Alterations of central norepinephrine, dopamine and serotonin in several strains of mice following acute stressor exposure

Exposure to inescapable footshock provoked region-specific alterations of norepinephrine (NE), dopamine (DA) and serotonin (5-HT) activity across six strains of mice (A/J, BALB/cByJ, C3H/HeJ, C57BL/6J, DBA/2J and CD-1). The stressor provoked reductions of hypothalamic NE and increased MHPG accumulation in all strains. In contrast, the effects of the stressor on NE activity in the hippocampus and locus coeruleus varied appreciably across strains. In the mesocortex and nucleus accumbens shock induced an increase of DOPAC accumulation and pronounced reductions of DA in some strains, while in others these variations were less pronounced or entirely absent. Stressor-provoked alterations of 5-HT and 5-HIAA were most evident in the mesocortex. Strain-specific neurochemical alterations following footshock are discussed relative to stressor-induced behavioral disturbances and animal models of depression.     

Stressor-induced alterations of natural killer cell activity and central catecholamines in mice

Natural killer (NK) cell cytotoxicity was determined at various intervals (0.5, 24 or 48 h) following exposure to uncontrollable footshock in 3 strains of mice. Stressor application provoked reductions of NK activity, but the time course of the NK changes varied across strains. Whereas NK cytotoxicity was markedly reduced in C57BL/6J mice 0.5-48 h following stressor exposure, this effect was delayed in C3H/HeJ mice, being evident 24-48 h following stressor application. In BALB/cByJ mice, NK activity was significantly reduced 24 h after footshock, but in contrast to the other strains returned to control levels within 48 h of stressor exposure. Central NE and DA concentrations and activity were influenced by the stressor treatment in a strain-dependent fashion. However, the relationship between the central amine variations and the alterations of NK cytotoxicity associated with the stressor was limited.     

Mouse strain differences in plasma corticosterone following uncontrollable footshock

Exposure to acute inescapable footshock provoked marked increases of plasma corticosterone concentrations in six strains of mice (A/J, Balb/cByJ, C57BL/6J, C3H/HeJ, DBA/2J and CD-1). However, the magnitude of the increase, as well as the time required for corticosterone to return to control values, varied appreciably across strains. Moreover, it appeared that the strain-specific corticoid increases ordinarily observed after acute shock were also evidence following a chronic stressor regimen. The data were related to previously observed strain differences in stressor-induced alterations of brain norepinephrine, dopamine and serotonin, as well as variations in performance in several behavioral paradigms.     

Habituation to repeated stress is stressor specific

Rats were exposed to 15 min of restraint or footshock or forced running in an activity wheel once a day for 10 days. Control groups were handled only. On the 11th day, rats from each stressor group and controls were exposed to 15 min of one stressor in a crossed design such that all combinations of one chronic stressor and one acute stressor were performed. Rats were sacrificed immediately following removal from their home cage or after 15 min stressor exposure on the 11th day and plasma corticosterone and prolactin and pituitary cyclic AMP levels were determined. There were no measured differences in these stress indices among groups of rats sacrificed immediately upon removal from their home cage on day 11 regardless of previous history on days 1 through 10. Plasma corticosterone and plasma prolactin and pituitary cyclic AMP levels were elevated in all rats exposed to any of the three stressors immediately prior to sacrifice as compared to all rats not exposed to stress immediately before sacrifice. However, plasma prolactin and pituitary cyclic AMP responses to each of the 3 stressors were attenuated in rats which had previous exposure to that specific stressor as compared to rats which had previous experience with a different or no stressor. We conclude that habituation results from behavioral experience with a particular stressor rather than biochemical adaptation resulting from repeated challenge to hormonal and neurochemical systems responsive to stress.     

Strain-specific effects of antidepressants on escape deficits induced by inescapable shock

The effects of several antidepressants (desmethylimipramine, amitriptyline and bupropion) on escape deficits induced by inescapable shock were assessed in four strains of mice. The extent of the escape interference engendered by inescapable shock varied across strains of mice. These deficits of escape performance were differentially affected by the drug treatments across strains. Repeated administration of desmethylimipramine eliminated the escape interference in A/J, but did not affect the performance in Balb/cByJ, C57BL/6J or CD-1 mice. Bupropion, in contrast, had a modest effect only in CD-1 mice. Unlike these compounds, the 5-HT reuptake blocker, amitriptyline, was found to influence escape performance irrespective of whether the drug was acutely or chronically applied. It is suggested that (a) the relative contributions of various mechanisms subserving the escape interference may vary across strains of mice, hence accounting for the strain-specific effects of the drug treatments, and (b) various antide-pressants influence performance by affecting different components of the behavioral output, some of which may be apparent after acute treatment while others are expressed only after repeated treatment with the compound.     

Quantitative effects of diet on fecal corticosterone metabolites in two strains of laboratory mice

The analysis of glucocorticoids excreted in feces is becoming a widespread technique for determining animal wellbeing in a wide variety of settings. In the present study an extraction protocol and an ELISA assay for quantifying fecal corticosterone metabolites (FCM) in BALB/c and C57bl/6 mice were validated. Lower ratios of solvent (ethanol) to mass of fecal sample were found to be sufficient in extracting FCM compared to what has been reported previously. Feeding mice a high energy diet, high in fat content (60% of calories from fat), significantly lowered the FCM excretion, approximately halving the FCM output. This diet also reduced the fecal mass voided to approximately a third of that of the regular diet. The two reductions were not correlated. A difference in defecation pattern was seen between the two strains, with the BALB/c mice having a more pronounced diurnal rhythm compared to the C57bl/6 mice. Furthermore, throughout the experiment, the C57bl/6 mice excreted significantly higher levels of FCM compared to the BALB/c mice. The mice were also challenged with synthetic adrenocorticotropic hormone (ACTH) and dexamethasone (DEX). The effect of the challenges could readily be detected, but had a considerably lesser impact on data than did the difference in diet. The study demonstrates some problematic consequences of expressing FCM excretion as a measure of fecal dry mass. The study also serves to emphasize the caution that must be exercised when interpreting FCM excretion in conjunction with an uncontrolled or varied diet, or perturbations of gastro-intestinal functioning.     

Prenatal ethanol exposure in C57 mice: effects on pregnancy and offspring development

Pregnant mice were fed lab chow or isocaloric liquid diets containing different concentrations of ethanol or sucrose from Day 5 through Day 17 of gestation. Ethanol added to the diet reduced ad lib consumption compared to that of the diet with sucrose. The reduced consumption was accompanied by an attenuated weight gain during pregnancy. The attenuated weight gain, however, was not specific to alcohol as evidenced by an equivalent attenuation for sucrose controls pair-fed to the ethanol group. Prenatal ethanol exposure increased neonatal mortality which appeared to be unrelated to the prenatal attenuated weight gain or to postnatal nurturance. Surviving offspring, reared by their biological mothers, had body weights similar to controls at birth and during lactation. However, in contrast to previous reports, mice prenatally exposed to ethanol manifested weight reductions near weaning that extended into adulthood (60 days). In spite of the increased mortality and reduced body weight, motor activity assessed by either longitudinal or cross-sectional methods was not influenced by the treatments. Possible mechanisms for the delayed weight reduction include retarded maturation and/or dysfunction of neural systems involving food regulation.     

Odor-induced variation in anxiety-like behavior in mice is associated with discrete and differential effects on mesocorticolimbic cholecystokinin mRNA expression.

The present investigation assessed alterations in mesocorticolimbic cholecystokinin (CCK) mRNA following novel predator and non-predator odor exposure and light-dark testing in CD-1 mice. In brief, acute exposure of CD-1 mice to the predator odor, 2,5-dihydro-2, 4,5-trimethylthiazoline (TMT; the major component of the anal gland secretions of the red fox), or the control odor, butyric acid (BA), suppressed rearing behavior during odor presentation, subsequently induced anxiety in the light dark test, and was associated with increased mesocorticolimbic CCK mRNA relative to saline treated mice. Only mice exposed to TMT displayed elevated freezing behaviors during odor treatment. In the light-dark test, mice exposed to either BA or TMT took longer to reenter the light section of the apparatus and spent less cumulative time in the light relative to mice exposed to saline. The decreased time spent in the light as well as light dark transitions were exaggerated among mice exposed to fox odor. Odor presentation was associated with increased CCK mRNA in mesocorticolimbic sites. Butyric acid was associated with enhanced CCK gene expression in the VTA, while both BA and TMT were associated with increased medial prefrontal cortex (mPFC) CCK mRNA levels. Increased CCK mRNA within the VTA and mPFC was evident among mice despite testing in the light-dark box. In contrast, basolateral nucleus of the amygdala (BLA) CCK mRNA was enhanced following odor exposure among mice in the light dark test relative only to saline treated mice which demonstrated a natural decrease in BLA CCK mRNA following the light dark test. The differential pattern of CCK mRNA associated with discrete psychogenic stressor manipulations and the provocation of anxiety-like behavior associated with such experiences is discussed.     

Variations of norepinephrine concentrations following chronic stressor application

Exposure to acute uncontrollable footshock increased utilization of central norepinephrine (NE), and in some brain regions, most notably the hypothalamus, a decline in amine concentrations was induced. Utilization of NE was likewise increased in mice exposed to footshock on 14 consecutive days, but the NE reduction was not evident, suggesting that the chronic stressor provoked a compensatory increase of amine synthesis. In mice that were decapitated 24 hr after the chronic shock regimen, NE concentrations exceeded those of nonshocked animals or mice decapitated immediately after the last shock session, possibly reflecting a sustained increase of amine synthesis. The altered NE utilization and concentrations associated with chronic footshock were evident irrespective of whether the stressor was applied on a predictable schedule or on an intermittent basis, although the former treatment was somewhat more effective in increasing concentrations and utilization.     

Immunomodulatory effects of dietary potassium perfluorooctane sulfonate (PFOS) exposure in adult Sprague-Dawley rats

Perfluorooctanesulfonate (PFOS) is a stable and environmentally persistent metabolic or degradation product of perfluorooctanyl compounds that were manufactured for a variety of industrial and consumer applications. PFOS itself was sold for use as a surfactant. The structurally related contaminants perfluorooctanoic acid (PFOA), perfluorodecanoic acid (PFDA), and N-ethyl perfluorooctane sulfonamide (N-EtPFOSA) were shown to suppress immune responses in laboratory rodents. Relatively low doses of PFOS were found to be immunosuppressive in mice. To assess effects of PFOS on the rat immune system at doses known to alter hepatic function, changes in the morphology and function of immune tissues and cells were measured in adult rats exposed to PFOS in their diet for 28 d at levels ranging from 2 to 100 mg PFOS/kg diet (corresponding to approximately 0.14 to 7.58 mg/kg body weight [bw]/d) and compared to those receiving control diet. Body weight reductions were significant in male and female rats exposed to 50 and 100 mg PFOS/kg diet. Liver/body weight was significantly increased in females exposed to 2 mg PFOS/kg diet and in males exposed to 20 mg PFOS/kg diet. Female rats exposed to 100 mg PFOS/kg diet exhibited a significant increase in spleen weight relative to body weight; these changes lacked a histologic correlate and were not observed in males. While thymus weights relative to body weights were not affected, numbers of apoptotic lymphocytes rose in thymus with increasing dietary PFOS. There was a significant dose-related increase in total peripheral blood lymphocyte numbers in female but not male rats. In both genders the percentages of cells within lymphocyte subclasses were altered. There was a significant trend toward increasing T and T-helper (Th) cells and decreasing B cells with higher PFOS dose. Serum total immunoglobulin (Ig) G1 levels were significantly reduced in males exposed to 2 and 20 mg PFOS/kg diet. The ability of male and female rats to mount delayed-type hypersensitivity (DTH) responses to the T-cell-dependent antigen keyhole limpet hemocyanin (KLH) was not altered by PFOS. There was a significant trend toward elevated KLH-specific IgG in serum from male rats exposed to increasing levels of PFOS in diet. Splenic T- and B-cell proliferation in response to ex vivo mitogen exposure was unaffected by exposure to dietary PFOS. In conclusion, changes in immune parameters in rat did not manifest as functional alterations in response to immune challenge with KLH and may be secondary to hepatic-mediated effects of PFOS in this model.     

Effects of acute alcohol consumption on the perception of eye gaze direction

Alcohol consumption is associated with increases in aggressive behaviour, but the mechanisms underlying this relationship are poorly understood. One mechanism by which alcohol consumption may influence behaviour is via alterations in the processing of social cues such as gaze. We investigated the effects of acute alcohol consumption on the perception of gaze, using a task in which participants determined whether a stimulus face was looking towards or away from them. Gaze direction varied across trials, allowing calculation of a threshold at which participants considered gaze to switch from direct to averted. Target faces varied in both sex and attractiveness. Thirty social drinkers attended three randomized experimental sessions. At each session, participants consumed 0.0, 0.2 or 0.4 g/kg alcohol, and completed the gaze perception task. A significant three-way interaction involving target sex, participant sex and alcohol dose indicated that alcohol increased the cone of gaze for females viewing male targets (i.e. females were biased towards making a direct gaze judgement), but decreased the cone of gaze for males viewing male targets. Our data indicate that alcohol consumption influences gaze perception, but that these effects vary across sex of both stimulus and rater. These effects may have important implications for alcohol-related violence.     

Barbiturate tolerance and dependence: effects on synaptosomal sodium transport and membrane fluidity

DBA mice were fed lab chow containing phenobarbital for seven or eight days. Upon withdrawal of the phenobarbital diet, dependence was evidenced by appearance of hypothermia, handling-induced convulsions and lethal seizures. Functional tolerance was determined by injecting phenobarbital into mice treated with the phenobarbital diet or a pair-fed control diet and measuring the brain concentration of phenobarbital at the time of loss of righting reflex and the time of regaining righting reflex. Both measures demonstrated that chronic consumption of phenobarbital resulted in functional tolerance. When the diet was withdrawn for two days, tolerance was no longer present, indicating a rapid reversal of the adaptive changes. The veratridine-stimulated uptake of 24Na by isolated brain synaptosomes was used as a measure of membrane function. Sodium uptake was inhibited in vitro by pentobarbital and ethanol, and the inhibitory effects of these drugs were attenuated by chronic in vivo phenobarbital treatment. The fluidity of brain synaptic plasma membranes was estimated by the fluorescence polarization of the fluorescent probe molecules 1-(4-trimethylammonium phenyl)-6-phenyl-1,3,5-hexatriene and 1,6-diphenyl-1,3,5-hexatriene. Synaptic membranes from mice treated chronically with phenobarbital did not differ from those of control mice with regard to either the baseline fluorescence polarization of the probes or the decrease in fluorescence polarization produced by in vitro exposure to phenobarbital or ethanol. Taken together, these results indicate that although chronic phenobarbital ingestion resulted in tolerance and dependence (studied in vivo), and adaptation of sodium channels (studied in vitro), there was no evidence that these changes were due to alterations in the membrane physical properties.     

Cross-tolerance between muscarinic agonists: role of muscarinic receptors

In order to explore the relationship between response to muscarinic agonists and brain muscarinic receptors, two mouse strains that differ in acute sensitivity (DBA and C3H) were injected chronically with DFP or infused with oxotremorine. Chronic DFP-treated DBA mice were not tolerant to DFP's effects on any measure, but they were cross-tolerant to the effects of oxotremorine on heart rate and body temperature. DFP-treated C3H mice were not tolerant to DFP or cross-tolerant to oxotremorine on any measure. Oxotremorine infusion resulted in tolerance to oxotremorine in both mouse strains, and chronically infused DBA mice were cross-tolerant to DFP on five of the six measures. Oxotremorine-infused C3H mice were cross-tolerant to DFP on two of the measures. These results suggest that genetic factors influence the development of tolerance or cross-tolerance. These genetic factors do not seem to be related to changes in brain QNB binding. Both mouse strains showed comparable changes in QNB binding following chronic DFP and oxotremorine with DFP eliciting reductions in QNB binding in striatum and hippocampus and oxotremorine eliciting reductions in nearly every brain region. However, tolerance and cross-tolerance did not seem to correlate with changes in binding which suggests that the relationship between receptor changes and responses to muscarinic agonists must be examined further.     

Behavioral and neurochemical changes following predatory stress in mice

This article had several objectives. First it aimed at investigating the anxiogenic-like behaviors elicited by unavoidable cat exposure and/or cat odor across nine strains of mice (BALB/c, C57BL/6, C3H, CBA, DBA/2, NMRI, NZB, SJL, Swiss) in a modified version of the free-exploration test. The second objective was to investigate possible neurochemical changes following cat exposure in Swiss mice by measuring the turnover of dopamine (DA), noradrenaline (NA) and serotonin (5-HT) in several brain regions known to be involved in the modulation of emotional processes (hippocampus, hypothalamus and striatum). Finally, the third objective was to examine the effects of anxiolytic drug treatments on the anxiogenic responses elicited by a cat odor (i.e. a feces) in Swiss mice previously exposed to a cat using the free-exploration test. Results from the strain comparison showed that mice could be divided into three distinct groups: two non-reactive strains (NZB and SJL) which were relatively insensitive to predatory exposure and/or odor; five intermediate-reactive strains (Swiss, NMRI, CBA, C3H and BALB/c) which displayed clear anxiogenic-like responses only when exposed to both cat and, subsequently, to feces; and two high reactive strains (C57BL/6 and DBA/2) which showed anxiogenic-like reactions following cat exposure, regardless of the stimulus (clay or feces) present in the free-exploration cage. Neurochemical data revealed that, while brain levels of NA, DA, 5-HT in cat exposed Swiss mice were not significantly different from those of control animals, turnover rates of these monoamines were increased in the hippocampus (NA and 5-HT), hypothalamus and striatum (DA) after cat exposure. Results from pharmacological experiments indicated that repeated administration of the 5-HT reuptake inhibitor fluoxetine (5-20 mg/kg, twice a day, for 5 days) completely abolished avoidance of the cat feces in Swiss mice previously exposed to the predator. Neither acute nor repeated administration of the classical anxiolytic diazepam was able to reduce avoidance behavior of the anxiogenic stimulus in the free-exploration test. Taken together, these findings indicate that the exposure of mice to unavoidable predatory stimuli is associated with behavioral and neurochemical changes consistent with increased anxiety.     

Influence of different types of stress on selected cardiovascular parameters in rats

Wistar strain male albino rats were exposed to different types of stressors like isolation, immobilization, overcrowding and forced swimming, for a duration of one day, 7 days, 15 days and 30 days and the effect on heart weight, adrenal weight, heart rate, P-R interval and serum transaminase levels were studied. There was a significant increase in the heart weight and adrenal weight in most of the stress subgroups. Tachycardia was seen in all the types of stress upto 7 days, except in the case of overcrowding stress. Serum transaminase level increased significantly in all the types of stress. Among the different types of stress, immobilization and forced swimming had greater effect on the heart weight and heart rate. Increase in the heart rate and heart weight was observed only in the initial period of exposure to a stressor and when the animals were exposed to a prolonged stressor like 15 days and 30 days, there was no further increase in the heart weight and heart rate which may be due to the adaptation of the animal to a chronic stressor.     

Food consumption and body weight changes with neotame, a new sweetener with intense taste: differentiating effects of palatability from toxicity in dietary safety studies

Safety studies done with neotame, a sweetener with intense taste, demonstrate that changes in bodyweight (BW) and BW gain (BWG) are due to reduced food consumption (FC) rather than toxicity. When offered a choice, rats preferred basal diet to diet with relatively low concentrations of neotame. When no choice was available, rats ate less as concentrations increased, demonstrating reduced palatability. Changes in dietary concentrations of neotame resulted in changes in FC. The maximum tolerable doses (MTDs) in rats, dogs, and mice were due to decreases in BWG secondary to poor palatability of diets when neotame concentrations exceeded approximately 35,000 ppm. Concentrations were increased as animals grew to maintain constant dosing on a "mg/kg bw/day" basis. Food conversion efficiency (FCE) was not changed in rats during periods of active growth. The only consistent findings across safety studies were reductions in BW, BWG, and FC with no dose-response in rats, mice, and dogs. In definitive safety studies, there were no adverse findings related to neotame treatment from clinical observations, physical examinations, water consumption, or clinical pathology evaluations; nor was there morbidity, mortality, organ toxicity, macroscopic or microscopic postmortem findings. Analysis of data from long-term studies in Sprague-Dawley rats support the conclusion that changes in FC alone can cause the observed changes in BWG in neotame studies when changes are scaled allometrically [Regul. Toxicol. Pharmacol. (2003)]. Consequently, BW parameters are not appropriate endpoints for setting no-observed-effect levels (NOELs) for neotame.     

Increased immunoreactivity of POMC-derived neuropeptides and immediate-early gene-derived proteins (c-Fos and Egr-1 proteins) as an early step of acute cocaine-induced stressor effects: comparison with the effects of immobilization stress.

The effects of an acute toxic dose of cocaine (COC) (60 mg/kg, i.p.) as a stressor were examined in rats both neuroendocrinally and behaviorally. The time course (5 min, 5, 12, and 24 h) of the alterations in the immunoreactivity of POMC (preopiomelanocortin)-derived neuropeptides [ACTH (adrenocorticotropin), beta-endorphin, and alpha-MSH (melanocyte stimulating hormone)] and immediate-early gene-derived proteins (c-fos and egr-1 proteins) was examined in the hypothalamus, including the regions reported to be neuroendocrinally sensitive to stressor effects, along with the accompanying alterations in the spontaneous behaviors in the cage and the forced swimming behaviors. Similar to the observations in rats treated with a 30 min immobilization stress (IM), an increase in the number of immunoreactive nerve cells for each neuroendocrinal product and a delayed depression in the swimming behaviors as compared to the alterations in the spontaneous activity, which seemed to be correlated with some intermediate steps, were characteristically caused by a toxic dose of COC. However, the early enhancement (at 5 h) of the swimming behaviors and the brain ACTH level might also be the characteristic acute COC effects, which could be differentiated from the effects of other non-psychostimulant stressors.     

An effective dietary method for chronic tryptophan depletion in two mouse strains illuminates a role for 5-HT in nesting behaviour

Physiological depletion of tryptophan, the precursor to serotonin has been shown to alter mood and cognition in both humans and rodents. Few studies have investigated the neurochemical and behavioural effects associated with tryptophan depletion in mice. Given that BALB/c and C57BL/6J mice differ in tryptophan hydroxylase (TPH) functionality, serotonin levels and behavioural phenotype, we hypothesised that a differential strain response to chronic dietary tryptophan manipulations would be observed. Therefore, the effects of four chronic dietary tryptophan manipulations were investigated, the diets include a depleted diet (0% tryptophan, TRP(-)), a deficient diet (0.25% tryptophan, TRP(-/+)), an enhanced diet (1.25% tryptophan, TRP(+)) and a control diet (0.7%). Diet-induced alterations in peripheral and central tryptophan levels and brain serotonin turnover were determined by high performance liquid chromatography. In addition, dietary-induced alterations in behaviour were assessed in several commonly used tasks. Peripheral and central tryptophan levels and consequently central serotonergic turnover were significantly decreased by the TRP(-) diet in both strains, however, no effect of tryptophan supplementation was observed on tryptophan or serotonin levels. Dietary tryptophan manipulation induced pronounced behavioural effects, particularly in nesting behaviour where a reduction in nesting was observed following depletion and an increase in nesting behaviour was observed with enhanced tryptophan in both strains. Additionally, depletion produces an anxiolytic-like effect and did not impede locomotion. This study demonstrates significant alterations in the levels of tryptophan, serotonin turnover and behaviour following chronic dietary tryptophan depletion.     

Effect of acute and chronic conditions of over-crowding on free choice ethanol intake in rats

Male albino rats of Wistar strain were exposed to overcrowding stress in two different groups for a period of seven days. One group of rats was kept under stress for six hours per day (acute stressed group) and the other group rats was kept under stress continuously (chronic stressed group). The effect of these acute and chronic stresses on voluntary alcohol (2% w/v) intake was monitored during the 7 days of stress exposure, and ethanol preference and total ethanol intake in terms of g/kg body weight were also studied. A significant increase in ethanol preference and ethanol intake was observed in one-day and 7 days chronic stressed group. No significant increase in ethanol intake was observed in acute stress. Thus a short lasting stressor may not increase ethanol-drinking behavior, whereas when animals were exposed to more intense stressor continuously for 7 days, an increase in voluntary drinking behavior may be seen.     

Biomonitoring of ciguatoxin exposure in mice using blood collection cards.

Ciguatera is a human food poisoning caused by consumption of tropical and subtropical fish that have, through their diet, accumulated ciguatoxins in their tissues. This study used laboratory mice to investigate the potential to apply blood collection cards to biomonitor ciguatoxin exposure. Quantitation by the neuroblastoma cytotoxicity assay of Caribbean ciguatoxin (C-CTX-1) spiked into mice blood was made with good precision and recovery. The blood collected from mice exposed to a sublethal dose of Caribbean ciguatoxic extract (0.59 ng/g C-CTX-1 equivalents) was analyzed and found to contain detectable toxin levels at least 12 h post-exposure. Calculated concentration varied from 0.25 ng/ml at 30 min post-exposure to 0.12 ng/ml at 12 h. A dose response mice exposure revealed a linear dose-dependent increase of ciguatoxin activity in mice blood, with more polar ciguatoxin congeners contributing to 89% of the total toxicity. Finally, the toxin measurement in mice blood exposed to toxic extracts from the Indian Ocean or from the Pacific Ocean showed that the blood collection card method could be extended to each of the three known ciguatoxin families (C-CTX, I-CTX and P-CTX). The low matrix effect of extracted dried-blood samples (used at 1:10 or 1:20 dilution) and the high sensitivity of the neuroblastoma assay (limit of detection 0.006 ng/ml C-CTX-1), determined that the blood collection card method is suitable to monitor ciguatoxin at sublethal doses in mice and opens the potential to be a useful procedure for fish screening, environmental risk assessment or clinical diagnosis of ciguatera fish poisoning in humans or marine mammals.