Effects of chronic ethanol administration on acetylcholinesterase activity in the somatosensory cortex and basal forebrain of the rat

Chronic Ethanol Exposure Potentiates Cholinergic Neurotransmission in the Basolateral Amygdala

Chronic intermittent ethanol (CIE) exposure dysregulates glutamatergic and GABAergic neurotransmission, facilitating basolateral amygdala (BLA) pyramidal neuron hyperexcitability and the expression of anxiety during withdrawal. It is unknown whether ethanol-induced alterations in nucleus basalis magnocellularis (NBM) cholinergic projections to the BLA mediate anxiety-related behaviors through direct modulation of GABA and glutamate afferents. Following 10 days of CIE exposure and 24 h of withdrawal, we recorded GABAergic and glutamatergic synaptic responses in BLA pyramidal neurons with electrophysiology, assessed total protein expression of cholinergic markers, and quantified acetylcholine and choline concentrations using a colorimetric assay. We measured α₇ nicotinic acetylcholine receptor (nAChR) dependent modulation of presynaptic function at distinct inputs in AIR- and CIE-exposed BLA coronal slices as a functional read-out of cholinergic neurotransmission. CIE/withdrawal upregulates the endogenous activity of α₇ nAChRs, facilitating release at both GABAergic' local' interneuron and glutamatergic synaptic responses to stria terminalis (ST) stimulation, with no effect at GABAergic lateral paracapsular cells (LPCs). CIE caused a three-fold increase in BLA acetylcholine concentration, with no changes in α₇ nAChR or cholinergic marker expression. These data illustrate that α₇ nAChR-dependent changes in presynaptic function serve as a proxy for CIE-dependent alterations in synaptic acetylcholine levels. Thus, cholinergic projections appear to mediate CIE-induced alterations at GABA/glutamate inputs.

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.

SPECT imaging of nicotinic acetylcholine receptors in nonsmoking heavy alcohol drinking individuals

BACKGROUND

The high rate of comorbidity of tobacco smoking with alcohol drinking suggests common neural substrates mediate the two addictive disorders. The beta(2)*-containing nicotinic acetylcholine receptor (beta(2)*-nAChR) has recently emerged as a prime candidate because some alpha and beta subunit genes have been linked to alcohol consumption and alcohol use behaviors. We hypothesized that beta(2)*-nAChR availability would be altered by alcohol in heavy drinking nonsmokers.

METHODS

Eleven heavy drinking (mean age 39.6+/-12.1 years) and 11 age and sex-matched control (mean age 40.8+/-14.1 years) nonsmokers were imaged using [(123)I]5-IA-85380 ([(123)I]5-IA) single photon emission computed tomography (SPECT). Heavy alcohol drinkers drank varied amounts of alcohol (70-428/month) to facilitate exploratory linear analyses of the possible effects of alcohol.

RESULTS

Heavy drinkers consumed on average 9.1+/-7.3 drinks/occasion; whereas controls drank 1.2+/-0.9 drinks/occasion. Heavy drinkers were imaged 2.0+/-1.6 days after last alcoholic beverage. Overall, there were no significant differences in beta(2)*-nAChR availability between the heavy drinking and control nonsmokers. Exploratory analyses of other factors that may be uniquely regulated by alcohol suggested no effects of age, number of alcohol drinks, years drinking, severity of drinking, craving or withdrawal.

CONCLUSIONS

These preliminary analyses do not suggest a decrease in receptor availability in heavy drinking nonsmokers as compared to control nonsmokers. However, a larger study is warranted to explore effects of heavy alcohol drinking on other variables, such as sex, smoking, and genetic make up.

Chronic ethanol consumption in rats produces residual increases in anxiety 4 months after withdrawal

The present study investigated the long-term effects of ethanol consumption in rats. Subjects were maintained on either an ethanol (alcohol) (2.7-6.7%, v/v) or an isocaloric liquid control diet for 26 consecutive days (M=13.7 g/kg/day). Testing for working memory was conducted in a Morris water maze (2 trials/day for 8 days) and commenced after either a short (19 days) or long (120 days) abstinence period. This was followed by assessment of 72 h retention of passive avoidance. Animals were killed either 41 (short abstinence) or 152 days (long abstinence) post-ethanol and their brains stained with cresyl violet. Assessments of dorsal-ventral and medial-lateral cortical vertices were measured in sections derived from eight coronal planes extending +4.20 to -4.16 mm from Bregma. Results indicated that subjects in the ethanol/long abstinence group exhibited increased state anxiety due to their propensity to be thigmotaxtic (i.e., wall-hugging) in the water maze. Unfortunately, such a swim pattern precluded assessment of working memory in our subjects. No evidence of ethanol-induced memory decrements were observed on retention of passive avoidance. There was some evidence that animals in the ethanol/long abstinent group suffered cortical thinning and slight compression of the CA1 layer within the hippocampus, although age might have contributed to the former effect. It was concluded that chronic ethanol consumption increases anxiety even after an extended period of withdrawal and may conspire with age to affect cortical integrity.

Neurotrophin ligand-receptor systems in somatosensory cortex of adult rat are affected by repeated episodes of ethanol

Ethanol exposure profoundly affects learning and memory and neural plasticity. Key players underlying these functions are neurotrophins. The present study explored the effects of ethanol on the distribution of neurotrophins in the cerebral cortex of the adult rat. Age- and weight-matched pairs of adult male, Long-Evans rats were fed a liquid, ethanol-containing (6.7% v/v) diet or pair-fed an isocaloric control diet three consecutive days per week for 6, 12, 18, or 24 weeks. Brains were processed immunohistochemically for nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) expression and for the expression of three neurotrophin receptors, p75, trkA, and trkB. Total numbers of immunolabeled neurons in specific layers of somatosensory cortex of ethanol- and control-fed animals were determined stereologically. Ethanol exposure induced an increase in the numbers of NGF- or BDNF-expressing neurons and in neurotrophin content per somata. These changes were (a) time and (b) laminar dependent. In contrast, the number of receptor-expressing neurons did not change due to ethanol exposure or to length of time on the ethanol diet. Thus, ethanol induces the recruitment of cortical neurons to express neurotrophins and an increase in the amount of neurotrophin expression per neuron.

THIS ARTICLE HAS BEEN RETRACTED: Functional nerve growth factor and trkA autocrine/paracrine circuits in adult rat cortex are revealed by episodic ethanol exposure and withdrawal

The hypothesis tested is that cortical neurotrophins communicate through an inducible autocrine/paracrine mechanism. As ethanol (Et) can induce cortical nerve growth factor (NGF) expression, adult rats were challenged with Et on three consecutive days per week for 6 weeks. The focus of the study was layer V, the chief repository of receptor-expressing neuronal cell bodies. Brains were collected immediately after the sixth Et exposure or 72 h later [i.e., following withdrawal (WD)]. Double-label in situ hybridization-immunohistochemistry studies showed that many neuronal somata co-expressed NGF mRNA with NGF, trkA, or phosphorylated trk (p-trk), essential components of an inducible autocrine system. The frequencies of co-labeling were affected by neither Et nor WD. On the contrary, Et increased the number of NGF mRNA-expressing neurons and the amount of NGF mRNA expressed per cell. Et also increased total cortical concentration of NGF protein, the number of layer V neurons expressing trkA transcript, the amount of trkA mRNA expressed per neuron, and trkA phosphorylation. Following WD, the frequency of NGF-mRNA-expressing cells increased, although transcript and protein content fell. WD induced an increase in trkA mRNA and protein expression, however, p-trk expression was unaffected. Thus, Et treatment reveals that layer V has inducible autocrine/paracrine and anterograde neurotrophin systems. WD unveils the dynamism and recruitability of these systems.

Changes in cholinergic function in the frontal cortex and hippocampus of rat exposed to ethanol and acetaldehyde

Our previous microdialysis study demonstrated that both ethanol (EtOH) and acetaldehyde (ACe) decrease in vivo acetylcholine (ACh) release in the medial frontal cortex of freely moving rats. To better understand the mechanisms of EtOH and ACe's effects on the cholinergic system in the brain, choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) expression was examined at 40 and 240 min after a dose of EtOH (1 g/kg) in the rat frontal cortex and hippocampus. The control group was treated with 0.9% saline, and other groups received EtOH or cyanamide (CY, 50 mg/kg, a potent aldehyde dehydrogenase inhibitor) and 60 min later by EtOH intraperitoneally. Reverse-transcription polymerase chain reaction (RT-PCR) analysis revealed that ChAT mRNA levels were decreased by 72.8% and 71.6% in the EtOH and CY+EtOH groups, respectively, at 40 min after EtOH injection compared with saline in the frontal cortex. The hippocampal ChAT levels were reduced by 76.5% and 53.0% in the EtOH and CY+EtOH groups, respectively, at this time. CY+EtOH-induced depletion in ChAT mRNA levels was markedly higher than EtOH in the hippocampus. A similar decrease pattern of ChAT was observed at protein levels as determined by Western blot, but the reduced ChAT levels were significantly higher in the CY+EtOH group as compared with the EtOH group both in the frontal cortex and hippocampus. At 240 min after EtOH injection, the EtOH group had no effect on ChAT at mRNA levels, as compared with saline, whereas CY+EtOH group induced a significant decrease in ChAT mRNA expression to 62.0% and 65.5% in the frontal cortex and hippocampus, respectively. These data were consistent with the results of the Western blot analysis. AChE expression at mRNA levels was not changed at either 40 or 240 min after EtOH dosing in either of these groups in the frontal cortex and hippocampus. Within 40 and 240 min, a statistically significant difference in ChAT expression at mRNA and protein levels was found in the EtOH and CY+EtOH groups both in the frontal cortex and hippocampus. The data obtained from this study demonstrate that EtOH and ACe concentrations decreased ChAT expression at 40 and 240 min after EtOH administration in the frontal cortex and hippocampus, and this result suggests that reduced ChAT expression is strongly related to a decrease in ACh release in the rat brain.

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.

The effects of chronic ethanol consumption and withdrawal on passive avoidance task and serum cholinesterase level in rats

The effects of chronic ethanol consumption and ethanol withdrawal on serum cholinesterase (ChE) activity and passive avoidance task in rats were investigated. Ethanol was administered to rats by a modified liquid diet with 4.8% (v/v) ethanol for 3 days followed by 25 days on a liquid diet in which the ethanol concentration was increased to 7.2%. Control rats were pair fed with an isocaloric liquid diet not containing ethanol. ChE activity and blood ethanol concentration were measured at the end of the 4.8% ethanol consumption and after 25 days of ethanol (7.2%) feeding and, just before and 24th and 72nd h of ethanol withdrawal period. Passive avoidance acquisition was evaluated for 150 s (cut-off time) in three individual groups of ethanol-administered, ethanol withdrawn (24th and 72nd h of withdrawal) and control rats. Locomotor activity of the rats was also measured and evaluated. The daily ethanol consumption of the rats ranged from 11.5 to 14.9 g/kg. ChE activities of the ethanol feeding rats were significantly increased as compared to control rats at the 3rd (4.8% ethanol) and 25th days of chronic ethanol (7.2%) consumption and 24th h of ethanol withdrawal. It returned to control values at the 72nd h of the withdrawal. Blood ethanol levels were measured as 200 and 2.2 mg/dl at just before ethanol withdrawal and 24th h of ethanol withdrawal, respectively. Both chronic ethanol consumption and late period of ethanol withdrawal produced some significant decreases in passive avoidance latency of the rats. Our results suggest that chronic ethanol consumption and late period of ethanol withdrawal may be related to impairment of passive avoidance task in rats. In addition, serum ChE levels do not seem to be involved in impairment of cognitive functions in ethanol dependent-rats.

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.

Repeated episodic exposure to ethanol affects neurotrophin content in the forebrain of the mature rat

Chronic exposure to ethanol can cause deficits in learning and memory. It has been suggested that withdrawal is potentially more damaging than the ethanol exposure per se. Therefore, we explored the effect of repeated episodic exposure to ethanol on key regulators of cortical activity, the neurotrophins. Rats were exposed to ethanol via a liquid diet for 3 days per week for 6-24 weeks. Control rats were pair-fed an isocaloric liquid diet or ad libitum fed chow and water. The concentrations of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) were determined using enzyme-linked immunosorbant assays (ELISAs). Five telencephalic structures were examined: parietal cortex, entorhinal cortex, hippocampus, the basal nucleus, and the septal nuclei. All five areas expressed each of the three neurotrophins; BDNF was most abundant and NGF the least. The parietal cortex was susceptible to ethanol exposure, NGF and BDNF content increased, and NT-3 content fell, whereas no changes were detectable in the entorhinal cortex. In the hippocampus, the amount all three neurotrophins increased following episodic ethanol exposure. Neurotrophin content in the two segments of the basal forebrain was affected; NGF and NT-3 content in the basal forebrain was reduced and NGF and BDNF content in the septal nuclei was increased by ethanol exposure. In many cases where ethanol had an effect, the change was transient so that by 24 weeks of episodic exposure, no significant changes were evident. Thus, the effects of ethanol are site- and time-dependent. This pattern differs from changes caused by chronic ethanol exposure, hence, neurotrophins must be vulnerable to the effects of withdrawal. Furthermore, the ethanol-induced changes do not appear to fit a model consistent with retrograde regulation, rather they suggest that neurotrophins act through autocrine/paracrine systems.

Residual behavioral and neuroanatomical effects of short-term chronic ethanol consumption in rats

The residual effects of short-term chronic ethanol consumption were investigated in rats maintained on an ethanol liquid diet for 26 consecutive days (mean intake = 16.1 g/kg/day). Animals were assessed for spontaneous motor activity (12 days post-ethanol), spatial working memory (17 days post-ethanol), spatial reference memory (184 days post-ethanol), and retention of passive avoidance (201 days post-ethanol). Measurements of brain weights and cortical thickness vertices within the dorsomedial and ventrolateral cortex of eight coronal planes were determined 260 days post-ethanol. Two-dimensional cell profile densities within six coronal planes and within CA1 region of the hippocampus were also obtained, along with the total volumetric measurement of the hippocampus proper. Results indicated between group differences when subjects were assessed on working memory with ethanol-treated animals exhibiting longer escape latencies in a Morris water maze, an effect partially attributed to the perseverance of ethanol-treated animals in exhibiting thigmotaxicity. No other ethanol-related behavioral impairment was noted. Neuroanatomically, ethanol-treated rats had thinner cortical mantles (6.3% and 6.6% reductions) within the frontoparietal cortex and had lower two-dimensional cell profile densities within the most caudal cortical region studied. Interestingly, control animals with thicker cortical mantles tended to perform better on the working memory task, whereas the opposite was true for ethanol-treated subjects. These data led to the conclusion that chronic ethanol consumption of a relatively short duration produces working memory impairments, albeit mild, that are partially related to an inability to abandon ineffectual behavioral strategies, and also produces neuroanatomical alterations within the cortex.

Chronic exposure to ethanol alters neurotrophin content in the basal forebrain-cortex system in the mature rat: Effects on autocrine-paracrine mechanisms

Neurotrophins are broadly expressed in the mammalian forebrain: notably in cerebral cortex and the basal forebrain (e.g., the septal and basal nuclei). These factors promote neuronal survival and plasticity, and have been implicated as key players in learning and memory. Chronic exposure to ethanol causes learning and memory deficits. We tested the hypothesis that ethanol affects neurotrophin expression and predicted that these changes would be consistent with alterations in retrograde or autocrine/paracrine systems. Mature rats were fed a liquid diet containing ethanol daily for 8 or 24 weeks. Weight-matched controls were pair-fed an isocaloric, isonutritive diet. Proteins from five structures (parietal and entorhinal cortices, hippocampus, and the basal and septal nuclei) were studied. ELISAs were used to determine the concentration of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3). All three neurotrophins were detected in each structure examined. Ethanol treatment significantly (p < 0.05) affected neurotrophin expression in time- and space-dependent manners. NGF content was generally depressed by ethanol exposure, whereas NT-3 content increased. BDNF concentration was differentially affected by ethanol: it increased in the parietal cortex and the basal forebrain and decreased in the hippocampus. With the exception of NGF in the septohippocampal system, the ethanol-induced changes in connected structures were inconsistent with changes that would be predicted from a retrograde model. Thus, the present data (a) support the concept that neurotrophins act through a nonretrograde system (i.e., a local autocrine/paracrine system), and (b) that chronic exposure to ethanol disrupts these regulatory mechanisms.

Theory for normal and impaired experience-dependent plasticity in neocortex of adult rats

We model experience-dependent plasticity in the cortical representation of whiskers (the barrel cortex) in normal adult rats, and in adult rats that were prenatally exposed to alcohol. Prenatal exposure to alcohol (PAE) caused marked deficits in experience-dependent plasticity in a cortical barrel-column. Cortical plasticity was induced by trimming all whiskers on one side of the face except two. This manipulation produces high activity from the intact whiskers that contrasts with low activity from the cut whiskers while avoiding any nerve damage. By a computational model, we show that the evolution of neuronal responses in a single barrel-column after this sensory bias is consistent with the synaptic modifications that follow the rules of the Bienenstock, Cooper, and Munro (BCM) theory. The BCM theory postulates that a neuron possesses a moving synaptic modification threshold, theta(M), that dictates whether the neuron's activity at any given instant will lead to strengthening or weakening of its input synapses. The current value of theta(M) changes proportionally to the square of the neuron's activity averaged over some recent past. In the model of alcohol impaired cortex, the effective theta(M) has been set to a level unattainable by the depressed levels of cortical activity leading to "impaired" synaptic plasticity that is consistent with experimental findings. Based on experimental and computational results, we discuss how elevated theta(M) may be related to (i) reduced levels of neurotransmitters modulating plasticity, (ii) abnormally low expression of N-methyl-d-aspartate receptors (NMDARs), and (iii) the membrane translocation of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) in adult rat cortex subjected to prenatal alcohol exposure.

Effects of combined exposure to aluminium and ethanol on food intake, motor behaviour and a few biochemical parameters in pubertal rats

Combined daily administration of aluminium chloride (260 mg/kg, oral) and ethanol (2 g/kg, oral), to pubertal male rats for 30 days was found to significantly decrease food intake, body weight gain and serum protein levels. Spontaneous motor activity and rota-rod motor coordination were also significantly impaired. Acetylcholinesterase activity was significantly diminished in the cerebrum and cerebellum. The results obtained in the present study are suggestive of a potentiation of cholinotoxic effects of the two compounds when administered together. Thus, when combined, ethanol may increase pubertal rat's susceptibility to the toxic effects of aluminium.

Changes of acetylcholinesterase activity in brain areas and liver of sucrose- and ethanol-fed rats

The effects of chronic ethanol or sucrose administration to rats on acetylcholinesterase from brain and liver were investigated. Membrane-bound and soluble acetylcholinesterase activities were determined in fractions prepared by centrifugation. The thermal stability and the effects of temperature and different types of alcohols on acetylcholinesterase activity were also studied. Membrane-bound acetylcholinesterase activity increased (p < 0.01) in the liver after chronic ethanol administration, whereas no differences among groups in the encephalic areas, except in the brain stem soluble form, were found. Membrane-bound acetylcholinesterase from the ethanol- and sucrose-treated groups was more stable at the different temperatures assayed between 10 and 50 degrees C than that corresponding to the control group. Non-linear Arrhenius plots were obtained with preparations of membrane-bound acetylcholinesterase from rat liver, with discontinuities at 30 degrees C (control or sucrose groups) or 34-35 degrees C (alcohol group). Assays made with membrane-bound or soluble enzyme from brain showed linear Arrhenius plots in all groups studied. The inhibitory effects of increasing concentrations of ethanol, n-propanol and n-butanol on acetylcholinesterase preparations from forebrain, cerebellum, brain stem and liver of the three experimental groups (control, sucrose-fed and ethanol-fed) were very similar. However, n-butanol displayed a biphasic action on particulate or soluble preparations of rat forebrain. n-butanol inhibited (competitive inhibition) at higher concentrations (250-500 mM), while at lower concentrations (10-25 mM), the alcohol inhibited at low substrate concentrations but activated at high substrate concentration. These results suggest that the liver is more affected by ethanol than the brain. Moreover, the lipid composition of membranes is probably modified by ethanol or sucrose ingestion and this would affect membrane fluidity and consequently the behaviour of acetylcholinesterase.

Effect of enriched environment rearing on impairments in cortical excitability and plasticity after prenatal alcohol exposure

The daily ingestion of alcohol by pregnant mammals exposes the fetal brain to varying levels of alcohol through the placental circulation. Here we focus on the lingering impact on cortical function of 6.5% alcohol administered in a liquid diet to pregnant rats throughout gestation, followed by 3 alcohol-free months before brain function was analyzed in the offspring. Both spontaneous activity of the neurons in the barrel cortex and the level of response to test stimuli applied to the whiskers remained reduced by >75% after alcohol exposure. Whisker pairing, a type of cortical plasticity induced by trimming all but two whiskers in adult rats, occurred in <1 d in controls, but required 14 d to reach significance after alcohol exposure. These long-term neuronal deficits are present in all layers of cortex and affect neurons with both fast and slow action potentials. Plasticity is first seen in the total sample of neurons at 14 d; however, by 7 d, neurons in layer II/III already show plasticity, with no change in layer IV neurons, and a reverse shift occurs toward the inactive whisker in layer V neurons. Analysis of NMDA receptor subunits shows a persistent, approximately 30-50% reduction of NR1, NR2A, and NR2B subunits at postnatal day 90 in the barrel field cortex. Exposing the prenatal alcohol-exposed rats to enriched rearing conditions significantly improves all measured cortical functions but does not restore normal values. The results predict that combinations of interventions will be necessary to completely restore cortical function after exposure of the fetal brain to alcohol.

Effects of prenatal exposure to ethanol on systems matching: the number of neurons in the ventrobasal thalamic nucleus of the mature rat

Following prenatal exposure to ethanol, rats have a 1/3 fewer neurons in the second order (principal sensory nucleus of the trigeminal nerve) and fourth order neurons (somatosensory cortex) of the trigeminal-somatosensory pathway than do controls. Based on the numerical matching hypothesis, we predict that the number of third-order neurons (in the ventrobasal nucleus of the thalamus; VB) also will show a similar effect of prenatal ethanol exposure. Stereological methods were used to determine the total number of neurons in the VB on postnatal day 30. Surprisingly, prenatal exposure to ethanol had no effect on the VB volume or on the number of VB neurons. Thus, prenatal exposure to ethanol induces numerical imbalances within the trigeminal-somatosensory system.

Effects of NMDA receptor blockade in the developing rat somatosensory cortex on the expression of the glia-derived extracellular matrix glycoprotein tenascin-C

The patterning of synaptic connections during development is thought to be influenced by the correlation of neuronal impulse activity. N-methyl-D-aspartate (NMDA) receptors have been implicated in the reorganization of thalamocortical afferents in the visual system. The topographic mapping of the periphery of sensory systems onto the somatosensory cortex in the whisker-barrel field of rodents has served as another important paradigm in the study of extrinsic influences on synaptic rearrangements. In a search for the molecular cues that may contribute to synaptic plasticity, we have investigated the distribution of the glia-derived extracellular matrix glycoprotein tenascin-C, which is highly expressed during the formation of the barrel field map around birth and delineates the boundaries between barrel fields after segregation of afferent inputs. Here we show that systemic and local application of NMDA receptor antagonists at postnatal day 2 inhibited the down-regulation of tenascin mRNA and protein by postnatal day 6 and prevented the appearance of tenascin-positive barrel field boundaries. Furthermore, barrels were not distinguishable by Nissl staining, and segregation of thalamocortical afferents as monitored by anterograde Dil tracing and acetylcholinesterase histochemistry was not complete. These observations indicate that expression of tenascin-C and segregation of afferent inputs are modified by NMDA receptor-dependent neuronal activity.