One stressful event blocks multiple actions of diazepam for up to at least a month

Time-Dependent Sensitization in Animals: A Possible Model of Multiple Chemical Sensitivity in Humans

It of ten happens in science that clues to the nature of a problem under study come from a completely different, seemingly unrelated, line of investigation. This may be the case with MCS and Time-Dependent Sensitization (TDS), a phenomenon we discovered in rats in the late 1970s and later named. TDS refers to the ability of mild stressors whether pharmacological or environmental to induce physiological and behavioral effects which then progress, i.e., get stronger, entirely as a function of the passage of time since stressor presentation. This strengthening is revealed when the organism is later exposed to either the original or another stressor. The characteristics of TDS bear a remarkable resemblance to the features of MCS and that similarity is the subject of this manuscript.

White Paper: Neuropsychiatric Aspects of Sensitivity to Low-Level Chemicals: A Neural Sensitization Model

The present paper summarizes the proposed time-dependent sensitization (TDS) and partial limbic kindling model for illness from low-level chemicals; reviews and critiques prior studies on CNS aspects of multiple chemical sensitivity (MCS); and outlines possible experimental approaches to future studies. TDS is the progressive and persistent amplification of behavioral, neurochemical, endocrine, and/or immunological responses to repeated intermittent stimuli over time. Partial limbic kindling is a progressive and persistent lowering of the threshold for eliciting electrical afterdischarges, but not motor seizures, in certain brain structures such as amygdala and hippocampus; behavioral consequences include increased avoidant behaviors.

The focus of the paper is the controversial claim of altered sense of smell and illness from low levels of environmental chemicals (i. e., cacosmia), levels that should not have any biologically harmful effects by the rules of classical neurotoxicology. A major perspective of this paper is that the phenomenology of MCS is similar to that of time-dependent sensitization (reverse tolerance) and tolerance as studied in the substance abuse literature.

The TDS model for MCS proposes that neurobiological amplification underlies the symptoms and phenomenology of these patients, including their behavioral features of heightened affective and somatic distress. It is hypothesized that MCS patients, who are mostly women, may be individuals who sensitize to substances rapidly and to the extreme, to the point of aversive symptomatology with less complete capacity for development of tolerance. Possible parallels between MCS and TDS include: (a) initiation by single or multiple intermittent

Activation of HDAC4 and GR signaling contributes to stress-induced hyperalgesia in the medial prefrontal cortex of rats

"Stress-induced hyperalgesia (SIH)" is a phenomenon that stress can lead to an increase in pain sensitivity. Epigenetic mechanisms have been known to play fundamental roles in stress and pain. Histone acetylation is an epigenetic feature that is changed in numerous stress-related disease situations. However, epigenetic mechanism for SIH is not well known. We investigated the effect of histone acetylation on pain hypersensitivity using SPS (single-prolonged stress) + CFA (complete Freund's adjuvant) model. We showed that the glucocorticoid receptor (GR)-pERK-pCREB-Fos signaling pathway was upregulated on stress-induced hyperalgesia and the paw withdrawal threshold in the SPS + CFA group dropped significantly compared with the SPS or CFA group. Histone deacetylases 4 (HDAC4)-expressing neurons in the medial prefrontal cortex (mPFC) were increased in the SPS + CFA-exposed group compared with CFA-exposed or SPS-exposed group. And we showed that the effects of stress-induced hyperalgesia were critically regulated via reversible acetylation (HDAC4) of the GR. Inhibiting HDAC4 by microinjection of sodium butyrate into the mPFC could disrupt glucocorticoid receptor (GR) signaling pathway, which lowered SPS + CFA-caused mechanical allodynia and alleviated anxiety-like behavior. Together, our studies suggest that HDAC inhibitors might involve in the process of stress-induced hyperalgesia.

Post-traumatic stress disorder and beyond: an overview of rodent stress models

Post-traumatic stress disorder (PTSD) is a psychiatric disorder of high prevalence and major socioeconomic impact. Patients suffering from PTSD typically present intrusion and avoidance symptoms and alterations in arousal, mood and cognition that last for more than 1 month. Animal models are an indispensable tool to investigate underlying pathophysiological pathways and, in particular, the complex interplay of neuroendocrine, genetic and environmental factors that may be responsible for PTSD induction. Since the 1960s, numerous stress paradigms in rodents have been developed, based largely on Seligman's seminal formulation of 'learned helplessness' in canines. Rodent stress models make use of physiological or psychological stressors such as foot shock, underwater trauma, social defeat, early life stress or predator-based stress. Apart from the brief exposure to an acute stressor, chronic stress models combining a succession of different stressors for a period of several weeks have also been developed. Chronic stress models in rats and mice may elicit characteristic PTSD-like symptoms alongside, more broadly, depressive-like behaviours. In this review, the major existing rodent models of PTSD are reviewed in terms of validity, advantages and limitations; moreover, significant results and implications for future research-such as the role of FKBP5, a mediator of the glucocorticoid stress response and promising target for therapeutic interventions-are discussed.

Activation of extracellular signal-regulated kinase1/2 in the medial prefrontal cortex contributes to stress-induced hyperalgesia

Stressful stimuli can exacerbate persistent pain disorder. However, the underlying mechanism is still unknown. Here, to reveal the underlying mechanism for stressful stimuli-induced hyperalgesia in chronic pain, we investigated the effect of extracellular signal-regulated kinase1/2 (ERK1/2) activation on pain hypersensitivity using single-prolonged stress (SPS) model, complete Freund's adjuvant (CFA) model and SPS + CFA model. The experimental results revealed significantly reduced paw withdrawal threshold in the SPS, CFA, and SPS + CFA group compared with the control group. However, the increased phosphorylation of ERK1/2 in the medial prefrontal cortex (mPFC) was observed in the SPS- or SPS + CFA-exposed group but not the CFA group compared with control group. There was also a significant increase in mPFC ERK1/2 phosphorylation and mechanical allodynia after SPS + CFA treatment compared to SPS or CFA treatment alone. Furthermore, inhibiting ERK1/2 phosphorylation by microinjection of U0126, a MAPK kinase (MEK) inhibitor, into the mPFC attenuated SPS + CFA- and SPS- but not CFA-induced mechanical allodynia, anxiety-like behavior, and cognitive impairments. These results suggest that the activation of ERK1/2 in the mPFC may contribute to the process of stress-induced cognitive and emotional disorders, leading to an increase in pain sensitivity.

A model for homeopathic remedy effects: low dose nanoparticles, allostatic cross-adaptation, and time-dependent sensitization in a complex adaptive system

Background

This paper proposes a novel model for homeopathic remedy action on living systems. Research indicates that homeopathic remedies (a) contain measurable source and silica nanoparticles heterogeneously dispersed in colloidal solution; (b) act by modulating biological function of the allostatic stress response network (c) evoke biphasic actions on living systems via organism-dependent adaptive and endogenously amplified effects; (d) improve systemic resilience.

Discussion

The proposed active components of homeopathic remedies are nanoparticles of source substance in water-based colloidal solution, not bulk-form drugs. Nanoparticles have unique biological and physico-chemical properties, including increased catalytic reactivity, protein and DNA adsorption, bioavailability, dose-sparing, electromagnetic, and quantum effects different from bulk-form materials. Trituration and/or liquid succussions during classical remedy preparation create “top-down” nanostructures. Plants can biosynthesize remedy-templated silica nanostructures. Nanoparticles stimulate hormesis, a beneficial low-dose adaptive response. Homeopathic remedies prescribed in low doses spaced intermittently over time act as biological signals that stimulate the organism’s allostatic biological stress response network, evoking nonlinear modulatory, self-organizing change. Potential mechanisms include time-dependent sensitization (TDS), a type of adaptive plasticity/metaplasticity involving progressive amplification of host responses, which reverse direction and oscillate at physiological limits. To mobilize hormesis and TDS, the remedy must be appraised as a salient, but low level, novel threat, stressor, or homeostatic disruption for the whole organism. Silica nanoparticles adsorb remedy source and amplify effects. Properly-timed remedy dosing elicits disease-primed compensatory reversal in direction of maladaptive dynamics of the allostatic network, thus promoting resilience and recovery from disease.

Summary

Homeopathic remedies are proposed as source nanoparticles that mobilize hormesis and time-dependent sensitization via non-pharmacological effects on specific biological adaptive and amplification mechanisms. The nanoparticle nature of remedies would distinguish them from conventional bulk drugs in structure, morphology, and functional properties. Outcomes would depend upon the ability of the organism to respond to the remedy as a novel stressor or heterotypic biological threat, initiating reversals of cumulative, cross-adapted biological maladaptations underlying disease in the allostatic stress response network. Systemic resilience would improve. This model provides a foundation for theory-driven research on the role of nanomaterials in living systems, mechanisms of homeopathic remedy actions and translational uses in nanomedicine.

Genetic Component of Noise Sensitivity

We investigated the genetic component of noise sensitivity using a twin-study design. The study sample consisted of 573 same-sexed twin pairs from the Finnish Twin Cohort. The 131 monozygotic (MZ) and 442 dizygotic (DZ) twin pairs with an age range of 31 to 88 years replied to a questionnaire on noise and health-related items in 1988. The noise sensitivity of respondents was defined as high, quite high, quite low or low. MZ pairs were more similar with regards noise sensitivity than DZ pairs, and quantitative genetic modeling indicated significant familiality. The best z-fitting genetic model provided an estimate of heritability of 36% (95% CI = .20–.50) and when hearing impaired subjects were excluded this rose to 40% (95% CI = .24–.54). In conclusion, noise sensitivity does aggregate in families and probably has a genetic component.

EEG ALPHA SENSITIZATION IN INDIVIDUALIZED HOMEOPATHIC TREATMENT OF FIBROMYALGIA

Fibromyalgia (FM) patients show evidence of sensitizability in pain pathways and electroencephalographic (EEG) alterations. One proposed mechanism for the claimed effects of homeopathy, a form of complementary medicine used for FM, is time-dependent sensitization (TDS, progressive amplification) of host responses. This study examined possible sensitization-related changes in EEG relative alpha magnitude during a clinical trial of homeopathy in FM. A 4-month randomized, placebo-controlled double-blind trial of daily orally administered individualized homeopathy in physician-confirmed FM, with an additional 2-month optional crossover phase, included three laboratory sessions, at baseline, 3 and 6 months (N = 48, age 49.2 +/- 9.8 years, 94% women). Nineteen leads of EEG relative alpha magnitude at rest and during olfactory administration of treatment and control solutions were evaluated in each session. After 3 months, the active treatment group significantly increased, while the placebo group decreased, in global alpha-1 and alpha-2 during bottle sniffs over sessions. At 6 months, the subset of active patients who stayed on active continued to increase, while the active-switch subgroup reversed direction in alpha magnitude. Groups did not differ in resting alpha. Consistent with the TDS hypothesis, sniff alpha-1 and alpha-2 increases at 6 months versus baseline correlated with total amount of time on active remedy over all subjects (r = 0.45, p = .003), not with dose changes or clinical outcomes in the active group. The findings suggest initiation of TDS in relative EEG alpha magnitude by daily oral administration of active homeopathic medicines versus placebo, with laboratory elicitation by temporolimbic olfactory stimulation or sniffing.

Long-term neuroendocrine and behavioural effects of a single exposure to stress in adult animals

There is now considerable evidence for long-lasting sequels of stress. A single exposure to high intensity predominantly emotional stressors such as immobilisation in wooden-boards (IMO) induces long-term (days to weeks) desensitization of the hypothalamic-pituitary-adrenal (HPA) response to the same (homotypic) stressor, whereas the response to novel (heterotypic) stressors was enhanced. In addition, long-lasting changes in behaviour have been described after a single exposure to brief or more prolonged sessions of shocks, predator, predator odour, underwater stress or a combination of three stressors on 1 day. The most consistent changes are reduced entries into the open arms of the elevated plus-maze and enhanced acoustic startle response, both reflecting enhanced anxiety. However, it is unclear whether there is any relationship between the intensity of the stressors, as evaluated by the main physiological indexes of stress (e.g. HPA axis), the putative traumatic experience they represent and their long-term behavioural consequences. This is particularly critical when trying to model post-traumatic stress disorders (PTSD), which demands a great effort to validate such putative models.

Potentiation of glucocorticoid release does not modify the long-term effects of a single exposure to immobilization stress

RATIONALE

Previous work has shown that a single exposure of rats to a severe stressor (immobilization, IMO) results, days to weeks later, in a reduced response (desensitization) of the hypothalamic-pituitary-adrenal (HPA) axis to a second exposure to the same stressor.

OBJECTIVES

In the present work, we studied the influence of both length of exposure to IMO and circulating levels of corticosterone on the first day on the degree of desensitization of two sets of physiological variables: HPA hormones and food intake.

METHODS

Rats were given SC saline or ACTH administration and then exposed to IMO for 0, 1 or 20 min. Seven days later, all rats were exposed to 20 min IMO. HPA response was followed on both experimental days by repeated blood sampling and food intake was measured on a 24-h basis.

RESULTS

Both ACTH administration and IMO activates the HPA axis and IMO reduced food intake for several days. A single previous experience with IMO enhanced the post-IMO return of HPA hormones to basal levels on day 8 and reduced the degree of anorexia. The protective effect of previous IMO on food intake was independent of, whereas that on HPA activation was positively related to, the length of exposure on day 1. Concomitant ACTH administration on day 1 did not modify the observed effects.

CONCLUSIONS

Long-term protective effects of a single exposure to IMO are observed even with a brief exposure, but they are not potentiated by increasing corticosterone levels during the first exposure.

Chronic psychosocial stress impairs learning and memory and increases sensitivity to yohimbine in adult rats

BACKGROUND

It is well known that intense and prolonged stress can produce cognitive impairments and hippocampal damage and increase noradrenergic activity in humans. This study investigated the hypothesis that chronic psychosocial stress would affect behavior, drug sensitivity, and hippocampal-dependent learning and memory in rats. The work provides a novel connection between animal and human studies by evaluating the effects of stress on a rat's response to yohimbine, an alpha(2) adrenergic receptor antagonist.

METHODS

Rats were exposed to a cat for 5 weeks and randomly housed with a different group of cohorts each day (psychosocial stress). The effects of the stress manipulations were then assessed on open field behavior, spatial learning and memory in the radial arm water maze and the behavioral response to a low dose of yohimbine (1.5 mg/kg).

RESULTS

Stressed rats displayed impaired habituation to a novel environment, heightened anxiety, and increased sensitivity to yohimbine. In addition, the stressed rats exhibited impaired learning and memory.

CONCLUSIONS

There are commonalities between the current findings on stressed rats and from studies on traumatized people. Thus, psychosocial stress manipulations in rats may yield insight into the basis of cognitive and neuroendocrine disturbances that commonly occur in people with anxiety disorders.

Maturational increases in c-fos expression in the ascending dopamine systems

The unique maturational period of adolescence is replete with numerous changes in anatomy and function that may yield clues as to why drug abuse emerges at this stage. The behavioral effects of amphetamine are diminished during periadolescence (35 days) relative to younger (21 days) and older (>60 days) rats, prompting us to examine amphetamine effects on neuronal activation with the immediate early gene, c-fos. Amphetamine (1 and 5 mg/kg, i.p.) increased c-fos immunoreactivity in rats 21, 35, and 60 days of age in a dose-dependent manner. When expressed as a percentage of vehicle for each age, amphetamine-induced effects on c-fos immunoreactivity were higher at 21 days of age compared with the effects at 35 and 60 days of age in the nucleus accumbens core and shell, striatum, and prefrontal cortex. These data provide a possible reason as to why stimulants produce dysphoria in children, before transitioning to euphoria during adolescence. Implications of these results are discussed for stimulant use in a pediatric population and the development of drug abuse.

Effects of social defeat and of diazepam on behavior in a resident-intruder test in male DBA/2 mice

Social stress induces robust behavioral and physiological changes, some of which may alter the responsiveness to pharmacological agents, including diazepam (DZP). We used a resident-intruder paradigm to (1) develop a comprehensive ethogram of behavioral changes following social defeat (SD) in the socially reactive strain, DBA/2 male mice, (2) determine whether acute exposure of DBA/2 mice to low-dose DZP would induce flight or aggressive behavior, both of which have been observed in other rodent models and (3) to test whether prior social stress affects responses to DZP. Behavioral responses to a nonaggressive intruder (NAI) mouse 24 h post-SD were measured in resident subject mice exposed to DZP (0, 0.5, 2.0 mg/kg, ip) either prior to the resident-intruder test (Experiment 1) or immediately post-SD (Experiment 2); control mice were not defeated (NOSD). In general, SD mice displayed increased passive and active avoidance, defense, immobility, and risk assessment relative to NOSD mice. In Experiment 1, mice treated acutely with 0.5 mg/kg DZP had more approach and flight behavior, while those treated with 2.0 mg/kg DZP had more avoidance than vehicle-treated mice, independent of SD. In Experiment 2, acute DZP (2 mg/kg) induced effects 24 h later, possibly secondary to withdrawal. In a nonsocial context (Experiment 3), DZP increased exploratory activity.

Single exposure to stressors causes long-lasting, stress-dependent reduction of food intake in rats

A single exposure to severe stressors has been shown to cause anorexia in the next 24 h, but the duration of such alterations is not known. Male Sprague-Dawley rats were subjected to different stressors, and food intake was measured for several days after stress. In experiment 1, 2 h of immobilization (Imo) and lipopolysaccharide (LPS) administration (1,000 microgram/kg) caused a marked anorexia in the 24 h after stress, which persisted on poststress day 3. In experiment 2, changes in food intake after LPS and Imo were followed until total recovery. As in experiment 1, LPS caused initially a greater degree of anorexia than Imo, but normal food intake recovered much faster (poststress day 3 vs. poststress day 9). Changing the period of exposure to Imo between 20 min and 6 h (experiment 3) only slightly modified the pattern of response to the stressor. When different doses of LPS (50, 250, and 1,000 microgram/kg) were tested in experiment 4, a dose-dependent effect on food intake was observed, the greatest doses causing the most marked and lasting effect. The present results showed stressor-specific lasting changes in food intake caused by a single exposure to some stressors, the effect of a severe psychological stressor such as Imo being more lasting than that of LPS, despite a lower initial anorexia. A severe psychological stressor and a physical stressor such as LPS appear to change food intake in different ways.

Diazepam has no beneficial effects on stress-induced behavioural and endocrine changes in male tree shrews

The present study evaluated the effect of subchronic oral treatment of psychosocially stressed male tree shrews with diazepam on locomotor activity, marking behavior, avoidance behavior, and urinary cortisol and noradrenaline. To mimic a realistic situation of anxiolytic intervention, the treatment started 14 days after the beginning of psychosocial stress; at that time, the stress-induced behavioral and endocrine alterations had been established. The drug (5 mg/kg/day) was administered orally in the morning, while the psychosocial stress continued during the whole treatment period; the therapeutic action of diazepam treatment was followed across 7 days. Twenty-four hours after the last application serum concentrations of diazepam and its major metabolites were determined via HPLC. The results revealed concentrations of 7 ng/ml for diazepam, 106 ng/ml for nordiazepam, 22 ng/ml for temazepam, and 30 ng/ml for oxazepam. Treatment of subordinate animals with diazepam did not reveal a beneficial effect to any of the parameters studied. This contrasts to earlier findings showing that the behavioral and neuroendocrine alterations produced by this stress paradigm are sensitive to chronic treatment with the tricyclic antidepressant clomipramine. The present results support the view that in male tree shrews the state induced by psychosocial stress might be more depression related than anxiety related.

Differential regulation of hippocampal glucocorticoid receptors mRNA and fast feedback: relevance to post-traumatic stress disorder

Hippocampal glucocorticoid receptors (GR and MR) play an important role in glucocorticoid negative feedback. Abnormalities in negative feedback are found in depression and in post-traumatic stress disorder (PTSD), suggesting that GR and MR might be involved in the pathophysiology of these disorders. Enhanced negative feedback, the PTSD-specific neuroendocrine abnormality, can be induced in animals using a single prolonged stress (SPS) paradigm (a number of different stressors in one prolonged session, 'no stress' interval and a testing session one week later). In the current study, we examined hippocampal GR and MR mRNA distribution in the same animals that exhibited altered negative feedback following the SPS. Seven groups of adult Sprague-Dawley male rats (seven animals each) were used in two studies, comparing unstressed controls to acutely stressed animals (SPS: 24 h group), SPS animals (seven and 14 days), and SPS + chronic stress animals. GR and MR mRNA distribution across hippocampal subfields was studied using in-situ hybridization with 35S-labelled cRNA probes. Acute stress produced down-regulation of GR and MR mRNA across all hippocampal subfields. Seven days later (SPS-7 group), there was a differential recovery, with GR mRNA reaching higher than the prestress levels, and MR mRNA remaining down-regulated. The same differential regulation was present in the 14-day group. Chronically stressed animals that exhibited normal fast feedback also had normalization in their GR and MR mRNA levels. The MR/GR ratio was decreased only in animals that had enhanced fast feedback. These findings suggest that the increase in GR, in hippocampus is involved in the fast feedback hypersensitivity observed in the SPS animals, and might also underlie enhanced dexamethasone sensitivity found in PTSD. Since differential activation of GR and MR can modulate memory, behavioural responsivity, anxiety and fear, change in MR/GR ratio might also explain other PTSD-related phenomena.

Clinical application of time-dependent sensitization to antidepressant therapy

1. A number of animal studies have shown that the actions of numerous drugs can grow or sensitize with the passage of time following even a single treatment, to achieve results equal to or greater than those seen after chronic administration. 2. Our laboratory earlier proposed that this principle might be applied to the treatment of human disorders. It was suggested that the same results might be achieved by giving drugs once every one or two weeks rather than daily, or, even more likely, several-times-daily. 3. Here the authors review the clinical literature relevant to that hypothesis, as it relates to antidepressant therapies. 4. The evidence uniformly supports our earlier thesis that the therapeutic influence of antidepressants would grow with the passage of time, even as their pharmacokinetic actions are declining.

The temporal dynamics of the stress response

This paper summarises the available evidence that failure of defense mechanisms in (semi)-natural social groups of animals may lead to serious forms of stress pathology. Hence the study of social stress may provide animal models with a high face validity. However, most of the animal models of human stress-disorders have concentrated on the consequences of chronic exposure to stressors. The present paper considers recent data, indicating that a single experience with a major stressor in the form of social defeat may have long-term consequences ranging from hours to days and weeks. It seems that the experience of a major stressor sensitizes the animal to subsequent stressors. The consequences of these long-term temporal dynamics of the stress response to the development of stress-related disorders and stress-vulnerability are discussed.

Stress-restress: effects on ACTH and fast feedback

Glucocorticoid secretion is tightly regulated by negative feedback. Glucocorticoid feedback has been found to be altered in depression and post-traumatic stress disorder (PTSD). While hyposensitive glucocorticoid feedback has been found in depression, hypersensitive or enhanced negative feedback was described in PTSD. Enhanced negative feedback, can be seen as a sensitization of the inhibitory elements of HPA axis, and stress-restress or time dependent sensitization (TDS) model, has been suggested as an animal model for PTSD. We have studied the effects of this model on the HPA axis to determine whether it will produce increased sensitivity to negative feedback as found in PTSD patients. Adult Sprague-Dawley male rats were exposed to a single session of prolonged stress (restraint followed by a forced swim and exposure to ether vapors) and briefly restressed 7 days later. The effects of single prolonged stress on plasma ACTH and corticosterone responses (0, 5, and 30 min) and on glucocorticoid fast feedback (cortisol vs. saline pretreatment) were assessed in two studies. Animals exposed to single prolonged stress showed enhanced negative feedback in comparison to naive animals (F = 4.6371, df = 3, p = .0107), but there was no difference in ACTH or corticosterone responses during the restress. Pretreatment with cortisol, in the first stress session, did not prevent the development of the enhanced fast feedback when restressed. This can be seen as a sensitization of the inhibitory elements of HPA axis, suggesting that stress-restress paradigm might serve as a good animal model for HPA abnormalities found in PTSD patients.

Differential behavioral effects of the neuroactive steroid allopregnanolone on neonatal rats prenatally exposed to alcohol

The effects of prenatal alcohol exposure on the behavioral response to the neuroactive steroid allopregnanolone (3 alpha-hydroxy-5 alpha-pregnan-20-one) were investigated in neonatal rats. Two behaviors were assessed: retention of an odor conditioning task and production of ultrasonic vocalizations after brief maternal separation. Subjects from one of the three prenatal conditions (lab chow, alcohol, or pair-fed) received either no injection or an ICV injection of vehicle or one of three doses (1.25-5.0 micrograms) of allopregnanolone either 20 min prior to or immediately after training in an appetitive odor association paradigm. Retention was assessed 1 h later in a two-choice odor preference chamber. Posttraining injections of allopregnanolone caused a dose-dependent impairment in retention in the odor task, but there was no differential sensitivity to allopregnanolone in the alcohol-exposed offspring. All pretraining injections, including the vehicle, resulted in impairments in retention on the task, suggesting an impairment due to stress but not due to allopregnanolone. Allopregnanolone also reduced ultrasonic vocalizations after brief maternal separation in all subjects in a second experiment, but alcohol-exposed offspring displayed a dose-dependent shift to the right in their anxiolytic response to this neurosteroid. This decreased sensitivity suggests that prenatal alcohol exposure may cause a decrease in the density or affinity of the GABA receptors involved in stress response, but not cognitive processes, at this age.

Sensitization to early life stress and response to chemical odors in older adults

This study examined the hypothesis that older persons who currently report illness from environmental chemical odors (cacosmia) may have experienced higher levels of stress early in life than did noncacosmic controls. The hypothesis derives from a time-dependent sensitization (TDS) model for cacosmia (Bell et al 1992) that predicts a relative interchangeability of stress and chemicals in inducing and eliciting sensitized responses in vulnerable individuals. Subjects were selected from those in the top 24% (cacosmic) and bottom 27% (noncacosmic) of a sample of 192 older adults (mean age 73.8 years) for self-reported frequency of illness form the odors of pesticide, car exhaust, paint, perfume, and new carpet. As in previous investigations, cacosmics were younger, more depressed, and more shy; cacosmics also included a higher proportion of women (83% versus 61%). As predicted, cacosmics rated themselves higher in stress for the first four decades of their lives, but not the recent past or present, even after controlling for depression, anxiety, hostility, shyness, age, and gender. Cacosmics reported increased prevalence of physician-diagnosed nasal allergies, breast cysts, hypothyroidism, sinusitis, food sensitivities, irritable bowel, and migraine headache. Only 4% of the overall sample (including 9% of the cacosmics) acknowledged the controversial physician diagnosis of "chemical sensitivity." The replicated observation of greater shyness in cacosmics is consistent with the ability of hyperreactivity to novelty to predict enhanced susceptibility to TDS from low levels of pharmacological agents in animals. The findings support a TDS model for cacosmia and suggest that cacosmia as a symptom identifies a large subset of the nonindustrial population with significant psychophysiological health problems that merit further objective examination.

Chronic administration of flumazenil increases life span and protects rats from age-related loss of cognitive functions: a benzodiazepine/GABAergic hypothesis of brain aging

Under barrier condition and with ad lib access to food and water, 20 Fischer-344 rats were chronically treated for 10 months with the benzodiazepine (BDZ) antagonist, flumazenil (FL; 4 mg/kg/day in drinking water acidified to pH = 3.0), beginning at the age of 13 months, while the group of 20 control age-matched rats received plain acidified water. The life span of the first 8 deceased rats treated with FL was significantly longer than that of the first 8 deceased rats in the age-matched control group. In tests for spontaneous ambulation and exploratory behavior in the Holeboard apparatus, conducted during the 3rd and the 8th month of treatment, the FL group, relative to controls, had significantly higher scores for the ambulation and exploratory behavior. In tests for unrewarded spontaneous alternation in the T maze, conducted at days 7, 39, 42, and 47 through 54 after drug withdrawal, i.e., at the age of 24-25 months, the FL-exposed group, compared to age-matched controls, showed a significantly higher percent of alternating choices, a behavior that was statistically comparable to that of the "young" 6-month-old controls. In the Radial Maze tests conducted 2 months after drug withdrawal, the FL group made significantly less "working memory" errors and "reference memory" errors, relative to the age-matched 25-month-old control group, a performance that was comparable to that of the young 7-month-old control group. In conclusion, chronic FL significantly protected rats from age-related loss of cognitive functions. It is postulated that the age-related alterations in brain function may be attributable to the negative metabolic/trophic influences of the "endogenous" benzodiazepine (BDZ) ligands and/or those ingested with food. A BDZ/GABAergic hypothesis of brain aging has been formulated which assumes that age-related and abnormally strong BDZ/GABAergic influences promote neurodegeneration by suppressing trophic functions of the aminergic and peptidergic neurons through opening of chloride channels in soma membrane and axon terminals, causing excessive hyperpolarizing and depolarizing inhibition, respectively. The review of human clinical and animal data indicates that FL has nootropic actions by enhancing vigilance cognitive and habituation processes.

Altered prolactin response to clomipramine rechallenge in healthy subjects

The effect of an initial challenge with the serotonin (5-HT) uptake inhibitor clomipramine (CMI) on subsequent rechallenge was studied in healthy men who served as volunteers. Carefully screened volunteers were assigned to one of three conditions: (1) CMI challenge followed 2 weeks later by CMI rechallenge; (2) placebo challenge followed 2 weeks later by CMI challenge; and (3) CMI challenge followed 4 weeks later by CMI rechallenge. We found significant blunting of the prolactin response to CMI rechallenge 2 weeks (Signed Rank = -12, p = 0.05), but not 4 weeks after an initial challenge. Placebo challenge did not effect CMI challenge 2 weeks later. These findings suggest that a single exposure to IV CMI may cause 5-HT receptor changes that are present 2, but not 4 weeks later. The ramifications of this finding with regard to the use of 5-HT challenge paradigms in a test-retest design are discussed.

5,7-Dihydroxytryptamine lesions in the fornix-fimbria attenuate latent inhibition

When animals are preexposed to a stimulus without consequence they are subsequently slower to associate this stimulus with an important event, such as footshock. This retarding effect of stimulus preexposure is called latent inhibition and can be demonstrated in a variety of classical and instrumental paradigms and in a wide range of species, including man. Latent inhibition is disrupted in acute schizophrenics and by amphetamine treatment in both rat and man. The present study investigated the role of hippocampal 5HT terminals in latent inhibition using a conditioned suppression procedure with male Sprague-Dawley rats. Microinjections of 5,7-dihydroxytryptamine in the fornix-fimbria significantly reduced hippocampal indoleamine levels and attenuated latent inhibition of conditioned suppression. This finding supports the hypothesis that the destruction of mesolimbic 5-hydroxytryptamine terminals reduces latent inhibition. This result is discussed in terms of the possible involvement of reduced serotonergic function in schizophrenic attentional disorder. In addition to the predicted lesion effect, biochemical analyses indicated that experimental treatments in the latent inhibition procedure altered neurotransmitter turnover: utilization ratios for 5-hydroxytryptamine and/or dopamine were increased in preexposed relative to nonpreexposed animals in four of the six brain regions sampled.

Criteria for rationally evaluating animal models of posttraumatic stress disorder

Animal models of stress have the potential to provide information about the course and etiology of posttraumatic stress disorder (PTSD). To date, however, there have been no systematic approaches for evaluating the relevance of animal models of stress to PTSD. It has been established in the animal literature that different types of stress paradigms lead to different biobehavioral consequences and that many different factors contribute to differential responsivity to stress. It becomes important therefore to differentiate between factors that are essential to the induction of PTSD-like symptoms and those that influence their manifestations. In the present commentary, we present five criteria that must be fulfilled by animal models of stress for them to be useful to understanding the induction of PTSD. We then evaluate two potential animal models of stress--inescapable shock-learned helplessness and time-dependent sensitization--to illustrate how to more successfully pair animal models of stress with the specific clinical syndrome of PTSD.

Effects of anxiolytic and antidepressant drugs on long-lasting behavioural deficits resulting from one short stress experience in male rats

Exposure of male Wistar rats to one single session of ten inescapable footshocks induces changes in the behavioural responses to environmental stimuli as measured in the "noise test" 14 days later. Shocked (S) rats showed decreased locomotion and rearing during the first 3 min of exposure to a novel environment compared to control (C) rats. When the 85 dB background noise was switched off a marked immobility response emerged in S rats, concomitant with a further decrease in locomotion and rearing. In response to noise off, C rats showed hardly any immobility and a much smaller reduction in locomotion and rearing compared to S rats. These long-lasting changes in behaviour were not reversed by acute treatment with the antidepressants fluvoxamine (3.0-30.0 mg/kg) and desmethylimipramine (DMI, 2.5-10.0 mg/kg) injected IP 30 min before the noise test on day 14 following the shock session. Chronic treatment (day 1 to day 14) with fluvoxamine or DMI did not reverse the behavioural deficits induced by shock exposure. Diazepam (0.6-5.0 mg/kg) administered acutely only reversed the effects of shock on locomotion during the first 3 min of the noise test. Chronic treatment with diazepam normalized the shock-induced decrease in locomotion and attenuated the rearing decrease during the first 3 min of the test, and partially restored shock-induced changes in behavioural response to switching off the noise. The most potent drug in this study was the 5-HT1A receptor agonist flesinoxan (0.3-3.0 mg/kg).(ABSTRACT TRUNCATED AT 250 WORDS)

Amphetamine or haloperidol 2 weeks earlier antagonized the plasma corticosterone response to amphetamine; evidence for the stressful/foreign nature of drugs

We inquired whether a single exposure to amphetamine (AM) or haloperidol (HALO) could modify the plasma corticosterone (CORT) response to a second injection of AM 2 weeks later. Male rats were injected with 4 mg/kg d-AM sulfate and tested for water intake for 5 h before sacrifice. Overall, AM induced water intake but none of the pretreatments altered this effect. By contrast, preexposure to AM, HALO or its vehicle 2 weeks earlier prevented the elevation of plasma CORT obtained when AM was administered without pretreatment. A combined pretreatment of HALO or its vehicle with AM produced an even greater blockade of AM-induced CORT elevation. Manipulations which prevented AM-induced drinking reduced the effectiveness of AM pretreatment in attenuating AM-induced elevation in CORT, suggesting that the pretreatment may have been sensitizing the effectiveness of a coping response--drinking--in reducing the CORT effect. Our findings also indicate that a dopamine agonist (AM), a dopamine antagonist (HALO) and a nonspecific stressor (acidic vehicle) can all induce the same, long-lasting action on CORT. This strongly suggests that the effects of AM and HALO in this instance cannot be explained in terms of their pharmacological actions, which are opposite to one another, but instead relate to their properties as stressful/foreign agents to the organism.

One experience with 'lower' or 'higher' intensity stressors, respectively enhances or diminishes responsiveness to haloperidol weeks later: implications for understanding drug variability

This laboratory has previously shown that acute exposure to a variety of brief stressful events can have a very long-lasting influence on subsequent responsiveness to pharmacological and non-pharmacological stressors. In some cases the response to these agents is enhanced, while in others it is diminished: the common denominator being that in each instance the influence of the initial stressor grows stronger with the passage of time. Here, we identify one factor that determines which time-dependent effect is manifest. In 3 separate experiments, male rats were subjected to a single exposure to stressors of either lower or higher intensity and their effects on haloperidol-induced catalepsy and dopamine and dihydroxyphenylacetic acid levels in the nucleus accumbens and medial frontal cortex, measured either 1-2 h or 2 weeks later. The stressors were either environmental (needle jab or 1 h of immobilization), metabolic (200 or 750 mg/kg, i.p. of 2-deoxy-D-glucose), or no effect on haloperidol-induced catalepsy when stressors preceded such behavioral testing by 1-2 h. By contrast, when the interval was 2 weeks, the lower-intensity stressors all increased haloperidol catalepsy, whereas the higher-intensity stressors decreased the same response. In other words, a process that progressed with the passage of time was observed regardless of whether sensitization or diminution of haloperidol's action occurred. In contrast to the uniform bipolar behavioral effects observed, depending on the intensity of the prestressor, the neurochemical findings failed to show any evidence of bipolarity whatever.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic administration of flumazenil (Ro 15-1788) enhances non-appetitive exploratory behavior of rats

The effects of chronic administration of the benzodiazepine receptor antagonist, flumazenil (Ro 15-1788; 4 mg/kg/day for 14 days in drinking water) on the performance of adult rats in the 12-arm radial maze were studied. Relative to controls, the animals treated with flumazenil showed an increase (P less than 0.002) in non-appetitively motived exploratory behavior, so called because it occurred in 88% of instances in non-baited alleys, facing the well-illuminated "enriched environment" of the center of the room, as opposed to the baited alleys, facing the "dull" corner of the room. This behavior emerged between day 5 and 7 of treatment with the drug, it continued to increase over the period of treatment with drug (P less than 0.002), and reached its peak at day 3, after withdrawal of the drug (P less than 0.008; a longer duration was not investigated). The occurrence of non-appetitively motivated exploratory behavior was inversely correlated with the scores for urination/defecation (P less than 0.003) and, therefore, most likely reflected the anxiolytic action of flumazenil. During treatment with drug or vehicle, the control and the drug groups made comparable numbers of "working memory" errors (P = 0.17). However, upon withdrawal of drug and introduction of alley gates (to confine the animal for 10 sec to the center platform, after an alley was explored), the working memory errors of the rats exposed to the drug, remained unchanged (P = 0.35), relative to the preceding three trials, while the performance of the control group was disrupted, as shown by an increase in the numbers of errors (P less than 0.004). At day seven of treatment with drug, the emergence of exploratory behavior was associated with an increased density and/or affinity of benzodiazepine receptors in cortex, hippocampus and brain stem, while three days after withdrawal of drug, when the exploratory behavior reached its peak, there was a reduction in GABA-enhanced binding of [3H]flunitrazepam in the cortex.

Learning and unlearning fear: a clinical and evolutionary perspective

Many fears, phobias and rituals seem to arise from prepared phylogenetic mechanisms which favor old over new evolutionary dangers and affect the rules of aversive learning which govern the acquisition of fear. Recent developments in several forms of aversive learning (sensitization, conditioning, extinction, observational learning) can improve them as paradigms of the acquisition, spread and maintenance of normal and clinical fears. The most reliable treatment for phobias and rituals is exposure, whose effects closely parallel the habituation of normal defensive responses and the extinction of conditioned fear and avoidance in animals. Habituation during exposure is usually slow and step by step, and generalizes little, but once attained tends to endure. Conditioned fear extinction and fear habituation have similar courses and may depend on similar neural processes. To be reduced, avoidance has to be prevented or the safety intervals that it heralds must be given up. Some phobias may result less from enhanced acquisition than from insufficient exposure to attain habituation. Finally, the review discusses the limits of habituation and the instability of fear extinction in relation to the long-term efficacy of exposure therapy.

Anticonvulsant and other effects of diazepam grow with time after a single treatment

The hypothesis was tested that some of the effects in rats of the prototypical benzodiazepine, diazepam, would grow (i.e., sensitize) with the passage of time after acute administration as we had previously observed following stimulants, antidepressants, neuroleptics and other compounds. Our principal findings indicate that: 1) A single pretreatment with 0.5 mg/kg of diazepam significantly enhances the anticonvulsant effect of this same dose administered again two weeks later. 2) One injection of 2.5 mg/kg of diazepam significantly sensitizes the catalepsy and ptosis observed following the administration of haloperidol two weeks but not two hours later. These data provide the first evidence for time-dependent sensitization after benzodiazepines and perhaps by implication, of GABA neurons. They may also suggest that acute stimulation of GABA neurons triggers the progressive development of a long-term, antidopaminergic influence. Finally, they raise the question of whether the progressive anxiolytic influence seen during the first week or so of benzodiazepine therapy depends on the passage of time rather than repeated drug treatment.

Prior stress attenuates the analgesic response but sensitizes the corticosterone and cortical dopamine responses to stress 10 days later

This study demonstrates that pre-exposure to stress influences subsequent effects of stress on pain sensitivity (stress-induced analgesia) and on plasma corticosterone and brain catecholamine activity. Animals exposed to a 30 min shock session (S1 = 8, 5.0 s shocks) 10 days earlier showed a significant attenuation of shock-induced analgesia, as measured by increased latency of tail withdrawal from a hot water bath immediately after a 40 s, 1.6 mA footshock (S2). Animals exposed to shock 10 days before testing also exhibited a higher plasma corticosterone response to testing than did all other groups. Norepinephrine (NE) levels in the frontal cortex and dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) levels in the frontal cortex and nucleus accumbens were not altered in any group. However, the DOPAC/DA ratio in the frontal cortex was increased by analgesia testing, and this increase was enhanced only by the combination of shock 10 days before testing and shock immediately before the test (S1 + S2). These results are consistent with previous reports from this laboratory which indicate that an animal's acute response to stress is strongly influenced by its past history of stress.

Persistent sensitization of clonidine-induced hypokinesia following one exposure to a stressor: possible relevance to panic disorder and its treatment

Based on previous findings of this laboratory that a single exposure to a stressful stimulus can induce a very long-lasting, sensitizing influence on the actions of drugs of multiple clinical and structural classes, the hypothesis was tested that a single stressful event might exert such an action on the alpha-2 norepinephrine agonist clonidine. Male rats received a single injection of the highly stressful convulsant stimulant pentylenetetrazole (PTZ; 40 mg/kg, IP) and were tested for locomotion after treatment with clonidine (25 micrograms/kg, IP) 1 h, 1 week or 2 weeks later. As expected, clonidine itself induced the hypokinesia typically associated with low doses of this compound. More importantly, all groups pretreated with PTZ showed a significant enhancement of this effect. The influence of PTZ 1 or 2 weeks prior to clonidine cannot be explained as simply due to a lingering impairment of locomotion by PTZ, since no hypokinesia was observed when activity in these groups was examined immediately prior to clonidine administration. Such impairment appears, however, to have been a factor in the heightened hypokinesia observed in the group receiving PTZ only 1 h before clonidine. Mass spectrometric analysis of norepinephrine and 3-methoxy-4-hydroxyphenylglycol levels in hippocampus and cortical areas failed to reveal any changes which could explain the persistent behavioral sensitization we observed. Plasma corticosterone determinations confirmed the stressful nature of PTZ but similarly failed to provide an explanation for the observed behavioral sensitization. The major finding of a long-term sensitizing influence on clonidine of an acute stressful experience is consistent with what is known of the precipitants and treatment of panic disorder.