Chronic low-level lead exposure affects the monoaminergic system in the mouse superior olivary complex

Lead exposure induces nitrative stress and disrupts ribbon synapses in the cochlea

Environmental exposure to heavy metal lead, a public health hazard in many post-industrial cities, causes hearing impairment upon long-term exposure. Lead-induced cochlear and vestibular dysfunction is well-documented in animal models. Although short-term exposure to lead at concentrations relevant to environmental settings does not cause significant shifts in hearing thresholds in adults, moderate- to low-level lead exposures induce neuronal damage and synaptic dysfunction. We reported that lead exposure induces oxidative stress in the mouse cochlea. However, lead-induced nitrative stress and potential damage to cochlear ribbon synapses are yet to be fully understood. Therefore, this study has evaluated cochlear synaptopathy and nitrative stress in young-adult mice exposed to 2 mM lead acetate for 28 days. Inductively coupled plasma mass spectrometry (ICP-MS) analysis indicated that this exposure significantly increased the blood lead levels. Assessment of hair cell loss by immunohistochemistry analysis and outer hair cell (OHC) activity by recording distortion product otoacoustic emissions (DPOAEs) indicated that the structure and function of the hair cells were not affected by lead exposure. However, this exposure significantly decreased the expression of C-terminal-binding protein-2 (CtBP2) and GluA2, pre- and post-synaptic protein markers in the inner hair cell synapses, particularly in the basal turn of the organ of Corti, suggesting lead-induced disruption of ribbon synapses. In addition, lead exposure significantly increased the nitrotyrosine levels in spiral ganglion cells, suggesting lead-induced nitrative stress in the cochlea. Collectively, these findings suggest that lead exposure even at levels that do not affect the OHCs induces cochlear nitrative stress and causes cochlear synaptopathy.

Developmental lead exposure affects dopaminergic neuron morphology and modifies basal slowing response in Caenorhabditis elegans: effects of ethanol

Lead (Pb) and ethanol (EtOH) are neurotoxicants that affect the dopaminergic (DAergic) system. We first sought to assess the morphology of the DAergic neurons in the Caenorhabditis elegans BY200 strain. The results demonstrated dose-dependent damage in these neurons induced by developmental Pb exposure. Secondly, transgenic worms exposed to 24μM Pb and administered with 200mM EtOH were evaluated in the basal slowing response (BSR). Pb induced impairment in the BSR in the wild-type strain that did not improve in response to EtOH, an effect also observed in strains that lack the DOP-1, DOP-2, and DOP-3 receptors. The animals that overexpress tyrosine hydroxylase (TH), or lack the vesicular transport (VMAT) showed a Pb-induced impairment in the BSR that seemed to improve after EtOH. Interestingly, a dramatic impairment in the BSR was observed in the Pb group in strains lacking the DOP-4 receptor, resembling the response of the TH-deficient strain, an effect that in both cases showed a non-significant reversal by EtOH. These results suggest that the facilitatory effect of EtOH on the impaired BSR observed in Pb-exposed null mutant strains may be the result of a compensatory effect in the altered DAergic synapse present in these animals.

Combined Exposure to Metals in Drinking Water Alters the Dopamine System in Mouse Striatum

Environmental exposure to arsenic (As), lead (Pb), and cadmium (Cd) frequently occurs; however, data on the specific effects of combined exposure on neurotransmission, specifically dopaminergic neurotransmission, are lacking. In this study, motor coordination and dopamine content, along with the expression of tyrosine hydroxylase (TH), dopamine transporter (DAT), vesicular monoamine transporter 2 (VMAT2), and dopamine receptors (DRs), were examined in the striatum of adult male mice following exposure to drinking water containing As, Pb, and/or Cd. We found that exposure to a metal mixture impaired motor coordination. After 4 weeks of treatment, a significant decrease in dopamine content and expression of TH, DAT, and VMAT2 was observed in the striatum of metal-mixture-treated mice, compared to the controls or single-metal-exposed groups. However, DRD1 and DRD2 expression did not significantly change with metal treatment. These results suggest that altered dopaminergic neurotransmission by the collective action of metals may contribute to metal-mixture-induced neurobehavioral disorders.

Lead (Pb) exposure induces dopaminergic neurotoxicity in Caenorhabditis elegans: Involvement of the dopamine transporter

Lead (Pb) is an environmental neurotoxicant, and has been implicated in several neurological disorders of dopaminergic dysfunction; however, the molecular mechanism of its toxicity has yet to be fully understood. This study investigated the effect of Pb exposure on dopaminergic neurodegeneration and function, as well as expression level of several dopaminergic signaling genes in wild type (N2) and protein kinase C (pkc) mutant Caenorhabditis elegans. Both N2 and pkc mutant worms were exposed to Pb²⁺ for 1 h. Thereafter, dopaminergic (DAergic) neurodegeneration, behavior and gene expression levels were assessed. The results revealed that Pb²⁺ treatment affects dopaminergic cell morphology and structure in worms expressing green fluorescent protein (GFP) under a DAergic cell specific promoter. Also, there was a significant impairment in dopaminergic neuronal function as tested by basal slowing response (BSR) in wild-type, N2 worms, but no effect was observed in pkc mutant worms. Furthermore, Pb²⁺ exposure increased dat-1 gene expression level when compared with N2 worms, but no alteration was observed in the pkc mutant strains. LC–MS analysis revealed a significant decrease in dopamine content in worms treated with Pb²⁺ when compared with controls. In summary, our results revealed that Pb²⁺ exposure induced dopaminergic dysfunction in C. elegans by altering dat-1 gene levels, but pkc mutants showed significant resistance to Pb²⁺ toxicity. We conclude that PKC activation is directly involved in the neurotoxicity of Pb.

Auditory Training Reverses Lead (Pb)-Toxicity-Induced Changes in Sound-Azimuth Selectivity of Cortical Neurons

Lead (Pb) causes significant adverse effects on the developing brain, resulting in cognitive and learning disabilities in children. The process by which lead produces these negative changes is largely unknown. The fact that children with these syndromes also show deficits in central auditory processing, however, indicates a speculative but disturbing relationship between lead-exposure, impaired auditory processing, and behavioral dysfunction. Here we studied in rats the changes in cortical spatial tuning impacted by early lead-exposure and their potential restoration to normal by auditory training. We found animals that were exposed to lead early in life displayed significant behavioral impairments compared with naïve controls while conducting the sound-azimuth discrimination task. Lead-exposure also degraded the sound-azimuth selectivity of neurons in the primary auditory cortex. Subsequent sound-azimuth discrimination training, however, restored to nearly normal the lead-degraded cortical azimuth selectivity. This reversal of cortical spatial fidelity was paralleled by changes in cortical expression of certain excitatory and inhibitory neurotransmitter receptor subunits. These results in a rodent model demonstrate the persisting neurotoxic effects of early lead-exposure on behavioral and cortical neuronal processing of spatial information of sound. They also indicate that attention-demanding auditory training may remediate lead-induced cortical neurological deficits even after these deficits have occurred.

Synergistic effects of Pb and repeated heat pulse on developmental neurotoxicity in zebrafish

Pollutant discharges to the aquatic environment often contain multiple environmental stressors, affecting aquatic organisms. To mimic the discharges from nuclear and industry facilities, the combined effects of two independent types of stressors, heavy metal Pb and repeated heat pulse were addressed in this study. We investigated the developmental toxicity of combined treatment, especially its toxic effects on zebrafish neurodevelopment. The normal embryos at 4 hpf were exposed to 0.2 mM of Pb dissolved in the bathing medium with different temperatures (30, 32, and 34 °C) and then maintained in an incubator at 28 °C. After performing above treatment once every 24 h for 6 days, we found that combined treatment significantly affected neural development, including loss of dopaminergic (DA) neurons and brain vasculature, disruption of locomotor activity and neurodevelopmental genes expression in a temperature-dependent manner as compared to the Pb alone exposure group, indicating that repeated heat pulse enhances these negative impacts induced by Pb. In contrast, no apparent toxicity was observed in repeated heat pulse alone groups, suggesting that Pb treatment reduces thermal tolerance in zebrafish, which emphasized the importance to evaluate synergistic effects of Pb and repeated heat pulse. Moreover, repeated heat pulse aggravated Pb-induced apoptosis in the zebrafish brain. Further study of the underlying mechanism suggested that Caspase 3 regulated apoptosis was involved in this process. Taken together, our findings shed light on the full understanding of toxic effects of discharges from industrial applications on living organisms and its environmental impact.

Effects of combined arsenic and lead exposure on the brain monoaminergic system and behavioral functions in rats: Reversal effect of MiADMSA

In this study, we evaluated the therapeutic efficacy of monoisoamyldimercaptosuccinic acid (MiADMSA) against individual and combined effects of arsenic (As) and lead (Pb) on the monoaminergic system and behavioral functions in rats. Pregnant rats were exposed to sodium metaarsenite (50 ppm) and lead acetate (0.2%) individually and in combination (As = 25 ppm + Pb = 0.1%) via drinking water from gestation day (GD) 6 to postnatal day (PND) 21. MiADMSA (50 mg/kg body weight) was given orally through gavage for 3 consecutive days to pups from PND 18 to PND 20. The results showed increases in synaptosomal epinephrine, dopamine, and norepinephrine levels with individual metal exposures and decreases with combined exposure to As and Pb in the cortex, cerebellum, and hippocampus in PND 21, PND 28, and 3 months age-group rats. We found decreased activity of mitochondrial monoamine oxidase in the selected brain regions following individual and combined exposures to Pb and As. In addition, rats treated with Pb and As alone or in combination showed significant deficits in open-field behavior, grip strength, locomotor activity, and exploratory behavior at PND 28 and 3 months of age. However, MiADMSA administration showed reversal effects against the As- and/or Pb-induced impairments in the monoaminergic system as well as in behavioral functions of rats. Our data demonstrated that the mixture of Pb and As induced synergistic toxicity to developing brain leading to impairments in neurobehavioral functions and also suggest therapeutic efficacy of MiADMSA against Pb- and/or As-induced developmental neurotoxicity.

Assessing ototoxicity due to chronic lead and cadmium intake with and without noise exposure in the mature mouse

Exposure to heavy metals may lead to hearing impairment. However, experimental studies have not explored this issue with and without noise exposure in mature animals with environmentally relevant doses. The aim of this study was to investigate ototoxicity produced by lead (Pb) and cadmium (Cd) and noise, singly and in combination, in the adult CBA/CaJ mouse. Metals were delivered via drinking water (0.03 mM, 1 mM, and 3 mM Pb; or 30, 100, and 300 μM Cd) for 12 weeks, resulting in environmentally- and occupationally relevant mean (± standard deviations) blood levels of Pb (2.89 ± 0.44, 38.5 ± 4.9, and 60.1 ± 6.6 μg/dl, respectively) and Cd (1.3 ± 0.23, 6.37 ± 0.87, 27.2 ± 4.1 μg/L, respectively). Metal treatment was also combined with a noise exposure consisting of a 105 dB broadband (2-20 kHz) stimulus for 2 hr or a sham exposure. Auditory performance was determined by comparing auditory brainstem responses (ABR) and distortion product otoacoustic emissions (DPOAE) at baseline and after 11 weeks of metal treatment. Metal-exposed animals did not develop significant auditory deficits and did not exhibit morphological damage to cochlear hair cells. In contrast, noise-exposed animals, including those exposed to combinations of metals and noise, demonstrated significant hair cell loss, reduced DPOAE amplitudes, and ABR threshold shifts of 42.2 ± 13 dB at 32 kHz (105 dB noise alone). No significant potentiation or synergistic effects were found in groups exposed to multiple agents. This study establishes a highly reproducible adult mouse model that may be used to evaluate a variety of environmental exposure mixtures.

Chronic lead exposure induces cochlear oxidative stress and potentiates noise-induced hearing loss

Acquired hearing loss is caused by complex interactions of multiple environmental risk factors, such as elevated levels of lead and noise, which are prevalent in urban communities. This study delineates the mechanism underlying lead-induced auditory dysfunction and its potential interaction with noise exposure. Young-adult C57BL/6 mice were exposed to: 1) control conditions; 2) 2 mM lead acetate in drinking water for 28 days; 3) 90 dB broadband noise 2 h/day for two weeks; and 4) both lead and noise. Blood lead levels were measured by inductively coupled plasma mass spectrometry analysis (ICP-MS) lead-induced cochlear oxidative stress signaling was assessed using targeted gene arrays, and the hearing thresholds were assessed by recording auditory brainstem responses. Chronic lead exposure downregulated cochlear Sod1, Gpx1, and Gstk1, which encode critical antioxidant enzymes, and upregulated ApoE, Hspa1a, Ercc2, Prnp, Ccl5, and Sqstm1, which are indicative of cellular apoptosis. Isolated exposure to lead or noise induced 8-12 dB and 11-25 dB shifts in hearing thresholds, respectively. Combined exposure induced 18-30 dB shifts, which was significantly higher than that observed with isolated exposures. This study suggests that chronic exposure to lead induces cochlear oxidative stress and potentiates noise-induced hearing impairment, possibly through parallel pathways.

Glycogen metabolism in brain and neurons - astrocytes metabolic cooperation can be altered by pre- and neonatal lead (Pb) exposure

Lead (Pb) is an environmental neurotoxin which particularly affects the developing brain but the molecular mechanism of its neurotoxicity still needs clarification. The aim of this paper was to examine whether pre- and neonatal exposure to Pb (concentration of Pb in rat offspring blood below the "threshold level") may affect the brain's energy metabolism in neurons and astrocytes via the amount of available glycogen. We investigated the glycogen concentration in the brain, as well as the expression of the key enzymes involved in glycogen metabolism in brain: glycogen synthase 1 (Gys1), glycogen phosphorylase (PYGM, an isoform active in astrocytes; and PYGB, an isoform active in neurons) and phosphorylase kinase β (PHKB). Moreover, the expression of connexin 43 (Cx43) was evaluated to analyze whether Pb poisoning during the early phase of life may affect the neuron-astrocytes' metabolic cooperation. This work shows for the first time that exposure to Pb in early life can impair brain energy metabolism by reducing the amount of glycogen and decreasing the rate of its metabolism. This reduction in brain glycogen level was accompanied by a decrease in Gys1 expression. We noted a reduction in the immunoreactivity and the gene expression of both PYGB and PYGM isoform, as well as an increase in the expression of PHKB in Pb-treated rats. Moreover, exposure to Pb induced decrease in connexin 43 immunoexpression in all the brain structures analyzed, both in astrocytes as well as in neurons. Our data suggests that exposure to Pb in the pre- and neonatal periods results in a decrease in the level of brain glycogen and a reduction in the rate of its metabolism, thereby reducing glucose availability, which as a further consequence may lead to the impairment of brain energy metabolism and the metabolic cooperation between neurons and astrocytes.

Individual and Combined Effects of Arsenic and Lead on Behavioral and Biochemical Changes in Mice

Arsenic (As) toxicity has caused an environmental tragedy affecting millions of people in the world. Little is known about the toxic effects of As on neurobehavioral and biochemical changes in vivo. Along this line of metal toxicity, co-exposure of lead (Pb) could aggravate the situation in the host. The present study was designed to explore the combined effects of As and Pb on behavioral changes like anxiety, spatial memory and learning impairment, and blood indices related to organ dysfunction. Exposure of mice to As (10 mg/kg body weight), Pb (10 mg/kg body weight), and As + Pb via drinking water significantly decreased the time spent exploring the open arms while it increased the time spent in the closed arms compared to control mice in the elevated plus maze. The mean latency time of the control group to find the platform decreased significantly during the learning for 7 days compared to all three treated groups in the Morris water maze test, and the As-exposed group spent significantly less time in the desired quadrant as compared to the control group in the probe trial. Both metals posed an anxiety-like behavior and deficits in spatial memory and learning, and also altered blood indices related to liver and kidney dysfunction, and a combined exposure of these metals inhibited the individual accumulation of As and Pb. Taken together, these data suggest that As has more toxic effects on neurobehavioral and biochemical changes than Pb, and there may be antagonism in the effects and accumulation between these two toxicants.

Pb exposure prolongs the time period for postnatal transient uptake of 5-HT by murine LSO neurons

Pb exposure is associated with cognitive deficits including Attention Deficit Hyperactivity Disorder (ADHD) in children and alters auditory temporal processing in humans and animals. Serotonin has been implicated in auditory temporal processing and previous studies from our laboratory have demonstrated that developmental Pb decreases expression of serotonin (5-HT) in the adult murine lateral superior olive (LSO). During development, certain non-serotonergic sensory neurons, including auditory LSO neurons, transiently take up 5-HT through the serotonin reuptake transporter (SERT). The uptake of 5-HT is important for development of sensory systems. This study examines the effect of Pb on the serotonergic system in the LSO of the early postnatal mouse. Mice were exposed to moderate Pb (0.01mM) or high Pb (0.1mM) throughout gestation and postnatal day 4 (P4) and P8. We found that Pb exposure prolongs the normal developmental expression of 5-HT by LSO neurons and this is correlated with expression of SERT on LSO cell bodies. The prolonged expression of 5-HT by postnatal LSO neurons is correlated with decreased synaptic immunolabeling within the LSO. This Pb-associated decrease in synaptic density within the LSO could contribute to the auditory temporal processing deficits and cognitive deficits associated with developmental Pb exposure.

Blood lead concentrations and attention deficit hyperactivity disorder in Korean children: a hospital-based case control study

Background

Because the developing brain of a child is vulnerable to environmental toxins, even very low concentration of neurotoxin can affect children’s neurodevelopment. Lead is a neurotoxic heavy metal which has the harmful effect on the striatal-frontal circuit of brain. This area of the brain is known to be closely related to attention deficit hyperactivity disorder (ADHD) pathophysiology. The primary objective of the present study was to investigate whether elevated blood lead concentration is a risk factor for ADHD. The secondary objective was to examine the association between blood lead concentration and symptom severity.

Methods

We conducted a frequency-matched, hospital-based case-control study with 114 medically diagnosed ADHD cases and 114 controls. The participants were matched for age and sex. The diagnoses of ADHD were assessed with semi-structured diagnostic interviews. The participants completed the continuous performance test (CPT), and their parents completed the ADHD-rating scale (ADHD-RS). Blood lead concentrations were measured by using graphite furnace atomic absorption spectrometry featuring Zeeman background correction.

Results

Children with ADHD exhibited blood lead concentrations that were significantly higher than those of the controls ( 1.90 ± 086 μg/dℓ vs. 1.59 ± 0.68 μg/dℓ, p = 0.003). The log transformed total blood lead concentration was associated with a higher risk of ADHD (OR: 1.60, 95 % CI: 1.04–2.45, p < 0.05). The analysis also revealed that the children with blood lead concentrations above 2.30 μg/dℓ were at a 2.5–fold (95 % CI: 1.09–5.87, p < 0.05) greater risk of having ADHD. After adjusting for covariates, our multivariate regression models indicated that blood lead concentrations were not significantly associated with ADHD-RS or CPT profiles among the ADHD cases.

Conclusion

Even low blood lead concentrations are a risk factor for ADHD in children. This study warrants primary prevention policies to reduce the environmental lead burden. Future studies may be required to ascertain the effects of lead on symptom severity in ADHD.

Development of early-born γ-Aminobutyric acid hub neurons in mouse hippocampus from embryogenesis to adulthood

Early‐born γ‐aminobutyric acid (GABA) neurons (EBGNs) are major components of the hippocampal circuit because at early postnatal stages they form a subpopulation of “hub cells” transiently supporting CA3 network synchronization (Picardo et al. [2011] Neuron 71:695–709). It is therefore essential to determine when these cells acquire the remarkable morphofunctional attributes supporting their network function and whether they develop into a specific subtype of interneuron into adulthood. Inducible genetic fate mapping conveniently allows for the labeling of EBGNs throughout their life. EBGNs were first analyzed during the perinatal week. We observed that EBGNs acquired mature characteristics at the time when the first synapse‐driven synchronous activities appeared in the form of giant depolarizing potentials. The fate of EBGNs was next analyzed in the adult hippocampus by using anatomical characterization. Adult EBGNs included a significant proportion of cells projecting selectively to the septum; in turn, EBGNs were targeted by septal and entorhinal inputs. In addition, most EBGNs were strongly targeted by cholinergic and monoaminergic terminals, suggesting significant subcortical innervation. Finally, we found that some EBGNs located in the septum or the entorhinal cortex also displayed a long‐range projection that we traced to the hippocampus. Therefore, this study shows that the maturation of the morphophysiological properties of EBGNs mirrors the evolution of early network dynamics, suggesting that both phenomena may be causally linked. We propose that a subpopulation of EBGNs forms into adulthood a scaffold of GABAergic projection neurons linking the hippocampus to distant structures. J. Comp. Neurol. 524:2440–2461, 2016. © 2016 Wiley Periodicals, Inc.

Lead Exposure in Different Organs of Mammals and Prevention by Curcumin-Nanocurcumin: a Review

Chronic lead exposure is related to many health diseases in mammals. Exposure to lead forms reactive oxygen species reducing body antioxidant enzymes inflicting injury to numerous macromolecules or cell necrosis. Recent studies have revealed oxidative stress as the vital mechanism for lead toxicity. Lead is found to be toxic to several organ systems such as hematopoietic, skeletal, renal, cardiac, hepatic, and reproductive systems and extremely toxic to the central nervous system (CNS). Curcumin, an active ingredient of the dietary spice, and nanocurcumin, a nanoform of curcumin, are found to decrease toxicity due to lead in various organ systems in mouse models. Higher bioavailability, chelating property, and retention time of nanocurcumin over bulk curcumin may pave the way to expand the utility of nanocurcumin to remove lead toxicity from various organ systems within humans.

Ultrastructural Correlates of Enhanced Norepinephrine and Neuropeptide Y Cotransmission in the Spontaneously Hypertensive Rat Brain

The spontaneously hypertensive rat (SHR) replicates many clinically relevant features of human essential hypertension and also exhibits behavioral symptoms of attention-deficit/hyperactivity disorder and dementia. The SHR phenotype is highly complex and cannot be explained by a single genetic or physiological mechanism. Nevertheless, numerous studies including our own work have revealed striking differences in central catecholaminergic transmission in SHR such as increased vesicular catecholamine content in the ventral brainstem. Here, we used immunolabeling followed by confocal microscopy and electron microscopy to quantify vesicle sizes and populations across three catecholaminergic brain areas—nucleus tractus solitarius and rostral ventrolateral medulla, both key regions for cardiovascular control, and the locus coeruleus. We also studied colocalization of neuropeptide Y (NPY) in norepinephrine and epinephrine-containing neurons as NPY is a common cotransmitter with central and peripheral catecholamines. We found significantly increased expression and coexpression of NPY in norepinephrine and epinephrine-positive neurons of locus coeruleus in SHR compared with Wistar rats. Ultrastructural analysis revealed immunolabeled vesicles of 150 to 650 nm in diameter (means ranging from 250 to 300 nm), which is much larger than previously reported. In locus coeruleus and rostral ventrolateral medulla, but not in nucleus tractus solitarius, of SHR, noradrenergic and adrenergic vesicles were significantly larger and showed increased NPY colocalization when compared with Wistar rats. Our morphological evidence underpins the hypothesis of hyperactivity of the noradrenergic and adrenergic system and increased norepinephrine and epinephrine and NPY cotransmission in specific brain areas in SHR. It further strengthens the argument for a prohypertensive role of C1 neurons in the rostral ventrolateral medulla as a potential causative factor for essential hypertension.

Serum neuron-specific enolase, biogenic amino-acids and neurobehavioral function in lead-exposed workers from lead-acid battery manufacturing process

Background:

The interaction between serum neuron-specific enolase (NSE), biogenic amino-acids and neurobehavioral function with blood lead levels in workers exposed to lead form lead-acid battery manufacturing process was not studied.

Objective:

To evaluate serum NSE and biogenic amino-acids (dopamine and serotonin) levels, and neurobehavioral performance among workers exposed to lead from lead-acid storage battery plant, and its relation with blood lead levels (BLLs).

Methods:

In a cross-sectional study, we performed biochemical and neurobehavioral function tests on 146 workers exposed to lead from lead-acid battery manufacturing process. BLLs were assessed by an atomic absorption spectrophotometer. Serum NSE, dopamine and serotonin were measured by ELISA. Neurobehavioral functions were assessed by CDC-recommended tests—simple reaction time (SRT), symbol digit substitution test (SDST), and serial digit learning test (SDLT).

Results:

There was a significant correlation (r 0.199, p<0.05) between SDST and BLL. SDLT and SRT had also a significant positive correlation (r 0.238, p<0.01). NSE had a negative correlation (r –0.194, p<0.05) with serotonin level. Multiple linear regression analysis revealed that both SRT and SDST had positive significant associations with BLL. SRT also had a positive significant association with age.

Conclusion:

Serum NSE cannot be used as a marker for BLL. The only domain of neurobehavioral function tests that is affected by increased BLL in workers of lead-acid battery manufacturing process is that of the "attention and perception" (SDST).

Influence of lead on repetitive behavior and dopamine metabolism in a mouse model of iron overload

Exposures to lead (Pb) are associated with neurological problems including psychiatric disorders and impaired learning and memory. Pb can be absorbed by iron transporters, which are up-regulated in hereditary hemochromatosis, an iron overload disorder in which increased iron deposition in various parenchymal organs promote metal-induced oxidative damage. While dysfunction in HFE (High Fe) gene is the major cause of hemochromatosis, the transport and toxicity of Pb in Hfe-related hemochromatosis are largely unknown. To elucidate the relationship between HFE gene dysfunction and Pb absorption, H67D knock-in Hfe-mutant and wild-type mice were given drinking water containing Pb 1.6 mg/ml ad libitum for 6 weeks and examined for behavioral phenotypes using the nestlet-shredding and marble-burying tests. Latency to nestlet-shredding in Pb-treated wild-type mice was prolonged compared with non-exposed wild-types (p < 0.001), whereas Pb exposure did not alter shredding latency in Hfe-mutant mice. In the marble-burying test, Hfe-mutant mice showed an increased number of marbles buried compared with wild-type mice (p = 0.002), indicating more repetitive behavior upon Hfe mutation. Importantly, Pb-exposed wild-type mice buried more marbles than non-exposed wild-types, whereas the number of marbles buried by Hfe-mutant mice did not change whether or not exposed to Pb. These results suggest that Hfe mutation could normalize Pb-induced behavioral alteration. To explore the mechanism of repetitive behavior caused by Pb, western blot analysis was conducted for proteins involved in brain dopamine metabolism. The levels of tyrosine hydroxylase and dopamine transporter increased upon Pb exposure in both genotypes, whereas Hfe-mutant mice displayed down-regulation of the dopamine transporter and dopamine D1 receptor with D2 receptor elevated. Taken together, our data support the idea that both Pb exposure and Hfe mutation increase repetitive behavior in mice and further suggest that these behavioral changes could be associated with altered dopaminergic neurotransmission, providing a therapeutic basis for psychiatric disorders caused by Pb toxicity.

Perceptual Training Restores Impaired Cortical Temporal Processing Due to Lead Exposure

Low-level lead exposure is a risk factor for cognitive and learning disabilities in children and has been specifically associated with deficits in auditory temporal processing that impair aural language and reading abilities. Here, we show that rats exposed to low levels of lead in early life display a significant behavioral impairment in an auditory temporal rate discrimination task. Lead exposure also results in a degradation of the neuronal repetition-rate following capacity and response synchronization in primary auditory cortex. A modified go/no-go repetition-rate discrimination task applied in adult animals for ∼50 days nearly restores to normal these lead-induced deficits in cortical temporal fidelity. Cortical expressions of parvalbumin, brain-derived neurotrophic factor, and NMDA receptor subunits NR2a and NR2b, which are down-regulated in lead-exposed animals, are also partially reversed with training. These studies in an animal model identify the primary auditory cortex as a novel target for low-level lead exposure and demonstrate that perceptual training can ameliorate lead-induced deficits in cortical discrimination between sound sequences.

Distribution of language-related Cntnap2 protein in neural circuits critical for vocal learning

Variants of the contactin associated protein-like 2 (Cntnap2) gene are risk factors for language-related disorders including autism spectrum disorder, specific language impairment, and stuttering. Songbirds are useful models for study of human speech disorders due to their shared capacity for vocal learning, which relies on similar cortico-basal ganglia circuitry and genetic factors. Here we investigate Cntnap2 protein expression in the brain of the zebra finch, a songbird species in which males, but not females, learn their courtship songs. We hypothesize that Cntnap2 has overlapping functions in vocal learning species, and expect to find protein expression in song-related areas of the zebra finch brain. We further expect that the distribution of this membrane-bound protein may not completely mirror its mRNA distribution due to the distinct subcellular localization of the two molecular species. We find that Cntnap2 protein is enriched in several song control regions relative to surrounding tissues, particularly within the adult male, but not female, robust nucleus of the arcopallium (RA), a cortical song control region analogous to human layer 5 primary motor cortex. The onset of this sexually dimorphic expression coincides with the onset of sensorimotor learning in developing males. Enrichment in male RA appears due to expression in projection neurons within the nucleus, as well as to additional expression in nerve terminals of cortical projections to RA from the lateral magnocellular nucleus of the nidopallium. Cntnap2 protein expression in zebra finch brain supports the hypothesis that this molecule affects neural connectivity critical for vocal learning across taxonomic classes.

Nuclei-specific differences in nerve terminal distribution, morphology, and development in mouse visual thalamus

Background

Mouse visual thalamus has emerged as a powerful model for understanding the mechanisms underlying neural circuit formation and function. Three distinct nuclei within mouse thalamus receive retinal input, the dorsal lateral geniculate nucleus (dLGN), the ventral lateral geniculate nucleus (vLGN), and the intergeniculate nucleus (IGL). However, in each of these nuclei, retinal inputs are vastly outnumbered by nonretinal inputs that arise from cortical and subcortical sources. Although retinal and nonretinal terminals associated within dLGN circuitry have been well characterized, we know little about nerve terminal organization, distribution and development in other nuclei of mouse visual thalamus.

Results

Immunolabeling specific subsets of synapses with antibodies against vesicle-associated neurotransmitter transporters or neurotransmitter synthesizing enzymes revealed significant differences in the composition, distribution and morphology of nonretinal terminals in dLGN, vLGN and IGL. For example, inhibitory terminals are more densely packed in vLGN, and cortical terminals are more densely distributed in dLGN. Overall, synaptic terminal density appears least dense in IGL. Similar nuclei-specific differences were observed for retinal terminals using immunolabeling, genetic labeling, axonal tracing and serial block face scanning electron microscopy: retinal terminals are smaller, less morphologically complex, and more densely distributed in vLGN than in dLGN. Since glutamatergic terminal size often correlates with synaptic function, we used in vitro whole cell recordings and optic tract stimulation in acutely prepared thalamic slices to reveal that excitatory postsynaptic currents (EPSCs) are considerably smaller in vLGN and show distinct responses following paired stimuli. Finally, anterograde labeling of retinal terminals throughout early postnatal development revealed that anatomical differences in retinal nerve terminal structure are not observable as synapses initially formed, but rather developed as retinogeniculate circuits mature.

Conclusions

Taken together, these results reveal nuclei-specific differences in nerve terminal composition, distribution, and morphology in mouse visual thalamus. These results raise intriguing questions about the different functions of these nuclei in processing light-derived information, as well as differences in the mechanisms that underlie their unique, nuclei-specific development.

Novel dose-dependent alterations in excitatory GABA during embryonic development associated with lead (Pb) neurotoxicity

Lead (Pb) is a heavy metal that is toxic to numerous physiological processes. Its use in industrial applications is widespread and results in an increased risk of human environmental exposure. The central nervous system (CNS) is most sensitive to Pb exposure during early development due to rapid cell proliferation and migration, axonal growth, and synaptogenesis. One of the key components of CNS development is the Gamma-aminobutyric acid (GABA)-ergic system. GABA is the primary inhibitory neurotransmitter in the adult brain. However, during development GABA acts as an excitatory neurotrophic factor which contributes to these cellular processes. Multiple studies report effects of Pb on GABA in the mature brain; however, little is known regarding the adverse effects of Pb exposure on the GABAergic system during embryonic development. To characterize the effects of Pb on the GABAergic system during development, zebrafish embryos were exposed to 10, 50, or 100 ppb Pb or a control treatment. Tissue up-take, gross morphological alterations, gene expression, and neurotransmitter levels were analyzed. Analysis revealed that alterations in gene expression throughout the GABAergic system and GABA levels were dose and developmental time point specific. These data provide a framework for further analysis of the effects of Pb on the GABAergic system during the excitatory phase and as GABA transitions to an inhibitory neurotransmitter during development.

Distribution of VGLUT3 in highly collateralized axons from the rat dorsal raphe nucleus as revealed by single-neuron reconstructions

This study aimed at providing the first detailed morphological description, at the single-cell level, of the rat dorsal raphe nucleus neurons, including the distribution of the VGLUT3 protein within their axons. Electrophysiological guidance procedures were used to label dorsal raphe nucleus neurons with biotinylated dextran amine. The somatodendritic and axonal arborization domains of labeled neurons were reconstructed entirely from serial sagittal sections using a computerized image analysis system. Under anaesthesia, dorsal raphe nucleus neurons display highly regular (1.72±0.50 Hz) spontaneous firing patterns. They have a medium size cell body (9.8±1.7 µm) with 2–4 primary dendrites mainly oriented anteroposteriorly. The ascending axons of dorsal raphe nucleus are all highly collateralized and widely distributed (total axonal length up to 18.7 cm), so that they can contact, in various combinations, forebrain structures as diverse as the striatum, the prefrontal cortex and the amygdala. Their morphological features and VGLUT3 content vary significantly according to their target sites. For example, high-resolution confocal analysis of the distribution of VGLUT3 within individually labeled-axons reveals that serotonin axon varicosities displaying VGLUT3 are larger (0.74±0.03 µm) than those devoid of this protein (0.55±0.03 µm). Furthermore, the percentage of axon varicosities that contain VGLUT3 is higher in the striatum (93%) than in the motor cortex (75%), suggesting that a complex trafficking mechanism of the VGLUT3 protein is at play within highly collateralized axons of the dorsal raphe nucleus neurons. Our results provide the first direct evidence that the dorsal raphe nucleus ascending projections are composed of widely distributed neuronal systems, whose capacity to co-release serotonin and glutamate varies from one forebrain locus to the other.

Expression patterns of Pax6 and Pax7 in the adult brain of a urodele amphibian, Pleurodeles waltl

Expression patterns of Pax6, Pax7, and, to a lesser extent, Pax3 genes were analyzed by a combination of immunohistochemical techniques in the central nervous system of adult specimens of the urodele amphibian Pleurodeles waltl. Only Pax6 was found in the telencephalon, specifically the olfactory bulbs, striatum, septum, and lateral and central parts of the amygdala. In the diencephalon, Pax6 and Pax7 were distinct in the alar and basal parts, respectively, of prosomere 3. The distribution of Pax6, Pax7, and Pax3 cells correlated with the three pretectal domains. Pax7 specifically labeled cells in the dorsal mesencephalon, mainly in the optic tectum, and Pax6 cells were the only cells found in the tegmentum. Large populations of Pax7 cells occupied the rostral rhombencephalon, along with lower numbers of Pax6 and Pax3 cells. Pax6 was found in most granule cells of the cerebellum. Pax6 cells also formed a column of scattered neurons in the reticular formation and were found in the octavolateral area. The rhombencephalic ventricular zone of the alar plate expressed Pax7. Dorsal Pax7 cells and ventral Pax6 cells were found along the spinal cord. Our results show that the expression of Pax6 and Pax7 is widely maintained in the brains of adult urodeles, in contrast to the situation in other tetrapods. This discrepancy could be due to the generally pedomorphic features of urodele brains. Although the precise role of these transcription factors in adult brains remains to be determined, our findings support the idea that they may also function in adult urodeles.

A method for the three-dimensional reconstruction of Neurobiotin™-filled neurons and the location of their synaptic inputs

Here, we describe a robust method for mapping the number and type of neuro-chemically distinct synaptic inputs that a single reconstructed neuron receives. We have used individual hypoglossal motor neurons filled with Neurobiotin by semi-loose seal electroporation in thick brainstem slices. These filled motor neurons were then processed for excitatory and inhibitory synaptic inputs, using immunohistochemical-labeling procedures. For excitatory synapses, we used anti-VGLUT2 to locate glutamatergic pre-synaptic terminals and anti-PSD-95 to locate post-synaptic specializations on and within the surface of these filled motor neurons. For inhibitory synapses, we used anti-VGAT to locate GABAergic pre-synaptic terminals and anti-GABA-A receptor subunit α1 to locate the post-synaptic domain. The Neurobiotin-filled and immuno-labeled motor neuron was then processed for optical sectioning using confocal microscopy. The morphology of the motor neuron including its dendritic tree and the distribution of excitatory and inhibitory synapses were then determined by three-dimensional reconstruction using IMARIS software (Bitplane). Using surface rendering, fluorescence thresholding, and masking of unwanted immuno-labeling, tools found in IMARIS, we were able to obtain an accurate 3D structure of an individual neuron including the number and location of its glutamatergic and GABAergic synaptic inputs. The power of this method allows for a rapid morphological confirmation of the post-synaptic responses recorded by patch-clamp prior to Neurobiotin filling. Finally, we show that this method can be adapted to super-resolution microscopy techniques, which will enhance its applicability to the study of neural circuits at the level of synapses.

Columnar distribution of catecholaminergic neurons in the ventrolateral periaqueductal gray and their relationship to efferent pathways

The periaqueductal gray (PAG) is a critical brain region involved in opioid analgesia and provides efferents to descending pathways that modulate nociception. In addition, the PAG contains ascending pathways to regions involved in the regulation of reward, including the substantia nigra (SN) and the ventral tegmental area (VTA). SN and VTA contain dopaminergic neurons that are critical for the maintenance of positive reinforcement. Interestingly, the PAG is also reported to contain a population of dopaminergic neurons. In this study, the distribution of catecholaminergic neurons within the ventrolateral (vl) PAG was examined using immunocytochemical methods. In addition, the catecholaminergic PAG neurons were examined to determine whether these neurons are integrated into ascending (VTA, SN) and descending rostral ventral medulla (RVM) efferent pathways from this region. The immunocytochemical analysis determined that catecholaminergic neurons in the PAG are both dopaminergic and noradrenergic and these neurons have a distinct rostrocaudal distribution within the ventrolateral column of PAG. Dopaminergic neurons were concentrated rostrally and were significantly smaller than noradrenergic neurons. Combined immunocytochemistry and tract tracing methods revealed that catecholaminergic neurons are distinct from, but closely associated with, both ascending and descending efferent projection neurons. Finally, by electron microscopy, catecholaminergic neurons showed close dendritic appositions with other neurons in PAG, suggesting a possible nonsynaptic mechanism for regulation of PAG output by these neurons. In conclusion, our data indicate that there are two populations of catecholaminergic neurons in the vlPAG that form dendritic associations with both ascending and descending efferents suggesting a possible nonsynaptic modulation of vlPAG neurons.

Development of the serotonergic cells in murine raphe nuclei and their relations with rhombomeric domains

The raphe nuclei represent the origin of central serotonergic projections. The literature distinguishes seven nuclei grouped into rostral and caudal clusters relative to the pons. The boundaries of these nuclei have not been defined precisely enough, particularly with regard to developmental units, notably hindbrain rhombomeres. We hold that a developmental point of view considering rhombomeres may explain observed differences in connectivity and function. There are twelve rhombomeres characterized by particular genetic profiles, and each develops between one and four distinct serotonergic populations. We have studied the distribution of the conventional seven raphe nuclei among these twelve units. To this aim, we correlated 5-HT-immunoreacted neurons with rhombomeric boundary landmarks in sagittal mouse brain sections at different developmental stages. Furthermore, we performed a partial genoarchitectonic analysis of the developing raphe nuclei, mapping all known serotonergic differentiation markers, and compared these results, jointly with others found in the literature, with our map of serotonin-containing populations, in order to examine regional variations in correspondence. Examples of regionally selective gene patterns were identified. As a result, we produced a rhombomeric classification of some 45 serotonergic populations, and suggested a corresponding modified terminology. Only a minor rostral part of the dorsal raphe nucleus lies in the midbrain. Some serotonergic neurons were found in rhombomere 4, contrary to the conventional assumption that it lacks such neurons. We expect that our reclassification of raphe nuclei may be useful for causal analysis of their differential molecular specification, as well as for studies of differential connectivity and function.

Increased hippocampal Disrupted-In-Schizophrenia 1 expression in mice exposed prenatally to lead

Disrupted-In-Schizophrenia 1 is a susceptibility gene for schizophrenia and other psychiatric disorders. Developmental lead exposure can cause neurological disorders similar to hyperactivity disorder, dyslexia and schizophrenia. In the present study, we examined the impact of developmental lead exposure, administered in vitro and in vivo, on hippocampal Disrupted-In- Schizophrenia 1 expression. Our results show that in cultured hippocampal neurons, in vitro exposure to 0.1-10 µM lead, inhibited neurite growth and increased Disrupted-In-Schizophrenia 1 mRNA and protein expression dose-dependently. In addition, blood lead levels in mice were increased with increasing mouse maternal lead (0.01-1 mM) exposure. Hippocampal neurons from these mice showed a concomitant increase in Disrupted-In-Schizophrenia 1 mRNA and protein expression. Overall our findings suggest that in vivo and in vitro lead exposure increases Disrupted-In-Schizophrenia 1 expression in hippocampal neurons dose-dependently, and consequently may influence synapse formation in newborn neurons.

Effects of chronic lead intoxication on rat serotoninergic system and anxiety behavior

Chronic lead exposure has been shown to produce behavioral disturbances in human and animal models. These disturbances are associated with alterations in monoaminergic neurotransmission in the central nervous system (CNS), some of which have been attributed to serotonin (5-HT). This study was undertaken to investigate the chronic effects of lead exposure on the serotoninergic system in the dorsal raphe nucleus (DRN) and the consequences of its toxicity on rat behavior. Adult male Wistar rats were chronically exposed for 3 months to 0.5% lead acetate in drinking water. The serotoninergic system was evaluated using immunohistochemistry and the anxiety behavior was assessed by the light/dark box test. The results show that chronic lead exposure induces a significant increase of blood and brain lead levels in treated rats compared with controls. The density of the immunoreactive serotoninergic cell bodies was significantly higher in treated rats in all parts of the DRN. Assessment of animal behavior using the light/dark box test showed that lead-treated rats spent significantly more time in the light chamber compared with controls (P=0.001). These findings suggest that lead exposure may possibly induce increased anxiety as a consequence of changes in neuronal 5-HT content in the DRN.

Distribution of vesicular monoamine transporter 2 protein in human brain: implications for brain imaging studies

The choice of reference region in positron emission tomography (PET) human brain imaging of the vesicular monoamine transporter 2 (VMAT2), a marker of striatal dopamine innervation, has been arbitrary, with cerebellar, whole cerebral, frontal, or occipital cortices used. To establish whether levels of VMAT2 are in fact low in these cortical areas, we measured VMAT2 protein distribution by quantitative immunoblotting in autopsied normal human brain (n=6). Four or five species of VMAT2 immunoreactivity (75, 55, 52, 45, 35 kDa) were detected, which were all markedly reduced in intensity in nigrostriatal regions of patients with parkinsonian conditions versus matched controls (n=9 to 10 each). Using the intact VMAT2 immunoreactivity, cerebellar and cerebral neocortices had levels of the transporter >100-fold lower than the VMAT2-rich striatum and with no significant differences among the cortical regions. We conclude that human cerebellar and cerebral cortices contain negligible VMAT2 protein versus the striatum and, in this respect, all satisfy a criterion for a useful reference region for VMAT2 imaging. The slightly lower PET signal for VMAT2 binding in occipital (the currently preferred reference region) versus cerebellar cortex might not therefore be explained by differences in VMAT2 protein itself but possibly by other imaging variables, for example, partial volume effects.

Chronic lead intoxication affects glial and neural systems and induces hypoactivity in adult rat

Lead is an environmental toxin and its effects are principally manifested in the brain. Glial and neuronal changes have been described during development following chronic or acute lead intoxication, however, little is known about the effects of chronic lead intoxication in adults. In this study we evaluated immunohistochemically the glial and dopaminergic systems in adult male Wistar rats. 0.5% (v/v) lead acetate in drinking water was administrated chronically over a 3-month period. Hypertrophic immunoreactive astrocytes were observed in the frontal cortex and other brain structures of the treated animals. Analysis of the astroglial features showed increased number of astrocyte cell bodies and processes in treated rats, an increase confirmed by Western blot. Particular distribution of glial fibrillary acidic protein immunoreactivity was observed within the blood vessel walls in which dense immunoreactive glial processes emanate from astrocytes. Glial changes in the frontal cortex were concomitant with reduced tyrosine hydroxylase immunoreactive neuronal processes, which seem to occur as a consequence of significantly reduced dopaminergic neurons within the nucleus of origin in the substantia nigra. These glial and neuronal changes following lead intoxication may affect animal behavior as evidenced by reduced locomotor activity in an open field test. These findings demonstrate that chronic lead exposure induces astroglial changes, which may compromise neuronal function and consequently animal behavior.

Developmental lead exposure causes startle response deficits in zebrafish

Lead (Pb(2+)) exposure continues to be an important concern for fish populations. Research is required to assess the long-term behavioral effects of low-level concentrations of Pb(2+) and the physiological mechanisms that control those behaviors. Newly fertilized zebrafish embryos (<2h post fertilization; hpf) were exposed to one of three concentrations of lead (as PbCl(2)): 0, 10, or 30 nM until 24 hpf. (1) Response to a mechanosensory stimulus: Individual larvae (168 hpf) were tested for response to a directional, mechanical stimulus. The tap frequency was adjusted to either 1 or 4 taps/s. Startle response was recorded at 1000 fps. Larvae responded in a concentration-dependent pattern for latency to reaction, maximum turn velocity, time to reach V(max) and escape time. With increasing exposure concentrations, a larger number of larvae failed to respond to even the initial tap and, for those that did respond, ceased responding earlier than control larvae. These differences were more pronounced at a frequency of 4 taps/s. (2) Response to a visual stimulus: Fish, exposed as embryos (2-24 hpf) to Pb(2+) (0-10 μM) were tested as adults under low light conditions (≈ 60 μW/m(2)) for visual responses to a rotating black bar. Visual responses were significantly degraded at Pb(2+) concentrations of 30 nM. These data suggest that zebrafish are viable models for short- and long-term sensorimotor deficits induced by acute, low-level developmental Pb(2+) exposures.

Assessment of auditory brainstem function in lead-exposed children using stapedius muscle reflexes

The purpose of this study was to investigate the neurological integrity and physiological status of the auditory brainstem tracts and nuclei in children with chronic lead (Pb) exposure using non-invasive acoustic stapedius reflex (ASR) measurements of afferent and efferent-neuromuscular auditory function. Following audiological examinations, uncrossed (ipsilateral) and crossed (contralateral) brainstem ASR responses were evoked by pure tone (500, 1000, and 2000 Hz), and broadband noise (bandwidth: 125-4000 Hz) stimulus activators. The ASR threshold (ASRT), amplitude growth, and decay/fatigue were measured by conventional clinical middle ear immittance methods in a group of Andean children (age range: 2-18 years) with a history of chronic environmental Pb exposure from occupational Pb glazing. Blood lead (PbB) levels of the study group (n=117) ranged from 4.0 to 83.7 μg/dL with a mean PbB level of 33.5 μg/dL (SD: 23.6; median: 33.0: CDC III Classification). The PbB distribution data indicated that 77.8% (n=91) of the children had PbB levels greater than the CDC action line of 10 μg/dL. Repeatable, normal ASRTs were elicited for ipsilateral (mean: ≤90 dB HL) and contralateral (mean: ≤97 dB HL) stimulation for each acoustic activator. Spearman Rho correlation analysis indicated no significant association between PbB level and ipsilateral or contralateral ASRT for any of the stimulus activators. The ASR amplitude growth results showed typical growth functions with no Pb-associated aberrations. No statistical association was found between ASR decay/adaptation (ASRD) and PbB level for any of the stimulus activators. The results of stapedius muscle reflex testing using several stimulus activators showed no significant relationship between PbB level and the physiological integrity of the auditory brainstem mediated ASR responses in children with chronic Pb exposure and elevated PbB levels.

Chronic low-level Pb exposure during development decreases the expression of the voltage-dependent anion channel in auditory neurons of the brainstem

Lead (Pb) exposure is a risk factor for neurological dysfunction. How Pb produces these behavioral deficits is unknown, but Pb exposure during development is associated with auditory temporal processing deficits in both humans and animals. Pb disrupts cellular energy metabolism and efficient energy production is crucial for auditory neurons to maintain high rates of synaptic activity. The voltage-dependent anion channel (VDAC) is involved in the regulation of mitochondrial physiology and is a critical component in controlling mitochondrial energy production. We have previously demonstrated that VDAC is an in vitro target for Pb, therefore, VDAC may represent a potential target for Pb in the auditory system. In order to determine whether Pb alters VDAC expression in central auditory neurons, CBA/CaJ mice (n=3-5/group) were exposed to 0.01mM, or 0.1mM Pb acetate during development via drinking water. At P21, immunohistochemistry reveals a significant decrease for VDAC in neurons of the Medial Nucleus of the Trapezoid Body. Western blot analysis confirms that Pb results in a significant decrease for VDAC. Decreases in VDAC expression could lead to an upregulation of other cellular energy producing systems as a compensatory mechanism, and a Pb-induced increase in brain type creatine kinase is observed in auditory regions of the brainstem. In addition, comparative proteomic analysis shows that several proteins of the glycolytic pathway, the phosphocreatine circuit, and oxidative phosphorylation are also upregulated in response to developmental Pb exposure. Thus, Pb-induced decreases in VDAC could have a significant effect on the function of auditory neurons.

M3 muscarinic acetylcholine receptor expression confers differential cholinergic modulation to neurochemically distinct hippocampal basket cell subtypes

Cholinergic neuromodulation of hippocampal circuitry promotes network oscillations and facilitates learning and memory through cellular actions on both excitatory and inhibitory circuits. Despite widespread recognition that neurochemical content discriminates between functionally distinct interneuron populations, there has been no systematic examination of whether neurochemically distinct interneuron classes undergo differential cholinergic neuromodulation in the hippocampus. Using GFP transgenic mice that enable the visualization of perisomatically targeting parvalbumin-positive (PV+) or cholecystokinin-positive (CCK+) basket cells (BCs), we tested the hypothesis that neurochemically distinct interneuron populations are differentially engaged by muscarinic acetylcholine receptor (mAChR) activation. Cholinergic fiber activation revealed that CCK BCs were more sensitive to synaptic release of ACh than PV BCs. In response to depolarizing current steps, mAChR activation of PV BCs and CCK BCs also elicited distinct cholinergic response profiles, differing in mAChR-induced changes in action potential (AP) waveform, firing frequency, and intrinsic excitability. In contrast to PV BCs, CCK BCs exhibited a mAChR-induced afterdepolarization (mADP) that was frequency and activity-dependent. Pharmacological, molecular, and loss-of-function data converged on the presence of M3 mAChRs in distinguishing CCK BCs from PV BCs. Firing frequency of CCK BCs was controlled through M3 mAChRs but PV BC excitability was altered solely through M1 mAChRs. Finally, upon mAChR activation, glutamatergic transmission enhanced cellular excitability preferentially in CCK BCs but not in PV BCs. Our findings demonstrate that cell type-specific cholinergic specializations are present on neurochemically distinct interneuron subtypes in the hippocampus, revealing an organizing principle that cholinergic neuromodulation depends critically on neurochemical identity.