Decreased ribosomal DNA transcription in dorsal raphe nucleus neurons differentiates between suicidal and non-suicidal death

The role of microglia in neuropsychiatric disorders and suicide

This narrative review examines the possible role of microglial cells, first, in neuroinflammation and, second, in schizophrenia, depression, and suicide. Recent research on the interactions between microglia, astrocytes and neurons and their involvement in pathophysiological processes of neuropsychiatric disorders is presented. This review focuses on results from postmortem, positron emission tomography (PET) imaging studies, and animal models of schizophrenia and depression. Third, the effects of antipsychotic and antidepressant drug therapy, and of electroconvulsive therapy on microglial cells are explored and the upcoming development of therapeutic drugs targeting microglia is described. Finally, there is a discussion on the role of microglia in the evolutionary progression of human lineage. This view may contribute to a new understanding of neuropsychiatric disorders.

Reduced ribosomal DNA transcription in the prefrontal cortex of suicide victims: consistence of new molecular RT-qPCR findings with previous morphometric data from AgNOR-stained pyramidal neurons

Prefrontal cortical regions play a key role in behavioural regulation, which is profoundly disturbed in suicide. The study was carried out on frozen cortical samples from the anterior cingulate cortex (dorsal and ventral parts, ACd and ACv), the orbitofrontal cortex (OFC), and the dorsolateral cortex (DLC) obtained from 20 suicide completers (predominantly violent) with unknown psychiatric diagnosis and 21 non-suicidal controls. The relative level of ribosomal RNA (rRNA) as a marker of the transcriptional activity of ribosomal DNA (rDNA) was evaluated bilaterally in prefrontal regions mentioned above (i.e. in eight regions of interest, ROIs) by reverse transcription and quantitative polymerase chain reaction (RT-qPCR). The overall statistical analysis revealed a decrease in rDNA activity in suicide victims versus controls, particularly in male subjects. Further ROI-specific post hoc analyses revealed a significant decrease in this activity in suicides compared to non-suicides in five ROIs. This effect was accentuated in the ACv, where it was observed bilaterally. Our findings suggest that decreased rDNA transcription in the prefrontal cortex plays an important role in suicide pathogenesis and corresponds with our previous morphometric analyses of AgNOR-stained neurons.

Ribosomal DNA transcription in prefrontal pyramidal neurons is decreased in suicide

Prefrontal cortical regions, which are crucial for the regulation of emotionally influenced behaviour, play most probably a dominant role in the pathogenesis of suicide. The study was carried out on paraffin-embedded brain tissue blocks containing specimens from the anterior cingulate cortex (dorsal and ventral parts), the orbitofrontal cortex, and the dorsolateral cortex obtained from 23 suicide completers (predominantly violent) with unknown psychiatric diagnosis and 25 non-suicidal controls. The transcriptional activity of ribosomal DNA (rDNA) as a surrogate marker of protein biosynthesis was evaluated separately in layers III and V pyramidal neurons in regions of interest (ROIs) mentioned above by the AgNOR silver staining method bilaterally. The overall statistical analysis revealed a decrease of AgNOR area suggestive of attenuated rDNA activity in suicide victims versus controls, particularly in male subjects. Further ROI-specific post-hoc analyses revealed decreases of the median AgNOR area in suicides compared to non-suicides in all 16 ROIs. However, this effect was only significant in the layer V pyramidal neurons of the right ventral anterior cingulate cortex. Our findings suggest that decreased rDNA transcription in prefrontal pyramidal neurons plays possibly an important role in suicide pathogenesis.

Modification of AgNOR staining to reveal the nucleolus in thick sections specified for stereological and pathological assessments of brain tissue

Background

Various stains have been devised to reveal degenerative or reactive cell phenotypes, or the disintegrative and/or neuropathic lesions associated with Alzheimer's, Parkinson's, and Pick's diseases, Down's syndrome, or chemical toxicity. Utilization of silver staining has allowed researchers to elucidate neural pathways promoting a greater understanding of the functional connections between brain regions. All of these methods employing silver can be characterized as ‘directed staining technologies’.

New methods

The argyrophilic proteins (AgNOR) staining protocol was modified to stain nucleoli in thick sections prepared for stereological evaluation of brain tissue. Nucleoli appeared as black dots against a pale amber background. Tissue sections were counterstained with Toluidine Blue, or reduced-strength Tyrosine Hydroxylase immunohistochemistry to facilitate visualization of basic cellular morphology and regional nucleus identification. Here, we present a modified method for nucleolar staining in free-floating thick sections of brain embedded in a gelatin matrix. The modifications in our procedure include incubation in HCl to denature (‘unravel’) the DNA, a bleaching step to reduce non-specific background silver staining, and counterstaining with Toluidine Blue or reduced-strength tyrosine hydroxylase immunohistochemistry.

Comparison with old methods

Prior to the development of immunohistochemistry, silver staining was used primarily to identify pathological profiles and trace axon pathways; however, in many cases, a combination of silver staining and immunohistochemistry are required to fully visualize pathomorphology. The mechanism of these stains requires the binding of silver ions to cellular components and the subsequent reduction of the ions to metallic silver. Dilutions of TH primary antibody were evaluated to maximize identification of neurons and the nucleolus amongst the soma and processes present in the thick section. The use of stereology as a tool to estimate cell number has become increasingly prevalent in neuroscience experiments. As requirements for the preparation of experimental tissue have been refined, researchers have begun to use thicker sections, between 40 to 80 microns, to increase the number of optical planes available for analysis. These thick sections require modified staining protocols to assure complete penetration of stains throughout the tissue section.

Conclusions

This method is particularly useful in nucleolar identification for Stereology, and automated counting methods. Use of the nucleolus avoids some of the problems associated with use of the nucleus. The nucleolus is smaller than the nucleus and is less susceptible to transection during sectioning. It has a higher density than the nucleus and is easier to visualize. It is generally darker staining than the immunohistochemical reaction product that provides the identification marker for the cells to be counted. Examples of the method in several brain sections of the rat are shown, though the method has been also proven in other mammalian models.

[The characteristic of protein biosynthesis in brain neurons with chronic alcohol intoxication]

The objective of the present study was to evaluate the possibilities for the use of the changes in the AgNOR staining patterns in the neurons of the dorsal raphe nucleus (DRN) for the purposes of the medical differential diagnostics of the cases of death from chronic alcohol intoxication. We elucidated the characteristics of the activity of protein biosynthesis including the number and the area of the nucleoli in the nuclei of the neurons of the individuals who had died from chronic alcohol intoxication (n=20) in comparison with the subjects of the control group (n=13). To reveal the morphological structures associated with protein biosynthesis in the nucleoli of the serotoninergic neurons of the dorsal raphe nucleus in the brain, the histological preparations were stained with the use of the silver-staining technique for nucleolar organizer regions (AgNOR). The comparative statistical analysis of the results thus obtained with the calculated confidence coefficients was carried out. The aggregated analysis of all the dorsal raphe subnuclei revealed the impairment of the AgNOR staining characteristics in the neurons of the subjects who had died from chronic alcohol intoxication in comparison with those of the subjects comprising the control group. It is concluded that the results of the study can be used for differential diagnostics of deaths from chronic alcohol intoxication and other causes.

[Determining the prescription of brain injuries based on the changes of the nucleolus organizer in astrocytes]

The well apparent signs of the proliferative reaction and activity of the nucleolus organizer in astrocytes within the zone of injury and at its periphery are considered to be the indicators of the participation of these cells in all the phases of the inflammatory and reparative processes associated with the brain injury. The objective of the present study was the evaluation of the changes in the number of the nucleoli in the nuclei of astrocytes during the acute post-traumatic period following the craniocerebral injury. A total of 26 cases of death of the men and women at the age from 36 to 50 years caused by the craniocerebral trauma were available for the examination. The tissue samples were stained with hematoxylin and eosin, based on the use of the Perls' Prussian blue staining protocol or by means of the AgNOR staining technique. The astrocytes in the regions immediately adjacent to the sites of brain injury were shown to undergo areactive necrosis during the first hours after the damage had been inflicted. The evaluation of the changes in the astrocytes required taking into consideration the influence of autolysis on the character of the signs being identified. The increase of the number of points in the astrocytes in which RNA replication occurs within days 2-4 after the injury can be accounted for by the accumulation of the granules containing silver in the cell nuclei. The cross reactions between hemosiderin and RNA await further investigations. It is concluded that the methods employed in this study may be of diagnostic significance for the purposes of forensic medical histology if used in the combination with other specialized techniques for determining the prescription of the craniocerebral injuries. The combination of the morphological and functional studies opens up the promising prospects for the investigations into the necrotic and proliferative processes in astrocytes associated with brain injuries of different origin.

Microglia in the dorsal raphe nucleus plays a potential role in both suicide facilitation and prevention in affective disorders

An involvement of the central serotonergic system has constantly been reported in the pathogenesis of suicide. The dorsal raphe nucleus (DRN) is the main source of serotonergic innervation of forebrain limbic structures disturbed in suicidal behaviour, in which an abnormal microglia reaction seems to play a role. In our present study, the density of microglia immunostained for the HLA-DR antigen was evaluated in the DRN. These analyses were carried out on paraffin-embedded brains from 24 suicidal and 21 non-suicidal patients; among them, 27 depressed (15 major depressive disorder and 12 bipolar disorder) and 18 schizophrenia (9 residual and 9 paranoid) patients and 22 matched controls without mental disorders. Only the non-suicidal depressed subgroup revealed significantly lower microglial reaction, i.e., a decreased density of HLA-DR positive microglia versus both depressed suicide victims and controls. The effect was not related to antidepressant or antipsychotic medication, as the former correlated positively with microglial density in non-suicidal depressed patients, and the latter had no effect. Moreover, the comparison of these results with previously published data from our workgroup in the same cohort (Krzyżanowska et al. in Psychiatry Res 241:43-46, 4) suggested a positive impact of microglia on ribosomal DNA transcription in DRN neurons in the non-suicidal depressed subgroup, but not in depressed suicidal cases. Therefore, the interaction between microglia and neurons in the DRN may be potentially involved in opposite ways regarding suicide facilitation and prevention in the tested subgroups of depressed patients.

Decreased ribosomal DNA transcription in dorsal raphe nucleus neurons is specific for suicide regardless of psychiatric diagnosis

The dorsal raphe nucleus (DRN) is the main source of serotonergic innervation of forebrain limbic structures disturbed in suicidal behaviour. We have evaluated the transcriptional activity of ribosomal DNA (rDNA) in DRN neurons by AgNOR silver staining method. The cohort (containing 24 suicidal and 20 non-suicidal patients, and 28 controls) was previously analysed regarding diagnosis-related differences between schizophrenia and affective disorders. Significant decreases in both AgNOR and nuclear areas suggestive of attenuated rDNA activity were currently found in suicidal versus non-suicidal patients. This effect, which was more accentuated in affective disorders patients, was not explained by antidepressant and antipsychotic medication.