DDT and pyrethroids—ecotoxicological considerations

• 1.1. DDT, and a DDT metabolite, DDOH, conjugated to palmitic acid, DDOH-PA, as well as bioallethrin and deltamethrin have all been shown to affect muscarinic cholinergic receptors (MAChR) in the neonatal mouse brain after administration to 10-day-old mice during the period of rapid brain growth.
• 2.2. This early exposure has also been shown to lead to permanent changes in cholinergic and behavioural variables in the animals as adults.

     

Binding of 1,1,1-trichloro-2,2-di-p-chlorophenylethane (DDT) with subcellular fractions of rat brain

DDT (1,1,1-trichloro-2,2-di-p-chlorophenylethane) and DDE (1,1-dichloro-2,2-di-p-chlorophenylethylene, a non-insecticidal analogue of DDT) were found to bind with various nerve components of rat brain. The amount of DDT binding exceeded that of DDE only in the fraction containing mainly the nerve endings. Among various components in the nerve-ending fraction, a subfraction containing mainly the pre- and post-synaptic complexes had the highest affinity for DDT in comparison with that for DDE. By using an ;acetone-powdering' technique on brain preparations, the Sephadex-column method was shown to provide reliable results for studies on the binding of DDT or DDE with soluble proteins in the nerve tissues. From these results it was concluded that DDE had a higher affinity for soluble components of the rat brain than did DDT.     

Non-classical actions of cholinesterases: Role in cellular differentiation, tumorigenesis and Alzheimer''s disease

The cholinesterases are members of the serine hydrolase family, which utilizes a serine residue at the active site. Acetylcholinesterase (AChE) is distinguished from butyrylcholinesterase (BChE) by its greater specificity for hydrolysing acetylcholine. The function of AChE at cholinergic synapses is to terminate cholinergic neurotransmission. However, AChE is expressed in tissues that are not directly innervated by cholinergic nerves. AChE and BChE are found in several types of haematopoietic cells. Transient expression of AChE in the brain during embryogenesis suggests that AChE may function in the regulation of neurite outgrowth. Overexpression of cholinesterases has also been correlated with tumorigenesis and abnormal megakaryocytopoiesis. Acetylcholine has been shown to influence cell proliferation and neurite outgrowth through nicotinic and muscarinic receptor-mediated mechanisms and thus, that the expression of AChE and BChE at non-synaptic sites may be associated with a cholinergic function. However, structural homologies between cholinesterases and adhesion proteins indicate that cholinesterases could also function as cell-cell or cell-substrate adhesion molecules. Abnormal expression of AChE and BChE has been detected around the amyloid plaques and neurofibrillary tangles in the brains of patients with Alzheimer's disease. The function of the cholinesterases in these regions of the Alzheimer brain is unknown, but this function is probably unrelated to cholinergic neurotransmission. The presence of abnormal cholinesterase expression in the Alzheimer brain has implications for the pathogenesis of Alzheimer's disease and for therapeutic strategies using cholinesterase inhibitors.     

Cholinergic neuromodulation of inhibitory interneurons facilitates functional integration in whole-brain models

Segregation and integration are two fundamental principles of brain structural and functional organization. Neuroimaging studies have shown that the brain transits between different functionally segregated and integrated states, and neuromodulatory systems have been proposed as key to facilitate these transitions. Although whole-brain computational models have reproduced this neuromodulatory effect, the role of local inhibitory circuits and their cholinergic modulation has not been studied. In this article, we consider a Jansen & Rit whole-brain model in a network interconnected using a human connectome, and study the influence of the cholinergic and noradrenergic neuromodulatory systems on the segregation/integration balance. In our model, we introduce a local inhibitory feedback as a plausible biophysical mechanism that enables the integration of whole-brain activity, and that interacts with the other neuromodulatory influences to facilitate the transition between different functional segregation/integration regimes in the brain.     

Involvement of the cholinergic mechanism in DDT and dieldrin action in the insect central nervous system

The effects of DDT and dieldrin on cholinergic neurotransmission were studied using the sixth abdominal ganglion of the cockroach. Spontaneous electrical discharges in the ganglion recorded with an extracellular electrode were augmented by 0.1 mM DDT and 1 microM dieldrin. This stimulating action was partly blocked by 0.5 mM d-tubocurarine and 0.1 mM hemicholinium-3 and disappeared in a high Mg2+-low Ca2+ medium. DDT and dieldrin increased both ACh release and ACh content in the ganglion. These results suggested that DDT and dieldrin stimulate both ACh release and synthesis.     

Lyophilized membranes as a test system for analyzing the properties of neuromediator receptors and activity of neurotropic agents

The effect of lyophilization and prolonged storage of rat brain membrane preparations on the properties of receptors of cholinergic and adrenergic neuromediator systems has been studied by the radioreceptor assay. Lyophilized membrane preparations have been shown to be highly stable as compared with fresh membranes and retain their binding properties during storage for 1 year.     

Novel strains of mice deficient for the vesicular acetylcholine transporter: insights on transcriptional regulation and control of locomotor behavior

Defining the contribution of acetylcholine to specific behaviors has been challenging, mainly because of the difficulty in generating suitable animal models of cholinergic dysfunction. We have recently shown that, by targeting the vesicular acetylcholine transporter (VAChT) gene, it is possible to generate genetically modified mice with cholinergic deficiency. Here we describe novel VAChT mutant lines. VAChT gene is embedded within the first intron of the choline acetyltransferase (ChAT) gene, which provides a unique arrangement and regulation for these two genes. We generated a VAChT allele that is flanked by loxP sequences and carries the resistance cassette placed in a ChAT intronic region (FloxNeo allele). We show that mice with the FloxNeo allele exhibit differential VAChT expression in distinct neuronal populations. These mice show relatively intact VAChT expression in somatomotor cholinergic neurons, but pronounced decrease in other cholinergic neurons in the brain. VAChT mutant mice present preserved neuromuscular function, but altered brain cholinergic function and are hyperactive. Genetic removal of the resistance cassette rescues VAChT expression and the hyperactivity phenotype. These results suggest that release of ACh in the brain is normally required to "turn down" neuronal circuits controlling locomotion.     

Vegetative nervous system's contribution to the development of stress induced gastric ulcers]

A vegetative nervous system contribution to the development of stress-induced gastric ulcers has been investigated. The experiments involved male Wistar rats. Vegetative nervous system activity has been assessed with acetylcholine brain and stomach tissue levels and synthesis as well as adrenaline and noradrenaline levels in adrenals and gastric wall. The results have shown, that ulcerogenic effect of stress is accompanied by the increase in both cholinergic and adrenergic activities. Moreover, it has been shown, that markedly strong stimulation of the adrenergic system in some rats, together with pharmacologic activation of alpha-adrenergic receptors, inhibits the development of stress-induced gastric ulcers.     

胆碱转运体与阿尔茨海默病

阿尔茨海默病主要病理学特征是在脑中形成大量的老年斑和神经元纤维缠结以及出现弥漫性脑萎缩.胆碱能系统的失调与阿尔茨海默病的发生机制关系密切.具体表现为基底前脑的胆碱能系统紊乱,胆碱乙酰化酶、乙酰胆碱含量显著减少,以及大量胆碱能神经元退化.胆碱转运体是胆碱能系统中用于转运胆碱进入细胞的关键蛋白体,有三种类型:高亲和力胆碱转运体、胆碱转运体类蛋白及非特异性有机阳离子转运体.近年,很多研究表明胆碱转运体的异常与一系列神经退行性紊乱有关.本文简要综述胆碱能系统中胆碱转运体的生理作用及其在阿尔茨海默病中异常代谢和可能机制的研究进展,以期为防治阿尔茨海默病提供进一步的理论和实验依据.     

Basic studies and applications on bioremediation of DDT: A review

The persistent insecticide DDT (1,1,1-trichloro-2,2-bis (4-chlorophenyl) ethane) has been widely used for pest control in the management of mosquito-borne malaria and is still used for that purpose in some tropical countries. Considering the potential for negative effects due to DDT contamination, it is necessary to determine effective methods of remediation. Several methods have been used to degrade or transform DDT into less toxic compounds. Bacteria and white-rot fungi (WRF) have been shown to enhance the degradation process in soil using both pure and mixed cultures. Recently, a biological approach has been used as an environmentally-friendly treatment, using new biological sources to degrade DDT, e.g. brown-rot fungi (BRF), cattle manure compost (CMC) and spent mushroom waste (SMW). In this review, the abilities of BRF, CMC and SMW to degrade DDT are discussed, including the mechanisms and degradation pathways. Furthermore, application of these sources to contaminated soil is also described. The review discusses which is the best source for bioremediation of DDT.     

Resistance and capacity function of blood vessels of the brain during activation of its cholinergic mechanisms]

Blood from the cat donor was perfused into the haemodynamically isolated cat brain. The changes of the vascular resistance and their capacity during the pharmacological activity of the endogenic cholinergic mechanism on the introduction of phosphacol into the bloodstream were investigated. Research has shown that the reduction of the activity of cholinergics leads to a decrease in pressure in the arteries of the brain and to an increase of the intercellular fluid absorption, caused by the neurogenic cholinergic influences. The possibility of a mediator realisation of the cholinergic influences on the brain vessels is discussed.     

Neuromediator mechanisms of wakefulness and the voluntary behavior of cats

Properties were studied of neurotransmitter provision of mechanisms of voluntary food-procuring behavior in cats. It has been shown that functional significance of monoamino- and cholinergic brain structures in these mechanisms are greatly determined by their participation in the control of the alertness level, the raising of which is necessary for solving complicated tasks and mastering new motor habits by animals.     

Maturation and maintenance of cholinergic medial septum neurons require glucocorticoid receptor signaling

Glucocorticoids have been shown to influence trophic processes in the nervous system. In particular, they seem to be important for the development of cholinergic neurons in various brain regions. Here, we applied a genetic approach to investigate the role of the glucocorticoid receptor (GR) on the maturation and maintenance of cholinergic medial septal neurons between P15 and one year of age by using a mouse model carrying a CNS-specific conditional inactivation of the GR gene (GRNesCre). The number of choline acetyltransferase and p75NTR immuno-positive neurons in the medial septum (MS) was analyzed by stereology in controls versus mutants. In addition, cholinergic fiber density, acetylcholine release and cholinergic key enzyme activity of these neurons were determined in the hippocampus. We found that in GRNesCre animals the number of medial septal cholinergic neurons was significantly reduced during development. In addition, cholinergic cell number further decreased with aging in these mutants. The functional GR gene is therefore required for the proper maturation and maintenance of medial septal cholinergic neurons. However, the loss of cholinergic neurons in the medial septum is not accompanied by a loss of functional cholinergic parameters of these neurons in their target region, the hippocampus. This pinpoints to plasticity of the septo-hippocampal system, that seems to compensate for the septal cell loss by sprouting of the remaining neurons.     

Immunoaffinity purification of intact, metabolically active, cholinergic nerve terminals from mammalian brain.

A method for the immunoaffinity purification of cholinergic nerve terminals from mammalian brain was developed. A sheep antiserum to Torpedo electric-organ synaptic membranes, previously shown to be specific for cholinergic terminals in mammalian brain, was incubated with crude mitochondrial fractions prepared from rat brain. Cholinergic nerve terminals sensitized by this serum were purified from the mitochondrial fractions on a high-capacity cellulose immunoadsorbent bearing a mouse monoclonal anti-(sheep immunoglobulin G) antibody. Adsorption of nerve terminals on to the immunoadsorbent was assessed by using a variety of enzyme markers and gave a maximum yield of 24% of choline acetyltransferase, whereas non-specific binding was less than 1.0% for all of the enzymes measured. Cholinergic terminals were purified 26-fold from rat caudate nucleus, 30-fold from rat hippocampus and 38-fold from rat cerebral cortex. The terminals were shown to be intact, osmotically sensitive and metabolically active.     

Inhibitory probes of mitochondrial ATPase and the action of DDT

Chemical inhibitors were used as probes of mitochondrial ATPase to determine the site of action of DDT on oligomycin-sensitive mitochondrial ATPase (OS-ATPase) using whole mitochondria isolated from red coxal muscle of the American cockroach. Several plotting procedures were employed to delineate the form of inhibition. Relative potency and joint action were used to detect similar action, synergism, and antagonism between DDT and the inhibitory probes DCCD, Nbf-CI, and oligomycin. DDT demonstrated not (strictly) competitive kinetics and may be acting as an uncompetitive inhibitor. DDT and DCCD produced similar additive action. At limiting concentrations of DCCD, inhibition was reduced in the presence of DDT. Effects shown by oligomycin were not altered by DDT. DDT enhanced the effects of Nbf-CI. These interactions, together with the demonstration of not (strictly) competitive kinetics, indicate that DDT may be acting on the membrane sector as an allosteric modifier.     

Application of in vivo microdialysis to the study of cholinergic systems

The application of in vivo microdialysis to the study of acetylcholine (ACh) release has contributed greatly to our understanding of cholinergic brain systems. This article reviews standard experimental procedures for dialysis probe selection and implantation, perfusion parameters, neurochemical detection, and data analysis as they relate to microdialysis assessments of cholinergic function. Particular attention is focused on the unique methodological considerations that arise when in vivo microdialysis is dedicated expressly to the recovery and measurement of ACh as opposed to other neurotransmitters. Limitations of the microdialysis technique are discussed, as well as methodological adaptations that may prove useful in overcoming these limitations. This is followed by an overview of recent studies in which the application of in vivo microdialysis has been used to characterize the basic pharmacology and physiology of cholinergic neurons. Finally, the usefulness of the microdialysis approach for testing hypotheses regarding the cholinergic systems' involvement in cognitive processes is examined. It can be concluded that, in addition to being a versatile and practical method for studying the neurochemistry of cholinergic brain systems, in vivo microdialysis represents a valuable tool in our efforts to better comprehend ACh's underlying role in a variety of behavioral processes.     

The influence of adrenergic and cholinergic blocking drugs on the glycogen content of the brain in rats deprived of paradoxical sleep

Recent studies have pointed out biochemical and pharmacological phenomena associated with the mechanism or mechanisms of sleep, especially in its paradoxical phase (Jouvet, 1964; Mandel, 1964). Our previous experiments have shown that paradoxical sleep (PS) deprivation leads to the fall of total glycogen content in certain regions of the brains of cats (Mr?ulja, Raki? and Radulova?ki, 1967; Mr?ulja and Raki?, 1968) and rats (Karad?i? and Mr?ulja, 1969). It was shown that changes of glycogen content correspond to PS deprivation and that PS deprivation is a specific stress to which the CNS responds selectively. Alterations in the glycogen concentration in a number of different brain structures lead us to conclude that neural areas affected by PS deprivation are widely distributed. Jouvet (1962) was one of the first to suggest that a neurohumoral mechanism may be concerned in the control of and characteristics of sleep. Experiments have shown that both cholinergic and adrenergic mechanisms may be involved in the initiation, maintenance and control of sleep. It has also been pointed out that paradoxical sleep can be started and maintained by cholinergic drugs (Matsuzaki, Okada and Shuto, 1967, 1968), blocked or reduced by anticholinergic compounds (Matsuzaki et al., 1968), and stimulated by noradrenaline or by its precursor, DOPA (Matsumoto and Jouvet, 1964). Bowers, Hartmann and Freedman (1966) showed that the ACh level of the rat telencephalon decreases with PS deprivation while the levels of norpinephrine and serotonin remain the same (Barchas and Freedman, 1963). More recently, Pujol, Mouret, Jouvet and Glowinski (1968) found the increased turnover of cerebral norepinephrine during rebound of PS in the rat. It is also of interest to point out that probably both adrenergic and cholinergic processes participate in the glycogenolytic effect of physostigmine (Mr?ulja, Terzi? and Varagi?, 1968). It was suggested that physostigmine initiates the cholinergic processes which then trigger off adrenergic processes. The aim in the present work was to determine the glycogen content in certain brain regions of rats which were subjected to PS deprivation lasting 72 hr and treated with some cholinergic or beta-adrenergic blocking agents, as well as with a catecholamine depleting drug.     

Distribution of cholineacetyltransferase histochemistry in isthmus and medulla of Onchorynchus masu. Tract-tracing observation on the ascending meso-pontine cholinergic system

The distribution of cholinergic neurons was studies in the brain steam, medulla and rostral spinal cord of the salmon Onchorynchus masu using histochemical choline acetyltransferase (ChAT) detection. Cholinergic neurons were observed in the isthmus, cranial nerve motor nuclei and spinal cord. In order to characterize several cholinergic nuclei observed in the isthmus of O. masu, their projections were studied by application of 1,1'-dioctadecyl-3,3,3',3,'-tetramethylindocarbocyanine perchlorate (DiI) to selected structures of the brain. The secondary gustatory nucleus projected mainly to the lateral hypothalamic lobes, whereas the nucleus isthmi projected to the optic tectum and parvocellular superficial pretectal nucleus, as it was earlier described for the other teleost group. In addition, the other isthmic cholinergic nuclei in O. masu may be homologous to the meso-pontine system of mammals. We conclude that the cholinergic systems of teleosts show many primitive features that have been presented during evolution, together with exclusive to the group characteristics.     

Acetylcholine turnover rates in rat brain regions during cocaine self-administration

The involvement of cholinergic neurons in the brain processes underlying reinforcement has been recently demonstrated. This experiment assessed the potential role of cholinergic neurons in cocaine reinforcement by measuring the turnover rates of acetylcholine in brain regions of rats self-administering cocaine and in yoked cocaine and yoked vehicle-infused controls. The activity of cholinergic innervations of and/or interneurons in the olfactory tubercle, caudate putamen, diagonal band-pre-optic region, ventral pallidum, lateral and medial hypothalamus, hippocampus, ventral tegmental area and visual cortices reflected by the turnover rates of acetylcholine were significantly altered in rats self-administering cocaine compared to yoked cocaine infused controls. These changes implicate the involvement of cholinergic neurons with cell bodies in the diagonal band-pre-optic region, the medial septum and several brainstem nuclei and interneurons in the caudate-putamen and ventral pallidum in the processes underlying cocaine self-administration. The identified cholinergic neuronal systems may have a broader role in the brain processes for natural reinforcers (i.e. food, water, etc.) since drugs of abuse are believed to produce reinforcing effects through these systems.