Changes in hippocampal theta following intrahippocampal corticotropin-releasing hormone (CRH) infusions in the rat

Childhood abuse and EEG source localization in crack cocaine dependence

Fourteen subjects with histories of sexual and/or physical abuse in childhood and 13 matched control subjects were selected from a consecutive series of clients in residential treatment for crack cocaine dependence. Standardized low-resolution electromagnetic brain tomography (sLORETA) was used to estimate the source generators of the EEG in a cortical mask with voxel z-scores referenced to normative data at frequency intervals of 039 Hz, with nonparametric permutation to correct by randomization for the number of comparisons and the intercorrelations and variance of distribution of voxel values. Subjects with histories of abuse in childhood had significantly greater EEG power than controls in the theta frequency range (3.51-7.41 Hz), with greatest differences in the 3.90-Hz band distributed mainly in the parahippocampal, fusiform, lingual, posterior cingulate, and insular gyri. The groups did not differ significantly with regard to delta (1.56-3.12 Hz), alpha (7.81-12.48 Hz), beta (12.87-19.89 Hz), and gamma (20.28-35.10 Hz) frequency power. In excess, theta EEG power, a bandwidth of transactions among hippocampus and amygdala and paralimbic and visual association cortex, may be a correlate of childhood exposure to abuse.

Sleep disturbances in highly stress reactive mice: modeling endophenotypes of major depression

Background

Neuronal mechanisms underlying affective disorders such as major depression (MD) are still poorly understood. By selectively breeding mice for high (HR), intermediate (IR), or low (LR) reactivity of the hypothalamic-pituitary-adrenocortical (HPA) axis, we recently established a new genetic animal model of extremes in stress reactivity (SR). Studies characterizing this SR mouse model on the behavioral, endocrine, and neurobiological levels revealed several similarities with key endophenotypes observed in MD patients. HR mice were shown to have changes in rhythmicity and sleep measures such as rapid eye movement sleep (REMS) and non-REM sleep (NREMS) as well as in slow wave activity, indicative of reduced sleep efficacy and increased REMS. In the present study we were interested in how far a detailed spectral analysis of several electroencephalogram (EEG) parameters, including relevant frequency bands, could reveal further alterations of sleep architecture in this animal model. Eight adult males of each of the three breeding lines were equipped with epidural EEG and intramuscular electromyogram (EMG) electrodes. After recovery, EEG and EMG recordings were performed for two days.

Results

Differences in the amount of REMS and wakefulness and in the number of transitions between vigilance states were found in HR mice, when compared with IR and LR animals. Increased frequencies of transitions from NREMS to REMS and from REMS to wakefulness in HR animals were robust across the light-dark cycle. Detailed statistical analyses of spectral EEG parameters showed that especially during NREMS the power of the theta (6-9 Hz), alpha (10-15 Hz) and eta (16-22.75 Hz) bands was significantly different between the three breeding lines. Well defined distributions of significant power differences could be assigned to different times during the light and the dark phase. Especially during NREMS, group differences were robust and could be continuously monitored across the light-dark cycle.

Conclusions

The HR mice, i.e. those animals that have a genetic predisposition to hyper-activating their HPA axis in response to stressors, showed disturbed patterns in sleep architecture, similar to what is known from depressed patients. Significant alterations in several frequency bands of the EEG, which also seem to at least partly mimic clinical observations, suggest the SR mouse lines as a promising animal model for basic research of mechanisms underlying sleep impairments in MD.

Effects of acidic-astressin and ovine-CRF microinfusions into the ventral hippocampus on defensive behaviors in rats

This study investigated a possible role for ventral hippocampal corticotropin-releasing factor (CRF) in modulating both unconditioned and conditioned defensive behaviors by examining the effects of pre-training ventral hippocampal ovine-CRF (oCRF) or acidic-astressin ([Glu(11,16)]Ast) microinfusions in male Long-Evans hooded rats exposed to various threat stimuli including the elevated plus-maze (EPM) (oCRF), cat odor (oCRF and [Glu(11,16)]Ast) and a live cat ([Glu(11,16)]Ast). Unconditioned defensive behaviors were assessed during threat exposure, while conditioned defensive behaviors were assessed in each predator context 24 h after the initial threat encounter. Pre-training infusions of the CRF(1) and CRF(2) receptor agonist oCRF significantly increased defensive behaviors during both the unconditioned and conditioned components of the cat odor test, as well as exposure to the EPM. In contrast to the behavioral effects of oCRF microinfusions, the CRF(1) and CRF(2) receptor antagonist [Glu(11,16)]Ast significantly decreased defensive behaviors during exposure to cat odor, while producing no discernible effects following a second injection in the cat exposure test. During conditioned test trials, pre-training infusions of [Glu(11,16)]Ast also significantly reduced defensive behaviors during re-exposure to both predator contexts. These results suggest a specific role for ventral hippocampal CRF receptors in modulating anxiety-like behaviors in several ethologically relevant animal models of defense.

Working memory performance after acute exposure to the cold pressor stress in healthy volunteers

Effects of acute stress exposure on learning and memory have been frequently studied in both animals and humans. However, only a few studies have focused specifically on working memory performance and the available data are equivocal. The present study examined working memory performance during the Sternberg item recognition task after exposure to a predominantly adrenergic stressor. Twenty four healthy subjects were randomly assigned to a stress group or a control group. The stress group was exposed to the cold pressor stress test (CPS; i.e. insertion of the dominant hand into ice water for 60s),while 37 degrees C warm water was used with the control group. Twenty minutes after the stress exposure, working memory performance was tested with the Sternberg item recognition task with three levels of cognitive load. Sympathetic nervous system and hypothalamic pituitary adrenocortical (HPA) axis activation during CPS, were assessed by measuring heart rate and salivary cortisol before and during (heart rate) or 30 min after (cortisol) the stress procedure. Exposure to the CPS test was associated with a significant increase in heart rate but no increase in salivary cortisol. Participants exposed to the stress procedure showed significantly shorter reaction times during trials with higher cognitive load but tended to show higher false alarm rates than control subjects. The present results indicate that exposure to CPS can be associated with signs of both enhanced and impaired working memory performance. The observed behavioral pattern might represent a form of streamlined information processing advantageous in a threatening situation.

Post-training administration of corticotropin-releasing hormone (CRH) enhances retention of a spatial memory through a noradrenergic mechanism in male rats

Hormones released in response to stress play important roles in cognition. In the present study, the effects of the stress peptide, corticotropin-releasing hormone (CRH), on spatial reference memory were assessed following post-training administration. Adult Long-Evans male rats were trained for 6 days on a standard water maze task of reference memory in which animals must learn and remember the fixed location of a hidden, submerged platform. Each day, immediately following three training trials, rats received bilateral infusions of CRH into the lateral ventricles over a range of doses (0.1, 0.33, 1.0, 3.3 microg) or a vehicle solution. Post-training infusions of CRH improved retention as indicated by significantly shorter latencies and path lengths to locate the hidden platform on the first training (retention) trial of days 2 and 3. Additionally, post-training administration of CRH increased spatial bias during probe trials as measured by proximity to the platform location. CRH did not enhance performance on retention or probe trials when administered 2h after daily training indicating that CRH facilitated consolidation specifically. The effects of CRH were attenuated by intraventricular co-administration of the beta-adrenergic antagonist, propanolol, at bilateral doses that had no effect on retention alone (0.1, 1.0 microg). Results indicate that post-training administration of CRH enhanced spatial memory as measured in a water maze, and this effect was mediated, at least partly, by a noradrenergic mechanism.

Coexpression of the cannabinoid receptor type 1 with the corticotropin-releasing hormone receptor type 1 in distinct regions of the adult mouse forebrain

The high abundance of the cannabinoid receptor type 1 (CB1) in the brain and the discovery of its endogenous ligands possessing neuromodulatory activities suggest an important potential of the endocannabinoid system to influence the functions of other receptor systems in the brain, including the corticotropin releasing hormone (CRH) system. Several studies evidenced a cross-talk between these two receptor systems. In trying to detail functional interactions between CB1 and the CRH receptor type 1 (CRHR1), we performed double-label-in situ hybridisation on mouse forebrain sections to localise the transcripts encoding the two receptors at a cellular level. Colocalisation of both receptor mRNAs was only detected in low CB1-expressing cells, which are mainly principal projecting neurons, whereas high CB1-expressing cells, which are considered to be mostly GABAergic did not contain mRNA encoding CRHR1. CB1 is differentially coexpressed with CRHR1 in olfactory regions, in several cortical and limbic structures, and in some hypothalamic and thalamic nuclei. These observations suggest a complex mechanism underlying the mutual interrelation and modulation of the two receptor systems. In particular, high levels of coexpressing cells in cortical and limbic areas may relate to cognitive functions, such as working memory, emotional and declarative learning. Colocalisation of CB1 and CRHR1 in hypothalamic regions strongly suggests functional interactions regarding the neuroendocrine homeostasis, including feeding behaviour.

The effects of corticotropin-releasing factor on the cortical EEG are reduced following adolescent nicotine exposure

Although smoking is highly prevalent among adolescents, relatively little is known about the lasting neurobehavioral consequences associated with adolescent nicotine exposure. Prior studies from our laboratory suggest that adolescent nicotine exposure induces an anxiogenic profile in adult rats. Corticotropin-releasing factor (CRF) systems are important modulators of anxiety and response to stress. Since acute nicotine administration has been shown to stimulate central CRF activity, the purpose of this study was to examine the effects of adolescent nicotine exposure on CRFs modulation of the cortical and hippocampal EEG in adult rats. Male Sprague-Dawley rats were exposed to nicotine (5 mg/kg/day) between postnatal days 35-40 using transdermal nicotine patches. Six weeks after nicotine exposure ended, the effects of intracerebroventricular administration of CRF (0.01-1.0 microg/5 microl) on EEG activity in the cortex and hippocampus were assessed in nicotine-exposed rats and age-matched control rats. The overall effects CRF were consistent with previous reports. CRF decreased low to moderate frequency EEG activity (1-32 Hz) and increased high frequency EEG activity (32-50 Hz). However, in nicotine-exposed rats the effects of CRF on the frontal and parietal cortical EEG were blunted by 30-50% compared to control rats. A similar pattern of decreased response to CRF was not observed in the hippocampus. These blunted effects of CRF on the cortical EEG suggest that long-term changes in systems responsive to CRF result from adolescent nicotine exposure. Given the role of CRF systems in behavioral responses to stress and anxiety, these data suggest that adolescent nicotine exposure may produce long-term decreases in neurophysiological responses to stress.

Interaction between the cholinergic system and CRH in the modulation of spatial discrimination learning in mice

Both cholinergic and CRH systems have been linked to cognitive processes such as learning and memory, and neuroanatomical as well as neurochemical evidence suggests important interactions between these two systems. Moreover, recent reports of pro-mnestic effects of CRH open the possibility that CRH could have beneficial effects in animals with cholinergic dysfunction. In a first experiment, spatial discrimination of C57BL/6 mice treated with various doses of scopolamine (0.5--2.0 mg/kg IP) was tested in a two-choice water maze task. Scopolamine, but not methylscopolamine, impaired accuracy and decreased responsivity. In contrast, similar doses of the nicotinic antagonist mecamylamine had no effect on choice accuracy but altered responsivity, as indicated by increased errors of omission and a reduction in swim speed during early experimental stages. ICV CRH (0.5--1.0 microg) also failed to significantly affect accuracy, but a strong tendency was observed to impair percentage correct responses. Measures of responsivity, such as errors of omission, choice latency and distance traveled, and of thigmotaxis were not significantly affected by CRH. However, initial swim speed was reduced by the peptide. Combined treatment with scopolamine (0.5 mg/kg IP) and CRH (0.5 microg ICV) had only mild, and primarily independent, effects, but overall suggested that concomitant blockade of muscarinic receptors and activation of the CRH system would rather act synergistically to disrupt spatial discrimination learning. Synergistic effects were also observed when animals receiving a combination of mecamylamine (2.0 mg/kg IP) and CRH (0.5 microg ICV) were tested, both in terms of responsivity and thigmotaxis, and there was limited evidence that part of these effects were potentiating. Thus, the cholinergic and CRH systems interact in the modulation of learning, but CRH, contrary to prediction, worsens the impairment caused by cholinergic blockade.