Pharmacological and neurochemical investigations of lead-induced hyperactivity

Vinpocetine, a Phosphodiesterase Type 1 Inhibitor, Mitigates Locomotor Hyperactivity in Female Mice Exposed to Lead During Development

Background/Objectives Studies in rodents indicate that disruptions in both cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) signaling pathways are involved in the development of hyperactive behavior. We examined whether vinpocetine, a phosphodiesterase type 1 inhibitor that enhances brain cAMP and cGMP levels, could mitigate locomotor hyperactivity in mice exposed to lead during early development. Methods Swiss mice were exposed to 90 ppm of lead in their drinking water throughout gestation and the first ten postnatal days. At postnatal day 10 (PN10), blood lead levels (BLLs) were about 30 µg/dL. At PN30, animals either received vinpocetine (20 mg/kg, i.p.) or a vehicle 4 h before the evaluation of locomotor activity in the open field. Results Lead-exposed males did not display differences in locomotor activity compared to controls, while lead-exposed females showed a significant increase in locomotion. Vinpocetine treatment significantly reversed the lead-induced hyperactivity in females. Conclusions These findings suggest that the cAMP and cGMP signaling pathways play a role in the hyperactivity induced by lead exposure.

Exploring Gut–Brain Interaction Disorders: Mechanisms and Translational Therapies Crossing Neurology to Gastroenterology

The bidirectional communication network between the gut and the brain, known as the gut–brain axis, plays a crucial role in health and disease. This review explores the mechanisms underlying gut–brain interaction disorders and highlights translational therapies bridging neurology and gastroenterology. Mechanisms encompass anatomical, endocrine, humoral, metabolic, and immune pathways, with the gut microbiota exerting profound influence. Clinical evidence links gut microbiota fluctuations to mood disorders, GI disruptions, and neurodevelopmental conditions, emphasizing the microbiome’s pivotal role in shaping brain–gut interactions. Pharmacological therapies such as amitriptyline and selective serotonin reuptake inhibitors modulate neurotransmitter activity, offering relief in functional gastrointestinal disorders like irritable bowel syndrome (IBS). Non-pharmacological interventions like cognitive–behavioral therapy and hypnotherapy address maladaptive thoughts and induce relaxation, alleviating gastrointestinal symptoms exacerbated by stress. Emerging therapies include gut microbiota modulation, dietary interventions, vagus nerve stimulation, and intestinal barrier modulation, offering novel approaches to manage neurological disorders via the gastrointestinal tract. Understanding and harnessing the gut–brain axis holds promise for personalized therapeutic strategies in neurogastroenterology.

Impact of Environmental Pollutants on Gut Microbiome and Mental Health via the Gut–Brain Axis

Over the last few years, the microbiome has emerged as a high-priority research area to discover missing links between brain health and gut dysbiosis. Emerging evidence suggests that the commensal gut microbiome is an important regulator of the gut–brain axis and plays a critical role in brain physiology. Engaging microbiome-generated metabolites such as short-chain fatty acids, the immune system, the enteric nervous system, the endocrine system (including the HPA axis), tryptophan metabolism or the vagus nerve plays a crucial role in communication between the gut microbes and the brain. Humans are exposed to a wide range of pollutants in everyday life that impact our intestinal microbiota and manipulate the bidirectional communication between the gut and the brain, resulting in predisposition to psychiatric or neurological disorders. However, the interaction between xenobiotics, microbiota and neurotoxicity has yet to be completely investigated. Although research into the precise processes of the microbiota–gut–brain axis is growing rapidly, comprehending the implications of environmental contaminants remains challenging. In these milieus, we herein discuss how various environmental pollutants such as phthalates, heavy metals, Bisphenol A and particulate matter may alter the intricate microbiota–gut–brain axis thereby impacting our neurological and overall mental health.

Modelling Autism Spectrum Disorder (ASD) and Attention-Deficit/Hyperactivity Disorder (ADHD) Using Mice and Zebrafish

Autism spectrum disorders (ASD) and attention-deficit/hyperactivity disorder (ADHD) are two debilitating neurodevelopmental disorders. The former is associated with social impairments whereas the latter is associated with inattentiveness, hyperactivity, and impulsivity. There is recent evidence that both disorders are somehow related and that genes may play a large role in these disorders. Despite mounting human and animal research, the neurological pathways underlying ASD and ADHD are still not well understood. Scientists investigate neurodevelopmental disorders by using animal models that have high similarities in genetics and behaviours with humans. Mice have been utilized in neuroscience research as an excellent animal model for a long time; however, the zebrafish has attracted much attention recently, with an increasingly large number of studies using this model. In this review, we first discuss ASD and ADHD aetiology from a general point of view to their characteristics and treatments. We also compare mice and zebrafish for their similarities and discuss their advantages and limitations in neuroscience. Finally, we summarize the most recent and existing research on zebrafish and mouse models of ASD and ADHD. We believe that this review will serve as a unique document providing interesting information to date about these models, thus facilitating research on ASD and ADHD.

The Interplay of Environmental Exposures and Mental Health: Setting an Agenda

BACKGROUND

To date, health-effects research on environmental stressors has rarely focused on behavioral and mental health outcomes. That lack of research is beginning to change. Science and policy experts in the environmental and behavioral health sciences are coming together to explore converging evidence on the relationship-harmful or beneficial-between environmental factors and mental health.

OBJECTIVES

To organize evidence and catalyze new findings, the National Academy of Sciences, Engineering, and Medicine (NASEM) hosted a workshop 2-3 February 2021 on the interplay of environmental exposures and mental health outcomes.

METHODS

This commentary provides a nonsystematic, expert-guided conceptual review and interdisciplinary perspective on the convergence of environmental and mental health, drawing from hypotheses, findings, and research gaps presented and discussed at the workshop. Featured is an overview of what is known about the intersection of the environment and mental health, focusing on the effects of neurotoxic pollutants, threats related to climate change, and the importance of health promoting environments, such as urban green spaces.

DISCUSSION

We describe what can be gained by bridging environmental and psychological research disciplines and present a synthesis of what is needed to advance interdisciplinary investigations. We also consider the implications of the current evidence for a) foundational knowledge of the etiology of mental health and illness, b) toxicant policy and regulation, c) definitions of climate adaptation and community resilience, d) interventions targeting marginalized communities, and e) the future of research training and funding. We include a call to action for environmental and mental health researchers, focusing on the environmental contributions to mental health to unlock primary prevention strategies at the population level and open equitable paths for preventing mental disorders and achieving optimal mental health for all. https://doi.org/10.1289/EHP9889.

The Association Between Parkinson's Disease and Attention-Deficit Hyperactivity Disorder

While Parkinson’s disease (PD) and attention-deficit hyperactivity disorder (ADHD) are two distinct conditions, it has been hypothesized that they share several overlapping anatomical and neurochemical changes. In order to investigate that hypothesis, this study used claims data from Taiwan’s Longitudinal Health Insurance Database 2000 to provide the significant nationwide population-based evidence of an increased risk of PD among ADHD patients, and the connection between the two conditions was not the result of other comorbidities. Moreover, this study showed that the patients with PD were 2.8 times more likely to have a prior ADHD diagnosis compared with those without a prior history of ADHD. Furthermore, an animal model of ADHD was generated by neonatally injecting rats with 6-hydroxydopamine (6-OHDA). These rats were subjected to behavior tests and the 99mTc-TRODAT-1 brain imaging at the juvenile stage. Compared to control group rats, the 6-OHDA rats showed a significantly reduced specific uptake ratio in the striatum, indicating an underlying PD-linked pathology in the brains of these ADHD phenotype-expressing rats. Overall, these results support that ADHD shares a number of anatomical and neurochemical changes with PD. As such, improved knowledge of the neurochemical mechanisms underlying ADHD could result in improved treatments for various debilitating neurological disorders, including PD.

Neurobehavioral effects of acute and chronic lead exposure in a desert rodent Meriones shawi: Involvement of serotonin and dopamine

Lead (Pb) is a non physiological metal that has been implicated in toxic processes affecting several organs and biological systems, including the central nervous system. Several studies have focused on changes in lead-associated neurobehavioral and neurochemical alterations that occur due to Pb exposure. The present study evaluates the effects of acute and chronic Pb acetate exposure on serotoninergic and dopaminergic systems within the dorsal raphe nucleus, regarding motor activity and anxiety behaviours. Experiments were carried out on adult male Meriones shawi exposed to acute lead acetate intoxication (25 mg/kg b.w., 3 i.p. injections) or to a chronic lead exposure (0,5%) in drinking water from intrauterine age to adult age. Immunohistochemical staining demonstrated that both acute and chronic lead exposure increased anti-serotonin (anti-5HT) and tyrosine hydroxylase (anti-TH) immuno-reactivities in the dorsal raphe nucleus. In parallel, our results demonstrated that a long term Pb-exposure, but not an acute lead intoxication, induced behavioural alterations including, hyperactivity (open field test), and anxiogenic like-effects. Such neurobehavioral impairments induced by Pb-exposure in Meriones shawi may be related to dopaminergic and serotoninergic injuries identified in the dorsal raphe nucleus.

Perinatal 6-Hydroxydopamine Modeling of ADHD

The neonatally 6-hydroxydopamine (n6-OHDA)-lesioned rat has been the standard for 40 years, as an animal model of attention-deficit hyperactivity disorder (ADHD). Rats so lesioned during postnatal ontogeny are characterized by ~99 % destruction of dopaminergic nerves in pars compacta substantia nigra, with comparable destruction of the nigrostriatal tract and lifelong ~99 % dopaminergic denervation of striatum, with lesser destructive effect on the ventral tegmental nucleus and associated lesser dopaminergic denervation of nucleus accumbens and prefrontal cortex. As a consequence of striatal dopaminergic denervation, reactive serotoninergic hyperinnervation of striatum ensues. The striatal extraneuronal milieu of DA and serotonin is markedly altered. Also, a variety of sensitization changes occur for dopaminergic D₁ and D₂ receptors, and for serotoninergic receptors. Behaviorally, these rats in adulthood display spontaneous hyperlocomotor activity, attentional deficits, and cognitive impairment-all of which are acutely attenuated by the psychostimulants amphetamine (AMPH) and methylphenidate (MPH) (i.e., opposite to the acute effects of AMPH and MPH in intact control rats). The acute behavioral effects of AMPH and MPH in intact and lesioned rats are analogous to their respective acute effects in non-ADHD and in ADHD humans. The neurochemical template of brain, and behavioral series of changes in n6-OHDA-lesioned rats, is described in the review. Despite the fact that nigrostriatal damage is not an underlying pathophysiological process of human ADHD (i.e., lacking construct validity), the described animal model has face validity (behavioral profile) and predictive validity (mirror of ADHD/MPH effects, as well as putative and new ADHD treatment effects). Also described in this review is a modification of the n6-OHDA rat, produced by adulthood partial lesioning of the serotoninergic fiber overgrowth. This ADHD model has even more accentuated hyperlocomotor and attentional deficits, counteracted by AMPH-thus providing a more robust means of animal modeling of ADHD. The n6-OHDA rat as a model of ADHD continues to be important in the search for new ADHD treatments.

Animal models of ADHD

Studies employing animal models of attention-deficit/hyperactivity disorder (ADHD) present clear inherent advantages over human studies. Animal models are invaluable tools for the study of underlying neurochemical, neuropathological and genetic alterations that cause ADHD, because they allow relatively fast, rigorous hypothesis testing and invasive manipulations as well as selective breeding. Moreover, especially for ADHD, animal models with good predictive validity would allow the assessment of potential new therapeutics. In this chapter, we describe and comment on the most frequently used animal models of ADHD that have been created by genetic, neurochemical and physical alterations in rodents. We then discuss that an emerging and promising direction of the field is the analysis of individual behavioural differences among a normal population of animals. Subjects presenting extreme characteristics related to ADHD can be studied, thereby avoiding some of the problems that are found in other models, such as functional recovery and unnecessary assumptions about aetiology. This approach is justified by the theoretical need to consider human ADHD as the extreme part of a spectrum of characteristics that are distributed normally in the general population, as opposed to the predominant view of ADHD as a separate pathological category.

Environmental exposure to lead, but not other neurotoxic metals, relates to core elements of ADHD in Romanian children: performance and questionnaire data

Neurobehavioral measures of attention, and clinical features of the attention-deficit hyperactivity disorder (ADHD) have been studied in pediatric environmental lead research. However rarely, if ever, have performance measures of attention or executive functions and questionnaire-based quantitative ADHD-observations been studied in the same subjects. We examined associations between pediatric blood lead concentrations (PbB), as well as those of mercury (Hg), and aluminum (Al), and performance in four different attention tasks, as well as behavioral ratings from an ICD-10 (hyperactivity) and DSM-IV-coded (attention deficit) German questionnaire (FBB-ADHS). Asymptomatic, 8-12 year old children from two Romanian cities were studied, namely Bucharest and Pantelimon, a city near a metal-processing plant. Blood was analyzed for Pb, Al, and Hg. Data from 83 children were available for final analysis. We assessed attention performance by means of four tasks of the computer-based ADHD-taylored German KITAP-battery. We also received questionnaire ratings from parents and teachers covering three ADHD-dimensions. Multiple linear regression analysis was used to estimate associations between the three neurotoxic trace metals in blood and the different ADHD features. After adjusting for eleven potentially confounding variables we found consistent borderline to significant associations between Pb, but not other metals, in blood and various performance- and questionnaire data. False alarm responses (FAR) in the KITAP subtests rather than response latencies exhibited positive associations with PbB. Questionnaire ratings for ADHD dimensions also revealed PbB-related adversity. With any two-fold increase of PbB outcome changed markedly, namely up to 35%. Restriction to children with PbBs<10mug/dl had only a marginal influence on outcome.The converging evidence from performance- and questionnaire data confirms that core elements of ADHD are adversely affected by low environmental PbB even below 10mug/dl, but not by other neurotoxic trace metals. Observed effect-sizes are considerably larger than those typically found for lead-related IQ-deficit, thus suggesting that attention deficit could be the more basic adverse effect of lead in children. This is the first study from Central and Eastern Europe dealing with links between environmental exposure of children to neurotoxic metals and ADHD.

Pharmacological models of ADHD

For more than 50 years, heavy metal exposure during pre- or post-natal ontogeny has been known to produce long-lived hyperactivity in rodents. Global brain injury produced by neonatal hypoxia also produced hyperactivity, as did (mainly) hippocampal injury produced by ontogenetic exposure to X-rays, and (mainly) cerebellar injury produced by the ontogenetic treatments with the antimitotic agent methylazoxymethanol or with polychlorinated biphenyls (PCBs). More recently, ontogenetic exposure to nicotine has been implicated in childhood hyperactivity. Because attention deficits most often accompany the hyperactivity, all of the above treatments have been used as models of attention deficit hyperactivity disorder (ADHD). However, the causation of childhood hyperactivity remains unknown. Neonatal 6-OHDA-induced dopaminergic denervation of rodent forebrain also produces hyperactivity - and this model, or variations of it, remain the most widely-used animal model of ADHD. In all models, amphetamine (AMPH) and methylphenidate (MPH), standard treatments of childhood ADHD, typically attenuate the hyperactivity and/or attention deficit. On the basis of genetic models and the noted animal models, monoaminergic phenotypes appear to most-closely attend the behavioral dysfunctions, notably dopaminergic, noradrenergic and serotoninergic systems in forebrain (basal ganglia, nucleus accumbens, prefrontal cortex). This paper describes the various pharmacological models of ADHD and attempts to ascribe a neuronal phenotype with specific brain regions that may be associated with ADHD.

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.

Developmental lead neurotoxicity: Alterations in brain cholinergic system

Developing brain has been shown to be susceptible to the neurotoxic effects of lead (Pb). Our earlier studies (Reddy GR, Riyaz Basha Md, Devi CB, Suresh A, Baker JL, Shafeek A, Heinz J, Chetty CS. Lead induced effects on acetylcholinesterase activity in cerebellum and hippocampus of developing rat. Int J Devl Neurosci 2003;21:347-52) have shown decrease in acetylcholinesterase (AChE) activity in the crude homogenates of cerebellum and hippocampus of rat brain exposed to Pb. In this study, we have further examined in detail, the alterations in AChE activity and acetylcholine (ACh) levels in different brain regions using histochemical and spectrophotometric methods. Rats were lactationally exposed to low level (0.2%) and high level (1%) Pb. The studies were conducted in young (1 month) and adult (3 months) rats. Pb exposure significantly decreased the specific activity of AChE and increased the levels of ACh in the synaptosomal fractions of cerebellum, hippocampus and cerebral cortex in a dose- and age-dependent manner. These alterations in AChE and ACh were more predominant in young rat brain as compared to adult brain. Maximum AChE activity and ACh level as well as maximum alterations following Pb exposure were observed in synaptosomes of hippocampus. Histochemical studies also showed higher AChE activity in the hippocampal region compared to other areas of brain as revealed by the intensity of AChE staining. Though high level Pb exposure remarkably decreased the intensity of AChE staining in the dentate gyrus, CA2 and CA3 areas of hippocampus, and different cell layers of cortex and cerebellum, highly significant loss of AChE activity was observed in the CA3 region of hippocampus, molecular layer of cerebellum and cortical cell layers. These data suggest that Pb exposure may selectively affect cholinergic system in brain areas controlling learning and cognitive behavior.

Zinc and Calcium Reduce Lead Induced Perturbations in the Aminergic System of Developing Brain

Since alterations in monoamines and monoamine oxidase (MAO) have been postulated to play a role in toxic effects of lead (Pb) on the central nervous system, we have examined the protective effects of calcium (Ca2+) and zinc (Zn2+) supplementation on Pb-induced perturbations in the levels of monoamines and the activity of MAO. Swiss albino mice were lactationally exposed to low (0.2%) and high (1%) levels of Pb-acetate via drinking water of the mother. Pb-exposure commenced on postnatal day (PND) 1, continued up to PND 21 and stopped at weaning. Ca2+ or Zn2+ (0.02% in 0.2% Pb-water or 0.1% in 1% Pb-water) was supplemented separately to the mother up to PND 21. The levels of monoamines (epinephrine, norepinephrine, dopamine and serotonin) and the activity of MAO in the brain regions such as hippocampus, cortex, cerebellum and medulla of young (1 month old) and adult (3 month old) mice were determined in the synaptosomal fractions. The synaptosomal monoamines though increased with low level (0.2%) Pb-exposure, significantly decreased with high level (1%) Pb-exposure in all the brain regions in both the age groups. In general, the young mice seem to be more vulnerable to Pb-neurotoxicity. Ca2+ or Zn2+ supplementation significantly reversed the Pb-induced perturbations both in the levels of monoamines and in the activity of MAO. However, the recovery in monoamine levels and MAO activity was more pronounced with Ca2+ supplementation as compared to Zn2+. These results provide evidence that dietary Ca2+ and/or Zn2+ provide protection against Pb-induced neurotoxic effects.

Protective effects of Hippophae rhamnoides L. juice on lead-induced neurotoxicity in mice

We examined the effect of Hippophae rhamnoides L. (HRL) juice on lead-induced memory impairment and neuronal damage in the brains of adult mice. Kunming mice were exposed to lead acetate 10 mg/kg body weight for 20 d. Twenty percent and 40% HRL prevented the lead-induced decrease in step-through latency. In the water maze test, the swimming time was lengthened in mice treated with lead acetate, but this time was decreased in mice that received 20% and 40% HRL. The malondialdehyde (MDA) levels were increased in lead-treated mice, which were reduced by 20% and 40% HRL in dose-dependent manner. The activities of acetylcholinesterase (AchE) and monoamine oxidase-A and -B were significantly increased in the lead-treated group, which were decreased by 40% HRL but not by 20% HRL. The levels of norepinephrine, serotonin, and 5-hydroxyindole acetic acid were decreased significantly in the lead-treated mice, and the decreases were antagonized by 40% HRL, except for than in dopamine, but 20% HRL had no effect on this change. These data suggest that the different doses of the HRL juice protect against the lead acetate-induced deficits in learning and memory and changes in neurobiochemical parameters.

Developmental lead exposure alters mitochondrial monoamine oxidase and synaptosomal catecholamine levels in rat brain

Rats were lactationally exposed to low- (0.2%) and high-level (1%) lead (Pb) from postnatal day 1 (PND1) through PND21 through the drinking water of the mother. The levels of catecholamines, epinephrine, norepinephrine and dopamine and the activity of the enzyme monoamine oxidase (MAO) were determined in the cerebellum, hippocampus and cerebral cortex in young (1-month-old) and adult (3-month-old) rats. Pb-exposure decreased the activity of mitochondrial MAO in all the brain regions in a dose-dependent manner. The synaptosomal catecholamines (epinephrine, norepinephrine and dopamine), however, increased with low level (0.2%) Pb-exposure and significantly decreased with high level (1%) Pb-exposure in both the age groups. In general, the young rats seem to be more vulnerable to Pb-neurotoxicity. These data suggest that Pb-exposure perturbs the aminergic system in the cerebral cortex, cerebellum and hippocampus and may contribute to the cognitive and behavioural impairments observed in Pb-exposed rats.

Lead induced effects on acetylcholinesterase activity in cerebellum and hippocampus of developing rat

Exposure to low-levels of lead (Pb) during early development has been implicated in behavioral abnormalities and cognitive deficits in children. The present study is focused on developmental changes in hippocampus and cerebellum of rats following perinatal exposure to Pb. Pregnant rats were exposed to 0.2% Pb-acetate from gestation day 6 (GD 6) through postnatal day (PND) 21 and the activity levels of acetylcholinesterase (AChE) were estimated in cerebellum and hippocampus of pups at specific time points for 5 weeks. In both the brain regions, Pb-exposure decreased AChE activity with an increase in age. Histochemical observations conducted in 35 days old rat brain showed decreased AChE activity conspicuously in stratum oriens and dentate gyrus of hippocampus, and molecular and granule cell layers of cerebellum. In vitro studies conducted in 35 days old rat brain showed a considerable decrease in the specific activity of AChE at high concentrations (50-100 microM) of Pb in a concentration-dependent manner. However, at low concentrations (5-20 microM), Pb failed to produce such changes. In the presence of eserine (physostigmine), the specific inhibitor of AChE, the inhibitory effect of Pb was potentiated and this was more pronounced at low-concentrations of Pb. The behavioral responses in open-field also showed a significant decrease in both Pb exposed as well as eserine administered rats. These data suggest that low-level perinatal Pb-exposure induces alterations in cholinergic system in the cerebellum and hippocampus of developing brain even after the withdrawal of Pb-exposure, that may contribute to behavioral and learning deficits.

Animal models of attention-deficit hyperactivity disorder

Attention-deficit hyperactivity disorder (ADHD) involves clinically heterogeneous dysfunctions of sustained attention, with behavioral overactivity and impulsivity, of juvenile onset. Experimental models, in addition to mimicking syndromal features, should resemble the clinical condition in pathophysiology, and predict potential new treatments. One of the most extensively evaluated animal models of ADHD is the spontaneously hypertensive rat. Other models include additional genetic variants (dopamine transporter gene knock-out mouse, coloboma mouse, Naples hyperexcitable rat, acallosal mouse, hyposexual rat, and population-extreme rodents), neonatal lesioning of dopamine neurons with 6-hydroxydopamine, and exposure to other neurotoxins or hippocampal irradiation. None is fully comparable to clinical ADHD. The pathophysiology involved varies, including both deficient and excessive dopaminergic functioning, and probable involvement of other monoamine neurotransmitters. Improved models as well as further testing of their ability to predict treatment responses are required.

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.

Short-term exposure to dietary Pb and/or DMSA affects dopamine and dopamine metabolite levels in the medulla, optic tectum, and cerebellum of rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) were randomly assigned to one of the following dietary exposure conditions: lead (Pb) solvent (2% nitric acid), meso-2,3-dimercaptosuccinic acid (DMSA) solvent (0.1 N NaOH), Pb, DMSA, Pb followed by Pb solvent, or Pb followed by DMSA. Medulla, cerebellum, and optic tectum homogenates were analyzed for dopamine (DA), homovanillic acid (HVA), and 3,4-dihydroxyphenylacetic acid (DOPAC). DA levels in all brain regions tended to be highest for trout exposed to dietary Pb followed by dietary DMSA. DA levels were elevated for trout exposed to dietary DMSA and Pb followed by Pb solvent. DA levels were below control levels for trout exposed to Pb only. HVA levels varied across brain regions. However, HVA levels in all brain regions tended to be elevated for trout exposed to dietary DMSA and Pb followed by Pb solvent. DOPAC levels across all brain regions were below control levels for trout dietary exposed to DMSA, Pb only, Pb followed by Pb solvent, and Pb followed by DMSA. These data indicate that Pb and/or DMSA have the potential of altering DA, HVA, and DOPAC levels in the medulla, cerebellum, and optic tectum. The animal model of short-term dietary exposure to Pb and DMSA, both alone and sequentially, to mimic dietary exposure to Pb and the oral delivery of DMSA, that our laboratory has developed, may be useful in future studies aimed at characterizing the neurobiological mechanisms by which Pb and/or DMSA alter neurotransmitter levels and behavior.

Alternative treatments for adults with attention-deficit hyperactivity disorder (ADHD)

A previous review of alternative treatments (Tx) of ADHD--those other than psychoactive medication and behavioral/psychosocial Tx--was supplemented with an additional literature search focused on adults with ADHD. Twenty-four alternative Tx were identified, ranging in scientific documentation from discrediting controlled studies through mere hypotheses to positive controlled double-blind clinical trials. Many of them are applicable only to a specific subgroup. Although oligoantigenic (few-foods) diets have convincing double-blind evidence of efficacy for a properly selected subgroup of children, they do not appear promising for adults. Enzyme-potentiated desensitization, relaxation/EMG biofeedback, and deleading also have controlled evidence of efficacy. Iron supplementation, magnesium supplementation, Chinese herbals, EEG biofeedback, massage, meditation, mirror feedback, channel-specific perceptual training, and vestibular stimulation all have promising prospective pilot data, many of these tests reasonably controlled. Single-vitamin megadosage has some intriguing pilot trial data. Zinc supplementation is hypothetically supported by systematic case-control data, but no systematic clinical trial. Laser acupuncture has promising unpublished pilot data and may be more applicable to adults than children. Essential fatty acid supplementation has promising systematic case-control data, but clinical trials are equivocal. RDA vitamin supplementation, non-Chinese herbals, homeopathic remedies, and antifungal therapy have no systematic data in ADHD. Megadose multivitamin combinations are probably ineffective for most patients and are possibly dangerous. Simple sugar restriction seems ineffective. Amino acid supplementation is mildly effective in the short term, but not beyond 2-3 months. Thyroid treatment is effective in the presence of documented thyroid abnormality. Some alternative Tx of ADHD are effective or probably effective, but mainly for certain patients. In some cases, they are the Tx of choice, and initial evaluation should consider the relevant etiologies. A few have failed to prove effective in controlled trials. Most need research to determine whether they are effective and/or to define the applicable subgroup. Some of them, although not safer than standard Tx, may be preferable for an etiologic subgroup.

Effects of lead exposure on licking and yawning behaviour in rats

In the present study, effects of lead exposure on licking and yawning behaviour have been studied. The dopaminergic receptor agonist, apomorphine (0.15, 0.25 and 0.5 mg/kg), induced dose-dependent licking in rats. The maximum response was obtained with 0.5 mg/kg of the apomorphine. Lead acetate (0.05%) exposure significantly increased apomorphine-induced licking. Yawning induced by the D2 dopaminergic agonist, bromocriptine (2, 3, 4, 8 mg/kg), and the cholinergic drug, physostigmine (0.1 or 0.3 mg/kg), was significantly decreased by lead acetate (0.05%) exposure. It may be concluded that the behaviour induced by dopaminergic or cholinergic agents can be affected by lead subchronic exposure.

The genetic effects of environmental lead

This article reviews the effects of lead on genetic systems in the context of lead's various other toxic effects and its abundance and distribution in the environment. Lead is perhaps the longest used and best recognized toxic environmental chemical, yet it continued be used recklessly until only very recently. Lead is thus a lesson in the limitations and strengths of science, human conscience and common sense. Lead has been tested and found to be capable of eliciting a positive response in an extraordinarily wide range of biological and biochemical tests; among them tests for enzyme inhibition, fidelity of DNA synthesis, mutation, chromosome aberrations, cancer and birth defects. It reacts or complexes with many biomolecules and adversely affects the reproductive, nervous, gastrointestinal, immune, renal, cardiovascular, skeletal, muscular and hematopoietic systems as well as developmental processes. It is likely that lead is a selective agent that continues to act on and influence the genetic structure and future evolution of exposed plant and animal populations.

Effects of lead-arsenic combined exposure on central monoaminergic systems

Lead acetate (116 mg/kg/day), arsenic (11 or 13.8 mg/kg/day as sodium arsenite), a lead-arsenic mixture or vehicle were administered to adult mice through gastric intubation during 14 days. Then, the regional content of norepinephrine (NE), dopamine (DA), serotonin (5-HT), 3,4 dihydroxyphenyl-acetic acid (DOPAC), 5-hydroxyindole-3-acetic acid (5-HIAA), arsenic, and lead were quantified. Compared with the accumulation after single element exposures, the mixture elicited a higher accumulation of lead and a lower arsenic accumulation in the brain. Compared to controls, lead induced only an augmentation of DOPAC (200%) in the hypothalamus. By contrast, the mixture provoked increases of DOPAC in the hypothalamus (250%), DA and 5-HIAA in the striatum (67 and 187%, respectively) and NE decreased in the hypothalamus (45%). Although these alterations were similar to those produced by arsenic alone, the mixture provoked a 38% decrease of NE in the hippocampus and increases of 5-HT in midbrain and frontal cortex (100 and 90%, respectively) over control values, alterations that were not elicited by either metal alone. These results demonstrate an interaction arsenic/lead on the central monoaminergic systems of the adult mouse.

Reduced densities of sodium-dependent [3H] hemicholinium-3 binding sites in hippocampus of developmental rats following perinatal low-level lead exposure

We investigated the effect of perinatal, low-level lead exposure on [3H]hemicholinium-3 (HC-3) binding in the hippocampus of postnatal rat. Rat pups were maternally lead-exposed from gestational day 16 through postnatal day 28 (PN28). In control animals, the [3H]HC-3 binding sites increased from 7 fmol/mg protein at postnatal day 1 (PN1) to 14 and 35 fmol/mg protein at PN7 and PN14, respectively, and reached adult values of 50 fmol/mg protein, at PN21 and PN28. In lead-exposed litters, the [3H]HC-3 binding was reduced by 30-40% throughout the early postnatal development and remained 40% below control values in PN60 animals, one month after termination of lead exposure. The Pb-induced reduction in HC-3 binding was associated with a similar decrease in ChAT activity and was comparable to the effect of localized lesion of medial septum. Septal cell counts in the lead-exposed PN21 rats indicated a 22% reduction in the number of ChAT-immunoreactive cells in the medial septum/vertical diagonal band (MS/vDB) complex although cell numbers in the horizontal limb of the diagonal band (hDB) were not altered. These results suggest that perinatal, low-level lead exposure results in a reduced density of cholinergic nerve terminals in the hippocampus, either due to impaired development or degeneration of the cholinergic projection neurons in the MS/vDB complex.

In vivo exposure to lead does not influence muscarinic receptors in the frontal cortex of the mouse brain

The effects of lead on muscarinic receptors in the brain of adult and juvenile mice were studied in vivo. Lead was administered for periods of 10, 30, and 90 days to adult mice. Perinatal exposure was achieved by treating gestating mice from the day of conception. The exposure was continued after birth and during weaning until 30 days postnatal. Both groups, adult mice and pups or their mothers were given a solution of 10, 100, and 1000 ppm inorganic lead in their drinking water, which was available ad libitum. Radioligand binding studies were performed in vitro to determine receptor densities (Bmax) and affinities (KD values) in brain membranes of the frontal cortex. In addition, the binding of a selective muscarinic agonist and of an antagonist to receptor subtypes was investigated. Inhibition curves of 3H-quinuclidinylbenzilate (3H-QNB) labelled membranes were determined with the m1-antagonist pirenzepine and the m2-agonist carbachol to distinguish between high- and low-affinity agonist and antagonist states in the cortex. Few important changes in density or affinity to the membrane receptors investigated were seen in animals treated with lead. Similarly the properties of high- and low-affinity muscarinic receptor binding were unchanged in the groups exposed to lead. In conclusion, the present results show that lead does not affect the muscarinic receptors in mouse brain under the experimental conditions used.

Effect of acute pretreatment of lead on picrotoxin-induced convulsions in rats

The effect of acute exposure to lead acetate (LA)/lead nitrate (LN) on onset and severity of convulsions induced by a low dose of picrotoxin was examined in rats. Both LA and LN reduced the time of onset and exacerbated the severity of convulsions, with a resultant high lethality. On comparison, it was noted that in the LA-pretreated group, convulsion scores and incidence of tonus and mortality were much higher; the appearance of tonus was more delayed than in the LN-pretreated group. In lead-pretreated animals, the potentiation of picrotoxin-induced convulsions was accompanied by higher lead levels in blood (p < 0.001). However, the whole-brain lead levels were not significantly different in these animals compared to the controls. The difference in the degree of potentiation by the two forms of lead could possibly be attributed either to the role of a combination of anions and cations or to the variable cerebral uptake and regional distribution of lead or due partly to the extent of competitive interaction involving d-aminolaevulinic acid--whose level is known to be elevated consequent to lead-induced disruption of haem biosynthesis--at GABA receptors.

[Physiopathology of inorganic lead poisoning]

This paper gives an overview of the hypotheses concerning the mechanisms of inorganic lead toxicity on cells and tissues, with emphasis on the effect of low-concentration lead. Inhibition of heme synthesis is responsible not only for lead-induced anaemia, but also for accumulation of delta-aminolaevulinic acid (ALA) and for lowering the concentration of cytochromes contained in the mitochondrial respiratory chain. Auto-oxidation of ALA is thought to result in the formation of free radicals. On the other hand, lead replaces ionic calcium in its role as second cell messenger. This mechanism would explain the abnormalities observed in synaptic transmission, arteriolar vasoreactivity and functioning of such cells as osteoclasts and osteoblasts. Nuclear toxicity, with abnormal expression of DNA genes and inhibition of certain enzymes such as membrane Na+/K+ ATPase, are also considered. The mechanisms of tissue toxicity are discussed.

Toxic effects of lead on neuronal development and function

The effects of lead on the development of the nervous system are of immediate concern to human health. While it is clear that lead can affect neuronal development at levels of exposure within the range found in the environment, the particular mechanism of the disruption is not readily ascertained. Lack of knowledge of the mechanisms of lead-induced damaged hampers its treatment and prevention. The goal of our research is to develop a model system in which the effects of lead on central nervous system development can be demonstrated. The complexity of the brain hampers such investigations because often it is not clear if apparent toxic effects represents changes secondary to somatic changes, such as endocrine or hematological defects, that could alter brain development, or even transneuronal effects caused by toxicity at a distal site that deprives a brain area of a synaptic input needed for its proper development. A related problem is the redundancy of compensatory systems in the brain. Such system may disguise the severity of the initial toxic insult and themselves can cause functional disturbances. To study neuronal development in a system that minimizes such difficulties, we have grafted discrete brain regions derived from rat fetuses into the anterior chamber of the eye of adult hosts. The brain pieces continue organotypic development of the eye, but are isolated from possible secondary changes due to alterations in the development of the endocrine and other somatic systems because the adult host has these systems already fully developed. Similarly, effects mediated by connecting brain areas are minimized since the transplant is isolated in the anterior chamber of the eye.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of low level lead exposure on the postnatal structuring of the rat cerebellum

Exposure of rat pups to lead (less than 45 micrograms/dl blood) caused no alterations in the rate of cerebellar cell acquisition, migration or final number when compared with age-matched controls. The rate of DNA biosynthesis was higher in the lead-exposed animals compared to controls and remained elevated until postnatal day 10. This observation suggests lengthening of the cell cycle. The expected increase in DNA biosynthetic rate was delayed in neuron-enriched fractions obtained from lead-exposed pups. This may have been due to the isolation procedure specifically selecting internal granular layer cells which migrated precociously during a protracted G1 phase in a lead-impaired cell cycle. Morphometric studies revealed no difference in the number, viability and migration of cells within and from the external granular layer of the cerebellum of lead-exposed animals. It is concluded that chronic low level lead exposure has no significant effect on the early structuring of the developing cerebellum.

Mechanistic approaches in the study of testicular toxicity: toxicants that affect the endocrine regulation of the testis

This review will expand on the themes presented by Heindel and Treinen (1988). As a prelude to describing where selected compounds act on the endocrine regulation of the testis and the theories about their mechanisms, we will briefly review some of the central pathways that underlie this control. After reviewing some studies that define the site of action of lead on the reproductive system, we will discuss the "signature" lesion caused by androgen deficiency, and then move on to an evaluation of the effects of an antiandrogen (flutamide) on the male reproductive system. Finally, some consideration will be given to alterations in hepatic function which modify circulating levels of androgens.

Influence of dietary deficiency of nicotinamide on lead toxicity in young rats

The influence of dietary nicotinamide deficiency on lead intoxication in young developing rats was investigated. The Pb induced an increase in brain dopamine and noradrenaline, inhibition in blood δ-aminolevulinic acid dehydratase activity, an elevation in urinary excretion of δ-aminolevulinic acid and blood and tissue uptake of Pb were significantly more marked in animals maintained on a nicotinamide-deficient diet than those fed a nicotinamide-sufficient diet. The nicotinamide deficiency may enhance the susceptibility to Pb intoxication possible by enhancing the absorption of Pb and altering nicotinic acid metabolism.

The combined effect of Pb2+ and Mn2+ on monoamine uptake and Na+, K+-ATPase in striatal synaptosomes

Rat striatal synaptosomes (P2-fraction) were subjected to lipoperoxidation by the addition of 120 microM Fe2+ and 200 microM ascorbic acid. This preparation (pretreated synaptosomes) was used to investigate the interaction of Pb2+ and Mn2+ on the uptake of tritiated catecholamines, Na+, K+-ATPase activity and malondialdehyde (MDA) formation in order to understand the mechanism of enhanced neurotoxicity by concurrent exposure to these metals. The combination of Pb2+ and Mn2+ (25 microM + 100 microM, respectively) produced a significant increase in the uptake of 3H-Dopamine only in the untreated synaptosomes. No significant effect was noted on the uptake of 3H-Norepinephrine in either pretreated or untreated synaptosomes. However, the combination of Pb2+ and Mn2+ produced a pronounced decrease in the activity of Na+, K+-ATPase, but the magnitude of the change was the sum of the individual metal effects. Metal interaction did not produce any significant change in the formation of MDA compared to the control (without addition of metals). These results indicate that Pb2+ and Mn2+ interaction may produce inhibition in the activity of transport ATPase in both the preparation of synaptosomes, with more pronounced effect of synaptosomes subjected to lipoperoxidation and these changes may be responsible for the disruption in the physiology of nerve impulse transmission.

Effect of combined exposure to lead and ethanol on some biochemical indices in the rat

We investigated the effect of daily oral administration to young rats of lead (10 mg/kg) and ethanol (10%, v/v, in drinking water), either alone or in combination, for 8 weeks on the uptake of lead in tissues, brain biogenic amines, hepatic alcohol dehydrogenase and cytosolic and mitochondrial aldehyde dehydrogenase and some selected lead-sensitive variables. Lead given in combination with ethanol produced more pronounced inhibition in the activities of hepatic glutamic oxalacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) as compared to lead alone treatment. Simultaneous exposure to lead and ethanol produced a greater depression of dopamine (DA) and 5-hydroxytryptamine (5-HT) levels in the whole brain of rats, compared to rats treated with lead alone. The concentrations of lead in blood, liver and brain were significantly higher in rats exposed simultaneously to lead and ethanol. Though ethanol treatment alone inhibited the activities of hepatic alcohol dehydrogenase and cytosolic and mitochondrial aldehyde dehydrogenase, no effect of lead treatment alone on these variables was observed. The results suggested that animals exposed to ethanol and lead are more vulnerable to the neurologic and hepatotoxic effects and the systemic toxicity of lead.

Psychopharmacological investigations of a lead-induced long-term cognitive deficit in monkeys

This study investigated pharmacological manipulations of the cholinergic (ACh) and dopaminergic (DA) transmitter systems in monkeys with a long-term lead-induced cognitive deficit on delayed spatial alternation (DSA). Both ACh and DA have been found to be affected by developmental lead exposure and to be involved with performance on spatial learning and memory tasks. The lead-induced deficit in performance accuracy on DSA persisted throughout the 2 years of this experiment, which ended more than 8 years after the end of the postnatal lead exposure. Acute administration of agonists and antagonists of the ACh and DA systems did not elicit differential effects from the lead-exposed and control groups in terms of DSA per cent correct performance. The ACh antagonist, scopolamine, caused a dose-related decline in performance in both groups. Significant amelioration of the lead-induced DSA deficit was achieved by chronic treatment with the DA agonist, L-dopa. After withdrawal from L-dopa, the lead-related deficit reappeared. Improvement in performance of the lead-treated group was also seen after chronic amphetamine administration, but this effect was not significant. These data implicate DA mechanisms in the long-lasting cognitive effects of developmental lead exposure. The alleviation of the deficit with chronic administration of a DA precursor points to a possible line of treatment for the cognitive effects of developmental lead exposure.

[Kidney function in lead burden]

Renal failure as a consequence of manifest lead intoxication (nephropathia saturnina) has almost completely disappeared in the FRG. However, there has been rising concern that increased lead burden, primarily as a result of environmental pollution, may adversely affect blood pressure and renal function even in the absence of extrarenal signs of lead intoxication. Such concern is based on epidemiological studies which demonstrated a relation between blood lead level and blood pressure and on experimental studies which showed that lead activates several pressor mechanisms. Furthermore, increased body lead burden is found in a substantial proportion of patients with renal failure, particularly when concomitant gout is present. Unfortunately, none of the above findings constitute irrefutable evidence and further studies are clearly necessary.

Effect of lead exposure on dopaminergic receptors in rat striatum and nucleus accumbens

Haloperidol- and sulpiride-displaceable [3H]spiroperidol binding and the dopamine-inhibited adenylate cyclase were measured in rats chronically exposed to lead acetate. Haloperidol-displaceable [3H]spiroperidol binding was unmodified while sulpiride-displaceable binding was increased in striatum and decreased in nucleus accumbens. In addition, the decrease of sulpiride-displaceable binding in nucleus accumbens was paralleled by a reduced ability of bromocriptine to inhibit cAMP formation in presence of the D1 receptor antagonist SCH 23390. The results support the concept that in vivo lead treatment affects dopaminergic receptors and that the binding sites labelled by [3H]spiroperidol displaced by haloperidol may be different from those which recognize sulpiride.

Regional modification of brain calcium antagonist binding after in vivo chronic lead exposure

Lead toxicity in the central nervous system seems to be partially related to specific effects of the metal on calcium metabolism and in particular on calcium transport. On this line, the present study investigates the characteristics of [3H]nitrendipine binding to several rat brain regions after in vitro lead addition or after in vivo chronic exposure to this metal. In vivo a lead induced increase in [3H]nitrendipine binding, Bmax, is observed in cerebral cortex and striatum while the binding is unmodified in hippocampus. The in vitro studies are in agreement with in vivo data; lead addition stimulates the binding in synaptic membranes prepared from cortex and striatum but not from hippocampus where the binding is slightly inhibited. The data suggest that lead interferes with neuronal calcium channels in an area-selective manner.

Effect of lead on Na+,K+ATPase activity in the developing brain of intra-uterine growth-retarded rats

Lead (Pb) intoxication in developing mammals, including humans, produces serious brain damage. In addition, it is known that nutritional status influences the susceptibility to Pb toxicity. We developed an in utero undernutrition model based on restriction of blood supply to fetuses on d 17 of pregnancy (IUGR rats). The aim of this study was to investigate in vitro the possible effect of Pb on Na+, K+ATPase activity in the brain of developing IUGR and control rats from 6 to 60 d after birth. In addition, we measured the stimulation of Na+, K+ATPase by the monoamines noradrenaline and serotonin. Our results show that: The neurotoxic effect of Pb is an age-related phenomenon. Both IUGR and control rats were more sensitive to Pb in the first week of life. In adults, Pb had a weak inhibitory potency; the delayed matured brain in IUGR animals seemed less sensitive to Pb when compared to age-paired control rats; in the IUGR group, at 15 and 22 d, low doses of Pb had a stimulatory effect on Na+, K+ATPase instead of an inhibitory effect; noradrenaline and serotonin stimulated Na+, K+ATPase activity to an equivalent extent, but this was greater in IUGR than control rats; and at low Pb concentrations, the studied monoamines reversed Pb-induced inhibition.

The behavioral effects of prenatal and early postnatal lead exposure in the primate Macaca fascicularis

Female Macaca fascicularis monkeys were given daily oral doses of 3.0 and 4.25 mg/kg lead, as lead nitrate, prior to breeding, and exposure was maintained throughout gestation and terminated at parturition. No overt signs of lead toxicity were observed in the maternal monkeys. The offspring were tested at 6 to 18 months of age on a three-choice non-spatial form discrimination paradigm, and at 19 to 26 months of age on a response inhibition task. When compared to controls, the lead-exposed infants showed a deficit in form discrimination performance which continued during the entire period of testing. A deficit in response inhibition performance was also observed in exposed infants when compared to controls. However, the deficit was temporary, as the performance of all groups was similar at the termination of testing. The observation of a persistent deficit in form discrimination up to 18 months following the termination of exposure suggests that lead-induced behavioral changes may be permanent. These findings are cause for concern since behavioral deficits in the offspring were observed at maternal gestational whole blood lead levels within a concentration range (30 to 70 micrograms/dl) associated with occupational exposure.

[3H]spiperone and [3H]quinuclidinyl benzilate binding in striatal membranes from rats chronically treated with manganese chloride throughout development and for over two years

Chronic treatment of rats with manganese (1 mg MnCl2 X 4H2O per ml of drinking water) from conception till adulthood only slightly decreased [3H]spiperone binding in striatal membranes whereas [3H]quinuclidinyl benzilate binding was not affected. The age-related decreases in dopaminergic and muscarinic cholinergic receptor binding in striatal membranes were not affected by the life-span manganese treatment.

Lifetime lead intoxication: influence on the amygdaloid kindling model of epileptogenesis

The nature of amygdaloid kindled seizures was studied in adult rats which were intoxicated with lead starting in neonatal life. Lactating females were exposed to lead via the drinking water (0.25% lead acetate) and the litters were continued on this level of lead after weaning at 27 days of age. When compared to controls, levels of lead in the blood and brain were significantly higher in lead-exposed rats, both at the time of weaning as well as postkindling, beyond 150 days of age. Parameters relating to amygdaloid kindled seizures, including the rate of kindling, seizure latency and seizure threshold were not significantly different in lead-treated rats than in controls. However, duration of behavioral seizures and afterdischarges was significantly longer in rats exposed to lead. Our data suggest that, although lead intoxication starting in neonatal life does not appear to affect the susceptibility to development of amygdaloid kindled seizures, it may enhance seizure severity in this model of epileptogenesis.

Postnatal lead exposure and the cholinergic system

Previous reports have suggested that the behavioral effects of early lead (Pb) exposure may be due to an underlying deficiency in cholinergic function. To further examine this possibility, Long-Evans hooded rat pups were exposed to Pb for the first 25 postnatal days via the maternal milk. Dams were fed either 4.0% PbCO3 (High Pb), 0.4% PbCO3 (low Pb) or a Na2CO3 control diet throughout this period. Beginning at 65 days of age, animals were tested on behavioral tasks sensitive to both Pb exposure and cholinergic deficiency. Exposure to both levels of Pb impaired passive avoidance acquisition and produced lower rates of spontaneous alternation. Pb, however, had no clear effects on open field activity. The cholinergic agonist physostigmine (0.05 and 0.075 mg/kg) did not affect the behavior of control animals on any task, but in both Pb exposed groups physostigmine improved passive avoidance acquisition, increased the rate of spontaneous alternation and lowered open field activity scores. The cholinergic antagonist scopolamine (0.4 mg/kg) impaired passive avoidance acquisition, lowered the rate of spontaneous alternation and increased open field activity scores in control animals. Consistent with behavior characteristic of an inverted U shaped response curve, scopolamine (0.2 and 0.4 mg/kg) improved passive avoidance acquisition in both Pb exposed groups and decreased open field activity scores in the High Pb group. In all cases, the behavioral response of the Pb exposed animals may be interpreted as responses characteristic of cholinergically deficient animals. These results thus provide further evidence for cholinergic system involvement in the behavioral changes observed following early exposure to Pb.