The effect of thiamine deficiency on the structure and physiology of the rat forebrain

Stem Cell Therapy and Thiamine Deficiency-Induced Brain Damage

Wernicke's encephalopathy (WE) is a major central nervous system disorder resulting from thiamine deficiency (TD) in which a number of brain regions can develop serious damage including the thalamus and inferior colliculus. Despite decades of research into the pathophysiology of TD and potential therapeutic interventions, little progress has been made regarding effective treatment following the development of brain lesions and its associated cognitive issues. Recent developments in our understanding of stem cells suggest they are capable of repairing damage and improving function in different maladys. This article puts forward the case for the potential use of stem cell treatment as a therapeutic strategy in WE by first examining the effects of TD on brain functional integrity and its consequences. The second half of the paper will address the future benefits of treating TD with these cells by focusing on their nature and their potential to effectively treat neurodegenerative diseases that share some overlapping pathophysiological features with TD. At the same time, some of the obstacles these cells will have to overcome in order to become a viable therapeutic strategy for treating this potentially life-threatening illness in humans will be highlighted.

Midline Thalamic Damage Associated with Alcohol-Use Disorders: Disruption of Distinct Thalamocortical Pathways and Function

The thalamus, a significant part of the diencephalon, is a symmetrical and bilateral central brain structure. The thalamus is subdivided into three major groups of nuclei based on their function: sensorimotor nuclei (or principal/relay nuclei), limbic nuclei and nuclei bridging these two domains. Anatomically, nuclei within the thalamus are described by their location, such as anterior, medial, lateral, ventral, and posterior. In this review, we summarize the role of medial and midline thalamus in cognition, ranging from learning and memory to flexible adaptation. We focus on the discoveries in animal models of alcohol-related brain damage, which identify the loss of neurons in the medial and midline thalamus as drivers of cognitive dysfunction associated with alcohol use disorders. Models of developmental ethanol exposure and models of adult alcohol-related brain damage and are compared and contrasted, and it was revealed that there are similar (anterior thalamus) and different (intralaminar [adult exposure] versus ventral midline [developmental exposure]) thalamic pathology, as well as disruptions of thalamo-hippocampal and thalamo-cortical circuits. The final part of the review summarizes approaches to recover alcohol-related brain damage and cognitive and behavioral outcomes. These approaches include pharmacological, nutritional and behavioral interventions that demonstrated the potential to mitigate alcohol-related damage. In summary, the medial/midline thalamus is a significant contributor to cognition function, which is also sensitive to alcohol-related brain damage across the life span, and plays a role in alcohol-related cognitive dysfunction.

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.

Role of astrocytes in thiamine deficiency

Thiamine deficiency (TD) is the underlying cause of Wernicke's encephalopathy (WE), an acute neurological disorder characterized by structural damage to key periventricular structures in the brain. Increasing evidence suggests these focal histological lesions may be representative of a gliopathy in which astrocyte-related changes are a major feature of the disorder. These changes include a loss of the glutamate transporters GLT-1 and GLAST concomitant with elevated interstitial glutamate levels, lowered brain pH associated with increased lactate production, decreased levels of GFAP, reduction in the levels of glutamine synthetase, swelling, alterations in levels of aquaporin-4, and disruption of the blood-brain barrier. This review focusses on how these manifestations contribute to the pathophysiology of TD and possibly WE.

Thiamine deficiency: an update of pathophysiologic mechanisms and future therapeutic considerations

Thiamine is an essential vitamin that is necessary to maintain the functional integrity of cells in the brain. Its deficiency is the underlying cause of Wernicke's encephalopathy (WE), a disorder primarily associated with, but not limited to, chronic alcoholism. Thiamine deficiency leads to the development of impaired energy metabolism due to mitochondrial dysfunction in focal regions of the brain resulting in cerebral vulnerability. The consequences of this include oxidative stress, excitotoxicity, inflammatory responses, decreased neurogenesis, blood-brain barrier disruption, lactic acidosis and a reduction in astrocyte functional integrity involving a loss of glutamate transporters and other astrocyte-specific proteins which together contribute in a major way to the resulting neurodegeneration. Exactly how these factors acting in concert lead to the demise of neurons is unclear. In this review we reassess their relative importance in the light of more recent findings and discuss therapeutic possibilities that may provide hope for the future for individuals with WE.

The impact of oxidative stress in thiamine deficiency: a multifactorial targeting issue

Thiamine (vitamin B1) deficiency, the underlying cause of Wernicke-Korsakoff syndrome, is associated with the development of focal neuronal loss in vulnerable areas of the brain. Although the actual mechanism(s) that lead to the selective histological lesions characteristic of this disorder remain unresolved, oxidative stress has been shown to play a major role in its pathophysiology. In this review, the multifactorial influence of oxidative stress on a variety of processes known to take part in the development of structural lesions in TD including excitotoxicity, neuroinflammation, blood-brain barrier integrity, mitochondrial integrity, apoptosis, nucleic acid function, and neural stem cells will be discussed, and therapeutic strategies undertaken for treating neurodegeneration examined which may have an impact on the future treatment of this important vitamin deficiency.

Pathophysiologic mechanisms responsible for the reversible (thiamine-responsive) and irreversible (thiamine non-responsive) neurological symptoms of Wernicke's encephalopathy

Chronic alcoholism results in thiamine deficiency as a result of poor nutrition and impaired gastrointestinal absorption of the vitamin. Pyrithiamine-induced thiamine deficiency in the rat reproduces a neurological syndrome and ultimately neuropathological damage of a nature and distribution that is similar to that encountered in Wernicke's encephalopathy in humans. Pyrithiamine-induced thiamine deficiency results in selective reversible decreases in activity of the thiamine-dependent enzyme alpha-ketoglutarate dehydrogenase and concomitant reversible changes in brain amino acids. It is proposed that these changes constitute "the biochemical lesion" in thiamine deficiency encephalopathy. If sufficiently severe and prolonged, decreased activities of alpha-ketoglutarate dehydrogenase may result in compromised brain energy metabolism and in lactate accumulation in brain, both of which could be responsible for neuronal cell death in this condition. In addition, it has been suggested that cell death results from NMDA-receptor mediated excitotoxic damage. Similar pathophysiologic mechanisms could be responsible for brain cell death in Wernicke's encephalopathy 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.

Prenatal exposure to ethanol affects postnatal neurogenesis in thalamus

The number of neurons in the ventrobasal thalamus (VB) in the adolescent rat is unaffected by prenatal exposure to ethanol. This is in sharp contrast to other parts of the trigeminal-somatosensory system, which exhibit 30-35% fewer neurons after prenatal ethanol exposure. The present study tested the hypothesis that prenatal ethanol exposure affects dynamic changes in the numbers of VB neurons; such changes reflect the sum of cell proliferation and death. Neuronal number in the VB was determined during the first postnatal month in the offspring of pregnant Long-Evans rats fed an ethanol-containing diet or pair-fed an isocaloric non-alcoholic liquid diet. Offspring were examined between postnatal day (P) 1 and P30. The size of the VB and neuronal number were determined stereologically. Prenatal exposure to ethanol did not significantly alter neuronal number on any individual day, nor was the prenatal generation of VB neurons affected. Interestingly, prenatal ethanol exposure did affect the pattern of the change in neuronal number over time; total neuronal number was stable in the ethanol-treated pups after P12, but it continued to rise in the controls until P21. In addition, the rate of cell proliferation during the postnatal period was greater in ethanol-treated animals. Thus, the rate of neuronal acquisition is altered by ethanol, and by deduction, there appears to be less ethanol-induced neuronal loss in the VB. A contributor to these changes is a latent effect of ethanol on postnatal neurogenesis in the VB and the apparent survival of new neurons.

Loss of astrocytic glutamate transporters in Wernicke encephalopathy

Wernicke encephalopathy (WE), a neurological disorder caused by thiamine deficiency (TD), is characterized by structural damage in brain regions that include the thalamus and cerebral cortex. The basis for these lesions is unclear, but may involve a disturbance of glutamatergic neurotransmission. We have therefore investigated levels of the astrocytic glutamate transporters EAAT1 and EAAT2 in order to evaluate their role in the pathophysiology of this disorder. Histological assessment of the frontal cortex revealed a significant loss of neurons in neuropathologically confirmed cases of WE compared with age-matched controls, concomitant with decreases in alpha-internexin and synaptophysin protein content of 67 and 52% by immunoblotting. EAAT2 levels were diminished by 71% in WE, with levels of EAAT1 also reduced by 62%. Loss of both transporter sites was confirmed by immunohistochemical methods. Development of TD in rats caused a profound loss of EAAT1 and EAAT2 in the thalamus accompanied by decreases in other astrocyte-specific proteins. Treatment of TD rats with N-acetylcysteine prevented the downregulation of EAAT2 in the medial thalamus, and ameliorated the loss of several other astrocyte proteins, concomitant with increased neuronal survival. Our results suggest that (1) loss of EAAT1 and EAAT2 glutamate transporters is associated with structural damage to the frontal cortex in patients with WE, (2) oxidative stress plays an important role in this process, and (3) TD has a profound effect on the functional integrity of astrocytes. Based on these findings, we recommend that early treatment using a combination of thiamine AND antioxidant approaches should be an important consideration in cases of WE.

Astrocytes are a major target in thiamine deficiency and Wernicke's encephalopathy

Thiamine deficiency (TD) is the underlying cause, and an established model, of Wernicke's encephalopathy (WE). Although the neurologic dysfunction and brain damage that results from TD has been well-described, the precise mechanisms that lead to the selective histological lesions characteristic of this disorder remain a mystery. Over the course of many years, various processes have been proposed that could lead to focal neuronal cell death in this disorder. But despite a concerted effort to relate these processes to a clear sequelae of events culminating in development of the focal neuropathology, little success has resulted. In recent years, however, a role for astrocytes in the pathophysiology of TD has been emerging. Here, alterations in glutamate uptake, and levels of the astrocytic glutamate transporters EAAT1 and EAAT2 in TD and WE, are discussed in terms of an excitotoxic event, along with the GABA transporter subtype GAT-3, and changes in other astrocytic proteins including GFAP and glutamine synthetase. Lactic acidosis, changes in the water channel protein AQP-4 and brain edema are also a focus of attention in relation to astrocyte dysfunction, while involvement of oxidative stress and inflammatory processes, along with white matter injury in terms of excitotoxicity are other key issues considered. In summary, a new appraisal of the extent of involvement of astrocytes in TD and WE is presented, with the evidence suggesting these cells represent a major target for damage during the disease process.

Enhanced head-twitch response to 5-HT-related agonists in thiamine-deficient mice

While many studies suggest an involvement of brain serotonergic systems in neuro-psychiatric disorders such as schizophrenia and depression, their role in Wernicke-Korsakoff syndrome (WKS) remains unclear. Since dietary thiamine deficiency (TD) in mice is considered as a putative model of WKS, it was used in the present study to investigate the function of serotonergic neurons in this disorder. After 20 days of TD feeding, the intensity of tryptophan hydroxylase immunofluorescence was found to be significantly decreased in the dorsal and medial raphe nuclei. In addition, the head-twitch response (HTR) elicited by the intracerebroventricular administration of the 5-HT(2A) agonist 2,5-dimethoxy-4-iodoamphetamine hydrochloride (DOI) was significantly increased in TD versus control mice, whereas the injection of ketanserin, a 5-HT(2A) receptor antagonist, prevented this enhancement. A single injection of thiamine HCl on the 19th day of TD feeding did not reduce the enhanced DOI-induced HTR. On the other hand, the administration of d-fenfluramine, a 5-HT releaser, did not enhance the HTR in TD mice. Together, our results indicate that TD causes a super-sensitivity of 5-HT(2A) receptors by reducing presynaptic 5-HT synthesis derived from degenerating neurons projecting from the raphe nucleus.

Hyperemesis gravidarum complicated by Wernicke encephalopathy: background, case report, and review of the literature

Wernicke encephalopathy (WE) is a rare but known complication of severe hyperemesis gravidarum caused by thiamine deficiency. This article presents an unusual case that occurred at our institution and reviews the 48 previously published cases of WE in pregnancy. Considering all the 49 cases, the mean (+/-standard deviation) patients' age was 26.7 +/- 4.9 years, the mean gestational age when WE manifested was 14.3 +/- 3.4 weeks, and the mean duration of vomiting and feeding difficulties was 7.7 +/- 2.8 weeks. Wernicke's classic triad (confusion, ocular abnormalities, and ataxia) manifested in only 46.9% (23 of 49) of the patients. Confusion affected 63.3% (31 of 49) of the patients, ocular signs 95.9% (47 of 49) and symptoms 57.1% (28 of 49), and ataxia 81.6% (40 of 49). Deterioration of consciousness affected 53.1% (26 of 49) of the subjects and memory impairment 61.2% (30 of 49). Complete remission of the disease occurred in only 14 of 49 cases. Symptom resolution required months and permanent impairments were common. The overall pregnancy loss rate, directly (spontaneous fetal loss) and indirectly (planned abortion) attributable to WE, was 47.9% (23 of 49). The diagnosis of WE is clinical and can be rapidly confirmed by magnetic resonance imaging. We emphasize the importance of thiamine supplementation to women with prolonged vomiting in pregnancy, especially before intravenous or parenteral nutrition. We also underline the necessity to promptly replace vitamin B1 when neurologic symptoms and/or signs develop in a patient with hyperemesis gravidarum.

Diffusion-weighted MR findings in a reversible case of acute Wernicke encephalopathy

We report a case of acute Wernicke encephalopathy (WE) in which apparent diffusion coefficient maps showed areas of increased diffusion in the bilateral medial thalami that corresponded to the hyperintense lesions on T2-weighted imaging. The hyperintense lesions on T2-weighted imaging disappeared with full recovery from symptoms. These findings suggest that the hyperintense lesions of the acute changes of WE include reversible vasogenic edema and are not caused by acute ischemia.

Glucose induced IEG expression in the thiamin-deficient rat brain

Glucose loading of rats made thiamin deficient by dietary deprivation of thiamin and the administration of pyrithiamin (40 microg/100 g, i.p.) precipitates an acute neuropathy, a model of Wernicke's encephalopathy in man (Zimitat and Nixon, Metab. Brain Dis. 1999;14:1-20). Immunohistochemical detection of Fos proteins was used as a marker to identify neuronal populations in the thiamin-deficient rat brain affected by glucose loading. As thiamin deficiency progressed, the extent and intensity of Fos-like immunoreactivity (FLI) in brain structures typically affected by thiamin deficiency (the thalamus, mammillary bodies, inferior colliculus, vestibular nucleus and inferior olives) were markedly increased when compared to thiamin-replete controls. Glucose loading for 1-3 days further increased the intensity of FLI in these same regions, consistent with a dependence of Fos expression on carbohydrate metabolism as well as on thiamin deficiency. The timed acute changes that follow a bolus glucose load administered to thiamin-deficient animals may provide a sequential account of events in the pathogenesis of brain damage in this model of Wernicke's encephalopathy.

In vivo microdialysis in an animal model of neurological disease: thiamine deficiency (Wernicke) encephalopathy

In vivo microdialysis allows for the constant monitoring of brain neurotransmitters in the extracellular fluid of awake and freely moving animals. Considerations including factors affecting probe recoveries, the blood-brain barrier, and tissue reactions to probe implantation are discussed in this paper. Details of the application of in vivo microdialysis to an animal model of encephalopathy are then presented. Thiamine deficiency encephalopathy is an animal model of Wernicke encephalopathy, a neurological disorder observed in alcoholics and in patients with severely compromised nutrition. Regionally selective neuronal cell death is observed in both patients and animals with thiamine deficiency (TD). Various thalamic nuclei suffer significant TD-induced cell death, and NMDA receptor-mediated glutamate excitotoxicity has been proposed as an underlying causative factor. A detailed methodology for the examination of the role of glutamate excitotoxicity using in vivo microdialysis in the neuronal cell death due to thiamine deficiency is presented.

JNK1 is inactivated during thiamine deficiency-induced apoptosis in human neuroblastoma cells

Thiamine deficiency results in selective neuronal damage. A number of mechanisms have been proposed to account for brain damage associated with thiamine deficiency and to account for the focal nature of the loss of neurons. One proposed mechanism is programmed cell death. We found efficient induction of apoptosis in human neuroblastoma cells when the cells were deprived of thiamine. Although extensive mitochondrial damage was seen, the release of cytochrome c was not the triggering mechanism for thiamine deficiency-induced apoptosis. Instead, the activity of the cJun amino terminal kinase Jnk1 was lost, and this loss correlated temporally with induction of apoptosis. The loss was specific for Jnk1; Jnk2/3 activity remained unchanged. Loss of Jnk1 activity was not found in lymphoblasts, a cell type that did not undergo apoptosis when deprived of thiamine. These findings suggest that thiamine deficiency results in a cellular stress that brings about the loss of Jnk1 activity and the loss of its function of protecting cells from programmed cell death. We postulate that focal sensitivity to thiamine deficiency results, in part, from specific neuronal cell types being susceptible to the inactivation of Jnk1 in response to depletion of cellular thiamine.

Increased histamine release and granulocytes within the thalamus of a rat model of Wernicke's encephalopathy

The current study examined the possible role of increased histamine release and granulocyte activity in the vascular changes that precede the onset of necrotic lesions with the thalamus of the pyrithiamine-induced thiamine deficiency (PTD) rat model of Wernicke's encephalopathy (WE). An increase in histamine release and the number of granulocytes was observed in lateral thalamus on day 9 and in medial thalamus on day 10 of PTD treatment, a duration of thiamine deficiency associated with perivascular edema in this brain region. Within the hippocampus, histamine release was significantly increased on day 9, declined to control levels on days 10-12, and was significantly elevated on days 12-14. No granulocytes were observed in hippocampus of either PTD or control rats. These observations suggest that the release of histamine from nerve terminals and histamine and other vasoactive substances from granulocytes may be responsible for thiamine deficiency-induced vascular breakdown and perivascular edema within thalamus.

Immunohistochemical estimation of rat brain somatostatin on avoidance learning impairment induced by thiamine deficiency

In rats, on the 25th day after the start of a thiamine-deficient (TD) diet, impairment of avoidance learning was significantly induced in proportion to the decrease somatostatin (SST) fluorescence intensity in the cortex, amygdala, thalamus, hypothalamus, and hippocampus, including the CA1, CA2, and dentate gyrus (DG). Only a single injection of thiamine HCl (0.5 mg/rat, subcutaneous) on the 14th day after the start of a TD diet improved the amnesia to the level of the pair-fed control and prevented the decrease in the SST level. Whereas these reversal effects of thiamine treatment were not found when the treatment was given on the 21st day after the start of a TD diet. These results indicate that, after a certain degree of thiamine deficiency, TD-induced behavioral effects might be reversible, but some neuronal fibers might be irreversibly damaged, probably due to the reduction of thiamine-dependent enzymes in brain mitochondria. The results also suggest the possibility that SST in the brain may be closely related to the avoidance learning impairment induced by TD.

Mechanisms of neuronal cell death in Wernicke's encephalopathy

Wernicke's Encephalopathy (WE) is a serious neurological disorder resulting from thiamine deficiency, encountered in chronic alcoholics and in patients with grossly impaired nutritional status. Neuropathologic studies as well as Magnetic Resonance Imaging reveal selective diencephalic and brainstem lesions in patients with WE. The last decade has witnessed major advances in the understanding of pathophysiologic mechanisms linking thiamine deficiency to the selective brain lesions characteristic of WE. Activities of the thiamine-dependent enzyme alpha-ketoglutarate dehydrogenase, a rate-limiting tricarboxylic acid cycle enzyme are significantly reduced in autopsied brain tissue from patients with WE and from rats treated with the central thiamine antagonist, pyrithiamine. In the animal studies, evidence suggests that such enzyme deficits result in focal lactic acidosis, cerebral energy impairment and depolarization resulting from increased release of glutamate in vulnerable brain structures. It has been proposed that this depolarization may result in N-Methyl-D-Aspartate receptor-mediated excitotoxicity as well as increased expression of immediate early genes such as c-fos and c-jun resulting in apoptotic cell death. Other mechanisms involved in thiamine deficiency-induced cell loss may involve free radicals and alterations of the blood-brain barrier. Additional studies are still required to identify the site of the initial cellular insult and to explain the predilection of diencephalic and brainstem structures due to thiamine deficiency.

Evaluation of the role of NMDA-mediated excitotoxicity in the selective neuronal loss in experimental Wernicke encephalopathy

The goal of the studies described was to evaluate the role of NMDA receptor-mediated glutamate excitotoxicity in the pathogenesis of selective neuronal loss due to thiamine deficiency. Administration of the central thiamine antagonist pyrithiamine to adult male rats resulted in a sequence of neurological symptoms including ataxia and loss of righting reflex followed by convulsions. Prior to the onset of convulsions, neuropathologic evaluation revealed significant neuronal loss in the ventral posterior medial thalamic nucleus. However, in vivo cerebral microdialysis at preconvulsive stages did not demonstrate significant increases of extracellular glutamate in this region and pretreatment with the NMDA receptor antagonist MK801 (1 mg/ kg/12 h, i.p.) did not afford significant neuroprotection. Following the onset of convulsions, microdialysate glutamate concentrations were increased fivefold (P > 0.05) and MK801 treatment resulted in significant attenuation of neuronal loss in some thalamic nuclei. A comparable degree of neuroprotection was afforded by pretreatment with an anticonvulsant dose of diazepam (10 mg/kg/12 h, i.p.) a compound whose action is not NMDA receptor mediated. These findings suggest that NMDA receptor-mediated excitotoxicity is not responsible for early selective neuronal loss in this model of thiamine deficiency encephalopathy and that the neuroprotective effect of MK801 at later stages are at least in part a consequence of its anticonvulsant properties.

Causality of parenchymal and vascular changes in rats with experimental thiamine deficiency encephalopathy

The causality of vascular and parenchymal damage to the central nervous system (CNS) was examined in rats with thiamine deficiency. Male Sprague-Dawley rats were divided into two groups; one was given a thiamine-deficient diet (TDD) and injected intraperitoneally with 10 micrograms/100 g bodyweight pyrithiamine (PT) in order to analyze morphometrically the topographical and sequential relationship between vascular and parenchymal changes and vasodilatation, and the other was given a TDD and 50 micrograms/100 g bodyweight PT in order to determine hemorrhagic sites using serial sections. Histological examination showed that spongiotic change occurred selectively in the inferior colliculus (100%) from day 19, and thereafter in the thalamus (95%), mammillary body (50%) and nuclei olivaris and vestibularis of the pons (25%), with or without hemorrhage. Simultaneously, glycogen accumulation was also observed in these regions at a frequency similar to that of hemorrhage. Ultrastructurally, however, hydropic swelling of astrocytic and neuronal processes without glycogen accumulation was observed as early as day 9 in the inferior colliculus, at which time an increase of glial fibrillary acidic protein-positive processes was also recognized. The superior colliculus was completely spared. From day 22 vasodilatation of the inferior colliculus occurred, concomitantly with bodyweight loss and neurological symptoms. Twenty-two examined hemorrhages, which occurred in the thalamus and inferior colliculus, were distributed along the arterioles or capillaries on the arterial side. In conclusion, the morphological CNS changes caused by thiamine deficiency with administration of low-dose PT in rats begin as hydropic swelling of neuronal and astrocytic processes, followed by hemorrhage and, thereafter, by vasodilation. The predilection for hemorrhage on the arterial side without parenchymal changes suggests that petechial hemorrhage is not simply secondary to parenchymal changes, but is due to hemodynamic change resulting from thiamine deficiency-induced vascular dysfunction.

Neuropathology of thiamine deficiency: an update on the comparative analysis of human disorders and experimental models

This paper provides a re-examination of the neuroanatomical consequences of thiamine deficiency in light of more recent studies of human disorders and models of experimental thiamine deficiency. A major goal is to elucidate the relative roles of thiamine deficiency and chronic alcohol consumption in the pathogenesis of Wernicke-Korsakoff syndrome (WKS). Particular emphasis is placed on the role of thiamine deficiency in lesions to basal forebrain, raphe, locus coeruleus, white matter and cortex and their role in the cognitive and memory disturbances of human WKS and experimental models of thiamine deficiency.

Immunohistochemical determination of rat spinal cord substance P, and antinociceptive effect during development of thiamine deficiency

During 30 days of thiamine deficiency (TD) feeding, the rat antinociceptive effect (pain threshold) to noxious heat stimulation was significantly increased in proportion to the decrease substance P (SP) fluorescent intensity in the spinal cord. Only a single injection of thiamine HCl (0.5 mg/kg, s.c.) on the early treatment day during TD feeding effectively reversed the analgesic effect to the pair-fed control level. Whereas this reversal effect by thiamine treatment was not found if this treatment was done on the relatively late day. However, either treatment day, except muricide, complete disappearance of various animal behaviours induced by TD was found. These results indicate that, after certain degree of TD development, TD-induced behavioral effects might be reversible, but the afferent nerve fibers might be irreversibly damaged, probably by the similar mechanism as found for an excitotoxin(s) mediated injury in the certain brain region(s). The results also suggest a possibility that SP and an excitotoxin, glutamate, in the dorsal part of the spinal cord greatly contribute to the pain transmission induced by noxious heat stimulation.

A quantitative autoradiographic study of muscarinic cholinergic receptor subtypes in the brains of pyrithiamine-treated rats

Previous studies describe decreased acetylcholine synthesis in brain as well as neurobehavioral evidence for a central muscarinic cholinergic deficit in pyrithiamine-induced thiamine-deficient rats. In order to further evaluate this possibility, quantitative autoradiographic procedures using [3H]quinuclidinyl benzilate (for total muscarinic binding sites), [3H]pirenzepine (for muscarinic M1 sites) and [3H]AF-DX 384 (for muscarinic M2 sites) were performed at early (presymptomatic) and late (symptomatic) stages of thiamine deficiency induced in rats by administration of the central thiamine antagonist, pyrithiamine. No significant alterations in densities of M1, M2 or total muscarinic binding sites were observed in any brain structure evaluated at either early or late stages of thiamine deficiency. These findings do not support a major role for modifications of muscarinic cholinergic function in the pathogenesis of the neurological symptoms of thiamine deficiency.

Accumulation of amyloid precursor protein-like immunoreactivity in rat brain in response to thiamine deficiency

Thiamine deficiency (TD) is a classical model of impaired cerebral oxidation. As in Alzheimer's disease (AD), TD is characterized by selective neuronal loss, decreased activities of thiamine pyrophosphate-dependent enzymes, cholinergic deficits and memory loss. Amyloid beta-protein (A beta), a approximately 4 kDa fragment of the beta-amyloid precursor protein (APP), accumulates in the brains of patients with AD or Down's syndrome. In the current study, we examined APP and A beta immunoreactivity in the brains of thiamine-deficient rats. Animals received thiamine-deficient diet ad libitum and daily injections of the thiamine antagonist, pyrithiamine. Immunocytochemical staining and immunoblotting utilized a rabbit polyclonal antiserum against human APP645-694 (numbering according to APP695 isoform). Three, 6 and 9 days of TD did not appear to damage any brain region nor change APP-like immunoreactivity. However, 13 days of TD led to pathological lesions mainly in the thalamus, mammillary body, inferior colliculus and some periventricular areas. While immunocytochemistry and thioflavine S histochemistry failed to show fibrillar beta-amyloid, APP-like immunoreactivity accumulated in aggregates of swollen, abnormal neurites and perikarya along the periphery of the infarct-like lesion in the thalamus and medial geniculate nucleus. Immunoblotting of the thalamic region around the lesion revealed increased APP-like holoprotein immunoreactivity. APP-like immunoreactive neurites were scattered in the mammillary body and medial vestibular nuclei where the lesion did not resemble infarcts. In the inferior colliculus, increased perikaryal APP-like immunostaining occurred in neurons surrounding necrotic areas. Regions without apparent pathological lesions showed no alteration in APP-like immunoreactivity. Thus, the oxidative insult associated with cell loss, hemorrhage and infarct-like lesions during TD leads to altered APP metabolism. This is the first report to show a relationship between changes in APP expression, oxidative metabolism and selective cell damage caused by nutritional/cofactor deficiency. This model appears useful in defining the role of APP in the reponse to central nervous system injury, and may also be relevant to the pathophysiology of Wernicke-Korsakoff syndrome and AD.

Pathogenesis of diencephalic lesions in an experimental model of Wernicke's encephalopathy

The relationship of thiamine deficiency to Wernicke's encephalopathy has been well established. The biochemical bases and physiologic mechanisms responsible for the pathologic changes and their selective distribution within the brain remain controversial. The present paper reviews recent biochemical, histopathological and pharmacological evidence of a glutamate-mediated excitotoxic mechanism of neuronal loss in pyrithiamine-induced thiamine deficiency (PTD), a rat model of Wernicke's encephalopathy. A mechanistic model involving the unique combination of thiamine deficiency-induced impairment of energy metabolism, increased release of histamine, and multidirectional glutamate inputs is presented to explain the selective vulnerability of thalamic nuclei to excitotoxic lesions in the PTD model.

Increased densities of binding sites for the "peripheral-type" benzodiazepine receptor ligand [3H]PK11195 in vulnerable regions of the rat brain in thiamine deficiency encephalopathy

Quantitative receptor autoradiography was used to evaluate the density of high-affinity binding sites for the "peripheral-type" benzodiazepine receptor (PTBR) ligand [3H]PK11195 in brain regions of the rat at different stages of pyrithiamine-induced thiamine deficiency encephalopathy, an experimental model of the Wernicke-Korsakoff syndrome (WKS). Assessment of the density of [3H]PK11195 binding sites in thiamine-deficient animals showing no neurologic signs of thiamine deficiency encephalopathy, and revealed no significant alterations compared with pair-fed control animals in any brain region studied. Densities of [3H]PK11195 binding sites were, however, significantly increased in brain regions of the rat at the symptomatic stage, where increased densities were seen in the inferior colliculus (233% increase, p < 0.001), inferior olivary nucleus (154% increase, p < 0.001) and thalamus (up to 107% increase, p < 0.001). Histologic studies of these same brain regions revealed evidence of neuronal cell loss and concomitant gliosis. Densities of [3H]PK11195 binding sites in nonvulnerable brain regions that showed no histologic evidence of neuronal loss, such as the cerebral cortex, hippocampus, and caudate-putamen, were not significantly different from those in control animals. Increased densities of binding sites for the PTBR ligand probably reflect glial proliferation and are consistent with an excitotoxic mechanism in the pathogenesis of neuronal cell loss in thiamine deficiency encephalopathy. Positron emission tomography (PET) using [11C]PK11195 could offer a potentially useful diagnostic tool in WKS in humans.

Extracellular glutamate is increased in thalamus during thiamine deficiency-induced lesions and is blocked by MK-801

The current study measured extracellular fluid (ECF) levels of excitatory amino acids before and during the onset of thiamine deficiency-induced pathologic lesions. Male Sprague-Dawley rats were treated with daily pyrithiamine (0.25 mg/kg i.p.) and a thiamine-deficient diet (PTD). Microdialysates were simultaneously collected from probes inserted acutely via guide cannulae into right paracentral and ventrolateral nuclei of thalamus and left hippocampus of PTD and pair-fed controls. Hourly samples were collected from unanesthetized and freely moving animals. Basal levels obtained at a prelesion stage (day 12 of PTD treatment) were unchanged from levels in pair-fed controls. In samples collected 4-5 h after onset of seizures (day 14 of PTD), the levels of glutamate were elevated an average 640% of basal levels in medial thalamus and 200% in hippocampus. Glutamine levels declined, taurine and glycine were elevated, and aspartate, GABA, and alanine were unchanged during this period. Within 7 h after seizure onset glutamine was undetectable in both areas, whereas glutamate had declined to approximately 200% in thalamus and 70% in hippocampus. No significant change in glutamate, aspartate, or other amino acids was observed in dialysates collected from probes located in undamaged dorsal-lateral regions of thalamus. Number of neurons within ventrolateral nucleus of thalamus was significantly greater in PTD animals in which the probe was dialyzed compared with nondialyzed, suggesting that removal of excitatory amino acids was protective. No significant pathologic damage was evident in hippocampus.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral vulnerability is associated with selective increase in extracellular glutamate concentration in experimental thiamine deficiency

Microdialysis in the awake, freely moving rat was used to determine the effect of pyrithiamine-induced thiamine deficiency on the levels of amino acids in the brain. Studies were carried out on (a) presymptomatic animals immediately before the development of behavioral changes and (b) acute symptomatic animals within 6 h following loss of righting reflexes. This latter stage precedes the appearance of histological lesions. The results were compared with pair-fed controls. Dialysis probes were implanted in one vulnerable structure [ventral posterior medial thalamus (VPMT)] and one nonvulnerable area [frontal parietal cortex (FPC)] on the contralateral side. In VPMT of acute symptomatic animals, the glutamate concentration was significantly increased (3.37 +/- 0.64 microM; p < 0.005) compared with control values (0.93 +/- 0.09 microM), whereas in FPC no change in glutamate content was evident. These results suggest that glutamate plays a significant role in the development of central thiamine deficiency lesions. The absence of any increase in glutamate levels in the nonvulnerable FPC suggests that a glutamate-mediated excitotoxic mechanism may be responsible for the selective cerebral vulnerability in thiamine deficiency.

Excitotoxicity and alcohol-related brain damage

Hyperexcitability following chronic alcohol exposure appears to result in enhanced activation of glutamatergic synapses in the brain. This enhanced glutamatergic transmission probably results from a combination of increased NMDA receptor activation, decreased GABAA receptor activation and increased function of voltage-activated calcium channels. Prolonged or repetitive bouts of enhanced excitatory transmission during withdrawal may destroy central neurons via "excitotoxic" mechanisms. Increased NMDA receptor activation might initiate toxicity by increasing intracellular calcium. Summation of these effects with increased intracellular calcium from voltage-activated channels might promote disinhibition and enhance cellular damage. Recent studies suggest that NMDA receptor-initiated excitotoxicity may result from thiamine deficiency. Alterations in neurotransmitter levels and receptor function during alcohol-related thiamine deficiency may contribute to this neuropathology. Thus, excitotoxic damage due to neural compensation for sustained alcohol levels and nutritional deficits may underlie aspects of alcohol-related brain damage.

Diencephalic lesions, learning impairments, and intact retrograde memory following acute thiamine deficiency in the rat

Previous studies have shown that following an acute bout of pyrithiamine-induced thiamine deficiency (PTD) rats are impaired in learning appetitively and aversively motivated T-maze tasks. The present study examined if PTD-treated rats exhibit both anterograde and retrograde memory loss of an aversively motivated spatial navigation task. Histological examination revealed two consistent lesions in the PTD treated rats: a bilateral, symmetrical destruction of medial thalamus centered on the internal medullary lamina (IML), and a lesion of the medial nucleus of the mammillary body. In Experiment 1, control and recovered PTD rats were trained to find a hidden platform in a Morris water maze. PTD rats with the IML lesion were impaired in learning the water maze task but were eventually able to perform as well as controls and PTD animals without the IML lesion. In Experiment 2, half of the pretrained CT animals underwent thiamine deficiency (PTD2), were recovered, and subsequently were tested for retention of the platform location. The remaining CT animals and the PTD1 group were also tested for retention. No significant group differences were observed on any of the four postretention trials. When compared to their performance on the last four preretention trials, the performance of PTD1 and PTD2 animals with IML lesions were similar to those of the controls. These results demonstrate that acute thiamine deficiency in rats produces damage of medial thalamic and mammillary body nuclei, a mild anterograde learning deficit, but no loss of retrograde memory of the Morris water maze task.

Effect of pyrithiamine treatment and subsequent thiamine rehabilitation on regional cerebral amino acids and thiamine-dependent enzymes

Pyrithiamine-induced thiamine-deficiency encephalopathy in the rat shows many neuropathological and biochemical similarities to Wernicke's encephalopathy in humans. Treatment of rats with pyrithiamine resulted in moderate reductions of glutamate in thalamus and pons and in generalized severe reductions of aspartate in pons (by 89%, p less than 0.01), thalamus (by 83%, p less than 0.01), cerebellum (by 53%, p less than 0.01), and cerebral cortex (by 33%, p less than 0.05). Alanine concentrations were concomitantly increased. Activities of the thiamine-dependent enzyme alpha-ketoglutarate dehydrogenase (alpha KGDH) were decreased in parallel with the aspartate decreases; pyruvate dehydrogenase complex activities were unchanged in all brain regions. Following thiamine administration to symptomatic pyrithiamine-treated rats, neurological symptoms were reversed and concentrations of glutamate, aspartate, and alanine, as well as alpha KGDH activities, were restored to normal in cerebral cortex and pons. Aspartate levels and alpha KGDH activities remained below normal values, however, in thalamus. Thus, pyrithiamine treatment leads to reductions of cerebral alpha KGDH and (1) decreased glucose (pyruvate) oxidation resulting in accumulation of alanine and (2) decreased brain content of glutamate and aspartate. Such changes may be of key significance in the pathophysiology of the reversible and irreversible signs of Wernicke's encephalopathy in humans.