The timing, hemispheric laterality, and mode of termination of input from the prefrontal association cortex to the neostriatum were studied in fetal and neonatal rhesus monkeys using autoradiography for tracing connections. In addition, the cytological maturation of the neostriatum was examined in Nissl-stained sections from the same and other monkeys of selected prenatal and postnatal ages. A small contingent of corticostriatal axons reaches both the caudate nucleus and the putamen by the 69th embryonic day (E69) of the 165-day gestation period in this species and steadily expands over the next 3 fetal months. Throughout this period, ipsilateral perfrontostriatal connections predominate, and only a small and variable amount of label is detectable over the contralateral neostriatum. A major feature of the developing corticostriatal projection is a transfiguration in the distribution of its terminals: from E69 to E95, cortical terminals are distributed uniformly among neostriatal neurons; beginning around E105, areas of higher and lower grain density begin to emerge until finally, by E133, 250- to 500-micrometers-wide circular and elliptically shaped label- free cores perforate a field of densely labeled cortical terminals as in the neostriatum of the adult monkey (Goldman, P. S., and W. J. H. Nauta (1977) J. Comp. Neurol. 171: 369–386). The cytoarchitectonic composition of the neostriatum also changes during gestation: from E69 through E95, the small postmitotic neurons of the immature neostriatum are packed densely and, for the most part, are distributed homogeneously; by E105, they become segregated into cellular islands consisting of densely packed neurons that are encapsulated by fiber- rich annuli and embedded in a matrix of less densely arrayed neurons. The shape and size of the islands in Nissl-stained sections correspond to label-free cores in autoradiograms of fetuses with cortical injections, while the surrounding annuli and adjacent matrix cells correspond to areas of dense accumulation of label. Thus, the formation of the corticostriatal projection in primates involves a transformation in the distribution of ingrowing terminals synchronized with changes in cellular organization of the neostriatum.

https://www.jneurosci.org/content/jneuro/1/7/721.full.pdf

Prenatal formation of cortical input and development of cytoarchitectonic compartments in the neostriatum of the rhesus monkey

The organization of certain of the major afferents to the hippocampus and dentate gyrus has been studied in normal and reeler mutant mice using the autoradiographic and the anterograde degeneration methods. The distribution of the hippocampal and dentate afferents which arise in the medial and lateral parts of the entorhinal cortex and the hippocampus of both sides, has been found to be generally similar to that previously described in the rat, but there are a few minor differences that are discussed in the text. Despite the marked ectopia of many of the neurons in the hippocampal formation in the reeler mouse, the principal afferents to the hippocampus and the dentate gyrus maintain many of the features seen in normal mice. In particular, they maintain a normal radial sequence and a characteristic laminated and complementary arrangement. However, there are a number of significant differences in their distribution; for example, in the reeler mouse, the entorhinal afferents occupy the entire radial extent of the stratum moleculare of the dentate gyrus, whereas in normal mice they are restricted to the outer four-fifths of this layer. Furthermore, in the mutant the commissural and associational afferents to the dentate gyrus do not occupy the inner one-fifth of the molecular layer (as they do in normal animals) but rather are spread throughout the zone containing granule cells, which includes both the poorly-defined stratum granulosum and most of the hilar region of the dentate gyrus. Some of the developmental and functional implications of these and other abnormalities in the organization of the afferents to the hippocampus and dentate gyrus are discussed.

The organization of certain afferents to the hippocampus and dentate gyrus in normal and reeler mice.

A comparison of the effect of mid-thoracic spinal hemisection in the neonatal or weanling rat on the distribution and density of dorsal root axons in the lumbosacral spinal cord of the adult

The olfactory epithelium of mice after axotomy was investigated to clarify the stem cells of olfactory cells by double immunostaining using antikeratin (MA903) and anti-bromodeoxyuridine (BrdU) antibodies and by conventional electron microscopy. When a single dose of BrdU was given to mice 9 days after axotomy, immunostaining for BrdU was found in the globose basal cells which were negative for MA903, but not in the basal cells proper which were positive for MA903. The BrdU-immunoreactive cells increased 3-to 6-fold over the number of these cells in the controls, indicating active cell proliferation. At other postoperative days (4 and 14 days), fewer BrdU-immunoreactive cells were found. Furthermore, three pulses of BrdU resulted in numerous BrdU-immunolabelings in the globose basal cells and a few in the basal cells proper. There was no detectable difference in the number of labeled basal cells proper in operated and unoperated mice. In the electron micrographs 9 days after axotomy, the basal cells proper, flat-shaped in unoperated mice, appeared cylindrical or pyramidal in shape and the globose basal cells often lay between the basal cells proper. In unoperated controls, the globose basal cells were located above the flat-shaped basal cells proper. The results suggest that the stem cells of the olfactory cells are globose basal cells and not basal cells proper, and that the shape of basal cells proper changes in relation to the active proliferation of stem cells.

Basal cells in the mouse olfactory epithelium after axotomy: immunohistochemical and electron-microscopic studies

The complementary distribution of the fibers from the olfactory bulb and the intracortical associational fibers to layers Ia and Ib, respectively, of the olfactory cortex has been examined in both adult and neonatal rats, using horseradish peroxidase (HRP) and 3H-leucine as double tracers in the same animal. The observations presented here confirm and extend the previous demonstration (Price, '73) that in the adult the two projections are essentially nonoverlapping throughout the olfactory cortex. Indeed, when the distribution of axons from the olfactory bulb (labeled by HRP inserted into a cut in the LOT) is compared on the same section with that of associational fibers (labeled by 3H-leucine injected into the cortex), the overlap between the two projections is limited to a zone only 5–10 μm in width in both the piriform cortex and olfactory tubercle.



In contrast, at P1 the two projections overlap throughout layer I, although the bulbar and associational fibers are slightly concentrated superficially and deeply in layer I, respectively. This overlap is especially prominent in the part of the anterior piriform cortex deep to the LOT. During the remainder of the first postnatal week, this overlap resolves and by P7 the segregation of the two sets of afferent fibers is nearly equivalent to that seen in the adult.



However, there are several instances in adults where the segregation of these afferents does not develop. First, a relatively small population of aberrant axons derived from the LOT may be traced from layer Ia into layer Ib and then back to layer Ia. Most of these axons are large in diameter and lack the boutonlike varicosities found on smaller axons in layer Ia. They are most prominent in areas where the cortex is highly curved. Second, in layer I of the nucleus of the lateral olfactory tract, bulbar and associational fibers are extensively intermingled. In this case also, the bulbar fibers are large in diameter with only a few boutonlike varicosities.



The developmental emergence of afferent segregation and its breakdown in cases where the fibers from the olfactory bulb do not form boutons suggest that an interaction between the two distinct sets of fibers and the dendritic field is responsible for the normal development of this segregation and that this interaction depends on the process of synaptogenesis.

The development of lamination of afferent fibers to the olfactory cortex in rats, with additional observations in the adult.

http://link.springer.com/content/pdf/10.1007/978-3-642-81055-8_25.pdf

Development and Plasticity of Complementary Afferent Fiber Systems to the Olfactory Cortex

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Development and Plasticity of Complementary Afferent Fiber Systems to the Olfactory Cortex