Biomedical subjects

Tim Karl

Publications and source records attributed to Tim Karl.

12 recordsLinked to original sources

PubMed2007

Neuropeptide Y (NPY) cleaving enzymes: structural and functional homologues of dipeptidyl peptidase 4.

N-terminal truncation of NPY has important physiological consequences, because the truncated peptides lose their capability to activate the Y1-receptor. The sources of N-terminally truncated NPY and related peptides are unknown and several proline specific peptidases may be involved. First, we therefore provide an overview on the peptidases, belonging to structural and functional homologues of dipeptidyl peptidase 4 (DP4) as well as aminopeptidase P (APP) and thus, represent potential candidates of NPY cleavage in vivo. Second, applying selective inhibitors against DP4, DP8/9 and DP2, respectively, the enzymatic distribution was analyzed in brain extracts from wild type and DP4 deficient F344 rat substrains and human plasma samples in activity studies as well as by matrix assisted laser desorption/ionisation-time of flight (MALDI-TOF)-mass spectrometry. Third, co-transfection of Cos-1 cells with Dpp4 and Npy followed by confocal lasermicroscopy illustrated that hNPY-dsRed1-N1 was transported in large dense core vesicles towards the membrane while rDP4-GFP-C1 was transported primarily in different vesicles thereby providing no clear evidence for co-localization of NPY and DP4. Nevertheless, the review and experimental results of activity and mass spectrometry studies support the notion that at least five peptidases (DP4, DP8, DP9, XPNPEP1, XPNPEP2) are potentially involved in NPY cleavage while the serine protease DP4 (CD26) could be the principal peptidase involved in the N-terminal truncation of NPY. However, DP8 and DP9 are also capable of cleaving NPY, whereas no cleavage could be demonstrated for DP2.

Animals↗

PubMed2006

Behavioral profiling of NPY in aggression and neuropsychiatric diseases.

The abundantly expressed neuropeptide Y (NPY) has potent effects on feeding, body weight, and blood pressure, and exhibits important functions in various behavioral domains such as motor activity and anxiety. The potent neurotransmitter exerts its biological effects through at least five G-protein coupled receptors termed Y(1), Y(2), Y(4), Y(5), and y(6). The behavioral profile of NPY function has been extensively studied using traditional pharmacological and classic genetic animal models. Based on these studies, variations in the profile of NPY and its receptors have been found. To limit the variability and inconsistencies in the behavioral profile of NPY and to clarify its effects on certain domains in further detail, it is important to design a rational standardized strategy for behavioral testing, using a complement of different well-established and reproducible tests. This strategy can minimize the risk that false positive or false negative results lead to a contradictory and inconsistent behavioral characterization of NPY function. Ideally, such screening should be composed of an initial monitoring of general health, sensory functions, and motor abilities, before specific behavioral domains such as anxiety or aggression are investigated using a multi-tiered phenotyping approach. In this review, we will focus on a brief description of the latest insights into the behavioral profile of NPY in the selective lesser investigated domains such as aggression and depression-schizophrenia-related behaviors. We will combine this information with possible strategies to evaluate the different specific phenotypes in more detail.

Aggression↗

PubMed2006

Effects of chronic risperidone treatment on the striatal protein profiles in rats.

Extrapyramidal symptoms (EPS) commonly occur as side effects of antipsychotic drugs (APDs) and are most likely to arise when the occupancy of dopamine D(2) receptors in the striatum by these drugs exceeds 80%. We aimed to characterize changes in the protein expression profile in the striatum of rats after chronic (4 week) supra-therapeutic (EPS-inducing) treatment with risperidone (RIS), an atypical antipsychotic drug. Administration of RIS (2.1 mg/kg/day, via subcutaneous osmotic minipumps) induced significant vacuous chewing movements and catalepsy in male Sprague-Dawley rats over a 28-day treatment period compared with a vehicle (VEH) control group (n=12) (Karl et al., unpublished observation). Using two-dimensional gel electrophoresis (2DE), total protein extracts from the rat brain striatum were separated and protein expression was analyzed by Phoretix 2D Expression and Image Beta V4.02 software followed by matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). 2DE gels resolved up to 450 protein spots, presumably different proteins and/or their isoforms. There were 30 protein spots showing statistically significant different densities between the RIS- and VEH-treated groups. All 30 proteins were successfully identified by MALDI-TOF MS, 28 of these were divided into groups based on their known functions. These included metabolic, signaling, transport, protein metabolism, chaperone, DNA binding and cell cycle categories. We conclude that chronic risperidone treatment accompanied by an EPS-like behavioral phenotype results in alterations in the striatal protein profile possibly subsequent to blockade of dopaminergic systems. These results suggest that possible mechanisms involved in APD-induced EPS include metabolic dysfunction and oxidative stress.

Analysis of Variance↗

PubMed2006

Distinct endocrine effects of chronic haloperidol or risperidone administration in male rats.

Antipsychotic drugs have been used effectively for the treatment of schizophrenia symptoms, but they are often associated with metabolic side effects such as weight gain and endocrine disruptions. To investigate the possible mechanisms of antipsychotic-induced metabolic effects, we studied the impact of chronic administration of a typical antipsychotic drug (haloperidol) and an atypical antipsychotic (risperidone) to male rats on food intake, body weight, adiposity, and the circulating concentrations of hormones and metabolites that can influence energy homeostasis. Chronic (28days) haloperidol administration had no effect on food intake, weight gain or adiposity in male rats, whereas risperidone treatment resulted in a transient reduction in food intake and significantly reduced body weight gain compared to vehicle-treated control rats. Whereas neither antipsychotic had any effect on serum lipid profiles, glucose tolerance or the circulating concentrations of hormones controlled by the hypothalamo-pituitary-thyroid (free T4), -adrenal (corticosterone), -somatotropic (IGF-1), or -gonadotropic axes (testosterone), haloperidol increased circulating insulin levels and risperidone increased serum glucagon levels. This finding suggests that haloperidol or risperidone induce distinct metabolic effects. Since metabolic disorders such as obesity and type 2 diabetes mellitus represent serious health issues, understanding antipsychotic-induced endocrine and metabolic effects may ultimately allow better control of these side effects.

Adipose Tissue↗

PubMed2006

Behavioural effects of chronic haloperidol and risperidone treatment in rats.

The therapeutic properties of typical antipsychotic drugs (APDs) such as haloperidol in schizophrenia treatment are mainly associated with their ability to block dopamine D2 receptors. This blockade is accompanied by side effects such as extrapyramidal symptoms (EPS). Atypical APDs such as risperidone have superior therapeutic efficacy possibly due to their activity at multiple receptors (in particular 5-HT2A receptors). Although the risk of EPS is significantly lower in atypical than in typical APDs, it is not negligible. To investigate and compare the behavioural profile and EPS-asssociated side effects of haloperidol and risperidone APD treatment we applied a multi-tiered, comprehensive behavioural phenotyping approach. Sprague-Dawley rats were treated chronically (28 days) with supratherapeutic EPS-inducing doses of haloperidol and risperidone using osmotic minipumps. Domains such as motor activity, exploration, memory, and anxiety were analysed together with EPS assessment ("early onset" vacuous chewing movements and catalepsy). Both APDs produced diminished motor activity and exploration, impaired working memory performances, and increased anxiety levels. These effects were more pronounced in haloperidol-treated animals. Chronic APD treatment also caused a time-course dependent elevation of EPS-like symptoms. Risperidone-treated animals showed a catalepsy-like phenotype, which differed to that of haloperidol-treated rats, indicating that processes other than the anticipated dopaminergic mechanisms are underlying this phenomenon. These EPS-related phenotypes are consistent with reported EPS-inducing D2 receptor occupancies of around 80%. Differences in the behavioural profile of haloperidol and risperidone, which were revealed by a comprehensive phenotyping strategy, are likely due to the unique receptor activation profiles of these APDs.

Animals↗

PubMed2006

Y2Y4 receptor double knockout protects against obesity due to a high-fat diet or Y1 receptor deficiency in mice.

Neuropeptide Y receptors are critical regulators of energy homeostasis, but the functional interactions and relative contributions of Y receptors and the environment in this process are unknown. We measured the effects of an ad libitum diet of normal or high-fat food on energy balance in mice with single, double, or triple deficiencies of Y1, Y2, or Y4 receptors. Whereas wild-type mice developed diet-induced obesity, Y2Y4 double knockouts did not. In contrast, Y1 knockout or Y1Y2 or Y1Y4 receptor double knockout mice developed an exacerbated diet-induced obesity syndrome. Remarkably, the antiobesity effect of Y2Y4 deficiency was stronger than the obesogenic effect of Y1 deficiency, since Y1Y2Y4 triple knockouts did not develop obesity on the high-fat diet. Resistance to diet-induced obesity in Y2Y4 knockouts was associated with reduced food intake and improved glucose tolerance in the absence of changes in total physical activity. Fecal concentration of free fatty acids was significantly increased in Y2Y4 knockouts in association with a significantly reduced bile acid pool and marked alterations in intestinal morphology. In addition, hypothalamic proopiomelanocortin expression was decreased in diet-induced obesity (in both wild-type and Y1 receptor knockout mice) but not in obesity-resistant Y2Y4 receptor knockout mice fed a high-fat diet. Therefore, deletion of Y2 and Y4 receptors synergistically protects against diet-induced obesity, at least partially via changes in food intake and hypothalamic proopiomelanocortin expression.

Animals↗

PubMed2005

Effect of Y1 receptor deficiency on motor activity, exploration, and anxiety.

Neuropeptide Y (NPY) in the CNS plays an important regulatory role in anxiety-related responses as exogenous administration of NPY exerts an anxiolytic-like effect in rodents. This effect is believed to be mediated by the Y(1) receptor system as pharmacological modulation of this Y(1) receptor system results in an increase in anxiety. Here we present a comprehensive phenotyping strategy for characterizing Y(1) receptor knockout animals at different times of the circadian rhythm using several motor activity-, exploration-, and anxiety-related behavioural tasks including open field, elevated plus maze, light-dark, and hole board test. We show that Y(1) deficiency has an important effect on motor activity and explorative-like behaviours and that it results in marked alterations in anxiety-related behaviours. Importantly, the behavioural phenotype of the Y(1) receptor knockout mice is circadian rhythm-dependent and also influenced by stimuli such as restraint stress. In addition, we found evidence for increases in working memory. Taken together, these findings suggest an important role of Y(1) receptors in the regulation of motor activity, exploration, and anxiety-related behaviours. This role is also influenced by several factors such as circadian rhythm and stress exposure confirming the importance of a comprehensive strategy and of using genetic animal models in behavioural neuroscience.

Analysis of Variance↗

PubMed2004

Y1 receptors regulate aggressive behavior by modulating serotonin pathways.

Neuropeptide Y (NPY) is pivotal in the coordinated regulation of food intake, growth, and reproduction, ensuring that procreation and growth occur only when food is abundant and allowing for energy conservation when food is scant. Although emotional and behavioral responses from the higher brain are known to be involved in all of these functions, understanding of the coordinated regulation of emotion/behavior and physiological functions is lacking. Here, we show that the NPY system plays a central role in this process because ablation of the Y1 receptor gene leads to a strong increase in territorial aggressive behavior. After exposure to the resident-intruder test, expression of c-fos mRNA in Y1-knockout mice is significantly increased in the medial amygdala, consistent with the activation of centers known to be important in regulating aggressive behavior. Expression of the serotonin [5-hydroxytryptamine (5-HT)] synthesis enzyme tryptophan hydroxylase is significantly reduced in Y1-deficient mice. Importantly, treatment with a 5-HT-1A agonist, (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin hydrobromide, abolished the aggressive behavior in Y1-knockout mice. These results suggest that NPY acting through Y1 receptors regulates the 5-HT system, thereby coordinately linking physiological survival mechanisms such as food intake with enabling territorial aggressive behavior.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed2003

Localization, transmission, spontaneous mutations, and variation of function of the Dpp4 (Dipeptidyl-peptidase IV; CD26) gene in rats.

Dipeptidyl-peptidase IV (DPPIV) is involved in endocrine and immune functions via cleavage of regulatory peptides with a N-terminal proline or alanine such as incretins, neuropeptide Y, or several chemokines. So far no systematic investigations on the localization and transmission of the Dpp4 gene or the natural variations of DPPIV-like enzymatic function in different rat strains have been conducted. Here we mapped the Dpp4 gene to rat chromosome 3 and describe a semi-dominant mode of inheritance for Dpp4 in a mutant F344/DuCrj(DPPIV-) rat substrain lacking endogenous DPPIV-like activity. This mutant F344/DuCrj(DPPIV-) rat substrain constantly exhibits a nearly complete lack of DPPIV-like enzymatic activity, while segregation of DPPIV-like enzymatic activity was observed in another DPPIV-negative F344/Crl(Ger/DPPIV-) rat substrain. Screening of 12 different inbred laboratory rat strains revealed dramatic differences in DPPIV-like activity ranging from 11 mU/microl (LEW/Ztm rats) to 40 mU/microl (BN/Ztm and DA/Ztm rats). A lack of DPPIV-like activity in F344 rats was associated with an improved glucose tolerance and blunted natural killer cell function, which indicates the pleiotropic functional role of DPPIV in vivo. Overall, the variations in DPPIV-like enzymatic activity probably represent important confounding factors in studies using rat models for research on regulatory peptides.

Animals↗

PubMed2003

Extreme reduction of dipeptidyl peptidase IV activity in F344 rat substrains is associated with various behavioral differences.

The enzyme and binding protein dipeptidyl peptidase IV (DPPIV/CD26) has a unique enzymatic specificity in cleaving dipeptides from neuropeptides, chemokines, and hormones. Thus, DPPIV is potentially involved in the regulation of functions of the immune, endocrine, and nervous systems. In the present study, we compared DPPIV-deficient, mutant Japanese [F344/DuCrj(DPPIV-)] and German [F344/Crl(Ger/DPPIV-)] F344 rat substrains with a wild-type-like F344 substrain [F344/Crl(Por)] from the United States in a multitiered strategy using a number of different behavioral tests. General health, neurological and motor functions, and sensory abilities of the different F344 substrains were not different. A reduced body weight and a reduced water consumption were observed in mutant animals. DPPIV-deficient rats exhibited increased pain sensitivity in a non-habituated hot plate test, indicative of a reduced stress-induced analgesia. In line with this finding, reduced stress-like responses in tasks like the open field (OF), social interaction (SI), and passive avoidance test were found. Differences in DPPIV-like activity appear to be involved in neurophysiological processes because DPPIV-deficient animals were less susceptible to the sedative effects of ethanol. The varying phenotypes of the F344 substrains are likely to be mediated by differential degradation of DPPIV substrates such as substance P, glucagon-like peptide (GLP)-1, enterostatin, and especially neuropeptide Y (NPY). Potentially, DPPIV-deficient substrains represent an important tool for biomedical research, focusing on the involvement of DPPIV and its substrates in behavioral and physiological processes.

Analysis of Variance↗

PubMed2003

Behavioral effects of neuropeptide Y in F344 rat substrains with a reduced dipeptidyl-peptidase IV activity.

Dipeptidyl-peptidase IV (DPPIV/CD26) is involved in several physiological functions by cleavage of dipeptides with a Xaa-Pro or Xaa-Ala sequence of regulatory peptides such as neuropeptide Y (NPY). Cleavage of NPY by DPPIV results in NPY(3-36), which lacks affinity for the Y(1) but not for other NPY receptor subtypes. Among other effects, the NPY Y(1) receptor mediates anxiolytic-like effects of NPY. In previous studies with F344 rat substrains lacking endogenous DPPIV-like activity we found a reduced behavioral stress response, which might be due to a differential degradation of NPY. Here we tested this hypothesis and administered intracerebroventricularly two different doses of NPY (0.0, 0.2, 1.0 nmol) in mutant and wildtype-like F344 substrains. NPY dose-dependently stimulated food intake and feeding motivation, decreased motor activity in the plus maze and social interaction test, and exerted anxiolytic-like effects. More important for the present hypothesis, NPY administration was found to be more potent in the DPPIV-negative substrains in exerting anxiolytic-like effects (increased social interaction time in the social interaction test) and sedative-like effects (decreased motor activity in the elevated plus maze). These data demonstrate for the first time a differential potency of NPY in DPPIV-deficient rats and suggest a changed receptor-specificity of NPY, which may result from a differential degradation of NPY in this genetic model of DPPIV deficiency. Overall, these results provide direct evidence that NPY-mediated effects in the central nervous system are modulated by DPPIV-like enzymatic activity.

Animals↗

PubMed2003

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.

Animals↗