Heidrun Fink

Perinatal elevation of hypothalamic insulin, acquired malformation of hypothalamic galaninergic neurons, and syndrome X-like alterations in adulthood of neonatally overfed rats

Overnutrition during critical developmental periods is suggested to be a risk factor for obesity and associated metabolic disorders in later life. Underlying mechanisms are unknown. Neuropeptides are essentially involved in the central nervous regulation of body weight. For instance, hypothalamic galanin (GAL) is a stimulator of food intake and body weight gain. To investigate long-term consequences of early postnatal overfeeding, the normal litter size of Wistar rats (n=10; controls) was reduced from day 3 to day 21 of life to only 3 pups per mother (small litters, SL; overnutrition). Throughout life, SL rats displayed hyperphagia (p<0.01), overweight (p<0.0001), hyperinsulinemia (p<0.01), impaired glucose tolerance (p<0.001), elevated triglycerides (p<0.001), and an increased systolic blood pressure (p<0.05). In adulthood, an increase of GAL-neurons in the arcuate hypothalamic nucleus (ARC) was found (p<0.001), positively correlated to body weight (p<0.001). A second experiment revealed hyperinsulinemia (p<0.001) and increased hypothalamic insulin levels (p<0.05) in SL rats during early postnatal life. Already on day 21 of life, i.e., at the end of the critical hypothalamic differentiation period, in SL rats the number of GAL-neurons was increased in the ARC (p<0.001), showing a positive correlation to body weight and insulin (p<0.05). In conclusion, neonatally acquired persisting malformation of hypothalamic galaninergic neurons, induced by early overfeeding and hyperinsulinism, might promote the development of overweight and syndrome X-like alterations during life.

Intracellular Serotonin Modulates Insulin Secretion from Pancreatic β-Cells by Protein Serotonylation

Non-neuronal, peripheral serotonin deficiency causes diabetes mellitus and identifies an intracellular role for serotonin in the regulation of insulin secretion.

Exaggerated aggression and decreased anxiety in mice deficient in brain serotonin

Serotonin is a major neurotransmitter in the central nervous system (CNS). Dysregulation of serotonin transmission in the CNS is reported to be related to different psychiatric disorders in humans including depression, impulsive aggression and anxiety disorders. The most frequently prescribed antidepressants and anxiolytics target the serotonergic system. However, these drugs are not effective in 20–30% of cases. The causes of this failure as well as the molecular mechanisms involved in the origin of psychological disorders are poorly understood. Biosynthesis of serotonin in the CNS is initiated by tryptophan hydroxylase 2 (TPH2). In this study, we used Tph2-deficient (Tph2−/−) mice to evaluate the impact of serotonin depletion in the brain on mouse behavior. Tph2−/− mice exhibited increased depression-like behavior in the forced swim test but not in the tail suspension test. In addition, they showed decreased anxiety-like behavior in three different paradigms: elevated plus maze, marble burying and novelty-suppressed feeding tests. These phenotypes were accompanied by strong aggressiveness observed in the resident–intruder paradigm. Despite carrying only one copy of the gene, heterozygous Tph2+/− mice showed only 10% reduction in brain serotonin, which was not sufficient to modulate behavior in the tested paradigms. Our findings provide unequivocal evidence on the pivotal role of central serotonin in anxiety and aggression.

Strain differences in fear-motivated behavior of rats

Studies have shown different and sometimes contradictory results in response to anxiolytic drugs. In the present study, the behavioral performance of rat strains, obtained from different breeders, was examined in four animal models of anxiety- or in exploration-related behavior to assess the potential contribution of genetic disposition or breeding factors to aversion-motivated behavior. Male rats: Wistar/Winkelmann, Wistar/Charles River, Wistar/BGVV, Lewis/Charles River, Fischer/Charles River, Brown Norway/Charles River were used in a conflict test in the open field, a free exploratory paradigm, social interaction test, and the holeboard test. The results show that robust behavioral differences in anxiety or exploration exist between different strains of rats and animals of one strain, obtained from different breeders. The differences shown in anxiety-related behavior might explain sometimes contradictory effects following the treatment with anxiolytic or anxiogenic drugs. The results indicate that genetic factors and breeding conditions substantially contribute to anxiety-motivated behaviors in animal models of anxiety. These differences in anxiety-related behavior may also be related to biochemical differences.

Effect of diazepam on cortical 5-HT release and behaviour in the guinea-pig on exposure to the elevated plus maze

Previous studies have used the elevated plus maze to test for “anxiolytic” drugs in rats. The present study demonstrates that guinea-pigs handled daily from birth exhibit similar behaviour to rats on the plus maze. Pretreatment with diazepam (1.0 mg/kg) significantly increased the time the animals spent in the open arms and amount of entries into the open arms. Using intra-cortical microdialysis on exposure of the guinea-pig to the elevated plus maze resulted in increased extracellular 5-HT in the frontal cortex. Diazepam reduced, but not significantly, the increase in extracellular 5-HT and produced an “anxiolytic” profile of behaviour. Pretreatment with the benzodiazepine antagonist flumazenil (10.0 mg/kg) fully antagonised the behavioural effects of diazepam. Flumazenil also reduced the effect of diazepam on the increase in extracellular 5-HT observed on exposure of the guinea-pig to the elevated plus maze. Flumazenil alone decreased basal extracellular cortical 5-HT but had no effect on behaviour in the elevated plus maze. The results show that an increase in extracellular 5-HT occurs in the guinea-pig exposed to aversive conditions. While it remains to be determined whether the “anxiolytic” effects of diazepam in the guinea-pig are causally associated with decreased extracellular 5-HT, it is of interest that the selective benzodiazepine antagonist also prevented the increase in basal extracellular 5-HT produced by the exposure to the elevated plus maze but had no effect on behaviour. Results indicate that there is no simple relationship between inhibition of 5-HT release and the “anxiolytic” action of benzodiazepines.

Major biological actions of CCK – a critical evaluation of research findings

Abstract Cholecystokinin (CCK) is one of the first discovered gastrointestinal hormones and one of the most abundant neuropeptides in the brain. Two types of CCK receptors have been identified: (1) CCK-A receptors are mainly located in the periphery, but are also found in some areas of the CNS; and (2) CCK-B receptors are widely distributed in the brain. Major biological actions of CCK are the reduction of food intake and the induction of anxiety-related behavior. Inhibition of feeding is mainly mediated by the A-type receptors, whereas anxiety-like behavior is induced by stimulating B-type receptors. This paper presents new findings on the effects of the biologically active CCK agonists, CCK-8S, CCK-4, and A71378. The results reviewed suggest that the hypophagic effects of CCK are strongly dependent on the experimental design, sex, and age of the rats. For example, food intake measured during the night or after food deprivation is reduced by CCK-8S in young adult and aged rats, whereas, under fixed feeding conditions, CCK-8S does not inhibit food intake in young adult rats. The sensitivity to the hypophagic CCK effect increases with age in male and female rats; however, female rats are less sensitive to the CCK action. Further, using a nongenetic and non-stressful model of obesity due to unspecific postnatal overfeeding, the satiating effect of moderate CCK-8S doses is weaker in obese than in normal rats. Again, the hypophagic effect is more pronounced in male than in female obese and normal rats. Considering that aversive reactions in rats are markedly influenced by strain and breeding-line variations, research results in this area are critically reviewed. It is shown that anxiety-like symptoms can only be induced by a selectively acting CCK-B agonist, whereas mixed CCK-A and -B agonists and selective CCK-A agonists fail to change behavior in anxiety tests. CCK-4 induces stable and reproducible anxiogenic-like behavior only in certain rat strains. Moreover, CCK-4 effects can be demonstrated in the conflict test, in the ultrasonic vocalization test in rat pups, on the elevated plus maze, and in the black and white box, but not in the social interaction test. CCK has also been reported to modulate memory processes. On the one hand, CCK-8S and CCK-4 enhanced habituation to the novelty of a hole board. On the other hand, repeated administration of CCK-8S did not improve maze performance in aged rats. The literature on the behavioral pharmacology of CCK is rife with inconsistency and contradiction. The major biological actions of CCK depend on the receptor selectivity of the CCK fragments used and on organismic and procedural variables. All these variables potentially influence behavioral responses in rats. Therefore, in CCK research more attention should be paid to the importance of these methodological factors.

Clozapine: a serotonin antagonist?

The effect of clozapine on the central serotonergic transmission system was studied by investigation of open-field motility of rats after microinjection of drugs into nucleus accumbens and median raphe nucleus. Previous work has shown that LSD in low doses potentiates apomorphine-induced hypermotility and that this LSD effect is induced by a serotonin agonist action in median raphe nucleus. Clozapine, injected into median raphe nucleus (0.05 micrograms), suppressed the LSD effect in the same manner as serotonin antagonists did. Since alpha-adrenergic drugs, injected into median raphe nucleus, caused locomotor stimulant effects, an alpha- adrenalytic action of clozapine was excluded. Clozapine, injected into nucleus accumbens (0.2 micrograms), increased apomorphine-induced hypermotility, whereas the dopamine antagonist haloperidol suppressed it. Our results suggest a serotonin antagonist action of clozapine.

Anxiolytic-like effects of kava-kava in the elevated plus maze test--a comparison with diazepam.

Kava-Kava, a drug derived from a traditional psychoactive beverage used in the South Pacific, is known for tranquilizing and anxiolytic effects. Extracts made from the roots of the Kava plant (Piper methysticum G. Forster) have anxiolytic and mild sedative effects in man. To our knowledge, there are only few data concerning the efficacy of Kava-Kava in animal tests of anxiety. This study was carried out to compare the anxiolytic potential of Kava-Kava extract LI 150 with diazepam. Acute effects of diazepam and a Kava-Kava preparation, compared to their respective controls, were examined in Wistar rats using the elevated plus maze (X-maze). The time spent on open arms, the percentage of open-arm visits and parameters describing the risk assessment were evaluated. LI 150 (120-240 mg/kg p.o.) affected the behaviour measured in the X-maze test, inducing an anxiolytic like behaviour similar to diazepam (15 mg/kg p.o.). These data support the use of Kava-Kava in the treatment of anxiety.

Effects of cholecystokinin tetrapeptide and sulfated cholecystokinin octapeptide in rat models of anxiety

The effects of the acutely administered cholecystokinin (CCK) agonists CCK tetrapeptide (BOC-CCK-4) and sulfated CCK octapeptide (CCK-8S) were examined in four animal models of anxiety in rats. In the elevated plus maze, BOC-CCK-4 reduced the time spent in the open arms and the number of entries into the open arms. BOC-CCK-4 but not the anorectic acting CCK-8S increased the suppression of feeding in a conflict paradigm based on novelty suppressed feeding in hungry rats. In the two-compartment black-and-white box, BOC-CCK-4 decreased the time spent and locomotor activity in the white compartment. In the ultrasound vocalization test, using rat pups separated from the mother, BOC-CCK-4 increased the number of distress calls. No evidence was found for inducing anxiety-like behaviour by CCK-8S.

Fischer 344 and wistar rats differ in anxiety and habituation but not in water maze performance.

The fact that various neuropharmacological substances have anxiolytic as well as amnesic effects suggests that neuronal mechanisms of anxiety and learning/memory closely interact. Hence, we hypothesized that differences in anxiety-related behavior could be accompanied with differences in cognition or habituation. Two rat strains with different levels of anxiety, more anxious Fischer 344 rats by Charles River (FC) and less anxious Wistar rats by Winkelmann (WW), were tested in the Morris water maze task and an open field test for habituation learning. Additionally, we investigated the effect of different light intensities on the performance in the Morris water maze and the elevated plus maze. The results of the water maze task indicate that differences in anxiety-related behavior do not go along with differences in this performance of learning/memory. Moreover, the test was not affected by different light intensities. In contrast, illumination did affect performance in the elevated plus maze test, wherein dim light provoked an anxiolytic effect in both rat strains. The findings that neither different baseline levels of anxiety nor fear modulating light conditions were accompanied by changes in the performance of rats in the Morris water maze led us to the suggestion that there is no connection between anxiety and learning/memory in this task. Contrarily, anxiety might be associated with habituation learning in the open field test, shown by the superior habituation of the anxious FC rats in comparison to the less anxious WW rats. In sum, these results indicate that anxiety and learning/memory seem to be independently regulated behaviors, whereas habituation might be more closely correlated with anxiety. Nevertheless, a general statement about the relation between emotionality and learning/memory mechanisms would be premature and the link between behaviors remains to be clarified.