Activation of the G-protein-coupled receptor GPR30 induces anxiogenic effects in mice, similar to oestradiol

RATIONALE

The influence of ovarian hormones on behaviour is well accepted, and oestrogen replacement therapy has proven to be beneficial in several cases of menopausal mood disorders. However, there are also some adverse effects of such a therapy, like anxiety and dysphoria. In fact, some women feel better at low levels of oestrogen and worse when levels fluctuate. Still, it is unclear which receptors might mediate negative emotional effects.

OBJECTIVES

The aim of this study was to identify which oestrogen receptor(s) are capable of mediating negative emotional effects and, therefore, may represent candidates responsible for the adverse side effects observed in oestrogen replacement therapy.

RESULTS

We provide evidence from mouse behavioural tests that oestrogen-induced anxiogenic-like effects might be mediated, at least in part, by the G protein-coupled receptor GPR30. The short-term application of specific agonists against the alpha and beta oestrogen receptors did not result in marked behavioural changes. In contrast, the specific stimulation of GPR30 in male and ovariectomized female mice induced anxiogenic effects. The anxiogenic effects induced by the specific GPR30 agonist G-1 were comparable (and non-accumulative) to those observed after low doses of the general oestrogen receptor agonist 17b-oestradiol in male mice, thereby reflecting the behavioural changes observed in intact female mice during early pro-oestrus.

CONCLUSIONS

Our data suggest that GPR30 induces acute anxiogenic effects of oestrogen in rodents. It is tempting to speculate that a potential imbalance in the expression of the anxiolytic beta oestrogen receptor and the anxiogenic GPR30 may also be involved in the negative symptoms of oestrogen replacement therapy in humans.

Sprouty2 and -4 regulate axon outgrowth by hippocampal neurons

Sprouty proteins act as negative feedback inhibitors of fibroblast growth factor (FGF) signaling. FGFs belong to the neurotrophic factors and are involved in axonal growth during development and repair. We investigated the expression of Sprouty isoforms in hippocampal neurons as well as the regulation of Sprouty2 and -4 during development and their role in axon growth. Sprouty2 and -4 were located in the nucleus, the cytoplasm, in dendrites, and axons of hippocampal neurons concentrated in growth cones. During development in vivo and differentiation in vitro, expression of Sprouty2 and -4 was gradually downregulated in hippocampal neurons. Between 5 and 24 days in culture expression of both Sprouty isoforms was reduced by 70%. In vivo expression of Sprouty2 was reduced by 79% and of Sprouty4 by 93% on postnatal day 14 compared to embryonic day 16.5. Downregulation of Sprouty2 and -4 by shRNAs strongly promoted elongative axon growth by cultured hippocampal neurons, which was further increased by FGF-2 treatment. In addition, FGF-2 reduced expression of Sprouty2 by 33% and of Sprouty4 by 44%. Together, our results imply that Sprouty2 and -4 are downregulated in the hippocampus during postnatal brain development and that they can act as regulators of developmental axon growth.

VEGF and its role in the early development of the long bone epiphysis

In long bones of murine species, undisturbed development of the epiphysis depends on the generation of vascularized cartilage canals shortly after birth. Despite its importance, it is still under discussion how this event is exactly regulated. It was suggested previously that, following increased hypoxia in the epiphyseal core, angiogenic factors are expressed and hence stimulate the ingrowth of the vascularized canals. In the present study, we tested this model and examined the spatio-temporal distribution of two angiogenic molecules during early development in mice. In addition, we investigated the onset of cartilage hypertrophy and mineralization. Our results provide evidence that the vascular endothelial growth factor is expressed in the epiphyseal resting cartilage prior to the moment of canal formation and is continuously expressed until the establishment of a large secondary ossification centre. Interestingly, we found no expression of secretoneurin before the establishment of the canals although this factor attracts blood vessels under hypoxic conditions. Epiphyseal development further involves maturation of the resting chondrocytes into hypertrophic ones, associated with the mineralization of the cartilage matrix and eventual death of the latter cells. Our results suggest that vascular endothelial growth factor is the critical molecule for the generation of the epiphyseal vascular network in mice long bones. Secretoneurin, however, does not appear to be a player in this event. Hypertrophic chondrocytes undergo cell death by a mechanism interpreted as chondroptosis.

Valerenic acid derivatives as novel subunit-selective GABAA receptor ligands - in vitro and in vivo characterization

BACKGROUND AND PURPOSE

Subunit-specific modulators of gamma-aminobutyric acid (GABA) type A (GABA(A)) receptors can help to assess the physiological function of receptors with different subunit composition and also provide the basis for the development of new drugs. Valerenic acid (VA) was recently identified as a beta(2/3) subunit-specific modulator of GABA(A) receptors with anxiolytic potential. The aim of the present study was to generate VA derivatives as novel GABA(A) receptor modulators and to gain insight into the structure-activity relation of this molecule.

EXPERIMENTAL APPROACH

The carboxyl group of VA was substituted by an uncharged amide or amides with different chain length. Modulation of GABA(A) receptors composed of different subunit compositions by the VA derivatives was studied in Xenopus oocytes by means of the two-microelectrode voltage-clamp technique. Half-maximal stimulation of GABA-induced chloride currents (I(GABA)) through GABA(A) receptors (EC(50)) and efficacies (maximal stimulation of I(GABA)) were estimated. Anxiolytic activity of the VA derivatives was studied in mice, applying the elevated plus maze test.

KEY RESULTS

Valerenic acid amide (VA-A) displayed the highest efficacy (more than twofold greater I(GABA) enhancement than VA) and highest potency (EC(50)= 13.7 +/- 2.3 microM) on alpha(1)beta(3) receptors. Higher efficacy and potency of VA-A were also observed on alpha(1)beta(2)gamma(2s) and alpha(3)beta(3)gamma(2s) receptors. Anxiolytic effects were most pronounced for VA-A.

CONCLUSIONS AND IMPLICATIONS

Valerenic acid derivatives with higher efficacy and affinity can be generated. Greater in vitro action of the amide derivative correlated with a more pronounced anxiolytic effect in vivo. The data give further confidence in targeting beta(3) subunit containing GABA(A) receptors for development of anxiolytics.

Efficient mRNA detection from human archival paraffin-embedded tissue: an update

We recently published an in situ hybridization protocol for archival tissue using a commercial hybridization buffer. This buffer is no more available. Therefore, we have developed an improved protocol with a defined hybridization buffer.

Kappa opioid receptor activation blocks progressive neurodegeneration after kainic acid injection

We recently demonstrated that endogenous prodynorphin-derived peptides mediate anticonvulsant, antiepileptogenic and neuroprotective effects via kappa opioid receptors (KOP). Here we show acute and delayed neurodegeneration and its pharmacology after local kainic acid injection in prodynorphin knockout and wild-type mice and neuroprotective effect(s) of KOP activation in wild-type mice. Prodynorphin knockout and wild-type mice were injected with kainic acid (3 nmoles in 50 nl saline) into the stratum radiatum of CA1 of the right dorsal hippocampus. Knockout mice displayed significantly more neurodegeneration of pyramidal cells and interneurons than wild-type mice 2 days after treatment. This phenotype could be mimicked in wild-type animals by treatment with the KOP antagonist GNTI and rescued in knockout animals by the KOP agonist U-50488. Minor differences in neurodegeneration remained 3 weeks after treatment, mostly because of higher progressive neurodegeneration in wild-type mice compared with prodynorphin-deficient animals. In wild-type mice progressive neurodegeneration, but not acute neuronal loss, could be mostly blocked by U-50488 treatment. Our data suggest that endogenous prodynorphin-derived peptides sufficiently activate KOP receptors during acute seizures, and importantly in situations of reduced dynorphinergic signaling-like in epilepsy-the exogenous activation of KOP receptors might also have strong neuroprotective effects during excitotoxic events.

Lasp1 misexpression influences chondrocyte differentiation in the vertebral column

The mouse mutant wavy tail Tg(Col1a1-lacZ)304ng was created through transgene insertion and exhibits defects of the vertebral column. Homozygous mutant animals have compressed tail vertebrae and wedge-shaped intervertebral discs, resulting in a meandering tail. Delayed closure of lumbar neural arches and lack of processus spinosi have been observed; these defects become most prominent during the transition from cartilage to bone. The spina bifida was resistant to folic acid treatment, while retinoic acid administration caused severe skeletal defects in the mutant, but none in wild type control animals. The transgene integrated at chromosome 11 band D, in an area of high gene density. The insertion site was located between the transcription start sites of the Rpl23 and Lasp1 genes. LASP1 (an actin binding protein involved in cell migration and survival) was found to be produced in resting and hypertrophic chondrocytes in the vertebrae. In mutant vertebrae, temporal and spatial misexpression of Lasp1 was observed, indicating that alterations in Lasp1 transcription are most likely responsible for the observed phenotype. These data reveal a yet unappreciated role of Lasp1 in chondrocyte differentiation during cartilage to bone transition.

Breaking the seals: efficient mRNA detection from human archival paraffin-embedded tissue

During our study on HOXA13, HOXD12, and HOXD13 mRNA expression in human adult and embryonic tissues, we were confronted with the fact that, within our specimen collection, as in other University Departments in Europe, <20% of all samples yielded reliable labeling, while most samples were resistant to hybridization by standard protocols due to over-fixation. Fixation is essential for specimen stability, especially when samples are stored at room temperature and used for histology, and people tend to be more worried about under- than over-fixation. On the other hand fixation inhibits penetration by the probe and may also trap mRNA within ribosomes. Therefore, we developed a nonradioactive in situ hybridization technique, which allows detection of mRNA expressed on low levels from a variety of differentially fixed tissues while maintaining tissue integrity. This was achieved by improving target retrieval and probe detection. In contrast with others, our method allows reliable staining from tissues that are fixed in paraformaldehyde from four hours to over one week, and archived samples that were stored at room temperature for several years (17-19 yr in some cases) and exceeds detection limits of purely fluorescent methods. Our protocol is highly suitable for detecting CDX-2 mRNA in carcinoma specimens, but especially designed to investigate mRNAs in nonpathological adult and embryonic tissues. Due to the use of standardized probes, we do not expect problems in detecting other mRNAs expressed in suitable amounts.

30 years of dynorphins--new insights on their functions in neuropsychiatric diseases

Since the first description of their opioid properties three decades ago, dynorphins have increasingly been thought to play a regulatory role in numerous functional pathways of the brain. Dynorphins are members of the opioid peptide family and preferentially bind to kappa opioid receptors. In line with their localization in the hippocampus, amygdala, hypothalamus, striatum and spinal cord, their functions are related to learning and memory, emotional control, stress response and pain. Pathophysiological mechanisms that may involve dynorphins/kappa opioid receptors include epilepsy, addiction, depression and schizophrenia. Most of these functions were proposed in the 1980s and 1990s following histochemical, pharmacological and electrophysiological experiments using kappa receptor-specific or general opioid receptor agonists and antagonists in animal models. However, at that time, we had little information on the functional relevance of endogenous dynorphins. This was mainly due to the complexity of the opioid system. Besides actions of peptides from all three classical opioid precursors (proenkephalin, prodynorphin, proopiomelanocortin) on the three classical opioid receptors (delta, mu and kappa), dynorphins were also shown to exert non-opioid effects mainly through direct effects on NMDA receptors. Moreover, discrepancies between the distribution of opioid receptor binding sites and dynorphin immunoreactivity contributed to the difficulties in interpretation. In recent years, the generation of prodynorphin- and opioid receptor-deficient mice has provided the tools to investigate open questions on network effects of endogenous dynorphins. This article examines the physiological, pathophysiological and pharmacological implications of dynorphins in the light of new insights in part obtained from genetically modified animals.

Epithelial and muscular regionalization of the human developing anorectum

In the past, interpretations of anorectal development were mainly based on analysis of serially sectioned embryos of various nonhuman species as well as some human specimens. A four-dimensional view of the developmental situation in the human has never been established nor connected to recent findings obtained from newer molecular techniques. We, therefore, investigated human embryonic and fetal pelves by means of immunohistochemistry and in situ hybridization to elucidate differentiation and interaction of epithelial and mesenchymal layers of the anorectum. To emphasize spatial as well as sequential morphological development, we produced three-dimensional reconstructions of the specimens at hand. Research conducted proved that the decisive steps of epithelial and muscular differentiation occur between the 7th and 9th week after conception. This study elucidates a biphasic epithelial "closure" in the anal canal and interactions between epithelium, smooth musculature, and skeletal musculature. Based on the results presented here, it is possible to describe the pathogenesis of two anorectal malformations: the imperforate anal membrane and the anal membrane stenosis. This study will now provide the basis for further research into developmental processes occurring before the ones examined.

Dynorphin knockout reduces fat mass and increases weight loss during fasting in mice

Endogenous opioids, particularly dynorphins, have been implicated in regulation of energy balance, but it is not known how they mediate this in vivo. We investigated energy homeostasis in dynorphin knockout mice (Dyn(-/-) mice) and probed the interactions between dynorphins and the neuropeptide Y (NPY) system. Dyn(-/-) mice were no different from wild types with regards to body weight and basal and fasting-induced food intake, but fecal output was increased, suggesting decreased nutrient absorption, and they had significantly less white fat and lost more weight during a 24-h fast. The neuroendocrine and thermal responses to fasting were at least as pronounced in Dyn(-/-) as in wild types, and there was no stimulatory effect of dynorphin knockout on 24-h energy expenditure (kilocalories of heat produced) or physical activity. However, Dyn(-/-) mice showed increased circulating concentrations of 3,4-dihydroxyphenlacetic acid and 3,4-dihydroxyphenylglycol, suggesting increased activity of the sympathetic nervous system. The respiratory exchange ratio of male but not female Dyn(-/-) mice was reduced, demonstrating increased fat oxidation. Interestingly, expression of the orexigenic acting NPY in the hypothalamic arcuate nucleus was reduced in Dyn(-/-) mice. However, fasting-induced increases in pre-prodynorphin expression in the arcuate nucleus, the paraventricular nucleus, and the ventromedial hypothalamus but not the lateral hypothalamus were abolished by deletion of Y(1) but not Y(2) receptors. Therefore, ablation of dynorphins results in increases in fatty acid oxidation in male mice, reductions in adiposity, and increased weight loss during fasting, possibly via increases in sympathetic activity, decreases in intestinal nutrient absorption, and interactions with the NPYergic system.

Endogenous dynorphin in epileptogenesis and epilepsy: anticonvulsant net effect via kappa opioid receptors

Neuropsychiatric disorders are one of the main challenges of human medicine with epilepsy being one of the most common serious disorders of the brain. Increasing evidence suggest neuropeptides, particularly the opioids, play an important role in epilepsy. However, little is known about the mechanisms of the endogenous opioid system in epileptogenesis and epilepsy. Therefore, we investigated the role of endogenous prodynorphin-derived peptides in epileptogenesis, acute seizure behaviour and epilepsy in prodynorphin-deficient mice. Compared with wild-type littermates, prodynorphin knockout mice displayed a significantly reduced seizure threshold as assessed by tail-vein infusion of the GABA(A) antagonist pentylenetetrazole. This phenotype could be entirely rescued by the kappa receptor-specific agonist U-50488, but not by the mu receptor-specific agonist DAMGO. The delta-specific agonist SNC80 decreased seizure threshold in both genotypes, wild-type and knockout. Pre-treatment with the kappa selective antagonist GNTI completely blocked the rescue effect of U-50488. Consistent with the reduced seizure threshold, prodynorphin knockout mice showed faster seizure onset and a prolonged time of seizure activity after intracisternal injection of kainic acid. Three weeks after local injection of kainic acid into the stratum radiatum CA1 of the dorsal hippocampus, prodynorphin knockout mice displayed an increased extent of granule cell layer dispersion and neuronal loss along the rostrocaudal axis of the ipsi- and partially also of the contralateral hippocampus. In the classical pentylenetetrazole kindling model, dynorphin-deficient mice showed significantly faster kindling progression with six out of eight animals displaying clonic seizures, while none of the nine wild-types exceeded rating 3 (forelimb clonus). Taken together, our data strongly support a critical role for dynorphin in the regulation of hippocampal excitability, indicating an anticonvulsant role of kappa opioid receptors, thereby providing a potential target for antiepileptic drugs.