The contribution of mild thiamine deficiency and ethanol consumption to central cholinergic parameter dysfunction and rats' open-field performance impairment

Sex differences in cholinergic circuits and behavioral disruptions following chronic ethanol exposure with and without thiamine deficiency

BACKGROUND

Few studies have investigated differences in the vulnerabilities of males and females to alcohol use disorder and alcohol-related brain damage (ARBD). According to epidemiological and clinical findings, females appear to be more sensitive to the effects of alcohol and thiamine deficiency and have a worse prognosis in recovery from neurocognitive deficits compared with males. This study aimed to characterize the effects of chronic ethanol (EtOH) toxicity and thiamine deficiency across the sexes using rodent models.

METHODS

Male and female Sprague Dawley rats were assigned to chronic forced EtOH treatment (CET), pyrithiamine-induced thiamine deficiency (PTD), combined CET-PTD, or pair-fed (PF) control treatment conditions. Following treatments, spatial working memory was assessed during a spontaneous alternation task while measuring acetylcholine (ACh) in the prefrontal cortex (PFC) and the hippocampus (HPC). The animals also underwent an operant-based attentional set-shifting task (ASST) for the analysis of behavioral flexibility.

RESULTS

Female and male rats did not differ in terms of EtOH consumption; however, the CET and CET-PTD-treated female rats had lower BECs than male rats. Compared with the PF group, the CET, PTD, and CET-PTD groups exhibited spatial working memory impairments with corresponding reductions in ACh efflux in the PFC and HPC. The ASST revealed that CET-PTD-treated males and females displayed impairments marked by increased latency to make decisions. Thalamic shrinkage was prominent only in the CET-PTD and PTD treatment conditions, but no sex-specific effects were observed.

CONCLUSIONS

Although the CET and CET-PTD-treated females had lower BECs than the males, they demonstrated similar cognitive impairments. These results provide evidence that female rats experience behavioral and neurochemical disruptions at lower levels of alcohol exposure than males and that chronic EtOH and thiamine deficiencies produce a unique behavioral profile.

Aging with alcohol-related brain damage: Critical brain circuits associated with cognitive dysfunction

Alcoholism is associated with brain damage and impaired cognitive functioning. The relative contributions of different etiological factors, such as alcohol, thiamine deficiency and age vulnerability, to the development of alcohol-related neuropathology and cognitive impairment are still poorly understood. One reason for this quandary is that both alcohol toxicity and thiamine deficiency produce brain damage and cognitive problems that can be modulated by age at exposure, aging following alcohol toxicity or thiamine deficiency, and aging during chronic alcohol exposure. Pre-clinical models of alcohol-related brain damage (ARBD) have elucidated some of the contributions of ethanol toxicity and thiamine deficiency to neuroinflammation, neuronal loss and functional deficits. However, the critical variable of age at the time of exposure or long-term aging with ARBD has been relatively ignored. Acute thiamine deficiency created a massive increase in neuroimmune genes and proteins within the thalamus and significant increases within the hippocampus and frontal cortex. Chronic ethanol treatment throughout adulthood produced very minor fluctuations in neuroimmune genes, regardless of brain region. Intermittent "binge-type" ethanol during the adolescent period established an intermediate neuroinflammatory response in the hippocampus and frontal cortex, that can persist into adulthood. Chronic excessive drinking throughout adulthood, adolescent intermittent ethanol exposure, and thiamine deficiency all led to a loss of the cholinergic neuronal phenotype within the basal forebrain, reduced hippocampal neurogenesis, and alterations in the frontal cortex. Only thiamine deficiency results in gross pathological lesions of the thalamus. The behavioral impairment following these types of treatments is hierarchical: Thiamine deficiency produces the greatest impairment of hippocampal- and prefrontal-dependent behaviors, chronic ethanol drinking ensues mild impairments on both types of tasks and adolescent intermittent ethanol exposure leads to impairments on frontocortical tasks, with sparing on most hippocampal-dependent tasks. However, our preliminary data suggest that as rodents age following adolescent intermittent ethanol exposure, hippocampal functional deficits began to emerge. A necessary requirement for the advancement of understanding the neural consequences of alcoholism is a more comprehensive assessment and understanding of how excessive alcohol drinking at different development periods (adolescence, early adulthood, middle-aged and aged) influences the trajectory of the aging process, including pathological aging and disease.

A Pivotal Role for Thiamine Deficiency in the Expression of Neuroinflammation Markers in Models of Alcohol-Related Brain Damage

BACKGROUND

Alcohol-related brain damage (ARBD) is associated with neurotoxic effects of heavy alcohol use and nutritional deficiency, in particular thiamine deficiency (TD), both of which induce inflammatory responses in brain. Although neuroinflammation is a critical factor in the induction of ARBD, few studies have addressed the specific contribution(s) of ethanol (EtOH) versus TD.

METHODS

Adult rats were randomly divided into 6 conditions: chronic EtOH treatment (CET) where rats consumed a 20% v/v solution of EtOH for 6 months; CET with injections of thiamine (CET + T); severe pyrithiamine-induced TD (PTD); moderate PTD; moderate PTD during CET; and pair-fed controls. After the treatments, the rats were split into 3 recovery phase time points: the last day of treatment (time point 1), acute recovery (time point 2: 24 hours posttreatment), and delayed recovery (time point 3: 3 weeks posttreatment). At these time points, vulnerable brain regions (thalamus, hippocampus, frontal cortex) were collected and changes in neuroimmune markers were assessed using a combination of reverse transcription polymerase chain reaction and protein analysis.

RESULTS

CET led to minor fluctuations in neuroimmune genes, regardless of the structure being examined. In contrast, PTD treatment led to a profound increase in neuroimmune genes and proteins within the thalamus. Cytokine changes in the thalamus ranged in magnitude from moderate (3-fold and 4-fold increase in interleukin-1β [IL-1β] and IκBα) to severe (8-fold and 26-fold increase in tumor necrosis factor-α and IL-6, respectively). Though a similar pattern was observed in the hippocampus and frontal cortex, overall fold increases were moderate relative to the thalamus. Importantly, neuroimmune gene induction varied significantly as a function of severity of TD, and most genes displayed a gradual recovery across time.

CONCLUSIONS

These data suggest an overt brain inflammatory response by TD and a subtle change by CET alone. Also, the prominent role of TD in the immune-related signaling pathways leads to unique regional and temporal profiles of induction of neuroimmune genes.

Comparative effects of EtOH consumption and thiamine deficiency on cognitive impairment, oxidative damage, and β-amyloid peptide overproduction in the brain

The effects of chronic EtOH consumption, associated or not with thiamine deficiency (TD), on cognitive impairment, oxidative damage, and β-amyloid (Aβ) peptide accumulation in the brain were investigated in male C57BL/6 mice. We established an alcoholic mouse model by feeding an EtOH liquid diet, a TD mouse model by feeding a thiamine-depleted liquid diet, and an EtOH treatment associated with TD mouse model by feeding a thiamine-depleted EtOH liquid diet for 7 weeks. The learning and memory functions of the mice were detected through the Y-maze test. Biochemical parameters were measured using corresponding commercial kits. The Aβ expression in the hippocampus was observed by immunohistochemical staining. Several results were obtained. First, EtOH significantly reduced cognitive function by significantly decreasing the Glu content in the hippocampus; increasing the AChE activity in the cortex; and reducing the thiamine level, and superoxide dismutase (SOD), glutathione peroxidase (GPx), and choline acetyltransferase (ChAT) activities in both the hippocampus and cortex. The treatment also increased the levels of malondialdehyde (MDA), protein carbonyl, 8-hydroxydeoxyguanosine (8-OHdG), and nitric oxide (NO) and the activities of total nitric oxide synthase (tNOS), inducible nitric oxide synthase (iNOS), and monoamine oxidase B (MAO-B). Furthermore, EtOH enhanced the expression levels of Aβ_1-42 and Aβ_1-40 in the hippocampus. Second, TD induced the same dysfunctions caused by EtOH in the biochemical parameters, except for learning ability, 8-OHdG content, and GPx, tNOS, and AChE activities in the cortex. Third, the modification of MDA, protein carbonyl and NO levels, and GPx, iNOS, ChAT, and MAO-B activities in the brain induced by chronic EtOH treatment associated with TD was greater than that induced by EtOH or TD alone. The synergistic effects of EtOH and TD on Aβ_1-40 and Glu release, as well as on SOD activity, depended on their actions on the hippocampus or cortex. These findings suggest that chronic EtOH consumption can induce TD, cognitive impairment, Aβ accumulation, oxidative stress injury, and neurotransmitter metabolic abnormalities. Furthermore, the association of chronic EtOH consumption with TD causes dramatic brain dysfunctions with a severe effect on the brain.

Impact of exercise and vitamin B1 intake on hippocampal brain-derived neurotrophic factor and spatial memory performance in a rat model of stress

Chronic stress affects brain areas involved in learning and emotional responses through modulation of neurotropic factors or neurotransmitters. Therefore, we investigated the role of exercise and thiamine supplementation on spatial memory and on brain-derived neurotrophic factor (BDNF) and acetylcholine (Ach) content in the hippocampus of the stressed animals. Male Wistar rats were randomly assigned to 4 groups (8 rats/group): control group; stress group; swimming and stress group; and thiamine and stress group. All animals were assessed by a T maze for spatial memory or open field test for locomotion and anxiety. BDNF and Ach were estimated in the hippocampus. Chronic immobilization stress resulted in a significant decrease in BDNF and Ach levels in the hippocampus and impairment in spatial memory functions and decreased basal activity. However, either swimming training or thiamine intake for 30 d was proved to induce a significant increase both in BDNF and Ach in conjunction with improved performance in the T maze, marked anxiolytic effect and enhanced ambulation in the open field test, as compared to the stress group. Interestingly, swimming-exercised rats showed significantly higher levels of BDNF versus thiamine-receiving rats, while thiamine-receiving rats showed higher locomotor activity and less freezing behavior in the open field test compared to the swimming group. It was concluded that decreased BDNF and Ach after stress exposure could be a mechanism for the deleterious actions of stress on memory function; swimming exercise or vitamin B1 supplementation for 30 d was a protective tool to improve coping with chronic stress by modulating BDNF and Ach content along with enhancement of memory functions and motor activities.

Interactions between chronic ethanol consumption and thiamine deficiency on neural plasticity, spatial memory, and cognitive flexibility

BACKGROUND

Many alcoholics display moderate to severe cognitive dysfunction accompanied by brain pathology. A factor confounded with prolonged heavy alcohol consumption is poor nutrition, and many alcoholics are thiamine deficient. Thus, thiamine deficiency (TD) has emerged as a key factor underlying alcohol-related brain damage (ARBD). TD in humans can lead to Wernicke Encephalitis that can progress into Wernicke-Korsakoff syndrome and these disorders have a high prevalence among alcoholics. Animal models are critical for determining the exact contributions of ethanol (EtOH)- and TD-induced neurotoxicity, as well as the interactions of those factors to brain and cognitive dysfunction.

METHODS

Adult rats were randomly assigned to 1 of 6 treatment conditions: chronic EtOH treatment (CET) where rats consumed a 20% v/v solution of EtOH over 6 months; severe pyrithiamine-induced TD (PTD-moderate acute stage); moderate PTD (PTD-early acute stage); moderate PTD followed by CET (PTD-CET); moderate PTD during CET (CET-PTD); and pair-fed (PF) control. After recovery from treatment, all rats were tested on spontaneous alternation and attentional set-shifting. After behavioral testing, brains were harvested for determination of mature brain-derived neurotrophic factor (BDNF) and thalamic pathology.

RESULTS

Moderate TD combined with CET, regardless of treatment order, produced significant impairments in spatial memory, cognitive flexibility, and reductions in brain plasticity as measured by BDNF levels in the frontal cortex and hippocampus. These alterations are greater than those seen in moderate TD alone, and the synergistic effects of moderate TD with CET lead to a unique cognitive profile. However, CET did not exacerbate thalamic pathology seen after moderate TD.

CONCLUSIONS

These data support the emerging theory that subclinical TD during chronic heavy alcohol consumption is critical for the development of significant cognitive impairment associated with ARBD.

Change in psychiatric symptomatology after benfotiamine treatment in males is related to lifetime alcoholism severity

BACKGROUND

Severe alcoholism can be associated with significant nutritional and vitamin deficiency, especially vitamin B1 (thiamine) which is associated with neurological deficits impacting mood and cognition. Alcohol consumption was reduced among female but not male alcoholics after supplementation with the high potency thiamine analog benfotiamine (BF). We examined the relationship between lifetime alcoholism severity, psychiatric symptoms and response to BF among the alcohol dependent men from this cohort.

METHODS

Eighty-five adult men (mean age=48±8 years) meeting DSM-IV-TR criteria for a current alcohol use disorder who were abstinent <30days participated in a randomized, double-blind, placebo-controlled trial of 600mg BF vs placebo (PL) for 6 months. Psychometric testing included a derived Lifetime Alcoholism Severity Score (AS), Symptom Checklist 90R (SCL-90R), and the Barratt Impulsivity Scale (BIS) at baseline and at 6 months.

RESULTS

Baseline SCL-90-R scale scores for men with high alcoholism severity (AS≥24; N=46 HAS) were significantly greater than for men with low alcoholism severity (AS<24; N=39 LAS), but BIS scores did not differ. MANOVA modeling at follow-up (N=50 completed subjects) identified a significant treatment effect (F=2.5, df=10, p<0.03) and treatment×alcoholism severity level interaction (F=2.5, dfnum=10, dfden=30, p<0.03) indicating reduced SCL-90-R scores among BF treated, HAS males. Above normal plasma thiamine levels at follow-up predicted reduced depression scores in a BF-treated subset (F=3.2, p<0.09, N=26).

CONCLUSION

BF appears to reduce psychiatric distress and may facilitate recovery in severely affected males with a lifetime alcohol use disorder and should be considered for adjuvant therapy in alcohol rehabilitation.

TRIAL REGISTRATION

#NCT00680121 High Dose Vitamin B1 to Reduce Abusive Alcohol Use.

Mild thiamine deficiency and chronic ethanol consumption modulate acetylcholinesterase activity change and spatial memory performance in a water maze task

Chronic thiamine deficiency may be responsible for pathologic changes in the brains of alcoholics, and subclinical episodes of this vitamin deficiency may cause cumulative brain damage. In the present work, the chronic effects of ethanol and its association to a mild thiamine deficiency episode (subclinical model) on neocortical and hippocampal acetylcholinesterase activity were assessed along with their possible association to spatial cognitive dysfunction. The results indicate that in the beginning of the neurodegenerative process, before the appearance of brain lesions, chronic ethanol consumption reverses the effects of mild thiamine deficiency on both spatial cognitive performance and acetylcholinesterase activity without having significant effects on any morphometric parameter.

Neurochemical and behavioural impact of C18 fatty acids in male mice postweaning

Dietary components, particularly essential fatty acids, affect the expression and maintenance of normal physiological phenotypes. However, the influence of C18 fatty acids that are abundantly present in the normal diet is unclear. We focused on the behavioural and neurochemical effects of C18 fatty acids during postweaning development in male mice. An AIN-93G diet supplemented with 8% stearic acid (C18:0), 3% oleic acid (C18:1), 3% linoleic acid (C18:2) or 3% α-linolenic acid (C18:3) was provided from four weeks of age for eight weeks. At 12 weeks of age, novel exploratory behaviour and social interaction tests were carried out. One week after the last behavioural test, the brain of each mouse was removed. The frequency of social interactive behaviour was decreased by approximately 70% in the C18:0 group compared to the basal diet group, but there was no difference in cumulative time. The frequency of social interaction showed a positive correlation to cumulative time in mice fed with the experimental diets except for C18:0. Dietary C18 fatty acids following weaning had no impact on brain fatty acid composition except for the C18:3 diet. Furthermore, the neurochemical properties to be especially noted were that choline acetyltransferase activity was absolutely higher in C18:0 diet-fed mice than in the other groups, especially in the frontal cortex where it was 1.7-fold higher than in the basal diet-fed group. The present results reveal a significant possibility of neurochemical and behavioural effects of dietary fatty acids, and saturated fatty acids are of special importance during the postweaning period.

Translational rodent models of Korsakoff syndrome reveal the critical neuroanatomical substrates of memory dysfunction and recovery

Investigation of the amnesic disorder Korsakoff Syndrome (KS) has been vital in elucidating the critical brain regions involved in learning and memory. Although the thalamus and mammillary bodies are the primary sites of neuropathology in KS, functional deactivation of the hippocampus and certain cortical regions also contributes to the chronic cognitive dysfunction reported in KS. The rodent pyrithiamine-induced thiamine deficiency (PTD) model has been used to study the extent of hippocampal and cortical neuroadaptations in KS. In the PTD model, the hippocampus, frontal and retrosplenial cortical regions display loss of cholinergic innervation, decreases in behaviorally stimulated acetylcholine release and reductions in neurotrophins. While PTD treatment results in significant impairment in measures of spatial learning and memory, other cognitive processes are left intact and may be recruited to improve cognitive outcome. In addition, behavioral recovery can be stimulated in the PTD model by increasing acetylcholine levels in the medial septum, hippocampus and frontal cortex, but not in the retrosplenial cortex. These data indicate that although the hippocampus and frontal cortex are involved in the pathogenesis of KS, these regions retain neuroplasticity and may be critical targets for improving cognitive outcome in KS.

Thiamine deficiency degrades the link between spatial behavior and hippocampal synapsin I and phosphorylated synapsin I protein levels

The links between spatial behavior and hippocampal levels of synapsin I and phosphosynapsin I were assessed in normal rats and in the pyrithiamine-induced thiamine deficiency (PTD) rat model of Wernicke-Korsakoff's syndrome. Synapsin I tethers small synaptic vesicles to the actin cytoskeleton in a phosphorylation-dependent manner, is involved in neurotransmitter release and has been implicated in hippocampal-dependent learning. Positive correlations between spontaneous alternation behavior and hippocampal levels of both synapsin I and phosphorylated synapsin I were found in control rats. However, spontaneous alternation performance was impaired in PTD rats and was accompanied by a significant reduction (30%) in phosphorylated synapsin I. Furthermore, no correlations were observed between either form of synapsin I and behavior in PTD rats. These data suggest that successful spontaneous alternation performance is related to high levels of hippocampal synapsin I and phosphorylated synapsin I. These results not only support the previous findings that implicate impaired hippocampal neurotransmission in the spatial learning and memory deficits associated with thiamine deficiency, but also suggest a presynaptic mechanism.

Brain and behavioral pathology in an animal model of Wernicke's encephalopathy and Wernicke-Korsakoff Syndrome

Animal models provide the opportunity for in-depth and experimental investigation into the anatomical and physiological underpinnings of human neurological disorders. Rodent models of thiamine deficiency have yielded significant insight into the structural, neurochemical and cognitive deficits associated with thiamine deficiency as well as proven useful toward greater understanding of memory function in the intact brain. In this review, we discuss the anatomical, neurochemical and behavioral changes that occur during the acute and chronic phases of thiamine deficiency and describe how rodent models of Wernicke-Korsakoff Syndrome aid in developing a more detailed picture of brain structures involved in learning and memory.

Alcohol-related amnesia and dementia: animal models have revealed the contributions of different etiological factors on neuropathology, neurochemical dysfunction and cognitive impairment

Chronic alcoholism is associated with impaired cognitive functioning. Over 75% of autopsied chronic alcoholics have significant brain damage and over 50% of detoxified alcoholics display some degree of learning and memory impairment. However, the relative contributions of different etiological factors to the development of alcohol-related neuropathology and cognitive impairment are questioned. One reason for this quandary is that both alcohol toxicity and thiamine deficiency result in brain damage and cognitive problems. Two alcohol-related neurological disorders, alcohol-associated dementia and Wernicke-Korsakoff syndrome have been modeled in rodents. These pre-clinical models have elucidated the relative contributions of ethanol toxicity and thiamine deficiency to the development of dementia and amnesia. What is observed in these models--from repeated and chronic ethanol exposure to thiamine deficiency--is a progression of both neural and cognitive dysregulation. Repeated binge exposure to ethanol leads to changes in neural plasticity by reducing GABAergic inhibition and facilitating glutamatergic excitation, long-term chronic ethanol exposure results in hippocampal and cortical cell loss as well as reduced hippocampal neurotrophin protein content critical for neural survival, and thiamine deficiency results in gross pathological lesions in the diencephalon, reduced neurotrophic protein levels, and neurotransmitters levels in the hippocampus and cortex. Behaviorally, after recovery from repeated or chronic ethanol exposure there is impairment in working or episodic memory that can recover with prolonged abstinence. In contrast, after thiamine deficiency there is severe and persistent spatial memory impairments and increased perseverative behavior. The interaction between ethanol and thiamine deficiency does not produce more behavioral or neural pathology, with the exception of reduction of white matter, than long-term thiamine deficiency alone.

Periadolescent ethanol exposure reduces adult forebrain ChAT+IR neurons: correlation with behavioral pathology

Substance abuse typically begins in adolescence; therefore, the impact of alcohol during this critical time in brain development is of particular importance. Epidemiological data indicate that excessive alcohol consumption is prevalent among adolescents and may have lasting neurobehavioral consequences. Loss of cholinergic input to the forebrain has been demonstrated following fetal alcohol exposure and in adults with Wernicke-Korsakoff syndrome. In the present study, immunohistochemistry for choline acetyltransferase (ChAT) was determined to assess forebrain cholinergic neurons (Ch1-4), and behavioral changes following periadolescent alcohol exposure. Wistar rats were exposed to intermittent ethanol vapor (14 h on/10 h off/day) for 35 days from postnatal day (PD) 22 to PD 57 (average blood alcohol concentration (BAC): 163 mg%). Rats were withdrawn from vapor and assessed for locomotor activity, startle response, conflict behavior in the open field, and immobility in the forced swim test, as adults. Rats were then sacrificed at day 71/72 and perfused for histochemical analyses. Ethanol vapor-exposed rats displayed: increased locomotor activity 8 h after the termination of vapor delivery for that 24 h period at day 10 and day 20 of alcohol vapor exposure, significant reductions in the amplitude of their responses to prepulse stimuli during the startle paradigm at 24 h withdrawal, and at 2 weeks following withdrawal, less anxiety-like and/or more "disinhibitory" behavior in the open field conflict, and more immobility in the forced swim test. Quantitative analyses of ChAT immunoreactivity revealed a significant reduction in cell counts in the Ch1-2 and Ch3-4 regions of the basal forebrain in ethanol vapor-exposed rats. This reduction in cell counts was significantly correlated with less anxiety-like and/or more "disinhibitory" behavior in the open field conflict test. These studies demonstrate that behavioral measures of arousal, affective state, disinhibitory behavior, and ChAT+IR, are all significantly impacted by periadolescent ethanol exposure and withdrawal in Wistar rats.

Stage-dependent alterations of progenitor cell proliferation and neurogenesis in an animal model of Wernicke-Korsakoff syndrome

Alcohol-induced Wernicke-Korsakoff syndrome (WKS) culminates in bilateral diencephalic lesion and severe amnesia. Using the pyrithiamine-induced thiamine deficiency (PTD) animal paradigm of WKS, our laboratory has demonstrated hippocampal dysfunction in the absence of gross anatomical pathology. Extensive literature has revealed reduced hippocampal neurogenesis following a neuropathological insult, which might contribute to hippocampus-based learning and memory impairments. Thus, the current investigation was conducted to determine whether PTD treatment altered hippocampal neurogenesis in a stage-dependent fashion. Male Sprague-Dawley rats were assigned to one of 4 stages of thiamine deficiency based on behavioral symptoms: pre-symptomatic stage, ataxic stage, early post-opisthotonus stage, or the late post-opisthotonus stage. The S-phase mitotic marker 5'-bromo-2'-deoxyuridine (BrdU) was administered at the conclusion of each stage following thiamine restoration and subjects were perfused 24 hours or 28 days after BrdU to assess cellular proliferation or neurogenesis and survival, respectively. Dorsal hippocampal sections were immunostained for BrdU (proliferating cell marker), NeuN (neurons), GFAP (astrocytes), Iba-1 (microglia), and O4 (oligodendrocytes). The PTD treatment increased progenitor cell proliferation and survival during the early post-opisthotonus stage. However, levels of neurogenesis were reduced during this stage as well as the late post-opisthotonus stage where there was also an increase in astrocytogenesis. The diminished numbers of newly generated neurons (BrdU/NeuN co-localization) was paralleled by increased BrdU cells that did not co-localize with any of the phenotypic markers during these later stages. These data demonstrate that long-term alterations in neurogenesis and gliogenesis might contribute to the observed hippocampal dysfunction in the PTD model and human WKS.

Memory for reward location is enhanced even though acetylcholine efflux within the amygdala is impaired in rats with damage to the diencephalon produced by thiamine deficiency

A rodent model of diencephalic amnesia produced by thiamine deficiency (pyrithiamine-induced thiamine deficiency [PTD]) was implemented to assess both changes in behavior and acetylcholine (ACh) efflux in the amygdala across four training sessions of a delayed alternation task. Two versions of the delayed alternation task were used. In one version, when a correct alternation was made a unique reward was paired with each spatial location ([left arm-chocolate milk] or [right arm-rat chow]). This paradigm is called the differential outcomes procedure (DOP). In the second version of the task, correct delayed alternation resulted in the same rewards but randomized across location (Nondifferential Outcomes Procedure [NOP]). The PTD rats were impaired on the first session of delayed alternation testing. However, both control and PTD rats using the DOP performed significantly better on delayed alternation than rats trained with the NOP.This effect was driven primarily by the PTD rats in the DOP condition outperforming all other groups on sessions 2-4. Although ACh efflux in the amygdala increased during delayed alternation testing in all groups, the NOP-trained rats had a greater rise in training-related ACh release in the post-training period. This suggests that increased amygdalar cholinergic activation is more critical for processing spatial information than episodic reward information. These data correspond with the idea that cholinergic activation of the amygdala promotes processing in other neural systems.

Cortical cholinergic abnormalities contribute to the amnesic state induced by pyrithiamine-induced thiamine deficiency in the rat

Although the key neuropathology associated with diencephalic amnesia is lesions to the thalamus and/or mammillary bodies, functional deactivation of the hippocampus and associated cortical regions also appear to contribute to the memory dysfunction. For example, there is loss of forebrain cholinergic neurons and alterations in stimulated acetylcholine (ACh) levels in the hippocampus and cortex in animal models of diencephalic amnesia associated with thiamine deficiency. In the present study, the pyrithiamine-induced thiamine deficiency rat model was used to assess the functional relationships between thalamic pathology, behavioral impairment, ACh efflux and cholinergic innervation of the hippocampus and cortex. In pyrithiamine-induced thiamine deficiency-treated rats, ACh efflux during behavioral testing was blunted to differing degrees in the hippocampus, medial frontal cortex and retrosplenial cortex. In addition, significant reductions in cholinergic fiber densities were observed in each of these regions. However, only hippocampal cholinergic fiber density correlated significantly with ACh efflux in the same region, suggesting that the reduction in cortical ACh efflux in cases of diencephalic amnesia cannot be fully explained by a loss of cholinergic fiber innervation. This notion supports the emerging theory that the functional consequences of the distal effects of lesions go beyond simple deafferentation. Specifically, some frontal cortical regions exhibit hypersensitivity to deafferentation that is only detected during behavioral and/or physiological demand.

Spatial memory deficits and thalamic serotonergic metabolite change in thiamine deficient rats

The purposes of the present study were to verify the effects of a severe thiamine deficiency episode on spatial cognitive aspects and thalamic serotonergic parameters. The animals were submitted to a severe thiamine deficiency treatment that was interrupted after the onset of the last neurological signs. The results obtained confirm previous findings about TD deficiency effects on cognitive function and, further show that this vitamin increases the thalamic serotonine metabolite, 5-hidroxyindolacetic acid (5-HIAA), level. In addition, the present data shed light on the importance of this metabolite in spatial cognitive function.

Ethanol promotes thiamine deficiency-induced neuronal death: involvement of double-stranded RNA-activated protein kinase

BACKGROUND

Heavy alcohol consumption causes cerebellar degeneration, and the underlying mechanism is unclear. Chronic alcoholism is usually associated with thiamine deficiency (TD) which is known to induce selective neurodegeneration in the brain. However, the role of TD in alcohol-induced cerebellar degeneration remains to be elucidated. The double-stranded RNA-activated protein kinase (PKR) is a potent antiviral protein. Viral infection or binding to dsRNA causes PKR autophosphorylation and subsequent phosphorylation of the alpha-subunit of eukaryotic translation factor-2alpha, leading to inhibition of translation or apoptosis. PKR can also be activated by cellular stresses.

METHODS

In this study, we used an in vitro model, cultured cerebellar granule neurons (CGNs), to investigate the interaction between TD and ethanol and evaluate the contribution of their interaction to neuronal loss. TD was induced by treatment with amprolium in association with ethanol. Cell viability was determined by 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyl tetrazolium bromide assay. PKR expression/phosphorylation and subcellular distribution was analyzed with immunoblotting and immunocytochemistry.

RESULTS

Thiamine deficiency caused death of CGNs but ethanol did not. However, TD plus ethanol induced a much greater cell loss than TD alone. TD-induced PKR phosphorylation and ethanol exposure significantly promoted TD-induced PKR phosphorylation as well as its nuclear translocation. A selective PKR inhibitor not only protected CGNs against TD toxicity, but also abolished ethanol potentiation of TD-induced loss of CGNs.

CONCLUSIONS

Ethanol promoted TD-induced PKR activation and neuronal death. PKR may be a convergent protein that mediates the interaction between TD and ethanol.

Neuroimaging of the Wernicke-Korsakoff syndrome

AIM

Presented is the neuroradiological signature of acute Wernicke's encephalopathy (WE), derived from different types of magnetic resonance imaging (MRI) sequences. WE results from thiamine depletion, and its most typical antecedent is chronic alcohol dependence. Brain regions observed with in vivo MRI affected in acute WE include the mammillary bodies, periaqueductal and periventricular gray matter, collicular bodies and thalamus. These affected areas are usually edematous and are best visualized and quantified with MRI sequences that highlight such tissue. Following the acute WE phase and resolution of edema and inflammation of affected brain tissue, WE, if not adequately treated with thiamine repletion, can herald Korsakoff's syndrome (KS), with its symptomatic hallmark of global amnesia, that is, the inability to commit newly encountered (episodic) information to memory for later recall or recognition.

METHODS

Neuropathology of KS detectable with MRI has a different neuroradiological signature from the acute stage and can be observed as tissue shrinkage or atrophy of selective brain structures, including the mammillary bodies and thalamus and ventricular expansion, probably indicative of atrophy of surrounding gray matter nuclei. Quantification of these and additional gray matter structures known to underlie global amnesia reveal substantial bilateral volume deficits in the hippocampus, in addition to the mammillary bodies and thalamus, and modest deficits in the medial septum/diagonal band of Broca. The infratentorium is also affected, exhibiting volume deficits in cerebellar hemispheres, anterior superior vermis and pons, contributing to ataxia of gait and stance.

RESULTS

Consideration of WKS structural brain changes in the context of the neuropathology of non-WKS alcoholism revealed a graded pattern of volume deficits, from mild in non-WKS alcoholics to moderate or severe in WKS, in the mammillary bodies, hippocampus, thalamus, cerebellum and pons. The development and resolution of brain structures affected in acute, chronic and treated WE was verified in longitudinal MRI study of rats that modeled of the interaction of extensive alcohol consumption and thiamine depletion and repletion.

CONCLUSIONS

Thus, neuroradiological examination with MRI is valuable in the diagnosis of acute WE and enables in vivo tracking of the progression of the brain pathology of WE from the acute pathological phase to resolution with thiamine treatment or to progression to KS without treatment. Further, in vivo MRI facilitates translational studies to model antecedent conditions contributing to the development, sequelae and treatment of WE.

Abolition of reperfusion-induced arrhythmias in hearts from thiamine-deficient rats

Extensive work has been done regarding the impact of thiamine deprivation on the nervous system. In cardiac tissue, chronic thiamine deficiency is described to cause changes in the myocardium that can be associated with arrhythmias. However, compared with the brain, very little is known about the effects of thiamine deficiency on the heart. Thus this study was undertaken to explore whether thiamine deprivation has a role in cardiac arrhythmogenesis. We examined hearts isolated from thiamine-deprived and control rats. We measured heart rate, diastolic and systolic tension, and contraction and relaxation rates. Whole cell voltage clamp was performed in rat isolated cardiac myocytes to measure L-type Ca2+current. In addition, we investigated the global intracellular calcium transients by using confocal microscopy in the line-scan mode. The hearts from thiamine-deficient rats did not degenerate into ventricular fibrillation during 30 min of reperfusion after 15 min of coronary occlusion. The antiarrhythmogenic effects were characterized by the arrhythmia severity index. Our results suggest that hearts from thiamine-deficient rats did not experience irreversible arrhythmias. There was no change in L-type Ca2+current density. Inactivation kinetics of this current in Ca2+-buffered cells was retarded in thiamine-deficient cardiac myocytes. The global Ca2+release was significantly reduced in thiamine-deficient cardiac myocytes. The amplitude of caffeine-releasable Ca2+was lower in thiamine-deficient myocytes. In summary, we have found that thiamine deprivation attenuates the incidence and severity of postischemic arrhythmias, possibly through a mechanism involving a decrease in global Ca2+release.

Selective septohippocampal - but not forebrain amygdalar - cholinergic dysfunction in diencephalic amnesia

A rodent model of diencephalic amnesia, pyrithiamine-induced thiamine deficiency (PTD), was used to investigate diencephalic-limbic interactions. In-vivo acetylcholine (ACh) efflux, a marker of memory-related activation, was measured in the hippocampus and the amygdala of PTD-treated and pair-fed (PF) control rats while they were tested on a spontaneous alternation task. During behavioral testing, all animals displayed increases in ACh efflux in both the hippocampus and amygdala. However, during spontaneous alternation testing ACh efflux in the hippocampus and the alternation scores were higher in PF rats relative to PTD-treated rats. In contrast, ACh efflux in the amygdala was not suppressed in PTD treated rats, relative to PF rats, prior to or during behavioral testing. In addition, unbiased stereological estimates of the number of choline acetyltransferase (ChAT) immunopositive neurons in the medial septal/diagonal band (MS/DB) and nucleus basalis of Meynert (NBM) also reveal a selective cholinergic dysfunction: In PTD-treated rats a significant loss of ChAT-immunopositive cells was found only in the MS/DB, but not in the NBM. Significantly, these results demonstrate that thiamine deficiency causes selective cholinergic dysfunction in the septo-hippocampal pathway.

Thiamine deficiency during pregnancy leads to cerebellar neuronal death in rat offspring: role of voltage-dependent K+ channels

Oxidative stress, selective neuronal loss, and diminished activity of thiamine-dependent enzymes play a role in many neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease and Huntington's disease. To further understand the major implications of thiamine deficiency (TD) in neuronal death, we induced TD during pregnancy and evaluated the effects on the offspring. The body and brain weights of pups from thiamine-deficient dams were significantly smaller than normal. Loss of neuronal viability was examined by trypan blue exclusion assay, and demonstrated increased cytotoxicity in primary cultures of TD neurons. Additionally, cerebellar cultures were exposed to thiamine-free cell culture medium to better explore the effects of thiamine withdrawal. Alterations in potassium current has previously been associated with the development of cell death. In this study, we examined the TD effects on delayed rectifier and A-type K+ channels, two well-known voltage-activated K+ channels involved in the regulation of action potential firing in cerebellar granule neurons. Current recordings were performed in cultured rat cerebellar granule neurons at day 7, using the whole-cell voltage-clamp technique. Our data demonstrate that thiamine deficiency provoked a significant decrease in the voltage-dependent K+ membrane conductance. Finally, TD markedly depressed the transient A-type K+ currents.

Blunted hippocampal, but not striatal, acetylcholine efflux parallels learning impairment in diencephalic-lesioned rats

A rodent model of diencephalic amnesia, pyrithiamine-induced thiamine deficiency (PTD), was used to investigate the dynamic role of hippocampal and striatal acetylcholine (ACh) efflux across acquisition of a nonmatching-to-position (NMTP) T-maze task. Changes in ACh efflux were measured in rats at different time points in the acquisition curve of the task (early=day 1, middle=day 5, and late=day 10). Overall, the control group had higher accuracy scores than the PTD group in the latter sessions of NMTP training. During the three microdialysis sampling points, all animals displayed significant increases in ACh efflux in both hippocampus and striatum, while performing the task. However, on day 10, the PTD group showed a significant behavioral impairment that paralleled their blunted hippocampal--but not striatal--ACh efflux during maze training. The results support selective diencephalic-hippocampal dysfunction in the PTD model. This diencephalic-hippocampal interaction appears to be critical for successful episodic and spatial learning/memory.

Dietary restriction protects against chronic-ethanol-induced changes in exploratory behavior in Wistar rats

Chronic ethanol intake causes various types of neural damage and behavioral impairments, probably acting through oxidative stress and excitotoxicity, while dietary restriction is considered by some authors to protect the central nervous system from these kinds of damage. In the present study, a factorial experimental design was used to investigate the effects of chronic ethanol and dietary restriction treatments, associated or not, on Wistar rats' exploratory behavior, spatial memory aspects and cortical and hippocampal acetylcholinesterase (AChE) activity. Dietary restriction lasted for the whole experiment, while ethanol treatment lasted for only 3 weeks. Despite the short ethanol treatment duration, for two behavior categories assessed, moving and rearing, an interaction was observed between the effects of chronic ethanol and dietary restriction. There were no significant differences in AChE activities among the groups. Cerebellar neural nitric oxide synthase (nNOs) activity was measured as a first step to assess oxidative stress. Dietary restriction significantly reduced NO formation. The present results indicate that dietary restriction might exert a protective effect against chronic-ethanol-induced changes in exploratory behavior. It is hypothesized that the mechanisms underlying this protection can involve prevention of oxidative stress.

Cholinergic parameters and the retrieval of learned and re-learned spatial information: a study using a model of Wernicke-Korsakoff Syndrome

This is a factorial (2 x 2 x 2) spatial memory and cholinergic parameters study in which the factors are chronic ethanol, thiamine deficiency and naivety in Morris water maze task. Both learning and retention of the spatial version of the water maze were assessed. To assess retrograde retention of spatial information, half of the rats were pre-trained on the maze before the treatment manipulations of pyrithiamine (PT)-induced thiamine deficiency and post-tested after treatment (pre-trained group). The other half of the animals was only trained after treatment to assess anterograde amnesia (post-trained group). Thiamine deficiency, associated to chronic ethanol treatment, had a significant deleterious effect on spatial memory performance of post-trained animals. The biochemical data revealed that chronic ethanol treatment reduced acetylcholinesterase (AChE) activity in the hippocampus while leaving the neocortex unchanged, whereas thiamine deficiency reduced both cortical and hippocampal AChE activity. Regarding basal and stimulated cortical acetylcholine (ACh) release, both chronic ethanol and thiamine deficiency treatments had significant main effects. Significant correlations were found between both cortical and hippocampal AChE activity and behaviour parameters for pre-trained but not for post-trained animals. Also for ACh release, the correlation found was significant only for pre-trained animals. These biochemical parameters were decreased by thiamine deficiency and chronic ethanol treatment, both in pre-trained and post-trained animals. But the correlation with the behavioural parameters was observed only for pre-trained animals, that is, those that were retrained and assessed for retrograde retention.

Thiamine pyrophosphate biosynthesis and transport in the nematode Caenorhabditis elegans

Thiamine (vitamin B1) is required in the diet of animals, and thiamine deficiency leads to diseases such as beri-beri and the Wernicke-Korsakoff syndrome. Dietary thiamine (vitamin B1) consists mainly of thiamine pyrophosphate (TPP), which is transformed into thiamine by gastrointestinal phosphatases before absorption. It is believed that TPP itself cannot be transported across plasma membranes in significant amounts. We have identified a partial loss-of-function mutation in the Caenorhabditis elegans gene (tpk-1) that encodes thiamine pyrophosphokinase, which forms TPP from thiamine at the expense of ATP inside cells. The mutation slows physiological rhythms and the phenotype it produces can be rescued by TPP but not thiamine supplementation. tpk-1 functions cell nonautonomously, as the expression of wild-type tpk-1 in one tissue can rescue the function of other tissues that express only mutant tpk-1. These observations indicate that, in contrast to expectation from previous evidence, TPP can be transported across cell membranes. We also find that thiamine supplementation partially rescues the phenotype of partial loss-of-function mutants of the Na/K ATPase, providing genetic evidence that thiamine absorption, and/or redistribution from the absorbing cells, requires the full activity of this enzyme.

Prenatal exposure to dichlorvos: physical and behavioral effects on rat offspring

The effects of prenatal exposure to dichlorvos (DDVP), an organophosphate (OP) pesticide, on pups' physical and neurobehavioral developments were investigated. Forty pregnant rats were treated by gavage with 8.0 mg/kg DDVP or its vehicle (1 ml/kg) from the 6th to the 15th day of pregnancy. At birth, pups were weighed, the litters culled to eight animals (four male and four female), and then observed for physical (pinna detachment, incisor eruption, eye opening, testes descent, and vaginal opening) and neurobehavioral developments (palmar grasp, surface righting, negative geotaxis, and open-field behaviors). As adults, open-field, apomorphine-induced stereotypy, and passive avoidance behaviors were also assessed. Results showed no differences between the body weight of DDVP and control-treated groups. No differences were observed on the measures of physical and neurobehavioral development. Locomotor activity of male pups at 21 days of age was decreased by DDVP exposure. Adult experimental offspring showed a decreased locomotor frequency and an increased immobility duration on open-field behavior in relation to control animals; the apomorphine-induced stereotyped behavior was decreased by the pesticide exposure as well as performance on the passive avoidance task. These data suggest that prenatal DDVP exposure was able to decrease offspring motor function (adolescence and adults) and conditioned response learning, probably by interference with the cholinergic-dopaminergic balance of activity involved with the control of motor function as well as the cholinergic system that modulates learning process.

Functional Development of Oligodendrocytes and Open-field Behavior in Developing Rats: An Approach Using Monoclonal Antibody to Immature Oligodendrocytes

To examine the relation between functional development of oligodendrocytes and open-field behavior during the postnatal period, a mouse monoclonal antibody termed 14F7, which predominantly labels stage-specific immature oligodendrocytes, was employed. Antibody 14F7 was administered intraperitoneally into male pups on day 3 and 4 after birth. The open-field test was performed on days 12 and 18 of the postnatal period. Horizontal activity increased remarkably with the growth of pups. On day 18, horizontal activity in the group with 14F7 was significantly higher than the control, while there was no significant difference between treatments on day 12. In contrast to the horizontal activity, the frequency of hind leg rearing, vertical activity, in the group with 14F7 was significantly lower than that in the control. On day 12, choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activities in the cerebral cortex were similar between the groups. These activities increased with the growth of pups in both groups. In the 14F7 group on day 18, ChAT activity was the same as the control, whereas AChE activity was significantly lower compared with the control. These results suggest that neonatal exposure to 14F7 induces abnormal neurotransmission by reducing the degradation of acetylcholine and alters the spontaneous activities in developing rats.

The effects of chronic ethanol consumption on neurotrophins and their receptors in the rat hippocampus and basal forebrain

Damage to the basal forebrain frequently results in deficits in learning and memory. Mnenonic dysfunction also occurs following prolonged ethanol consumption in humans and in animal models of chronic ethanol intake, accompanied by specific abnormalities in synaptic transmission between the basal forebrain and hippocampus. The integrity of at least some of the reciprocal neuronal connections between these brain regions is influenced by target-derived neurotrophic factors. We used a semiquantitative reverse transcription polymerase chain reaction technique to measure the messenger RNA for neurotrophins BDNF and NGF, and for their receptors trkB, trkA, and the low affinity receptor, p75(NTR) in the hippocampus and basal forebrain of rats after 28 weeks of alcohol consumption without malnutrition. This chronic ethanol treatment (CET) resulted in a marked and selective reduction in basal forebrain trkA mRNA. Western blotting revealed a similar reduction of basal forebrain trkA protein. CET effects on basal forebrain trkA may reflect impaired NGF signaling that could compromise septohippocampal synaptic connections, cholinergic differentiation, and emergent functional abilities dependent on these properties.