Preventive Effects of Baclofen but Not Diazepam on Hippocampal Memory and Glucocorticoid Alterations After Prolonged Alcohol Withdrawal in Mice

Our study aims at comparing in C57/Bl male mice, the impact of repeated injections of baclofen (an agonist of GABAB receptor) or diazepam (a benzodiazepine acting through a positive allosteric modulation of GABAA receptor) administered during the alcohol-withdrawal period on hippocampus-dependent memory impairments and brain regional glucocorticoid dysfunction after a short (1-week) or a long (4-week) abstinence. Hence, mice were submitted to a 6-month alcohol consumption (12%v/v) and were progressively withdrawn to water. Then, after a 1- or 4-weeks abstinence, they were submitted to a contextual memory task followed by measurements of corticosterone concentrations in the dorsal hippocampus (dHPC), the ventral hippocampus (vHPC) and the prefrontal cortex (PFC). Results showed that 1- and 4-week withdrawn mice exhibited a severe memory deficit and a significant abnormal rise of the test-induced increase of corticosterone (TICC) in the dHPC, as compared to water-controls or to mice still under alcohol consumption. Repeated daily systemic administrations of decreasing doses of diazepam (ranged from 0.5 to 0.12 mg/kg) or baclofen (ranged from 1.5 to 0.37 mg/kg) during the last 15 days of the withdrawal period, normalized both memory and TICC scores in the dHPC in 1-week withdrawn animals; in contrast, only baclofen-withdrawn mice showed both normal memory performance and TICC scores in the dHPC after a 4-week withdrawal period. In conclusion, the memory improvement observed in 4-week withdrawn mice administered with baclofen stem from the protracted normalization of glucocorticoid activity in the dHPC, a phenomenon encountered only transitorily in diazepam-treated withdrawn mice.

Alcohol withdrawal induces long-lasting spatial working memory impairments: relationship with changes in corticosterone response in the prefrontal cortex

This study intends to determine whether long-lasting glucocorticoids (GCs) dysregulation in the prefrontal cortex (PFC) or the dorsal hippocampus (dHPC) play a causal role in the maintenance of working memory (WM) deficits observed after alcohol withdrawal. Here, we report that C57/BL6 male mice submitted to 6 months alcohol consumption (12 percent v/v) followed by 1 (1W) or 6 weeks (6W) withdrawal periods exhibit WM deficits in a spatial alternation task and an exaggerated corticosterone rise during and after memory testing in the PFC but not the dHPC. In contrast, emotional reactivity evaluated in a plus-maze is altered only in the 1W group. No behavioral alterations are observed in mice still drinking alcohol. To determine the causal role of corticosterone in the withdrawal-associated long-lasting WM deficits, we further show that a single intraperitoneal injection injection of metyrapone (an inhibitor of corticosterone synthesis) 30 minutes before testing, prevents withdrawal-associated WM deficits and reestablishes PFC activity, as assessed by increased phosphorylated C-AMP Response Element-binding protein (CREB) immunoreactivity in withdrawn mice. Finally, we show that intra-PFC blockade of mineralocorticoid receptors by infusion of spironolactone and, to a lesser extent, of GCs receptors by injection of mifepristone reverses the WM deficits induced by withdrawal whereas the same injections into the dHPC do not. Overall, our study evidences that long-lasting GCs dysfunction selectively in the PFC is responsible for the emergence and maintenance of WM impairments after withdrawal and that blocking prefrontal mineralocorticoid receptors receptors restores WM in withdrawn animals.

Different implications of the dorsal and ventral hippocampus on contextual memory retrieval after stress

This study assessed the relative contributions of dorsal (dHPC) and ventral (vHPC) hippocampus regions in mediating the rapid effects of an acute stress on contextual memory retrieval. Indeed, we previously showed that an acute stress (3 electric footschocks; 0.9 mA each) delivered 15 min before the 24 h-test inversed the memory retrieval pattern in a contextual discrimination task. Specifically, mice learned in a four-hole board two successive discriminations (D1 and D2) varying by the color and texture of the floor. Twenty-four hours later, nonstressed animals remembered accurately D1 but not D2 whereas stressed mice showed an opposite memory retrieval pattern, D2 being more accurately remembered than D1. We showed here that, at the time of memory testing in that task, stressed animals exhibited no significant changes neither in pCREB activity nor in the time-course evolution of corticosterone into the vHPC; in contrast, a significant decrease in pCREB activity and a significant increase in corticosterone were observed in the dHPC as compared to nonstressed mice. Moreover, local infusion of the anesthetic lidocaine into the vHPC 15 min before the onset of the stressor did not modify the memory retrieval pattern in nonstress and stress conditions whereas lidocaine infusion into the dHPC induced in nonstressed mice an memory retrieval pattern similar to that observed in stressed animals. The overall set of data shows that memory retrieval in nonstress condition involved primarily the dHPC and that the inversion of memory retrieval pattern after stress is linked to a dHPC but not vHPC dysfunction.

Authorship affiliations in original articles submitted to the International Journal of Tuberculosis and Lung Disease

OBJECTIVE

To ascertain whether the first (principal) and last (senior) authors of articles are affiliated to an organisation belonging to the study country in an analysis of high- and upper-middle-income countries, and low- and lower-middle-income countries.

DESIGN

Prospective review of all original articles (n = 911) submitted to the International Journal of Tuberculosis and Lung Disease (IJTLD) from June 2006 to May 2008.

RESULTS

In 81% of the submitted articles both the first and the last authors were affiliated to the country of the study. Slightly more articles from low (10%) than from lower-middle-income, high- and upper-middle-income countries (all 4%) had neither the first author nor the last author affiliated to the study country. For 17% of articles from low-income countries the senior author was not from the study country.

CONCLUSION

Although acceptance of articles for publication in the IJTLD is not dependent on this criterion, we find that a substantial proportion of authors from low- and middle-income countries were listed as principal and senior authors in articles submitted.

Long-term behavioral consequences of soman poisoning in mice

We investigated the long-term (up to 90 days) consequences of soman intoxication in mice on weight, motor performances (grip strength, rotarod) and mnemonic cognitive processes (T-maze, Morris water maze test). First, a relative weight loss of 20%, measured 3 days after intoxication, was evidenced as a threshold beyond which neuropathological damage was observed in the hippocampus. Animals were then distributed into either low weight loss (LWL) or high weight loss (HWL) groups according to the relative 20% weight loss threshold. Compared to controls, both groups of poisoned mice quickly exhibited a decrease in their motor performance subsequent to an acute soman toxicity phase. Then, total motor recovery occurred for the LWL group. Comparatively, HWL mice showed only transient recovery prior to a second decrease phase due to soman-induced delayed toxicity. One month after intoxication, mnemonic cognitive performances of the LWL group were similar to controls while the HWL group did not exhibit any learning skill. Three months after poisoning, compared to controls, the LWL group showed similar mnemonic performances in the maze test but a mild deficit in the Morris water maze task. At the same time, learning skills slightly recovered in the HWL group. Mnemonic cognitive data are discussed in relation to the neuropathology, neurogenesis and sprouting occurring in the hippocampus of soman-intoxicated animals.

Recovery after prolonged sleep deprivation: residual effects of slow-release caffeine on recovery sleep, sleepiness and cognitive functions

A long work schedule often results in sleep deprivation, sleepiness, impaired performance and fatigue. We investigated the residual effects of slow-release caffeine (SRC) on sleep, sleepiness and cognitive performance during a 42-hour recovery period following a 64-hour continuous wakefulness period in 16 healthy males, according to a double-blind, randomised, placebo-controlled, crossover study. Three hundred milligrams of SRC or placebo was given twice a day at 21:00 and 9:00 during the first 48 h of wakefulness. Recovery sleep was analysed with electroencephalography (EEG) and wrist actigraphy, daytime sleepiness with continuous EEG, sleep latency tests and actigraphy and cognitive functions with computerized tests from the NATO AGARD STRES battery. Both drug groups exhibited almost the same sleep architecture with a rebound of slow-wave sleep during both recovery nights and of REM sleep during the second night. Wakefulness level and cognitive functions were similarly impaired in both groups on the first day of recovery and partially returned to baseline on the second. To conclude, SRC appears to have no unwanted side-effects on recovery sleep, wakefulness and cognitive performance after a long period of sleep deprivation and might therefore be a useful choice over other psychostimulants for a long work schedule.

Effects of ibotenic acid lesions of the mediodorsal thalamus on memory: relationship with emotional processes in mice

The effects of ibotenic acid lesions of the mediodorsal nucleus of the thalamus (MD) on memory and fear reactivity in mice were studied. In the first experiment, MD subjects were submitted to a behavioral design allowing to study the relationship between memory and anxiety [Krazem A, Borde N, Beracochea D. Effects of diazepam and beta-CCM on working memory in mice: relationship with emotional reactivity. Pharmacol Biochem Behav 2001;68:235-44; Beracochea D, Krazem A, Jaffard R. Methyl beta carboline-3-carboxylate reverses the working memory deficits induced either by chronic alcohol consumption or mammillary body lesions in mice. Psychobiology 1995;23:52-8]. In a second experiment, MD-lesioned subjects were submitted to a GO/NOGO temporal alternation task involving two intertrial intervals (ITIs: 0 and 30 s). Lesioned subjects exhibited large bilateral mediodorsal thalamic lesions with small damage into the centromedial thalamic nucleus. In the first experiment, MD-lesioned animals performed normally a sequential alternation task involving fixed ITIs over seven successive trials (5 or 30 s); in contrast, MD-lesioned subjects exhibited deficits in the sequential task involving the same but mixed ITIs (30-5 s versus 5-30 s) the deficit being observed for the last trials of the series, regardless the ITIs used. MD lesions increased fear reactivity in an elevated-plus maze, and scores of anxiety were negatively correlated with performance in the mixed alternation schedule. The second experiment involving non spatial information extended results of the first experiment in showing that the deficit of MD-lesioned animals was not dependent on the ITIs separating trials. Overall, our data show that MD-lesioned subjects exhibit a cognitive impairment characterized by a difficulty to maintain an alternation rule in situations involving procedural variance, and this deficit could stem primarily from an increase of fear reactivity.

BetaCCM but not physostigmine enhancement of memory retrieval depends on emotional processes in mice

RATIONALE

The effects of methyl beta-carboline-3-carboxylate (betaCCM, an inverse agonists of GABA/benzodiazepine receptors) or physostigmine (a cholinesterase inhibitor) on retrieval processes and relationships with anxiety have been only marginally studied.

OBJECTIVE

This study investigates in mice the effects of acute betaCCM or physostigmine injections on retrieval of previously acquired discriminations involving distinct contextual cues (serial contextual discrimination; SCD) in a four-hole-board. Animals submitted to SCD were also evaluated for emotional reactivity in an elevated-plus maze.

METHODS

Mice were injected before the learning session began with a saline solution. Twenty-four hours later, mice were replaced on the context of the initial acquisition and a single dose of saline or betaCCM (0.5 or 1.5 mg/kg) or physostigmine (0.05 and 1.0 mg/kg) was injected 20 min before testing.

RESULTS

The highest dose of either betaCCM or physostigmine improved performance of the first discrimination in the SCD task. The higher dose of betaCCM produced anxiety-like reactivity in the plus maze, and scores of "anxiety" were significantly correlated with memory scores; in contrast, memory performance of physostigmine-treated subjects were totally independent of emotional reactivity.

CONCLUSION

These results show that, as opposed to physostigmine, betaCCM acts on retrieval processes specifically through its emotional component.

Enhancement of learning processes following an acute modafinil injection in mice

Modafinil is a wakeness-promoting drug, which is effective in the treatment of narcolepsy; its effects on learning processes are however little studied. Thus, the present study was aimed at determining the effects of an acute modafinil injection on a serial reversal discrimination task performed in a T-maze in mice. Independent groups of mice varying by the level of pretest training (either 1 or 4 days of training) were used. Mice were injected each day with a gum arabic solution before each session began. On the second or the fifth day of training, a single dose of modafinil was injected before testing. Modafinil at 64 mg/kg but not at 32 mg/kg dramatically improved performance as compared to controls in subjects being trained 4 days, but not in subjects being trained 1 day. This improvement of learning was due to the more rapid emergence of a win-stay strategy in modafinil-treated subjects as compare to controls. Thus, our data show that an acute modafinil injection enhances learning processes.

Effects of ibotenic acid lesions of the dorsal hippocampus on contextual fear conditioning in mice: comparison with mammillary body lesions

The goals of the present study were to determine if ibotenic acid lesions of the dorsal hippocampus (dHPC) or of mammillary body (MB) of the hypothalamus would induce similar contextual conditioning deficit in a fear-conditioning paradigm, previously developed in mice [Eur. J. Neurosci. 12 (2000) 2575]. Results showed that ibotenic acid lesions of the dHPC or of the MB both induced severe deficits on contextual conditioning but spared auditory conditioning, as compared to controls. This study provides direct evidence for an involvement of dHPC neurones in contextual fear conditioning and is first to demonstrate an involvement of the MB in the mediation of contextual fear conditioning.

??CCM enhances retrieval of serial contextual but not of serial spatial memory in mice

The effects of inverse agonists of the gamma-aminobutyric acid (GABA)/benzodiazepine receptors such as beta-carboline-3-carboxylate (betaCCM) on retrieval processes have not been studied extensively. This study investigates the effects in mice of an acute betaCCM injection on retrieval of previously acquired serial discriminations, involving distinct contextual cues (Contextual Serial Discrimination, CSD) or identical cues (Serial Spatial Discrimination, SSD) in a four-hole board. Animals submitted to CSD were also evaluated for emotional reactivity in an elevated-plus maze. In both the CSD and the SSD tasks, mice were injected with saline before the learning session began. Twenty-four hours later, mice were replaced on the hole-board following a single dose of saline or betaCCM (0.5 mg/kg or 1.5 mg/kg) injected 20 min before testing. The highest dose of betaCCM improved performance of the first discrimination in the contextual task but not in the spatial task. Moreover, the higher dose of betaCCM produced anxiety-like reactivity in an elevated-plus maze, and scores of 'anxiety' were positively correlated with memory scores. Overall, the data show that the betaCCM enhancement of memory processes depends on: (1) the cues associated with the to-be-remembered information; and (2) the emotional effects of the drug.

Improvement of learning processes following chronic systemic administration of modafinil in mice

This study was aimed at determining the effects of a chronic modafinil intraperitoneal administration on the rate of learning in a series of five serial spatial discrimination reversals (SSDR) in a T-maze. Results showed that a daily modafinil administration at 64 mg/kg but not at 32 mg/kg induced a faster learning rate as compared to controls. This learning improvement in experimental mice was due to the faster emergence of a win-stay rule over days of testing. In contrast, a second experiment showed that the same modafinil treatment had no significant effect on contingently reinforced alternation rates over five successive days of testing, as compared to controls. Thus, the results show that modafinil spared the ability to shift responses over trials and consequently, that the use of the win-stay rule to solve the SSDR task observed in modafinil-treated animals is due to an improvement of learning processes.

Slow release caffeine and prolonged (64-h) continuous wakefulness: effects on vigilance and cognitive performance

Some long work or shift work schedules necessitate an elevated and prolonged level of vigilance and performance but often result in sleep deprivation (SD), fatigue and sleepiness, which may impair efficiency. This study investigated the effects of a slow-release caffeine [(SRC) at the daily dose of 600 mg] on vigilance and cognitive performance during a 64 h continuous wakefulness period. Sixteen healthy males volunteered for this double-blind, randomised, placebo controlled, two-way crossover study. A total of 300-mg SRC or placebo (PBO) was given twice a day at 21:00 and 9:00 h during the SD period. Vigilance was objectively assessed with continuous electroencephalogram (EEG), the multiple sleep latency tests (MSLT) and wrist actigraphy. Cognitive functions (information processing and working memory), selective and divided attention were determined with computerised tests from the AGARD-NATO STRES Battery (Standardised Tests for Research with Environmental Stressors). Attention was also assessed with a symbol cancellation task and a Stroop's test; alertness was appreciated from visual analogue scales (VAS). Tests were performed at the hypo (02:00-04:00 h, 14:00-16:00 h) and hypervigilance (10:00-12:00 h, 22:00-00:00 h) periods during SD. Central temperature was continuously measured and safety of treatment was assessed from repeated clinical examinations. Compared with PBO, MSLT showed that SRC subjects were more vigilant from the onset (P=0.001) to the end of SD (P < 0.0001) whereas some cognitive functions were improved till the thirty third of SD but others were ameliorated through all the SD period and alertness was better from the thirteenth hour of SD, as shown by Stroop's test (P=0.048). We showed that 300-mg SRC given twice daily during a 64-h SD is able to antagonize the impairment produced on vigilance and cognitive functions.

Functional magnetic resonance imaging of mental strategy in a simulated aviation performance task

BACKGROUND

The objective of this study was to analyze the sensory and cognitive functions associated with activated brain regions characterizing mental strategy relative to degree of expertise in aviation-related tasks.

METHODS

We used echo-planar functional magnetic resonance imaging (fMRI) technique to examine brain activity in expert pilots (n = 6) compared with novice pilots (n = 6) during performance of a simulated aviation track-following task at 200 knots vs. 100 knots.

RESULTS

Expert pilots showed reduced activity in visual and motor regions that contrasted with predominant activation within anterior structures including the frontal and prefrontal cortices; structures involved in visual working memory, planning, selective attention and decision making functions. Novice pilots showed widespread activation of anterior and posterior brain structures, with a rise in activity in the visual, parietal and motor cortices as task difficulty increased.

CONCLUSIONS

A high level of performance in the track-following task related to a high degree of expertise in the aviation field. This corresponded to experts performing perceptual and mnemonic processing through a network of specialized functions from visual through multiple prefrontal areas. By contrast, the novice pilots predominantly show activity associated with non-specific perceptual processing and without subsequent representation of selective information in working memory.

Effects of prolonged exercise on brain ammonia and amino acids

The aim of this study was to investigate if enhanced peripheral ammonia production during exhaustive exercise increases ammonia detoxication in brain mediated by glutamine synthesis, and subsequently influences glutamate and gamma-aminobutyric acid (GABA) levels. This neurotransmitter production is related to the metabolism of glutamine. A group of rats was trained for 6 weeks by treadmill running (TR). They were compared to a group of untrained rats (UN). At the end of training, half of TR and UN rats were submitted to one session of treadmill running until exhaustion (288+/-12 min and 62+/-5 min in TR and UN group, respectively). At exhaustion, running and control rats were sacrificed in order to collect blood and to take samples of the following brain structures: cortex, striatum and cerebellum. Treadmill running until exhaustion induced an increase in blood ammonia by 140% without significant differences between TR and UN groups. Brain ammonia increased in both groups. However, TR group exhibited values 50% higher than those observed in UN group. Brain glutamine was increased at exhaustion in all groups of running rats by 30-75% of basal value whereas the glutamate only decreased in TR rats which were able to run for a longer time. In this group, the GABA level decreased in striatum. These data confirm that enhanced brain ammonia level during exercise stimulates glutamine synthesis as a mechanism of detoxication. After several hours of running, a reduction in brain glutamate levels was observed in all brain structures in trained rats but only in the striatum in untrained animals. The reduced availability of this GABA precursor decreases GABA levels only in the striatum of TR group by 45% of the resting value. These results suggest a relation between cerebral changes in neurotransmitters and excitatory amino acids, such as glutamate and GABA, and central fatigue.