Lead attenuates the antipunishment effects of ethanol

Developmental lead exposure induces opposite effects on ethanol intake and locomotion in response to central vs. systemic cyanamide administration

Lead (Pb) is a developmental neurotoxicant that elicits differential responses to drugs of abuse. Particularly, ethanol consumption has been demonstrated to be increased as a consequence of environmental Pb exposure, with catalase (CAT) and brain acetaldehyde (ACD, the first metabolite of ethanol) playing a role. The present study sought to interfere with ethanol metabolism by inhibiting ALDH2 (mitochondrial aldehyde dehydrogenase) activity in both liver and brain from control and Pb-exposed rats as a strategy to accumulate ACD, a substance that plays a major role in the drug's reinforcing and/or aversive effects. To evaluate the impact on a 2-h chronic voluntary ethanol intake test, developmentally Pb-exposed and control rats were administered with cyanamide (CY, an ALDH inhibitor) either systemically or intracerebroventricularly (i.c.v.) on the last 4 sessions of the experiment. Furthermore, on the last session and after locomotor activity was assessed, all animals were sacrificed to obtain brain and liver samples for ALDH2 and CAT activity determination. Systemic CY administration reduced the elevated ethanol intake already reported in the Pb-exposed animals (but not in the controls) accompanied by liver (but not brain) ALDH2 inactivation. On the other hand, a 0.3 mg i.c.v. CY administration enhanced both ethanol intake and locomotor activity accompanied by brain ALDH2 inactivation in control animals, while an increase in ethanol consumption was also observed in the Pb-exposed group, although in the absence of brain ALDH2 blockade. No changes were observed in CAT activity as a consequence of CY administration. These results support the participation of liver and brain ACD in ethanol intake and locomotor activity, responses that are modulated by developmental Pb exposure.

Lead and conditioned fear to contextual and discrete cues

Male Fischer 344 rats received either tap water or water containing 250 ppm lead for 90 days prior to training in either Pavlovian fear conditioning or consummatory contrast, an aversive reward reduction paradigm. In Experiment 1, lead-exposed and -unexposed rats were trained in operant chambers over a 6-min session. After 3 min elapsed, three tone-shock pairings were presented over the remainder of the session. Rats then received 7 days of extinction training in an identical procedure with only tones presented, no shocks. Lead-exposed rats exhibited greater behavioral suppression to both the contextual and auditory cues that predicted shock. In Experiment 2, rats were placed in operant chambers daily and allowed to consume either a 15% or a 5% fructose solution for 7 days. On Day 8, the rats consuming the 15% fructose solution were shifted to the 5% solution for 3 days. Lead-exposed rats did not differ from their controls in either initial consumption of either solution or in the suppression of their consumption after shifting to the 5% solution. Taken together, these findings suggest that lead impairs the extinction of fear conditioning and this finding is not due to a nonspecific increase in aversive emotionality.

Influence of ethanol on lead distribution and biochemical changes in rats exposed to lead

In the present study, an attempt has been made to investigate the effect of ethanol consumption on the distribution of lead in different regions of brain and body organs of male albino rats. Lead when administered intragastrically, for a period of eight weeks resulted in almost uniform accumulation of this metal in all the regions of brain, which increased by almost two fold when ethanol was given along with lead. Lead was also seen to compartmentalise in almost all the tissues of the body to varying extents, with the highest accumulation in the kidney. A progressive and appreciable accumulation of lead was seen in blood with a concomitant increase in ZPP levels in animals during the course of treatment, which increased further when ethanol was administered along with lead. The activity of delta-ALAD and AChE in blood was significantly decreased in lead as well as ethanol treated animals. However, in animals coexposed to lead and ethanol, the inhibition of delta-ALAD was not significantly different, when compared to only lead-treated animals. The results suggested that animals exposed to ethanol and lead simultaneously accumulate higher levels of lead in blood and brain of animals making them more vulnerable to the haematological and neurological toxic effects of lead.

Effects of chronic lead administration on ethanol-induced locomotor and brain catalase activity

Several reports have demonstrated that chronic lead administration decreases brain catalase activity in animals. Other reports have shown a role of brain catalase on ethanol-induced behaviors. In the present study, we questioned whether mice treated chronically with lead, and therefore functionally devoid of brain catalase activity, exhibit some alterations in ethanol-induced behaviors. Swiss-Webster mice were exposed to drinking fluid containing either 500 ppm lead acetate or sodium acetate (control group) for 0, 15, 30, or 60 days before an acute ethanol administration. Following ethanol injection (2.5 g/kg, i.p.), animals were placed in open field chambers and locomotor activity was measured. Lead exposure had no effect on spontaneous locomotor activity. However, a reduction in ethanol-induced locomotor activity was found at all periods of lead exposure. After 60 days of treatment, the lead group demonstrated 35% less activity than the control group. Brain catalase activity was significantly reduced in the lead group following 60 days of exposure. This reduction in ethanol-induced locomotor activity and in brain catalase activity persisted after 40 days of lead withdrawal. The fact that brain catalase and ethanol-induced locomotor activity followed a similar pattern could suggest a relationship between both lead acetate effects and also a role for brain catalase in ethanol-induced behaviors.

Cadmium exposure attenuates the initiation of behavioral sensitization to cocaine

Employing a paired-watering procedure to control for differential fluid intake confounds, adult male rats were exposed in the home cage to water containing 100 ppm cadmium chloride, or a control solution containing no added cadmium chloride. On Day 61 of exposure to their respective watering regimens, half the animals from each condition received 12 repeated daily i.p. injections of 10 mg/kg cocaine-HCl, or saline. Locomotor activity (total distance traveled) was recorded in Digiscan Activity Monitors for a 20-min baseline period prior to each injection, and for a 40-min period post-injection. On Day 13 of testing, all animals received saline injections only in the test chambers, in an effort to evaluate the role of conditioned cues in the expression of cocaine sensitization. On Day 14-16 of testing, all animals received successive daily challenges of 10, 20, and 40 mg/kg cocaine in the test chamber. The results indicated that the initiation (development) of behavioral sensitization to 10 mg/kg cocaine was attenuated in cadmium-exposed rats. Moreover, the supersensitivity to higher doses of cocaine during dose-effect testing that was registered by control animals pretreated with cocaine, was not evident in cadmium-exposed pretreatment animals. These data suggests that environmental contaminants may alter drug responsiveness, and thereby may influence patterns of drug selection and use.

Chronic lead exposure attenuates ethanol-induced hypoalgesia

Adult male rats were exposed to drinking fluid containing either 500 ppm lead acetate (group lead), or an equivalent concentration of sodium acetate (group control) for 61 days prior to pain reactivity testing using a tail-flick procedure. Rats were placed in restraining tubes for a 20 min acclimation period, and then baseline tail-flick latencies in response to a radiant heat source were measured. Subsequently, half the animals from each group were serially injected IP with either 1.0, 2.0, or 3.0 g/kg body weight of a 20% v/v ethanol solution, and the other half were injected with an equivalent volume of saline. Tail-flick latencies were reassessed at 20-min intervals over the next 2 h. Results indicated dose-dependent ethanol-induced hypoalgesia at all doses, but at the two higher doses the magnitude of the hypoalgesic response was significantly greater in the group control animals than in the group lead animals across the 2-h postinjection period. Results are discussed in terms of an attenuation of the pharmacological properties of ethanol by lead.

Attenuation of cocaine-induced elevation of nucleus accumbens dopamine in lead-exposed rats

Fourteen adult male rats were placed on an ad lib watering regimen where they received water containing 500 ppm lead acetate (group lead) or an equivalent concentration of sodium acetate (group control) for 61 days. Subsequently, a microdialysis cannula was surgically implanted in the nucleus accumbens. Following recovery, the seven animals in group lead and the seven animals in group control were presented with a challenge of 10 mg/kg cocaine HCL (IP). Dopamine efflux was measured prior to and at 20, 40, and 60 min postinjection, using HPLC technology. The results of this experiment showed that cocaine caused a significantly greater increase in extracellular nucleus accumbens dopamine in control animals relative to lead-treated animals.

Lead/ethanol interactions. II: pharmacokinetics

Adult male rats were exposed ad libitum to water containing either 500 ppm lead acetate (group-lead) or an equivalent amount of sodium acetate (group-control) for 60 days prior to receiving ip injections of either 1.0, 2.0, or 3.0 g/kg ethanol (20% v/v). Blood alcohol concentrations (BACs) were recorded over a 6-h time period postinjection, and the groups were compared at each dose for differences in the pattern of ethanol pharmacokinetics. While there was a dose-related effect obtained with increasing ethanol doses producing increasing BAC values, at no dose was there any evidence of group separation at any point during the 6-h postinjection period. These data are instructive with respect to understanding the nature of previously demonstrated lead/ethanol interactions, and rule out the possibility that lead-induced disturbances in the catalysis of ethanol, or some other pharmacokinetic operation, is the basis for the effects of lead on ethanol intake and ethanol administration. Alternative possible accounts of this curious interaction between a xenobiotic contaminant and alcohol are discussed.

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.

Chronic exposure to lead attenuates cocaine-induced behavioral activation

Adult, male rats were exposed to a diet containing 500 ppm (0.05%) lead for 105 days before testing for cocaine-related changes in activity using a Digiscan activity system. Behavioral testing occurred on 6 successive test days. Activity was recorded for 20 min prior to and 40 min after IP injections of either 10, 20, or 40 mg/kg cocaine HCl, with saline injections on the day preceding each drug test day. Cocaine-induced behavioral activation was evident in control diet animals for all three doses (10, 20, and 40 mg/kg). While 10 mg/kg cocaine HCl did not produce behavioral activation in lead-treated animals, both 20 and 40 mg/kg did result in increased activity comparable to that observed in control counterparts.