André Rex

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.

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.

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.

Anxiolytic action of diazepam and abecarnil in a modified open field test.

The effects of acutely administered diazepam and the beta-carboline abecarnil were examined in two animal models of anxiety in rats, and for their effects on food intake and locomotor activity. In the elevated x-maze diazepam (0.6-2.5 mg/kg) and abecarnil (0.03-0.3 mg/kg) induced anxiolytic-like effects. The second paradigm is based upon the suppression of feeding by exposure to a novel environment, adapted from Bodnoff et al. (1989). Food-deprived rats were placed in a corner of the open field containing food in the centre. The number of rats beginning to eat in the first 5 min was recorded. Diazepam (2.5-5.0 mg/kg) and abecarnil (0.01-0.3 mg/kg) increased the number of rats eating. Flumazenil, the benzodiazepine antagonist, was without effect, but antagonised the effects of diazepam and abecarnil. In a seperate series of experiments the effects of diazepam and abecarnil on feeding and locomotor activity were excluded as having influenced the the anxiolytic effects of these compounds in the animal models of anxiety.

Behavioral and neurochemical differences between Fischer 344 and Harlan-Wistar rats raised identically.

Inbred Fisher 344 and outbred Harlan–Wistar rats were compared in the elevated plus maze, the black-and-white box, the social interaction test, and a modified open-field test, to assess the contribution of genetic factors to aversion-motivated behavior. All animals used were born and raised under identical conditions. Compared to the Wistar rats, the Fischer rats displayed a more pronounced fearful behavior in all tests. In a separate microdialysis study, the relationship between behavioral variations to biochemical differences was assessed, with serotonin (5-HT) release in the ventral hippocampus being measured during the elevated plus-maze test. Exposure to the elevated plus-maze induced an increase in hippocampal 5-HT in the (more anxious) Fischer rats but not in the (less anxious) Wistar rats. The results confirm the influence of genetic factors on emotionality in rats and demonstrate a close, although not simple, relationship between the serotonergic system and “anxiety-related” behavior.

Anxiety but not arousal increases 5‐hydroxytryptamine release in the rat ventral hippocampus in vivo

Central serotonin [5‐hydroxytryptamine (5‐HT)] is involved in the aetiology of numerous disease states, including depression and anxiety disorders. Studies have shown that exposure of rats to animal tests of anxiety increases extracellular 5‐HT in the cortex or hippocampus determined by in vivo microdialysis. To discriminate whether this increase is caused by the aversive conditions of an animal test for anxiety or by an unconditioned stressor evoking mainly arousal, the present study investigates the effects of an unconditioned acoustic stimulus and exposure to the elevated plus maze (X‐maze), respectively, on the release of 5‐HT in the ventral hippocampus compared with hippocampal 5‐HT release in the home cage and in a non‐aversive unfamiliar environment in freely moving rats. Our results showed a distinct pattern of 5‐HT release in the ventral hippocampus depending on the stimulus used. Exposure to the X‐maze for 20 min was accompanied by an ‘anxious’ behaviour in the rats and increased extracellular 5‐HT to 165% of basal release, whereas exposure to a less aversive ‘deactivated’ plus maze (115 ± 6%) or to white noise for 20 min in the familiar surroundings of the home cage (98 ± 6%) did not change hippocampal 5‐HT release significantly, despite similar behavioural activation indicated by increased locomotor activity. While both the X‐maze and white noise may model anxiety and stress to a certain extent, it seems that the X‐maze is more aversive. The results suggest a close relationship between anxiety‐related behaviour, but not arousal/non‐specific behavioural activation, and 5‐HT release in the ventral hippocampus.

Feeding and 8-OH-DPAT-related release of serotonin in the rat lateral hypothalamus.

Based on the different effects of somatodendritic 5-HT1A agonist 8-OH-DPAT on food intake whether given to food-deprived rats or freely feeding rats, we hypothesized that the effects of 8-OH-DPAT on extracellular serotonin (5-HT) in the lateral hypothalamus (LH) will interfere with different feeding states, eventually resulting in different patterns of 5-HT release. In a microdialysis study we measured extracellular 5-HT in the LH after 8-OH-DPAT under four experimental conditions, i.e., in freely feeding rats with no food available, freely feeding rats with access to food, in food-deprived rats with no food available, and in food-deprived rats with good available after treatment. The results show a significant decrease of 5-HT release after 300 microg/kg 8-OH-DPAT (i.p.) in freely feeding rats. This effect is not seen when food is provided after drug treatment. In contrast, the same dose of 8-OH-DPAT has no effect on 5-HT release in food-deprived rats. In addition, providing food after drug treatment does not change the release pattern significantly in food-deprived rats, suggesting more complexity in the underlying mechanisms. The present study describes the effects of 8-OH-DPAT on 5-HT release in the LH, depending on feeding conditions and feeding-related behavioral states.

Brain angiotensin and anxiety-related behavior: The transgenic rat TGR(ASrAOGEN)680

The transgenic rat TGR(ASrAOGEN)680, characterized by a transgene-producing antisense RNA against angiotensinogen in the brain, provides an opportunity to study the behavioral effects of angiotensin. While exposed to the elevated plus-maze (EPM) and the light/dark box, TGR(ASrAOGEN)680 rats showed more signs of anxiety compared to parental Sprague-Dawley (SD) rats. In the EPM, they made fewer entries into the open arms, spent less time there and more time on the closed arms. Head dips were reduced and U-turns were increased. In the light/dark box, the latency to the first re-entry into the light compartment was higher in TGR(ASrAOGEN)680. They displayed more SAP out from the dark and a reduced number of transitions between the two compartments. In the social interaction test, active social contacts were reduced, further suggesting an anxious phenotype. Although there was no transgenic effect on distance traveled in the open field, the more anxious TGR(ASrAOGEN)680 spent less time in the inner zone. Self-grooming was increased in TGR(ASrAOGEN)680 during exposure to the EPM and the open field, but was decreased in the social interaction test. In TGR(ASrAOGEN)680, tissue content of 5-HT and its metabolite 5-HIAA was lower in the hippocampus, frontal, and parietal cortex. HIAA and 5-HIAA/5-HT ratios were reduced in the hypothalamus, striatum, and septum. In the open field, the anxiogenic effect of the 5-HT2C/1B receptor agonist mCPP (0.5-1 mg/kg IP) was more pronounced in TGR(ASrAOGEN)680. The data suggest an anxious phenotype in rats with low brain angiotensinogen, possibly related to secondary dysfunctions of the brain serotonergic system.

Antidepressant-like effect of nicotinamide adenine dinucleotide in the forced swim test in rats

Nicotinamide adenine dinucleotide (NADH), a cosubstrate for energy transfer in the oxidative phosphorylation, has supposedly beneficial effects on central nervous system (CNS)-related diseases, e.g., shown in an open study with depressive patients. To our knowledge there are no data concerning the efficacy of NADH in animal tests. Acute effects of NADH and the precursor nicotinamide, compared to controls and the antidepressants desipramine and fluoxetine, were examined in the forced swim test (FST) in Wistar rats. NADH, but not nicotinamide, reduced immobility and increased swimming behaviour in the FST, with a minimum effective dose of 5 mg/kg. NADH-induced behavioural profile was similar to fluoxetine, but different from desipramine. Since NADH did not induce hyperlocomotion but even decreased motor activity in the open field test, the antidepressant-like effect cannot be attributed to an increase in motor activity. These data support an antidepressant potential of NADH.