Structural and functional compartmentalization of the cell nucleus in supraoptic neurons

Visualizing enteric nervous system activity through dye-free dynamic full-field optical coherence tomography

Major advances have been achieved in imaging technologies but most methodological approaches currently used to study the enteric neuronal functions rely on exogenous contrast dyes that can interfere with cellular functions or survival. In the present paper, we investigated whether full-field optical coherence tomography (FFOCT), could be used to visualize and analyze the cells of the enteric nervous system. Experimental work on whole-mount preparations of unfixed mouse colons showed that FFOCT enables the visualization of the myenteric plexus network whereas dynamic FFOCT enables to visualize and identify in situ individual cells in the myenteric ganglia. Analyzes also showed that dynamic FFOCT signal could be modified by external stimuli such veratridine or changes in osmolarity. These data suggest that dynamic FFOCT could be of great interest to detect changes in the functions of enteric neurons and glia in normal and disease conditions.

Trafficking of tachykinin neurokinin 3 receptor to nuclei of neurons in the paraventricular nucleus of the hypothalamus following osmotic challenge

Tachykinin neurokinin 3 receptor (NK3R) is a G-protein (GTP binding protein) -coupled receptor that is heavily expressed by magnocellular neurons of the paraventricular nucleus of the hypothalamus (PVN). Osmotic challenge is reported to activate NK3R expressed by magnocellular neurons and cause the NK3R to be internalized to the cytoplasm and perhaps the cell nucleus. In this study we show using immuno-electron microscopy that isolated nuclei from neurons in the PVN of osmotic challenged animals (rats) show a robust labeling for the NK3R. NK3R immunoreactivity was detected by Western blot in isolated nuclei of PVN neurons following the 2 M NaCl injection. No nuclear NK3R immunoreactivity was detected in control animals. NK3R antibody specificity was confirmed by small interfering (SI) RNA technology. This study establishes that the NK3R is trafficked to the nucleus of PVN neurons following a peripheral osmotic challenge.

Intranuclear rodlets in human pancreatic islet cells

OBJECTIVES

Intranuclear rodlets (INRs) are rod-shaped intranuclear inclusions that we have described in neurons of the human brain. We recently identified these structures in pancreatic islet cells. The objectives of this study are to describe the light microscopic features and cellular pattern of distribution of INRs in human pancreatic islet cells.

METHODS

Double immunofluorescence staining was performed on 5 human pancreatic tissue samples for the detection of class III beta tubulin (C3T) to detect INRs and for promyelocytic leukemia (PML) protein to examine the relationship between PML and INRs.

RESULTS

Intranuclear rodlets were detected in 22.99% of pancreatic B cells compared with only 3.11%, 1.80%, and 1.60% of A, D, and PP cells, respectively. Twenty-four percent of C3T-immunoreactive INRs showed partial or complete immunoreactivity for PML. Promyelocytic leukemia staining within the nuclei of B cells was confined to INRs and was not present in the typical PML bodies present in other cell types. Spatially, PML and C3T staining of islet cell INRs appeared to be mutually exclusive within individual INRs.

CONCLUSIONS

Intranuclear rodlets are present within the nuclei of pancreatic islet cells, where they reside predominantly but not exclusively in B cells. Immunoreactivity of B-cell INRs for PML suggests that the functional significance of INRs may be related to that of PML and/or PML bodies. Conversely, the exclusive localization of PML staining to INRs in B cells indicates that PML's function in B cells is selectively associated with INRs. The mutually exclusive pattern of PML and C3T staining suggests dynamic interactions between these 2 proteins in B-cell INRs. In light of evidence for the involvement of INRs and of PML bodies in disease, it will be of interest to investigate these structures in animal models of diabetes and in human diabetes.

Both increases in immature dentate neuron number and decreases of immobility time in the forced swim test occurred in parallel after environmental enrichment of mice

A direct relation between the rate of adult hippocampal neurogenesis in mice and the immobility time in a forced swim test after living in an enriched environment has been suggested previously. In the present work, young adult mice living in an enriched environment for 2 months developed considerably more immature differentiating neurons (doublecortin-positive, DCX(+)) than control, non-enriched animals. Furthermore, we found that the more DCX(+) cells they possessed, the lower the immobility time they scored in the forced swim test. This DCX(+) subpopulation is composed of mostly differentiating dentate neurons independently of the birthdates of every individual cell. However, variations found in this subpopulation were not the result of a general effect on the survival of any newborn neuron in the granule cell layer, as 5-bromo-2-deoxyuridine (BrdU)-labeled cells born during a narrow time window included in the longer lifetime period of DCX(+) cells, were not significantly modified after enrichment. In contrast, the survival of the mature population of neurons in the granule cell layer of the dentate gyrus in enriched animals increased, although this did not influence their performance in the Porsolt test, nor did it influence the dentate gyrus volume or granule neuronal nuclei size. These results indicate that the population of immature, differentiating neurons in the adult hippocampus is one factor directly related to the protective effect of an enriched environment against a highly stressful event.

The effect of prenatal X-irradiation on the developing cerebral cortex of rats. II: A quantitative assessment of glial cells in the somatosensory cortex

The developing central nervous system is known to be highly vulnerable to X-irradiation. Although glial cells are involved in various brain functions, knowledge on the effects of X-irradiation on glial cells is limited. Therefore, the purpose of the present study was to evaluate the effects of prenatal X-irradiation on glial cells. Pregnant Wistar rats were exposed to X-irradiation at a dose of 1.0 Gy on day 15 of gestation. Their offspring were examined at 7 weeks of age. The forebrain weight of X-irradiated rats was significantly lower than that of the age-matched controls. Histological quantification with stereology of the somatosensory cortex (SC) revealed no significant difference in the numerical density of glial cells between the X-irradiated and control rats. However, the glial cells in the X-irradiated animals had significantly larger nuclear size. We had previously reported that a similar X-irradiation paradigm resulted in no significant change in the numerical density of neurons in the SC. According to the results of the present study, there were no significant differences in the glial cell-to-neuron ratios between the X-irradiated and control animals. Taken together, it is speculated that prenatal X-irradiation has an equal effects on the numerical densities of glial cells and neurons.

Age-related changes in growth hormone-immunoreactive cells in the anterior pituitary gland of Jcl: Wistar-TgN (ARGHGEN) 1Nts rats (Mini rats)

Rats of the Jcl: Wistar-TgN (ARGHGEN) 1Nts strain (Mini rats) are transgenic animals carrying an antisense RNA transgene for rat growth hormone (GH); they show poor somatic growth and a low blood GH level compared to age-matched wild-type Wistar (non-Mini) rats. The purpose of the present study was to investigate age-related changes in growth hormone-immunoreactive (GH-IR) cells in the anterior pituitary gland (AP) of Mini rats at four, six, and eight weeks of age. The body weight and size of the GH-IR cells of Mini rats was significantly lower than that of non-Mini rats at six and eight weeks of age; however, this difference was not observed at four weeks of age. The AP volume and the number of GH-IR cells in Mini rats were significantly smaller than those of the age-matched non-Mini rats at the three ages. These results suggest that the abnormal development of GH-IR cells in the AP induced by the GH antisense RNA transgene is responsible for the poor somatic growth and the low blood GH levels in Mini rats.

Nuclear organization and dynamics of transcription sites in rat sensory ganglia neurons detected by incorporation of 5'-fluorouridine into nascent RNA

In this study we have used the transcription assay with 5'-fluorouridine incorporation into nascent RNA to analyze the nuclear organization and dynamics of transcription sites in rat trigeminal ganglia neurons. The 5'-FU administrated by i.p. injection was successfully incorporated into nuclear domains containing actively transcribing genes of trigeminal neurons. 5'-Fluorouridine RNA-labeling was detected with immunocytochemistry at light and electron microscopy levels. The 5'-fluorouridine incorporation sites were detected in the nucleolus, particularly on the dense fibrillar component, and in numerous transcription foci spread throughout the euchromatin regions, without preferential positioning at the nuclear periphery or in the nuclear interior. Double labeling experiments to combine 5'-fluorouridine incorporation with molecular markers of nuclear compartments showed the absence of transcription sites in Cajal bodies and nuclear speckles of splicing factors. Similarly, no 5'-fluorouridine labeling was detected in well-characterized chromatin silencing domain, the telomeric heterochromatin. The specificity and sensitivity of the run-on transcription assay in trigeminal ganglia neurons was verified by the i.p. administration of the transcription inhibitor actinomycin D. The dramatic reduction in RNA synthesis upon actinomycin D treatment was associated with two important cellular events, heterochromatin silencing and formation of DNA damage/repair nuclear foci, demonstrated by the expression of tri-methylated histone H4 and phosphorylated H2AX, respectively. 5'-Fluorouridine incorporation in animal models provides a useful tool to investigate the organization of gene expression in mammalian neurons in both normal physiology and experimental pathology systems.

Plasticity of nonapeptidergic neurosecretory cells in fish hypothalamus and neurohypophysis

The structure and function of nonapeptidergic neurosecretory cells (NP-NSC) are considered in terms of comparative morphology. Among NSC of different ergicity for NP-NSC the most characteristic involve massive accumulation and storage of neurohormonal products. Only in NP-NSC are the secretory cycles of functioning clearly expressed. Their highest reactivity is established during experimental and physiological stresses. In contrast, liberinergic, statinergic, and monoaminergic NSC, unlike NP-NSC, are characterized even in the "norm" by a constantly high level of extrusion processes. As signs of maximum NP-NSC plasticity, we consider the largest size of elementary neurosecretory granules, the diversity of secretion forms, and the maximum development of Herring bodies-clear manifestations of secretory cycles of functioning. In particular, phases of massive storage of neurosecretory granules in the extrusion cycle of NP-NSC neurosecretory terminals express accumulation of neurosecretory products. It is concluded that a particularly high degree of plasticity of NP-NSC is provided by their capability for functional reversion. This reversion is manifested first in the form of the restoration of the initial moderate level of functioning and especially in the accumulation of neurosecretory products. The reversion is considered an important mechanism providing a high degree of NSC plasticity. This degree turns out to be sufficient for participation of NP-NSC in the integration of fish reproduction. It is shown that NP-NSC are organized by the principle of a triad of the balanced system. This system consists of two alternative states: accumulation and release of neurosecretory products and the center of control of dynamics of their interrelations, the self-regulating center. In the latter, the key role is probably played by the Golgi complex.

The PML-nuclear inclusion of human supraoptic neurons: a new compartment with SUMO-1- and ubiquitin-proteasome-associated domains

It is well known that the cell nucleus is organized in structural and functional compartments involved in transcription, RNA processing and protein modifications such as conjugation with SUMO-1 and proteolysis. Promyelocytic leukaemia (PML) bodies are dynamic nuclear structures that concentrate PML protein, SUMO-1 and several sumoylated and non-sumoylated protein regulators of nuclear functions. PML bodies and their associated CBP has been involved in neuronal survival. By light and electron microscopy immunocytochemistry and in situ hybridization we reported the presence, in non-pathological conditions, of a large PML-nuclear inclusion (PML-NI) in human supraoptic neurons. This inclusion appears as a single nuclear structure composed of a capsule enriched in PML, SUMO-1 and CBP proteins and a central lattice of filaments immunoreactive for class III beta-tubulin, ubiquitinated proteins and proteasomes. Furthermore, the PML-NI concentrates the SUMO-conjugating enzyme E2 (UBC9). The PML-NI may be considered a nuclear factory involved in sumoylation and proteolysis via ubiquitin-proteasome system, two nuclear pathways engaged in the control of the nucleoplasmic concentration of active transcriptional regulators. Interestingly, the structural and molecular organization of the PML-NI is related to the Marinesco bodies, age-associated ubiquitinated intranuclear inclusions, and to the intranuclear rodlets enriched in class III beta-tubulin, which are nuclear structures markedly decreased in Alzheimer's disease.

Prenatal stress reduces interneuronal connectivity in the rat cerebellar granular layer

The development and functioning of the central nervous system have been shown to be affected by maternal stress. To investigate the effects of prenatal stress on the cerebellar interneuronal connectivity, rat embryos are exposed to stress on their embryonic day (E) 7 and 14, by keeping the dam in close-fitting wire mesh cylinders, for 6 h. After completion of the cerebellar development at postnatal day (P) 30, stereological procedures were used at the light and electron microscopic level to analyze growth parameters of the granule cells and synapse-to-neuron ratios. Neither the volume fraction (V(V)) of the granular layer to whole cortex, nor the numerical density of granule cells (N(Vg)) per unit volume of granular layer was affected by exposure to stress. However, the mean granule cell nuclear diameter was significantly decreased in stressed animals. Within the neuropil region, the number and mean diameter of synaptic disc profiles were used to estimate the numerical density of synapses (N(Vs)). Synapse-to-neuron ratio was obtained by dividing N(Vs) with N(Vg), and found significantly lower in the stressed group than the control group. In addition, synaptophysin immunoreactivity showed a significant decrease (41%) in the granular layer of the cerebellum. Collectively, these results demonstrate that intrauterine stress alters the morphology of granule cells and causes a profound and fairly long-lasting deficit in their interneuronal connectivity.

Expression of nitrergic system and protein nitration in adult rat brains submitted to acute hypobaric hypoxia

Changes in the nitric oxide (NO) system of the rat cerebral cortex were investigated by immunohistochemistry, immunoblotting, and NO synthase (NOS) activity assays in adult rats submitted for 30 min to hypoxia, in a hypobaric chamber at a simulated altitude of 38,000 ft (11000 m) (154.9 mm Hg). The cerebral cortex was studied after different survival times, 0 and 24 h, 5, 8, 15, and 30 days of reoxygenation. This situation led to morphological alterations in the large type I interneurons, as well as immunoreactive changes in the appearance and number of the small neurons (type II), both containing neuronal NOS (nNOS). Some of these small neurons showed immunoreactive cytoplasm and short processes; others, the more numerous during all reoxygenation periods, contained the immunoreactive product mainly related to a perinuclear ring. Ultrastructurally, these small neurons exhibited changes in nuclear structures as in the shape of the nuclear membrane, in the distribution of heterochromatin, and in the nucleolar morphology. The reaction product for nitrotyrosine, as a marker of protein nitration, showed modifications in distribution of the immunoreactive product. No expression was found for inducible NOS (iNOS). All these modifications were accompanied by increased nNOS and nitrotyrosine production as demonstrated by Western blotting and calcium-dependent activity, returning to control conditions after 30 days of reoxygenation, suggesting a reversible NO mechanism of action.