Role of hypothalamus-pituitary-adrenal axis modulation in the stress-resilient phenotype of DPP4-deficient rats.

BACKGROUND: Dipeptidyl peptidase 4 (DPP4, CD26) is a moonlighting enzyme responsible for the proteolytic inactivation of neuropeptide Y (NPY), a peptide known for its anxiolytic effect in the central nervous system. Our previous work revealed a stress-resilient phenotype and a potentiation of short-term fear extinction in a congenic rat model deficient for DPP4 activity (DPP4mut). Here, we investigated neuroendocrine mechanisms underlying the phenotype of the DPP4mut animals. We studied the function of the hypothalamus-pituitary-adrenal (HPA) axis including the expression levels of its key genes and explored the possibility of structural NPY system changes. METHODS AND RESULTS: We find decreased expression of Nr3c1 (glucocorticoid receptor - GR) and Fkbp5 (FK506 binding protein 5) in the amygdala and the hypothalamus of the DPP4mut rats, as well as the lower stress-induced peripheral corticosterone (CORT) levels. We detect no significant alterations in basal and DEX-induced CORT levels in the DPP4mut animals. The abundance of NPY-ergic neurons in the basolateral amygdala, dentate gyrus and hippocampus did not differ between the DPP4mut and their wild type littermates. CONCLUSION: DPP4mut rats show blunted CORT response in line with their lower behavioral stress-response profile. These results are consistent with the hypothesis that increased central NPY levels elevate the threshold of stress response. We suggest that changes in the expression levels of key HPA axis genes (Nr3c1 and Fkbp5) are a consequence of the altered stress-perception of DPP4mut animals, thus further contributing to the stress-resilient phenotype.

Novel role of NPY in neuroimmune interaction and lung growth after intrauterine growth restriction.

Individuals with intrauterine growth restriction (IUGR) are at risk for chronic lung disease. Using a rat model, we showed in our previous studies that altered lung structure is related to IL-6/STAT3 signaling. As neuropeptide Y (NPY), a coneurotransmitter of the sympathetic nervous system, regulates proliferation and immune response, we hypothesized that dysregulated NPY after IUGR is linked to IL-6, impaired myofibroblast function, and alveolar growth. IUGR was induced in rats by isocaloric low-protein diet; lungs were analyzed on embryonic day (E) 21, postnatal day (P) 3, P12, and P23. Finally, primary neonatal lung myofibroblasts (pnF) and murine embryonic fibroblasts (MEF) were used to assess proliferation, apoptosis, migration, and IL-6 expression. At E21, NPY and IL-6 expression was decreased, and AKT/PKC and STAT3/AMPKα signaling was reduced. Early reduction of NPY/IL-6 was associated with increased chord length in lungs after IUGR at P3, indicating reduced alveolar formation. At P23, however, IUGR rats exhibited a catch-up of body weight and alveolar growth coupled with more proliferating myofibroblasts. These structural findings after IUGR were linked to activated NPY/PKC, IL-6/AMPKα signaling. Complementary, IUGR-pnF showed increased survival, impaired migration, and reduced IL-6 compared with control-pnF (Co-pnF). In contrast, NPY induced proliferation, migration, and increased IL-6 synthesis in fibroblasts. Additionally, NPY-/- mice showed reduced IL-6 signaling and less proliferation of lung fibroblasts. Our study presents a novel role of NPY during alveolarization: NPY regulates 1) IL-6 and lung STAT3/AMPKα signaling, and 2) proliferation and migration of myofibroblasts. These new insights in pulmonary neuroimmune interaction offer potential strategies to enable lung growth.

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 Ca²âº channels and descending monoaminergic projections. Altogether, available data currently suggest both, a therapeutic as well as an abuse potential.

Altered hypothalamic protein expression in a rat model of Huntington's disease.

Huntington's disease (HD) is a neurodegenerative disorder, which is characterized by progressive motor impairment and cognitive alterations. Changes in energy metabolism, neuroendocrine function, body weight, euglycemia, appetite function, and circadian rhythm can also occur. It is likely that the locus of these alterations is the hypothalamus. We used the HD transgenic (tg) rat model bearing 51 CAG repeats, which exhibits similar HD symptomology as HD patients to investigate hypothalamic function. We conducted detailed hypothalamic proteome analyses and also measured circulating levels of various metabolic hormones and lipids in pre-symptomatic and symptomatic animals. Our results demonstrate that there are significant alterations in HD rat hypothalamic protein expression such as glial fibrillary acidic protein (GFAP), heat shock protein-70, the oxidative damage protein glutathione peroxidase (Gpx4), glycogen synthase1 (Gys1) and the lipid synthesis enzyme acylglycerol-3-phosphate O-acyltransferase 1 (Agpat1). In addition, there are significant alterations in various circulating metabolic hormones and lipids in pre-symptomatic animals including, insulin, leptin, triglycerides and HDL, before any motor or cognitive alterations are apparent. These early metabolic and lipid alterations are likely prodromal signs of hypothalamic dysfunction. Gaining a greater understanding of the hypothalamic and metabolic alterations that occur in HD, could lead to the development of novel therapeutics for early interventional treatment of HD.

Generalization of contextual fear depends on associative rather than non-associative memory components.

Posttraumatic stress disorder (PTSD) is characterized by the presence of three major symptom clusters: persistent fear memories, hyperarousal, and avoidance. With a passage of time after the trauma, PTSD patients show an increase in unspecific fear and avoidance, a phenomenon termed "fear generalization". It is not clear whether fear generalization arises from the time-dependent growth of hyperarousal or changes in associative fear. The present study investigated behavioral and neuroanatomical correlates of non-associative and associative fear memory one week vs. one month after a trauma in a mouse model of PTSD with immediate vs. delayed foot shock application. The immediate shock procedure led to a lower contextual fear, but did not influence the hyperarousal (i.e. increased acoustic startle responses) assessed within the first week after the trauma. Only delayed shocked mice demonstrated generalization of contextual fear and an increase in generalized avoidance behavior, with no changes in hyperarousal one month after trauma. We observed the same increase in c-Fos expression following delayed and immediate shock presentation within the lateral, basolateral, central amygdala and CA1, CA3 and dentate gyrus of hippocampus, suggesting that all of these structures contribute to the development of hyperarousal. Only basolateral amygdala and dentate gyrus appeared to be additionally involved in encoding of contextual information. In summary, our results demonstrate the independence of associative and non-associative trauma-related fear. They support the hypothesis that generalized fear emerges in consequence of forgetting specific stimulus attributes associated with the shock context.

Behavioral and in vivo electrophysiological evidence for presymptomatic alteration of prefrontostriatal processing in the transgenic rat model for huntington disease.

Cognitive decline precedes motor symptoms in Huntington disease (HD). A transgenic rat model for HD carrying only 51 CAG repeats recapitulates the late-onset HD phenotype. Here, we assessed prefrontostriatal function in this model through both behavioral and electrophysiological assays. Behavioral examination consisted in a temporal bisection task within a supra-second range (2 vs.8 s), which is thought to involve prefrontostriatal networks. In two independent experiments, the behavioral analysis revealed poorer temporal sensitivity as early as 4 months of age, well before detection of overt motor deficits. At a later symptomatic age, animals were impaired in their temporal discriminative behavior. In vivo recording of field potentials in the dorsomedial striatum evoked by stimulation of the prelimbic cortex were studied in 4- to 5-month-old rats. Input/output curves, paired-pulse function, and plasticity induced by theta-burst stimulation (TBS) were assessed. Results showed an altered plasticity, with higher paired-pulse facilitation, enhanced short-term depression, as well as stronger long-term potentiation after TBS in homozygous transgenic rats. Results from the heterozygous animals mostly fell between wild-type and homozygous transgenic rats. Our results suggest that normal plasticity in prefrontostriatal circuits may be necessary for reliable and precise timing behavior. Furthermore, the present study provides the first behavioral and electrophysiological evidence of a presymptomatic alteration of prefrontostriatal processing in an animal model for Huntington disease and suggests that supra-second timing may be the earliest cognitive dysfunction in HD.

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.

Increased numbers of motor activity peaks during light cycle are associated with reductions in adrenergic alpha(2)-receptor levels in a transgenic Huntington's disease rat model.

Huntington's disease (HD) is a neurodegenerative disorder caused by a CAG repeat expansion in the HD gene. Besides psychiatric, motor and cognitive symptoms, HD patients suffer from sleep disturbances. In order to screen a rat model transgenic for HD (tgHD rats) for sleep-wake cycle dysregulation, we monitored their circadian activity peaks in the present study. TgHD rats of both sexes showed hyperactivity during the dark cycle and more frequent light cycle activity peaks indicative for a disturbed sleep-wake cycle. Focusing on males at the age of 4 and 14 months, analyses of receptor levels in the hypothalamus and the basal forebrain revealed that 5-HT(2A)- and adrenergic alpha(2)-receptor densities in these regions were significantly altered in tgHD rats compared to their wild-type littermates. Adrenergic receptor densities correlated negatively with the light cycle hyperactivity peaks at later stages of the disease in male tgHD rats. Furthermore, reduced leptin levels, a feature associated with circadian misalignment, were present. Our study demonstrates that the male tgHD rat is a suitable model to investigate HD associated sleep alterations. Further studies are warranted to elucidate the role of adrenergic- and 5-HT(2A)-receptors as therapeutic targets for dysregulation of the circadian activity in HD.

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.