Exposure to Cadmium During Gestation and Lactation Decreases Cocaine Self-Administration in Rats

The longitudinal effects of early developmental cadmium exposure on conditioned place preference and cardiovascular physiology in zebrafish

Cadmium (Cd) is a naturally occurring trace metal that is widely considered to be highly toxic to aquatic organisms and a significant health hazard to humans (Amzal et al., 2009; Bernhoft 2013; Burger, 2008; Satarug et al., 2009). The zebrafish (Danio rerio) has been used as a model organism for toxicological studies with Cd (Banni et al., 2011; Blechinger et al., 2007; Chow et al., 2009; Chow et al., 2008; Favorito et al., 2011; Kusch et al., 2007; Matz et al., 2007; Wang and Gallagher, 2013). We asked what the lasting longitudinal effects would be from short early developmental Cd exposure (between 24 and 96h post-fertilization) in a range that larvae might experience living atop typical Cd-containing surface sediments (0, 0.01, 0.1, 1.0 and 10μM CdCl2: 1.124, 11.24, 112.4 and 1124μg Cd/L). The goal of this exposure window was to specifically target secondary neurogenesis, monoaminergic differentiation and cardiovascular development, without affecting earlier patterning processes. Developmental abnormalities in body size and CNS morphology increased with concentration, but were statistically significant only at the highest concentration used (10μM). Heart rate for Cd-treated larvae increased with concentration, and was significant even at the lowest concentration used (0.01μM). Longitudinal survival was significantly lower for fish developmentally exposed to the highest concentration. Except for brain weight, overall morphology was not affected by developmental Cd exposure. However, developmental exposure to lower concentrations of Cd (0.01, 0.1, and 1.0μM) progressively lowered cocaine-induced conditioned place preference (CPP), used to measure function of the reward pathways in the brain. Baseline heart rate was significantly lower in longitudinal fish developmentally exposed to 1.0μM Cd. Cardiovascular response to isoproterenol, a potent ß-adrenergic agonist, in longitudinal adults was also significantly affected by developmental exposure to Cd at low doses (0.01, 0.1 and 1.0μM). Surviving longitudinal adult fish exposed to the highest concentration of Cd showed normal CPP and cardiovascular physiology. The data imply that even lower exposure concentrations can potentially result in fitness-affecting parameters without affecting survival in a laboratory setting.

Cocaine self-administration in male and female rats perinatally exposed to PCBs: Evaluating drug use in an animal model of environmental contaminant exposure

Polychlorinated biphenyls (PCBs) are ubiquitous environmental toxicants known to adversely impact human health. Ortho-substituted PCBs affect the nervous system, including the brain dopaminergic system. The reinforcing effects of psychostimulants are typically modulated via the dopaminergic system, so this study used a preclinical (i.e., rodent) model to evaluate whether developmental contaminant exposure altered intravenous self-administration (IV SA) for the psychostimulant cocaine. Long-Evans rats were perinatally exposed to 6 or 3 mg/kg/day of PCBs throughout gestation and lactation and compared with nonexposed controls. Rats were trained to lever press for a food reinforcer in an operant chamber under a fixed-ratio 5 (FR5) schedule and later underwent jugular catheterization. Food reinforcers were switched for infusions of 250 μg of cocaine, but the response requirement to earn the reinforcer remained. Active lever presses and infusions were higher in males during response acquisition and maintenance. The same sex effect was observed during later sessions which evaluated responding for cocaine doses ranging from 31.25-500 μg. PCB-exposed males (not females) exhibited an increase in cocaine infusions (with a similar trend in active lever presses) during acquisition, but no PCB-related differences were observed during maintenance, examination of the cocaine dose-response relationship, or progressive ratio (PR) sessions. Overall, these results indicated perinatal PCB exposure enhanced early cocaine drug-seeking in this preclinical model of developmental contaminant exposure (particularly the males), but no differences were seen during later cocaine SA sessions. As such, additional questions regarding substance abuse proclivity may be warranted in epidemiological studies evaluating environmental contaminant exposures. (PsycINFO Database Record

Neurotoxicants, Micronutrients, and Social Environments

SUMMARY—Systematic research evaluating the separate and interacting impacts of neurotoxicants, micronutrients, and social environments on children's cognition and behavior has only recently been initiated. Years of extensive human epidemiologic and animal experimental research document the deleterious impact of lead and other metals on the nervous system. However, discrepancies among human studies and between animal and human studies underscore the importance of variations in child nutrition as well as social and behavioral aspects of children's environments that mitigate or exacerbate the effects of neurotoxicants.

In this monograph, we review existing research on the impact of neurotoxic metals, nutrients, and social environments and interactions across the three domains. We examine the literature on lead, mercury, manganese, and cadmium in terms of dispersal, epidemiology, experimental animal studies, effects of social environments, and effects of nutrition.

Research documenting the negative impact of lead on cognition and behavior influenced reductions by the Center for Disease Control in child lead-screening guidelines from 30 micrograms per deciliter (μg/dL) in 1975 to 25 μg/dL in 1985 and to 10 μg/dL in 1991. A further reduction is currently being considered. Experimental animal research documents lead's alteration of glutamate-neurotransmitter (particularly N-methyl-D-aspartate) activity vital to learning and memory. In addition, lead induces changes in cholinergic and dopaminergic activity. Elevated lead concentrations in the blood are more common among children living in poverty and there is some evidence that socioeconomic status influences associations between lead and child outcomes. Micronutrients that influence the effects of lead include iron and zinc.

Research documenting the negative impact of mercury on children (as well as adults) has resulted in a reference dose (RfD) of 0.1 microgram per kilogram of body weight per day (μg/kg/day). In animal studies, mercury interferes with glutamatergic, cholinergic, and dopaminergic activity. Although evidence for interactions of mercury with children's social contexts is minimal, researchers are examining interactions of mercury with several nutrients.

Research on the effects of cadmium and manganese on child cognition and behavior is just beginning. Experimental animal research links cadmium to learning deficits, manganese to behaviors characteristic of Parkinson's disease, and both to altered dopaminergic functioning.

We close our review with a discussion of policy implications, and we recommend interdisciplinary research that will enable us to bridge gaps within and across domains.

Link between low-dose environmentally relevant cadmium exposures and asthenozoospermia in a rat model

OBJECTIVE

To define the mechanism(s) underlying an association between asthenozoospermia and elevated blood, seminal plasma, and testicular cadmium levels in infertile human males using a rat model of environmentally relevant cadmium exposures.

SETTING

University medical center andrology research laboratory.

ANIMAL(S)

Male Wistar rats (n = 60), documented to be sensitive to the testicular effects of cadmium.

INTERVENTION(S)

Rats were given ad libitum access to water supplemented with 14% sucrose and 0 mg/L, 5 mg/L, 50 mg/L, or 100 mg/L cadmium for 1, 4, or 8 weeks beginning at puberty.

MAIN OUTCOME MEASURE(S)

Testicular cadmium levels were determined by atomic absorption, cauda epididymal sperm motility by visual inspection, and testicular gene expression by DNA microarray hybridization.

RESULT(S)

Chronic, low-dose cadmium exposures produced a time- and dose-dependent reduction in sperm motility. Transcription of genes regulated by calcium and expression of L-type voltage-dependent calcium channel mRNA splicing variants were altered by cadmium exposure. Expression of calcium binding proteins involved in modulation of sperm motility was unaffected.

CONCLUSION(S)

A causal relationship between elevated testicular cadmium and asthenozoospermia was identified. Aberrrant sperm motility was correlated with altered expression of L-type voltage-dependent calcium channel isoforms found on the sperm tail, which regulate calcium and cadmium influx.