Genotypic influences on lead-induced hyperactivity in mice

Animal models of attention-deficit hyperactivity disorder

Although animals cannot be used to study complex human behaviour such as language, they do have similar basic functions. In fact, human disorders that have animal models are better understood than disorders that do not. ADHD is a heterogeneous disorder. The relatively simple nervous systems of rodent models have enabled identification of neurobiological changes that underlie certain aspects of ADHD behaviour. Several animal models of ADHD suggest that the dopaminergic system is functionally impaired. Some animal models have decreased extracellular dopamine concentrations and upregulated postsynaptic dopamine D1 receptors (DRD1) while others have increased extracellular dopamine concentrations. In the latter case, dopamine pathways are suggested to be hyperactive. However, stimulus-evoked release of dopamine is often decreased in these models, which is consistent with impaired dopamine transmission. It is possible that the behavioural characteristics of ADHD result from impaired dopamine modulation of neurotransmission in cortico-striato-thalamo-cortical circuits. There is considerable evidence to suggest that the noradrenergic system is poorly controlled by hypofunctional α₂-autoreceptors in some models, giving rise to inappropriately increased release of norepinephrine. Aspects of ADHD behaviour may result from an imbalance between increased noradrenergic and decreased dopaminergic regulation of neural circuits that involve the prefrontal cortex. Animal models of ADHD also suggest that neural circuits may be altered in the brains of children with ADHD. It is therefore of particular importance to study animal models of the disorder and not normal animals. Evidence obtained from animal models suggests that psychostimulants may not be acting on the dopamine transporter to produce the expected increase in extracellular dopamine concentration in ADHD. There is evidence to suggest that psychostimulants may decrease motor activity by increasing serotonin levels. In addition to providing unique insights into the neurobiology of ADHD, animal models are also being used to test new drugs that can be used to alleviate the symptoms of ADHD.

Cross generation lead ingestion: behavioral and physiological effects in mice

We examined some developmental and behavioral sequelae of exposing Binghamton Heterogeneous Stock (HET) mice to a 0.5% aqueous lead acetate solution (as the only available fluid source) for either none, one, two, or three generations. Lead exposure, regardless of generation, resulted in decreased body weight and a delay in age of first eye opening relative to controls, but did not delay home nest return latencies. Drinking the lead solution, across two and three successive generations, resulted in a marked and apparently cumulative decrease in pup viability, as well as an increase in dam fatality rates. However, no such cumulative or residual effects were observed on the behavioral activity of those mice who managed to survive. Perhaps a selection effect for lead-tolerant mice occurred in the present study; such an effect could account for the apparent lack of cumulative and residual behavioral effects.

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.