Selective effect of chronic lead ingestion on tyrosine hydroxylase activity in brain regions of rats

The Effect of Lead Exposure on Autism Development

Autism Spectrum Disorder (ASD) remains one of the most detrimental neurodevelopmental conditions in society today. Common symptoms include diminished social and communication ability. Investigations on autism etiology remain largely ambiguous. Previous studies have highlighted exposure to lead (Pb) may play a role in ASD. In addition, lead has been shown to be one of the most prevalent metal exposures associated with neurological deficits. A semi-systematic review was conducted using public databases in order to evaluate the extent of lead's role in the etiology of autism. This review examines the relationship between autistic comorbid symptoms-such as deterioration in intelligence scores, memory, language ability, and social interaction-and lead exposure. Specifically, the mechanisms of action of lead exposure, including changes within the cholinergic, dopaminergic, glutamatergic, gamma aminobutyric acid (GABA)ergic systems, are discussed. The goal of this review is to help illustrate the connections between lead's mechanistic interference and the possible furthering of the comorbidities of ASD. Considerations of the current data and trends suggest a potential strong role for lead in ASD.

Developmental changes of the activity of monoamine oxidase in pre- and postnatally lead exposed rats

The effects of prenatal and postnatal lead exposure on monoamine oxidase (MAO) activity were investigated in rat brain. MAO activity was examined in 2, 4, 6, and 8 weeks old rat to investigate the effects of lead in the different stages of rat brain development. Prenatal lead exposure was achieved by providing mother rats with drinking water containing either low (0.05%) or high (0.2%) concentration of lead acetate from gestation to birth. Postnatal lead treatment was performed through drinking water to mothers and pups from birth to the day of experiment. MAO activity was gradually increased with the development in all the brain regions examined, i.e. telencephalon, diencephalons, midbrain, pons/medulla, and cerebellum. Lead exposure increased MAO activity in most of the brain regions especially at early developmental stages (2 weeks of age) and the toxicity was gradually decreased with the development of rats. High concentration of lead showed greater effects on MAO activity compared to low concentration. Postnatal lead exposure showed stronger effects on MAO activity compared to prenatal lead exposure demonstrating the importance of preventing lead exposure to lactating mother. The increased MAO activity by lead intoxication may contribute to the neurobehavioral changes such as cognitive and attention deficit as well as hyperactivity, which is commonly observed both in lead intoxication and perturbed monoaminergic neurotransmission.

Effect of lead exposure on dopaminergic transmission in the rat brain

Lead is a neurotoxicant with known behavioral and neurochemical effects. In this study we attempted to relate the behavioral effects of lead to neurotransmission. Oral administration of 1000 ppm of lead acetate to young rats for 30 days caused a reduction in locomotor activity and stereotypic exploratory behavior during a 20 min testing period. This locomotor hypoactivity induced by lead was accompanied by a reduction in stereotypic behavior (sniffing, lickings, biting and grooming). These outcomes suggested that lead might interfere with catecholaminergic and particularly dopaminergic neurotransmission. Therefore, we examined the effect of the lead acetate on the uptake of dopamine in striatal synaptosomal preparations. The collected data showed a clear inhibition of the uptake of 3H-DA with an IC50 of 3.5 x 10(-5)M. This inhibition of the uptake of dopamine suggests that the behavioral effects of lead may be involved in dopaminergic neurotransmission.

Effects of postnatally administered inorganic lead on the tyrosine hydroxylase immunoreactive norepinephrinergic neurons of the locus ceruleus of the rat

The neurotoxic effects of inorganic lead are known to include peripheral neuropathy in adults and encephalopathy in children. The purpose of this study was to determine the effect of inorganic lead (PbCl2) administration on norepinephrinergic neurons of the locus ceruleus in neonatal rats by immunocytochemical and electron microscopic analyses. Lead chloride solutions, 0.05%, 0.1% and 0.2% in concentrations, were prepared in distilled water and administered orally via drinking water. After 4, 8, or 12 weeks of continuous administration, the rats were sacrificed and brains were immunostained with the tyrosine hydroxylase antibody. The number of immunoreactive cell bodies in the locus ceruleus was estimated. Densitometric analysis of immunoreactive profiles visualized by electron microscopy was performed using an image analyzer. The numbers of immunoreactive neurons in the locus ceruleus were increased statistically by lead administration. The intensity of the immunoreaction, both under the light and electron microscopes was also increased. Degenerative changes, including intra-axonal vacuole formation and widening of the extracellular spaces, were found by electron microscopy in and around the tyrosine hydroxylase immunoreactive axons. Increased tyrosine hydroxylase immunoreactivity may correlate with the hyper-reactivity of lead intoxicated children. Degenerative changes may account for the reported deficits in intellectual attainment and achievement in lead intoxicated children.