An animal model for measuring behavioral responses to anxiogenic and anxiolytic manipulations

Sex differences in addiction-relevant behavioral outcomes in rodents following early life stress

In humans, exposure to early life stress (ELS) is an established risk factor for the development of substance use disorders (SUDs) during later life. Similarly, rodents exposed to ELS involving disrupted mother-infant interactions, such as maternal separation (MS) or adverse caregiving due to scarcity-adversity induced by limited bedding and nesting (LBN) conditions, also exhibit long-term alterations in alcohol and drug consumption. In both humans and rodents, there is a range of addiction-related behaviors that are associated with drug use and even predictive of subsequent SUDs. In rodents, these include increased anxiety-like behavior, impulsivity, and novelty-seeking, altered alcohol and drug intake patterns, as well as disrupted reward-related processes involving consummatory and social behaviors. Importantly, the expression of these behaviors often varies throughout the lifespan. Moreover, preclinical studies suggest that sex differences play a role in how exposure to ELS impacts reward and addiction-related phenotypes as well as underlying brain reward circuitry. Here, addiction-relevant behavioral outcomes and mesolimbic dopamine (DA) dysfunction resulting from ELS in the form of MS and LBN are discussed with a focus on age- and sex-dependent effects. Overall, these findings suggest that ELS may increase susceptibility for later life drug use and SUDs by interfering with the normal maturation of reward-related brain and behavioral function.

Antidepressant-Like Effect of Selected Egyptian Cultivars of Flaxseed Oil on a Rodent Model of Postpartum Depression

Flaxseed (Linum usitatissimum L.) is a multipurpose crop with health promoting potential. This study was undertaken to investigate the fatty acid profile and yield of fixed oil of six Egyptian flaxseed cultivars. The selected cultivars with the highest content of polyunsaturated fatty acids (PUFAs) (G9 and G10) were assessed for their antidepressant-like effect in rat model of postpartum depression (PPD) induced by hormone-simulated pregnancy followed by hormone withdrawal and compared to fluoxetine. As compared to control group, administration of G9 and G10 (270 mg/kg/day, p.o) for two weeks during the postpartum period can alleviate anxiety and depressive-like behaviors and biochemical changes in PPD-induced rats. This was confirmed by evaluation of anxiety-like behaviors (elevated plus maze, open field test, and forced swim test tests), in addition to biochemical analysis (brain monoamine oxidase-A, corticosterone level, proinflammatory cytokines, and hippocampal redox state). In conclusion, flaxseed oil of Egyptian cultivars G9 and G10 exhibited significant antidepressant-like effect in rat model of PPD without affecting locomotor activity. At the treatment doses, the antidepressant-like activity of Giza 9 oil is comparable to fluoxetine.

Reprint of: Locus coeruleus neuronal activity determines proclivity to consume alcohol in a selectively-bred line of rats that readily consumes alcohol

Sprague-Dawley rats selectively-bred for susceptibility to stress in our laboratory (Susceptible, or SUS rats) voluntarily consume large amounts of alcohol, and amounts that have, as shown here, pharmacological effects, which normal rats will not do. In this paper, we explore neural events in the brain that underlie this propensity to readily consume alcohol. Activity of locus coeruleus neurons (LC), the major noradrenergic cell body concentration in the brain, influences firing of ventral tegmentum dopaminergic cell bodies of the mesocorticolimbic system (VTA-DA neurons), which mediate rewarding aspects of alcohol. We tested the hypothesis that in SUS rats alcohol potently suppresses LC activity to markedly diminish LC-mediated inhibition of VTA-DA neurons, which permits alcohol to greatly increase VTA-DA activity and rewarding aspects of alcohol. Electrophysiological single-unit recording of LC and VTA-DA activity showed that in SUS rats alcohol decreased LC burst firing much more than in normal rats and as a result markedly increased VTA-DA activity in SUS rats while having no such effect in normal rats. Consistent with this, in a behavioral test for reward using conditioned place preference (CPP), SUS rats showed alcohol, given by intraperitoneal (i.p.) injection, to be rewarding. Next, manipulation of LC activity by microinfusion of drugs into the LC region of SUS rats showed that (a) decreasing LC activity increased alcohol intake and increasing LC activity decreased alcohol intake in accord with the formulation described above, and (b) increasing LC activity blocked both the rewarding effect of alcohol in the CPP test and the usual alcohol-induced increase in VTA-DA single-unit activity seen in SUS rats. An important ancillary finding in the CPP test was that an increase in LC activity was rewarding by itself, while a decrease in LC activity was aversive; consequently, effects of LC manipulations on alcohol-related reward in the CPP test were perhaps even larger than evident in the test. Finally, when increased LC activity was associated with (i.e., conditioned to) i.p. alcohol, subsequent alcohol consumption by SUS rats was markedly reduced, indicating that SUS rats consume large amounts of alcohol because of rewarding physiological consequences requiring increased VTA-DA activity. The findings reported here are consistent with the view that the influence of alcohol on LC activity leading to changes in VTA-DA activity strongly affects alcohol-mediated reward, and may well be the basis of the proclivity of SUS rats to avidly consume alcohol.

Locus coeruleus neuronal activity determines proclivity to consume alcohol in a selectively-bred line of rats that readily consumes alcohol

Sprague-Dawley rats selectively-bred for susceptibility to stress in our laboratory (Susceptible, or SUS rats) voluntarily consume large amounts of alcohol, and amounts that have, as shown here, pharmacological effects, which normal rats will not do. In this paper, we explore neural events in the brain that underlie this propensity to readily consume alcohol. Activity of locus coeruleus neurons (LC), the major noradrenergic cell body concentration in the brain, influences firing of ventral tegmentum dopaminergic cell bodies of the mesocorticolimbic system (VTA-DA neurons), which mediate rewarding aspects of alcohol. We tested the hypothesis that in SUS rats alcohol potently suppresses LC activity to markedly diminish LC-mediated inhibition of VTA-DA neurons, which permits alcohol to greatly increase VTA-DA activity and rewarding aspects of alcohol. Electrophysiological single-unit recording of LC and VTA-DA activity showed that in SUS rats alcohol decreased LC burst firing much more than in normal rats and as a result markedly increased VTA-DA activity in SUS rats while having no such effect in normal rats. Consistent with this, in a behavioral test for reward using conditioned place preference (CPP), SUS rats showed alcohol, given by intraperitoneal (i.p.) injection, to be rewarding. Next, manipulation of LC activity by microinfusion of drugs into the LC region of SUS rats showed that (a) decreasing LC activity increased alcohol intake and increasing LC activity decreased alcohol intake in accord with the formulation described above, and (b) increasing LC activity blocked both the rewarding effect of alcohol in the CPP test and the usual alcohol-induced increase in VTA-DA single-unit activity seen in SUS rats. An important ancillary finding in the CPP test was that an increase in LC activity was rewarding by itself, while a decrease in LC activity was aversive; consequently, effects of LC manipulations on alcohol-related reward in the CPP test were perhaps even larger than evident in the test. Finally, when increased LC activity was associated with (i.e., conditioned to) i.p. alcohol, subsequent alcohol consumption by SUS rats was markedly reduced, indicating that SUS rats consume large amounts of alcohol because of rewarding physiological consequences requiring increased VTA-DA activity. The findings reported here are consistent with the view that the influence of alcohol on LC activity leading to changes in VTA-DA activity strongly affects alcohol-mediated reward, and may well be the basis of the proclivity of SUS rats to avidly consume alcohol.

Repeated social defeat stress enhances the anxiogenic effect of bright light on operant reward-seeking behavior in rats

Repeated stress can trigger episodes of depression, along with symptoms of anhedonia and anxiety. Although often modeled separately, anxiogenic factors potently modulate hedonic, or appetitive, behavior. While repeated stress can increase anxiety and decrease appetitive behavior, it is not clear whether repeated stress can influence the impact of anxiogenic factors on appetitive behavior. This study tests whether repeated stress shifts behavior in a task that measures anxiogenic-appetitive balance. To test this, adult male rats were trained to lever press for sucrose pellet reward, and the effect of anxiogenic bright light on this behavior was measured. The impact of the bright light anxiogenic stimulus on lever pressing was compared between groups exposed to either daily repeated social defeat stress or control handling. We found that repeated stress reduced exploration in the open field and decreased social interaction, but had minimal effect on baseline lever pressing for reward. Repeated stress substantially enhanced the effect of anxiogenic bright light on lever pressing. This effect was greater two days after the last stress exposure, and began to diminish within two weeks. These data demonstrate that the anxiogenic and anhedonic features induced by repeated stress can be separately measured, and that the impact of anxiogenic stimuli can be greatly enhanced after repeated stress, even in the face of appetitive drive. The data also demonstrate that some apparent anhedonic-like effects of repeated stress can be due to increased sensitivity to anxiogenic stimuli, and may reflect an imbalance in an appetitive approach-withdrawal continuum.

Classical and novel approaches to the preclinical testing of anxiolytics: A critical evaluation

Over 80% of current anxiety studies employ one of the tests that were developed earlier than, or concurrently with the elevated plus-maze, i.e. before 1985. Considering 1985 as a historical reference point, we briefly review here 115 new tests and models of anxiety, the development of which was likely prompted by the poor predictive validity of classical tests as shown here by the comparison of preclinical and clinical findings with putative novel anxiolytics. The new approaches comprise major innovations to classical tests, the pre-test application of manipulations that mimic etiological factors of anxiety disorders, and entirely new approaches including anxiety disorder-specific tests. Thus, intensive test development over the last 27 years created a large pool of novel approaches. However, these are infrequently used and as such, their impact on anxiolytic drug development remains low. We suggest here that test/model development should step over the intensive phase when several new methods are proposed each year and should start selecting and establishing the methodologies that would successfully replace or complement classical tests. We propose here a novel strategy for improving the validity of anxiety testing that includes the retrospective analysis of the predictive validity of new procedures (as opposed to classical pharmacological validation), and a call for concerted international efforts at both the conceptual and practical levels. Similar endeavors proved recently successful with other psychiatric disorders.

Animal models of anxiety disorders in rats and mice: some conceptual issues

Animal models can certainly be useful to find out more about the biological bases of anxiety disorders and develop new, more efficient pharmacological and/or behavioral treatments. However, many of the current "models of anxiety" in animals do not deal with pathology itself, but only with extreme forms of anxiety which are still in the normal, adaptive range. These models have certainly provided a lot of information on brain and behavioral mechanisms which could be involved in the etiology and physiopathology of anxiety disorders, but are usually not satisfactory when confronted directly with clinical syndromes. Further progress in this field will probably depend on the finding of endophenotypes which can be studied in both humans and animals with common methodological approaches. The emphasis should be on individual differences in vulnerability, which have to be included in animal models. Finally, progress will also depend on refining theoretical constructs from an interdisciplinary perspective, including psychiatry, psychology, behavioral sciences, genetics, and other neurosciences.

Anxiolytic effects of lavender oil inhalation on open-field behaviour in rats

To establish a valid animal model of the effects of olfactory stimuli on anxiety, a series of experiments was conducted using rats in an open-field test. Throughout, effects of lavender oil were compared with the effects of chlordiazepoxide (CDP), as a reference anxiolytic with well-known effects on open-field behaviour. Rats were exposed to lavender oil (0.1-1.0 ml) for 30 min (Experiment 1) or 1h (Experiment 2) prior to open-field test and in the open field or injected with CDP (10 mg/kg i.p.). CDP had predicted effects on behaviour, and the higher doses of lavender oil had some effects on behaviour similar to those of CDP. In Experiment 3, various combinations of pre-exposure times and amounts of lavender oil were used. With sufficient exposure time and quantity of lavender the same effects were obtained as in Experiment 2. Experiment 4 demonstrated that these behavioural effects of lavender could be obtained following pre-exposure, even if no oil was present in the open-field test. In Experiments 2-4, lavender oil increased immobility. Together, these experiments suggest that lavender oil does have anxiolytic effects in the open field, but that a sedative effect can also occur at the highest doses.

Behavioral changes induced by cocaine in mice are modified by a hyperlipidic diet or recombinant leptin

The objective of the present study was to determine if the acute behavioral effects of cocaine acutely administered intraperitoneally (ip) at doses of 5, 10 and 20 mg/kg on white male CF1 mice, 90 days of age, would be influenced by leptin acutely administered ip (at doses of 5, 10 and 20 microg/kg) or by endogenous leptin production enhanced by a high-fat diet. The acute behavioral effects of cocaine were evaluated in open-field, elevated plus-maze and forced swimming tests. Results were compared between a group of 80 mice consuming a balanced diet and a high-fat diet, and a group of 80 mice fed a commercially available rodent chow formula (Ralston Purina) but receiving recombinant leptin (rLeptin) or saline ip. Both the high-fat-fed and rLeptin-treated mice showed decreased locomotion in the open-field test, spent more time in the open arms of the elevated plus-maze and showed less immobility time in the forced swimming test (F(1,68) = 7.834, P = 0.007). There was an interaction between diets and cocaine/saline treatments in locomotion (F(3,34) = 3.751, P = 0.020) and exploration (F(3,34) = 3.581, P = 0.024). These results suggest that anxiolytic effects and increased general activity were induced by leptin in cocaine-treated mice and that low leptin levels are associated with behavioral depression. Chronic changes in diet composition producing high leptin levels or rLeptin treatment may result in an altered response to cocaine in ethologic tests that measure degrees of anxiety and depression, which could be attributed to an antagonistic effect of leptin.

Dissociation in the effects of neonatal maternal separations on maternal care and the offspring's HPA and fear responses in rats

The development of the hypothalamic-pituitary-adrenal (HPA) response to stress is influenced by the early mother-infant relationship. In rats, early handling (brief daily mother-offspring separations) attenuates the adult offspring's HPA and fear responses compared to both nonhandling (no separations) and maternal separation (prolonged daily separations). It has been proposed that variation in the amount of maternal care mediates these effects of neonatal manipulations on the adult offspring's stress and fear responses. Here we tested this hypothesis by assessing maternal care and the adult offspring's HPA and fear responses in Lister hooded rats which were subjected to either early handling (EH) or maternal separation (MS) from postnatal day 1-13, or were left completely undisturbed (nonhandled, NH) throughout this period. Both EH and MS induced a more active nursing style and elevated levels of maternal care compared to NH. Total levels of maternal care were indistinguishable between EH and MS, but diurnal distribution differed. MS dams showed elevated levels of maternal care following the 4-h separation period, thereby fully compensating for the amount of maternal care provided by EH dams during the time MS dams were separated from their pups. However, while EH resulted in reduced HPA and fear responses in the adult offspring compared to NH, MS and NH offspring did not differ. Our findings therefore demonstrate dissociation in the effects of EH and MS on maternal care and on the stress and fear responses in the offspring. This indicates that maternal care cannot be the sole mediator of these effects.

Does amygdaloid corticotropin-releasing hormone (CRH) mediate anxiety-like behaviors? Dissociation of anxiogenic effects and CRH release

The brain corticotropin-releasing hormone (CRH) circuits are activated by stressful stimuli, contributing to behavioral and emotional responses. The present study assessed anxiety-like responses and in vivo neurochemical alterations at the central nucleus of the amygdala (CeA) evoked by exposure to an unfamiliar (anxiogenic) environment. Also, the impact of anxiolytic treatments and those that affect CRH were assessed in this paradigm. Novel environment (new cage) markedly suppressed ingestion of a palatable snack. This effect was dose-dependently antagonized by diazepam and was utilized as an index of anxiety in the rodent. Although exposure to a novel environment also stimulated the in vivo release of CRH and glutamate at the CeA, various CRH antagonists (e.g. alphah-CRH, Calpha-MeCRH, CP-154,526, antisauvagine-30, preproTRH178-199) did not attenuate the stressor-elicited behavioral suppression, although Calpha-MeCRH was found to attenuate the freezing response elicited by contextual stimuli that were associated with previously administered footshock. Moreover, central infusion of CRH failed to suppress snack consumption in the home cage. Although diazepam had potent anxiolytic effects in this paradigm, this treatment did not prevent the stressor-associated release of CRH and glutamate at the CeA. Thus, while neural circuits involving CRH and/or glutamatergic receptors at the CeA may be activated by an unfamiliar environment, the data challenge the view that activation of these receptors is necessary for the expression of anxiety-like behavioral responses. Rather than provoking anxiety, these systems might serve to draw attention to events or cues of biological significance, including those posing a threat to survival.

Anxiety in rats selectively bred for Fast and Slow kindling rates: situation-specific outcomes

Rats selectively bred for amygdala excitability, realized by fast or slow kindling epileptogenesis, were previously reported to exhibit differential levels of anxiety. Although the Slow kindling rats generally appeared more anxious in several behavioral tests, under certain test conditions the Fast kindling rats displayed greater anxiety or stressor reactivity. The present investigation confirmed that in a test of anxiety comprising suppression of consumption of a palatable snack in an unfamiliar environment, the Slow kindling rats exhibited greater anxiety and that this effect was attenuated by diazepam. Likewise, the acoustic startle response was greater in the Slow kindling rats. However, the fear-potentiated startle response was more pronounced in Fast kindling rats, particularly among females, irrespective of whether the test parameters elicited moderate or high startle amplitudes. The elevated startle in the Slow rats, and the fear potentiated startle in the Fast rats, were attenuated by diazepam. These data indicate the need to differentiate subtypes of anxiety in animal models, and raise the issue that anxiety elicited by specific environmental triggers may interact with genetically determined trait characteristics.

Differential involvement of amygdaloid CRH system(s) in the salience and valence of the stimuli

Anxiety is a heterogeneous term encompassing not only state or trait characteristics but also a wide range of pathologies such as generalized anxiety disorders, phobias, panic and obsessive-compulsive disorders, acute stress disorder, and posttraumatic stress disorder. Given that diverse forms of anxiety exist, numerous animal models have been developed, which are considered to be useful in identifying mechanisms underlying anxiety states. Examples of such animal models include paradigms that assess the behavioral response to neurogenic (or painful stimuli) or psychogenic stressors or to cues that had previously been associated with painful stimuli. The present report presents data regarding the impact of stressors on corticotropin-releasing hormone (CRH), and relates these to changes in anxiety-like states. Specifically, we demonstrate that (1) psychogenic stressors influence the in vivo release of CRH at the central nucleus of the amygdala (CeA); (2) although CRH changes within the CeA are exquisitely sensitive to stressors, they are also elicited by positive stimuli; and (3) while treatment with diazepam attenuates behavioral signs of anxiety, the CRH release associated with a stressor is unaffected by the treatment. The position is offered that although release of CRH within the CeA is increased under stressful conditions, it is not a necessary condition for the consequent behavioral expression of anxiety-like reactions, at least not in minimally threatening situations. We suggest that the CRH responses at the CeA may be involved in a preparatory capacity and, as such, may accompany a range of emotionally significant stimuli, be they appetitive or aversive.

Validation of a simple, ethologically relevant paradigm for assessing anxiety in mice

Although numerous behavioral tests are available to assess anxiety, we introduce a simplified version of a previously established test that is exquisitely sensitive and reliable. The latency to consume a palatable snack (graham wafer crumbs) was assessed among mice in their home cage and in an unfamiliar environment, as well as in the presence or absence of predator scent. The effects of various anxiolytics and nonanxiolytics were evaluated in these paradigms. When offered the palatable snack in a familiar environment, mice readily approached and began consumption; however, in a novel environment (cage with fresh bedding), or in the presence of predator scent (rat feces), response latencies increased 10-fold. Anxiolytics, including diazepam, chlordiazepoxide, propranolol, or chronic treatment with either buspirone or the antidepressant desmethylimipramine attenuated the effects in the novel environment without affecting home-cage responding. In contrast, nonanxiolytic agents (haloperidol, amphetamine, acute buspirone or desmethylimipramine) failed to exclusively affect novel environment-induced prolongation of response latencies. The simplicity of design, the absence of food deprivation or neurogenic stressors, the possibility of using it in a repeated measures design, the reliability and magnitude of response, and the specificity and sensitivity to anxiolytic drugs makes this an ideal preparation with which to assess anxiety and anxiety-altering manipulations.

A PET study following treatment with a pharmacological stressor, FG7142, in conscious rhesus monkeys

FG7142 is a benzodiazepine partial inverse agonist, which is known as a pharmacological stressor. Several reports demonstrated that FG7142 produced anxiety in humans, non-human primates, and rodents, and impaired working memory in non-human primates and rodents. In this study, we examined the effect of FG7142 on cerebral blood flow and glucose metabolism using positron emission tomography (PET) in conscious rhesus monkeys. Male rhesus monkeys were intramuscularly treated with FG7142 (0.2 or 1.0 mg/kg, n=5, respectively), and regional cerebral blood flow (rCBF) and regional cerebral metabolic rate of glucose (rCMRglc) were measured by PET 20 min and 40 min after treatment, respectively. During PET measurement, physiological parameters and plasma cortisol levels were monitored. FG7142 significantly decreased rCBF in the thalamus and rCMRglc in all brain regions examined in a dose-dependent manner without changes in physiological parameters. FG7142 also significantly increased plasma cortisol levels. The present study may provide an important insight into the understanding of the pathophysiology of anxiety and stress-related disorders in humans, and strongly suggesting that prevention of anxiety or stress is important when measuring conscious brain function.

Corticosterone response in the chick separation-stress paradigm

Corticosterone response to separation stress and its sensitivity to the anxiolytic, chlordiazepoxide (CDP), were examined in 7-day-old domestic fowl (Gallus gallus). Saline or CDP (8.0 mg/kg) was injected intramuscularly 30 min before tests. Chicks were placed in isolation either with or without mirrors for a 15-min observation period, in which distress vocalizations were recorded. After testing, chicks were euthanized and blood was collected for the corticosterone assay. Chicks tested in the No-Mirror condition displayed an increase in vocalizations that was attenuated by CDP. Similarly, corticosterone levels were highest in chicks tested in the No-Mirror condition; however, CDP only modestly attenuated corticosterone levels. The present findings demonstrate that corticosterone levels parallel the behavioral marker of distress vocalizations in this paradigm, but this biological marker may be less sensitive than the behavioral marker to benzodiazepine anxiolytic manipulations.

Neurochemical and behavioral alterations elicited by a chronic intermittent stressor regimen: implications for allostatic load

Although stressors induce a series of adaptive neurochemical changes, sustained physiological activation associated with protracted stressor exposure may engender adverse effects (allostatic load). In the present investigation CD-1 mice exposed to a series of different stressors, twice a day over 54 days, exhibited increased signs of depression and anxiety, including increased passivity in a forced swim test, reduced aggression in a social interaction test, and delayed approach to food in a novel environment. Consistent with the view that a chronic stressor regimen affects immune-related processes, sickness behavior elicited by the proinflammatory cytokine, interleukin-1beta, was augmented in response to a chronic but not an acute stressor. Relative to nonstressed mice, median eminence serotonin was augmented by the cytokine treatment administered 24 h after chronic stressor exposure. Treatment with IL-1beta diminished plasma growth hormone levels and increased circulating corticosterone levels irrespective of the animals stressor history. It is suggested that chronic stressor exposure may instigate relatively protracted neurochemical effects, thereby influencing the behavioral responses to later psychological and systemic challenges.

Administration of high-dose ketoconazole, an inhibitor of steroid synthesis, prevents posttraumatic anxiety in an animal model

Acute psychological stress is the presumed immediate cause of post-traumatic stress disorder (PTSD), and may also contribute to other anxiety disorders. Abnormal activity of the hypothalamic-pituitary-adrenal (HPA) axis has been tentatively implicated in some of the features of these disorders. Ketoconazole (KTCZ), an imidazole derivative, is a potent inhibitor of gonadal and adrenal steroidogenesis. The aim of this study was to explore the effects of KTCZ blockade of adrenal steroidogenesis, and consequent elevation of adreno-corticotropic hormone (ACTH), on a model of chronic post-traumatic anxiety in rats. Amelioration of anxious behaviors after reduction of corticosterone would suggest that corticosterone (and by implication cortisol in humans) is an important mediator of anxious symptoms: exacerbation of such behaviors would suggest that corticosterone elevations are only secondary, and possibly implicate corticotropin releasing hormone (CRH) and/or ACTH in the pathogenesis of anxious symptoms. We exposed rats for 10 min to cat scent, a prima facie valid model for acute psychological stress, with and without high dose KTCZ for 14 days. Treatment with KTCZ abolished the chronic behavioral effects of acute exposure to a cat scent. Lower levels of anxious behavior in KTCZ-treated and exposed rats were accompanied by lower plasma corticosterone, ACTH and prolactin (PRL) levels compared to untreated exposed rats. Results in this model implicate corticosterone, but not ACTH, in the pathogenesis of chronic anxiety following acute psychological stress.

T-lymphocyte activation increases hypothalamic and amygdaloid expression of CRH mRNA and emotional reactivity to novelty

Stimulation of T-cells with staphylococcal enterotoxin B (SEB) significantly elevates interleukin-2 (IL-2) and contemporaneous activation of the hypothalamic-pituitary-adrenal (HPA) axis and c-fos in the paraventricular nucleus (PVN) of BALB/cByJ mice. Such neural signaling may promote cognitive and emotional adaptation before or during infectious illness. Because corticotropin-releasing hormone (CRH) is an anxiogenic neuropeptide that may mediate the stressor-like effects of immunological stimuli, we measured neuronal CRH mRNA alterations in mice challenged with SEB. Increased CRH mRNA levels were observed in the PVN and central nucleus of the amygdala (ceA) 4-6 hr after SEB administration. This was associated with plasma ACTH increases, which could be abrogated by the systemic administration of anti-CRH antiserum. Additional experiments did not support a role for IL-2 or prostaglandin synthesis in activating the HPA axis. Behavioral experiments testing for conditioned taste aversion did not confirm that SEB challenge promotes malaise. However, consistent with the notion that central CRH alterations induced by SEB may affect emotionality (e.g., fear), SEB challenge augmented appetitive neophobia in a context-dependent manner, being marked in a novel and stressful environment. It is hypothesized that immunological stimuli generate a cascade of events that solicit integrative neural processes involved in emotional behavior. As such, these data support the contention that affective illness may be influenced by immunological processes and the production of cytokines and are consistent with other evidence demonstrating that autoimmune reactivity is associated with enhanced emotionality.

Selective breeding of rats for high and low motor activity in a swim test: toward a new animal model of depression

Because low motor activity ina swim test has been found to represent "depression-like" behavior in the rat, Sprague-Dawley (SD) albino rats were selectively bred for low motor activity (low struggling time/high floating time) in a swim test, while others were bred for high motor activity (high struggling time/low floating time). Eighty-four male and 42 female SD rats were initially purchased from Charles-River Breeding Laboratories in 1987, their behavior assessed in a 15-min swim test, and selective breeding carried out by mating those male and female rats that showed either low or high levels of motor activity in the test; results from behavioral testing of the first 18 generations produced by this selective breeding process are reported here. Two rat lines have been obtained, Swim Low-Active (SwLo) and Swim High-Active (SwHi) rats, which differ dramatically in swim-test behavior--SwLo rats show little struggling and much floating, while SwHi rats show the reverse. Activity scores of individual SwLo and SwHi rats now show no overlap. Selective breeding has produced bidirectional changes; that is, SwLo rats are considerably less active than randomly bred Sprague-Dawley albino rats, while SwHi rats are considerably more active than randomly bred rats. Measuring activity of SwLo and SwHi rats in other situations--ambulation in the home cage, open-field activity, exploratory activity in a novel, home cage-like situation, and immobility in the Porsolt swim test--revealed that differences are most pronounced when animals respond to acute challenges; under these conditions, SwHi rats show active, assertive behavior, whereas SwLo rats show a distinct absence of this type of response. When SwLo rats from the 8th to the 11th generations were given antidepressant medication [desipramine, (DMI), a tricyclic, or phenelzine, an MAO inhibitor], chronic but not acute administration of both drugs increased swim-test activity of SwLo rats. Buspirone, an anxiolytic, did not increase activity of SwLo rats. Use of animals selectively bred for high and low activity in the swim test may represent a new tool for studying physiological processes relevant to affective disorders and for testing antidepressant drugs/treatments.

Anxiogenic-like effects of Tagetes minuta L essential oil on T-maze and tonic immobility behaviour in domestic chicks

In a first experiment, four doses (ranging between 0.04 and 0.45 mg/kg of body weight) of the essential oil from Tagetes minuta L. were subcutaneously injected in two-day-old chicks and a dose-response curve assessed for escape performance in a T-maze test. The 0.1, 0.25 and 0.45 mg/kg doses impaired the first escape performance suggesting an anxiogenic-like effect of the essential oil. After 3 h the same chicks were tested for a second escape performance, without being injected again, and no differences were observed compared to controls, suggesting that the essential oil did not affect retention. Furthermore, the effects of the essential oil were observed in the three sections of the T-maze apparatus. So, the performance was impaired in the isolation chamber section, suggesting the induction of increased anxiogenic behaviour, and also in the mirror section, suggesting that the social reinstatement behaviour was modified by an increased anxiety level. Changes in the principal corridor section were not observed, suggesting that the locomotor activity was not affected by these oil doses. The second escape performance was not affected in any of the T-maze sections, confirming that these doses did not affect learning ability. In a second experiment, a middle dose of the essential oil (0.25 mg/kg) increased the tonic immobility reaction in 15 days old chicks similarly to an anxiogenic dose of FG 7142 (1 mg/kg), while an anxiolytic dose of diazepam (0.08 mg/kg) did not affect this behaviour. Taken together, the present results suggest that the essential oil from Tagetes minuta L. may exert a negative modulation on the GABAergic function without affecting the learning ability.

A primate model of anxiety

Pentylenetetrazol (PTZ; 30 mg/kg, i.m.) produced an acute anxiogenic effect on the behaviour of a social colony of rhesus monkeys acclimatized to laboratory conditions. The animals exhibited hypervigilance, aggressiveness, tachypnea, piloerection and frequent change of posture and also had raised plasma cortisol levels. These effects of PTZ were antagonized by benzodiazepines (diazepam; 1 mg/kg, i.v. and alprazolam; 0.05 mg/kg, p.o.). Non-benzodiazepine anxiolytic drug (buspirone; 10 mg/kg, p.o.) blocked the behavioural effects but not the rise in plasma cortisol concentration. On the other hand, pretreatment with hypnosedative (promethazine; 5 mg/kg, i.m.) or anticonvulsant (sodium valproate; 40 mg/kg, p.o.) agents did not attenuate the effects of PTZ indicating the specificity of its anxiogenic response. The model, thus, seems suitable for evaluation of potential anxiolytic agents.

Diazepam attenuation of restraint stress-induced corticosterone levels is enhanced by prior exposure to repeated restraint

Prior research has demonstrated that diazepam decreases hypothalamic-pituitary-adrenal cortex (HPA) axis activity in stressful contexts but, paradoxically, acts as a stimulator of basal axis activity. Also, several investigators have reported that low doses of diazepam are not effective in reducing stress-induced corticosterone (CORT) levels, yet similar doses typically produce anxiolytic effects on behavioral measures of fear and anxiety. We have examined the effects of diazepam on plasma CORT levels in male Sprague-Dawley rats utilizing a repeated restraint paradigm. Consistent with most literature, diazepam administered IP (1.5, 3.0, or 6.0 mg/kg) 1 h prior to restraint increased non-stress, baseline plasma CORT levels in a dose-dependent fashion. During the first exposure to the 1 h restraint-stress procedure, CORT levels of diazepam-injected rats did not differ from the stress levels of controls except at the 60-min stress time point in those subjects receiving 6.0 mg/kg. However, diazepam at all three doses was able to attenuate the stress-induced increase in CORT following 5 days of diazepam+restraint treatment. Using the 3.0 mg/kg dose as a probe, it was found that this effect was not dependent on the repeated administration of diazepam, but rather on repeated exposure to restraint. These results suggest that repeated restraint produces a change in neural sensitivity to benzodiazepines.

Inositol has behavioral effects with adaptation after chronic administration

Inositol is a simple dietary polyol that serves as a precursor in important second messenger systems. Inositol in pharmacological doses has been reported recently to be therapeutic in depression, panic disorder and obsessive compulsive disorder. We hereby report effects of inositol on the elevated plus maze model of anxiety. These results should allow development of new inositol analogs that could expand psychoactive drug development possibilities via second messenger manipulation.

Effects of diazepam on conflict behaviour and on plasma corticosterone levels in male and female rats

The anxiolytic properties of diazepam and its effects on plasma corticosterone levels were compared in male and female, water deprived rats exposed to the punished (0.8 mA) drinking procedure. The effects of diazepam on unpunished licking, tested under familiar or unfamiliar conditions, and on the lick latency were also studied and a comparison between the two sexes was made. Both punished and unpunished drinking were less in females than in males. In both sexes, a clear anticonflict effect, i.e. a much greater effect on punished than on unpunished drinking, was obtained with 2 and 4 mg/kg, but not with 1 mg/kg, of diazepam i.p. Plasma corticosterone levels were higher in water deprived females than in males. Following the punished and unpunished drinking procedure, plasma corticosterone levels were found to have decreased more in female than in male rats, especially after administration of 1 mg/kg of diazepam. Diazepam had similar anticonflict effects in rats of both sexes but had a greater suppressive effect on the plasma corticosterone levels in female rats. There was no correlation between the anxiolytic effects of diazepam and its effect on the plasma corticosterone levels. When testing was done under unfamiliar conditions, the latency to licking was greater in female than in male rats and diazepam (1, 2 and 4 mg/kg) increased this latency in both sexes. The results suggest sex differences in the neuroendocrine, but not in the anxiolytic, effects of diazepam.

Depression and anxiety: role of the locus coeruleus and corticotropin-releasing factor

Based on studies of depression and anxiety using animal (rat) models, it is suggested that, contrary to a widely accepted theory, increased activity of locus coeruleus (LC) neurons does not appear to potentiate anxiety; instead, the influence of LC activity may be opposite to this. First, studies are described that indicate that behavioral changes resembling what is seen in human clinical depression occur in rats exposed to highly stressful conditions, and the research is then traced, which links this stress-induced depression to disturbance of normal noradrenergic regulation of LC activity. Second, the potential role of corticotrophin releasing factor (CRF) in stress-induced behavioral depression is explored. CRF infused into the LC did not produce behavioral depression in the swim test but did increase anxiety; by comparison, CRF infused into the parabrachial nucleus lateral to LC increased both depression and anxiety. Finally, to further explore the relationship between LC activity and anxiety, drugs were infused into LC region to attempt to specifically activate or depress firing of LC neurons. In contrast to expectations, infusion to decrease firing of LC cells increased anxious behavior, while infusion to increase firing decreased anxious behavior. Several other studies are discussed that point to a similar conclusion. It is suggested that, at least in rats, the capacity of stress-inducing or aversive stimuli to activate LC neurons does not potentiate anxiety under environmental conditions that elicit this response, but, rather, the increased activity of the LC/dorsal noradrenergic system under such conditions may exert a counterbalancing, antianxiety influence.