The DNA loops plus the NM constitute a nucleoid, a very large nucleoprotein aggregate generated by lysis of nuclei at pH 8.0 in non-ionic detergent and the presence of high salt concentration. In nucleoids the DNA remains essentially intact but it lacks the nucleosome structure because of the dissociation of histones and other chromatin proteins; yet the naked DNA loops remain topologically constrained and supercoiled being attached to the NM. Nucleoids are a standard preparation for evaluating the NHOS. After treating the N1 and N2 populations for extraction of nucleoids the resulting preparations are highly enriched in NeuN-positive neuronal nucleoids while the presence of NeuN-negative nucleoids from glial cells is significantly reduced, indicating that the glial-cell nuclei are poorly resistant to the NMextraction conditions. This fact underlines the overall higher stability of the NHOS from neurons when compared to that of glial cells. Moreover, we have recently shown that NeuN/ Fox-3 is an intrinsic component of the neuronal NM and so it is a reliable marker of the neuronal NHOS. Nucleoids are also known as nuclear halos since exposure of such structures to DNA-intercalating agents like ethidium bromide leads to unwinding of the DNA loops that form a fluorescent DNA halo around the NM periphery. The EB acts as a molecular lever causing the unwinding of loop DNA and this process induces strong tearing forces that impinge upon the NM as the DNA rotates and expands during unwinding. Thus the stability of the DNA-NM interactions and of the NM itself can be evaluated by titrating the response of the nucleoids to increasing concentrations of EB since weak DNA-NM interactions are eliminated at lower EB concentrations. Hence, exposing the corresponding nucleoids to a high concentration of EB leads to maximum halo expansion and under such conditions any significant change in the distribution of the DNA-NM interactions or any significant weakness in the strength of such interactions is revealed as distortions and heterogeneities in the resulting halo Gomisin-D surrounding the NM. Moreover, a weak NM can be fractured by the tearing forces resulting from DNA loop unwinding an expansion. After exposure to high the nucleoids from neurons of the four post-natal ages studied display well defined DNA halos that surround the undisturbed NM framework. This is in contrast with nucleoids from P0 and P7 hepatocytes that are destroyed by the resulting EB-induced DNA unwinding while only the nucleoids from P80 and P540 hepatocytes are able to withstand the effects of EB-induced DNA unwinding, in a similar fashion as the neuronal nucleoids. We determined the average diameter of both nucleus and NM in neurons from all post-natal ages studied. The results indicate that the NM diameter is greater than the corresponding nuclear diameter at all ages studied, suggesting that the neuronal NM is resilient as it has been observed in lower eukaryotes. The average DNA halo size has been correlated with the average DNA-loop size, therefore by measuring the average DNA-halo radius after maximum halo expansion it is possible to estimate the average DNA-loop size. The results indicate that there is no real significant change in the average DNA loop size in neurons from maturity to old age. This is in contrast to what we have observed in hepatocytes in which the average DNA loop size is reduced by 36% from P80 to P540. Lomitapide Mesylate Nevertheless, the average DNA loop size in neurons from all ages studied is significantly shorter than that in aged P540 hepatocytes.