Hippocampal mossy fiber-CA3 synapses after chronic alcohol consumption and withdrawal

The Inferior Colliculus in Alcoholism and Beyond

Post-mortem neuropathological and in vivo neuroimaging methods have demonstrated the vulnerability of the inferior colliculus to the sequelae of thiamine deficiency as occurs in Wernicke-Korsakoff Syndrome (WKS). A rich literature in animal models ranging from mice to monkeys-including our neuroimaging studies in rats-has shown involvement of the inferior colliculi in the neural response to thiamine depletion, frequently accomplished with pyrithiamine, an inhibitor of thiamine metabolism. In uncomplicated alcoholism (i.e., absent diagnosable neurological concomitants), the literature citing involvement of the inferior colliculus is scarce, has nearly all been accomplished in preclinical models, and is predominately discussed in the context of ethanol withdrawal. Our recent work using novel, voxel-based analysis of structural Magnetic Resonance Imaging (MRI) has demonstrated significant, persistent shrinkage of the inferior colliculus using acute and chronic ethanol exposure paradigms in two strains of rats. We speculate that these consistent findings should be considered from the perspective of the inferior colliculi having a relatively high CNS metabolic rate. As such, they are especially vulnerable to hypoxic injury and may be provide a common anatomical link among a variety of disparate insults. An argument will be made that the inferior colliculi have functions, possibly related to auditory gating, necessary for awareness of the external environment. Multimodal imaging including diffusion methods to provide more accurate in vivo visualization and quantification of the inferior colliculi may clarify the roles of brain stem nuclei such as the inferior colliculi in alcoholism and other neuropathologies marked by altered metabolism.

Effect of Alcohol on Hippocampal-Dependent Plasticity and Behavior: Role of Glutamatergic Synaptic Transmission

Problematic alcohol drinking and alcohol dependence are an increasing health problem worldwide. Alcohol abuse is responsible for approximately 5% of the total deaths in the world, but addictive consumption of it has a substantial impact on neurological and memory disabilities throughout the population. One of the better-studied brain areas involved in cognitive functions is the hippocampus, which is also an essential brain region targeted by ethanol. Accumulated evidence in several rodent models has shown that ethanol treatment produces cognitive impairment in hippocampal-dependent tasks. These adverse effects may be related to the fact that ethanol impairs the cellular and synaptic plasticity mechanisms, including adverse changes in neuronal morphology, spine architecture, neuronal communication, and finally an increase in neuronal death. There is evidence that the damage that occurs in the different brain structures is varied according to the stage of development during which the subjects are exposed to ethanol, and even much earlier exposure to it would cause damage in the adult stage. Studies on the cellular and cognitive deficiencies produced by alcohol in the brain are needed in order to search for new strategies to reduce alcohol neuronal toxicity and to understand its consequences on memory and cognitive performance with emphasis on the crucial stages of development, including prenatal events to adulthood.

Gene expression profiling in the hippocampus of adolescent rats after chronic alcohol administration

In South Korea, the average age of onset of alcohol drinking is 13.3 years and half of adolescents drink alcohol more than once a month; 8.45% of the Korean adolescent population become future high-risk alcohol drinkers. Chronic alcohol abuse causes physical and psychiatric health problems such as alcohol addiction, liver disease, stroke and cognitive impairments. This study aimed to investigate the effect of alcohol on gene expression and their function in the hippocampus of adolescent rats. After chronic alcohol administration in male (control, n = 6; alcohol, n = 6) Sprague-Dawley rats for 6 weeks, we analysed up- or down-regulated genes using RNA-sequencing technology. We found 83 genes more than 1.5-fold up- or down-regulated in the alcohol-treated group. Among them, genes (Dnai1, Cfap206 and Dnah1) associated with cilium movement were up-regulated in the alcohol-treated group. Mlf1, related to cell cycle arrest, was also up-regulated in the alcohol-treated group. On the other hand, genes (Smad3 and Plk5) involved in negative regulation of cell proliferation were down-regulated in the hippocampus by chronic alcohol administration. In addition, expression levels of genes associated with oxidative stress (Krt8 and Car3) and migration (Vim) were changed by chronic alcohol administration. These results pave a path for a better understanding of the neuromolecular mechanisms mediated by chronic alcohol exposure in the hippocampus of adolescents and negative pathology due to chronic alcohol abuse.

Jacobian Maps Reveal Under-reported Brain Regions Sensitive to Extreme Binge Ethanol Intoxication in the Rat

Individuals aged 12-20 years drink 11% of all alcohol consumed in the United States with more than 90% consumed in the form of binge drinking. Early onset alcohol use is a strong predictor of future alcohol dependence. The study of the effects of excessive alcohol use on the human brain is hampered by limited information regarding the quantity and frequency of exposure to alcohol. Animal models can control for age at alcohol exposure onset and enable isolation of neural substrates of exposure to different patterns and quantities of ethanol (EtOH). As with humans, a frequently used binge exposure model is thought to produce dependence and affect predominantly corticolimbic brain regions. in vivo neuroimaging enables animals models to be examined longitudinally, allowing for each animal to serve as its own control. Accordingly, we conducted 3 magnetic resonance imaging (MRI) sessions (baseline, binge, recovery) to track structure throughout the brains of wild type Wistar rats to test the hypothesis that binge EtOH exposure affects specific brain regions in addition to corticolimbic circuitry. Voxel-based comparisons of 13 EtOH- vs. 12 water- exposed animals identified significant thalamic shrinkage and lateral ventricular enlargement as occurring with EtOH exposure, but recovering with a week of abstinence. By contrast, pretectal nuclei and superior and inferior colliculi shrank in response to binge EtOH treatment but did not recover with abstinence. These results identify brainstem structures that have been relatively underreported but are relevant for localizing neurocircuitry relevant to the dynamic course of alcoholism.

Hippocampal neural progenitor cells play a distinct role in fear memory retrieval in male and female CIE rats

Adult male and female GFAP-TK transgenic rats experienced six weeks of chronic intermittent ethanol vapor inhalation (CIE). During the last week of CIE, a subset of male and female TK rats were fed with Valcyte to ablate neural progenitor cells (NPCs). Seventy-two hours after CIE cessation, all CIE and age-matched ethanol naïve controls experienced auditory trace fear conditioning (TFC). Twenty-four hours later all animals were tested for cue-mediated retrieval in the fear context. Adult male CIE rats showed a significant burst in NPCs paralleled by reduction in fear retrieval compared to naïve controls and Valcyte treated CIE rats. Adult female CIE rats did not show a burst in NPCs and showed similar fear retrieval compared to naïve controls and Valcyte treated CIE rats, indicating that CIE-mediated impairment in fear memory and its regulation by NPCs was sex dependent. Valcyte significantly reduced Ki-67 and NeuroD labeled cells in the dentate gyrus (DG) in both sexes, demonstrating a role for NPCs in reduced fear retrieval in males. Valcyte prevented adaptations in GluN2A receptor expression and synaptoporin density in the DG in males, indicating that NPCs contributed to alterations in plasticity-related proteins and mossy fiber projections that were associated with reduced fear retrieval. These data suggest that DG NPCs born during withdrawal and early abstinence from CIE are aberrant, and could play a role in weakening long-term memory consolidation dependent on the hippocampus.

Moderate alcohol consumption as risk factor for adverse brain outcomes and cognitive decline: longitudinal cohort study

Objectives To investigate whether moderate alcohol consumption has a favourable or adverse association or no association with brain structure and function.Design Observational cohort study with weekly alcohol intake and cognitive performance measured repeatedly over 30 years (1985-2015). Multimodal magnetic resonance imaging (MRI) was performed at study endpoint (2012-15).Setting Community dwelling adults enrolled in the Whitehall II cohort based in the UK (the Whitehall II imaging substudy).Participants 550 men and women with mean age 43.0 (SD 5.4) at study baseline, none were "alcohol dependent" according to the CAGE screening questionnaire, and all safe to undergo MRI of the brain at follow-up. Twenty three were excluded because of incomplete or poor quality imaging data or gross structural abnormality (such as a brain cyst) or incomplete alcohol use, sociodemographic, health, or cognitive data.Main outcome measures Structural brain measures included hippocampal atrophy, grey matter density, and white matter microstructure. Functional measures included cognitive decline over the study and cross sectional cognitive performance at the time of scanning.Results Higher alcohol consumption over the 30 year follow-up was associated with increased odds of hippocampal atrophy in a dose dependent fashion. While those consuming over 30 units a week were at the highest risk compared with abstainers (odds ratio 5.8, 95% confidence interval 1.8 to 18.6; P≤0.001), even those drinking moderately (14-21 units/week) had three times the odds of right sided hippocampal atrophy (3.4, 1.4 to 8.1; P=0.007). There was no protective effect of light drinking (1-<7 units/week) over abstinence. Higher alcohol use was also associated with differences in corpus callosum microstructure and faster decline in lexical fluency. No association was found with cross sectional cognitive performance or longitudinal changes in semantic fluency or word recall.Conclusions Alcohol consumption, even at moderate levels, is associated with adverse brain outcomes including hippocampal atrophy. These results support the recent reduction in alcohol guidance in the UK and question the current limits recommended in the US.

Chronic ethanol intake induces partial microglial activation that is not reversed by long-term ethanol withdrawal in the rat hippocampal formation

Neuroinflammation has been implicated in the pathogenesis of several disorders. Activation of microglia leads to the release of pro-inflammatory mediators and microglial-mediated neuroinflammation has been proposed as one of the alcohol-induced neuropathological mechanisms. The present study aimed to examine the effect of chronic ethanol exposure and long-term withdrawal on microglial activation and neuroinflammation in the hippocampal formation. Male rats were submitted to 6 months of ethanol treatment followed by a 2-month withdrawal period. Stereological methods were applied to estimate the total number of microglia and activated microglia detected by CD11b immunohistochemistry in the hippocampal formation. The expression levels of the pro-inflammatory cytokines TNF-α, COX-2 and IL-15 were measured by qRT-PCR. Alcohol consumption was associated with an increase in the total number of activated microglia but morphological assessment indicated that microglia did not exhibit a full activation phenotype. These data were supported by functional evidence since chronic alcohol consumption produced no changes in the expression of TNF-α or COX-2. The levels of IL-15 a cytokine whose expression is increased upon activation of both astrocytes and microglia, was induced by chronic alcohol treatment. Importantly, the partial activation of microglia induced by ethanol was not reversed by long-term withdrawal. This study suggests that chronic alcohol exposure induces a microglial phenotype consistent with partial activation without significant increase in classical cytokine markers of neuroinflammation in the hippocampal formation. Furthermore, long-term cessation of alcohol intake is not sufficient to alter the microglial partial activation phenotype induced by ethanol.

Tiliacora triandra, an Anti-Intoxication Plant, Improves Memory Impairment, Neurodegeneration, Cholinergic Function, and Oxidative Stress in Hippocampus of Ethanol Dependence Rats

Oxidative stress plays an important role in brain dysfunctions induced by alcohol. Since less therapeutic agent against cognitive deficit and brain damage induced by chronic alcohol consumption is less available, we aimed to assess the effect of Tiliacora triandra extract, a plant possessing antioxidant activity, on memory impairment, neuron density, cholinergic function, and oxidative stress in hippocampus of alcoholic rats. Male Wistar rats were induced ethanol dependence condition by semivoluntary intake of alcohol for 15 weeks. Alcoholic rats were orally given T. triandra at doses of 100, 200, and 400 mg·kg⁻¹BW for 14 days. Memory assessment was performed every 7 days while neuron density, activities of AChE, SOD, CAT, and GSH-Px and, MDA level in hippocampus were assessed at the end of study. Interestingly, the extract mitigated the increased escape latency, AChE and MDA level. The extract also mitigated the decreased retention time, SOD, CAT, and GSH-Px activities, and neurons density in hippocampus induced by alcohol. These data suggested that the extract improved memory deficit in alcoholic rats partly via the decreased oxidative stress and the suppression of AChE. Therefore, T. triandra is the potential reagent for treating brain dysfunction induced by alcohol. However, further researches are necessary to understand the detail mechanism and possible active ingredient.

Plasmin-mediated degradation of laminin gamma-1 is critical for ethanol-induced neurodegeneration

BACKGROUND

Alcoholism may result in severe neurological deficits and cognitive impairments. Many of the central effects of ethanol (EtOH) can be explained by upregulation of N-methyl-D-aspartate (NMDA) and downregulation of gamma-aminobutyric acid (GABA) A receptors (GABAA) in response to long-term EtOH consumption. Abrupt ethanol withdrawal (EW) may result in neuronal hyperexcitability leading to hallucinations, seizures, neurodegeneration, and sometimes death.

METHODS

Using a multidisciplinary approach in wild-type and genetically modified mice, we examined the contribution of the tissue plasminogen activator (tPA), plasminogen, and laminin to EW-induced cell death.

RESULTS

Here we show that EW-induced neurodegeneration is mediated by the tPA/plasmin system. During EW, tPA is upregulated in the hippocampus and converts plasminogen to plasmin, which in turn degrades an extracellular matrix component laminin, leading to caspase-3-dependent cell death. Consequently, mice in which the tPA or plasminogen genes have been deleted do not show EW-induced laminin degradation, mitochondrial dysfunction, and neurodegeneration. Finally, we demonstrated that disruption of the hippocampal laminin gamma-1 renders the mice resistant to neurotoxic effects of EW.

CONCLUSIONS

Our data identify laminin gamma-1 as a novel target to combat neurodegeneration.

Complex plastic changes in the neuropeptide Y system during ethanol intoxication and withdrawal in the rat brain

Previous studies show that chronic ethanol treatment induces prominent changes in brain neuropeptide Y (NPY). The purpose of the present study was to explore ethanol effects at a deeper NPY-system level, measuring expression of NPY and its receptors (Y1, Y2, Y5) as well as NPY receptor binding and NPY-stimulated [(35)S]GTPgammaS functional binding. Rats received intragastric ethanol repeatedly for 4 days, and the NPY system was studied in the hippocampal dentate gyrus (DG), CA3, CA1, and piriform cortex (PirCx) and neocortex (NeoCx) during intoxication, peak withdrawal (16 hr), late withdrawal (3 days), and 1 week after last ethanol administration. NPY mRNA levels decreased during intoxication and at 16 hr in hippocampal regions but increased in the PirCx and NeoCx at 16 hr. NPY mRNA levels were increased at 3 days and returned to control levels in most regions at 1 week. Substantial changes also occurred at the receptor level. Thus Y1, Y2, and Y5 mRNA labelling decreased at 16 hr in most regions, returning to control levels at 3 days, except for PirCx Y2 mRNA, which increased at 3 days and 1 week. Conversely, increases in NPY receptor binding occurred in hippocampal regions during intoxication and in functional binding in the DG and NeoCx during intoxication and at 16 hr and in PirCx during intoxication and at 1 week. Thus this study shows that ethanol intoxication and withdrawal induce complex plastic changes in the NPY system, with decreased/increased gene expression or binding occurring in a time- and region-specific manner. These changes may play an important role in mediating ethanol-induced changes in neuronal excitability.

Red wine antioxidants protect hippocampal neurons against ethanol-induced damage: A biochemical, morphological and behavioral study

Chronic ethanol consumption increases oxidative stress, which accounts for the striking neurological changes seen in this condition. Notwithstanding, there is well-documented evidence that polyphenols, present in grape skin and seeds, exhibit a strong antioxidant activity. As red wine is rich in polyphenols, the aim of the present work was to evaluate their putative protective effects on the hippocampal formation by applying biochemical, morphological and behavioral approaches. Six-month old male Wistar rats were fed with red wine (ethanol content adjusted to 20%) and the results were compared with those from ethanol-treated (20%) rats and pair-fed controls. Biochemical markers of oxidative stress (lipid peroxidation, glutathione levels and antioxidant enzyme activities) were assessed on hippocampal homogenates. Lipofuscin pigment, an end product of lipid peroxidation, was quantified in hippocampal cornu ammonis 1 and 3 (CA1 and CA3) pyramidal neurons using stereological methods. All animals were behaviorally tested on the Morris water maze in order to assess their spatial learning and memory skills. In red wine-treated rats, lipid peroxidation was the lowest while presenting the highest levels of reduced glutathione and an induction of antioxidant enzyme activities. Morphological findings revealed that, contrary to ethanol, red wine did not increase lipofuscin deposition in CA1 and CA3 pyramidal neurons. Besides, red wine-treated animals learned the water maze task at a higher rate than ethanol group and had better performance scores by the end of the training period and on a probe trial. Actually, no significant differences were found between pair-fed controls and red wine-treated rats in morphological and behavioral data. Thus, our findings demonstrate that chronic consumption of red wine, unlike the ethanol solution alone, does not lead to a decline in hippocampal-dependent spatial memory. This may be due to the ability of red wine polyphenols to improve the antioxidant status in the brain and to prevent free radical-induced neuronal damage.

Vitamin E Deficiency and Aging Effect on Expression Levels of GAP-43 and MAP-2 in Selected Areas of the Brain

The expression levels of GAP-43 and MAP-2, two proteins involved, respectively, in axonal and dendritic remodeling, in control adult (11 months), old (24 months), and vitamin E-deficient (11 months) rats were evaluated. mRNA levels were determined by means of a quantitative in situ hybridization procedure in subregions of hippocampus and cerebellum. Though a general trend can be observed indicating a reduction in GAP-43 expression in aging as compared to adult animals and an increase in vitamin E-deprived rats in comparison with adult animals, no statistically significant change was found in any region analyzed. In the same way, MAP-2 mRNA levels show an increase in vitamin E-deprived rats in comparison with other groups tested; only one variation was statistically significant, namely the increase in cerebellar cortex MAP-2 nRNA levels in vitamin E-deficient versus adult rats. These results suggest that oxidative stress and aging negatively affect neuroplasticity, showing different characteristics at the dendritic and axonal levels.

The effects of alcohol intake and withdrawal on the seizures frequency and hippocampal morphology in rats with epilepsy

The aim of our study, using the pilocarpine model of epilepsy, was to investigate the effects of alcohol administration and withdrawal on the spontaneous recurrent seizures (SRSs). Four groups of adult, male Wistar rats were studied: (A). control rats (n=10), received neither pilocarpine nor alcohol, (B). alcohol-treated rats (n=10), received a daily dose of 3.0 g x kg(-1) of a 30% alcohol solution via an oesophagic probe for 30 days, (C). rats with epilepsy (n=10), (D). rats with epilepsy with alcohol intake (n=10). SRSs were induced by a single dose of pilocarpine (i.p.) and the basal frequency of SRSs was video monitored (24h per day) for 30 days. Following this period, the animals of group D received a daily dose of alcohol solution as described above and at the end of this period, alcohol administration was stopped and the seizure frequency was assessed for more 30 days. The basal seizure frequency observed in groups C and D during the first 30 days was 2.2+/-1.8 seizures per week per animal. In group D, it was observed an increase to 12.2+/-5.8 during the first 2 weeks of alcohol administration. During the last 2 weeks of alcohol administration, the number of SRSs returned to the previous basal level. During alcohol withdrawal the seizure frequency increased to 14.3+/-7.4 seizures per week per animal for the first 2 weeks, and returned to the basal level in the remaining period of observation. The Neo-Timm and Nissl staining of hippocampal formation and of the dentate gyrus in rats with epilepsy showed a cell loss in the hippocampal subfield CA1 and in the hillus of dentate gyrus. In rats with epilepsy with alcohol intake, we observed a cell loss in hippocampal subfields CA3 and hillus of the dentate gyrus, with significant neuronal death in subfield CA1, when compared with control animals. The alcohol withdrawal syndrome is a crucial event for the development of functional and neuropathological alterations associated with epilepsy.

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.

Age-related effects of moderate alcohol consumption on GAP-43 levels in rat hippocampus

The effects of moderate intake of ethanol and ageing were investigated on the levels of the growth-associated protein GAP-43, whose expression has been used as an indicator of axonal growth during development, regeneration and remodelling of synaptic connections. Groups of female Wistar rats (12 and 24 months of age), were alcohol-fed for one month while age-matched control groups received an isocaloric diet. A quantitative evaluation of GAP-43 was performed in hippocampus and in hippocampal selected areas in view of the vulnerability of this complex to alcohol aggression by means of two different methods, namely Western blot analysis and immunohistochemistry. While the former measures total extractable GAP-43, the latter allows visualisation of in situ changes in topographical distribution of GAP-43. Western blot analysis revealed an age-dependent reduction (-47%) and an ethanol-associated increase (81%) of GAP-43 demonstrated only in the old group. Conversely, quantitative immunohistochemistry of GAP-43 in the entire hippocampus showed a non-significant ethanol-related decrement in 24-month-old rats (-30%), although the age-dependent reduction was confirmed. Ageing was associated with a decrement of GAP-43 immunostaining in CA3 stratum radiatum (CA3) and in inner molecular layer of dentate gyrus (IML). Treatment determined a decrease of GAP-43 immunostaining in adult rat CA3 and IML and no change in CA1 stratum radiatum (CA1). Our results suggest that immunohistochemistry evaluation underestimates GAP-43 levels in ethanol-treated animals possibly as a consequence of conformational changes induced by alcohol, resulting in non-targeting of the specific antibody. Western blot analysis demonstrate that although there is a reduction of GAP-43 levels in hippocampus of aged rats, this structure retain a remarkable potential to compensate for ethanol toxicity during ageing.

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.

Prenatal and postnatal exposure to ethanol induces changes in the shape of the dendritic spines from hippocampal CA1 pyramidal neurons of the rat

20%-ethanol was provided to adult female rats since a pregestational stage until weaning of the pups, and percentage proportion of thin, mushroom-shaped, stubby, or wide spines from the apical dendrite of hippocampal CA1 pyramidal cells, was counted at 15, 21, 40, and 90 days of age. By-kind-of-spine analysis revealed higher fluctuation of experimental spines, and less percentage of thin spines was observed in the ethanol-intoxicated rats concomitantly with a higher proportion of stubby or wide spines; through development. Because thin spines may propagate the synaptic potentials more efficiently than stubby or wide spines, this findings suggest that the electrical excitability and thereafter the firing pattern of those cells may be altered, due to the toxic effects of chronic ethanol ingestion.

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.

Long-term voluntary ethanol consumption affects neither spatial nor passive avoidance learning, nor hippocampal acetylcholine release in alcohol-preferring rats

Long-term ethanol consumption in humans and laboratory animals is associated with morphological and functional alterations of brain structures involved in cognitive processes. In the present experiments, we assessed whether voluntary long-term consumption of ethanol by alcohol-preferring (sP) rats under free choice condition with water (also) caused alterations in memory performance and hippocampal acetylcholine (ACh) release in vivo. A group of sP rats were offered a 10% v/v ethanol solution in a free choice with water for 36 weeks; controls had only tap water available. After withdrawal of ethanol, rats were tested in one trial passive avoidance test and thereafter were trained in a food-reinforced radial arm maze task for 12 days. One day after the last session in the radial-arm maze, rats were implanted with a microdialysis probe in the dorsal hippocampus and dialysate concentrations of ACh were measured. No significant differences were observed between sP drinking and control rats in retention latencies in the passive avoidance test, in radial arm-maze performance or in basal levels of hippocampal ACh release. These results show that long-term ethanol consumption by sP rats is not associated with cognitive impairments or with alterations in the hippocampal cholinergic function. To the extent that chronic ethanol intoxication can be considered a causal factor in the development of memory and neurochemical alterations, these results suggest that sP rats self-regulate ethanol consumption so as to avoid intoxication. These findings may challenge the notion that sP rat lines can be considered a valid model of human alcoholism.

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.

Effects of alcohol on the synthesis and expression of hypothalamic peptides

Studies aimed at analyzing the deleterious effects of excess alcohol in the brain have revealed structural alterations that are often associated with functional and behavioral disturbances. Among the neuronal damage related to prolonged alcohol exposure, alterations in the synthesizing capabilities and levels of expression of neuroactive peptides have been increasingly reported. Actually, such changes frequently represent the sole repercussion of acute and short-term exposure to ethanol. This review gathers the existing data on the effects of ethanol exposure on the synthesis and expression of hypothalamic peptides. Amid those that can act both as neurotransmitters and neurohormones, we allude to vasopressin, corticotropin-releasing hormone, thyrotropin-releasing hormone and pro-opiomelanocortin and related peptides produced by paraventricular, supraoptic and arcuate neurons. With respect to peptides that act exclusively as neurotransmitters, we address the effects of alcohol on vasoactive intestinal polypeptide, gastrin-releasing peptide, somatostatin and vasopressin synthesized by suprachiasmatic neurons. Hypothalamic neurons that produce peptides that act as neurotransmitters are supposed to be modulated primarily by influences exerted by neuronal afferents, whereas those producing peptides that additionally act as neurohormones are also regulated by peripheral stimuli (e.g., plasma levels of circulating hormones, osmotic challenges). These peculiar features endue the hypothalamus with characteristics that are particularly propitious to enlighten the still cryptic mechanisms underlying the ethanol effects on protein synthesis.

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.

Chronic alcohol consumption and withdrawal do not induce cell death in the suprachiasmatic nucleus, but lead to irreversible depression of peptide immunoreactivity and mRNA levels

There is evidence that chronic ethanol treatment (CET) disrupts the biological rhythms of various brain functions and behaviors. Because the suprachiasmatic nucleus (SCN) is widely recognized as the dominant pacemaker of the circadian system, we have examined the effects of CET and withdrawal on the main morphological features and chemoarchitecture of this hypothalamic nucleus. Groups of rats ethanol-treated for 6 and 12 months were compared with withdrawn rats (ethanol-treated for 6 months and then switched to a normal diet for an additional 6 months) and with groups of age-matched control and pair-fed control rats. The volume and the total number of neurons of the SCN were estimated from conventionally stained material, whereas the total number of astrocytes and of neurons containing vasopressin (AVP), vasoactive intestinal polypeptide (VIP), gastrin-releasing peptide (GRP), and somatostatin (SS) were estimated from immunostained sections. The estimates were obtained using unbiased stereological methods, based on Cavalieri's principle and the optical fractionator. The volume of the SCN and the total number of SCN neurons and astrocytes did not vary among groups. We found, however, that CET induced a significant reduction in the total number of AVP-, VIP-, GRP-, and SS-containing neurons. Withdrawal from alcohol did not reduce but rather augmented the loss of VIP- and GRP-immunoreactive neurons. The CET-induced neurochemical alterations seem to result from a decrease in neuropeptide synthesis, as revealed by the reduction in AVP and VIP mRNA levels demonstrated by in situ hybridization with radioactively labeled 48-mer AVP and 30-mer VIP probes. It is thus possible to conclude that the irreversible CET-induced changes in the neurochemistry of the SCN might underpin the disturbances in circadian rhythms observed after long-term alcohol consumption.

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.

Metabolic mapping of the effects of chronic voluntary ethanol consumption in rats

The 2-[14C]deoxyglucose method was used to examine the effects of chronic, voluntary ethanol consumption on rates of local cerebral glucose utilization (LCGU). LCGU was measured in male Long-Evans rats immediately following the completion of a 60-min schedule-induced polydipsia drinking session. Three groups of animals were examined: animals with a history of ethanol consumption that received ethanol on the test day (ethanol-ethanol), animals with a similar ethanol history that were presented with water on the test day (ethanol-water), and a control group that received water throughout the experiment (water-water). Ethanol consumption on the test day resulted in a highly discrete pattern of metabolic changes, with significant decreases in glucose utilization in the hippocampal complex, habenula, anterior ventral thalamus, and mammillary bodies, whereas increases were observed in the nucleus accumbens and locus coeruleus. Rates of LCGU in the ethanol-water group were increased throughout all regions of the central nervous system examined, indicating that the long-term consumption of moderate ethanol doses that do not produce physical dependence can cause significant changes in functional brain activity.

Piracetam promotes mossy fiber synaptic reorganization in rats withdrawn from alcohol

Prolonged alcohol intake affects the morphology of the hippocampal formation of the rat and the resulting alterations do not reverse after withdrawal. Actually, an increase of the degenerative activity might occur in this condition. This unexpected observation prompted us to test the efficacy of neuronoprotective drugs during withdrawal. Because in a previous study we found that piracetam, a cyclic derivative of GABA, once added during withdrawal impedes hippocampal cell loss, we decided to evaluate the effect of this compound at the synaptic level. Using unbiased stereological techniques, we estimated the total number of contacts between mossy fibers and CA3 pyramids, as well as the volume and the surface area of the respective pre- and postsynaptic compartments. We found that in piracetam-treated withdrawn rats the number of synapses was higher than that observed in nonpiracetam-treated and alcohol-fed animals. The mechanisms leading to the synaptic reorganization took place at the mossy fiber level. The postsynaptic compartment does not seem to participate in the reorganization. It is suggested that the role of piracetam in this process might depend on the protective effect that this compound has upon glutamatergic receptors.

Time scale and extent of neuronal and synaptic loss in the hippocampal formation of malnourished adult rats

We have demonstrated that a prolonged low-protein diet induces neuronal and synaptic loss in the hippocampal formation of the adult rat. Because 6 months of protein deprivation was the shortest period analyzed in the previous investigations, in the present study we have evaluated the length of the treatment period necessary to induce significant changes in the numbers of neurons and synapses. Groups of 2-month-old rats were analyzed: (1) and (2) malnourished for 1 and 3 months with a low-protein diet (8% casein): (3) and (4) age-matched control rats fed with a standard diet. Stereological methods were employed to estimate the total number of granule, hilar, CA3 and CA1 pyramidal cells and the volume of the respective cell layers, the volume of the mossy fiber system and the number and related quantitative features of mossy fiber-CA3 synapses. No differences in the number of cells or synapses were found between 1-month malnourished rats and the respective controls. However, in rats treated for 3 months the total number of granule cells. CA3 and CA1 pyramidal cells was reduced, as was the total number of synapses. These findings indicate that the changes induced by protein deprivation progressively increase during the early phases of treatment and that they are already evident after 3 months of protein deprivation.

Synapse-to-neuron ratio in the lateral geniculate nucleus of rats exposed chronically to ethanol

Effects of chronic ethanol exposure on synapse-to-neuron ratio in the rat lateral geniculate nucleus were investigated. Male Sprague-Dawley rats were exposed to ethanol, using the Lieber-DeCarli liquid diets, for 4 months starting at the age of 5 weeks. Brains were perfusion-fixed, and the region containing the dorsal lateral geniculate nucleus was cut into slabs (500 microns thick) that were epoxy resin-embedded. From each rat, three slabs containing the structure were serially sectioned for electron microscopy. Using the double disector method, the study shows an unaltered synapse-to-neuron ratio in ethanol-treated rats when compared with controls. The findings are in agreement with previous studies on the visual system using the same exposure model. In contrast, a previous study has shown that the synapse-to-neuron ratio in locus ceruleus of ethanol-treated rats is reduced by 50%. Other studies have shown that, whereas the glutamatergic NMDA receptor is very sensitive to ethanol, the kainate/AMPA type of receptor is very much less so. Thus, the difference in ethanol-induced synapse elimination between the two regions may reflect this different sensitivity of the glutamatergic receptors, which are of the kainate/AMPA type in the lateral geniculate nucleus and of the NMDA type in the locus ceruleus.

Structural reorganization in the supraoptic nucleus of withdrawn rats following long-term alcohol consumption

We have recently shown in the supraoptic nucleus (SON) of the rat that prolonged ethanol consumption induces cell degeneration and enlargement of the surviving neurons and of their subcellular organelles. We analyzed the SON of withdrawn rats to evaluate whether it displays any evidence of morphological reorganization following abstinence from ethanol, inasmuch as in this condition the ethanol-induced changes in the plasma levels of neurohormones and plasma osmolality are no longer detectable. A group of 18-month-old withdrawn rats was compared with age-matched, pair-fed control and ethanol-treated rats. To differentiate between the effects of withdrawal and the effects of rehydration, a group of 18-month-old rehydrated rats was also included in this study and compared with age-matched, pair-fed control and dehydrated rats. We estimated the volume of SON, and the total number and mean volume of its neurons. The cross-sectional areas of the vasopressinergic and oxytocinergic populations were also evaluated. At the ultrastructural level, we determined the volumes and surface areas of the rough endoplasmic reticulum and Golgi apparatus, and the volumes of neurosecretory granules and nucleoli. In withdrawn animals, the total number of SON neurons was smaller than in controls, although the neuronal volume was greater. The number of SON neurons did not differ between withdrawn and ethanol-treated rats, despite the reduced volume of SON in the former animals. The decrease of SON volume correlated with and was caused by a reduction in the volume of SON neurons and in the size of the organelles involved in neuro-hormone synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Piracetam impedes hippocampal neuronal loss during withdrawal after chronic alcohol intake

In previous studies we have demonstrated that prolonged ethanol consumption induced hippocampal neuronal loss. In addition, we have shown that withdrawal after chronic alcohol intake augmented such degenerative activity leading to increased neuronal death in all subregions of the hippocampal formation but in the CA3 field. In an attempt to reverse this situation, we tested, during the withdrawal period, the effects of piracetam (2-oxo-1-pyrrolidine acetamide), a cyclic derivative of gamma-aminobutyric acid, as there is previous evidence that it might act as a neuronoprotective agent. The total number of dentate granule, hilar, and CA3 and CA1 pyramidal cells of the hippocampal formation were estimated using unbiased stereological methods. We found out that in animals treated with piracetam the numbers of dentate granule, hilar, and CA1 pyramidal cells were significantly higher than in pure withdrawn animals, and did not differ from those of alcohol-treated rats that did not undergo withdrawal. These data suggest that piracetam treatment impedes, during withdrawal, the pursuing of neuronal degeneration.

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

The specific aim of this study was to evaluate whether the cholingeric innervation of the hippocampal formation is affected by chronic alcohol consumption in the rat. Choline acetyltransferase-immunoreactive fibres and neurons were analysed in both alcohol-fed and control rats using a monoclonal antibody against choline acetyltransferase and quantitative methods. We found a global reduction in the cholinergic plexus, which was more pronounced in the hippocampus proper than in the dentate gyrus. The areal density of choline acetyltransferase immunoreactive neurons was also reduced. Differences from controls in neuronal number were particularly striking in the stratum lacunosum moleculare of the regio superior, which is precisely the zone of the hippocampal formation where choline acetyltransferase immunoreactive neurons are more abundant in controls. In conclusion, our results show that prolonged ethanol consumption leads to a substantial reduction in the cholinergic innervation of the hippocampal formation, as there was a loss of cholinergic fibres and also an apparent loss of hippocampal cholingeric neurons. These findings may help to explain the cognitive dysfunctions observed after chronic alcohol consumption.

Stability of [3H]MK-801 binding sites following chronic ethanol consumption

Previous work has demonstrated that short periods (1-2 weeks) of exposure to ethanol produce an upregulation of the N-methyl-D-aspartate (NMDA) receptor complex in hippocampus; an alteration that appears to be associated with the development of physical dependence, because a return to control levels occurs over a 24- to 48-hr abstinence period. Prolonged periods of chronic ethanol treatment (CET; 4-8 months of treatment) have been shown to produce severe and permanent alterations in the morphological and functional characteristics of hippocampal pyramidal neurons. Several lines of research have demonstrated that the NMDA receptor complex is involved in excitotoxic cell loss during certain pathological states. On the basis of this evidence, we hypothesized that prolonged ethanol exposure would be accompanied by an enduring increase in NMDA receptors and that NMDA receptor binding in cells surviving CET would be altered. To test this hypothesis, we measured the binding characteristics of the NMDA receptor complex in a variety of brain structures following CET. Animals were fed a nutritionally complete, ethanol-containing diet for 28 weeks and then allowed a 48-hr abstinence period. A control group was fed the same diet, except sucrose was isocalorically substituted for ethanol. We first examined the effect of CET on the binding properties of a noncompetitive antagonist to the NMDA receptor channel, [3H]diclozipene ([3H]MK-801). Next, as an indirect examination of NMDA receptor function, we measured the ability of glutamate to stimulate channel opening and thus [3H]MK-801 binding. In all brain structures examined, neither the Kd nor the Bmax of [3H]MK-801 binding to the NMDA receptor was altered following CET. In addition, no effect of treatment was seen on the ability of glutamate to stimulate [3H]MK-801 binding.

The vasopressinergic innervation of the lateral septum of the rat after chronic alcohol consumption and withdrawal

We have recently reported that ethanol ingestion induces morphological changes in the vasopressinergic neurons of the supraoptic nucleus and that withdrawal from alcohol partially reverses these alterations. Since the production of vasopressin is not restricted to the magnocellular neurons of the hypothalamus, we investigated the effects of long-term ethanol intake and withdrawal on the lateral septum, an area heavily innervated by vasopressinergic fibers. Besides, as ethanol leads to a decrease of the plasma levels of testosterone, a hormone which plays a pivotal role in the development and maintenance of the vasopressinergic innervation of the lateral septum, we included groups of alcohol-fed animals submitted to testosterone replacement both in physiological and supraphysiological doses. In ethanol-treated rats there was a marked reduction in the number of vasopressin-immunoreactive fibers in the lateral septum. Following ethanol withdrawal a partial recovery in the number of vasopressin-immunoreactive fibers was observed. In both groups of ethanol + testosterone-treated animals the vasopressinergic innervation was increased when compared to the alcohol-fed group, although a complete reversal was not achieved. Therefore, two mechanisms might be regarded as underlying the impoverishment of the vasopressinergic innervation in the lateral septum after prolonged alcohol consumption: alcohol-induced cell death in the bed nucleus of the stria terminalis, from where these fibers arise, and/or alcohol-induced decrease in testosterone plasma levels.

Long-term effects of intermittent versus continuous ethanol exposure on hippocampal synapses of the rat

The hippocampus is known to be very sensitive to a large spectrum of different neurotoxins including ethanol. Ethanol administered continuously or intermittently may affect the hippocampus in different ways. Intermittent administration of ethanol has many features in common with the low level electrical stimulation protocols which lead to the functional changes associated with the phenomenon of kindling. In this study, the differential effects of intermittent intraperitoneal ethanol injections (3 g/kg twice daily) and continuously administered ethanol in drinking water (20%) on hippocampal synapses in the rat were studied using ethanolic phosphotungstic acid staining and electron microscopy. After 1 month of intermittent exposure a significant reduction (18%) of synapses was seen in the stratum lucidum of the CA3 region. Continuously treated animals showed no significant change over this time despite a higher total ethanol intake. In the dentate gyrus, a compensatory increase in supragranular synaptic number was seen only in continuously treated animals. These findings demonstrate the sensitivity of synapses of the hippocampus to the presence of ethanol and the larger effects of peaking ethanol concentrations compared to more constant levels. These results emphasize the need to consider the differential effects of various types of ethanol consumption also on the human brain.

Reorganization of mossy fiber synapses in male and female hypothyroid rats: a stereological study

Thyroid hormone deficiency has been reported to interfere with synaptogenesis, particularly in those regions of the brain where the neurons display a late and protracted histogenesis, although the extent of the synaptic alterations remains unknown. To provide detailed quantitative data on the effects of hypothyroidism upon synapses, a link of the hippocampal circuitry was selected: the contact between mossy fibers and dendritic excrescences of CA3 pyramidal cells (MF-CA3 synapses). Groups of six male and six female rats aged 30 and 180 days were analyzed separately after being treated as follows: (1) hypothyroid from day 0 until day 30 (30 day old hypothyroid group); (2) hypothyroid from day 0 until day 180 (180 day old hypothyroid group); (3) hypothyroid until day 30 and thenceforth maintained euthyroid (recovery group); and (4) and (5) 30 and 180 day old control groups, respectively. Timm staining, Golgi impregnation, and electron microscopy were employed to estimate the volume of the mossy fiber system, the number and size of mossy fiber boutons, and the number and related features of MF-CA3 synapses. The volume of the mossy fiber system and the number of synaptic boutons were reduced in all experimental groups. The total number of synapses was decreased in 30 day old hypothyroid rats, but did not differ among 180 day old animals. Postsynaptic densities were shorter in hypothyroid and recovery groups than in controls, although the reduction was not as marked in recovery rats as it was in hypothyroid animals. Structural alterations were noted in the pre- and postsynaptic compartments of MF-CA3 synapses of both 180 day old hypothyroid and recovery rats. These changes can be regarded as mechanisms of reorganization as they underlie the compensation for the hypothyroid-induced numerical reduction of synapses observed in 30 day old animals and enable a complete catch-up of their total number. However, synaptic reorganization was not fully achieved, as revealed by the reduction in the size of the synaptic sites in hypothyroid and recovery animals. Finally, we demonstrate that hypothyroidism did not interfere with the sex-related differences of MF-CA3 synapses described in normal rats.

Effects of chronic alcohol consumption and of dehydration on the supraoptic nucleus of adult male and female rats

Ethanol ingestion affects the hypothalamo-neurohypophysial system resulting in increased diuresis, dehydration and hyperosmolality. We studied the supraoptic nucleus, of the hypothalamus, in ethanol-treated rats, to determine if ethanol alone and/or the associated disturbances of water metabolism lead to structural alterations in a nucleus known to play a central role in fluid homeostasis. Groups of male and female rats were ethanol-treated until 12 and 18 months of age and compared with age-matched pair-fed controls. Twelve and 18-month-old control groups and 12-month-old water control groups (rats submitted to chronic dehydration) were also included in this study in an attempt to differentiate between the effects of undernutrition and dehydration/hyperosmolality, and the specific neurotoxic effects of ethanol. We estimated the volume of the supraoptic nucleus and the numerical density of its neurons and calculated the total number of supraoptic neurons. The volume of both supraoptic neurons and neuropil were also estimated. In immunostained material the ratio of vasopressin to oxytocin neurons and the cross-sectional areas of the two neuronal types were evaluated. There was marked neuronal loss in alcohol-treated rats, but the volume of the supraoptic nucleus was increased. The increase in the volume of the supraoptic nucleus correlated with and was due to increases in the volume was particularly marked for vasopressin neurons. No significant differences were found between controls and pair-fed controls in any of the parameters investigated. In water control rats, the volume of the supraoptic nucleus and of the supraoptic neurons and neuropil was also greater than in pair-fed controls. However, the variations found were not as marked as in ethanol-treated rats and there was no cell loss. These findings reveal, for the first time, that chronic ethanol consumption affects the morphology of supraoptic neurons and neuropil and, consequently, the structure of the entire supraoptic nucleus. Moreover, this study supports the view that ethanol has direct neurotoxic effects on supraoptic neurons because the alterations that occur are not mimicked in animals in which water metabolism alone is disturbed.

Effects of chronic alcohol consumption and withdrawal on the somatostatin-immunoreactive neurons of the rat hippocampal dentate hilus

Previous studies have demonstrated that the dentate granule and the CA3 pyramidal cells of the rat hippocampal formation are neuronal populations vulnerable to the toxic effects of ethanol. It also has been shown that the resulting alterations do not end after withdrawal from ethanol. As the neurons in the dentate hilus are heavily interconnected with the dentate granule cells, the authors decided to examine the fate of the hilar neurons after chronic alcohol consumption and withdrawal, inasmuch as the hilar somatostatin-immunoreactive (SS-I) neurons were found to be sensitive to cerebral ischemia and to seizures. The following groups of adult rats were studied: (1) alcohol-fed for 6 and 12 months; (2) alcohol-fed for 6 months and then switched to water for a further 6 months; (3) pair-fed controls; and (4) controls fed ad libitum. The authors determined the numerical density of hilar neurons and the number of its SS-I subpopulation. These were found to be significantly reduced in both the alcohol-fed and withdrawal groups when compared with the respective age-matched controls. The consequent loss of the integrative action of the hilar neurons, including the SS-Is, could explain some of the alcohol-related functional deficits as well as their persistence after withdrawal.

Decreased synapse-to-neuron ratio in rat locus ceruleus following chronic ethanol feeding

Effects of chronic ethanol exposure on the synapse-to-neuron ratio of rat locus ceruleus were investigated. Male Sprague-Dawley rats were given an ethanol-containing liquid diet for 4 months starting at an age of 5 weeks. Littermates, given isocaloric amounts of an ethanol-free diet, served as control. The animals were perfusion fixed using a mixture of glutaraldehyde and paraformaldehyde. Synapse-to-neuron ratio was estimated by the double disector method and calculated from (Ns/A) x (Nsec -1) / (Nn/A) where Ns/A is the number of synapses per unit area estimated in a disector with a height of on section and Nsec -1 is height of the disector, i.e., the number of sections, used for estimating the number of neurons per area (Nn/A). The mean estimated synapse-to-neuron ratio was 2046 +/- 544 (SD) in ethanol-fed rats and 4291 +/- 1171 (SD) in control rats. The difference is statistically significant (p < 0.05). The finding may be of relevance for understanding the development of abuse, tolerance, drug dependence, and abstinence reactions.

Effect of chronic ethanol on the septohippocampal system: a role for neurotrophic factors?

The mechanisms by which chronic ethanol exposure produces neuronal damage have not been established. Potentially ethanol may reduce normal neurotrophic influences necessary for neuronal survival, growth, and function. We hypothesized that chronic ethanol exposure might produce a decrease in the synthesis, availability, upregulation, delivery, and/or the biological activity of normally occurring neurotrophic factors, or may alter the capacity of target neurons to respond to these factors. The available evidence leading to this hypothesis and supporting data from our laboratory are discussed.

Structural changes in the hippocampal formation after long-term alcohol consumption and withdrawal in the rat

The effects of long-term alcohol consumption and withdrawal upon the structure of the rat hippocampal formation were studied by applying morphometric methods to material processed for light and electron microscopy. The somatostatinergic neurons of the hilus were also studied. Groups of 6 rats were treated as follows: (a) given alcohol for 6, 12 and 18 months; (b) paired controls; and (c) rats switched to a normal diet in the 6 months after 6 and 12 months of alcohol intake. A progressive loss of hippocampal neurons after chronic alcohol consumption was found. The loss was aggravated during withdrawal from alcohol, with the exception of the hilar cells. The dendrites of granule cells from the alcohol-treated rats displayed signs of regrowing, but they did not do so in rats withdrawn from alcohol. The synapses between mossy fibre terminals and CA3 dendrites appear to be rather resistant to alcohol insult, and evidence of morphological plasticity was found in withdrawn rats. If an homology can be established between humans and rodents then the changes observed in alcohol-fed rats can be regarded as underpinning some of the functional and behavioural alterations depicted under these circumstances. The peculiar changes found in some nerve cell populations after withdrawal of alcohol could be related to the deficient or incomplete functional recovery often seen after abstinence from alcohol.

Selective vulnerability of the hippocampal pyramidal neurons to hypothyroidism in male and female rats

Thyroid hormone deficiency has long been considered to affect profoundly such cognitive functions as learning and memory, which are known to depend on the structural integrity of the hippocampal formation. Since we previously found that the number of granule cells of the dentate gyrus is reduced in hypothyroid animals, we decided to extend our observations to the pyramidal cells of the hippocampus in order to gain further insight into the effects of hypothyroidism upon the other neuronal links of the hippocampal trisynaptic circuitry, inasmuch as CA1 neurons are known to be particularly vulnerable to aggressive agents. Groups of 6 male and 6 female rats aged 30 and 180 days were analysed separately after being treated as follows: (1) hypothyroid from day 0 until day 30 (30-day-old hypothyroid group); (2) respective 30-day-old control; (3) hypothyroid from day 0 until day 180 (180-day-old hypothyroid group); (4) hypothyroid until day 30 and thenceforth maintained euthyroid (recovery group); (5) hypothyroid since day 30 (adult hypothyroid group); and (6) respective 180-day-old control. The volume of the pyramidal cell layer of the CA1 and CA3 regions and the numerical density of the respective neurons were evaluated, thereby allowing us to estimate the total number of pyramidal cells in each hippocampal region. The areal density and the mean nuclear volume of CA1 and CA3 pyramidal cells were also estimated. In the CA3 region, we found that hypothyroidism, whatever its duration and time of onset, induces a reduction in the volume of the pyramidal cell layer and a parallel increase in the numerical density of its neurons, without interfering with the total number of pyramidal cells. Conversely, in the CA1 region, thyroid hormone deficiency started either neonatally or during maturity was found to lead to a decrease in the total number of pyramidal cells. Reductions ranging between 14.2 and 22.5% were found in 30 and 180-day-old hypothyroid groups. The reestablishment of a euthyroid state did not ameliorate the referred neuronal loss. The present results support the view that hypothyroidism induces small alterations in the structural organization of the hippocampal CA3 region, contrary to what happens in CA1 in which neuronal death occurs. Furthermore, the data presented herein demonstrate that the total number of CA1 pyramidal cells displays sexual dimorphism that is not affected by thyroid hormone manipulations.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of GM1 ganglioside upon neuronal degeneration during withdrawal from alcohol

In previous studies we demonstrated that chronic alcohol consumption induced hippocampal cell and synapse loss in offset with an increase in the length of granule cell dendrites. In addition we observed that withdrawal after long periods of alcohol intake worsened the degenerative processes and that dendritic alterations were no longer apparent. In an attempt to reverse these structural changes we tested the action of GM1 ganglioside during the withdrawal period as there is evidence that GM1 may enhance neuronal recovery after different kinds of brain lesions. Cell and synaptic quantifications were performed and the branching pattern of the granule cell dendritic arborizations was analysed. The number of dentate granule and CA3 pyramidal cells from GM1-treated animals was found not to be significantly different from that of the alcohol-treated and withdrawal groups. No quantitative changes were found in the number of mossy fiber-CA3 pyramidal cell synapses when the aforementioned groups were compared. Whether the lack of effectiveness of GM1 can be related to the model employed or not is thoroughly discussed.

Long-term low-protein diet reduces the number of hippocampal mossy fiber synapses

Previously we have reported a loss of the dentate granule cells and hippocampal CA3 pyramidal cells in adult animals after lengthy periods of low-protein diet. In this study we examined the effects of this cell loss upon the synaptic connections between the granule cell axons (the mossy fibers) and CA3 pyramidal cell dendrites. Three groups of five rats each were given a low-casein (8%) diet for 6, 12, and 18 months, respectively, and the results of the ultrastructural morphometric analysis compared with similarly processed control rats kept on a control diet. The numerical density of synapses was decreased in undernourished rats and the fraction of the mossy fiber terminal membrane occupied by synaptic specializations was reduced. It can be inferred that the synaptic connectivity pattern between mossy fiber terminals and CA3 dendrites is altered due to a reduction in the number of contacts. Besides, as the synapses of low-protein-treated animals do not display any increase in the length of their active zones, evidence is not provided for the existence of morphological synaptic plasticity, contrary to what has been recently described in other experimental circumstances.

Nucleus basalis magnocellularis lesions impair mossy fiber system in rat hippocampus: a quantitative histochemical and ultrastructural study

Lesions of the nucleus basalis magnocellularis (NBM) cause depletion of choline acetyltransferase (ChAT) in the cerebral cortex and behavioral changes consisting of impaired ability to learn avoidance tasks. Since hippocampal mossy fibers (MF) are involved in the elaboration of passive avoidance responses, we analyzed MF by means of Timm's histochemical technique and electron microscopy, to find out whether monolateral lesions of NBM had any effect on MF system. NBM-lesioned rats, 3 weeks after lesioning, showed a significant and progressive decrease in the density of Timm staining as well as significant changes of the morphology of synapic boutons of the MF. These results suggest that, although NBM does not send direct projections to the hippocampus, lesions of this nucleus may have a neurodegenerative effect on the intrahippocampal pathway involved in avoidance responses.

Metric analysis of hippocampal granule cell dendritic trees after alcohol withdrawal in rats

It was previously demonstrated that after prolonged alcohol consumption, dendrites might display either degenerative or plastic changes according to the central nervous system areas studied. Furthermore, and rather unexpectedly, we also found that withdrawal from alcohol led to a decrease of the relative number of granule cells in the fascia dentata. Thus, it seemed worthwhile to quantify, using a semiautomatic measuring system, the dendritic arborizations of hippocampal granule cells of rats alcohol-fed for 12 months followed by 6 months of abstinence and compare the results with age-matched control and alcohol-fed groups. The results indicate smaller dendritic trees in the abstinent group when compared with the higher values of the dendritic parameters found in alcohol-fed rats.