Electrophysiological actions of acetate, a metabolite of ethanol, on hippocampal dentate granule neurons: interactions with adenosine

Ethanol, neurosteroids and cellular stress responses: Impact on central nervous system toxicity, inflammation and autophagy

Alcohol intake can impair brain function, in addition to other organs such as the liver and kidney. In the brain ethanol can be detrimental to memory formation, through inducing the integrated stress response/endoplasmic reticulum stress/unfolded protein response and the molecular mechanisms linking stress to other events such as NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammation and autophagy. This literature review aims to provide an overview of our current understanding of the molecular mechanisms involved in ethanol-induced damage with endoplasmic reticulum stress, integrated stress response, NLRP3 inflammation and autophagy, while discussing the impact of neurosteroids and oxysterols, including allopregnanolone, 25-hydroxycholesterol and 24S-hydroxycholesterol, on the central nervous system.

Alcohol metabolite acetic acid activates BK channels in a pH-dependent manner and decreases calcium oscillations and exocytosis of secretory granules in rat pituitary GH3 cells

Acetaldehyde and acetic acid/acetate, the active metabolites of alcohol (ethanol, EtOH), generate actions of their own ranging from behavioral, physiological, to pathological/cancerogenic effects. EtOH and acetaldehyde have been studied to some depth, whereas the effects of acetic acid have been less well explored. In this study, we investigated the effect of acetic acid on big conductance calcium-activated potassium (BK) channels present in GH3 rat pituitary tumor cells in more detail. In whole cell voltage clamp recordings, extracellular application of acetic acid increased total outward currents in a dose-dependent manner. This effect was prevented after the application of the specific BK channel blocker paxilline. Acetic acid action was pH-dependent-in whole cell current and single BK channel recordings, open probability (Po) was significantly increased by extracellular pH reduction and decreased by neutral or base pH. Acetic acid hyperpolarized the membrane potential, whereas acidic physiological solution had a depolarizing effect. Moreover, acetic acid reduced calcium (Ca2+) oscillations and exocytosis of growth hormone contained secretory granules from GH3 cells. These effects were partially prevented by BK inhibitors-tetraethylammonium or paxillin. In conclusion, our experiments indicate that acetic acid activates BK channels in GH3 cells which eventually contribute to acetic acid-induced membrane hyperpolarization, cessation of Ca2+ oscillations, and decrease of growth hormone release.

Brain metabolism modulates neuronal excitability in a mouse model of pyruvate dehydrogenase deficiency

Glucose is the ultimate substrate for most brain activities that use carbon, including synthesis of the neurotransmitters glutamate and γ-aminobutyric acid via mitochondrial tricarboxylic acid (TCA) cycle. Brain metabolism and neuronal excitability are thus interdependent. However, the principles that govern their relationship are not always intuitive because heritable defects of brain glucose metabolism are associated with the paradoxical coexistence, in the same individual, of episodic neuronal hyperexcitation (seizures) with reduced basal cerebral electrical activity. One such prototypic disorder is pyruvate dehydrogenase (PDH) deficiency (PDHD). PDH is central to metabolism because it steers most of the glucose-derived flux into the TCA cycle. To better understand the pathophysiology of PDHD, we generated mice with brain-specific reduced PDH activity that paralleled salient human disease features, including cerebral hypotrophy, decreased amplitude electroencephalogram (EEG), and epilepsy. The mice exhibited reductions in cerebral TCA cycle flux, glutamate content, spontaneous, and electrically evoked in vivo cortical field potentials and gamma EEG oscillation amplitude. Episodic decreases in gamma oscillations preceded most epileptiform discharges, facilitating their prediction. Fast-spiking neuron excitability was decreased in brain slices, contributing to in vivo action potential burst prolongation after whisker pad stimulation. These features were partially reversed after systemic administration of acetate, which augmented cerebral TCA cycle flux, glutamate-dependent synaptic transmission, inhibition and gamma oscillations, and reduced epileptiform discharge duration. Thus, our results suggest that dysfunctional excitability in PDHD is consequent to reduced oxidative flux, which leads to decreased neuronal activation and impaired inhibition, and can be mitigated by an alternative metabolic substrate.

Role of Alcohol Oxidative Metabolism in Its Cardiovascular and Autonomic Effects

Several review articles have been published on the neurobehavioral actions of acetaldehyde and other ethanol metabolites as well as in major alcohol-related disorders such as cancer and liver and lung disease. However, very few reviews dealt with the role of alcohol metabolism in the adverse cardiac and autonomic effects of alcohol and their potential underlying mechanisms, particularly in vulnerable populations. In this chapter, following a brief overview of the dose-related favorable and adverse cardiovascular effects of alcohol, we discuss the role of ethanol metabolism in its adverse effects in the brainstem and heart. Notably, current knowledge dismisses a major role for acetaldehyde in the adverse autonomic and cardiac effects of alcohol because of its low tissue level in vivo. Contrary to these findings in men and male rodents, women and hypertensive individuals are more sensitive to the adverse cardiac effects of similar amounts of alcohol. To understand this discrepancy, we discuss the autonomic and cardiac effects of alcohol and its metabolite acetaldehyde in a model of hypertension, the spontaneously hypertensive rat (SHR) and female rats. We present evidence that enhanced catalase activity, which contributes to cardioprotection in hypertension (compensatory) and in the presence of estrogen (inherent), becomes detrimental due to catalase catalysis of alcohol metabolism to acetaldehyde. Noteworthy, studies in SHRs and in estrogen deprived or replete normotensive rats implicate acetaldehyde in triggering oxidative stress in autonomic nuclei and the heart via (i) the Akt/extracellular signal-regulated kinases (ERK)/nitric oxide synthase (NOS) cascade and (ii) estrogen receptor-alpha (ERα) mediation of the higher catalase activity, which generates higher ethanol-derived acetaldehyde in female heart. The latter is supported by the ability of ERα blockade or catalase inhibition to attenuate alcohol-evoked myocardial oxidative stress and dysfunction. More mechanistic studies are needed to further understand the mechanisms of this public health problem.

Persistent increase in ecto‑5'‑nucleotidase activity from encephala of adult zebrafish exposed to ethanol during early development

Prenatal alcohol exposure causes alterations to the brain and can lead to numerous cognitive and behavioral outcomes. Long-lasting effects of early ethanol exposure have been registered in glutamatergic and dopaminergic systems. The purinergic system has been registered as an additional target of ethanol exposure. The objective of this research was to evaluate if the ecto‑5'‑nucleotidase and adenosine deaminase activities and gene expression of adult zebrafish exposed to 1% ethanol during early development could be part of the long-lasting targets of ethanol. Zebrafish embryos were exposed to 1% ethanol in two distinct developmental phases: gastrula/segmentation (5-24 h post-fertilization) or pharyngula (24-48 h post-fertilization). At the end of three months, after checking for morphological outcomes, the evaluation of enzymatic activity and gene expression was performed. Exposure to ethanol did not promote gross morphological defects; however, a significant decrease in the body length was observed (17% in the gastrula and 22% in the pharyngula stage, p < 0.0001). Ethanol exposure during the gastrula/segmentation stage promoted an increase in ecto‑5'‑nucleotidase activity (39.5%) when compared to the control/saline group (p < 0.0001). The ecto‑5'‑nucleotidase gene expression and the deamination of adenosine exerted by ecto and cytosolic adenosine deaminase were not affected by exposure to ethanol in both developmental stages. HPLC experiments did not identify differences in adenosine concentration on the whole encephala of adult animals exposed to ethanol during the gastrula stage or on control animals (p > 0.05). Although the mechanism underlying these findings requires further investigation, these results indicate that ethanol exposure during restricted periods of brain development can have long-term consequences on ecto‑5'‑nucleotidase activity, which could have an impact on subtle sequels of ethanol early exposure.

Impact of dietary induced precocious gut maturation on cecal microbiota and its relation to the blood-brain barrier during the postnatal period in rats

BACKGROUND

Precocious maturation of the gastrointestinal barrier (GIB) in newborn mammals can be induced by dietary provocation, but how this affects the gut microbiota and the gut-brain axis remains unknown. The objective of this study was to investigate effects of induced GIB maturation on gut microbiota composition and blood-brain barrier (BBB) permeability.

METHODS

Suckling rats were studied at 72 h after gavage with phytohemagglutinin (PHA) or microbial protease (PT) to induce maturation of GIB. For comparison, untreated suckling and weaned rats were included (n = 10). Human serum albumin (HSA) was administered orally and analyzed in blood to assess permeability of the GIB, while intraperitoneally injected bovine serum albumin (BSA) was measured in the brain tissue for BBB permeability. The cecal microbial composition, plasma lipopolysaccharide-binding protein (LBP) levels and short-chain fatty acids in serum and brain were analyzed.

KEY RESULTS

Cessation of HSA passage to blood after PHA or PT treatment was similar to that seen in weaned rats. Interestingly, concomitant increases in cecal Bacteroidetes and plasma LBP levels were observed after both PHA and PT treatments. The BBB passage of BSA was surprisingly elevated after weaning, coinciding with lower plasma LBP levels and specific microbial taxa and increased acetate uptake into the brain.

CONCLUSIONS & INFERENCES

This study provides evidence that the gut microbiota alteration following induced precocious GIB maturation may induce low-grade systemic inflammation and alter SCFAs utilization in the brain which may also play a potential role in GIB-BBB dysfunction disorders in neonates.

Ethanol Tolerance Affects Endogenous Adenosine Signaling in Mouse Hippocampus

Ethanol has many pharmacological effects, including increases in endogenous adenosine levels and adenosine receptor activity in brain. Ethanol consumption is associated with both positive and negative health outcomes, but tolerance to the behavioral effects of ethanol can lead to increased consumption, which increases the risk of negative health outcomes. The present study was performed to test whether a 7-day treatment with ethanol is linked to reduced adenosine signaling and whether this is a consequence of reduced ecto-5′-nucleotidase activity. Wild-type (CD73^+/+) and ecto-5′-nucleotidase-deficient (CD73^−/−) mice were treated with ethanol (2 g/kg) or saline for 7 days. In CD73^+/+ mice, repeated ethanol treatment reduced the hypothermic and ataxic effects of acute ethanol, indicating the development of tolerance to the acute effects of ethanol. In CD73^+/+ mice, this 7-day ethanol treatment led to increased hippocampal synaptic activity and reduced adenosine A₁ receptor activity under both basal and low Mg²⁺ conditions. These effects of ethanol tolerance were associated with an 18% decrease in activity of ecto-5′-nucleotidase activity in hippocampal cell membranes. In contrast, ethanol treatment was not associated with changes in synaptic activity or adenosine signaling in hippocampus from CD73^−/− mice. These data indicate that ethanol treatment is associated with a reduction in adenosine signaling through adenosine A₁ receptors in hippocampus, mediated, at least in part, via reduced ecto-5′-nucleotidase activity.

Acetate as an active metabolite of ethanol: studies of locomotion, loss of righting reflex, and anxiety in rodents

It has been postulated that a number of the central effects of ethanol are mediated via ethanol metabolites: acetaldehyde and acetate. Ethanol is known to produce a large variety of behavioral actions such anxiolysis, narcosis, and modulation of locomotion. Acetaldehyde contributes to some of those effects although the contribution of acetate is less known. In the present studies, rats and mice were used to assess the acute and chronic effects of acetate after central or peripheral administration. Male Sprague-Dawley rats were used for the comparison between central (intraventricular, ICV) and peripheral (intraperitoneal, IP) administration of acute doses of acetate on locomotion. CD1 male mice were used to study acute IP effects of acetate on locomotion, and also the effects of chronic oral consumption of acetate (0, 500, or 1000 mg/l, during 7, 15, 30, or 60 days) on ethanol- (1.0, 2.0, 4.0, or 4.5 g/kg, IP) induced locomotion, anxiolysis, and loss of righting reflex (LORR). In rats, ICV acetate (0.7–2.8 μmoles) reduced spontaneous locomotion at doses that, in the case of ethanol and acetaldehyde, had previously been shown to stimulate locomotion. Peripheral acute administration of acetate also suppressed locomotion in rats (25–100 mg/kg), but not in mice. In addition, although chronic administration of acetate during 15 days did not have an effect on spontaneous locomotion in an open field, it blocked ethanol-induced locomotion. However, ethanol-induced anxiolysis was not affected by chronic administration of acetate. Chronic consumption of acetate (up to 60 days) did not have an effect on latency to, or duration of LORR induced by ethanol, but significantly increased the number of mice that did not achieve LORR. The present work provides new evidence supporting the hypothesis that acetate should be considered a centrally-active metabolite of ethanol that contributes to some behavioral effects of this alcohol, such as motor suppression.

Enhanced catabolism to acetaldehyde in rostral ventrolateral medullary neurons accounts for the pressor effect of ethanol in spontaneously hypertensive rats

We have previously shown that ethanol microinjection into the rostral ventrolateral medulla (RVLM) elicits sympathoexcitation and hypertension in conscious spontaneously hypertensive rats (SHRs) but not in Wistar-Kyoto (WKY) rats. In this study, evidence was sought to implicate the oxidative breakdown of ethanol in this strain-dependent hypertensive action of ethanol. Biochemical experiments revealed significantly higher catalase activity and similar aldehyde dehydrogenase (ALDH) activity in the RVLM of SHRs compared with WKY rats. We also investigated the influence of pharmacological inhibition of catalase (3-aminotriazole) or ALDH (cyanamide) on the cardiovascular effects of intra-RVLM ethanol or its metabolic product acetaldehyde in conscious rats. Compared with vehicle, ethanol (10 μg/rat) elicited a significant increase in blood pressure in SHRs that lasted for the 60-min observation period but had no effect on blood pressure in WKY rats. The first oxidation product, acetaldehyde, played a critical role in ethanol-evoked hypertension because 1) catalase inhibition (3-aminotriazole treatment) virtually abolished the ethanol-evoked pressor response in SHRs, 2) intra-RVLM acetaldehyde (2 μg/rat) reproduced the strain-dependent hypertensive effect of intra-RVLM ethanol, and 3) ALDH inhibition (cyanamide treatment) uncovered a pressor response to intra-RVLM acetaldehyde in WKY rats similar to the response observed in SHRs. These findings support the hypothesis that local production of acetaldehyde, due to enhanced catalase activity, in the RVLM mediates the ethanol-evoked pressor response in SHRs.

SIAM-Like phenomenon caused by low doses of alcohol

BACKGROUND

Swift increase in alcohol metabolism (SIAM) is usually evoked by a large dose of ethanol, which is often demonstrated by an abrupt increase in oxygen uptake. SIAM was induced by low doses of ethanol and evaluated by pharmacokinetic analyses of ethanol and its metabolites.

METHODS

Rabbits were initially administered 1.0 g/kg of ethanol solution and the same dose was given to the bolus group 6 hours after the first injection. The infusion group was administered 0.25 g/kg/h of ethanol 2 hours after the first injection. Blood concentrations of ethanol, acetaldehyde, and acetate were then determined and comparisons were made using pharmacokinetic parameters.

RESULTS

A significantly higher ethanol elimination rate was observed after re-administration of ethanol to the bolus group. Other pharmacokinetic parameters were unaffected. The concentration at steady state (Css) for the infusion group was stable. A significantly higher level of mean residence time (MRT) in blood acetaldehyde was observed for the bolus group, whereas no MRT changes were observed for the infusion group. A significantly higher level of blood acetate Css was observed after re-administration of ethanol to the bolus group, following the changes in area under concentration and MRT. No Css changes were observed for the infusion group. The Css of acetate at stage 2 was significantly higher for the bolus group, compared to the infusion group.

CONCLUSION

Low doses of ethanol enhanced alcohol metabolism in rabbits, according to a pharmacokinetic analysis of circulating ethanol concentrations. Simultaneous analyses of its metabolites followed the kinetic of ethanol.

The role of acetaldehyde in the neurobehavioral effects of ethanol: A comprehensive review of animal studies

Acetaldehyde has long been suggested to be involved in a number of ethanol's pharmacological and behavioral effects, such as its reinforcing, aversive, sedative, amnesic and stimulant properties. However, the role of acetaldehyde in ethanol's effects has been an extremely controversial topic during the past two decades. Opinions ranged from those virtually denying any role for acetaldehyde in ethanol's effects to those who claimed that alcoholism is in fact "acetaldehydism". Considering the possible key role of acetaldehyde in alcohol addiction, it is critical to clarify the respective functions of acetaldehyde and ethanol molecules in the pharmacological and behavioral effects of alcohol consumption. In the present paper, we review the animal studies reporting evidence that acetaldehyde is involved in the pharmacological and behavioral effects of ethanol. A number of studies demonstrated that acetaldehyde administration induces a range of behavioral effects. Other pharmacological studies indicated that acetaldehyde might be critically involved in several effects of ethanol consumption, including its reinforcing consequences. However, conflicting evidence has also been published. Furthermore, it remains to be shown whether pharmacologically relevant concentrations of acetaldehyde are achieved in the brain after alcohol consumption in order to induce significant effects. Finally, we review current evidence about the central mechanisms of action of acetaldehyde.

Inhibition of slow Ca(2+)-activated K(+) current by 4-aminopyridine in rat hippocampal CA1 pyramidal neurones

1. The effect of 4-aminopyridine (4-AP) on the slow afterhyperpolarization (sAHP) seen after high frequency dendritic or somatic firing was investigated in rat hippocampal CA1 pyramidal neurones (PC). Intracellular recordings were obtained from the distal apical dendrites and somata and suprathreshold depolarizing current pulses were used to evoke a sAHP. The sAHP was blocked by low concentrations of carbacholine (Cch) but insensitive to high concentrations of apamin. 2. In the presence of extracellular 4-AP, the first dendritic sAHP evoked was reduced compared to a maximal sAHP evoked in the absence of 4-AP. The reduction was evident at submillimolar concentration and increased to about 80% with 4 mM 4-AP. 3. The stability of the 4-AP-induced block was affected by the type of anion used in the electrode solution. With K(+) acetate (KAc) or K(+) methylsulphate (KMeSO(4)) containing electrodes, the block was progressively removed during the initial 300 - 400 s of recordings. With KCl containing electrodes, the block remained stable and was 10% larger than that obtained with acetate. Detailed investigations showed that intracellular acetate promotes the removal of the 4-AP-induced block in an activity-dependent manner. 4. Intracellularly applied 4-AP also induced an acetate-sensitive block of the dendritic sAHP. 5. 4-AP also blocked the somatic sAHP and the stability of the block showed the same sensitivity towards anions as the dendritic sAHP. 6. Thus 4-AP appears to block the slow Ca(2+)-activated K(+) current underlying the sAHP in a complex manner which is sensitive to certain types of anions.

Effects of ethanol and acetate on adenosine production in rat hippocampal slices

Since adenosine has been shown to mediate some actions of ethanol we have examined the effect of ethanol (20 and 80 mM) or its metabolite acetate (5 and 20 mM) on the formation and release of adenosine by rat hippocampal slices. The ATP pool of the slices was radioactively labelled by preincubation with [3H]-adenine. The efflux of radioactivity under basal conditions and following ATP breakdown induced by combined hypoxia/hypoglycaemia was examined. Ethanol or acetate did not increase the total efflux of [3H]-purines, but changed the composition to a larger proportion of [3H]-adenosine. The release of endogenous adenosine was also increased. This type of effect exactly mirrors that previously reported for purine nucleoside transport inhibitors. The present results thus show that ethanol (20 mM) can increase adenosine release from a brain slice by a mechanism that probably involves transport inhibition.

Combined inhibitory effects of ethanol and adenosine on the responses of rabbit platelets to thrombin

We have previously shown that acutely administered ethanol, resulting in blood alcohol concentrations of 40-90 mM, inhibits experimentally induced arterial thrombosis in rabbits. This inhibition by ethanol in vivo is more pronounced than that observed on stimulated platelets in vitro, when a similar concentration of ethanol is added before an aggregating agent. It may be, then, that ethanol has combined effects in vivo with other inhibitors of platelet function. Adenosine has been found to be an important mediator of some of the in vivo effects of ethanol, and we investigated whether ethanol has combined inhibitory effects with adenosine on thrombin-stimulated platelet responses in vitro. Aggregation and secretion of [14C]serotonin from washed, prelabeled rabbit platelets, pretreated with aspirin, were studied. Maximal aggregation induced by 0.15 units thrombin/ml was slightly inhibited by 87 mM ethanol; secretion of serotonin was reduced from 24% to 12%. However, when thrombin-induced aggregation was significantly reduced by 1 microM adenosine, ethanol, at 44 and 87 mM, further inhibited aggregation. Secretion of [14C]serotonin was reduced to < 3%, with the combination of adenosine and the higher concentration of ethanol. Ethanol did not increase platelet cyclic AMP (cAMP) above basal levels, nor did it affect the increase in cAMP caused by adenosine. The adenosine receptor antagonist, 8-phenyltheophylline, at 1 microM, blocked the inhibitory effects of adenosine on platelet responses and prevented the adenosine-induced increase in cAMP. Unexpectedly, however, 8-phenyltheophylline (1-2 microM) did not completely block the combined inhibitory effects of ethanol and adenosine; this incomplete reversal was not associated with increases in cAMP over basal levels.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of acetate as a potential mediator of the effects of ethanol in the brain

Acetate is the primary product of ethanol catabolism and can accumulate in the blood at concentrations of up to 2 mM following ethanol consumption. It has been suggested that some of the pharmacological actions of ethanol are mediated via acetate, which can lead indirectly to the release of endogenous adenosine. In the present experiments this hypothesis was tested by examining the effects of exogenous sodium acetate on the physiology of hippocampal slices from rat brain. Acetate had no significant effect on intracellular responses recorded from CA1 pyramidal neurons or on extracellular field potentials evoked from the either the CA1 region or the dentate gyrus. There was also no significant difference in responses to the adenosine receptor antagonist theophylline in CA1 pyramidal neurons recorded using intracellular filling solutions containing potassium acetate, KCl, or potassium methylsulfate. These results suggest that the presence of acetate, either in the extracellular medium or within an intracellular electrode, does not induce a significant increase in adenosine receptor activation in the hippocampus.

Acetate-mediated effects of ethanol

Ethanol has been shown to increase markedly portal blood flow, primarily by increasing intestinal blood flow. This effect of ethanol is reproduced by acetate, infused at rates equivalent to those leading to endogenous acetate production following ethanol administration. The physiological mediator, adenosine, is also known to increase markedly intestinal and portal tributary blood flow. We have shown that adenosine receptor blockade with 8-phenyltheophylline completely abolishes the effects of ethanol, acetate, and adenosine on intestinal and portal blood flow, suggesting that increases in adenosine tone may constitute a common mechanism mediating the actions of both ethanol and acetate on the splanchnic vasculature. Studies are also presented that show that acetate administration has marked effects on central nervous system function. On two tests, motor coordination and anesthetic potency, both ethanol and acetate showed similar effects. The effects of acetate were fully abolished by 8-phenyltheophylline. The effects of ethanol were partially blocked by 8-phenyltheophylline, with a greater effect of this blocker being seen at low doses of alcohol. Whereas ethanol at low doses increased locomotor activity in mice, acetate markedly reduced it. The effect of acetate on locomotion was fully reversed by the adenosine receptor blocker 8-phenyltheophylline, whereas the activating effect of ethanol on locomotion was markedly enhanced by this blocker. These data suggest that the actions of ethanol on locomotor activity normally result from the combination of a direct stimulatory effect of ethanol per se and an inhibitory effect of acetate, produced endogenously from ethanol. When the latter effect of acetate is abolished by adenosine receptor blockade, the activating effect of ethanol is fully expressed.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of adenosine in mediating cellular and molecular responses to ethanol

We have found that ethanol-induced increases in extracellular adenosine activate adenosine receptors which, in turn, mediate many of the acute and chronic effects of ethanol in the nervous system. Several laboratories have demonstrated the importance of adenosine in mediating the acute and chronic effects of ethanol at multiple levels of investigation in the nervous system. These include genetic selection for ethanol sensitivity in mice, behavioral responses to ethanol in naive and tolerant animals, neurophysiologic responses in hippocampal slices, and at the level of cAMP signal transduction and gene expression in cultured neural cells. In this review we present results from our laboratory which document the role of adenosine in mediating ethanol-induced changes in neural function at a cellular and molecular level. A schematic summary of our findings is: Etoh-->decreases Ado uptake-->increases Extracellular Ado-->Activation of Adenosine A2 receptor-->increases cAMP-->increases PKA-->-->-->Heterologous Desensitization (decreases cAMP)-->-->-->insensitivity of adenosine uptake to ETOH

Lead/ethanol interactions. I: rate-depressant effects

Adult male rats were exposed to a diet containing 500 ppm added lead as lead acetate (group lead-diet) or a control diet containing no added chemicals (group control-diet) for 61 days prior to commencing fixed-ratio 32 (FR 32) lever press training for water reinforcement. After steady state responding was achieved, all animals received serial administrations of acute doses of ethanol prior to the daily training session. Specifically, lead-diet and control-diet rats received i.p. injections of .25, .5, .75, 1.0, and 1.25 g/kg ethanol, in ascending order, alternating daily with injections of saline. The results revealed a dose-dependent rate-depressant effect, with higher doses of ethanol producing more behavioral suppression than lower doses for both groups. In addition, at the dose of 1.0 g/kg it was observed that the suppressive effects of ethanol on schedule-controlled responding were reduced among lead-treated animals relative to controls. These data are discussed in terms of lead-induced attenuation of the pharmacologic effects of ethanol.