Stephan von Hörsten

The neurocircuitry and receptor subtypes mediating anxiolytic-like effects of neuropeptide Y.

This review aims to give a brief overview of NPY receptor distribution and physiology in the brain and summarizes series of studies, test by test and region by region, aimed at identification receptor subtypes and neuronal circuitry mediating anxiolytic-like effects of NPY. We conclude that from four known NPY receptor subtypes in the rat (Y(1), Y(2), Y(4), Y(5)), only the NPY Y(1) receptor can be linked to anxiety-regulation with certainty in the forebrain, and that NPY Y(2) receptor may have a role in the pons. Microinjection studies with NPY and NPY receptor antagonists support the hypothesis that the amygdala, the dorsal periaqueductal gray matter, dorsocaudal lateral septum and locus coeruleus form a neuroanatomical substrate that mediates anxiolytic-like effects of NPY. The release of NPY in these areas is likely phasic, as NPY receptor antagonists are silent on their own. However, constant NPY-ergic tone seems to exist in the dorsal periaqueductal gray, the only brain region where NPY Y(1) receptor antagonists had anxiogenic-like effects. We conclude that endogenous NPY has an important role in reducing anxiety and serves as a physiological stabilizer of neural activity in circuits involved in the regulation of arousal and anxiety.

Behavioral phenotyping of mice in pharmacological and toxicological research.

The evaluation of behavioral effects is an important component for the in vivo screening of drugs or potentially toxic compounds in mice. Ideally, such screening should be composed of monitoring general health, sensory functions, and motor abilities, right before specific behavioral domains are tested. A rational strategy in the design and procedure of testing as well as an effective composition of different well-established and reproducible behavioral tests can minimize the risk of false positive and false negative results in drug screening. In the present review we describe such basic considerations in planning experiments, selecting strains of mice, and propose groups of behavioral tasks suitable for a reliable detection of differences in specific behavioral domains in mice. Screening of general health and neurophysiologic functions (reflexes, sensory abilities) and motor function (pole test, wire hang test, beam walking, rotarod, accelerod, and footprint) as well as specific hypothesis-guided testing in the behavioral domains of learning and memory (water maze, radial maze, conditioned fear, and avoidance tasks), emotionality (open field, hole board, elevated plus maze, and object exploration), nociception (tail flick, hot plate), psychiatric-like conditions (porsolt swim test, acoustic startle response, and prepulse inhibition), and aggression (isolation-induced aggression, spontaneous aggression, and territorial aggression) are described in further detail. This review is designed to describe a general approach, which increases reliability of behavioral screening. Furthermore, it provides an overview on a selection of specific procedures suitable for but not limited to behavioral screening in pharmacology and toxicology.

Guidelines for preclinical animal research in ALS/MND: A consensus meeting

The development of therapeutics for ALS/MND is largely based on work in experimental animals carrying human SOD mutations. However, translation of apparent therapeutic successes from in vivo to the human disease has proven difficult and a considerable amount of financial resources has been apparently wasted. Standard operating procedures (SOPs) for preclinical animal research in ALS/MND are urgently required. Such SOPs will help to establish SOPs for translational research for other neurological diseases within the next few years. To identify the challenges and to improve the research methodology, the European ALS/MND group held a meeting in 2006 and published guidelines in 2007 (1). A second international conference to improve the guidelines was held in 2009. These second and improved guidelines are dedicated to the memory of Sean F. Scott.

Neurodegeneration and Motor Dysfunction in a Conditional Model of Parkinson's Disease

α-Synuclein (α-syn) has been implicated in the pathogenesis of many neurodegenerative disorders, including Parkinsons disease. These disorders are characterized by various neurological and psychiatric symptoms based on progressive neuropathological alterations. Whether the neurodegenerative process might be halted or even reversed is presently unknown. Therefore, conditional mouse models are powerful tools to analyze the relationship between transgene expression and progression of the disease. To explore whether α-syn solely originates and further incites these alterations, we generated conditional mouse models by using the tet-regulatable system. Mice expressing high levels of human wild-type α-syn in midbrain and forebrain regions developed nigral and hippocampal neuropathology, including reduced neurogenesis and neurodegeneration in absence of fibrillary inclusions, leading to cognitive impairment and progressive motor decline. Turning off transgene expression in symptomatic mice halted progression but did not reverse the symptoms. Thus, our data suggest that approaches targeting α-syn-induced pathological pathways might be of benefit rather in early disease stages. Furthermore, α-syn-associated cytotoxicity is independent of filamentous inclusion body formation in our conditional mouse model.

Relevance of Neuropeptide Y for the neuroimmune crosstalk

Both cellular and humoral functions of the immune system are modulated by the sympathetic nervous system (SNS). This interaction is mainly mediated by the release of catecholamines (CA) and their receptor-specific action on immune cells. However, neuropeptide Y (NPY), also present in sympathetic nerve terminals, is released upon SNS-stimulation. NPY modulates potent immunological effects in vitro and in vivo, such as differentiation of T helper cells, monocyte mediator release, NK cell activation, and immune cell redistribution. In addition to this direct action within the neuroimmune crosstalk, NPY is also able to modulate the immunomodulatory effects of other neurotransmitters, thereby acting as a neuroimmune co-transmitter. This review will discuss key findings from recent studies, provide implications for the clinical situation, and integrate the pleiotropic functions of NPY in the context of neuroimmune interactions.

From Kratom to mitragynine and its derivatives: Physiological and behavioural effects related to use, abuse, and addiction

Kratom (or Ketum) is a psychoactive plant preparation used in Southeast Asia. It is derived from the plant Mitragyna speciosa Korth. Kratom as well as its main alkaloid, mitragynine, currently spreads around the world. Thus, addiction potential and adverse health consequences are becoming an important issue for health authorities. Here we reviewed the available evidence and identified future research needs. It was found that mitragynine and M. speciosa preparations are systematically consumed with rather well defined instrumentalization goals, e.g. to enhance tolerance for hard work or as a substitute in the self-treatment of opiate addiction. There is also evidence from experimental animal models supporting analgesic, muscle relaxant, anti-inflammatory as well as strong anorectic effects. In humans, regular consumption may escalate, lead to tolerance and may yield aversive withdrawal effects. Mitragynine and its derivatives actions in the central nervous system involve μ-opioid receptors, neuronal Ca²⁺ channels and descending monoaminergic projections. Altogether, available data currently suggest both, a therapeutic as well as an abuse potential.

Sex differences in a transgenic rat model of Huntington's disease: decreased 17β-estradiol levels correlate with reduced numbers of DARPP32+ neurons in males

Recent clinical studies have highlighted that female sex hormones represent potential neuroprotective mediators against damage caused by acute and chronic brain diseases. This evidence has been confirmed by experimental studies documenting the protective role of female sex hormones both in vitro and in vivo, although these studies did not specifically focus on Huntingtons disease (HD). We therefore investigated the onset and course of HD in female and male transgenic (tg) HD (CAG(n51)) and control rats across age and focused on three aspects: (i) behavioral and physiological alterations (energy expenditure, home-cage activity, emotional disturbance and motor dysfunction), (ii) morphological markers (numbers and characteristics of striatal DARPP32(+) medium-sized spiny neurons (MSNs) and dopamine receptor autoradiography) and (iii) peripheral sex hormone levels as well as striatal estrogen receptor expression. Independent of their sex, tgHD rats exhibited increased levels of food intake, elevated home-cage activity scores and anxiolytic-like behavior, whereas only males showed an impairment of motor function. In line with the latter finding, loss and atrophy of DARPP32(+) MSNs were apparent only in male tgHD rats. This result was associated with a decreased striatal dopamine D1 receptor density and lower plasma levels of 17beta-estradiol at the age of 14 months. As DARPP32(+) MSNs expressed both alpha- and beta-estrogen receptors and showed a correlation between cell numbers and 17beta-estradiol levels, our findings suggest sex-related differences in the HD phenotype pointing to a substantial neuroprotective effect of sex hormones and opening new perspectives on the therapy of HD.

Neuropeptide Y (NPY) Suppresses Experimental Autoimmune Encephalomyelitis: NPY1 Receptor-Specific Inhibition of Autoreactive Th1 Responses In Vivo

Prior studies have revealed that the sympathetic nervous system regulates the clinical and pathological manifestations of experimental autoimmune encephalomyelitis (EAE), an autoimmune disease model mediated by Th1 T cells. Although the regulatory role of catecholamines has been indicated in the previous works, it remained possible that other sympathetic neurotransmitters like neuropeptide Y (NPY) may also be involved in the regulation of EAE. Here we examined the effect of NPY and NPY receptor subtype-specific compounds on EAE, actively induced with myelin oligodendrocyte glycoprotein 35–55 in C57BL/6 mice. Our results revealed that exogenous NPY as well as NPY Y1 receptor agonists significantly inhibited the induction of EAE, whereas a Y5 receptor agonist or a combined treatment of NPY with a Y1 receptor antagonist did not inhibit signs of EAE. These results indicate that the suppression of EAE by NPY is mediated via Y1 receptors. Furthermore, treatment with the Y1 receptor antagonist induced a significantly earlier onset of EAE, indicating a protective role of endogenous NPY in the induction phase of EAE. We also revealed a significant inhibition of myelin oligodendrocyte glycoprotein 35–55-specific Th1 response as well as a Th2 bias of the autoimmune T cells in mice treated with the Y1 receptor agonist. Ex vivo analysis further demonstrated that autoimmune T cells are directly affected by NPY via Y1 receptors. Taken together, we conclude that NPY is a potent immunomodulator involved in the regulation of the Th1-mediated autoimmune disease EAE.

Regulation of Expression and Function of Dipeptidyl Peptidase 4 (DP4), DP8/9, and DP10 in Allergic Responses of the Lung in Rats

The expression of dipeptidyl peptidase 4 (DP4, CD26) affects T-cell recruitment to lungs in an experimental rat asthma model. Furthermore, the gene of the structural homologous DP10 represents a susceptibility locus for asthma in humans, and the functional homologous DP8/9 are expressed in human leukocytes. Thus, although several mechanisms may account for a role of DP4-like peptidases in asthma, detailed information on their anatomical sites of expression and function in lungs is lacking. Therefore, bronchi and lung parenchyma were evaluated using immunohistochemistry and histochemical/enzymatic activity assays, as well as quantitative real-time PCR for this family of peptidases in naïve and asthmatic rat lungs derived from wild-type F344 and DP4-deficient F344 rat strains. Surprisingly, results show not only that the induction of experimental asthma increases DP4 enzymatic activity in the bronchoalveolar lavage fluid and parenchyma, but also that DP8/9 enzymatic activity is regulated and, as well as the expression of DP10, primarily found in the bronchial epithelium of the airways. This is the first report showing a differential and site-specific DP4-like expression and function in the lungs, suggesting a pathophysiologically significant role in asthma.

BEHAVIORALLY CONDITIONED IMMUNOSUPPRESSION USING CYCLOSPORINE A : CENTRAL NERVOUS SYSTEM REDUCES IL-2 PRODUCTION VIA SPLENIC INNERVATION

Bi-directional interactions between the central nervous system (CNS) and immune system are demonstrated by the modification of immune function using behavioral conditioning. However, the mechanisms by which the CNS achieves conditioned immunomodulation are still in question. Here, we report that the immunosuppressive effects of cyclosporine A (CsA) can be behaviorally conditioned in rats using saccharin as a gustatory conditioned stimulus. The conditioned effects were compared to control groups that received CsA paired with water (sham-conditioned), CsA injection on test days (CsA-treated), and unhandled rats (untreated). In conditioned animals, the mitogen-induced lymphocyte proliferation in the spleen is significantly suppressed, and the survival time of heterotopic heart allografts prolonged. These effects are paralleled by conditioned inhibition of IL-2 and IFN-gamma synthesis by splenocytes. Furthermore, the CNS-induced immunosuppression is mediated neuronally and not via the blood, since the conditioned reduction of proliferation and cytokine production is completely abrogated after surgical denervation of the spleen. Thus, during conditioning, the CNS learns to reinstate at demand a CsA-like immunosuppression via splenic innervation. This might be used as a supportive therapy for controlling immune functions.