In situ labeling of apoptotic cell death in the cerebral cortex and thalamus of rats during development

Abstract

Apoptosis is a form of naturally occurring cell death that plays a fundamental role during development and is characterized by internucleosomal DNA fragmentation. In this study we used specific in situ labeling of DNA breaks (Gavrieli et al. [1992] J. Cell. Biol. 119:493-501) to analyze the distribution of apoptotic cells in rat cerebral cortex and thalamus at different developmental stages from embryonic day 16 to adulthood. Control experiments and electron microscopy confirmed that the reaction product was confined to the nucleus of selected cells. Plotting and counting of labeled nuclei in counterstained paraffin sections showed that apoptosis occurred mainly during the first postnatal week and was absent in embryonic and adult samples. In the cortex, the number of apoptotic cells progressively increased from birth to the first postnatal week, with a peak between postnatal (P) day 5 and P8, and subsequently decreased. At the time of maximal expression of apoptosis, labeled nuclei were present mainly in layer VIb and underlying white matter and at the border between cortical plate and layer I. Only a few apoptotic cells were found scattered in the thalamus, without a particular concentration in selected areas, but with a peak at P5. Differences in the number of apoptotic cells between cortex and thalamus suggest that apoptotic cell death may have a different functional significance in the two brain areas.

Neurochemical characterization of tyrosine hydroxylase-immunoreactive interneurons in the developing rat cerebral cortex

“…As reported previously (Ferrer et al, 1994;Spreafico et al, 1995;Thomaidou et al, 1997), apoptotic cells were still present three weeks after birth, decreasing in frequency with increasing age. However, double-labeling for TH and TUNEL at P14, P16, P20, and P24 failed to demonstrate DNA fragmentation in cortical TH-IR neurons (data not shown).…”

“…Although overlap existed between the ages at which we observed the maximal number of cortical TH-IR cell profiles and ages previously reported to contain TUNEL-positive cells (Ferrer et al, 1994;Spreafico et al, 1995;Thomaidou et al, 1997), we found no evidence for the death of these TH-IR cells. In a previous study using chromatin condensation and electrophoretic laddering of DNA as criteria to identify cell death, apoptosis was concluded to be the probable explanation for transient expression of neuropeptide Y in the developing hamster paraventricular area (Botchkina et al, 1996).…”

“…One explanation for this decline in TH neuron number is that these cells undergo programmed cell death. Previous studies demonstrated DNA fragmentation, an indicator of apoptosis, in cortical cells at ages partially overlapping those during which the number of TH-IR neurons decreased (Ferrer et al, 1994;Spreafico et al, 1995;Thomaidou et al, 1997). Our assays revealed no DNA fragmentation in cortical TH-IR neurons.…”

Insulin-Like Growth Factor-I Accelerates the Cell Cycle by Decreasing G1Phase Length and Increases Cell Cycle Reentry in the Embryonic Cerebral Cortex

“…The incidence of apoptosis in progenitor cells of the cerebral wall is estimated to be as low as 0.14% per day in normal mice (Haydar et al, 2000). The majority of neuronal apoptosis in the cerebral cortex occurs during early postnatal development (Spreafico et al, 1995;Thomaidou et al, 1997;Verney et al, 2000). Therefore, inhibition of apoptosis by IGF-I likely makes a relatively small contribution to neuron output from the proliferative zones of the cerebral wall.…”

A Novel p75NTR Signaling Pathway Promotes Survival, Not Death, of Immunopurified Neocortical Subplate Neurons

“…They are the first cortical neurons to differentiate and become incorporated into functional neuronal circuits, where they are needed for the establishment of thalamocortical connections (Friauf et al, 1990;Ghosh et al, 1990;Ghosh and Shatz, 1993). However, unlike later-generated cortical neurons, large numbers of subplate neurons undergo programmed cell death during early postnatal development (Allendoerfer and Shatz, 1994;Spreafico et al, 1995;Price et al, 1997). This raises the question of how a mature population of CNS neurons that is fully integrated into a functioning circuit are selectively eliminated, and conversely, what signal transduction pathways control their survival.…”