Gene expression profile during functional maturation of a central mammalian synapse

Calyx of Held giant presynaptic terminals in the auditory brainstem form glutamatergic axosomatic synapses that have advanced to one of the best-studied synaptic connections of the mammalian brain. As the auditory system matures and adjusts to high-fidelity synaptic transmission, the calyx undergoes extensive structural and functional changes - in mice, it is formed at about postnatal day 3 (P3), achieves immature function until hearing onset at about P10 and can be considered mature from P21 onwards. This setting provides a unique opportunity to examine the repertoire of genes driving synaptic structure and function during postnatal maturation. Here, we determined the gene expression profile of globular bushy cells (GBCs), neurons giving rise to the calyx of Held, at different maturational stages (P3, P8, P21). GBCs were retrogradely labelled by stereotaxic injection of fluorescent cholera toxin-B, and their mRNA content was collected by laser microdissection. Microarray profiling, successfully validated with real time quantitative polymerase chain reaction and nCounter approaches, revealed genes regulated during maturation. We found that mostly genes implicated in the general cell biology of the neuron were regulated, while most genes related to synaptic function were regulated around the onset of hearing. Among these, voltage-gated ion channels and calcium-binding proteins were strongly regulated, whereas most genes involved in the synaptic vesicle cycle were only moderately regulated. These results suggest that changes in the expression patterns of ion channels and calcium-binding proteins are a dominant factor in defining key synaptic properties during maturation of the calyx of Held.

KIBRA (KIdney/BRAin protein) regulates learning and memory and stabilizes Protein kinase Mζ

The WWC1 gene has been genetically associated with human episodic memory performance, and its product KIdney/BRAin protein (KIBRA) has been shown to interact with the atypical protein kinase protein kinase M ζ (PKMζ). Although recently challenged, PKMζ remains a candidate postsynaptic regulator of memory maintenance. Here, we show that PKMζ is subject to rapid proteasomal degradation and that KIBRA is both necessary and sufficient to counteract this process, thus stabilizing the kinase and maintaining its function for a prolonged time. We define the binding sequence on KIBRA, a short amino acid motif near the C-terminus. Both hippocampal knock-down of KIBRA in rats and KIBRA knock-out in mice result in decreased learning and memory performance in spatial memory tasks supporting the notion that KIBRA is a player in episodic memory. Interestingly, decreased memory performance is accompanied by decreased PKMζ protein levels. We speculate that the stabilization of synaptic PKMζ protein levels by KIBRA may be one mechanism by which KIBRA acts in memory maintenance. KIBRA/WWC1 has been genetically associated with human episodic memory. KIBRA has been shown to be post-synaptically localized, but its function remained obscure. Here, we show that KIBRA shields PKMζ, a kinase previously linked to memory maintenance, from proteasomal degradation via direct interaction. KIBRA levels in the rodent hippocampus correlate closely both to spatial memory performance in rodents and to PKMζ levels. Our findings support a role for KIBRA in memory, and unveil a novel function for this protein.

The functional genome of CA1 and CA3 neurons under native conditions and in response to ischemia

BACKGROUND

The different physiological repertoire of CA3 and CA1 neurons in the hippocampus, as well as their differing behaviour after noxious stimuli are ultimately based upon differences in the expressed genome. We have compared CA3 and CA1 gene expression in the uninjured brain, and after cerebral ischemia using laser microdissection (LMD), RNA amplification, and array hybridization.

RESULTS

Profiling in CA1 vs. CA3 under normoxic conditions detected more than 1000 differentially expressed genes that belong to different, physiologically relevant gene ontology groups in both cell types. The comparison of each region under normoxic and ischemic conditions revealed more than 5000 ischemia-regulated genes for each individual cell type. Surprisingly, there was a high co-regulation in both regions. In the ischemic state, only about 100 genes were found to be differentially expressed in CA3 and CA1. The majority of these genes were also different in the native state. A minority of interesting genes (e.g. inhibinbetaA) displayed divergent expression preference under native and ischemic conditions with partially opposing directions of regulation in both cell types.

CONCLUSION

The differences found in two morphologically very similar cell types situated next to each other in the CNS are large providing a rational basis for physiological differences. Unexpectedly, the genomic response to ischemia is highly similar in these two neuron types, leading to a substantial attenuation of functional genomic differences in these two cell types. Also, the majority of changes that exist in the ischemic state are not generated de novo by the ischemic stimulus, but are preexistant from the genomic repertoire in the native situation. This unexpected influence of a strong noxious stimulus on cell-specific gene expression differences can be explained by the activation of a cell-type independent conserved gene-expression program. Our data generate both novel insights into the relation of the quiescent and stimulus-induced transcriptome in different cells, and provide a large dataset to the research community, both for mapping purposes, as well as for physiological and pathophysiological research.

Global transcriptome analysis of genetically identified neurons in the adult cortex

The enormous cellular complexity of the brain is a major obstacle for gene expression profiling of neurological disease models, because physiologically relevant changes of transcription in a specific neuronal subset are likely to be lost in the presence of other neurons and glia. We solved this problem in transgenic mice by labeling genetically defined cells with a nuclear variant of GFP. When combined with laser-directed microdissection, intact RNA from unfixed, freeze-dried sections can be isolated, which is a prerequisite for high-quality global transcriptome analysis. Here, we compared gene expression profiles between pyramidal motor neurons and pyramidal somatosensory neurons captured from layer V of the adult neocortex. One striking feature of motor neurons is the elevated expression of ribosomal genes and genes involved in ATP synthesis. This suggests a molecular adaptation of the upper motor neurons to longer axonal projections and higher electrical activity. These molecular signatures were not detected when cortical layers and microareas were analyzed in toto. Additionally, we used microarrays to determine the global mRNA expression profiles of microdissected Purkinje cells and cellularly complex cerebellar cortex microregions. In summary, our analysis shows that cellularly complex targets lead to averaged gene expression profiles that lack substantial amounts of cell type-specific information. Thus, cell type-restricted sampling strategies are mandatory in the CNS. The combined use of a genetic label with laser-microdissection offers an unbiased approach to map patterns of gene expression onto practically any cell type of the brain.

Effects of antidepressant treatment on gene expression profile in mouse brain: cell type-specific transcription profiling using laser microdissection and microarray analysis

A gene expression study of mice treated with the tricyclic antidepressant amitriptyline was performed. To enable the detection of cell type-specific expression changes, laser-microdissected nucleus accumbens was analysed after 4 and 28 days of treatment. After 4 days of treatment no significantly regulated genes could be detected in this study. In contrast, 95 genes exhibited different expression levels in animals treated for 28 days with amitrityline compared with sham animals. This observation reflects the long-term effects and adaptation processes observed in patients treated with this drug. Among the regulated genes are receptors belonging to the dopamine-dependent signalling cascade, ion channels (mainly voltage-dependent potassium and calcium channels) potentially involved in signalling cascades and neuropeptides. The results support the hypothesis that the therapeutic effect of this antidepressant is much more complex and not confined to a reuptake inhibition of neurotransmitters. Paradigms inducing only weak expression changes, which may be limited to certain cell types within the highly complex brain structure, can therefore be reliably investigated by applying a cell type-specific expression profiling technique based on laser microdissection and subsequent RNA amplification followed by DNA microarray analysis.

Verbessern intraven�ses Fentanyl oder Midazolam vor Durchf�hrung einer peripheren Regionalan�sthesie Patientenakzeptanz und Kooperativit�t bei der Katheteranlage?

BACKGROUND

The procedure of placing a catheter for continuous regional anaesthesia is often associated with fear and pain in the patient. Thus, we evaluated the use of midazolam and fentanyl to improve patient's comfort and cooperation.

METHODS

After an oral dose of 20 mg clorazepate, 174 patients receiving peripheral nerve catheters for regional anaesthesia where randomized into 3 groups to receive either intravenous placebo, 3 mg midazolam or 0.1 mg fentanyl immediately before catheter placement in a double-blind manner. Stepwise regression analysis was used to identify factors associated with patient's assessment of subjective discomfort (measured using a VAS 0-10) during the procedure. Amnesia was evaluated 24 h later. The anaesthetist rated patient's cooperation during catheter placement.

RESULTS

Female sex and longer duration of catheter placement had significant negative impact on patient's comfort, whereas fentanyl showed an improvement. Age, body mass index, midazolam and the type of catheter had no influence. The following day 27% of the midazolam group, 6% of the placebo group and 9% of the fentanyl patients did not remember catheter placement. Patient's cooperation was poor in 26% of the midazolam patients but only in 9% of the placebo and 3% of the patients receiving fentanyl. Of the placebo patients 18.4% had to be supplemented with fentanyl because they found the procedure of catheter placement unbearable. No side effects occurred in either group.

CONCLUSION

As patient's comfort and cooperation were significantly improved by fentanyl, we recommend fentanyl to facilitate catheter placement for regional anaesthesia.

Role of heteromer formation in GABAB receptor function

Recently, GBR1, a seven-transmembrane domain protein with high affinity for gamma-aminobutyric acid (GABA)B receptor antagonists, was identified. Here, a GBR1-related protein, GBR2, was shown to be coexpressed with GBR1 in many brain regions and to interact with it through a short domain in the carboxyl-terminal cytoplasmic tail. Heterologously expressed GBR2 mediated inhibition of adenylyl cyclase; however, inwardly rectifying potassium channels were activated by GABAB receptor agonists only upon coexpression with GBR1 and GBR2. Thus, the interaction of these receptors appears to be crucial for important physiological effects of GABA and provides a mechanism in receptor signaling pathways that involve a heterotrimeric GTP-binding protein.

Analysis of antibody responses directed against two Onchocerca volvulus antigens defined by monoclonal antibodies

Monoclonal antibodies, reactive with antigens solubilised from the body wall of intact female Onchocerca volvulus using 2% 2-beta-mercaptoethanol, have been characterised. Two IgG1 antibodies, Cam1 and Cam28, recognised antigens of apparent molecular weights of 18,000 and 28,000; and 120,000, respectively. The target antigens of Cam1 and Cam28 could be localised in the cuticle. Inhibition ELISAs showed that target epitopes of both monoclonal antibodies induce an antibody response in onchocerciasis patients. 153 sera from Sierra Leonean patients were tested for their individual antibody levels against antigen epitopes recognised by Cam1 and Cam28. Patients within the age of 5-8 years had the highest levels of antibodies against the Cam28-epitope, whereas patients above 60 years had almost none. Amicrofilaremic patients had higher anti-Cam28 antibody levels than microfilaremic patients and there was a significant difference between groups with no chronic skin disease and those with mild or severe signs. A high percentage of patients (80.4%) recognised the Cam1-epitope, highest antibody levels being found in patients within the age group of 15 to 45 years and in microfilaremic patients. However, levels of antibodies inhibiting monoclonal antibody Cam1 could not be correlated with presence or absence of skin disease.

Plateletpheresis with the new COBE Spectra

The COBE Spectra was evaluated in 71 plateletpheresis procedures. Using the collection and anticoagulant algorithms of the system (n = 57) we collected 4.3 +/- 1.2 x 10(11) platelets with a mean separation efficiency of 70.2 +/- 12.1%. The cell contamination was very low (leukocytes 0.5 +/- 1.0 x 10(7), red cells 1.5 +/- 2.2 x 10(7]. In four different modifications of the standard separation protocols, we tried to reduce the ACD consumption in order to shorten the donation time and to improve donor safety. A constant ACD/blood ratio of 1:9 and increase of the blood flow to 50 ml/min (n = 14) caused significantly lower yields (3.1 +/- 0.7, p less than 0.01) and visible spontaneous platelet aggregates in the collection line in 50% and in the PC's in 29% of the runs. In order to prevent platelet activation the ACD algorithm had to be maintained, but a reduction of the ACD/blood ratio to about 15% was acceptable.

Plateletpheresis with the new COBE Spectra^® / Thrombozytapherese mit der neuen COBE Spectra^®

The COBE Spectra was evaluated in 71 plateletpheresis procedures. Using the collection and anticoagulant algorithms of the system (n=57) we collected 4.3 ± 1.2×10¹¹ platelets with a mean separation efficiency of 70.2+12.1%. The cell contamination was very low (leukocytes 0.5 ± 1.0×10⁷, red cells 1.5 ± 2.2×10⁷). In four different modifications of the standard separation protocols, we tried to reduce the ACD consumption in order to shorten the donation time and to improve donor safety. A constant ACD/blood ratio of 1 : 9 and increase of the blood flow to 50ml/min (n=14) caused significantly lower yields (3.1+0.7, p < 0.01) and visible spontaneous platelet aggregates in the collection line in 50% and in the PC’s in 29% of the runs. In orderto prevent platelet activation the ACD algorithm had to be maintained, but a reduction of the ACD/ blood ratio to about 15% was acceptable.