Role of brain acetylcholine and dopamine in acute neurotoxic effects of DDT

Sex-specific Effects of Endocrine-disrupting Chemicals on Brain Monoamines and Cognitive Behavior

The period of brain sexual differentiation is characterized by the development of hormone-sensitive neural circuits that govern the subsequent presentation of sexually dimorphic behavior in adulthood. Perturbations of hormones by endocrine-disrupting chemicals (EDCs) during this developmental period interfere with an organism's endocrine function and can disrupt the normative organization of male- or female-typical neural circuitry. This is well characterized for reproductive and social behaviors and their underlying circuitry in the hypothalamus and other limbic regions of the brain; however, cognitive behaviors are also sexually dimorphic, with their underlying neural circuitry potentially vulnerable to EDC exposure during critical periods of brain development. This review provides recent evidence for sex-specific changes to the brain's monoaminergic systems (dopamine, serotonin, norepinephrine) after developmental EDC exposure and relates these outcomes to sex differences in cognition such as affective, attentional, and learning/memory behaviors.

DDT poisoning of big brown bats, Eptesicus fuscus, in Hamilton, Montana

Dichlorodiphenyltrichloroethane (DDT) is an insecticidal organochlorine pesticide with; known potential for neurotoxic effects in wildlife. The United States Environmental Protection Agency (US EPA) registration for this pesticide has been cancelled and there are currently no federally active products that contain this ingredient in the U.S. We present a case of a colony of big brown bats (E. Fuscus) found dead in the attic roost of an administrative building; in the city of Hamilton, Montana from unknown cause. DDT and its metabolites; dichlorodiphenyldichloroethylene (DDE) and dichlorodiphenyldichloroethane (DDD) were detected in bat tissues by gas chromatography/mass spectrometry (GC-MS) and quantified by gas chromatography tandem quadrupole mass spectrometry (GC-MS/MS). Concentrations of 4081 ppm DDT and 890 ppm DDE wet weight were found in the brain of one bat and are the highest reported concentrations in such a mortality event to date. This case emphasizes the importance of testing wildlife mortalities against a comprehensive panel of toxicologic agents including persistent organic pollutants in the absence of other more common disease threats.

(-)-Epigallocatechin-3-gallate (EGCG), a green tea polyphenol, reduces dichlorodiphenyl-trichloroethane (DDT)-induced cell death in dopaminergic SHSY-5Y cells

Results from epidemiological studies indicated that there exists an inverse correlation between consumption of green tea and neurodegenerative diseases including Parkinson's disease. We hypothesized that consumption of green tea would activate endogenous protective mechanisms against environmental toxin-induced cell injury, which is believed to play a causative role in the etiology of Parkinson's disease. Here, we found that epigallocatechin-3-gallate (EGCG), a major green tea polyphenol, concentration-dependently (1 microM, 3 microM and 10 microM) reduced dichlorodiphenyl-trichloroethane (DDT) (100 microM)-induced cell death in dopaminergic neuroblastoma SHSY-5Y cells. The cell viability was determined by trypan blue exclusion assays. We also found that preconditioning the SHSY-5Y cells with EGCG by multiple, brief, prior exposures of the cells to EGCG can subsequently protect the cells from DDT-induced cell death. The EGCG-induced protective effect positively correlated with the number of exposures to EGCG. These results suggest that EGCG has a protective effect against DDT-induced cell death, and that prior exposures to EGCG activate an endogenous protective mechanism in the dopaminergic cells which can mitigate organochlorine pesticide-induced cell injury.

Antidepressant-like effects of apigenin and 2,4,5-trimethoxycinnamic acid from Perilla frutescens in the forced swimming test

We studied the effects of apigenin and 2,4,5-trimethoxycinnamic acid (TMCA) on the behavioral despair test (forced swimming test), and the central noradrenergic, dopaminergic and serotonergic activities in mice. Apigenin at intraperitoneal doses of 12.5 and 25 mg/kg significantly decreased the duration of immobility in the forced swimming test in mice. At 100 mg/kg, the duration of immobility was returned to the control level in the test. On the other hand, TMCA treatment (25-200 mg/kg, i.p.) failed to significantly alter the duration of immobility. Based on the behavioral data, we examined changes in the monoamine turnover in mice having been subjected to forced swimming for 40 min. The monoamine turnover was measured in seven brain regions. Forced swimming exposure induced a significant decrease in dihydroxyphenylacetic acid (DOPAC)/dopamine (DA) in the striatum and amygdala and in 5-hydroxyindoleacetic acid (5-HIAA)/5-hydroxytriptamine (5-HT) in the hypothalamus, and a significant increase in DOPAC/DA in the thalamus and hypothalamus and in 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG)/norepinephrine (NE) in the amygdala, frontal cortex, hypothalamus, and midbrain. Apigenin (25 mg/kg) treatment produced attenuation of forced swim test-induced decrease of DA turnover in the amygdala and increase of DA turnover in the hypothalamus. Furthermore, intraperitoneal administration of haloperidol (0.2 mg/kg), a dopamine D(2) antagonist, blocked the apigenin (25 mg/kg)-induced decrease in immobility in the forced swimming test. These behavioral and biochemical results indicate the antidepressant properties of apigenin, which may be mediated by the dopaminergic mechanisms in the mouse brain.

Determination of a tolerable daily intake of DDT for consumers of DDT contaminated fish from the lower Yakima River, Washington

DDT, DDE, and DDD have been detected at elevated concentrations in sediments and fish of the Yakima River, its tributaries and drainages. An assessment was conducted to evaluate the public health significance of eating fish from the river. This was accomplished by establishing a daily intake level of DDT for the population of greatest concern, and comparing this level to a tolerable daily intake. The most sensitive and highly exposed group was determined to be breastfeeding infants. Infant daily intakes of DDT, based on estimated mother's DDT-breast milk levels, were compared to a recommended tolerable daily intake. Results indicate that mothers who frequently consume Yakima River bottom-feeding fish could have breast milk DDT concentrations sufficiently high to expose their infants to levels above the tolerable daily intake.

The organochlorine insecticide 1,2,3,4,5,6-hexachlorocyclohexane (lindane) but not 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) augments the nocturnal increase in pineal N-acetyltransferase activity and pineal and serum melatonin levels

The effect of organochlorine insecticides lindane (1,2,3,4,5,6-hexachlorocyclohexane) and DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane) were studied in terms of their effects on the rat pineal N-acetyltransferase (NAT) activity, hydroxyindole-O-methyltransferase (HIOMT) activity and pineal and serum melatonin levels during the day (2000h) and at night (2300 and 0100h). Additionally, pineal levels of 5-hydroxytryptophan (5-HTP), serotonin (5-HT), and 5-hydroxyindole acetic acid (5-HIAA) were estimated. Nocturnal NAT activity was increased after lindane administration; likewise, lindane augmented pineal and serum melatonin levels at 2300h. Conversely, DDT was without a statistically significant effect on either NAT activity or on pineal or serum melatonin levels. Neither lindane nor DDT significantly influenced pineal HIOMT values either during the day or at night. Likewise, neither insecticide consistently influenced pineal levels of either 5-HTP, 5-HT or 5-HIAA. The results indicate that the organochlorine insecticide, lindane, modifies pineal melatonin synthesis in vivo.

Milacemide increases 5-hydroxytryptamine and dopamine levels in rat brain--possible mechanisms of milacemide antimyoclonic property in the p,p'-DDT-induced myoclonus

Milacemide, a glycine prodrug that is able to enter the brain readily, has been shown to have an antimyoclonic property in the p,p'-DDT-induced myoclonus syndrome. Milacemide increased regional 5-HT and dopamine and decreased 5-HIAA, DOPAC and HVA levels in naive rats. In p,p'-DDT-treated rats, 5-HT levels were unchanged at the time the rats experienced spontaneous myoclonus in all brain regions except in the striatum, where it increased. 5-HIAA levels increased but did not reach significant levels except in the striatum. Dopamine, DOPAC, HVA and norepinephrine were unchanged. When rats were treated concurrently with both p,p'-DDT and milacemide, regional 5-HT levels were increased and NE levels in the brainstem and cerebellum decreased. Depletion of brain serotonin by pretreatment with PCPA or with 5,7-DHT, or blocking 5-HT receptors with different 5-HT antagonists, failed to eliminate the antimyoclonic property of milacemide. This antimyoclonic effect of milacemide may be mediated through other mechanisms besides its ability to increase brain 5-HT levels. Possible mechanisms to be considered are its antiepileptic property, and its ability to increase brain glycine levels. Milacemide may have potential for therapeutic trials in patients with myoclonus.

Glycine involvement in DDT-induced myoclonus

The DDT syndrome in rats consists of tremor, myoclonus, running seizures, hyperthermia, episodic boxing, and excessive grooming. DDT did not change whole-brain glycine levels when the rats had stimulus-sensitive myoclonus, spontaneous myoclonus, or seizures. However, regional analysis showed a decrease in glycine levels in the pons and medulla initially, but they rose again despite worsening of the myoclonus. Glycine given intraventricularly and the glycine prodrug, milacemide, given intraperitoneally suppressed DDT-induced myoclonus. A dose of milacemide that prevented DDT-induced myoclonus caused a significant increase in glycine levels in cortex, septum accumbens, cerebellum, striatum, hippocampus diencephalon, midbrain, pons, and medulla. The increase was most marked in the forebrain structures. There was no change in serine levels in these areas. These data suggest that the glycinergic system may be playing an important role in the manifestation of DDT-induced myoclonus.

Effect of acute sublethal and chronic administration of DDT (chlorophenotane) on brain lipid metabolism of rhesus monkeys

Either a single oral dose of 1,1,1-trichloro-2,2-bis-(p-chlorophenyl) ethane (DDT), 150 mg/kg body weight or a long-term chronic dose of the pesticide, 10 mg/kg body weight daily for 100 days was administered to rhesus monkeys and the level of various lipid classes was studied in the brain. A significant decrease was observed in total lipid, unesterified cholesterol and phospholipid (PL) level. Individual PL fractions showed a generalized pattern of reduction, so also did the cholesterol (chol)/PL ratio. Sphingomyelin (SM) registered a significant increase, while no significant alteration was observed in the brain galactolipid and ganglioside level. Lipid lowering effect of DDT was more pronounced in the chronic group. Lipids associated with the myelin sheath were found to be more resistant to pesticide injury, while cholesterol and PL metabolism were more affected.

Neurochemical effects of DDT in rat brain in vivo

p,p'-DDT and related agents act to hold the sodium channel open once opened and this effect is believed to be responsible for neurological effects of tremor and hyperexcitability in vivo. There is a good correlation between DDT-induced tremor and an increase in the levels of the metabolites of norepinephrine (NE), serotonin (5HT) and, to a lesser extent, dopamine (DA) in the brain stem (BS), hypothalamus (HYP), striatum (STR), or hippocampus (HPC). DDT also increases levels of excitatory amino acids glutamate (GLU) and aspartate (ASP), but the effect occurs only in the brain stem. These effects are dose- and time-related. Pharmacological studies found that blockade of alpha 1-adrenergic receptors attenuate DDT-induced tremor, while blockade of serotonergic, cholinergic muscarinic, and dopaminergic receptors augment the toxicity of DDT. Tremor was almost completely blocked in rats pretreated with hydantoin, an anticonvulsant believed to block repetitive firing of nerves by interfering with the inactivation gate of the sodium channel. A similar antagonism was observed for permethrin, a Type I pyrethroid believed to have a mechanism of action very similar to that of DDT. However, hydantoin increased the tremorigenic effects of chlordecone, an organochlorine whose mechanism has not been linked to the sodium channel. These data are consistent with the hypothesis that the in vivo neurotoxicity of some organochlorine insecticides is related to their effects on the sodium channel.

Effects of p,p'-DDT on the rat brain concentrations of biogenic amine and amino acid neurotransmitters and their association with p,p'-DDT-induced tremor and hyperthermia

Male, Fischer strain 344 adult rats were given various doses (25-100 mg/kg) of p,p'-DDT by oral gavage, and levels of biogenic amines, their metabolites, and amino acid neurotransmitters, tremor activity, and rectal temperature were measured at several intervals (2, 5, 12, and 24 h) after dosing. Dose-related increases in rectal temperature and in tremor activity were observed at 50-100 mg/kg 12 h after dosing. Tremorigenic doses of DDT increased the 5-hydroxyindoleacetic acid (5-HIAA) level in hypothalamus, brainstem, and striatum, whereas doses of 75 and 100 mg/kg increased the 3-methoxy-4-hydroxyphenylglycol (MHPG) level in hypothalamus and brainstem and the 3,4-dihydroxyphenylacetic acid level in striatum. Six amino acids were assayed in the brainstem, hypothalamus, and striatum; aspartate and glutamate levels were increased only in brainstem at 25-100 mg/kg. No consistent changes in concentrations of taurine, glutamine, glycine, or gamma-aminobutyric acid were observed in any of the regions assayed. Time-related increases in rectal temperature were seen 2-12 h after dosing, and the presence of tremor was observed 5-12 h after dosing; for both the time of peak effect was at 12 h. The DDT-induced hyperthermia and tremor were associated with dose- and time-related increases in levels of 5-HIAA, MHPG, aspartate, and glutamate. It is suggested that an increase in the turnover rate of 5-hydroxytryptamine (5-HT) may be responsible for the DDT-induced hyperthermia, whereas increases in the metabolism of 5-HT and norepinephrine may be involved in the tremor.

DDT-induced tremor in rats: effects of pharmacological agents

Rats given a tremorigenic dose of DDT (75 mg/kg, PO) were treated with pharmacological agents either 30 min prior to DDT or 1-2 h prior to testing at the time of peak effect (12 h postdosing). The administration of mephenesin (a centrally acting muscle relaxant) or Dilantin (an anticonvulsant) prior to DDT significantly attenuated tremor. Pretreatment with pizotifen (a serotonergic receptor antagonist) had no significant effect on tremor. Administration of the same agents 1-2 h prior to measurement had minimal effects. Trihexyphenidyl (a muscarinic cholinergic receptor antagonist) exacerbated the tremor produced by DDT. These data suggest that cholinergic neurotransmitter systems may be involved in DDT-induced tremor. That DDT-induced tremor was significantly attenuated by mephenesin and Dilantin is in accord with the conclusion that DDT-induced tremor is a manifestation of repetitive discharge due to interference with ionic conductance.

Effects of DDT on muscarine- and nicotine-like binding sites in CNS of immature and adult mice

Immature (10 days of age) and adult (60 days of age) mice were given a single peroral administration of 0.5 mg p,p'-DDT/kg body wt. or a fat emulsion vehicle. The mice were killed 24 h or 7 days post-treatment and the muscarine- and nicotine-like binding sites were measured in the cerebral cortex and in the cerebellum using [3H]quinuclidinyl benzilate ([3H]QNB) and [3H]alpha-bungarotoxin ([3H]alpha-BTX), respectively, as ligands. A significant decrease in the [3H]QNB binding to the muscarine-like receptors in the cerebral cortex was seen in the 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT)-treated adults after 7 days. The effects on the muscarine-like receptors appeared to be different in the immature mice compared to the adults, showing an increase between 24 h and 7 days post-treatment in the immature and a decrease in the adults. No change was seen on the nicotine-like receptors.

Changes in body temperature after administration of antipyretics, LSD, delta 9-THC, CNS depressants and stimulants, hormones, inorganic ions, gases, 2,4-DNP and miscellaneous agents

This survey concludes a series of complications of data from the literature, primarily published since 1965, on thermoregulatory effects of antipyretics in afebrile as well as in febrile subjects, LSD and other hallucinogens, cannabinoids, general CNS depressants, CNS stimulants including xanthines, hormones, inorganic ions, gases and fumes, 2,4-dinitrophenol and miscellaneous agents including capsaicin, cardiac glycosides, chemotherapeutic agents, cinchona alkaloids, cyclic nucleotides, cycloheximide, 2-deoxy-D-glucose, dimethylsulfoxide, insecticides, local anesthetics, poly I:poly C, spermidine and spermine, sugars, toxins and transport inhibitors. The information listed includes the species used, route of administration and dose of drug, the environmental temperature at which the experiments were performed, the number of tests, the direction and magnitude of body temperature change and remarks on the presence of special conditions such as age or lesions, or on the influence of other drugs, such as antagonists, on the response to the primary agents.