Two distinct pools of large-conductance calcium-activated potassium channels in the somatic plasma membrane of central principal neurons.

Although nerve cell membranes are often assumed to be uniform with respect to electrical properties, there is increasing evidence for compartmentalization into subdomains with heterogeneous impacts on the overall cell function. Such microdomains are characterized by specific sets of proteins determining their functional properties. Recently, clustering of large-conductance calcium-activated potassium (BK(Ca)) channels was shown at sites of subsurface membrane cisterns in cerebellar Purkinje cells (PC), where they likely participate in building a subcellular signaling unit, the 'PLasmERosome'. By applying SDS-digested freeze-fracture replica labeling (SDS-FRL) and postembedding immunogold electron microscopy, we have now studied the spatial organization of somatic BK(Ca) channels in neocortical layer 5 pyramidal neurons, principal neurons of the central and basolateral amygdaloid nuclei, hippocampal pyramidal neurons and dentate gyrus (DG) granule cells to establish whether there is a common organizational principle in the distribution of BK(Ca) channels in central principal neurons. In all cell types analyzed, somatic BK(Ca) channels were found to be non-homogenously distributed in the plasma membrane, forming two pools of channels with one pool consisting of clustered channels and the other of scattered channels in the extrasynaptic membrane. Quantitative analysis by means of SDS-FRL revealed that about two-thirds of BK(Ca) channels belong to the scattered pool and about one-third to the clustered pool in principal cell somata. Overall densities of channels in both pools differed in the different cell types analyzed, although being considerably lower compared to cerebellar PC. Postembedding immunogold labeling revealed association of clustered channels with subsurface membrane cisterns and confirmed extrasynaptic localization of scattered channels. This study indicates a common organizational principle for somatic BK(Ca) channels in central principal neurons with the formation of a clustered and a scattered pool of channels, and a cell-type specific density of this channel type.

Apoptosis signals in sporadic amyotrophic lateral sclerosis: an immunocytochemical study.

Sporadic amyotrophic lateral sclerosis (sALS) is a neurodegenerative disorder of unknown cause characterized by selective loss of both upper and lower motor neurons. Whether neuronal death in sALS is due to apoptosis has so far not been clarified. In this study, the expression and distribution patterns of pro- and anti-apoptotic bcl-2 family members as well as the executioner caspase-3 were investigated in post-mortem CNS tissue of eight sALS patients and seven age-matched controls. Sparse motor neurons were immunoreactive for bcl-2, bax, bak, and CM1 on serial sections through the spinal cord and motor cortex of individual sALS patients and controls. However, there was no obvious difference in the numbers of immunoreactive (IR) neurons between the two groups. The study did not find evidence for apoptosis as a major mechanism of motor neuronal cell death in sALS.

Lipid-mediated in vivo gene transfer replaces the loss of choline acetyltransferase activity after unilateral fimbria-fornix aspiration.

In Alzheimer's disease cholinergic neurons degenerate, resulting in loss of hippocampal acetylcholine. The fimbria-fornix aspiration is a well-known animal model mimicking hippocampal cholinergic deficiency. The aim of the present study was to use in vivo lipid-mediated gene transfer to introduce an expression vector coding for the acetylcholine synthesizing enzyme choline acetyltransferase into the hippocampus to replace the loss of enzyme activity after unilateral fimbria-fornix aspiration. Our data show that the lipid FuGene is useful to transfer DNA in vitro into 3T3 fibroblasts, C6 glioma cells, and primary astroglia and to express the respective enzyme. Lipid-mediated gene transfer in vivo resulted in a marked but transient expression of green fluorescent protein below the injection site peaking 5 days after the injection. Unilateral fimbria-fornix aspiration led to a marked reduction in the activity of choline acetyltransferase in the hippocampus, which was completely replaced 5 days after lipid-mediated gene transfer of the choline acetyltransferase vector. In conclusion, our data provide evidence that lipid-mediated gene transfer using FuGene is a useful tool to replace loss of choline acetyltranseferase activity in the hippocampus after fimbria-fornix aspiration; however, the lack of good gene transfer efficiency and the transient nature of expression limit its use for clinical applications.

Respiration and parturition affected by conditional overexpression of the Ca2+-activated K+ channel subunit, SK3.

In excitable cells, small-conductance Ca2+-activated potassium channels (SK channels) are responsible for the slow after-hyperpolarization that often follows an action potential. Three SK channel subunits have been molecularly characterized. The SK3 gene was targeted by homologous recombination for the insertion of a gene switch that permitted experimental regulation of SK3 expression while retaining normal SK3 promoter function. An absence of SK3 did not present overt phenotypic consequences. However, SK3 overexpression induced abnormal respiratory responses to hypoxia and compromised parturition. Both conditions were corrected by silencing the gene. The results implicate SK3 channels as potential therapeutic targets for disorders such as sleep apnea or sudden infant death syndrome and for regulating uterine contractions during labor.

Distribution of chromogranin B-like immunoreactivity in the human hippocampus and its changes in Alzheimer's disease.

Synapse loss is crucially involved in cognitive decline in Alzheimer's disease (AD). This study was performed to investigate the distribution and density of chromogranin B-like immunoreactivity in the hippocampus of control compared to AD brain. Chromogranin B is a large precursor molecule found in large dense-core vesicles. For immunocytochemistry we used an antiserum raised against a synthetic peptide (PE- 11) present in the chromogranin B molecule. Chromogranin B-like immunoreactivity was concentrated in the terminal field of mossy fibers, the inner molecular layer of the dentate gyrus and in layer II of the entorhinal cortex. In AD, chromogranin B was detected in neuritic plaques. The density of chromogranin B-like immunoreactivity was significantly reduced in the inner molecular layer of the dentate gyrus and in layers II, III and V of the entorhinal cortex in AD brains. The present study demonstrates that chromogranin B is a marker for human hippocampal pathways. It is particularly suitable for studying nerve fibers terminating at the inner molecular layer of the dentate gyrus. It is present in neuritic plaques, and its density is reduced in a layer-specific manner.

3,4-Methylenedioxymetamphetamine (ecstasy) induces c-fos-like protein and mRNA in rat organotypic dorsal striatal slices.

3,4-Methylenedioxymetamphetamine (MDMA, "ecstasy") is an increasingly abused drug, which has significant effects on the dopamine system in the striatum. The isolated single organotypic slice model allows investigation of the effects of drugs of abuse on the expression of transcription factors in the striatum without dopaminergic and glutamatergic interactions. In this study the effects of MDMA on the expression of c-fos mRNA by in situ hybridization as well as the c-fos-like protein by immunohistochemistry in isolated dorsal striatum was investigated. It was shown that 100 microM MDMA induced c-fos mRNA expression 30 min after treatment. Expression of c-fos-like protein was transiently detected 3 h afterwards. The c-fos expression was inhibited by MK 801 and metoclopramide, indicating the involvement of dopaminergic D2 receptors and glutamatergic NMDA receptors. The dopaminergic D1 receptor antagonist SCH 23390 did not affect c-fos expression. We conclude that MDMA treatment leads to the induction of c-fos expression in isolated rat striatal slices. This effect is independent of extrinsic neuronal circuitry and seems to be associated with direct interactions between MDMA and the dopamine/glutamate receptor system.

Improved lipid-mediated gene transfer in C6 glioma cells and primary glial cells using FuGene.

Gene therapy is a potent method to counteract neurodegeneration by introducing genetic information encoding neuroprotective factors. In this study cationic lipids were used to transfer DNA into C6 glioma cells and primary glial cells. When comparing the novel compound FuGene with other commercially-available lipids, it was found that FuGene markedly enhanced gene transfer of a beta-galactosidase reporter plasmid into C6 glioma cells. FuGene had several advantages compared to other lipids, such as a very low toxicity and the capability of transfection under serum conditions. When optimizing, a DNA-lipid ratio of 150 ng DNA/1 microl FuGene and a concentration of 3 microl FuGene/1 ml medium was found to be optimal. The incubation time peaked after 8 h and the expression time reached an optimum between 2 and 6 days. When cells were transfected on 3 consecutive days for 6 h each ('boosting'), the transfection efficiency was markedly enhanced in primary glial cells. When using endotoxin-free DNA the transfection efficiency could be enhanced up to 3 times. The optimal transfection efficiency in C6 glioma cells and in primary glial cells was found to be 16.3 +/- 0.3% and 5.1 +/- 0.37% of total cells, respectively. In conclusion this study shows that the novel compound FuGene has a very high potential to transfer DNA into cells of glial origin, and it might be an interesting canditate for ex vivo and in vivo gene therapeutic approaches.

Dopamine neurons in a simple GDNF-treated meso-striatal organotypic co-culture model.

Neurodegeneration of dopamine neurons in the ventral mesencephalon projecting to the dorsal striatum (meso-striatal system) plays a major role in Parkinson's disease. The aim of this study was to establish a simple organotypic, in vitro co-culture model for investigating the survival of dopamine neurons stimulated by the novel growth factor, glial-cell-line-derived neurotrophic factor. This model should allow investigation of the effects of the dopaminergic neurotoxin, 6-hydroxydopamine, on the expression of the transcription factor c-fos and on TUNEL staining in vitro. The dopaminotrophic factor, glial-cell-line-derived neurotrophic factor, markedly enhanced dopamine tissue levels and dopamine neuron number. Nerve-fiber ingrowth of dopamine neurons into its striatal target was found to be enhanced with glial-cell-line-derived neurotrophic factor. Using an optimized protocol, it was shown that the neurotoxin 6-hydroxydopamine selectively destructed dopamine neurons. C-fos-like immunoreactivity was enhanced in the mesencephalic part of the co-slices 3 h after application of the neurotoxin. The TUNEL staining occurred 2-5 days after the application of the neurotoxin, but did not seem to be related to dopamine neurons. In conclusion, the organotypic co-culture model provides a simple model for studying survival of dopamine neurons and for observing expression of genes and proteins that could be related to Parkinson's disease. This simple model is useful for screening novel drugs and growth factors and may markedly reduce severe animal experiments.

PE-11, a peptide derived from chromogranin B, in the human brain.

This study was performed to investigate the distribution of chromogranin B in the human central nervous system. We used an antiserum raised against a synthetic peptide (PE-11) present in the chromogranin B molecule. PE-11-like immunoreactivity was characterized by molecular size exclusion and reversed-phase high-performance liquid chromatography. Its localization was studied using immunocytochemistry. Only the free peptide and an N-terminally elongated peptide were detected by molecular size exclusion high-performance liquid chromatography, indicating that proteolytic processing of chromogranin B is quite extensive. PE-11-like immunoreactivity was present in differently shaped fibers, varicosities and neurons, but not in glial cells. Its density varied throughout the brain. An especially high density was observed in the bed nucleus of the stria terminalis, the central and cortical nuclei of the amygdala, the hypothalamus, the hippocampus, the raphe complex, the nucleus interpeduncularis, the nucleus of the solitary tract, and laminae I and II of the spinal cord. This study demonstrates a significant processing of chromogranin B and indicates that chromogranin B constitutes a precursor for smaller peptides which are derived by endoproteolytic processing. It provides the neuroanatomical basis to investigate the chromogranin B molecule as a widespread component of large dense-core vesicles in the human central nervous system.

Synaptic loss reflected by secretoneurin-like immunoreactivity in the human hippocampus in Alzheimer's disease.

Secretoneurin is a recently described peptide derived by endoproteolytic processing from secretogranin II, previously named chromogranin C. In this study, we have investigated the distribution of secretoneurin-like immunoreactivity in the human hippocampus in controls and in Alzheimer's disease patients, and compared the staining pattern to that of calretinin. Secretoneurin-like immunoreactivity is present throughout the hippocampal formation. At the border of the dentate molecular layer and the granule cell layer, a band of dense secretoneurin immunostaining appeared. In this part, as in the area of the CA2 sector, the high density of secretoneurin-immunoreactivity coincided with calretinin-like immunoreactivity. The mossy fibre system displayed a moderate density of secretoneurin-immunoreactivity. In the entorhinal cortex, a particularly high density of secretoneurin-immunoreactivity was observed. The density of secretoneurin-like immunoreactivity was significantly reduced in the innermost part of the molecular layer and in the outer molecular layer of the dentate gyrus in Alzheimer's disease. For calretinin-like immunoreactivity, a less pronounced decrease was found in the innermost part of the molecular layer. About 40-60% of neuritic plaques were secretoneurin-immunopositive. This study shows that secretoneurin is distinctly distributed in the human hippocampus and that significant changes of secretoneurin-like immunoreactivity occur in Alzheimer's disease, reflecting synaptic loss.

Ontogenic development of secretogranin II and of its processing to secretoneurin in rat brain.

The ontogenic development of secretogranin II was studied by immunochemistry and immunohistochemistry. Extracts of brains from various developmental stages were analyzed by a radioimmunoassay for secretoneurin, a peptide derived from secretogranin II. From gestational day 13 to adulthood the levels increased from 0.1 to 94 fmol/mg wet weight. Characterization of the immunoreactivity by molecular sieve chromatography revealed that throughout all developmental stages the proprotein secretogranin II was fully processed to the free peptide secretoneurin. In immunohistochemistry secretoneurin-IR was first detected at embryonic day 13. Between embryonic days 14 and 18 a strong increase in the number of secretoneurin immunopositive cells was observed in many brain areas, notably in the amygdala, hypothalamus, olfactory bulb and several brainstem nuclei. The pattern of staining during development is quite similar to that in the adult. The present paper demonstrates that secretoneurin immunoreactivity appears early in embryonic life. Processing of the proprotein secretogranin II starts when the protein is first synthesized apparently at about the same time when the prohormone convertase PC1 and PC2 can be demonstrated.

Neurochemical compartments in the human forebrain: evidence for a high density of secretoneurin-like immunoreactivity in the extended amygdala.

Secretoneurin is a 33-amino acid neuropeptide produced by endoproteolytic processing from secretogranin II, which is a member of the chromogranin/ secretogranin family. In this immunocytochemical study we investigated the localization of secretoneurin-like immunoreactivity in the human substantia innominata in relation to the ventral striatopallidal system, the bed nucleus-amygdala complex and the basal nucleus of Meynert. A high density of secretoneurin immunostaining was found in the medial part of the nucleus accumbens. All subdivisions of the bed nucleus of the stria terminalis displayed a very prominent immunostaining for secretoneurin, whereas substance P and enkephalin showed a more restricted distribution. A high concentration of secretoneurin immunoreactivity was also observed in the central and medial amygdaloid nuclei. In the lateral bed nucleus of the stria terminalis and the sublenticular substantia innominata, the appearance of secretoneurin immunoreactivity was very similar to that of enkephalin-like immunoreactivity, exhibiting mostly peridendritic and perisomatic staining. The ventral pallidum and the inner pallidal segment displayed strong secretoneurin immunostaining. Secretoneurin did not label cholinergic neurons in the basal forebrain. This study demonstrates that secretoneurin-like immunoreactivity is prominent in the bed nucleus-amygdala complex, referred to as extended amygdala. The distribution of secretoneurin-like immunoreactivity in comparison with that of other neuroanatomical markers suggests that this forebrain system is a discret compartment in the human forebrain.