughout the subplate depth. They were classified into four cell types according to the dendritic morphology: radially oriented, horizontally oriented, multipolars, and inverted pyramids. These findings extend to the human brain some of the evidence obtained in animals concerning the development of the cerebral cortex, especially those that are relevant to the formation of a transitory circuitry in the subplate.

Diaphorase-positive neurons in the cingulate cortex of human fetuses during the second half of gestation

“…3A) resembled closely those of callosally-projecting SP cells (lower row in Fig. 3B), previously described (deAzevedo et al 1997). Likewise, diaphorase-positive cells could be classified into four types, according to the alignment of their dendritic arbors in relation to the pia mater: radially-oriented ( Fig.…”

“…In a previous work we have shown that by 25 wpo both SP and CP cingulate neurons already project through the corpus callosum (deAzevedo et al 1997). Thirty-five wpo is considered to mark the beginning of SP dissolution stage for the somatosensory cortex (Kostovic and Rakic 1990).…”

Early history of subplate and interstitial neurons: from Theodor Meynert (1867) to the discovery of the subplate zone (1974)

“…Early synaptogenesis and a waiting compartment for thalamocortical afferents were demonstrated in the human cingulate cortex (Kostović & Krmpotić, 1976), the human auditory cortex (Krmpotić-Nemanić et al 1983), human and monkey prefrontal cortex (Kostović & Goldman-Rakic, 1983), human and monkey visual cortex (Kostović & Rakic, 1984), and human and monkey somatosensory and visual cortex (Kostović & Rakic, 1990). It was also demonstrated that the subplate in humans serves as a waiting compartment for basal forebrain cholinergic afferents (Kostović, 1986), and in rhesus monkeys for callosal and ipsilateral corticocortical afferents (Goldman- , which was later confirmed for human brain, too (DeAzevedo et al 1997). The subplate zone was also incorporated in the first revision of the original Boulder Committee (1970) scheme, as well as in its recent revision (Bystron et al 2008).…”

Populations of subplate and interstitial neurons in fetal and adult human telencephalon

“…Although the rapid differentiation of subplate neurons into five neuronal types between 17 and 25 PCW coincided with the ingrowth of thalamocortical (Kostovic & Goldman-Rakic 1983;Kostovic & Rakic 1984;Kostovic & Rakic, 1990), basal forebrain cholinergic (Kostović, 1986), and cortico-cortical afferent fibres (DeAzevedo et al 1997) into the subplate zone, subplate neurons continued with further dendritic growth even after these afferents had relocated to the cortical plate, up to the seventh postnatal month (Mrzljak et al 1988(Mrzljak et al , 1990(Mrzljak et al , 1992. Fusiform neurons with very long dendrites were the most frequently impregnated interstitial cell type in the gyral white matter after birth (Mrzljak et al 1990), but slightly modified pyramidal neurons and multipolar non-pyramidal interstitial neurons were also present (Kostovic & Rakic, 1980;Mrzljak et al 1990).…”