Postnatal Development of NPY and Somatostatin-28 Peptidergic Populations in the Human Angular Bundle

Abstract

The angular bundle is a white matter fiber fascicle, which runs longitudinally along the parahippocampal gyrus. It is best known for carrying fibers from the entorhinal cortex (EC) to the hippocampus through the perforant and alvear pathways, as well as for carrying hippocampal output to the neocortex, and distributing fibers to polysensory cortex. The angular bundle is already present prenatally at the beginning of the fetal period. Connections between the EC and the hippocampus are established by the 20th gestational week (gw). In the postnatal period, it shows increasing myelination. The angular bundle, as well as other white matter portions of gyral surfaces in the brain, presents interstitial neurons, a remnant of subplate neurons. Those interstitial neurons show neurochemical phenotypes both prenatally and postnatally, among which, neuropeptide Y (NPY) and Somatostatin-28 (SOM-28) peptidergic populations are noticeable, and accompany the fiber connections in the maturation of the hippocampal formation. We sought to investigate the topography of the postnatal distribution and relative density of neurons immunoreactive for NPY or SOM in the angular bundle along the rostrocaudal axis of the hippocampus. The study was carried out in 15 cases, ranging from 35 gws, up to 14 year old. All cases showed positive neurons showing a polygonal or spindle shaped morphology for both peptides, scattered throughout the angular bundle. The highest number of positive neurons appeared around birth and the ensuing weeks. Up to one and a half years, the density of both peptidergic populations decreased slightly. However, cases older than 2 years of age showed a substantial decrease in density of immunolabeled neurons, density that did not showed a minor decrease in density of positive neurons in cases older than 2 years. In addition, a topography from caudal to rostral levels of the angular bundle was detected at all ages. The functional significance of interstitial cells is unknown, but the existence of SOM and NPY peptidergic neurons, presumably inhibitory, in the white matter of the angular bundle, could contribute to the basic wiring of the hippocampal formation, through which autobiographical and spatial memories can begin to be stored in the infant brain.

The distribution, number, and certain neurochemical identities of infracortical white matter neurons in a chimpanzee (Pan troglodytes) brain

“…For the potentially inhibitory subpopulations of WMICs in the chimpanzee, in relation to the estimates of the total number of WMICs, the largest subpopulation was the CR+ neurons (~12.1%), followed by the nNOS+ neurons (~10.5%), and a very small subpopulation of PV immunopositive cells. Combining the CR and nNOS results, we can provisionally report that the percentage of immunohistochemically identified inhibitory WMICs is ~22.6% of the total estimate of WMICs; however, this proportion is tentative, as the possible presence, or neurochemical overlap, with the markers used and other potential markers such as neuropeptide Y or somatostatin (e.g., Cebada‐Sánchez et al, 2019), were not explored in the current study. Our analysis of the proportion of inhibitory WMICs is well within the estimates provided for cortical inhibitory neurons in human and nonhuman primates, which ranges from 20% to 29% (Džaja et al, 2014; Hornung & de Tribolet, 1994; Krienen et al, 2020; Rudy et al, 2011; Sherwood et al, 2007, 2010).…”

Cytoarchitecture and myeloarchitecture of the entorhinal cortex of the common marmoset monkey (Callithrix jacchus)

“…In the rostral and middle levels (Figure b′,c′,d′), the amc, the anterior part of the angular bundle (ab) that forms the ventral border of the amygdaloid complex (Morais et al, ), was observed. At the caudal levels, the perforant pathway (pep) fibers entered the underlying ab, which corresponds to the tract placed in the ventromedial part of the medial temporal lobe (Cebada‐Sánchez, Marcos Rabal, Insausti, & Insausti, ). The entorhinal fibers then traversed the subiculum and crossed the hippocampal fissure to enter the dentate gyrus, or the subiculum and the hippocampus (Figure e′,f′).…”

Distribution, number, and certain neurochemical identities of infracortical white matter neurons in the brains of three megachiropteran bat species

“…Of these potential five types identified with the restricted approach used herein, four are specifically identified as GABAergic inhibitory due to these cells being immunopositive for parvalbumin, calbindin, calretinin (although calretinin can be excitatory, Gabbott, 2016) excitatory neuron within the WMIC population in the megachiropterans. It is likely that additional neurochemical types of both excitatory and inhibitory neurons will be present, in particular inhibitory neurons producing somatostatin, neuropeptide Y or neurotensin (Barbaresi et al, 2014;Cebada-Sánchez, Rabal, Insausti, & Insausti, 2019;Tomioka & Rockland, 2007), and with the potential for different combinations of marker coexpression. Given that in the current study the calbindin and nNOS immunopositive WMICs account for~26% of the total WMIC population, the numbers/proportions of these additional inhibitory neuronal types are likely to be minimal, as this proportion of inhibitory WMIC neurons is in line with the proportions of inhibitory WMICs reported in rodents (15-25%, Clancy et al, 2009), the lar gibbon (23.1%, Swiegers et al, 2019), and humans (25%, García-Marin et al, 2010).…”