Age-related vulnerability to diencephalic amnesia produced by thiamine deficiency: the role of time of insult

Adolescent Binge-Type Ethanol Exposure in Rats Mirrors Age-Related Cognitive Decline by Suppressing Cholinergic Tone and Hippocampal Neurogenesis

Heavy alcohol consumption followed by periods of abstinence (i.e., binge drinking) during adolescence is a concern for both acute and chronic health issues. Persistent brain damage after adolescent intermittent ethanol exposure in rodents, a model of binge drinking, includes reduced hippocampal neurogenesis and a loss of neurons in the basal forebrain that express the cholinergic phenotype. The circuit formed between those regions, the septohippocampal pathway, is critical for learning and memory. Furthermore, this circuit is also altered during the aging process. Thus, we examined whether pathology in septohippocampal circuit and impairments in spatial behaviors are amplified during aging following adolescent intermittent ethanol exposure. Female and male rats were exposed to intermittent intragastric gavage of water (control) or 20% ethanol (dose of 5 g/kg) for a 2 days on/off cycle from postnatal days 25-55. Either 2 (young adult) or 12-14 (middle-age) months post exposure, rats were tested on two spatial tasks: spontaneous alternation and novel object in place. Acetylcholine efflux was assessed in the hippocampus during both tasks. There was no adolescent ethanol-induced deficit on spontaneous alternation, but middle-aged male rats displayed lower alternation rates. Male rats exposed to ethanol during adolescence had blunted behavioral evoked acetylcholine during spontaneous alternation testing. All ethanol-exposed rats displayed suppression of the cholinergic neuronal phenotype. On the novel object in place task, regardless of sex, ethanol-exposed rats performed significantly worse than control-treated rats, and middle aged-rats, regardless of sex or ethanol exposure, were significantly impaired relative to young adult rats. These results indicate that male rats display earlier age-related cognitive impairment on a working memory task. Furthermore, male rats exposed to ethanol during adolescence have blunted behavior-evoked hippocampal acetylcholine efflux. In addition, middle-aged and ethanol-exposed rats, regardless of sex, are impaired at determining discrete spatial relationship between objects. This type of pattern separation impairment was associated with a loss of neurogenesis. Thus, binge-type adolescent ethanol exposure does affect the septohippocampal circuit, and can accelerate age-related cognitive impairment on select spatial tasks.

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.

Thiamine Deficiency Modulates p38MAPK and Heme Oxygenase-1 in Mouse Brain: Association with Early Tissue and Behavioral Changes

Thiamine deficiency (TD) produces severe neurodegenerative lesions. Studies have suggested that primary neurodegenerative events are associated with both oxidative stress and inflammation. Very little is known about the downstream effects on intracellular signaling pathways involved in neuronal death. The primary aim of this work was to evaluate the modulation of p38^MAPK and the expression of heme oxygenase 1 (HO-1) in the central nervous system (CNS). Behavioral, metabolic, and morphological parameters were assessed. Mice were separated into six groups: control (Cont), TD with pyrithiamine (Ptd), TD with pyrithiamine and Trolox (Ptd + Tr), TD with pyrithiamine and dimethyl sulfoxide (Ptd + Dmso), Trolox (Tr) and DMSO (Dmso) control groups and treated for 9 days. Control groups received standard feed (AIN-93M), while TD groups received thiamine deficient feed (AIN-93DT). All the groups were subjected to behavioral tests, and CNS samples were collected for cell viability, histopathology and western blot analyses. The Ptd group showed a reduction in weight gain and feed intake, as well as a reduction in locomotor, grooming, and motor coordination activities. Also, Ptd group showed a robust increase in p38^MAPK phosphorylation and mild HO-1 expression in the cerebral cortex and thalamus. The Ptd group showed a decreased cell viability, hemorrhage, spongiosis, and astrocytic swelling in the thalamus. Groups treated with Trolox and DMSO displayed diminished p38^MAPK phosphorylation in both the structures, as well as attenuated thalamic lesions and behavioral activities. These data suggest that p38^MAPK and HO-1 are involved in the TD-induced neurodegeneration in vivo, possibly modulated by oxidative stress and neuroinflammation.

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.

BDNF regains function in hippocampal long-term potentiation deficits caused by diencephalic damage

Thiamine deficiency (TD), commonly associated with chronic alcoholism, leads to diencephalic damage, hippocampal dysfunction, and spatial learning and memory deficits. We show a decrease in the magnitude of long-term potentiation (LTP) and paired-pulse facilitation (PPF) at CA3–CA1 synapses, independent of sex, following diencephalic damage induced by TD in rats. Thus, despite a lack of extensive hippocampal cell loss, diencephalic brain damage down-regulates plastic processes within the hippocampus, likely contributing to impaired hippocampal-dependent behaviors. However, both measures of hippocampal plasticity (LTP, PPF) were restored with brain-derived neurotrophic factor (BDNF), revealing an avenue for neural and behavioral recovery following diencephalic damage.

Thiamine deficiency induces anorexia by inhibiting hypothalamic AMPK

Obesity and eating disorders are prevailing health concerns worldwide. It is important to understand the regulation of food intake and energy metabolism. Thiamine (vitamin B1) is an essential nutrient. Thiamine deficiency (TD) can cause a number of disorders in humans, such as Beriberi and Wernicke-Korsakoff syndrome. We demonstrated here that TD caused anorexia in C57BL/6 mice. After feeding a TD diet for 16days, the mice displayed a significant decrease in food intake and an increase in resting energy expenditure (REE), which resulted in a severe weight loss. At the 22nd day, the food intake was reduced by 69% and 74% for male and female mice, respectively in TD group. The REE increased by ninefolds in TD group. The loss of body weight (17-24%) was similar between male and female animals and mainly resulted from the reduction of fat mass (49% decrease). Re-supplementation of thiamine (benfotiamine) restored animal's appetite, leading to a total recovery of body weight. The hypothalamic adenosine monophosphate-activated protein kinase (AMPK) is a critical regulator of food intake. TD inhibited the phosphorylation of AMPK in the arcuate nucleus (ARN) and paraventricular nucleus (PVN) of the hypothalamus without affecting its expression. TD-induced inhibition of AMPK phosphorylation was reversed once thiamine was re-supplemented. In contrast, TD increased AMPK phosphorylation in the skeletal muscle and upregulated the uncoupling protein (UCP)-1 in brown adipose tissues which was consistent with increased basal energy expenditure. Re-administration of thiamine stabilized AMPK phosphorylation in the skeletal muscle as well as energy expenditure. Taken together, TD may induce anorexia by inhibiting hypothalamic AMPK activity. With a simultaneous increase in energy expenditure, TD caused an overall body weight loss. The results suggest that the status of thiamine levels in the body may affect food intake and body weight.

Thiamine deficiency induced neurochemical, neuroanatomical, and neuropsychological alterations: a reappraisal

Nutritional deficiency can cause, mainly in chronic alcoholic subjects, the Wernicke encephalopathy and its chronic neurological sequela, the Wernicke-Korsakoff syndrome (WKS). Long-term chronic ethanol abuse results in hippocampal and cortical cell loss. Thiamine deficiency also alters principally hippocampal- and frontal cortical-dependent neurochemistry; moreover in WKS patients, important pathological damage to the diencephalon can occur. In fact, the amnesic syndrome typical for WKS is mainly due to the damage in the diencephalic-hippocampal circuitry, including thalamic nuclei and mammillary bodies. The loss of cholinergic cells in the basal forebrain region results in decreased cholinergic input to the hippocampus and the cortex and reduced choline acetyltransferase and acetylcholinesterase activities and function, as well as in acetylcholine receptor downregulation within these brain regions. In this narrative review, we will focus on the neurochemical, neuroanatomical, and neuropsychological studies shedding light on the effects of thiamine deficiency in experimental models and in humans.

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.

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.

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.

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.

Blocking GABA-A receptors in the medial septum enhances hippocampal acetylcholine release and behavior in a rat model of diencephalic amnesia

Wernicke-Korsakoff syndrome (WKS), a form of diencephalic amnesia caused by thiamine deficiency, results in severe anterograde memory loss. Pyrithiamine-induced thiamine deficiency (PTD), an animal model of WKS, produces cholinergic abnormalities including decreased functional hippocampal acetylcholine (ACh) release and poor spatial memory. Increasing hippocampal ACh levels has increased performance in PTD animals. Intraseptal bicuculline (GABA(A) antagonist) augments hippocampal ACh release in normal animals and we found it (0.50 microg/microl and 0.75 microg/microl) also increased in-vivo hippocampal ACh release in PTD animals. However, the 0.75 microg/microl dose produced a greater change in hippocampal ACh release in control animals. The 0.50 microg/microl dose of bicuculline was then selected to determine if it could enhance spontaneous alternation performance in PTD animals. This dose of bicuculline significantly increased hippocampal ACh levels above baseline in both PTD and control rats and resulted in complete behavioral recovery in PTD animals, without altering performance in control rats. This suggests that balancing ACh-GABA interactions in the septohippocampal circuit may be an effective therapeutic approach in certain amnestic syndromes.

The role of cholinergic and GABAergic medial septal/diagonal band cell populations in the emergence of diencephalic amnesia

The septohippocampal pathway, which is mostly composed of cholinergic and GABAergic projections between the medial septum/diagonal band (MS/DB) and the hippocampus, has an established role in learning, memory and disorders of cognition. In Wernicke-Korsakoff's syndrome (WKS) and the animal model of the disorder, pyrithiamine-induced thiamine deficiency (PTD), there is both diencephalic damage and basal forebrain cell loss that could contribute to the amnesic state. In the current experiment, we used the PTD animal model to access both cholinergic (choline acetyltransferase [ChAT] immunopositive) and GABAergic (parvalbumin [PV]; calbindin [CaBP]) neuronal loss in the MS/DB in relationship to midline-thalamic pathology. In addition, to gain an understanding about the role of such neuropathology in behavioral dysfunction, animals were tested on a non-rewarded spontaneous alternation task and behavioral performance was correlated to neuropathology. Unbiased stereological assessment of neuronal populations revealed that ChAT-positive neurons were significantly reduced in PTD rats, relative to control pair-fed rats, and thalamic mass and behavioral performance correlated with ChAT neuronal estimates. In contrast, both the PV- and CaBP-positive neurons in the MS/DB were not affected by PTD treatment. These results support an interactive role of both thalamic pathology and cholinergic cell loss in diencephalic amnesia.

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.

Increasing hippocampal acetylcholine levels enhance behavioral performance in an animal model of diencephalic amnesia

Pyrithiamine-induced thiamine deficiency (PTD) was used to produce a rodent model of Wernicke-Korsakoff syndrome that results in acute neurological disturbances, thalamic lesions, and learning and memory impairments. There is also cholinergic septohippocampal dysfunction in the PTD model. Systemic (Experiment 1) and intrahippocampal (Experiment 2) injections of the acetylcholinesterase inhibitor physostigmine were administered to determine if increasing acetylcholine levels would eliminate the behavioral impairment produced by PTD. Prior to spontaneous alternation testing, rats received injections of either physostigmine (systemic=0.075 mg/kg; intrahippocampal=20, 40 ng/muL) or saline. In Experiment 2, intrahippocampal injections of physostigmine significantly enhanced alternation rates in the PTD-treated rats. In addition, although intrahippocampal infusions of 40 ng of physostigmine increased the available amount of ACh in both pair-fed (PF) and PTD rats, it did so to a greater extent in PF rats. The increase in ACh levels induced by the direct hippocampal application of physostigmine in the PTD model likely increased activation of the extended limbic system, which was dysfunctional, and therefore led to recovery of function on the spontaneous alternation task. In contrast, the lack of behavioral improvement by intrahippocampal physostigmine infusion in the PF rats, despite a greater rise in hippocampal ACh levels, supports the theory that there is an optimal range of cholinergic tone for optimal behavioral and hippocampal function.

Cognitive performance of detoxified alcoholic Korsakoff syndrome patients remains stable over two years

Excessive alcohol consumption is assumed to promote cognitive decline, eventually increasing the risk of dementia. However, little is known about the time course of cognitive functions in patients with chronic alcoholic Korsakoff syndrome (KS). Therefore, we assessed neuropsychological performance in 20 detoxified chronic KS inpatients at time 1 (T1) with a follow-up after two years (T2). The neuropsychological tests assessed verbal and visual short- and long-term memory, working memory, basic executive functions, language, general knowledge, and visual-spatial abilities. Surveys with caregivers and medical records provided information about current and previous disease-related parameters, drinking history, additional pathologies, as well as psychosocial and cognitive therapy within the two-year period. At both sessions, the majority of the KS patients' results were inferior to those of normal subjects. Comparing T1 and T2 revealed no significant decline in any of the investigated functions. Instead, general knowledge, visual long-term memory, and verbal fluency improved slightly after two years, though they still remained within pathological range. Comparing most improved and most deteriorated patients, better outcome occurred more frequently in men than women and was associated with higher premorbid education and fewer detoxifications in the past. In this sample of detoxified KS patients there was no indication of accelerated cognitive decline or onset of dementia-like symptoms over two years.

Impaired, spared, and enhanced ACh efflux across the hippocampus and striatum in diencephalic amnesia is dependent on task demands

Diencephalic amnesia manifests itself through a host of neurological and memory impairments. A commonly employed animal model of diencephalic amnesia, pyrithiamine-induced thiamine deficiency (PTD), results in brain lesions and impairments similar in nature and distribution to those observed in humans with Wernicke-Korsakoff syndrome (WKS). In the current investigation, 2 separate experiments were conducted in which acetylcholine (ACh) efflux was assessed in the hippocampus and striatum of PTD-treated and pair-fed (PF) control male Sprague-Dawley rats. The goal was to determine under what behavioral conditions and in which brain structures ACh efflux was spared, impaired, or adaptively enhanced. In Experiment 1, rats were assessed on a spontaneous alternation task; in Experiment 2, rats were tested on a T-maze discrimination task that could be learned via a hippocampal- or striatal-based strategy. In Experiment 1, PTD-treated rats were impaired on the spontaneous alternation task and ACh efflux in the hippocampus during testing was significantly reduced, but spared in the striatum. In Experiment 2, PTD- and PF-treated rats did not differ in the number of trials to criterion, but PTD-treated rats demonstrated greater reliance upon egocentric cues to solve the task. Furthermore, ACh efflux in the striatum was greater during maze learning in the PTD-treated animals when compared to the PF animals. These results suggest that there is behavioral and systems level plasticity that can facilitate the use of alternative strategies to solve a task following diencephalic damage and WKS.

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.

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.

Thiamine pyrophosphate riboswitches are targets for the antimicrobial compound pyrithiamine

Thiamine metabolism genes are regulated in numerous bacteria by a riboswitch class that binds the coenzyme thiamine pyrophosphate (TPP). We demonstrate that the antimicrobial action of the thiamine analog pyrithiamine (PT) is mediated by interaction with TPP riboswitches in bacteria and fungi. For example, pyrithiamine pyrophosphate (PTPP) binds the TPP riboswitch controlling the tenA operon in Bacillus subtilis. Expression of a TPP riboswitch-regulated reporter gene is reduced in transgenic B. subtilis or Escherichia coli when grown in the presence of thiamine or PT, while mutant riboswitches in these organisms are unresponsive to these ligands. Bacteria selected for PT resistance bear specific mutations that disrupt ligand binding to TPP riboswitches and derepress certain TPP metabolic genes. Our findings demonstrate that riboswitches can serve as antimicrobial drug targets and expand our understanding of thiamine metabolism in bacteria.

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.