Hippocampal 5-HT and NE release in the transgenic rat TGR(mREN2)27 related to behavior on the elevated plus maze

The transgenic rat TGR(mREN2)27 was generated to study mechanisms involved in the hypertensive process. A characteristic of this rat is a high expression of the murine renin-2 gene in several peripheral tissues and in the brain. The high expression of the transgene is associated with increased local formation of angiotensin II. In a previous study, we studied for the first time the behavior of male TGR(mREN2)27 rat in the open field and on the elevated plus maze. There were no differences between TGR(mREN2)27 and SPRD-controls in locomotor activity measured in the open field. While placed on the elevated plus maze, however, the TGR(mREN2)27 rats showed a greater "anxiogenic" profile than the SPRD-rats. The present study was aimed to characterize neurotransmitter release involved in anxiety in hippocampus of TGR(mREN2)27 rats during exposure to the elevated plus maze. Exposure to the maze resulted in an increased intrahippocampal serotonin release with the same maximum both in the transgenic rats and in the control rats. However, the subsequent decrease was significantly faster in the TGR(mREN2)27 compared to the SPRD-controls. The latter suggests that the serotonergic system is functionally changed in the TGR(mREN2) rat, too. In contrast, norepinephrine release did not change during exposure to the maze and there were no significant differences in norepinephrine release between transgenics and controls.

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.

Learning and anxiety in angiotensin-deficient mice

Angiotensin II in the brain was shown to be involved in mechanisms influencing cardiovascular and electrolyte homeostasis, anxiety and learning. Here, we report behavioural studies in mice lacking angiotensinogen. We analysed learning and anxiety related behaviour using the Morris water maze task and the elevated plus maze task, respectively. In both tests no differences were found between control mice and angiotensin-deficient mice. This implicates that angiotensin does not influence learning and anxiety-related behaviour in mice under normal conditions.

Risk of iodine-induced thyrotoxicosis after coronary angiography: an investigation in 788 unselected subjects

In this study, the risk of iodine-induced thyrotoxicosis in unselected patients from an iodine-deficient area was investigated. The patients were consecutively enrolled. Thyroid hormone values and urinary iodine excretion were determined before, as well as 1, 4 and 12 weeks after iodine contamination by coronary angiography. Two of 788 unselected patients developed hyperthyroidism within 12 weeks. The two patients did not belong to a risk group for iodine-induced thyrotoxicosis (i.e. old people, patients with goiter or possible thyroid autonomy, low TSH). Both patients had normal TSH levels at baseline and ultrasound of the thyroid was without evidence of nodules. The study shows that in euthyroid unselected patients from an iodine-deficient area short-term iodine contamination by contrast media rarely leads to hyperthyroidism. On account of these facts, prophylactic therapy, e.g. by perchlorate or thiamazole, is not generally recommended, because the risk of side-effects is perhaps even greater than the risk of iodine-induced thyrotoxicosis.

Role of cholecystokinin type B receptors in ultrasound induced behavior in rats

The cholecystokinin-tetrapeptide (CCK-4) can induce panic attacks in humans. The present study investigates the effects of CCK-4 and the CCK-B receptor antagonist L-365.260 on ultrasound induced defense behavior in the rat that may model the unconditioned aspects of panic behavior in man. CCK-4 (50 microg/kg) increased the defense response induced by ultrasound (95 dB) an effect prevented by pretreatment with L-365.260 (10 microg/kg). Compared with other antipanic/panicogenic drugs the effects of CCK-4 and L-365.260 were relatively small. In conclusion, drugs acting at the CCK-B receptor appear to have only a minor role in the modulation of an unconditioned aversive response.

Kinetics of acute and chronic iodine excess

Iodine plays an important role in thyroid physiology resulting from its importance as a requisite substrate for the synthesis of thyroid hormones and from its action as a regulator of thyroid function. Following intestinal absorption, inorganic iodide is largely confined to the extracellular fluid. Serum concentrations of inorganic iodide well reflect the amount of iodine present in the extracellular compartment. Since serum inorganic iodide levels are important determinants of thyroid iodine uptake, serum iodide measurement offers a valuable tool for the investigation of many basic and clinical aspects of thyroid iodine metabolism. Here we summarize important aspects of iodine metabolism and focus selectively on technical aspects of serum inorganic iodide measurement and on the kinetics of inorganic iodide in various states of iodine excess. Presently, paired-ion, reversed-phase HPLC with electrochemical detection is obviously the best method for measurement of serum inorganic iodide being highly sensitive, easy to perform, and almost completely insensitive to interfering substances. Using this method, we could demonstrate an acute increase of serum inorganic iodide during the administration of large amounts of iodide as Lugol's solution given preoperatively in patients with Graves' hyperthyroidism. In patients under treatment with the iodine containing drug amiodarone (n=37), serum inorganic iodide levels were highly elevated (range 3.5-208.2 microg/dl, median 36.6 microg/dl). Serum concentrations of inorganic iodide were correlated neither to the daily amiodarone dose, nor to the serum levels of amiodarone.

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

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.

Sustained long term potentiation and anxiety in mice lacking the Mas protooncogene

The Mas protooncogene is a maternally imprinted gene encoding an orphan G protein-coupled receptor expressed mainly in forebrain and testis. Here, we provide evidence for a function of Mas in the central nervous system. Targeted disruption of the Mas protooncogene leads to an increased durability of long term potentiation in the dentate gyrus, without affecting hippocampal morphology, basal synaptic transmission, and presynaptic function. In addition, Mas-/- mice show alterations in the onset of depotentiation. The permissive influence of Mas ablation on hippocampal synaptic plasticity is paralleled by behavioral changes. While spatial learning in the Morris water maze is not significantly influenced, Mas-deficient animals display an increased anxiety as assessed in the elevated-plus maze. Thus, Mas is an important modulating factor in the electrophysiology of the hippocampus and is involved in behavioral pathways in the adult brain.

Extracellular dopamine in the anterior nucleus accumbens is distinctly affected by ventral tegmental area administration of cholecystokinin and apomorphine: data from in vivo voltammetry

The interaction of cholecystokinin (CCK) and dopamine (DA) in the mesolimbic system was investigated. The study focused on DAergic cells not containing colocalized CCK projecting from the ventral tegmental area (VTA) to the anterior nucleus accumbens (NA). Differential pulse voltammetry in pargyline pretreated and anesthetized rats was used to measure extracellular DA in the anterior NA following microinjection of apomorphine either alone or in combination with CCK-8s into the VTA. In agreement with an earlier study there was a dose-dependent increase in the DA signal in the anterior NA after microinjection of CCK-8s into the VTA. Apomorphine microinjected into the VTA produced a biphasic effect on extracellular DA in the anterior NA with an increase from basal levels of approximately 50% by 1 ng, whereas 10 ng was ineffective and 100 ng apomorphine caused a slight decrease in the DA signal. Apomorphine (1 ng) microinjected together with 1 ng CCK-8s produced an increase in the DA signal to approximately 180% of the baseline value, whereas the combination of 1 ng apomorphine and 100 ng CCK-8s was ineffective. When 100 ng apomorphine were microinjected in combination with either 1 ng or 100 ng CCK-8s, the DA signal in the anterior NA was unchanged. These results suggest that low doses of apomorphine injected into the VTA synergistically influence the effects of CCK-8s on extracellular DA in the anterior NA, whereas higher doses of apomorphine suppress the effect of CCK-8s on DAergic cells projecting to the anterior NA.

Pharmacological evaluation of a modified open-field test sensitive to anxiolytic drugs

In a recent study it has been shown that benzodiazepine receptor agonists attenuate novelty-induced suppression of feeding and increase the percentage of animals feeding in the open field. Food-deprived rats were placed in one corner of the open field containing food in the center. The number of rats beginning to eat in the first 5 min was recorded. In the present study this test was validated pharmacologically using known "anxiolytic" or "nonanxiolytic" drugs. The following substances (effective doses, given IP) increased the number of rats feeding within 5 min in the center of the open field: meprobamate (30.0-300 mg/kg), 8-OH-DPAT (10 and 30 microg/kg), ipsapirone (1.0 and 2.0 mg/kg), ritanserin (0.125-0.5 mg/kg), tropisetron (0.1-10.0 microg/kg), ondansetron (0.3-3.0 microg/kg), lisuride (0.28-0.55 mg/kg), morphine (0.3 and 1.0 mg/kg), propranolol (0.3 and 1.0 mg/kg), clozapine (1.0 mg/kg). Drugs without "anxiolytic" effects in other animal models or in humans, including amphetamine, apomorphine, haloperidol, sulpiride, and mCPP did not increase the incidence of food intake in this test. Ethanol and hexobarbital, in nonsedative doses, had no effect in this paradigm. Drugs and doses effective in the modified open-field test caused no increase in food intake in an independent food consumption test using food-deprived rats staying in the familiar cages. The results suggest that the modified open-field test can detect "anxiolytic" drug properties and is valid for the assessment of "anxiolytic" effects from different classes of drugs.

Modulation of memory, reinforcement and anxiety parameters by intra-amygdala injection of cholecystokinin-fragments Boc-CCK-4 and CCK-8s

This series of experiments examined the effects of the cholecystokinin (CCK) fragments Boc-CCK-4 and CCK-8s on memory, reinforcement and anxiety following unilateral injection into the central nucleus of the amygdala (CeA). In experiment 1, rats with chronically implanted cannulae were injected with CCK-8s or Boc-CCK-4 and were tested on a one-trial uphill avoidance task. Post-trial injection of 20 ng Boc-CCK-4 or 1 ng CCK-8s was found to improve the retention performance, whereas lower and higher doses had no effect. The hypermnestic effects of Boc-CCK-4 and CCK-8s were no longer evident when injection was performed 5 h, rather than immediately, after the learning trial. In experiment 2, the elevated plus-maze was used to gauge anxiogenous properties of intra-amygdala injections of Boc-CCK-4 and CCK-8s in memory-enhancing doses. The treatment with 20 ng Boc-CCK-4 and 1 ng CCK-8s did not influence the number of entries into and time spent on the open and enclosed arms of the maze as well as other anxiety-related behaviors. In experiment 3, possible reinforcing effects of the CCK-fragments were examined. After intra-amygdala injection of Boc-CCK-4 or CCK-8s in memory-enhancing doses the rats were placed into one of four restricted quadrants of a circular open field (closed corral) for a single conditioning trial. Subsequent tests for conditioned corral preference revealed no evidence for reinforcing or aversive effects of the CCK-fragments. In sum, these findings indicate that Boc-CCK-4 and CCK-8s facilitate memory processing upon injection into the CeA without exerting reinforcing or anxiogenous effects.

Effects of cholecystokinin-receptor agonists on cortical 5-HT release in guinea pigs on the X-maze

Exposure of guinea pigs to the elevated plus maze (X-maze), an animal model of anxiety, causes an increase of extracellular serotonin (5-HT) in the lateral prefrontal cortex monitored by microdialysis. The neuropeptide cholecystokinin (CCK) plays a role in the modulation of anxiety. To compare the roles of CCK receptors, the effects of the CCK-A receptor agonist A-71378, the CCK-A/B receptor agonist CCK-8S and the CCK-B receptor agonist BOC-CCK-4 on anxiety-related behavior and the 5-HT release in the prefrontal cortex were determined. None of the drugs changed the behavior of the guinea pigs and the cortical 5-HT release under resting conditions in the familiar home cage. A-71378 and CCK-8S had no effect on the behavior on exposure to the X-maze whereas BOC-CCK-4 induced an 'anxious' behavior. The results suggest that 'anxious' behavior induced by CCK is associated with selective CCK-B receptor stimulation. A-71378 inhibited the rise in 5-HT on exposure to the X-maze. CCK-8S had no effect and the anxiogenic BOC-CCK-4 potentiated the rise in 5-HT on the X-maze. Both CCK receptors mediate changes in 5-HT release under aversive conditions, but not in a resting state. The results suggest a receptor subtype-specific influence of CCK on behavior and 5-HT activity under aversive conditions.

CCK-8S facilitates 5-HT release in the rat hypothalamus

The effects of the neurotransmitter serotonin (5-HT) and the neuropeptide cholecystokinin (CCK) on food intake are well established. Based on pharmacological studies, an interactive model for 5-HT and CCK was proposed. The present microdialysis study was aimed to provide neurochemical evidence for a facilitatory effect of CCK-8S on 5-HT release in the lateral hypothalamus under in vivo conditions. The results indicate an increase of extracellular hypothalamic 5-HT both during food intake in previously food-deprived rats and also after systemic administration of 8 microg/kg and 40 microg/kg CCK-8s in food-deprived rats. The results show that peripherally administered CCK-8s induces central serotonergic effects, possibly related to feeding.

Cortical 5-HT-CCK interactions and anxiety-related behaviour of guinea-pigs: a microdialysis study

Serotonin (5-HT) and cholecystokinin (CCK) are involved in the development of anxiety. There are only few data suggesting interactions between CCK and 5-HT under aversive conditions. In our study the cholecystokinin tetrapeptide (CCK-4) (10 microg/kg) induced 'anxious' behaviour and potentiated the increase of 5-HT release on the elevated plus maze (X-maze). The 'anxiolytic' 5-HT1A agonist 8-hydroxy-2-(di-n-propyl amino) tetralin (8-OH-DPAT; 0.3 mg/kg) reduced basal 5-HT and the increase in 5-HT release on the X-maze. 8-OH-DPAT given simultaneously with CCK-4, blocked the effects of CCK-4. The results demonstrate an interaction between CCK and 5-HT1A mechanisms via the influence on cortical 5-HT release.

Cholecystokinin increases extracellular dopamine overflow in the anterior nucleus accumbens via CCK(B) receptors in the VTA assessed by in vivo voltammetry

Differential pulse voltammetry was used to investigate the extracellular dopamine (DA) and DOPAC signal in the anterior part of nucleus accumbens (N.acc.) after microinjection of cholecystokinin (CCK) derivatives into the ventral tegmental area (VTA). Both the mixed CCK(A)/CCK(B) receptor agonist CCK-8s and the selective CCK(B) receptor agonist CCK-4 caused a dose-dependent increase in the DA signal after doses of 10 ng and 100 ng while CCK-8s had no effect on the DOPAC signal. The CCK(A) receptor antagonist L 364,718 (25 microg/kg i.p.) as well as the CCK(B) receptor antagonist L 365,260 (25 microg/kg i.p.) were administered prior to microinjection of 100 ng CCK-8s and L 365,260, but not L 364,718, completely inhibiting the DA increase produced by CCK-8s. Analysis of the tissue levels of DA and its main metabolites in the anterior part of N.acc. revealed no changes after CCK-8s microapplication into VTA. The presented data indicate a CCK(B) receptor-mediated increase in extracellular DA in the anterior N.acc. after microapplication of CCK derivatives into the VTA.

Effect of L364.718 during suckling on the sensitivity to the hypophagic effect of cholecystokinin in adult rats

1. In the present study it was investigated whether drugs acting at the cholecystokinin (CCK)-A receptor given to rat pups may result in long-lasting changes in body weight or regulation of food intake controlled by CCK. 2. From day 3 to day 10 of life, male and female Wistar rat pups were treated with the CCK-A receptor antagonist L-364.718 and the CCK-A + B agonist CCK-8S. 3. In adult rats, treated with L364.718 during suckling, the sensitivity to the acute hypophagic action of CCK-8S was weaker or abolished compared to adults treated with saline during suckling. In adult rats given CCK-8S during suckling acute treatment with CCK-8S reduced food intake to the same extent as in the group treated with saline postnatally. 4. These data show that early postnatal treatment with the CCK-A receptor antagonist L364.718 has an impact on the hypophagic response to CCK-8S in later life.

Behaviour of the transgenic (mREN2)27 rat

The first model of genetically engineered hypertension, the transgenic rat TGR (mREN2)27, provides a unique opportunity to study the behavioural effects of an altered brain renin-angiotensin system. The TGR (mREN2)27 rats, characterised by fulminant hypertension, show differences in both the peripheral and central angiotensin systems. The behaviour of male transgenic TGR (mREN2)27 and male Sprague-Dawley rats were determined by 4 behavioural tests. While on the elevated X-maze the TGR (mREN2)27 rat showed a greater 'anxiogenic' profile (fewer open arm entries) than the control Sprague-Dawley rats, this 'anxiogenic' profile increased further during a second exposure to the elevated X-maze 24 h later. In comparison the behaviour of the male Sprague-Dawley rats was not different between the two exposures to the elevated X-maze. Locomotor activity did not differ between either the TGR (mREN2)27 or Sprague-Dawley rats when placed in a 1 m2 open-field for 10 min. A short period of fluid-deprivation (3 h) reversed the 'anxiogenic' profile of the TGR (mREN2)27 on the elevated X-maze. Administration of captopril (20 mg . kg-1 body weight) in the drinking water of the TGR (mREN2)27 rats and Sprague-Dawley rats reversed the anxiogenic profile of the TGR (mREN2)27 rat on the elevated X-maze but did not alter the behaviour of the Sprague-Dawley rats.

Memory-enhancing effects of benzodiazepines in mice

In the present study, post-trial effects of clonazepam and diazepam on inhibitory avoidance learning under two different experimental conditions (i.e., 0.25 or 0.75 mA footshock) have been investigated. Both clonazepam (0.5 mg/kg) and diazepam (2 and 8 mg/kg) enhanced retention when administered immediately after the 0.25 mA footshock applied during training of the inhibitory avoidance task. In contrast, clonazepam and diazepam proved ineffective after the 0.75 mA footshock. The results suggest a post-training memory-enhancing effect of clonazepam and diazepam depending on the experimental conditions.

Obesity induced by unspecific early postnatal overfeeding in male and female rats: hypophagic effect of CCK-8S

The response to cholecystokinin (CCK) as a satiety peptide in obesity or anorexia has been tested mainly in extreme models of food intake control. In the present study, the effect of CCK-8S on food intake was investigated in a nongenetic and less-stressful model of obesity due to unspecific early postnatal overfeeding in male and female rats. Reducing the normal litter size of ten to three newborn rats on day 3 of life led to an enhanced food intake resulting in an increased body weight until adulthood. Freely fed male and female, normal and obese rats were given 10 micrograms/kg CCK-8S i.p. on day 41 and 40 micrograms/kg CCK-8S on day 91 of life and food intake was measured for 24 h. Compared with treatment with saline (i.p.) 1 day before the test, the lower dose of 10 micrograms/kg CCK-8S reduced food intake for 2 h in normal, but not in obese rats. Conversely, the higher dose of 40 micrograms/kg CCK-8S reduced food intake in both normal and obese rats for 2 h, but this effect was more evident in the obese rats. Moreover, the satiating effect of CCK-8S was more pronounced and longer lasting in male than in female rats. In summary, the data suggest that the response to CCK-8S differs in normal and obese rats and depends on sex.