Aggression and open-field activity of lead-exposed mice

Waterborne Lead Exposure Affects Brain Endocannabinoid Content in Male but not Female Fathead Minnows (Pimephales promelas)

There are several similarities between the behavioral and neurochemical effects of lead (Pb2+) and the cannabinoids. Both Pb2+ exposure and cannabinoid treatment decrease exploratory behavior. Pb2+-induced hyperactivity has been observed in rats and fish. By comparison, cannabinoids increase locomotor activity at higher doses in rats. Moreover, Pb2+ exposure produces learning and memory impairments as do the cannabinoids. Many of the behavioral effects of Pb2+ are thought to be due, in part, to the ability of Pb2+ to either inhibit or mimic the actions of calcium (Ca2+). At low concentrations, Pb2+ enhances basal release of neurotransmitter from presynaptic terminals by increasing intracellular free Ca2+ concentrations. Pb2+ also decreases evoked neurotransmitter release due to blockade of voltage-gated Ca2+ channels. Interestingly, the endocannabinoids (eCBs) including N-arachidonylethanolamine (AEA) and 2-arachidonylglycerol (2-AG) are synthesized in response to increases in intracellular Ca2+ and activate the CB1 receptor that inhibits voltage-gated Ca2+ channels. We tested the hypothesis that waterborne Pb2+ exposure significantly affects whole-brain eCB content in adult male and female fathead minnows (Pimephales promelas). Waterborne Pb2+ exposure (1.0 ppm) resulted in a time-dependent accumulation of Pb2+ in bone in both males and females. Brain AEA and 2-AG content were significantly greater in females compared to males. Pb2+ exposure increased brain AEA content in males at 7 and 14 days of exposure and increased brain 2-AG content at 14 days. Pb2+ exposure had no effect on either brain AEA or 2-AG content in females at any of the time points examined. As eCBs serve as activity-dependent retrograde inhibitors of neurotransmitter release, the increase in brain eCB content would accentuate Pb2+-induced decreases in evoked neurotransmitter release in male but not female fathead minnows.

Effects of dietary lead and/or dimercaptosuccinic acid exposure on regional serotonin and serotonin metabolite content in rainbow trout (Oncorhynchus mykiss)

The lead (Pb) chelator, meso-2,3-dimercaptosuccinic acid (DMSA) may be effective in reversing some of the adverse effects of Pb exposure. Pb-induced behavioral deficits observed in fish are due to disruptions in the integrative functioning of the medulla, cerebellum, and optic tectum. Pb exposure increased serotonin (5-HT) content in all three brain regions without an effect on 5-hydroxy-3-indoleacetic acid (5-HIAA). Pb exposure followed by no Pb in the diet increased 5-HT and 5-HIAA content in all three brain regions. The replacement of dietary Pb with DMSA had no effect on 5-HT and increased 5-HIAA content. DMSA increased 5-HIAA content in all three brain regions and increased 5-HT content only the optic tectum. Treatment with DMSA may be more effective than removal of Pb from the diet in reversing Pb-induced alterations in 5-HT.

Lead effects on food competition and predatory aggression in Binghamton HET mice

The ubiquity of lead in our environment, its toxic nature and its potential to alter behavior of humans and animals has stimulated much research. In addition to the well known, but complex, changes in activity and performance of learned tasks following exposure to lead, an increasing body of literature suggests that changes in social behavior also occur. This study examined the impact of ingesting a 0.5% lead acetate solution (as the only available fluid)--a protocol that results in ca. 100 micrograms/dl blood-levels in our Binghamton Heterogenous (HET) mice--on food competition in both male and female HET mice. Effects of this lead exposure on cricket predation by the same HET mice also were observed. Our results from the food competition study (Experiment I) show, compared with water controls, that such exposure to lead increases both food possession time and amount of social contact after food consumption; but very little agonistic behavior took place in either the water control or lead-exposed competition testing sessions. In the cricket predation observations (Experiment II) there was a tendency for lead exposure to reduce the latency of males to attack, and the indication that lead-exposed females initially attacked a cricket's legs more often than any of the other groups. In fact, suggestions of such gender x treatment interactions occurred in both the food competition and the predation work. Overall, we believe our results, in conjunction with other relevant literature, suggest that exposure to lead reduced the individual's general fitness, even when levels are relatively low.

The comparative developmental neurotoxicity of lead in humans and animals

The effects of lead on neurobehavioral development have been extensively investigated in humans as well as animals. This valuable lode of research findings offers a basis for comparing the developmental neurobehavioral toxicity of lead across species and for assessing the validity of animal models of developmental neurotoxicity. Comparisons of human and animal findings suggest that the greatest qualitative similarities involve relatively complex behavioral processes such as cognition and learning. Quantitative comparisons based on dose-response relationships for these endpoints are difficult to make because the relationships are sometimes nonmonotonic (U-shaped) and because blood lead levels may not be directly comparable between species. However, the lowest levels of exposure at which developmental neurobehavioral effects have been observed are similar: 10-15 micrograms/dl in children, less than 15 micrograms/dl in primates, and less than 20 micrograms/dl in rodents. Although the convergence between animal and human findings for other neurobehavioral endpoints is not as striking, sensory-evoked potentials and communicative processes offer two promising areas for continued investigation and cross-species comparison.

Postpartum aggression and plasma prolactin levels in mice exposed to lead

Young-adult, female Binghamton Heterogeneous Stock (HET) mice either were exposed to lead via drinking water from birth, or not. Eight days after giving birth to their first litter of pups (at about 70-75 days of age), postpartum aggression tests were conducted. Unfamiliar Het male intruders were introduced to the primiparous dams' nesting cages, and dyadic behavioral interactions were observed for 10 min. We also obtained plasma prolactin levels of these females, or others who had similar histories, but were not tested for maternal aggression. Behaviorally, the intensity of fighting was greater in lead-exposed pairs than in water-control pairs that fought. However, the percentage of pairs displaying aggressive behavior and average latency to initial contact were similar, regardless of dietary history. Plasma prolactin levels implied that lead exposure alone decreased circulating prolactin in primiparous Het dams eight days postpartum, but confrontation with a male intruder also was sufficient to reduce prolactin levels in water-control dams. It would be reasonable to assume that such changes in prolactin are dopaminergically mediated. The data suggest that lead ingestion may, in a species and strain specific manner, modify: 1) neurotransmitter and hormonal systems and 2) social behavior. The major effect of "subclinical" lead toxicity may be to change the limits of an organism's ability to cope with its environment.

Effects of aluminum ingestion on spontaneous motor activity of mice

Aluminum (Al) as aluminum lactate in a purified diet was fed to adult female Swiss-Webster mice over a six week period. Comparison groups were: controls (CON), 25 micrograms Al/g diet; low Al (LO), 500 micrograms Al/g diet; high Al (HI), 1000 micrograms Al/g diet; and pair fed (PF) 25 micrograms Al/g diet pair fed to HI group. Weights, food intake and toxic signs were recorded at 3-day intervals and activity levels were measured during a 24-hr session during week 5 using an automated apparatus. Food intake was not reduced overall in Al-treated groups but they demonstrated a cyclic pattern of food intake. Mean weight gain over the 6-week period in the HI (0.5 g) and PF(0.1 g) groups was somewhat less than that in the CON (2.3 g) and LO (2.0 g) groups. No neurotoxic signs were recorded in any group, but a dose dependent increase in localized fur loss was seen. Overall activity level was 20% lower in HI than CON groups, with vertical movement more affected than horizontal movement. HI mice were less active during the diurnal period of peak activity than CON mice and their activity periods were also somewhat shorter (130 vs. 200 min). Activity of LO and PF mice did not differ significantly from controls, although PF activity levels were more variable. These data demonstrate that short term feeding of aluminum at levels within an order of magnitude of estimated human intake can influence neurobehavioral function as indexed by motor activity.

Lead exposure, environmental temperature, nesting and consummatory behavior of adult male mice of two ages

Both younger (60-day-old) and older (365-day-old) male, heterogeneous stock mice were exposed to either a 0.5% lead acetate solution or water as their sole source of fluid for four weeks prior to testing their nest building and consummatory behavior in a temperature chamber. During the three weeks in the temperature chambers lead and water maintenance were continued, and fluid and food consumption, body weight and nest building were monitored. Temperature in the chambers was 21 degrees C during the first week, then reduced to 5 degrees C during the second week, and returned to 21 degrees C in the last week of testing. In general, younger animals responded more rapidly and more intensely than older mice to changes in temperature as reflected in consummatory behavior, but lead ingestion decreased the magnitude of the change in fluid intake. Lead ingestion also altered the pattern of change in food ingestion of older mice as a function of the reduced temperature challenge. The complexity of nests built increased when temperatures were lowered from 21 degrees C to 5 degrees C, but this measure was unaffected by lead ingestion or age.

The persistent threat of lead: medical and sociological issues

Lead exposure is an ancient malady. Its history serves as a useful paradigm through which to understand many other pollutants that our technological society has inserted into the human environment and may guide preventive steps for other agents. Lead poisoning was first recognized in workers exposed to high doses. The discovery of childhood toxicity occurred a century ago in Australia, when children with striking symptoms of paralysis, ophthalmoplegia, or meningitis were found to be highly lead exposed. Encephalopathy generally occurs at blood lead levels of 80 micrograms/dL or more, but unequivocal brain damage has been demonstrated at doses well below this level. At lower doses, the neurocognitive effects of lead are expressed as diminished psychometric intelligence, attention deficits, conduct problems, alterations in the electroencephalogram, school failure, and increased referral rates for special needs. Careful epidemiologic studies, which have controlled for the important confounders, have set the effect level at 10-15 micrograms/dL. Elegant animal studies in which confounding is not an issue have confirmed these findings. Although blood lead levels in the population have dropped over time for a number of reasons, there are some 3-4 million American children with blood lead levels of more than 15 micrograms/dL. Biochemical and functional changes have been demonstrated in the heme biosynthetic pathway and in the renal, cardiovascular, endocrine, immune, and nervous systems. The threshold for effect depends on the sensitivity of the methods used. A no-effect level has not been found. Further, this is not a disease of the poor alone. But the poor are exposed to much more lead than are the more economically favored. Deficiencies in body calcium, zinc, iron, and protein stores are associated with increased uptake. Optimizing nutrition enhances the resistance to lead. All children should be screened for lead at regular intervals, especially those with anemia, growth failure, and developmental or behavioral problems. Treatment protocols are well worked out, but chelation is only part of the therapy. Controlling the environment, strengthening the family's supports, enhancing nutrition, and offering remedial education are essential to a successful therapeutic outcome. Lead control has involved a continuing struggle between vested economic interests and regulatory agencies. In one area, the control of airbone lead, science, and public health have prevailed. In the past decade, the amount of alkyl lead consumed in gasoline additives has been reduced by 99%. Body lead burdens have dropped in close correspondence.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of lead in the laboratory mouse. Development and social behaviour after lifelong exposure to 12 microM lead in drinking fluid

The effects of chronic exposure to 12 microM lead, from conception onwards, on development and social behaviour were investigated in the laboratory mouse. Lead was administered as 0.25% solution of lead acetate in the drinking fluid. This level of exposure did not affect reproductive success, but caused decreased birthweight and retarded early development in offspring of treated dams. Mortality prior to weaning was significantly greater in pups treated with lead, and animals treated with lead had significantly reduced body weights throughout their lives. Levels of lead in tissues were greatly increased in all treated animals, with females showing significantly higher levels than males. Behaviour was assessed by ethological methods in paired encounters between unfamiliar animals in a novel environment. At age 3-4 weeks Exploratory Behaviour and Social Investigation were significantly increased and Immobility was significantly decreased in animals of both sexes treated with lead. Social Investigation was also increased at age 7-8 weeks but Exploratory Behaviour was decreased. At age 15-16 weeks Non-Social Activity was increased in males and decreased in females, although Social and Sexual Investigation was not affected in these male-female encounters. Lead-treated males, aged 17-18 weeks, showed significantly shorter latencies to aggression towards unfamiliar males than did controls.

Two types of chronic lead treatment in C57BL/6 mice: interaction with behavioural determinants of pain

The male C57BL/6 mice used in this study were the offspring either of untreated or lead treated (0.1% lead acetate (PbAc) instead of drinking water) parents. Offspring of lead treated parents were reared on 0.1% PbAc until weaning, and also given 0.5% PbAc to drink for 3 weeks prior to testing (Pb2 group). Offspring of untreated parents were either given 0.5% PbAc to drink (Pb1 group) or maintained on tap water throughout (Control group). Control (C) and lead treated mice were subdivided according to single- or group-housing; no confrontation ("unfought") or confrontation with a trained aggressor mouse ("defeated"). All the mice were then given a hot-plate pain test, in which paw-lick and escape latencies were recorded. In untreated mice, latencies were reduced after defeat. This effect was not seen in lead treated animals. Lead treatment increased latencies in most instances relative to the appropriate control group. The paw-lick latencies were less consistently affected than the escape latencies. Escape latencies, with one exception, were longer in the Pb2 group than in the Pb1 group. Treatment with naloxone of single-housed C and Pb2 was without effect, except for Pb2 treated undefeated mice: here, naloxone abolished the analgesic effect of lead treatment. Lead-induced analgesia is discussed in terms of central mechanisms of pain reception.

Lead, age and aggression in male mice

The impact of eleven weeks of ingestion of a 0.5% lead acetate solution on agonistic behavior of male Binghamton Heterogeneous stock mice (either 120 or 660 days of age) was examined. Similar aged mice were paired for aggression testing. Not surprisingly, younger mice, regardless of fluid history fought more vigorously than older mice. However, when mice of similar fluid history were paired together, lead ingestion decreased the latency to fight only in older mice. Regardless of their prior fighting history, when lead treated mice fought similar aged controls, the lead exposed mice in younger pairs were typically subordinate; but in older pairs, lead exposed mice were dominant. These results, coupled with extant literature concerning age-related changes in endocrine function, pituitary-adrenal activity, and lead-induced changes in hippocampal function suggest that future work directed at mechanism(s) underlying lead-induced alterations in agonistic behavior should consider life span changes in biobehavioral profiles.