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.

"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.

Effects of cholecystokinin octapeptide (CCK-8) on food intake in adult and aged rats under different feeding conditions

The effects of CCK on food intake were investigated under fixed feeding conditions in comparison to a test meal taken after 16 h of food deprivation. The experiments were performed on young adult rats (8 weeks old) as well on aged rats (23 months old). Intraperitoneal CCK-8 (8 and 40 micrograms/kg) significantly reduced the size of a test meal following 16-h food deprivation. This effect was independent of the age of the rats. However, under fixed feeding conditions neither of the doses used in this study reduced food intake in the young adult rats, whereas the highest dose of 40 micrograms/kg did so in the aged rats. These results suggest that the hypophagic effect of exogenous CCK-8 depends on experimental conditions, food intake being reduced after a period of food deprivation but not under a fixed feeding regimen in adult animals. Furthermore, the data suggest that age is a factor contributing to the complex behavioral actions of CCK, because only old animals were more susceptible to an anorectic action of CCK under the fixed feeding schedule. An explanation may lie in an interaction of other known behavioral effects of CCK (e.g., anxiogenic, mnemonic action) with its effects under the different feeding schedules.

Comparison of the satiating effect of the CCKA receptor agonist A71378 with CCK-8S

The satiating effect of the selective cholecystokininA (CCKA) receptor agonist A71378 and the mixed A and B receptor agonist CCK-8S were compared in 24-h food-deprived rats. After systemic application of 1.6, 8.0, and 40 micrograms/kg A71378 or CCK-8S, respectively, food intake was measured for 24 h. During the first hour A71378 and CCK-8S decreased food intake similarly. Two and 4 h after treatment, the satiating effect of A71378 continued. In contrast, 2 h after administration of CCK-8S a slight effect was observed at the highest dose (40 micrograms/kg), which totally disappeared after 4 h. In summary, the effect of A71378 on food intake is longer lasting compared to CCK-8S.

Involvement of 5 -HT1D receptors in cortical extracellular 5-HT release in guinea-pigs on exposure to the elevated plus maze

Previous studies have shown that guinea-pigs handled daily from birth exhibit on exposure to the elevated plus maze similar behaviour to rats and increased cortical extracellular 5-HT determined by in vivo microdialysis. The present study investigates the effects of a non-selective 5-HT(1) agonist 5-carboxamidotryptamine (5-CT) and the 5-HT(1D) antagonist GR 127935 on behaviour and the release of cortical extracellular 5-HT both in a familiar environment and on exposure to the elevated plus maze. In the familiar environment of the home cage GR 127935 (0.3mg/kg i.p.) had no effect on extracellular 5-HT. The non-selective agonist 5-CT (0.1 mg/kg i.p) produced a prolonged decrease (-25%) in cortical 5-HT release, an effect noT antagonized by GR 127935 (0.3mg/kg). Under aversive conditions, exposure to the elevated plus maze, the release of extracellular 5-HT increased (155% of basal release), an effect abolished by 5-CT. Pre-treatment with the selective 5.HT(1D) antagonist GR 127935 antagonized the effect of 5-CT on the aversion-induced increase in extracellular 5-HT on exposure to the elevated plus maze, but did not change the effects of 5-CT on basal 5-HT release. The results suggest that GR 127935 is an effective antagonist at the 5 -HT(1D) terminal autoreceptor in vivo under conditions of increased 5- HT function. Furthermore, the results indicate that the 5-HT( 1D) receptor in the frontal cortex is functionally active under aversive conditions.

Diagnosis of iron deficiency anemia in renal failure patients during the post-erythropoietin era

The purpose of this study was to evaluate the sensitivity and specificity of laboratory methods in the diagnosis of posterythropoietin-era, iron-deficient, chronic renal failure patients. The patient population comprised 25 anemic (hemoglobin < 11 g/dL) patients with creatinine greater than 3 mg/dL; 20 were dialysis patients, two were transplant patients, and three patients had renal failure from other causes. Criteria for study inclusion were as follows: bone marrow iron was the reference standard and was graded 0 to +4, ranging from absent to diffuse homogeneous iron staining; serum ferritin concentration and serum transferrin saturation were tested in terms of sensitivity and specificity. The reference standard indicated that iron deficiency existed in 40% of patients. Neither serum ferritin nor transferrin saturation were completely adequate diagnostic tools. Serum ferritin levels less than 200 ng/dL were 100% specific for the diagnosis but only 41% sensitive. Transferrin saturation of less than 20% was 88% sensitive, but only 63% specific. By excluding patients with hypoproteinemia (transferrin values of < 150 mg/dL), the sensitivity of the test increased to 100% and the specificity to 80%. We conclude that transferrin saturation is an adequate screening tool in anemic chronic renal failure patients, provided that hypoproteinemia is not present. By determining both the serum ferritin concentration and the transferrin saturation, a high sensitivity and specificity can be achieved, even in patients with hypoproteinemia. Furthermore, we believe that on this basis, iron therapy in patients with renal insufficiency can be improved.

Evidence for the involvement of the 5-HT1A receptor in CCK induced satiety in rats

The present study was designed to examine possible interactions between exogenous CCK and the 5-HT1A receptor subtype mediated serotonergic effects on feeding in rats. The somatodendritic 5-HT1A receptor agonist 8-OH-DPAT (0.32 mg/kg sc) evoked feeding in freely feeding rats. This effect was attenuated by treatment with CCK-8 (1, 5 and 25 micrograms/kg ip). In food deprived rats, CCK-8 (40 micrograms/kg ip) significantly reduced the size of a test meal. Treatment with the 5-HT1A receptor antagonist WAY-100135 (10 mg/kg ip) antagonized this anorectic effect of CCK-8. WAY-100135 on its own did not affect food intake. These results suggest the involvement of the 5-HT1A receptor subtype in mediating 5-HT-CCK interactions in the control of food intake in rats.

Application of 'nose-poke habituation' validation with post-trial diazepam- and cholecystokinin-induced hypo- and hypermnesia

The present study describes the use of nose-poke habituation as a memory task and demonstrates that it is sensitive to hypo- and hypermnestic pharmacological treatments administered post-trial. Habituation of nose-poke behavior of rats was defined as a reduction in number of nose-pokes compared to baseline. It was measured using a board with 16 holes, to which animals were exposed on 2 consecutive days (baseline and test) for 10 min, respectively. After the first exposure, rats were injected intraperitoneally (i.p.) immediately or with a delay of 2.5 h with doses of diazepam (0.9-4.5 mg/kg) known to be hypomnestic, or cholecystokinin (CCK-8S; 0.2-25 micrograms/kg), which was reported to have memory facilitating effects. An enhancement of habituation in comparison with vehicle controls was interpreted in terms of a hypermnestic effect of the treatment. Conversely, hypomnestic action of the drug treatment was inferred from a reduced habituation. The results show that when diazepam was injected immediately post-trial, the normal reduction in number of nose-pokes during test was prevented, indicative of a failure to habituate presumably due to an amnesia for the baseline/training trial. In contrast, enhanced habituation (facilitation of memory) was induced when CCK-8S was injected immediately post-trial, as reflected by a decrease in number of nose-pokes during test compared to control animals. The effects were not due to enduring proactive effects of the compounds on performance during test, since post-trial injections of diazepam or CCK-8S with a delay of 2.5 h did not have the effects that immediate post-trial injection had.(ABSTRACT TRUNCATED AT 250 WORDS)

Social interaction increases 5-HT release and cAMP efflux in the rat ventral hippocampus in vivo

The aim of the present study was to combine in vivo microdialysis in the rat with behaviour in the social interaction test in order to investigate changes in both 5-HT release and cyclic AMP (cAMP) efflux in the ventral hippocampus with simultaneous measurement of behaviour. Exposure of the rat to a 10min period of social interaction with an unfamiliar partner in a brightly lit, unfamiliar arena resulted in an increase in extracellular 5-HT and extracellular cAMP in the ventral hippocampus. Pretreatment with diazepam (1mg/kg i.p.) 30min prior to the social interaction test significantly inhibited the increases in both extracellular 5-HT and cAMP while significantly increasing the amount of time the pair of rats spent in active social contact over the 10min period. During the 30min prior to the social interaction test diazepam reduced basal levels of 5-HT, but had no effect on the basal efflux of cAMP. Pretreatment with a selective 5-HT(1A) antagonist, WAY 100135 (5mg/kg s.c.), 30min the social interaction test, significantly potentiated the increase in extracellular 5-HT observed in saline-treated rats during the social interaction test. In contrast, WAY 100135 pretreatment significantly attenuated the increase in extracellular cAMP observed in saline-treated rats during the social interaction test but had no effect on the time spent in active social contact between pairs of rats. The results suggest that social interaction results in activation of a post-synaptic 5-HT receptor (5-HT(1A) or 5-HT(6)/5-HT(7)) coupled to adenylate cyclase but that this receptor is not responsible for the aversion-induced behaviour. Furthermore antagonism of the 5-HT(1A) somatodendritic autoreceptor under conditions of 5-HT neuronal activation, but not under basal conditions, potentiates 5-HT release.

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.

Effects of BOC-CCK-4 and L 365.260 on cortical 5-HT release in guinea-pigs on exposure to the elevated plus maze

The elevated plus maze is a well-established model of anxiety, with previous results showing that guinea-pigs handled daily from birth exhibit behaviour in this test similar to rats. In the present microdialysis study exposure of the guinea-pig to the elevated plus maze increased extracellular 5-HT in the lateral prefrontal cortex. The CCK-B receptor agonist BOC-CCK-4 (10 micrograms/kg) produced 'anxious' behaviour and potentiated the rise in 5-HT observed on exposure to the X-maze. The basal release of cortical extracellular 5-HT was not affected by BOC-CCK-4. Pretreatment with the selective CCK-B antagonist L 365.260 (100 micrograms/kg) antagonized both the 'anxious' behaviour and the neurochemical changes induced by BOC-CCK-4 while L 365.260 alone produced 'anxiolytic' behaviour, decreased basal extracellular 5-HT and prevented the increase in extracellular 5-HT seen when the guinea-pigs were exposed to the X-maze. Our results show that CCK-B receptor stimulation and blockade induce changes in central extracellular 5-HT levels associated with 'anxious' and 'anxiolytic' behaviour, respectively.

Evidence for mnemotropic action of cholecystokinin fragments Boc-CCK-4 and CCK-8S

Memory-modulating and reinforcing effects of the cholecystokinin (CCK) fragments, CCK-8S and Boc-CCK-4, after systemic application in rats were investigated. Habituation to the novelty of environmental stimuli was used to test for mnemonic effects using two different tasks (rearing behavior in an open field; head-dips in a hole-board). Immediate posttrial administration of CCK-8S and Boc-CCK-4 resulted in a reduction of rearing and head-dip behavior during testing, indicative of enhanced habituation and, thus, facilitation of memory. In contrast, administration of CCK-8S and Boc-CCK-4 with a delay of 2.5 or 5 h after training or pretrial injection of CCK-8S did not enhance habituation. No evidence for reinforcing or aversive properties of CCK-8S and Boc-CCK-4 was observed in a conditioned place preference task. In summary, the results indicate memory-enhancing effects of peripherally, posttrial-administered CCK-8S and Boc-CCK-4.

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.

5-HT 1A receptors and changes in extracellular 5-HT in the guinea-pig prefrontal cortex: involvement in aversive behaviour

The study demonstrates that guinea-pigs handled daily from birth exhibit similar behaviour to rats on the elevated plus maze. Simultaneously performed intra-cortical microdialysis showed that placing guinea-pigs on the elevated plus maze results in an increase in extracellular 5-HT in the frontal cortex. 8-OH-DPAT (0.3 mg/kg s.c.) reduced significantly the increase in cortical extracellular 5-HT and resulted in an 'anxiolytic' profile of behaviour. Pre-treatment with the 5-HT(1) antagonist methiothepin (10.0 mg/kg) antagonized the behavioural effects and prevented the increase in cortical extracellular 5-HT normally produced by exposure to the elevated plus maze. Methiothepin alone had no effect on behaviour in the elevated plus maze. 5-CT (0.1 mg/kg i.p.) abolished the rise in extracellular 5-HT, but did not produce an 'anxiolytic' profile of behaviour on the elevated plus maze. The results show that an increase in cortical extracellular 5-HT occurs in the saline- treated guinea-pig exposed to aversive conditions. It remains to be determined whether the 'anxiolytic' effect of 8-OH-DPAT in the guinea-pig is causally associated with decreased basal extracellular 5-HT. The results however indicate that there is no simple relationship between inhibition of 5-HT release and behaviour indicative of 'anxiolytic' drug actions.

CCK-8 modulates D2 receptor agonist-induced hypermotility in the nucleus accumbens

The influence of CCK-8 on locomotor effects associated with independent D2 receptor stimulation was studied. To selectively stimulate mesolimbic D2 receptors LY 171555 was injected into the nucleus accumbens of awake rats. Locomotor activity was measured in the open-field test. LY 171555 induced a biphasic effect: low doses stimulated, whereas higher doses inhibited locomotor activity. CCK-8 injected into the posteromedial part of the nucleus accumbens suppressed hyperlocomotion induced by LY 171555. The CCK-8 effect was prevented by the CCK-antagonist L 364,718. Our results indicate that CCK-8 modulates D2 receptor-mediated effects in the mesolimbic system.

2-Bromolisuride, an ergot derivative, with dopamine antagonistic and serotonin agonistic properties

The open-field test was used to study the involvement of dopaminergic and serotonergic mechanisms in the effects of 2-bromolisuride on locomotor activity in the rat. 2-Bromolisuride produced a dose-dependent inhibition of spontaneous locomotor activity. This is most likely due to an antagonistic action at postsynaptic dopamine receptors. Low doses of 2-bromolisuride potentiated apomorphine-induced hypermotility. This potentiating effect was not mediated by a blockade of presynaptic dopamine receptors, because it was not prevented by 6-OHDA lesion of the nucleus accumbens. The potentiating effect of 2-bromolisuride was completely blocked by the serotonin antagonists cyproheptadine and ritanserin. It is suggested that 2-bromolisuride possesses dopamine antagonistic and serotonin agonistic properties.

Atypical neuroleptics suppress dopaminergic behavioral supersensitivity

Seven days after bilateral 6-OHDA denervation of the nucleus accumbens locomotor activity was recorded in rats. 6-OHDA lesion strongly enhanced hypermotility induced by apomorphine (1.0 mg/kg IP) as a sign of behavioral dopaminergic supersensitivity. The potency of the classical neuroleptic haloperidol (0.03-0.25 mg/kg IP) to antagonize apomorphine-induced hypermotility was reduced in 6-OHDA-pretreated rats. The atypical neuroleptics sulpiride (5.0-20.0 mg/kg IP), thioridazine (1.0-5.25 mg/kg IP) and clozapine (0.5-2.0 mg/kg IP) and the 5-HT antagonists cyproheptadine (0.2 mg/kg IP) and ritanserin (0.01 mg/kg IP) suppressed the augmented apomorphine response in 6-OHDA-lesioned animals to the level of the apomorphine effect in controls. It is concluded that the model of denervation supersensitivity is capable of differentiating typical and atypical neuroleptics. The abolition of the 6-OHDA-induced increase of the apomorphine hypermotility by the atypical neuroleptics cannot be explained solely by postsynaptic dopamine receptor antagonism. Serotonergic mechanism may be involved in this action.

The quantification of eight enzymes from the ageing rat lens, with respect to sex differences and special reference to aldolase

Eight enzymes, e.g. lactate dehydrogenase, malate dehydrogenase, fructose-diphosphate aldolase, sorbitol dehydrogenase, glucose-6-phosphate dehydrogenase, hexokinase, phosphofructokinase and pyruvate kinase were estimated quantitatively in the rat lens from 37 to 1,211 days of age, by spectrophotometric methods. The activity was expressed as mU/g LWW. All enzymes measured showed declining activities, but LDH, ALD, SDH, G-6-PDH, HK and PFK gave a significant decrease during ageing when plotted semi-logarithmically from 37 to 1,211 days. SDH and G-6-PDH showed a statistically significant difference between the enzymes from the male and the female lenses. The female lens always had a lower activity than the male lens. Of all enzymes the specific activity, expressed as mU/l mg protein, was calculated. This specific activity appeared to be rather constant during ageing, except for ALD. In the female lenses, the specific activity of 7 enzymes was lower than in the male lenses. For ALD the specific activity decreased significantly in the male lens from 5.32 at 37 days to 0.88 at 1,211 days. In the female lens this significant decrease was from 4.97 to 0.81.