Effects of chronic alcohol consumption on the cholinergic innervation of the rat hippocampal formation as revealed by choline acetyltransferase immunocytochemistry

Alcohol as a Modifiable Risk Factor for Alzheimer's Disease-Evidence from Experimental Studies

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by cognitive impairment and memory loss. Epidemiological evidence suggests that heavy alcohol consumption aggravates AD pathology, whereas low alcohol intake may be protective. However, these observations have been inconsistent, and because of methodological discrepancies, the findings remain controversial. Alcohol-feeding studies in AD mice support the notion that high alcohol intake promotes AD, while also hinting that low alcohol doses may be protective against AD. Chronic alcohol feeding to AD mice that delivers alcohol doses sufficient to cause liver injury largely promotes and accelerates AD pathology. The mechanisms by which alcohol can modulate cerebral AD pathology include Toll-like receptors, protein kinase-B (Akt)/mammalian target of rapamycin (mTOR) pathway, cyclic adenosine monophosphate (cAMP) response element-binding protein phosphorylation pathway, glycogen synthase kinase 3-β, cyclin-dependent kinase-5, insulin-like growth factor type-1 receptor, modulation of β-amyloid (Aβ) synthesis and clearance, microglial mediated, and brain endothelial alterations. Besides these brain-centric pathways, alcohol-mediated liver injury may significantly affect brain Aβ levels through alterations in the peripheral-to-central Aβ homeostasis. This article reviews published experimental studies (cell culture and AD rodent models) to summarize the scientific evidence and probable mechanisms (both cerebral and hepatic) by which alcohol promotes or protects against AD progression.

Synaptic Effects Induced by Alcohol

Ethanol (EtOH) has effects on numerous cellular molecular targets, and alterations in synaptic function are prominent among these effects. Acute exposure to EtOH activates or inhibits the function of proteins involved in synaptic transmission, while chronic exposure often produces opposing and/or compensatory/homeostatic effects on the expression, localization, and function of these proteins. Interactions between different neurotransmitters (e.g., neuropeptide effects on release of small molecule transmitters) can also influence both acute and chronic EtOH actions. Studies in intact animals indicate that the proteins affected by EtOH also play roles in the neural actions of the drug, including acute intoxication, tolerance, dependence, and the seeking and drinking of EtOH. The present chapter is an update of our previous Lovinger and Roberto (Curr Top Behav Neurosci 13:31-86, 2013) chapter and reviews the literature describing these acute and chronic synaptic effects of EtOH with a focus on adult animals and their relevance for synaptic transmission, plasticity, and behavior.

Cholinergic and Neuroimmune Signaling Interact to Impact Adult Hippocampal Neurogenesis and Alcohol Pathology Across Development

Alcohol (ethanol) use and misuse is a costly societal issue that can affect an individual across the lifespan. Alcohol use and misuse typically initiates during adolescence and generally continues into adulthood. Not only is alcohol the most widely abused drug by adolescents, but it is also one of the most widely abused drugs in the world. In fact, high rates of maternal drinking make developmental ethanol exposure the most preventable cause of neurological deficits in the Western world. Preclinical studies have determined that one of the most consistent effects of ethanol is its disruption of hippocampal neurogenesis. However, the severity, persistence, and reversibility of ethanol’s effects on hippocampal neurogenesis are dependent on developmental stage of exposure and age at assessment. Complicating the neurodevelopmental effects of ethanol is the concurrent development and maturation of neuromodulatory systems which regulate neurogenesis, particularly the cholinergic system. Cholinergic signaling in the hippocampus directly regulates hippocampal neurogenesis through muscarinic and nicotinic receptor actions and indirectly regulates neurogenesis by providing anti-inflammatory regulatory control over the hippocampal environmental milieu. Therefore, this review aims to evaluate how shifting maturational patterns of the cholinergic system and its regulation of neuroimmune signaling impact ethanol’s effects on adult neurogenesis. For example, perinatal ethanol exposure decreases basal forebrain cholinergic neuron populations, resulting in long-term developmental disruptions to the hippocampus that persist into adulthood. Exaggerated neuroimmune responses and disruptions in adult hippocampal neurogenesis are evident after environmental, developmental, and pharmacological challenges, suggesting that perinatal ethanol exposure induces neurogenic deficits in adulthood that can be unmasked under conditions that strain neural and immune function. Similarly, adolescent ethanol exposure persistently decreases basal forebrain cholinergic neuron populations, increases hippocampal neuroimmune gene expression, and decreases hippocampal neurogenesis in adulthood. The effects of neither perinatal nor adolescent ethanol are mitigated by abstinence whereas adult ethanol exposure-induced reductions in hippocampal neurogenesis are restored following abstinence, suggesting that ethanol-induced alterations in neurogenesis and reversibility are dependent upon the developmental period. Thus, the focus of this review is an examination of how ethanol exposure across critical developmental periods disrupts maturation of cholinergic and neuroinflammatory systems to differentially affect hippocampal neurogenesis in adulthood.

Effects of chronic alcohol consumption and withdrawal on the cholinergic neurons of the pedunculopontine and laterodorsal tegmental nuclei of the rat: An unbiased stereological study

The brain cholinergic system comprises two main recognized subdivisions, the basal forebrain and the brainstem cholinergic systems. The effects of chronic alcohol consumption on the basal forebrain cholinergic nuclei have been investigated extensively, but there is only one study that has examined those effects on the brainstem cholinergic nuclei. The last one comprises the pedunculopontine tegmental (PPT) and the laterodorsal tegmental (LDT) nuclei, which are known to give origin to the main cholinergic projection to the ventral tegmental area, a key brain region of the neural circuit, the mesocorticolimbic system, that mediates several behavioral and physiological processes, including reward. In the present study, we have examined, using stereological methods, the effects of chronic alcohol consumption (6 months) and subsequent withdrawal (2 months) on the total number and size of PPT and LDT choline acetyltransferase (ChAT)-immunoreactive neurons. The total number of PPT and LDT ChAT-immunoreactive neurons was unchanged in ethanol-treated and withdrawn rats. However, ChAT-immunoreactive neurons were significantly hypertrophied in ethanol-treated rats, an alteration that did not revert 2 months after ethanol withdrawal. These results show that prolonged exposure to ethanol leads to long-lasting, and potentially irreversible, cytoarchitectonic and neurochemical alterations in the brainstem cholinergic nuclei. These alterations suggest that the alcohol-induced changes in the brainstem cholinergic nuclei might play a role in the mechanisms underlying the development of addictive behavior to alcohol.

Persistent Alterations of Accumbal Cholinergic Interneurons and Cognitive Dysfunction after Adolescent Intermittent Ethanol Exposure

Adolescent binge drinking renders young drinkers vulnerable to alcohol use disorders in adulthood; therefore, understanding alcohol-induced brain damage and associated cognitive dysfunctions is of paramount importance. Here we investigated the effects of binge-like adolescent intermittent ethanol (AIE) exposure on nonspatial working memory, behavioral flexibility and cholinergic alterations in the nucleus accumbens (NAc) in male and female rats. On postnatal days P25-57 rats were intubated with water or ethanol (at a dose of 5 g/kg) on a 2-day-on/2-day-off cycle and were then tested in adulthood on social recognition and probabilistic reversal learning tasks. During the social recognition task AIE-treated rats spent similar amounts of time interacting with familiar and novel juveniles, indicating an impaired ability to sustain memory of the familiar juvenile. During probabilistic reversal learning, AIE-treated male and female rats showed behavioral inflexibility as indicated by a higher number of trials needed to complete three reversals within a session, longer response latencies for lever selection, and for males, a higher number of errors as compared to water-treated rats. AIE exposure also reduced the number of cholinergic interneurons in the NAc in males and females. These findings indicate AIE-related pathologies of accumbal cholinergic interneurons and long lasting cognitive-behavioral deficits, which may be associated with cortico-striatal hypofunction.

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.

Alterations in cognitive function in prepubertal mice with protein malnutrition: Relationship to changes in choline acetyltransferase

We have found that protein malnutrition (PM) causes a significant impairment of memory-related behavior on the 15th and 20th day after the start of PM (5% casein) feeding in prepubertal mice but not in postpubertal mice, as measured by a passive-avoidance task. This impairment was almost completely reversed by merely switching to a standard protein (20% casein) diet on the 10th day after the start of PM. However, the reversal was not observed when the switching to a standard protein regimen was done on the 15th day of the PM diet. Interestingly, the impairment of memory-related behavior on the 20th day was improved by the chronic administration of physostigmine (0.1 mg/kg/day x last 10 days, i.p.), a cholinesterase inhibitor. To correlate brain cholinergic neuron function with the memory-related behavior impairment induced by PM, microphotometry was used to determine the histological distribution of the imunofluorescence intensity for choline acetyltransferase (ChAT), a functional marker of presynapse in cholinergic neurons. The change in the intensity of fluorescence indicated that ChAT protein was decreased in the hippocampus (CA1, CA3 and dentate gyrus) on the 20th day after PM feeding in comparison with controls. These results suggest the possibility that the memory-related behavior deficits observed in prepubertal mice with PM are caused by a dysfunction of the cholinergic neurons in the hippocampus.

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.

Age-dependent effects of moderate chronic ethanol administration on different forms of memory expression in mice

A large number of studies have investigated the effects of chronic ethanol administration (CEA) on performance in different types of learning and memory tasks in adult rodents. As a general rule, CEA has been reported to impair performance, although this depends both on the condition of administration (e.g. duration, presence or not of a withdrawn period) and on task demands (e.g. spatial versus non-spatial). Indeed, either no impairment or even a facilitation of performance have been reported following CEA. However, no study has directly addressed the issue as to whether the effect of CEA depends on the age of subjects. In this study, C57Bl/6 mice of two age ranges (i.e. 2-3- and 16-18-month-old) were given either a solution of ethanol (12% v/v) as their only source of fluid for 5 months (experimental groups) or were pair-fed with an isocaloric solution of dextri-maltose (control groups). Then, they were submitted to a place discrimination task in an 8-arm radial maze. Additionally, mice were tested for long-term retention following a 21-day interval. Confirming our previous findings, the results showed that, with respect to adults (7-8-month-old at the time of testing), aged mice (21-23-month-old) of the control group displayed impaired relational memory but not procedural memory performance. Further they exhibited a higher level of forgetting than adults over the 21-day interval. In the same paradigm, CEA resulted in an overall attenuation of both type of deficit in aged subjects without altering their procedural memory. Furthermore these ethanol-consuming aged mice displayed significantly less levels of forgetting than their age-matched controls. Conversely, in the adult group, CEA resulted in an overall, although, somewhat less selective impairment of relational memory with respect to procedural memory but had no effect on long-term forgetting. While confirming the deleterious effect of CEA on learning and memory processes in adults, our present findings provide evidence that CEA can selectively ameliorate certain cognitive deficits normally associated with ageing.

Nerve growth factor prevents cell death and induces hypertrophy of basal forebrain cholinergic neurons in rats withdrawn from prolonged ethanol intake

We have previously reported that the hippocampal cholinergic fiber network is severely damaged in animals withdrawn from ethanol, and that a remarkable recovery in fiber density occurs following hippocampal grafting, a finding that we suggested to be underpinned by the graft production of neurotrophic factors, which are known to be decreased after ethanol exposure. It is widely accepted that nerve growth factor (NGF) signals the neurons of the brain cholinergic system, including those of the medial septum/vertical limb of the diagonal band of Broca (MS/VDB) nuclei, from which the septohippocampal projection arises. Because neurons in these nuclei are vulnerable to ethanol consumption and withdrawal we thought of interest to investigate, in withdrawn rats previously submitted to a prolonged period of ethanol intake, the effects of intraventricular delivery of NGF upon the MS/VDB cholinergic neurons. Stereological methods were applied to estimate neuron numbers and neuronal volumes in choline acetyltransferase (ChAT)-immunostained and Nissl-stained material. We have found that in ethanol-fed rats there was a significant reduction in the total number of Nissl-stained and cholinergic neurons in the MS/VDB, and that the suppression of ethanol intake further decreased neuron numbers. In addition, the somatic size of ChAT-IR neurons was reduced by ethanol intake, and withdrawal further aggravated neuronal atrophy. NGF treatment prevented the withdrawal-associated loss, and induced hypertrophy, of cholinergic neurons. These findings show that exogenous NGF protects the phenotype and prevents the withdrawal-induced degeneration of cholinergic neurons in the MS/VDB. These effects might be due to the trophic action of NGF upon the basal forebrain cholinergic neurons, including the hippocampal fiber network that conveys this neurotrophin retrogradely to the MS/VDB, and/or upon their targets, that is, the hippocampal formation neurons.

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.

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

We studied at the biochemical, morphological, and behavioral levels the effect of chronic ethanol consumption, associated or not with a mild thiamine deficiency episode. We found that (i) thiamine deficiency induced a significant decrease of the acetylcholinesterase (AChE) activity both in cortex and hippocampus; (ii) chronic ethanol treatment has no effect on cortical AChE activity, but induced a significant decrease of hippocampal enzyme activity; (iii) the reduction in cortical and hippocampal AChE activity induced by chronic ethanol treatment associated with a 1-week thiamine deficiency was also significant and was greater than that induced by ethanol alone. Furthermore, either chronic ethanol or thiamine deficiency induced a significant decrease in the release of acetylcholine (ACh) in the stimulated condition using high potassium concentration; and when both treatments were associated the decrease was even greater. In the unstimulated condition, the reduction in the release of ACh was greater for ethanol treatment than for thiamine deficiency. Open-field tests showed that only in the "sniffing" category were there significant differences among the experimental groups. No morphological change was detected by optical microscopy, suggesting that the injury process was in its initial stages in which only functional and behavioral changes are displayed. In addition, our biochemical results indicate that cortical cholinergic susceptibilities to ethanol and thiamine deficiency are significantly different.

Hippocampal AgNOR activity after chronic alcohol consumption and alcohol deprivation in rats

Chronic alcohol consumption induces morphological changes in the central nervous system and withdrawal does not reverse these changes. It is well known that the hippocampal formation is one of the brain regions most sensitive to prolonged alcohol ingestion. The aim of our study was to evaluate the transcriptional neuronal activity by measuring the argyrophilic nucleolar organizer regions (AgNORs) in the dentate gyrus, CA3, and CA1 hippocampal areas from adult male rats receiving chronic administration of ethanol (ALC) and after withdrawal (WDL). The parameters evaluated were the number and area of AgNORs, together with the area of nucleus and the proportion between AgNOR and nuclear areas (ratio). The animals from ALC and WDL groups showed a reduction in the number of AgNOR per cell as compared to the control group. CA3 was the hippocampal area most affected by chronic alcohol intake. No improvement was observed in animals after withdrawal. Our data support the idea that the chronic intake of alcohol decreases protein synthesis in hippocampal neurons at an early age. This decrease may explain the memory impairment showed by rats receiving chronic treatment with alcohol because, both in humans and rats, it is associated with a reduction in the number of cholinergic neurons in the basal forebrain that would in turn affect the hippocampal function.

Synaptic reorganization in the hippocampal formation of alcohol-fed rats may compensate for functional deficits related to neuronal loss

We have examined the behavioral and neuroanatomical effects of long-term alcohol intake in rats ingesting a 20% solution of ethanol for 30 weeks. Previous studies have shown that this treatment provokes neuronal degeneration in the hippocampal formation, which occurs in parallel with remodeling processes. Spatial reference and working memory of alcohol-fed rats were evaluated during last 4 weeks of treatment by comparison of their performance with age-matched controls on the Morris water maze. Alcohol consumption did not affect the performance of rats in the reference memory task as indicated by the measures derived from the acquisition trials and from the probe-trial, which were highly similar for alcohol-fed and control animals. Also, performance in the working memory task was not significantly altered in alcohol-treated animals. No treatment-related changes in swim speed or impairments of sensorimotor abilities, tested in the visible platform task, were detected. Stereological methods were applied to evaluate the damage inflicted by alcohol intake in the structure of the hippocampal formation. In the alcohol-treated animals, there was a noticeable cell loss in the granular layer of the dentate gyrus (10%), and in CA3 (18%) and CA1 (19%) hippocampal subdivisions. In spite of the neuronal loss, the total number of synapses between mossy fibers and CA3 pyramids was unaffected by alcohol treatment suggesting that new synaptic contacts were formed between the surviving neurons. We show that, regardless the marked hippocampal cell loss in rats exposed to chronic alcohol intake, the reorganization that takes place at the synaptic level may alleviate the expected functional deficits.

GM1 and piracetam do not revert the alcohol-induced depletion of cholinergic fibers in the hippocampal formation of the rat

Chronic alcohol consumption causes a depletion of the cholinergic fiber network in the rat hippocampal formation, which is not ameliorated by alcohol withdrawal. Following withdrawal from alcohol, there is a further loss of intrinsic hippocampal cholinergic neurons. In this study, we investigated whether treatment with putative neuroprotective agents during the entire withdrawal period would have beneficial effects upon the hippocampal cholinergic innervation. Adult male rats were alcohol-fed for 6 months and subsequently withdrawn from alcohol for 6 months. Some animals were treated with either ganglioside GM1 (35 mg/kg body weight s.c.), vehicle (saline s.c.), or piracetam (800 mg/kg body weight p.o.) for the entire withdrawal period. Choline acetyltransferase (ChAT) immunoreactive (IR) fibers and neurons were analyzed quantitatively in all four animal groups. There were no significant differences in the density of the ChAT-IR hippocampal fiber network when the pure withdrawal and withdrawal + vehicle groups were compared to the withdrawal + GM1 or withdrawal + piracetam groups. In contrast, the number of ChAT-IR interneurons in the hippocampal formation was higher in the withdrawal + GM1 or withdrawal + piracetam groups than in the pure withdrawal and withdrawal + vehicle groups. These results indicate that, in the doses used, neither neuroprotective agent had an effect upon the extrinsic cholinergic innervation, but they had a beneficial effect upon the hippocampal intrinsic cholinergic system.

Behavioral and neuroanatomical consequences of chronic ethanol intake and withdrawal

We have examined if long-term (13 months) alcohol consumption and the same treatment followed by a 6-week withdrawal period cause different neuropathological changes in rats. Spatial reference and working memory of alcohol-consuming and withdrawn rats were evaluated by comparison of their performance with age-matched controls in the Morris water maze. In the reference memory task we did not observe significant cognitive deficits in rats continuously exposed to ethanol, whereas withdrawn animals showed an obvious impairment of their overall performance. The reference memory deficit in withdrawn rats was evident in the spatial probe trial; these animals required significantly longer swimming distances to approach the former position of the platform when compared with controls and alcohol-consuming animals. In contrast, working memory was not significantly altered in either experimental group. Stereological methods were applied to compare the neurodegenerative changes produced by alcohol intake and withdrawal in the hippocampal formation. In the alcohol-consuming animals there was a significant cell loss in CA1 (18%) and CA3 (19%) hippocampal regions. Moreover, in withdrawn rats there was a further decay in the total number of pyramidal neurons, which amounted to 15% relative to nonwithdrawn animals. In the granular layer of the dentate gyrus there was a trend in the same direction, but it did not reach significance. Thus, our findings indicate that withdrawn rats are cognitively impaired relative to animals submitted to continuous alcohol consumption and to age-matched controls, which fits the morphological data showing that withdrawal aggravates ethanol-induced degenerative processes in the hippocampal formation.

The reaction of astrocytes and neurons in the hippocampus of adult rats during chronic ethanol treatment and correlations to behavioral impairments

Chronic ethanol treatment of Wistar rats to 10% (v/v) ethanol over a period of 4, 12, and 36 weeks produced distinct alterations of the glial fibrillary acidic protein immunoreactivity (GFAP-IR) of dorsal hippocampal astrocytes. Ethanol consumption over a period of 4 weeks caused an increase in the total GFAP-IR of the astrocytes. Down-regulation of the total GFAP-IR was measured in all examined brain regions after 36 weeks of ethanol treatment. Prolonged ethanol treatment induced a significant loss of the total number of hippocampal pyramidal and dentate gyrus granule cells. Regional differences in the vulnerability to the neurotoxic effects of chronic ethanol intake over 36 weeks were found: CA3 > CA1 + CA2 > > CA4 > GD. In agreement with the degree of neuronal cell loss, ethanol-induced behavioral impairments were found. The acquisition of maze performance using a complex elevated labyrinth was deteriorated after 36 weeks of ethanol treatment, suggesting a deficit in learning and memory. These findings illustrate the importance of time-response analysis when determining the structural and functional changes produced by chronic ethanol treatment.

Intracerebral grafts promote recovery of the cholinergic innervation of the hippocampal formation in rats withdrawn from chronic alcohol intake. An immunocytochemical study

We have previously found that alcohol withdrawal aggravates the neuronal cell loss induced by chronic alcohol consumption in the rat hippocampal formation. We have also shown that intracerebral grafts of immature hippocampal tissue could reverse the progressive degeneration that occurs during this withdrawal. Furthermore, we have shown that chronic alcohol consumption reduces the areal density of choline acetyltransferase-immunoreactive neurons and the density of choline acetyltransferase-immunoreactive fibres in the hippocampal formation. Thus, we thought it would be of interest to investigate the effects of alcohol withdrawal in the hippocampal cholinergic innervation and to determine whether the intracerebral grafting of immature hippocampal tissue would have beneficial effects upon the cholinergic system in this condition. Choline acetyltransferase-immunoreactive fibres and perikarya were analysed in 14-month-old control, alcohol-fed, withdrawal and withdrawal-grafted groups of rats. The areal density of choline acetyltransferase-immunoreactive neurons was reduced in all experimental groups when compared to controls. The density of choline acetyltransferase-immunoreactive fibres was lower in the alcohol-fed and withdrawal groups than in the control and withdrawal-grafted groups. We conclude that the grafted tissue probably produced neurotrophic factors which allowed a recovery of the hippocampal cholinergic fibre network. This recovery might be of importance to reverse the cognitive dysfunction described after chronic alcohol consumption and withdrawal.

Can megadoses of thiamine prevent ethanol-induced damages of rat hippocampal CA1 pyramidal neurones?

The specific aim of this study was to evaluate whether high doses of thiamine can compensate or prevent alcohol-induced damages of rat hippocampus CA1 pyramids. Twenty weeks of ethanol consumption together with a dose of thiamine in the range of 1.19 mg/100 mg food induced significant enlargement (parameters measured were length of the whole spine and diameter of the end-bulb) of dendritic spines. Hypertrophy can be interpreted as a compensation process due to alcohol-induced cell death because viable spines are in search of new synaptic contacts. In contrast, dendritic spines of the alcohol group fed at the same time with a high dose of thiamine (119 mg/ 100 g food = megavitamintherapy) showed normal data concerning these parameters. From these results it may be concluded that a megavitamin therapy supports a neuron's carbohydrate metabolism and therefore could be able to prevent or reduce alcohol-induced damages of hippocampal CA1 pyramidal cells in rat central nervous system.

Protein malnutrition alters the cholinergic and GABAergic systems of the hippocampal formation of the adult rat: an immunocytochemical study

We attempted to find out if the cholinergic and GABAergic systems that regulate the hippocampal circuitries are disturbed after long periods of protein deprivation and, in the affirmative, to investigate if the changes are reversible following nutritional rehabilitation. A group of 2 month old rats fed with a low-protein diet for 12 months was compared with age-matched controls and with nutritionally rehabilitated rats. We have evaluated the length density of the cholinergic fiber network and estimated the numerical densities of the choline acetyltransferase and GABAergic immunoreactive neurons of the hippocampal formation. Our results show that prolonged malnutrition leads to a substantial, but reversible, reduction in the cholinergic innervation of the hippocampal formation and to an irreversible loss of hippocampal cholinergic and GABAergic neurons.