Social stress and glucocorticoids alter PERIOD2 rhythmicity in the liver, but not in the suprachiasmatic nucleus.

Circadian (~24 h) rhythms in behavior and physiological functions are under control of an endogenous circadian pacemaker in the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN directly drives some of these rhythms or serves as a coordinator of peripheral oscillators residing in other tissues and organs. Disruption of the circadian organization may contribute to disease, including stress-related disorders. Previous research indicates that the master clock in the SCN is resistant to stress, although it is unclear whether stress affects rhythmicity in other tissues, possibly mediated by glucocorticoids, released in stressful situations. In the present study, we examined the effect of uncontrollable social defeat stress and glucocorticoid hormones on the central and peripheral clocks, respectively in the SCN and liver. Transgenic PERIOD2::LUCIFERASE knock-in mice were used to assess the rhythm of the clock protein PERIOD2 (PER2) in SCN slices and liver tissue collected after 10 consecutive days of social defeat stress. The rhythmicity of PER2 expression in the SCN was not affected by stress exposure, whereas in the liver the expression showed a delayed phase in defeated compared to non-defeated control mice. In a second experiment, brain slices and liver samples were collected from transgenic mice and exposed to different doses of corticosterone. Corticosterone did not affect PER2 rhythm of the SCN samples, but caused a phase shift in PER2 expression in liver samples. This study confirms earlier findings that the SCN is resistant to stress and shows that clocks in the liver are affected by social stress, which might be due to the direct influence of glucocorticoids released from the adrenal gland.

Maternal regulation of the infant's hypothalamic-pituitary-adrenal axis stress response: Seymour 'Gig' Levine's legacy to neuroendocrinology.

Thirty years ago, Seymour 'Gig' Levine published a serendipitous, yet, seminal finding with respect to the regulatory role of maternal presence on the corticosterone stress response of neonatal rats during the developmental period known as the stress hyporesponsive period. At the same time, his group of students also investigated the stress response of infant monkeys with respect to maternal separation, as a means of understanding the stress to the primary caregiver resulting from disruptions of attachment. Gig and his group of students and collaborators, mainly in the USA and the Netherlands, investigated how initial social relationships buffer the stress response of nonhuman primates and rodent infants. His work in rodents involved determining how prolonged deprivation of maternal care disinhibits the stress response of neonates and how maternal behaviours regulate specific aspects of the hypothalamic-pituitary-adrenal axis. Maternal deprivation for 24 hours was useful for determining the importance of nutrition in suppressing the corticosterone stress response, whereas anogenital licking and grooming inhibited stress-induced adrenocortoctrophic hormone release, with the combination of both behaviours preventing the effects of maternal deprivation on the central hypothalamic stress response. Levine's group also studied the consequences of maternal deprivation on basal and stress-induced activity of the hypothalamic-pituitary-adrenal axis in juveniles and the persistent effects of the replacement of maternal behaviours on these parameters. Gig's legacy allowed many groups around the world to use the 24-hour maternal deprivation paradigm as an animal model of vulnerability and resilience to stress-related psychiatric disorders, as well as in studies of the neurobiological underpinnings of disruption of the mother-infant relationship and loss of parental care, a highly prevalent condition in humans. This review pays homage to a great scientist and mentor, whose discoveries paved the way for the understanding of how early social relationsships build resilience or lead to susceptibility to emotional disorders later in life.

Chronic social defeat stress suppresses locomotor activity but does not affect the free-running circadian period of the activity rhythm in mice.

In mammals, daily rhythms in behavior and physiology are under control of an endogenous clock or pacemaker located in the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN assures an optimal temporal organization of internal physiological process and also synchronizes rhythms in physiology and behavior to the cyclic environment. The SCN receives direct light input from the retina, which is capable of resetting the master clock and thereby synchronizes internally driven rhythms to the external light-dark cycle. In keeping with its function as a clock and pacemaker, the SCN appears to be well buffered against influences by other stimuli and conditions that contain no relevant timing information, such as acute stressors. On the other hand, it has been suggested that chronic forms of stress may have gradually accumulating effects that can disturb normal clock function and thereby contribute to stress-related disorders. Therefore, in the present study we investigated whether chronic intermittent social stress affects the endogenous period and phase of the free-running activity rhythm in mice. Adult male mice were maintained in constant dim red light conditions and exposed to a daily 20 min social defeat stress session for 10 consecutive days, either during the first half of their activity phase or the first half of their resting phase. The overall amount of running wheel activity was strongly suppressed during the 10 days of social defeat, to about 50% of the activity in non-defeated control mice. Activity levels gradually normalized during post-defeat recovery days. Despite the strong suppression of activity in defeated animals, the endogenous free-running circadian period of the activity rhythm and the phase of activity onset were not affected. These findings are thus in agreement with earlier studies suggesting that the circadian pacemaker in the SCN that is driving the rhythmicity in activity is well-protected against stress. Even severe social defeat stress for 10 consecutive days, which has a major effect on the levels of activity, does not affect the pace of the endogenous clock.

Neuroendocrine Regulation of Anxiety: Beyond the Hypothalamic-Pituitary-Adrenal Axis.

The central nervous system regulates and responds to endocrine signals, and this reciprocal relationship determines emotional processing and behavioural anxiety. Although the hypothalamic-pituitary-adrenal (HPA) axis remains the best-characterised system for this relationship, other steroid and peptide hormones are increasingly recognised for their effects on anxiety-like behaviour and reward. The present review examines recent developments related to the role of a number of different hormones in anxiety, including pregnane neurosteroids, gut peptides, neuropeptides and hormonal signals derived from fatty acids. Findings from both basic and clinical studies suggest that these alternative systems may complement or occlude stress-induced changes in anxiety and anxiety-like behaviour. By broadening the scope of mechanisms for depression and anxiety, it may be possible to develop novel strategies to attenuate stress-related psychiatric conditions. The targets for these potential therapies, as discussed in this review, encompass multiple circuits and systems, including those outside of the HPA axis.

Activation of HPA axis and remodeling of body chemical composition in response to an intense and exhaustive exercise in C57BL/6 mice.

Several deleterious effects may occur when intense and exhaustive exercise (IE) is not well-planned. This study aimed to investigate the effects of a short duration IE on body chemical composition and hypothalamic-pituitary-adrenal (HPA) axis. C57Bl/6 mice were distributed into four groups (10 mice per group): control (C-4D and C-10D), 4 days (E-4D), and 10 days of IE (E-10D). IE program consisted of a daily running session at 85 % of maximum speed until the animal reached exhaustion. Body weight as well as total body water, fat and protein content were determined from animal carcasses. HPA activation was assessed by plasma corticosterone levels measured by radioimmunoassay and the weight of both the adrenal glands and thymus were measured. Plasma corticosterone levels increased by 64 % in both the E-4D and E-10D groups. The weight of the adrenal glands augmented by 74 % and 45 %, at 4 and 10 days of IE, respectively, whereas thymus weight diminished by 15 % only in the E-10D group. The total carcass fat content decreased by 20 % only at 4 days IE, whereas protein content decreased by 20 % in both E-4D and E-10D groups. A relationship between corticosterone plasma levels and loss of body protein content in both E-4D and E-10D groups was observed (R(2)=0.999). We concluded that IE may be related to HPA axis activation associated with remodeling of body chemical composition in C57BL/6 mice.

Long-term impact of early life events on physiology and behaviour.

This review discusses the effects of stress and nutrition throughout development and summarises studies investigating how exposure to stress or alterations in nutrition during the pre-conception, prenatal and early postnatal periods can affect the long-term health of an individual. In general, the data presented here suggest that that anything signalling potential adverse conditions later in life, such as high levels of stress or low levels of food availability, will lead to alterations in the offspring, possibly of an epigenetic nature, preparing the offspring for these conditions later in life. However, when similar environmental conditions are not met in adulthood, these alterations may have maladaptive consequences, resulting in obesity and heightened stress sensitivity. The data also suggest that the mechanism underlying these adult phenotypes might be dependent on the type and the timing of exposure.

Cognitive-behavioural group therapy improves a psychophysiological marker of stress in caregivers of patients with Alzheimer's disease.

BACKGROUND: Family caregivers of patients with dementia frequently experience psychological stress, depression and disturbed psychophysiological activity, with increased levels of diurnal cortisol secretion. OBJECTIVES: To compare the effects of a cognitive-behavioural group therapy (CBT) to a psychoeducation group programme (EDUC) on cortisol secretion in caregivers of patients with moderate Alzheimer's disease (AD). METHOD: Caregivers of AD outpatients were semi-randomly allocated to one of two intervention programmes (CBT or EDUC) consisting of eight weekly sessions. Twenty-six participants completed the study. Before and after intervention, salivary cortisol was collected at four different times of the day. Effects of the interventions were evaluated with self-report psychological scales and questionnaires related to functional abilities and neuropsychiatric symptoms of the AD relative. RESULTS: Only in the CBT group did salivary cortisol levels significantly decrease after intervention, with a large effect size and high achieved power. Both groups reported a reduction of neuropsychiatric symptoms of their AD relative after intervention. CONCLUSION: Psychoeducation for caregivers may contribute to a reduction of neuropsychiatric symptoms of AD patients while CBT additionally attenuates psychophysiological responses to stressful situations in caregivers, by reducing diurnal cortisol levels. This may lead to a positive impact in the general health of the caregiver, eventually resulting in better care of the AD patient.

Repetitive noxious neonatal stimuli increases dentate gyrus cell proliferation and hippocampal brain-derived neurotrophic factor levels.

Neonatal noxious stimulation has been proposed to model pain triggered by diagnostic/therapeutic invasive procedures in premature infants. Previous studies have shown that hippocampal neurogenesis rate and the behavioral repertoire of adult rats may be altered by neonatal noxious stimuli. The purpose of this study was to evaluate whether noxious stimulation during neonatal period alters the nociceptive response and dentate gyrus neurogenesis when compared to rats subjected to a single noxious stimulus in late infancy. Plasma corticosterone and hippocampal brain-derived neurotrophic factor (BDNF) levels were measured. Neurogenesis in the dentate gyrus was evaluated in adolescent rats (postnatal day 40; P40) exposed twice to intra-plantar injections of Complete Freund's adjuvant (CFA) on P1 and P21 (group P1P21) or P8 and P21 (P8P21) or exposed once on P21 (pubertal). On P21, one subset of animals received 5-bromo-2'-deoxyuridine (BrdU) and was euthanized on P40 for identification of proliferating cells in the dentate gyrus. Another subset was sampled for thermal response or plasma corticosterone measurement and hippocampal BDNF levels. Proliferative cell rate in dentate gyrus was the highest in all re-exposed groups (P < 0.001), except for P8 females (P8P21F), revealing also a sex difference, where P8P21 males showed higher rate than females (P < 0.001). Stimulated groups took longer than CTL animals to lick the paws (P < 0.001), regardless of the age when the noxious stimulus was applied. Re-exposed groups had lower corticosterone plasma level (P1P21 M and F, P8P21M) than controls. On the contrary, hippocampal BDNF was increased in males from both re-exposed groups. These results show that infant noxious stimulation in neonatally previously stimulated rats is related to high proliferation in the DG and this association seems to be modified by the animal's sex. The new generated dentate granule cells in the hippocampus may have a role in the long-term behavioral responses to neonatal nociceptive stimulation. Noxious stimulation in the neonatal period results in sex-dependent neurogenic response.

Sex-dependent effects of maternal separation on plasma corticosterone and brain monoamines in response to chronic ethanol administration.

Prolonged and repeated periods of maternal separation produce behavioral phenotype of increased vulnerability to neuropsychiatric disorders and drug abuse. Most of the changes in behavior, corticosterone (CORT) and monoamine levels induced by long maternal separation (LMS) are observed after a challenge, but not in basal conditions. LMS increases ethanol-induced locomotor response and self-administration, possibly due to changes in CORT release and/or monoamine concentrations. This study examined the effects of LMS in association with chronic ethanol treatment on plasma CORT and brain monoamine concentrations in male and female Swiss mice, which were kept undisturbed (animal facility rearing - AFR) or separated from their mothers for 3h/day, from 2 to 14 days of age (LMS). As adults, one set of male and female mice received no drug treatment to assess the effect of LMS per se. Another set of animals received saline injections for 20 days and one ethanol injection (2.2g/kg, i.p.) on day 21 (acute) or ethanol for 21 days (chronic). Locomotor activity, plasma CORT levels and monoamines in the frontal cortex, striatum and hippocampus of AFR and LMS mice were evaluated in non-treated, acute and chronic ethanol-treated animals. In non-treated mice, no differences were found in CORT or locomotor activity, with small changes in monoamines content. In LMS females, chronic ethanol increased dopamine and serotonin concentrations in the frontal cortex, relative to acute ethanol LMS and to chronic ethanol-treated AFR groups (p<0.05). In LMS males, chronic ethanol increased hippocampal noradrenaline, dopamine, serotonin and metabolites when compared to respective AFR controls, as well as acute LMS. Moreover, chronic ethanol treatment resulted in higher CORT concentrations in LMS than in AFR males. Overall, these results indicate that LMS mice were more susceptible to the effects of chronic ethanol administration on CORT and brain monoamine concentrations, and that these effects were sex-dependent.

Paradoxical sleep deprivation and sleep recovery: effects on the hypothalamic-pituitary-adrenal axis activity, energy balance and body composition of rats.

Numerous studies indicate that sleep deprivation alters energy expenditure. However, this conclusion is drawn from indirect measurements. In the present study, we investigated alterations of energy expenditure, body composition, blood glucose levels, plasma insulin, adrenocorticotropic hormone (ACTH) and corticosterone levels immediately after 4 days of sleep deprivation or after 4 days of sleep recovery. Rats were sleep deprived or maintained in a control environment (groups sleep-deprived/deprivation and control/deprivation). One half of these animals were sacrificed at the end of the deprivation period and the other half was transported to metabolic cages, where they were allowed to sleep freely (groups sleep-deprived/recovery and control/recovery). At the end of the sleep recovery period, these rats were sacrificed. After sleep deprivation, sleep-deprived rats exhibited loss of body weight, augmented energy expenditure and reduced metabolic efficiency compared to control rats. These alterations were normalised during the sleep recovery period. The body composition of sleep-deprived rats was altered insofar as there was a loss of fat content and gain of protein content in the carcass compared to control rats. However, these alterations were not reversed by sleep recovery. Finally, plasma levels of insulin were reduced during the sleep deprivation period in both control and sleep deprived groups compared to the recovery period. After the deprivation period, plasma ACTH and corticosterone levels were increased in sleep-deprived rats compared to control rats, and although ACTH levels were similar between the groups after the sleep recovery period, corticosterone levels remained elevated in sleep-deprived rats after this period. By means of direct measurements of metabolism, our results showed that sleep deprivation produces increased energy expenditure and loss of fat content. Most of the alterations were reversed by sleep recovery, except for corticosterone levels and body composition.

c-Fos expression induced by electroacupuncture at the Zusanli point in rats submitted to repeated immobilization.

In laboratory animals, acupuncture needs to be performed on either anesthetized or, if unanesthetized, restrained subjects. Both procedures up-regulate c-Fos expression in several areas of the central nervous system, representing therefore a major pitfall for the assessment of c-Fos expression induced by electroacupuncture. Thus, in order to reduce the effect of acute restraint we used a protocol of repeated restraint for the assessment of the brain areas activated by electroacupuncture in adult male Wistar rats weighing 180-230 g. Repeated immobilization protocols (6 days, 1 h/day and 13 days, 2 h/day) were used to reduce the effect of acute immobilization stress on the c-Fos expression induced by electroacupuncture at the Zusanli point (EA36S). Animals submitted to immobilization alone or to electroacupuncture (100 Hz, 2-4 V, faradic wave) in a non-point region were compared to animals submitted to electroacupuncture at EA36S (4 animals/subgroup). c-Fos expression was measured in 41 brain areas by simple counting of cells and the results are reported as number of c-Fos-immunoreactive cells/10,000 m . The protocols of repeated immobilization significantly reduced the immobilization-induced c-Fos expression in most of the brain areas analyzed (P < 0.05). Animals of the EA36S groups had significantly higher levels of c-Fos expression in the dorsal raphe nucleus, locus coeruleus, posterior hypothalamus and central medial nucleus of the thalamus. Furthermore, the repeated immobilization protocols intensified the differences between the effects of 36S and non-point stimulation in the dorsal raphe nucleus (P < 0.05). These data suggest that high levels of stress can interact with and mask the evaluation of specific effects of acupuncture in unanesthetized animals.

c-Fos expression induced by electroacupuncture at the Zusanli point in rats submitted to repeated immobilization

In laboratory animals, acupuncture needs to be performed on either anesthetized or, if unanesthetized, restrained subjects. Both procedures up-regulate c-Fos expression in several areas of the central nervous system, representing therefore a major pitfall for the assessment of c-Fos expression induced by electroacupuncture. Thus, in order to reduce the effect of acute restraint we used a protocol of repeated restraint for the assessment of the brain areas activated by electroacupuncture in adult male Wistar rats weighing 180-230 g. Repeated immobilization protocols (6 days, 1 h/day and 13 days, 2 h/day) were used to reduce the effect of acute immobilization stress on the c-Fos expression induced by electroacupuncture at the Zusanli point (EA36S). Animals submitted to immobilization alone or to electroacupuncture (100 Hz, 2-4 V, faradic wave) in a non-point region were compared to animals submitted to electroacupuncture at EA36S (4 animals/subgroup). c-Fos expression was measured in 41 brain areas by simple counting of cells and the results are reported as number of c-Fos-immunoreactive cells/10,000 æm². The protocols of repeated immobilization significantly reduced the immobilization-induced c-Fos expression in most of the brain areas analyzed (P < 0.05). Animals of the EA36S groups had significantly higher levels of c-Fos expression in the dorsal raphe nucleus, locus coeruleus, posterior hypothalamus and central medial nucleus of the thalamus. Furthermore, the repeated immobilization protocols intensified the differences between the effects of 36S and non-point stimulation in the dorsal raphe nucleus (P < 0.05). These data suggest that high levels of stress can interact with and mask the evaluation of specific effects of acupuncture in unanesthetized animals.

Palatable solutions during paradoxical sleep deprivation: reduction of hypothalamic-pituitary-adrenal axis activity and lack of effect on energy imbalance.

Paradoxical sleep deprivation (PSD) induces increased energy expenditure in rats, insofar as rats eat more but loose weight throughout the deprivation period. In the present study, rats were offered water, saccharin or sucrose to drink during the deprivation period, since it has been proposed that carbohydrates reduce the hypothalamic-pituitary-adrenal (HPA) axis response to stress. Rats were submitted to the flower pot technique for 96 h. During the PSD period, they were weighed daily and food and fluid intake was assessed twice a day. At the end of the PSD period, rats were killed and plasma concentrations of glucose, adrenocorticotropic hormone (ACTH) and corticosterone were assayed. Compared to their control counterparts, all paradoxical sleep-deprived rats consumed more food, but lost weight. Paradoxical sleep-deprived rats given sucrose drank more than their control counterparts (especially in the light phase of the light/dark cycle). Paradoxical sleep-deprived rats showed increased food intake during all periods throughout the experiment, with peak intake during the dark phase and nadir during the light phase of the light/dark cycle. All paradoxical sleep-deprived rats showed lower glucose plasma levels than control rats and increased relative adrenal weight. However, when given saccharin or sucrose, paradoxical sleep-deprived rats showed lower concentrations of ACTH and corticosterone than their water-provided counterparts, indicating that palatable fluids were capable of lowering HPA axis activation produced by PSD. The fact that PSD induced energy imbalance regardless of the relative attenuation of the HPA axis activity produced by saccharin or sucrose suggests that the HPA axis may play only a secondary role in this phenomenon, and that other mechanisms may account for this effect. The data also suggest that supply of palatable fluids can be an additional modification to reduce the stress of the flower pot method.

Hormonal and behavioural responses of paradoxical sleep-deprived rats to the elevated plus maze.

Activation of the hypothalamic-pituitary-adrenal (HPA) axis is observed immediately after 96 h of paradoxical sleep (PS) deprivation. However, when individually or group PS-deprived rats are challenged with a mild stressor, they exhibit a facilitation of the corticosterone response, and a faster return to basal levels than control rats. Because the housing condition influences coping behaviour, we tested whether the type of PS deprivation (individually or in group) influenced anxiety-like behaviour in the elevated plus-maze and the accompanying adrenocorticotropin (ACTH) and corticosterone responses. Individually (I-DEP) or group deprived (G-DEP) rats and their appropriate control groups were either killed immediately after 96 h of sleep deprivation (time-point 0 or 'basal') or exposed to a 5-min test on the elevated plus maze and sampled 5, 20 or 60 min after test onset. Control of I-DEP rats showed reduced locomotor activity and augmented anxiety-like behaviour, replicating the effects of social isolation. Although I-DEP rats exhibited higher motor activity than cage control rats, these groups did not differ in regard to the percentage of entry and time spent in the open arms. G-DEP rats, in turn, ambulated more, entered and remained longer in the open arms, exhibiting less anxiety-like behaviour. PS-deprived rats exhibited higher ACTH and corticosterone 'basal' secretion than control rats. For all groups, peak ACTH secretion was reached at the 5-min time-point, returning to unstressed basal levels 60 min after the test, except for G-DEP rats, which showed a return at 20 min. Peak levels of corticosterone occurred at 5 min for PS-deprived groups and at 20 min for control groups. G-DEP rats showed a return to 'basal' unstressed levels at 20 min, whereas the I-DEP and control groups did so at 60 min. A negative correlation between exploration in the open arms and hormone concentrations was observed. These data indicate that housing condition influences the subsequent behaviour of PS-deprived rats in the EPM which, in turn, seems to determine the secretion profile of ACTH and corticosterone in response to the test.

The variability of the apnoea-hypopnoea index.

This study was designed to evaluate the variability of the apnoea-hypopnoea index (AHI) in 20 patients with obstructive sleep apnoea-hypopnoea syndrome (OSAHS) and to determine possible relationships of this variability with other polysomnographic parameters. The subjects were recorded on four consecutive nights. The mean AHI values were not significantly altered throughout the four recording nights (P=0.67). The intraclass correlation coefficient of the AHI on the four nights was 0.92. However, the Bland and Altman plot showed that, individually, the AHI presented an important variability, which was not related to its initial value. In regard to the OSAHS severity, 50% of the patients changed the classification from the first to the subsequent nights. Thirteen of the 20 patients (65%) presented a variation in the AHI value equal or higher than 10 events h(-1). When we evaluated the AHI mean values for a specific body position and sleep stage, no difference was observed among the nights. In both supine and lateral-ventral decubitus, higher AHI was observed during Stages 1 and 2 than the other stages. Additionally, the AHI during Stages 1 and 2 and REM sleep was higher on the supine than on the lateral-ventral decubitus. The AHI in OSAHS patients presented a good correlation among the four recording nights; however, a significant individual variability should be considered, especially when AHI is applied in OSAHS classification or as a criterion of therapeutic success.

Sleep rebound in animals deprived of paradoxical sleep by the modified multiple platform method.

The objective of the present study was to assess the sleep rebound of animals exposed to the modified multiple platform method (MMPM), in which cage-mate rats were placed onto narrow platforms (NP=6.5 cm in diameter), onto wide platforms (WP=14 cm in diameter) or onto a grid (GR). The last two groups were included as environmental controls for the deprivation method. Animals were implanted with bipolar electrodes in the cortex, hippocampus and neck muscle. Baseline sleep was recorded for 6 h, after which the animals were placed in one of the above-mentioned settings for 90 h and their sleep was again recorded. Comparison between baseline and post-GR recordings revealed no sleep differences in these animals. Placement of animals onto WP resulted in augmented sleep time (16%), time spent in PS (+99%), duration of PS episodes (+77%), sleep efficiency (+16%), and in reduced latency to PS (-84.8%). Finally, NP animals exhibited a dramatic increase in sleep time (+34.3%), time spent in PS (+184.7%), duration of PS episodes (+106%), and in sleep efficiency (+34.4%). Moreover, sleep latency (-52.2%) and time spent in SWS (-12.2%) were reduced. Based on the results of sleep rebound, the data indicated that placement of animals onto narrow platforms in the MMPM was an effective PS deprivation method and the grid should be considered as an adequate environmental control.

Pituitary-adrenal axis and behavioural responses of maternally deprived juvenile rats to the open field.

Adult rats submitted to maternal deprivation (DEP) on post-natal day (pnd) 11 show smaller corticosterone (CORT) response to a saline injection than non-deprived (NDEP) rats, mainly at 30 days of age. In the present study we sought to investigate the pituitary-adrenal axis response of 30-day-old DEP rats to a 5-min open-field session, with lights and sound on. Hormone levels were assessed immediately or 20 min after the end of the stress, and were compared to basal levels. The immediate ACTH response of DEP females was the highest; this difference was no longer observed at 20 min, but hormone levels were still higher than basal. Both males and females showed an augmented CORT secretion immediately after the open field session, although only the response of NDEP females was higher than that of male counterparts. Moreover, DEP females showed a lower CORT response than their NDEP counterparts immediately after the stress. The CORT stress response remained equally elevated in males and females at the 20-min time point. Finally, DEP animals, regardless of the gender, ambulated more in the centre of the open field and displayed less grooming behaviour than NDEP pups, suggesting that DEP rats are less emotional than NDEP animals.

Differential effects of acute cold and footshock on the sleep of rats.

Several studies have shown that 1 h of immobilisation stress during the rat's active period results in rebound of paradoxical (PS) and slow wave sleep (SWS). Since the effects of stress on behaviour and physiological parameters vary according to the stimulus, the present study sought to examine the activation of the hypothalamic-pituitary-adrenal (HPA) axis and the sleep pattern of rats submitted to 1 h of footshock, immobilisation or cold, or 18 h of PS deprivation (PSD). Stress sessions began between 0900 and 0930 h. Immediately after the end of the stress session, or at the corresponding time for controls, animals were blood sampled for determination of ACTH and corticosterone (CORT) plasma levels. In Experiment 2, animals were implanted with electrodes for basal and post-stress polysomnographic recording (6 h long). The results showed that all stressors produced an activation of the HPA axis; however, footshock induced the largest ACTH levels, whereas cold resulted in the highest CORT levels. In regard to the sleep data, immobilisation and PSD led to a rebound of SWS (+16.87% and +9.37%, respectively) and PS (+42.45% and +55.25%, respectively). Immobilisation, however, induced an increased number of PS episodes, whereas PSD resulted in longer PS episodes. Cold stress produced an exclusive rebound of SWS (+14.23%) and footshock promoted sustained alertness during the animal's resting period (+47.18%). These results indicate that different stimuli altered the sleep pattern in a distinct manner; and these alterations might be related to the state of the HPA axis activation.