Repetitive and compulsive behavior after Early-Life-Pain associated with reduced long-chain sphingolipid species

BACKGROUND

Pain in early life may impact on development and risk of chronic pain. We developed an optogenetic Cre/loxP mouse model of "early-life-pain" (ELP) using mice with transgenic expression of channelrhodopsin-2 (ChR2) under control of the Advillin (Avil) promoter, which drives expression of transgenes predominantly in isolectin B4 positive non-peptidergic nociceptors in postnatal mice. Avil-ChR2 (Cre +) and ChR2-flfl control mice were exposed to blue light in a chamber once daily from P1-P5 together with their Cre-negative mother.

RESULTS

ELP caused cortical hyperexcitability at P8-9 as assessed via multi-electrode array recordings that coincided with reduced expression of synaptic genes (RNAseq) including Grin2b, neurexins, piccolo and voltage gated calcium and sodium channels. Young adult (8-16 wks) Avil-ChR2 mice presented with nociceptive hypersensitivity upon heat or mechanical stimulation, which did not resolve up until one year of age. The persistent hypersensitivy to nociceptive stimuli was reflected by increased calcium fluxes in primary sensory neurons of aged mice (1 year) upon capsaicin stimulation. Avil-ChR2 mice behaved like controls in maze tests of anxiety, social interaction, and spatial memory but IntelliCage behavioral studies revealed repetitive nosepokes and corner visits and compulsive lickings. Compulsiveness at the behavioral level was associated with a reduction of sphingomyelin species in brain and plasma lipidomic studies. Behavioral studies were done with female mice.

CONCLUSION

The results suggest that ELP may predispose to chronic "pain" and compulsive psychopathology in part mediated by alterations of sphingolipid metabolism, which have been previously described in the context of addiction and psychiatric diseases.

Skewed distribution of spines is independent of presynaptic transmitter release and synaptic plasticity, and emerges early during adult neurogenesis

Dendritic spines are crucial for excitatory synaptic transmission as the size of a spine head correlates with the strength of its synapse. The distribution of spine head sizes follows a lognormal-like distribution with more small spines than large ones. We analysed the impact of synaptic activity and plasticity on the spine size distribution in adult-born hippocampal granule cells from rats with induced homo- and heterosynaptic long-term plasticity in vivo and CA1 pyramidal cells from Munc13-1/Munc13-2 knockout mice with completely blocked synaptic transmission. Neither the induction of extrinsic synaptic plasticity nor the blockage of presynaptic activity degrades the lognormal-like distribution but changes its mean, variance and skewness. The skewed distribution develops early in the life of the neuron. Our findings and their computational modelling support the idea that intrinsic synaptic plasticity is sufficient for the generation, while a combination of intrinsic and extrinsic synaptic plasticity maintains lognormal-like distribution of spines.

Increased Network Inhibition in the Dentate Gyrus of Adult Neuroligin-4 Knock-Out Mice

Loss-of-function mutations in neuroligin-4 (Nlgn4), a member of the neuroligin family of postsynaptic adhesion proteins, cause autism spectrum disorder in humans. Nlgn4 knockout (KO) in mice leads to social behavior deficits and complex alterations of synaptic inhibition or excitation, depending on the brain region. In the present work, we comprehensively analyzed synaptic function and plasticity at the cellular and network levels in hippocampal dentate gyrus of Nlgn4 KO mice. Compared with wild-type littermates, adult Nlgn4 KO mice exhibited increased paired-pulse inhibition of dentate granule cell population spikes, but no impairments in excitatory synaptic transmission or short-term and long-term plasticity in vivo In vitro patch-clamp recordings in neonatal organotypic entorhino-hippocampal slice cultures from Nlgn4 KO and wild-type littermates revealed no significant differences in excitatory or inhibitory synaptic transmission, homeostatic synaptic plasticity, and passive electrotonic properties in dentate granule cells, suggesting that the increased inhibition in vivo is the result of altered network activity in the adult Nlgn4 KO. A comparison with prior studies on Nlgn 1-3 knock-out mice reveals that each of the four neuroligins exerts a characteristic effect on both intrinsic cellular and network activity in the dentate gyrus in vivo.

Structural plasticity of the axon initial segment in rat hippocampal granule cells following high frequency stimulation and LTP induction

The axon initial segment (AIS) is the site of action potential initiation and important for the integration of synaptic input. Length and localization of the AIS are dynamic, modulated by afferent activity and contribute to the homeostatic control of neuronal excitability. Synaptopodin is a plasticity-related protein expressed by the majority of telencephalic neurons. It is required for the formation of cisternal organelles within the AIS and an excellent marker to identify these enigmatic organelles at the light microscopic level. Here we applied 2 h of high frequency stimulation of the medial perforant path in rats in vivo to induce a strong long-term potentiation of dentate gyrus granule cells. Immunolabeling for βIV-spectrin and synaptopodin were performed to study structural changes of the AIS and its cisternal organelles. Three-dimensional analysis of the AIS revealed a shortening of the AIS and a corresponding reduction of the number of synaptopodin clusters. These data demonstrate a rapid structural plasticity of the AIS and its cisternal organelles to strong stimulation, indicating a homeostatic response of the entire AIS compartment.

Adult hippocampal neurogenesis in the context of lipopolysaccharide-induced neuroinflammation: A molecular, cellular and behavioral review

The continuous generation of new neurons occurs in at least two well-defined niches in the adult rodent brain. One of these areas is the subgranular zone of the dentate gyrus (DG) in the hippocampus. While the DG is associated with contextual and spatial learning and memory, hippocampal neurogenesis is necessary for pattern separation. Hippocampal neurogenesis begins with the activation of neural stem cells and culminates with the maturation and functional integration of a portion of the newly generated glutamatergic neurons into the hippocampal circuits. The neurogenic process is continuously modulated by intrinsic factors, one of which is neuroinflammation. The administration of lipopolysaccharide (LPS) has been widely used as a model of neuroinflammation and has yielded a body of evidence for unveiling the detrimental impact of inflammation upon the neurogenic process. This work aims to provide a comprehensive overview of the current knowledge on the effects of the systemic and central administration of LPS upon the different stages of neurogenesis and discuss their effects at the molecular, cellular, and behavioral levels.

Circadian glucocorticoid oscillations preserve a population of adult hippocampal neural stem cells in the aging brain

A decrease in adult hippocampal neurogenesis has been linked to age-related cognitive impairment. However, the mechanisms involved in this age-related reduction remain elusive. Glucocorticoid hormones (GC) are important regulators of neural stem/precursor cells (NSPC) proliferation. GC are released from the adrenal glands in ultradian secretory pulses that generate characteristic circadian oscillations. Here, we investigated the hypothesis that GC oscillations prevent NSPC activation and preserve a quiescent NSPC pool in the aging hippocampus. We found that hippocampal NSPC populations lacking expression of the glucocorticoid receptor (GR) decayed exponentially with age, while GR-positive populations decayed linearly and predominated in the hippocampus from middle age onwards. Importantly, GC oscillations controlled NSPC activation and GR knockdown reactivated NSPC proliferation in aged mice. When modeled in primary hippocampal NSPC cultures, GC oscillations control cell cycle progression and induce specific genome-wide DNA methylation profiles. GC oscillations induced lasting changes in the methylation state of a group of gene promoters associated with cell cycle regulation and the canonical Wnt signaling pathway. Finally, in a mouse model of accelerated aging, we show that disruption of GC oscillations induces lasting changes in dendritic complexity, spine numbers and morphology of newborn granule neurons. Together, these results indicate that GC oscillations preserve a population of GR-expressing NSPC during aging, preventing their activation possibly by epigenetic programming through methylation of specific gene promoters. Our observations suggest a novel mechanism mediated by GC that controls NSPC proliferation and preserves a dormant NSPC pool, possibly contributing to a neuroplasticity reserve in the aging brain.

Lack of β-amyloid cleaving enzyme-1 (BACE1) impairs long-term synaptic plasticity but enhances granule cell excitability and oscillatory activity in the dentate gyrus in vivo

BACE1 is a β-secretase involved in the cleavage of amyloid precursor protein and the pathogenesis of Alzheimer's disease (AD). The entorhinal cortex and the dentate gyrus are important for learning and memory, which are affected in the early stages of AD. Since BACE1 is a potential target for AD therapy, it is crucial to understand its physiological role in these brain regions. Here, we examined the function of BACE1 in the dentate gyrus. We show that loss of BACE1 in the dentate gyrus leads to increased granule cell excitability, indicated by enhanced efficiency of synaptic potentials to generate granule cell spikes. The increase in granule cell excitability was accompanied by prolonged paired-pulse inhibition, altered network gamma oscillations, and impaired synaptic plasticity at entorhinal-dentate synapses of the perforant path. In summary, this is the first detailed electrophysiological study of BACE1 deletion at the network level in vivo. The results suggest that BACE1 is important for normal dentate gyrus network function. This has implications for the use of BACE1 inhibitors as therapeutics for AD therapy, since BACE1 inhibition could similarly disrupt synaptic plasticity and excitability in the entorhinal-dentate circuitry.

Adult-born dentate granule cell excitability depends on the interaction of neuron age, ontogenetic age and experience

Early during their maturation, adult-born dentate granule cells (aDGCs) are particularly excitable, but eventually develop the electrophysiologically quiet properties of mature cells. However, the stability versus plasticity of this quiet state across time and experience remains unresolved. By birthdating two populations of aDGCs across different animal ages, we found for 10-month-old rats the expected reduction in excitability across cells aged 4-12 weeks, as determined by Egr1 immunoreactivity. Unexpectedly, cells 35 weeks old (after genesis at an animal age of 2 months) were as excitable as 4-week-old cells, in the dorsal hippocampus. This high level of excitability at maturity was specific for cells born in animals 2 months of age, as cells born later in life did not show this effect. Importantly, excitability states were not fixed once maturity was gained, but were enhanced by enriched environment exposure or LTP induction, indicating that any maturational decrease in excitability can be compensated by experience. These data reveal the importance of the animal's age for aDGC excitability, and emphasize their prolonged capability for plasticity during adulthood.

Differential Postnatal Expression of Neuronal Maturation Markers in the Dentate Gyrus of Mice and Rats

The dentate gyrus (DG) is a unique structure of the hippocampus that is distinguished by ongoing neurogenesis throughout the lifetime of an organism. The development of the DG, which begins during late gestation and continues during the postnatal period, comprises the structural formation of the DG as well as the establishment of the adult neurogenic niche in the subgranular zone (SGZ). We investigated the time course of postnatal maturation of the DG in male C57BL/6J mice and male Sprague-Dawley rats based on the distribution patterns of the immature neuronal marker doublecortin (DCX) and a marker for mature neurons, calbindin (CB). Our findings demonstrate that the postnatal DG is marked by a substantial maturation with a high number of DCX-positive granule cells (GCs) during the first two postnatal weeks followed by a progression toward more mature patterns and increasing numbers of CB-positive GCs within the subsequent 2 weeks. The most substantial shift in maturation of the GC population took place between P7 and P14 in both mice and rats, when young, immature DCX-positive GCs became confined to the innermost part of the GC layer (GCL), indicative of the formation of the SGZ. These results suggest that the first month of postnatal development represents an important transition phase during which DG neurogenesis and the maturation course of the GC population becomes analogous to the process of adult neurogenesis. Therefore, the postnatal DG could serve as an attractive model for studying a growing and functionally maturing neural network. Direct comparisons between mice and rats revealed that the transition from immature DCX-positive to mature CB-positive GCs occurs more rapidly in the rat by approximately 4–6 days. The remarkable species difference in the speed of maturation on the GC population level may have important implications for developmental and neurogenesis research in different rodent species and strains.

Personalized translational epilepsy research - Novel approaches and future perspectives: Part I: Clinical and network analysis approaches

Despite the availability of more than 15 new "antiepileptic drugs", the proportion of patients with pharmacoresistant epilepsy has remained constant at about 20-30%. Furthermore, no disease-modifying treatments shown to prevent the development of epilepsy following an initial precipitating brain injury or to reverse established epilepsy have been identified to date. This is likely in part due to the polyetiologic nature of epilepsy, which in turn requires personalized medicine approaches. Recent advances in imaging, pathology, genetics and epigenetics have led to new pathophysiological concepts and the identification of monogenic causes of epilepsy. In the context of these advances, the First International Symposium on Personalized Translational Epilepsy Research (1st ISymPTER) was held in Frankfurt on September 8, 2016, to discuss novel approaches and future perspectives for personalized translational research. These included new developments and ideas in a range of experimental and clinical areas such as deep phenotyping, quantitative brain imaging, EEG/MEG-based analysis of network dysfunction, tissue-based translational studies, innate immunity mechanisms, microRNA as treatment targets, functional characterization of genetic variants in human cell models and rodent organotypic slice cultures, personalized treatment approaches for monogenic epilepsies, blood-brain barrier dysfunction, therapeutic focal tissue modification, computational modeling for target and biomarker identification, and cost analysis in (monogenic) disease and its treatment. This report on the meeting proceedings is aimed at stimulating much needed investments of time and resources in personalized translational epilepsy research. Part I includes the clinical phenotyping and diagnostic methods, EEG network-analysis, biomarkers, and personalized treatment approaches. In Part II, experimental and translational approaches will be discussed (Bauer et al., 2017) [1].

Personalized translational epilepsy research - Novel approaches and future perspectives: Part II: Experimental and translational approaches

Despite the availability of more than 15 new "antiepileptic drugs", the proportion of patients with pharmacoresistant epilepsy has remained constant at about 20-30%. Furthermore, no disease-modifying treatments shown to prevent the development of epilepsy following an initial precipitating brain injury or to reverse established epilepsy have been identified to date. This is likely in part due to the polyetiologic nature of epilepsy, which in turn requires personalized medicine approaches. Recent advances in imaging, pathology, genetics, and epigenetics have led to new pathophysiological concepts and the identification of monogenic causes of epilepsy. In the context of these advances, the First International Symposium on Personalized Translational Epilepsy Research (1st ISymPTER) was held in Frankfurt on September 8, 2016, to discuss novel approaches and future perspectives for personalized translational research. These included new developments and ideas in a range of experimental and clinical areas such as deep phenotyping, quantitative brain imaging, EEG/MEG-based analysis of network dysfunction, tissue-based translational studies, innate immunity mechanisms, microRNA as treatment targets, functional characterization of genetic variants in human cell models and rodent organotypic slice cultures, personalized treatment approaches for monogenic epilepsies, blood-brain barrier dysfunction, therapeutic focal tissue modification, computational modeling for target and biomarker identification, and cost analysis in (monogenic) disease and its treatment. This report on the meeting proceedings is aimed at stimulating much needed investments of time and resources in personalized translational epilepsy research. This Part II includes the experimental and translational approaches and a discussion of the future perspectives, while the diagnostic methods, EEG network analysis, biomarkers, and personalized treatment approaches were addressed in Part I [1].

Forebrain-specific loss of synaptic GABAA receptors results in altered neuronal excitability and synaptic plasticity in mice

Mutations that result in the defective trafficking of γ2 subunit containing GABAA receptors (γ2-GABAARs) are known to reduce synaptic inhibition. Whether perturbed clustering of non-mutated GABAARs similarly reduces synaptic inhibition in vivo is less clear. In this study we provide evidence that the loss of postsynaptic γ2-GABAARs upon postnatal ablation of gephyrin, the major scaffolding protein of inhibitory postsynapses, from mature principal neurons within the forebrain results in reduced induction of long-term potentiation (LTP) and impaired network excitability within the hippocampal dentate gyrus. The preferential reduction in not only synaptic γ2-GABAAR cluster number at dendritic sites but also the decrease in γ2-GABAAR density within individual clusters at dendritic inhibitory synapses suggests that distal synapses are more sensitive to the loss of gephyrin expression than proximal synapses. The fact that these mice display behavioural features of anxiety and epilepsy emphasises the importance of postsynaptic γ2-GABAAR clustering for synaptic inhibition.

Differential Structural Development of Adult-Born Septal Hippocampal Granule Cells in the Thy1-GFP Mouse, Nuclear Size as a New Index of Maturation

Adult neurogenesis is frequently studied in the mouse hippocampus. We examined the morphological development of adult-born, immature granule cells in the suprapyramidal blade of the septal dentate gyrus over the period of 7–77 days after mitosis with BrdU-labeling in 6-weeks-old male Thy1-GFP mice. As Thy1-GFP expression was restricted to maturated granule cells, it was combined with doublecortin-immunolabeling of immature granule cells. We developed a novel classification system that is easily applicable and enables objective and direct categorization of newborn granule cells based on the degree of dendritic development in relation to the layer specificity of the dentate gyrus. The structural development of adult-generated granule cells was correlated with age, albeit with notable differences in the time course of development between individual cells. In addition, the size of the nucleus, immunolabeled with the granule cell specific marker Prospero-related homeobox 1 gene, was a stable indicator of the degree of a cell's structural maturation and could be used as a straightforward parameter of granule cell development. Therefore, further studies could employ our doublecortin-staging system and nuclear size measurement to perform investigations of morphological development in combination with functional studies of adult-born granule cells. Furthermore, the Thy1-GFP transgenic mouse model can be used as an additional investigation tool because the reporter gene labels granule cells that are 4 weeks or older, while very young cells could be visualized through the immature marker doublecortin. This will enable comparison studies regarding the structure and function between young immature and older matured granule cells.

Deletion of the amyloid precursor-like protein 1 (APLP1) enhances excitatory synaptic transmission, reduces network inhibition but does not impair synaptic plasticity in the mouse dentate gyrus

Amyloid precursor-like protein 1 (APLP1) is a transmembrane synaptic protein belonging to the amyloid precursor protein (APP) gene family. Although the role of this gene family-in particular of APP-has been intensely studied in the context of Alzheimer's disease, the physiological roles of its family members remain poorly understood. In particular, the function of APLP1, which is predominantly expressed in the nervous system, has remained enigmatic. Since APP has been implicated in synaptic plasticity, we wondered whether APLP1 could play a similar role. First, using in situ hybridization and laser microdissection combined with reverse transcription-quantitative polymerase chain reaction (PCR) we observed that Aplp1 mRNA is highly expressed in dentate granule cells. Having this examined, we studied synaptic plasticity at the perforant path-granule cell synapses in the dentate gyrus of APLP1-deficient mice in vivo. Analysis of field excitatory postsynaptic potentials evoked by stimulation of perforant path fibers revealed increased excitatory transmission in APLP1-deficient mice. Moreover, we observed decreased paired-pulse inhibition of population spikes indicating a decrease in network inhibition upon deletion of APLP1. In contrast, short-term presynaptic plasticity (STP) as well as long-term synaptic plasticity (LTP) was unchanged in the absence of APLP1. Based on these results we conclude that APLP1 deficiency on its own does not lead to defects in synaptic plasticity, but affects synaptic transmission and network inhibition in the dentate gyrus.

Functional genomics suggest neurogenesis in the adult human olfactory bulb

The human olfactory bulb displays high morphologic dynamics changing its volume with olfactory function, which has been explained by active neurogenetic processes. Discussion continues whether the human olfactory bulb hosts a continuous turnover of neurons. We analyzed the transcriptome via RNA quantification of adult human olfactory bulbs and intersected the set of expressed transcriptomic genes with independently available proteomic expression data. To obtain a functional genomic perspective, this intersection was analyzed for higher-level organization of gene products into biological pathways established in the gene ontology database. We report that a fifth of genes expressed in adult human olfactory bulbs serve functions of nervous system or neuron development, half of them functionally converging to axonogenesis but no other non-neurogenetic biological processes. Other genes were expectedly involved in signal transmission and response to chemical stimuli. This provides a novel, functional genomics perspective supporting the existence of neurogenesis in the adult human olfactory bulb.

High-frequency stimulation induces gradual immediate early gene expression in maturing adult-generated hippocampal granule cells

Increasing evidence shows that adult neurogenesis of hippocampal granule cells is advantageous for learning and memory. We examined at which stage of structural maturation and age new granule cells can be activated by strong synaptic stimulation. High-frequency stimulation of the perforant pathway in urethane-anesthetized rats elicited expression of the immediate early genes c-fos, Arc, zif268 and pCREB133 in almost 100% of mature, calbindin-positive granule cells. In contrast, it failed to induce immediate early gene expression in immature doublecortin-positive granule cells. Furthermore, doublecortin-positive neurons did not react with c-fos or Arc expression to mild theta-burst stimulation or novel environment exposure. Endogenous expression of pCREB133 was increasingly present in young cells with more elaborated dendrites, revealing a close correlation to structural maturation. Labeling with bromodeoxyuridine revealed cell age dependence of stimulation-induced c-fos, Arc and zif268 expression, with only a few cells reacting at 21 days, but with up to 75% of cells activated at 35-77 days of cell age. Our results indicate an increasing synaptic integration of maturing granule cells, starting at 21 days of cell age, but suggest a lack of ability to respond to activation with synaptic potentiation on the transcriptional level as long as immature cells express doublecortin.

Makorin ring zinc finger protein 1 (MKRN1), a novel poly(A)-binding protein-interacting protein, stimulates translation in nerve cells

The poly(A)-binding protein (PABP), a key component of different ribonucleoprotein complexes, plays a crucial role in the control of mRNA translation rates, stability, and subcellular targeting. In this study we identify RING zinc finger protein Makorin 1 (MKRN1), a bona fide RNA-binding protein, as a binding partner of PABP that interacts with PABP in an RNA-independent manner. In rat brain, a so far uncharacterized short MKRN1 isoform, MKRN1-short, predominates and is detected in forebrain nerve cells. In neuronal dendrites, MKRN1-short co-localizes with PABP in granule-like structures, which are morphological correlates of sites of mRNA metabolism. Moreover, in primary rat neurons MKRN1-short associates with dendritically localized mRNAs. When tethered to a reporter mRNA, MKRN1-short significantly enhances reporter protein synthesis. Furthermore, after induction of synaptic plasticity via electrical stimulation of the perforant path in vivo, MKRN1-short specifically accumulates in the activated dendritic lamina, the middle molecular layer of the hippocampal dentate gyrus. Collectively, these data indicate that in mammalian neurons MKRN1-short interacts with PABP to locally control the translation of dendritic mRNAs at synapses.

Neuroanatomical characteristics of the human pre-Bötzinger complex and its involvement in neurodegenerative brainstem diseases

The pre-Bötzinger complex has been identified as an essential part of the medullary respiratory network in mammals. Although well described in experimental animals, its localization in the human brain has remained elusive. Using serially sectioned brainstems from 19 normal individuals and patients suffering from neurodegenerative diseases (multiple system atrophy, n = 10; spinocerebellar ataxia type 3, n = 8), we have identified a circumscribed area of the ventrolateral medulla that represents the human homologue of the pre-Bötzinger complex and have mapped its longitudinal and horizontal extents. The presumed human pre-Bötzinger complex is characterized by an aggregation of loosely scattered, small and lipofuscin-rich neurons, which contain neurokinin 1 receptor as well as somatostatin, but are negative for markers of monoaminergic neurons and of motoneurons. In brains of patients suffering from multiple systems atrophy (with central respiratory deficits but without swallowing problems), pre-Bötzinger complex neurons were reduced, whereas pharyngeal motoneurons of the ambigual nucleus were not affected. In contrast, in brains of patients with spinocerebellar ataxia 3 (no reported central respiratory deficits but with dysphagia), pre-Bötzinger complex neurons were preserved, whereas ambigual motoneurons, which control swallowing, were diminished. These pathoanatomical findings support the view, that affection of the central respiratory network, including the pre-Bötzinger complex, contributes to breathing disorders in multiple system atrophy, whereas damage to ambigual motoneurons is important for pathogenesis of breathing disturbances and dysphagia in patients with spinocerebellar ataxia type 3. On the basis of these findings, the putative human homologue of the pre-Bötzinger complex can now be reliably delineated on pigment-Nissl-stained sections, making neuropathological investigations of central respiratory disturbances feasible.

CIN85 regulates dopamine receptor endocytosis and governs behaviour in mice

Despite extensive investigations of Cbl-interacting protein of 85 kDa (CIN85) in receptor trafficking and cytoskeletal dynamics, little is known about its functions in vivo. Here, we report the study of a mouse deficient of the two CIN85 isoforms expressed in the central nervous system, exposing a function of CIN85 in dopamine receptor endocytosis. Mice lacking CIN85 exon 2 (CIN85(Deltaex2)) show hyperactivity phenotypes, characterized by increased physical activity and exploratory behaviour. Interestingly, CIN85(Deltaex2) animals display abnormally high levels of dopamine and D2 dopamine receptors (D2DRs) in the striatum, an important centre for the coordination of animal behaviour. Importantly, CIN85 localizes to the post-synaptic compartment of striatal neurons in which it co-clusters with D2DRs. Moreover, it interacts with endocytic regulators such as dynamin and endophilins in the striatum. Absence of striatal CIN85 causes insufficient complex formation of endophilins with D2DRs in the striatum and ultimately decreased D2DR endocytosis in striatal neurons in response to dopamine stimulation. These findings indicate an important function of CIN85 in the regulation of dopamine receptor functions and provide a molecular explanation for the hyperactive behaviour of CIN85(Deltaex2) mice.

Reduced excitability in the dentate gyrus network of betaIV-spectrin mutant mice in vivo

The submembrane cytoskeletal meshwork of the axon contains the scaffolding protein betaIV-spectrin. It provides mechanical support for the axon and anchors membrane proteins. Quivering (qv(3j)) mice lack functional betaIV-spectrin and have reduced voltage-gated sodium channel (VGSC) immunoreactivity at the axon initial segment and nodes of Ranvier. Because VGSCs are critically involved in action potential generation and conduction, we hypothesized that qv(3j) mice should also show functional deficits at the network level. To test this hypothesis, we investigated granule cell function in the dentate gyrus of anesthetized qv(3j) mice after electrical stimulation of the perforant path in vivo. This revealed an impaired input-output relationship between stimulus intensity and granule cell population spikes and an enhanced paired-pulse inhibition of population spikes, indicating a reduced ability of granule cells to generate action potentials and decreased network excitability. In contrast, the input-output curve for evoked field excitatory postsynaptic potentials (fEPSPs) and paired-pulse facilitation of fEPSPs were unchanged, suggesting normal excitatory synaptic transmission at perforant path-granule cell synapses in qv(3j) mutants. To corroborate our findings, we analyzed the influence of VGSC density reduction on dentate network activity using an established computational model of the dentate gyrus network. This in silico approach confirmed that the loss of VGSCs is sufficient to explain the electrophysiological changes observed in qv(3j) mice. Taken together, our findings demonstrate that betaIV-spectrin is required for normal granule cell firing and for physiological levels of network excitability in the mouse dentate gyrus in vivo.

3D-reconstruction and functional properties of GFP-positive and GFP-negative granule cells in the fascia dentata of the Thy1-GFP mouse

Granule cells of the mouse fascia dentata are widely used in studies on neuronal development and plasticity. In contrast to the rat, however, high-resolution morphometric data on these cells are scarce. Thus, we have analyzed granule cells in the fascia dentata of the adult Thy1-GFP mouse (C57BL/6 background). In this mouse line, single neurons in the granule cell layer are GFP-labeled, making them amenable to high-resolution 3D-reconstruction. First, calbindin or parvalbumin-immunofluorescence was used to identify GFP-positive cells as granule cells. Second, the dorsal-ventral distribution of GFP-positive granule cells was studied: In the dorsal part of the fascia dentata 11% and in the ventral part 15% of all granule cells were GFP-positive. Third, GFP-positive and GFP-negative granule cells were compared using intracellular dye-filling (fixed slice technique) and patch-clamp recordings; no differences were observed between the cells. Finally, GFP-positive granule cells (dorsal and ventral fascia dentata) were imaged at high resolution with a confocal microscope, 3D-reconstructed in their entirety and analyzed for soma size, total dendritic length, number of segments, total number of spines and spine density. Sholl analysis revealed that dendritic complexity of granule cells is maximal 150-200 mum from the soma. Granule cells located in the ventral part of the hippocampus revealed a greater degree of dendritic complexity compared to cells in the dorsal part. Taken together, this study provides morphometric data on granule cells of mice bred on a C57BL/6 background and establishes the Thy1-GFP mouse as a tool to study granule cell neurobiology.

A role for the spine apparatus in LTP and spatial learning

Long-term potentiation (LTP) of synaptic strength is a long-lasting form of synaptic plasticity that has been linked to information storage. Although the molecular and cellular events underlying LTP are not yet fully understood, it is generally accepted that changes in dendritic spine calcium levels as well as local protein synthesis play a central role. These two processes may be influenced by the presence of a spine apparatus, a distinct neuronal organelle found in a subpopulation of telencephalic spines. Mice lacking spine apparatuses (synaptopodin-deficient mice) show deficits in LTP and impaired spatial learning supporting the involvement of the spine apparatus in synaptic plasticity. In our review, we consider the possible roles of the spine apparatus in LTP1 (protein synthesis-independent), LTP2 (translation-dependent and transcription-independent) and LTP3 (translation- and transcription-dependent) and discuss the effects of the spine apparatus on learning and memory.

High sensitivity to neuromodulator-activated signaling pathways at physiological [K+] of confocally imaged respiratory center neurons in on-line-calibrated newborn rat brainstem slices

The pre-Bötzinger complex (PBC) inspiratory center remains active in a transverse brainstem slice. Such slices are studied at high (8-10 mM) superfusate [K+], which could attenuate the sensitivity of the PBC to neuromodulators such as opiates. Findings may also be confounded because slice boundaries, drug injection sites, or location of rhythmogenic interneurons are rarely verified histologically. Thus, we first generated PBC slices with defined boundaries using novel "on-line histology" based on our finding that rostrocaudal extensions of brainstem respiratory marker nuclei are constant in newborn rats between postnatal days 0-4. At physiological superfusate [K+] (3 mM), 500- and 600-microm-thick slices with the PBC in the center and the caudal boundary 0.70 and 0.76 mm caudal to the facial motonucleus generated rhythm for >2 and approximately 4 h, respectively. Rhythm was abolished by low nanomolar concentrations of the mu-opiate receptor agonist DAMGO ([D-Ala2, N-Me-Phe4, Gly5-ol]enkephalin). After spontaneous arrest of bursting, rhythm was reactivated at clinically relevant or physiological concentrations by 3,5-dihydroxyphenylglycine, thyrotropin-releasing hormone, or rolipram, each affecting distinct second-messenger pathways. Two-photon/confocal Ca2+ imaging revealed that these agents reactivated the same PBC neurons initially active in 3 mM [K+]. The data show that "calibrated" PBC slices at physiological [K+] generate rhythm with a high sensitivity to neuromodulators for extended time periods, whereas spontaneous "in vitro apnea" is an important tool to study the interaction of signaling pathways that modulate rhythm. Our approaches and findings provide the basis for a pharmacological and structure-function analysis of the isolated respiratory center in a histologically well defined substrate at physiological [K+].

Neuronal hyperactivity induces astrocytic expression of neurocan in the adult rat hippocampus

Extracellular matrix molecules are involved in the cellular functions of proliferation, migration, morphological differentiation, and synaptic plasticity. One candidate molecule of the extracellular matrix is the chondroitin sulfate proteoglycan neurocan. To determine whether neurocan expression is regulated by neuronal activity in the adult rat brain, we studied changes in hippocampal neurocan mRNA and protein expression following electrical stimulation of the perforant pathway in urethane-anesthetized rats. After 24 h of intermittent, unilateral 20 Hz stimulation, in situ hybridization revealed increased neurocan mRNA in glial fibrillary acidic protein (GFAP)-positive astrocytes bilaterally in all hippocampal subfields. These changes were quantified in the dentate molecular layer, the termination zone of the perforant pathway, using laser microdissection in combination with quantitative reverse transcription-polymerase chain reaction (RT-PCR). Immediately after 24 h stimulation, a six-fold upregulation was detected, which returned to control levels by 3 days post-stimulation. Neurocan immunoreactivity was similarly upregulated bilaterally. Immunostaining intensity reached a maximum by 4 days and returned to control levels by 14 days. The pattern of neurocan expression in the hippocampus depended on the intensity and duration of electrical stimulation. Under conditions of less intense afferent stimulation (4-24 h of 2.0 Hz paired-pulse stimulation, interpulse interval 40 ms), increases in neurocan mRNA and immunoreactivity were restricted to the ipsilateral termination zone of the stimulated perforant pathway. This layer-specific neurocan upregulation was not affected by intraperitoneal application of the NMDA-receptor antagonist MK-801. In conclusion, our data indicate that synaptic activity regulates the astrocytic expression of neurocan in a graded manner.

Excitotoxic hippocampal neuron loss following sustained electrical stimulation of the perforant pathway in the mouse

Prolonged electrical stimulation of the perforant pathway in the rat evokes epileptiform discharges in dentate granule cells and irreversibly damages hilar neurons. In this in vivo study, we demonstrate that similar perforant path stimulation in C57Bl/6 mice causes the same pattern of hippocampal neuron loss. Therefore, this mouse model of seizure-induced hippocampal injury can be used for a wide variety of studies in genetically altered conditions not available in rats.

Endogenous 5-HT2B receptor activation regulates neonatal respiratory activityin vitro

An implication of 5-HT(2B) receptors in central nervous system has not yet been clearly elucidated. We studied the role of different 5-HT(2) receptor subtypes in the medullary breathing center, the pre-Bötzinger complex, and on hypoglossal motoneurons in rhythmically active transversal slice preparations of neonatal rats and mice. Local microinjection of 5-HT(2) receptor agonists revealed tonic excitation of hypoglossal motoneurons. Excitatory effects of the 5-HT(2B) receptor agonist BW723C86 could be blocked by bath application of LY272015, a highly selective 5-HT(2B) receptor antagonist. Excitatory effects of the 5-HT(2A/B/C) receptor agonist alpha-methyl 5-HT could be blocked by the preferential 5-HT(2A) receptor antagonist ketanserin. Therefore, 5-HT-induced excitation of hypoglossal motoneurons is mediated by convergent activation of 5-HT(2A) and 5-HT(2B) receptors. Local microinjection of BW723C86 in the pre-Bötzinger complex increased respiratory frequency. Bath application of LY272015 blocked respiratory activity, whereas ketanserin had no effect. Therefore, endogenous 5-HT appears to support tonic action on respiratory rhythm generation via 5-HT(2B) receptors. In preparations of 5-HT(2B) receptor-deficient mice, respiratory activity appeared unaltered. Whereas BW723C86 and LY272015 had no effects, bath application of ketanserin disturbed and blocked rhythmic activity. This demonstrates a stimulatory role of endogenous 5-HT(2B) receptor activation at the pre-Bötzinger complex and hypoglossal motoneurons that can be taken up by 5-HT(2A) receptors in the absence of 5-HT(2B) receptors. The presence of functional 5-HT(2B) receptors in the neonatal medullary breathing center indicates a potential convergent regulatory role of 5-HT(2B) and -(2A) receptors on the central respiratory network.

Subcellular vesicular aggregations of GABAB R1a and R1b receptors increase with age in neurons of the developing mouse brain

GABA(B) receptors play a critical neuromodulatory role in the central nervous system. It has been suggested that both the functional role and the cellular distribution of GABA(B) receptors in the neuronal network change during post-natal maturation. In the present study, the cellular and subcellular distribution patterns of the GABA(B) R1a/b receptors have been analysed in different brain regions of the mouse using immunocytochemistry with isoform-specific antisera. GABA(B) R1-immunoreactivity (IR) was present from the first post-natal day (P0) on in most regions of the brain. Neurones exhibited diffuse GABA(B) R1-IR labelling throughout somata and larger proximal dendrites as well as some fine neuronal processes. After P5, distinct punctuated staining was apparent. The number of such GABA(B) IR granules per cell increased with age in a sigmoidal manner from P5 to P60. Electron microscopy revealed GABA(B) IR as clusters of small clear vesicles of 30-50 nm diameter within the cytoplasm and close to the cell membrane at extrasynaptic locations, as well as at pre-synaptic and post-synaptic specialisations. The increase in GABA(B) R1-IR punctuate staining during brain maturation points to increasing functional participation and heterogeneity of GABA(B) receptors as the complexity of the central nervous system expands with growth and development.

Serotonergic modulation of respiratory motoneurons and interneurons in brainstem slices of perinatal rats

Respiration-related membrane potential fluctuations were recorded in hypoglossal (XII) motoneurons and pre-Bötzinger complex (pre-BötC) interneurons in medullary slices from perinatal rats. Bath application of serotonin (5-HT) evoked a ketanserine-sensitive depolarization (approximately 11 mV) and tonic spike discharge in XII motoneurons, whereas pre-BötC neurons responded with a <6 mV depolarization and no tonic discharge. The membrane effects were accompanied by an increase in respiratory frequency by up to 260% in 64% of preparations. A frequency decrease leading to block of respiratory activity could also occur (20%) as well as an initial acceleration that turned into a frequency depression (16%). In contrast, iontophoresis of 5-HT into the pre-BötC exclusively increased respiratory frequency by 30-220%, whereas iontophoresis into the XII nucleus did not change respiratory frequency but induced tonic nerve discharge. The effects of local iontophoretic administration of 5-HT on membrane properties of XII and pre-BötC cells were very similar to those upon bath application. Bath application and iontophoresis of the 5-HT2 receptor agonist -methyl-hydroxytryptamine mimicked the effects of 5-HT. Bath application of the 5-HT1A receptor agonist 8-hydroxydipropylaminotetralin hydrobromide did not affect XII nerve bursting or pre-BötC neurons. Iontophoresis of 8-hydroxydipropylaminotetralin hydrobromide had almost no effect on respiratory frequency and induced in the interneurons either a depolarization or hyperpolarization (<5 mV) which was blocked by the 5-HT1A receptor antagonist N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)N-2-pyridinylcyclohexane carboxamide. In conclusion, 5-HT-evoked tonic excitation of respiratory XII motoneurons is mediated by postsynaptic 5-HT2 receptors. The excitatory effects on respiratory rhythm are also primarily attributable to postsynaptic 5-HT2 receptors of pre-BötC neurons. Additional modulatory effects on the interneurons appear to be mediated by postsynaptic 5-HT1A receptors.

Cajal's prophetic functional considerations on respiratory reflexes: new questions about old answers

In the "Histology of the Nervous System" (Histologie, Spanish edition, 1899, 1904; French translation, 1909, 1911; all citations are from the American translation, 1995) Cajal did not only describe the origins and central pathways of cranial nerves but his detailed observations led him to numerous conclusions about the functional organization of brainstem reflexes. From studies of vagal and glossopharyngeal afferents he proposed a structural organization of the nucleus tractus solitarii (NTS). His view has been considerably changed by several authors on the basis of modern tracing studies. However, detailed histological examinations of functionally identified sensory fibers provided new understanding of a functional organization of the solitary nucleus that is very well in line with Cajal's original descriptions. The prophetic character of Cajal's concepts of structural-functional relations becomes even more evident by a reconsideration of his explanations of the reflexes underlying respiration, coughing and vomiting. Recent electrophysiological studies of spontaneously rhythmically active in vitro preparations have provided us with new insights in respiratory control. However, it appears that quite a number of Cajal's key questions concerning respiratory reflexes are still not solved. Therefore, a reconsideration of old and partly forgotten concepts might indeed provide a novel understanding of the structural and functional organization of brainstem reflexes.

Blockade of synaptic inhibition within the pre-Bötzinger complex in the cat suppresses respiratory rhythm generation in vivo

1. The role of synaptic inhibition in respiratory rhythm generation was analysed by microinjections of GABAA and glycine receptor antagonists into the bilateral pre-Botzinger complex (PBC) of anaesthetized cats. Central respiratory activity was monitored by phrenic nerve recordings. 2. Bilateral injections of bicuculline (50 or 100 microM) irreversibly slowed respiratory frequency and induced apneustic patterns. 3. Bilateral injections of strychnine (50 or 100 microM) greatly reduced phrenic burst amplitudes leading to increased burst frequency or irreversibly blocked rhythmic phrenic discharges. After unilateral tetrodotoxin (TTX) blockade in the PBC, strychnine injection into the contralateral PBC blocked rhythmic phrenic discharges. 4. Bilateral blockade of both GABAergic and glycinergic inhibition abolished rhythmic burst discharges and only tonic phrenic activity remained. Such tonic activity was blocked only by TTX (1 microM). 5. Potentiation of synaptic inhibition by the serotonin 1A receptor agonist 8-hydroxydipropylaminotetralin (8-OH-DPAT; 50 microM) restored rhythmic activity only when given shortly after strychnine and bicuculline applications. It was, however, ineffective after blockade of synaptic inhibition was complete. 6. The study demonstrates the significance of synaptic inhibition in the process of respiratory generation in the adult cat in vivo.

Selective lesioning of the cat pre-Bötzinger complex in vivo eliminates breathing but not gasping

1. To examine the functional importance of the pre-Bötzinger complex for breathing we micro-injected, under in vivo conditions, the calcium channel blocker omega-conotoxin GVIA and the sodium channel blocker tetrodotoxin (TTX) into the ventrolateral medulla of adult cats, while monitoring respiratory rhythmic motor output in the phrenic nerve. 2. omega-Conotoxin GVIA caused a highly localized synaptic ablation by blocking presynaptic N-type calcium channels. When injecting 5-60 fmol omega-conotoxin GVIA unilaterally, the amplitude of phrenic nerve activity decreased bilaterally and sometimes disappeared, indicating central apnoea. These effects were reversible and could only be induced in a very localized area of the pre-Botzinger complex. By injecting omega-conotoxin GVIA several times during an experiment and analysing the areas where injections affected respiratory activity, it was possible to map exactly the anatomical extent of the area critical for respiratory rhythm generation. 3. Following the precise localization of the pre-Bötzinger complex with omega-conotoxin GVIA, we injected TTX to induce an irreversible inactivation of this region. TTX injected unilaterally into the pre-Bötzinger complex irreversibly reduced the amplitude of phrenic nerve activity. Bilateral TTX injections eliminated respiratory rhythmic activity, causing a persistent central apnoea. 4. After bilateral lesioning of the pre-Bötzinger complex, it was still possible to induce gasping during hypoxia or asphyxia, indicating that respiration and gasping are generated by two different neuronal networks. 5. We propose that omega-conotoxin GVIA as employed in this study to investigate the functional role of the pre-Bötzinger complex can also be used as a general pharmacological approach to map other neuronal networks. We call this the 'omega-conotoxin GVIA tracing' method.

5-HT2 receptor-controlled modulation of medullary respiratory neurones in the cat

1. The effects of the 5-HT2 receptor agonist alpha-methyl-5-HT were studied on the membrane of expiratory (E2) and post-inspiratory (PI) neurones, by intracellular recordings in the caudal medulla of anaesthetized cats. 2. Ionophoresis of alpha-Me-5-HT depolarized membrane potential and increased action potential frequency in a majority of neurones tested. Depolarization of neurones by alpha-Me-5-HT was accompanied by increased input resistance throughout all phases of the respiratory cycle. These effects were antagonized by ionophoresis of cinanserin, a receptor-blocking agent with high affinity for 5-HT2 receptors. 3. E2 neurones were voltage clamped to measure membrane current changes induced by alpha-Me-5-HT ionophoresis. alpha-Me-5-HT induced a net inward current by reducing inspiratory-phase outward currents and increasing expiratory-phase inward currents. These changes were equivalent with steady membrane depolarization, decreased inspiratory phase membrane hyperpolarization and increased expiratory drive potential recorded from the same neurones in current clamp. 4. The effects of alpha-Me-5-HT are consistent with activation of 5-HT2 receptors on E2 and PI neurones leading to blockade of synaptically activated and persistent conductances to potassium ions.

Pre-Bötzinger complex in the cat

1. Patterns of respiratory neuronal activity were examined in pentobarbitone anesthetized adult cats in a circumscribed area of the ventrolateral medulla, which has previously been defined as the pre-Bötzinger complex (pre-BOTC) from electrophysiological and morphological criteria in the brain stem-spinal cord preparation of the neonatal rat. The pre-BOTC has been proposed to play a critical role in respiratory rhythm generation in mammals, but electrophysiological properties of the region have not been thoroughly characterized in the adult brain stem in vivo. 2. From intra- and extracellular recordings, we verified the existence of a well-defined zone with a distinct profile of neuronal activity between the rostral Bötzinger complex containing expiratory neurons and the more caudal medullary pool of inspiratory neurons of the ventral respiratory group (VRG) in the para-ambigual region. This zone corresponds to the pre-BOTC. It was characterized by a concentration of the various types of respiratory neurons, particularly those proposed to be involved in respiratory phase transitions, including neurons discharging immediately before the onset of inspiratory phase activity (pre-inspiratory neurons), early-inspiratory, and postinspiratory neurons. The majority of these neurons were presumed interneurons because they were not antidromically activated by spinal cord or cranial nerve stimulation. 3. The locus of the pre-BOTC corresponded histologically to the rostral part of the nucleus ambiguus and ventrolateral reticular formation. It was located caudal to the retrofacial nucleus and rostral to the lateral reticular nucleus, extending 3.0-3.5 mm rostral to the obex, and 3.2-4.0 mm lateral from the midline. This location was homologous to that established in the neonatal rat. 4. Pre-inspiratory neurons (pre-I neurons) were specifically found in the pre-BOTC. Intracellular recordings from these neurons revealed two types of activity patterns. Type 1 of pre-I neurons exhibited a steady membrane depolarization during expiration and a steep membrane depolarization with a high-frequency burst of action-potential discharge during the phase transition from expiration to inspiration. This was followed by a decline of depolarization and spike discharge during the remainder of the inspiratory phase. A second type of pre-I neurons exhibited a secondary graded membrane depolarization and burst discharge during the late-inspiratory period. 5. Synaptic events were examined in other respiratory neurons during the 40-160 ms preceding the onset of phrenic nerve activity when pre-I neurons exhibited peak spike discharge. Early-inspiratory, throughout-respiratory, and postinspiratory neurons were disinhibited during this period, whereas stage-2 expiratory neurons exhibited a decrease in spike activity and repolarization.(ABSTRACT TRUNCATED AT 400 WORDS)

The medullary respiratory network in the rat

1. In urethane or Nembutal anaesthetized and artificially ventilated Wistar rats, respiratory neurones of the ventrolateral medulla oblongata were analysed in extracellular (n = 74) and intracellular (n = 43) recordings. 2. Some respiratory neurones were identified as bulbospinal by their antidromic response to spinal cord stimulation at the C4 level. The neurones examined were not antidromically excited by vagal nerve stimulation. 3. Based on their discharge pattern in relation to efferent phrenic and vagal nerve activity, six types of respiratory neurones were classified: early-inspiratory, throughout-inspiratory, late-inspiratory, post-inspiratory, expiratory, and phase-spanning expiratory-inspiratory neurones. 4. Analysis of postsynaptic activities and IPSP reversal following chloride injection revealed post-inspiratory and expiratory inhibition in inspiratory neurones a pronounced early-inspiratory and a relatively weak expiratory inhibition in post-inspiratory neurones, and an early-inspiratory and post-inspiratory inhibition in expiratory neurones. 5. In phase-spanning expiratory-inspiratory neurones the post-inspiratory inhibition was strong and effectively blocked action potential discharge. Expiratory-inspiratory neurones were quite similar to the group of inspiratory neurones, but seemed to receive tonic excitatory inputs not shunted by weak expiratory inhibition. This pre-inspiratory discharge was readily blocked by weak negative DC injection. 6. Under conditions of experimental hypoxia, or long lasting lung inflation and non-inflation, post-inspiratory neurones displayed a second burst of discharge at the end of the expiratory phase in addition to their longer lasting post-inspiratory discharge. 7. We conclude that in the rat the central respiratory rhythm is organized in three (inspiratory, post-inspiratory, expiratory) phases, and that synaptic interaction within the medullary respiratory network of the rat occurs similarly to that described for the cat.

Complex anomalies of the human aortic arch system: unique case with both vertebral arteries as additional branches of the aortic arch

We describe a case of an aortic arch with five primary branches arising in a sequence that has previously never been reported. From right to left, the brachiocephalic trunk and left common carotid, left vertebral, and subclavian arteries originated from the convexity of the aortic arch. The last branch was the right vertebral artery that arose from the dorsal aspect of the aortic arch opposite the ligamentum arteriosum. Presenting a dilatation at its commencement, the right vertebral ran to the right behind the esophagus and entered the foramen transversarium of the seventh cervical vertebra, whereas the left vertebral passed to the foramen transversarium of the fifth cervical vertebra. The left vertebral artery gave off the left thyroid artery; a thyrocervical trunk was absent on the left side. A thyroidea ima arose from the brachiocephalic trunk. The embryology of this complex anomaly as well as its potential clinical significance are discussed.