Cholinergic and dopaminergic alterations in the mouse central nervous system following acute trimethyltin exposure

Inhibitors of Lipoxygenase and Cyclooxygenase-2 Attenuate Trimethyltin-Induced Neurotoxicity through Regulating Oxidative Stress and Pro-Inflammatory Cytokines in Human Neuroblastoma SH-SY5Y Cells

Trimethyltin (TMT) is an environmental neurotoxin that mediates dopaminergic neuronal injury in the brain. In this study, we characterized the toxic mechanism and possible protective compounds against TMT-induced neurotoxicity in human dopaminergic neuroblastoma SH-SY5Y cells. Antioxidants such as melatonin, N-acetylcysteine (NAC), α-tocopherol, and allopurinol alleviated TMT toxicity. Apoptosis induced by TMT was identified by altered expression of cleaved caspase-3, Bax, Bcl-2, and Bcl-xL through Western blot analysis. The iron chelator deferoxamine ameliorated the alteration of apoptosis-related proteins through TMT exposure. TMT also induced delayed ultrastructural necrotic features such as mitochondrial swelling and cytoplasmic membrane rupture; NAC reduced these necrotic injuries. Esculetin, meloxicam, celecoxib, and phenidone decreased TMT toxicity. Elevation of the pro-inflammatory cytokines IL-1β, TNF-α, and NF-ĸB and reduction of the antioxidant enzymes catalase and glutathione peroxidase-1 (GPx-1) were induced by TMT and ameliorated by inhibitors of LOX and COX-2 enzymes. Both NMDA and non-NMDA antagonists attenuated TMT toxicity. The free calcium ion modulators nimodipine and BAPTA/AM contributed to neuronal survival against TMT toxicity. Inhibitors of the phosphoinositide 3-kinase/protein kinase B/mammalian target of rapamycin pathway, an autophagy regulator, decreased TMT toxicity. These results imply that TMT neurotoxicity is the chief participant in LOX- and COX-2-mediated apoptosis, partly via necrosis and autophagy in SH-SY5Y cells.

Synaptophysin and the dopaminergic system in hippocampus are involved in the protective effect of rutin against trimethyltin-induced learning and memory impairment

OBJECTIVES

This study aimed to investigate the protective effect of rutin against trimethyltin-induced spatial learning and memory impairment in mice. This study focused on the role of synaptophysin, growth-associated protein 43 and the action of the dopaminergic system in mechanisms associated with rutin protection and trimethyltin-induced spatial learning and memory impairment.

METHODS

Cognitive learning and memory was measured by Morris Water Maze. The expression of synaptophysin and growth-associated protein 43 in hippocampus was analyzed by western blot. The concentrations of dopamine, homovanillic acid, and dihyroxyphenylacetic acid in hippocampus were detected using reversed phase high-performance liquid chromatography with electrochemical detection.

RESULTS

Trimethyltin-induced spatial learning impairment showed a dose-dependent mode. Synaptophysin but not growth-associated protein 43 was decreased in the hippocampus after trimethyltin administration. The concentration of dopamine decreased, while homovanillic acid increased in the hippocampus after trimethyltin administration. Mice pretreated with 20 mg/kg of rutin for 7 consecutive days exhibited improved water maze performance. Moreover, rutin pretreatment reversed the decrease of synaptophysin expression and dopamine alteration.

DISCUSSION

These results suggest that rutin may protect against spatial memory impairment induced by trimethyltin. Synaptophysin and the dopaminergic system may be involved in trimethyltin-induced neuronal damage in hippocampus.

Changes in APP, PS1 and other factors related to Alzheimer's disease pathophysiology after trimethyltin-induced brain lesion in the rat

Trimethyltin (TMT) chloride induces limbic system neurodegeneration, resulting in behavioral alterations including cognitive deficits. Different factors related to Alzheimer's disease (AD) were studied after TMT lesion in Sprague-Dawley rats. The expression of amyloid precursor protein (APP) containing 695 amino acids (APP695), APP containing the Kuniz protease inhibitor domain (APP- KPI), presenilin 1 (PS1), c- fos and IL- 1Beta was investigated at different timepoints after a single TMT injection (7 mg/kg i.p.) using in situ hybridization and immunohistochemistry. After the TMT treatment, extensive degeneration of pyramidal neurons was observed in the CA3 region of the hippocampus, concomitant with neurodegeneration in the outer layer of the CA1 region and layer II of entorhinal and piriform cortex. The affected regions showed abundant condensed eosinophilic and TUNEL-positive neuronal cells, that were apparent at day 4 after TMT, increasing to day 7 and subsequently disappearing. In the affected regions the levels of APP695 mRNA gradually declined with time after the TMT injection. While there was no apparent alteration in the overall expression of APP- KPI or PS1 mRNA, detailed analysis of the CA3c region showed that the mRNA expression shifted from neurons to glial cells. Three days after TMT, neurons in the piriform cortex, the CA3 region and DG expressed high levels of c-fos mRNA that slowly declined to become normalized when analyzed at day 28. At day 7 after TMT a few distinct IL- 1Beta mRNA expressing glial cells were observed in the CA3c region. Thus, TMT exposure leads to alterations in the expresson of APP, APP- KPI, PS1, c-fos and IL- 1Beta in the limbic system. These findings suggest that TMT lesions, not only share certain key features of AD symptomatology and regional neurodegeneration, but also induce effects on important factors related to the pathophysiology of AD.

Neurotoxicologic sequelae of tributyltin intoxication in rats

Tributyltin oxide (TBTO) is a commonly used biocide. The purpose of this study is to correlate the toxicity of TBTO with the alterations of brain neurotransmitters and ATPases. TBTO was given by stomach tube to rats at either 37.5 or 75 mg x kg (-1)for 3 consecutive days. Nervous signs appeared in treated animals and the mortality reached 12 and 30%, respectively. The levels of brain dopamine, norepinephrine and serotonin decreased in a dose-dependent manner. The activities of brain total ATPase, Mg (2+)-ATPase and Na (+)/K (+)- ATPase were suppressed. The activity of Na (+)/K (+)- ATPase was more severely affected than that of Mg (2+)-ATPase. Histopathological changes in brain included hyperaemia, focal haemorrhages in vacuolated myelinated fibres, chromatolysis, or complete necrosis of neurons, degenerative changes, or complete absence of purkinje cells in the cerebellum.

The effect of trimethyltin on acetylcholine release in the guinea-pig trachea

The purpose of the present work was to characterise the effects of trimethyltin on the release of acetylcholine from parasympathetic nerves and its effect on the postjunctional cholinergic stimulation of a smooth muscle. The guinea-pig trachea has been used as a model. Prejunctionally, trimethyltin (3.0 × 10(-3) M) significantly enhanced in a reversible manner the high K(+) (75 mM) evoked release of endogenous acetylcholine and [(3)H]acetylcholine. The evoked release of endogenous acetylcholine and [(3)H]acetylcholine was released from a pool of acetylcholine being independent of extraneuronal Ca(2+) in the presence, but not in the absence of trimethyltin. The effect of trimethyltin on the release was not inhibited by low Ca(2+) (0 mM and 1.0 × 10(-4) M) or by Ca(2+) channel blockers (verapamil, 1.0 × 10(-4) M, flunarizine, 1.0 × 10(-4) M, ω-conotoxin GVIA, 2.0 × 10(-7) M and ω-agatoxin, 2.0 × 10(-7) M). The present results also demonstrate that trimethyltin induce emptying of a non-vesicular, probably a cytoplasmic storage pool of acetylcholine, since AH5183 (2.0 × 10(-5) M), an inhibitor of the translocation of acetylcholine into synaptic vesicles, and α-latrotoxin (1.0 × 10(-8) M), a toxin from black widow spider venom inducing vesicle depletion, had no inhibitory effects on the release of [(3)H]acetylcholine evoked by trimethyltin (3.0 × 10(-3) M). The release of [(3)H]acetylcholine was moreover enhanced by trimethyltin when the vesicular uptake of [(3)H]acetylcholine was inhibited by AH5183, probably as a result of a higher cytoplasmic concentration of [(3)H]acetylcholine. Trimethyltin also reduced the neuronal uptake of [(3)H]choline and this was probably due to a depolarising effect of trimethyltin on the cholinergic nerve terminals. A similar depolarisation induced by trimethyltin was observed during patch clamping of GH(4) C(1) neuronal cells. Postjunctionally, trimethyltin had no effect by itself or on the carbachol-induced smooth muscle contraction, indicating that trimethyltin did not have a general depolarising effect on smooth muscle cells or an effect on muscarinic receptors. Furthermore, the reduced electrical field-induced contraction and the subsequent increase in the basal smooth muscle tension that was observed by addition of trimethyltin was activity-dependent, and was most probably due to emptying of a nervous non-vesicular storage pool of acetylcholine, followed by rapid hydrolysis of acetylcholine by acetyl- and pseudocholinesterases.

Elevation of intracellular calcium levels in spiral ganglion cells by trimethyltin

The neurotoxicant, trimethyltin (TMT) produces cochlear impairment at far lower dose levels and far more rapidly than it does central nervous system effects. The initial effects of TMT in the cochlea, in vivo, are consistent with disruption of the inner hair cell type-1 spiral ganglion cell synapse although it is uncertain whether the effect is on presynaptic and/or postsynaptic units. This synapse is believed to be an excitatory glutamatergic one, providing the possibility that TMT could induce an excitotoxic process resulting in elevations in intracellular calcium ([Ca2+]i). The objective of this study was to determine whether TMT had direct toxic effects on the postsynaptic spiral ganglion cells studied in primary culture and to identify the role of extracellular calcium in such an effect. The marker of interest was the effect of this agent on [Ca2+]i levels as determined using quantitation of the fluorescent calcium dye, Fura-2. TMT did induce a marked and sustained elevation in [Ca2+]i level in the spiral ganglion cells that appeared to have a rapid initial phase and a slower saturating phase. Studies performed using calcium-free medium showed that elevation of [Ca2+]i in spiral ganglion cells by TMT was attenuated but not entirely blocked. Further, the L-type calcium channel blocker, nifedipine, was able to inhibit the initial increase in [Ca2+]i, suggesting that at least this phase of the TMT effect was mediated by calcium channels, although nifedipine had no significant effect on the time to reach the maximal [Ca2+]i level. Parallel control experiments performed using application of exogenous glutamate and depolarizing K+ concentrations also produced elevation in [Ca2+]i levels. The data indicate that TMT elevates [Ca2+]i in isolated spiral ganglion cells both by increasing extracellular uptake via Ca2+ channels and also by releasing Ca2+ from intracellular stores. Thus TMT ototoxicity appears to include a direct postsynaptic toxic event.

Interactive effects of prenatal cocaine and nicotine exposure on maternal toxicity, postnatal development and behavior in the rat

Two experiments were performed to investigate the interactive effects of prenatal coadministration of cocaine hydrochloride (C) and nicotine tartrate (N). Experiment I was designed to determine doses of C and N that could be coadministered without altering maternal gestational parameters and/or fetal viability. Exposure of Sprague-Dawley rats to combined high-dose C (20 mg/kg) and high-dose N (5.0 mg/kg) on gestation days 8-21 was not more toxic to dam or fetus that that of exposure to C alone. Experiment II investigated pregnancy outcome, postnatal development, and behavior of the offspring following drug exposure to either high-dose cocaine (20 mg/kg: CS), high-dose nicotine (5.0 mg/kg: NS), or both (NC) on gestation days 8-21. N was administered by osmotic minipump and C by sc injection. Saline-injected dams, fitted with saline-fitted pumps (SS), and untreated dams, pair-fed (PF) to NC females, served as controls. Alterations in maternal variables were limited to a 10-15% decrease in food consumption in NC and CS groups. Pregnancy outcome and birth statistics were unaffected by prenatal treatment, as was offspring body weight during the first four postnatal weeks. However, the development of surface righting was delayed inC CS pups, and only CS offspring were underresponsive to the stimulatory effects of dopamine agonists on activity and stereotypy. Behavioral responses to N challenge were similar in all groups. In addition, only CS offspring showed altered behavioral responses in a spontaneous alternation task. Treatment effects on dopamine D1 and D2 binding in the caudate nucleus were not observed. The combination of N and C did not exacerbate any of the behavioral changes seen in CS offspring. These results support the hypothesis that C is a behavioral teratogen in rodents, and suggest that in the present model, nicotine can mitigate some of the consequences of in utero exposure to cocaine.

The effect of time following exposure to trimethyltin (TMT) on cholinergic muscarinic receptor binding in rat hippocampus

Adult male Long-Evans rats were given 6 mg/kg trimethyltin (TMT). Rats were killed 1, 3, 7, 14, 21, 35, or 60 d later. An untreated control group was included. Brain sections were processed using film autoradiography to visualize in the hippocampus either total muscarinic receptor binding ([3H]quinuclidinyl benzilate; [3H]QNB), or M1 receptors ([3H]pirenzepine; [3H]PZ), or M2 receptors ([3H]oxotremorine-M; [3H]OXO-M). A reduction in [3H]QNB binding was found in CA1 and CA3c 7 d after TMT, but not in CA3a, b, or the dentate gyrus. [3H]PZ binding was decreased throughout Ammon's horn by 14 d after treatment. [3H]OXO-M binding decreased 1 d after exposure in CA1 and in all subfields of Ammon's horn by d 3. Neither [3H]PZ or [3H]OXO-M binding decreased in the dentate gyrus of TMT-treated rat at any time point. The temporal patterns of receptor loss may be explicable by reference to timing of fiber and cell body degeneration reported in previous studies and the regional differences may account for discrepancies between reports of either substantial decreases or no loss in hippocampal muscarinic receptors after TMT exposure.

Changes in muscarinic (M1 and M2 subtypes) and phencyclidine receptor density in the rat brain following trimethyltin intoxication

The main purpose of this study was to determine whether one or both of the muscarinic receptor subtypes (M1 and M2) contributed to the total cholinergic receptor loss found in trimethyltin (TMT) treated rats and to assess the effect of TMT on phencyclidine (PCP) receptor density in several regions of the rat brain. The distribution and changes in muscarinic (M1 and M2) receptor and PCP receptor sites were analysed by means of quantitative autoradiography using [3H]quinuclidinyl benzilate (QNB) and [3H] N-(1-(2-thienyl) cyclohexyl) 3,4-piperidine (TCP) respectively. The results demonstrate a TMT induced decrease in [3H]QNB binding in a large number of brain regions particularly the hippocampal formation, for both M1 and M2 muscarinic receptor subtypes. There is also a decrease in [3H]TCP binding in several brain regions. The effects of TMT on PCP receptors suggest that TMT induced damage is not restricted to the cholinergic system and that N-methyl-D-aspartate (NMDA) receptors are also affected.

Prenatal haloperidol exposure: effects on brain weights and caudate neurotransmitter levels in rats

Monoamines may exert a trophic effect on early brain development. To assess the role of dopamine in prenatal neurological development of the rat, haloperidol (HAL) was given in daily 2.5 or 5 mg/kg SC doses to dams over gestational days 6 to 20. This treatment regime did not enhance fetal mortality, but did produce reliable, if modest, stunting of the body and brain weight of offspring. The 5 mg/kg HAL dose consistently reduced offspring brain weight to roughly 90% of controls. This effect was probably permanent, in that it was seen throughout maturation and in adults as late as 140 days of postnatal age. Appropriate controls showed that this effect was not due to drug-induced reductions in food intake, to the presence of HAL in maternal milk, or to behavioral abnormalities in HAL-exposed dams. These effects had, at best, modest regional specificity, in that most brain regions were affected, independently of degree of dopaminergic innervation. Closer investigation of HAL effects on the striatum suggested that this permanent weight reduction was not accompanied by alterations in striatal concentrations of monoamines, monoamine metabolites, amino acids, choline, acetylcholine, DNA, protein, or water. It is concluded that prenatal HAL does stunt growth, but that this effect may not involve a direct drug influence restricted to the fetal dopamine system in the brain.

Effect of methyl bromide on regional brain glutathione, glutathione-S-transferases, monoamines, and amino acids in F344 rats

Both metabolic and neurotransmitter changes have been implicated in the pathogenesis of monohalomethane neurotoxicity in rodents. This study in male and female F344 rats examined the effects of methyl bromide (MeBr) on regional brain glutathione-S-transferase (GST) activities and concentrations of glutathione (GSH), monoamines, and amino acid. Inhalation exposure to 150 ppm MeBr (6 hr/day x 5 days) yielded no histologic evidence of brain lesions but resulted in a number of biochemical changes. GSH depletion and GST inhibition were detected in the frontal cortex, caudate nucleus, hippocampus (examined for GSH only), brain stem, and cerebellum from animals of both sexes. Differences between sexes were detected for GSH depletion. Simultaneous treatment of rats with the inhibitor of monohalomethane toxicity, BW 755C (3-amino-1-[m-(trifluoromethyl)phenyl]-2-pyrazoline; 10 mg/kg bw ip, 1 hr pre- and 1 hr postexposure) completely protected against GST inhibition in all brain regions of both sexes. Partial protection by BW 755C against GSH depletion was observed in the cerebral cortex and in the cerebellum only. In males, MeBr exposure had no effect on the regional concentrations of the monoamines dopamine and serotonin and the amino acids glutamate, glutamine, taurine, and gamma-aminobutyric acid. Regional increases of brain aspartate and glycine levels were observed after exposure of males to MeBr but BW 755C had no effect on these changes induced by MeBr. Thus, of all the parameters studied, only GST, and in some brain areas GSH, correlated with inhibition of toxicity. It is concluded that, in contrast to the monoamines and the amino acids, GST and GSH are sensitive and potentially relevant indicators of MeBr neurotoxicity which could explain sex and regional differences in response to the monohalomethanes.

Chronic marijuana smoke exposure in the rhesus monkey. IV: Neurochemical effects and comparison to acute and chronic exposure to delta-9-tetrahydrocannabinol (THC) in rats

THC is the major psychoactive constituent of marijuana and is known to produce psychopharmacological effects in humans. These studies were designed to determine whether acute or chronic exposure to marijuana smoke or THC produces in vitro or in vivo neurochemical alterations in rat or monkey brain. For the in vitro study, THC was added (1-100 nM) to membranes prepared from different regions of the rat brain and muscarinic cholinergic (MCh) receptor binding was measured. For the acute in vivo study, rats were injected IP with vehicle, 1, 3, 10, or 30 mg THC/kg and sacrificed 2 h later. For the chronic study, rats were gavaged with vehicle or 10 or 20 mg THC/kg daily, 5 days/week for 90 days and sacrificed either 24 h or 2 months later. Rhesus monkeys were exposed to the smoke of a single 2.6% THC cigarette once a day, 2 or 7 days a week for 1 year. Approximately 7 months after the last exposure, animals were sacrificed by overdose with pentobarbital for neurochemical analyses. In vitro exposure to THC produced a dose-dependent inhibition of MCh receptor binding in several brain areas. This inhibition of MCh receptor binding, however, was also observed with two other nonpsychoactive derivatives of marijuana, cannabidiol and cannabinol. In the rat in vivo study, we found no significant changes in MCh or other neurotransmitter receptor binding in hippocampus, frontal cortex or caudate nucleus after acute or chronic exposure to THC. In the monkey brain, we found no alterations in the concentration of neurotransmitters in caudate nucleus, frontal cortex, hypothalamus or brain stem.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute effects of 3,4-methylenedioxymethamphetamine (MDMA) on monoamines in rat caudate

Extracellular levels of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA) and serotonin (5-HT) were assayed in the caudate of freely moving rats using microdialysis and high performance liquid chromatography with electrochemical detection (HPLC-EC) to detect changes in their release. Dialysates were assayed at 20-minute intervals for four hours after an intraperitoneal (IP) injection of MDMA (10 mg/kg). In a separate study to determine MDMA effects on total caudate levels of the above neurochemicals, animals were injected IP with MDMA (10 mg/kg) and then sacrificed at 20, 60, 120 and 180 minutes after treatment. Brains were quickly removed, and caudate nuclei were dissected for neurochemical analysis using HPLC-EC. MDMA elicited an amphetamine-like increase in DA release, followed by an increase in DA content. DOPAC and HVA were both reduced in homogenate. 5-HT release was also increased, followed by a drop in caudate homogenate levels by three hours. DA extracellular content was 686% of control at 80 minutes; caudate homogenate levels were 122% at 120 minutes. 5-HT extracellular release was 123% at 20 minutes, then decreased thereafter. It is concluded that the acute effect of MDMA on caudate is at least as great on the DA as it is on the 5-HT system.

"Isolation stress" revisited: isolation-rearing effects depend on animal care methods

Early reports of enhanced behavioral reactivity in isolation-reared rats attributed this syndrome to "isolation stress." In the studies reported here, this "isolation stress syndrome" was reliably obtained in adult rats reared from weaning in individual hanging metal cages. Such isolates showed behavioral and adrenocortical symptoms of profound fear during open-field testing, unlike group-housed controls or littermate isolates reared singly in plastic cages. Animals in hanging metal cages are never touched by human caretakers, whereas rats reared in plastic cages are picked up and put in clean cages twice weekly. Handling hanging-cage isolates twice weekly to model the handling associated with cage changes completely protected against this syndrome. Further, there was no hormonal, neurochemical or anatomical evidence of chronic stress even in hanging-cage isolates. Littermates housed in social groupings (three rats per plastic cage) also froze and defecated in the open field at rates comparable to hanging-cage isolates if they were the first animals to be tested from their social group cage. It is probable that odor cues from familiar cagemates in the open field protected socially reared animals tested subsequently from the same cage from this syndrome. It is concluded that isolates are not chronically stressed, and that rearing effects are the result of a complex interaction between prior handling, social experience and test conditions.

Effect of trimethyltin on amino acid concentrations in different regions of the mouse brain

Trimethyltin (TMT) is a neurotoxic compound known to cause marked alterations in brain chemistry. We have previously demonstrated that a single oral dose of TMT produced a dose-dependent decrease in muscarinic cholinergic receptors in mouse brain and significantly elevated glutamine in several regions of the rat brain. This study was designed to determine if TMT produced dose- and time-related alterations in amino acid concentrations in the adult male C57BL/6N mouse brain and in peripheral organs and plasma. In the dose-response study, TMT was administered orally as a single dose of 0, 0.5, 1.0, 3.0 or 5.0 mg/kg and animals were sacrificed 24 hr after treatment. In the time-course study, mice were dosed with TMT at 3.0 mg/kg and sacrificed 4, 12, 24, 48 or 96 hr after dosing. Amino acid concentrations were quantified by HPLC/EC following precolumn derivatization with o-phthalaldehyde-tert-butylthiol. TMT produced dose-dependent increases in aspartate, glutamine and glycine in the caudate nucleus (CN), frontal cortex (FC) and hippocampus (HIP) at 3.0 and 5.0 mg/kg. TMT at 3.0 mg/kg produced significant increases of aspartate in FC and HIP after 48 hr. Glutamine concentrations were significantly increased at 24 and 48 hr in HIP and at 48 hr in CN. Glycine and GABA concentrations were significantly increased at 48 and 96 hr respectively in the HIP. Glutamine was increased in plasma at 4 and 12 hr and in liver at 24 hr. Hyperammonemia occurred in plasma after 8 hr and continued through 24 hr and was accompanied by an increase in serum urea nitrogen.(ABSTRACT TRUNCATED AT 250 WORDS)

Age-dependent changes in receptor-stimulated phosphoinositide turnover in the rat hippocampus

To study the changes in the hippocampal cholinergic system of chronologically old and behaviorally impaired animals, old (21 months of age) and young (3 months of age) male, Fischer-344 rats were used. The aged animals were tested on a reference memory task (Morris water maze) and found to be functionally impaired as compared to the young controls. Carbachol-stimulated phosphoinositide metabolism was measured in hippocampal slices from young and old rats. Slices were prelabeled with 3H-inositol for 120 min and subjected to muscarinic stimulation in the presence of lithium. Following extraction of the slices with acidified solvent mixture, the inositolphosphates present in the aqueous fraction were isolated by ion exchange chromatography. Receptor-stimulated release of inositolphosphates (IPs) was found to be increased in the hippocampus of older animals. This age-related enhancement of IP release was in contrast to the decrease in choline acetyltransferase (CHAT) activity in the hippocampus. We postulate that alterations in the G-protein coupling with the muscarinic receptor leads to an increase in the phosphoinositide turnover in part as a compensatory mechanism for neuronal cell death and reduced transmitter levels.

Age-related changes in receptor-mediated phosphoinositide hydrolysis in various regions of rat brain

The effects of age on cholinergic markers and receptor-stimulated phosphoinositide hydrolysis was examined in the frontal cortex and striatum of male Fischer-344 rats. Choline acetyltransferase activity was decreased 27% in the striatum of aged (24 month) rats compared to young (3 month) controls. Muscarinic receptor density as measured by [3H]-quinuclidinyl benzilate binding showed a similar 26% decrease in the striatum of aged rats. Phosphoinositide hydrolysis was measured by the release of inositol phosphate (IP) from tissue slices prelabeled with [3H]myoinositol in response to carbachol, norepinephrine, and quisqualate. In the cortex, stimulated IP release was significantly greater in slices from aged rats compared to young rats for all three agonists. In contrast, stimulated IP release was significantly decreased in striatal slices from aged rats compared to young for all three agonists. These data indicate a differential effect of age on agonist-stimulated phosphoinositide hydrolysis in the cortex and striatum. The decreased responsiveness in the latter area may result from the age-related loss of postsynaptic receptors.

Behavioral and neurochemical effects of prenatal methylenedioxymethamphetamine (MDMA) exposure in rats

MDMA is a hallucinogenic drug that is used by the general public as a recreational drug of abuse. The neurobehavioral consequences of prenatal MDMA exposure are unknown. Groups of pregnant rats were gavaged with 0, 2.5, or 10 mg/kg MDMA during gestation on alternate gestational days 6-18. Gestational duration, litter size, neonatal birth weights and physical appearance at birth were unaffected by MDMA treatments. Pregnancy weight gain was significantly reduced by MDMA treatment. Progeny growth, maturational parameters (eye opening and incisor eruption times), surface righting reflex, swimming performance, forelimb grip strength, milk-induced behaviors, passive avoidance behavior, figure-8 maze activity over 48 hours, the density of brain serotonin (5-HT) uptake sites, and brain 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) levels were unaffected by MDMA treatments. Olfactory discrimination on postnatal days (PND) 9-11 was enhanced in both male and female MDMA-treated progeny, while negative geotaxis (PND 7-10) was delayed in female pups. In contrast to progeny, MDMA caused dose-dependent decreases in 5-HT and 5-HIAA levels in discrete brain areas of the dam. It is concluded that prenatal exposure to MDMA at the levels used here produces only subtle behavioral alterations in developing rats. The dam is more at risk for MDMA-induced 5-HT depletion than is the conceptus.

Organometal-induced increases in oxygen reactive species: the potential of 2',7'-dichlorofluorescin diacetate as an index of neurotoxic damage

The effects of the neurotoxic metals methylmercury (MeHg) and trimethyltin (TMT) on oxygen reactive species formation within a crude synaptosomal fraction (P2), using the probe 2',7'-dichlorofluorescin diacetate (DCFH-DA), and intracellular calcium ([Ca2+]i), with the fluorescent indicator fluo-3, have been investigated. Two and seven days after a single injection of MeHg (1 mg/kg) the formation rate of cerebellar oxygen reactive species was significantly increased. Hippocampal and frontocortical oxygen reactive species were elevated 2 days after TMT injection (3 mg/kg). In vitro exposure to MeHg (10-20 microM) increased the formation rate of oxygen reactive species, while TMT (5-40 microM) was without effect. Levels of [Ca2+]i were unaltered in P2 fractions from cerebellum and hippocampus of animals treated with either organometal. The data demonstrate that oxygen reactive species are elevated in brain regions, cerebellum (MeHg) and hippocampus (TMT), believed to be selectively vulnerable to these toxic agents. Findings suggest that oxidative damage may be a mechanism underlying the toxicity of both organometals. The use of DCFH-DA may have potential in the nervous system as an indicator of neurotoxic damage.

Neurochemical effects of prenatal haloperidol exposure

The neurochemical effects of prenatal exposure to dopamine receptor antagonists are as yet poorly characterized. To further examine this problem, pregnant rats were given daily subcutaneous injections of vehicle, 2.5 or 5.0 mg/kg haloperidol over gestational days 6 through 20. Membrane binding of [3H]SCH-23390 (D1-specific) and [3H]spiroperidol (D2-specific in most brain areas) was measured in four regions of the cerebral dopamine system at postnatal day (PND) 30. Dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) levels were measured in caudate on PND 30 following a d-amphetamine challenge. Prenatal haloperidol exposure reduced [3H]SCH-23390 and [3H]spiroperidol binding in caudate in a dose-dependent manner. [3H]Spiroperidol binding was similarly reduced in nucleus accumbens, but only the low dose (2.5 mg/kg) group showed decreased [3H]SCH-23390 binding in this region. Binding of neither compound was significantly altered in amygdala or frontal cortex. Basal or drug-stimulated levels of caudate DA and DOPAC were unaltered. It is concluded that prenatal haloperidol exposure reduces D1 and D2 binding in some, but not all regions of the forebrain dopamine system.

Characterization of receptor-coupled phosphoinositide hydrolysis in the rat hippocampus after intradentate colchicine

Lesions produced by intradentate hippocampal administration of colchicine have been reported to produce several time-dependent behavioral and neurochemical changes, including a possible change in the signal transduction process for the cholinergic muscarinic receptor. To characterize further the effects of colchicine on receptor-coupled hydrolysis of phosphoinositides, colchicine was injected stereotaxically into the dentate gyrus of rats at a dose of 2.5 micrograms/site. The animals were killed 1, 3, or 12 weeks after injection and the hippocampi removed and sliced. [3H]Inositol was incorporated into slices, and various receptor agonists known to stimulate inositol phosphate (IP) metabolism were studied. Colchicine administration altered agonist-stimulated turnover in the hippocampus in a time-dependent manner. This hyperstimulation was receptor-mediated, because it was blocked by pirenzepine. The hyperstimulation of turnover was observed also with norepinephrine and serotonin. Colchicine had no effect on IP turnover in vitro. The effect of the colchicine lesion was observed only in the hippocampus, because no change in cholinergic muscarinic receptor-stimulated phosphatidylinositol turnover was observed in the cortex. These studies indicate that intradentate administration of colchicine produces a compensatory change in the signal transduction process in the hippocampus detectable 12 weeks after the lesion.

Colchicine administered into the area of the nucleus basalis decreases cortical nicotinic cholinergic receptors labelled by [3H]-acetylcholine

Lesions in the nucleus basalis in the rat are known to decrease presynaptic markers for acetylcholine, including levels of cholineacetyltransferase (CHAT), high affinity uptake of choline and levels of acetylcholinesterase. Effects of lesions of the nucleus basalis on populations of nicotinic and muscarinic receptors are less well understood. After bilateral injection of the neurotoxic agent, colchicine into the nucleus basalis in the rat, levels of CHAT in the cerebral cortex were reduced 44%. Muscarinic cholinergic [( 3H]QNB) and dopaminergic [( 3H]spiroperidol) binding was not changed in the cortex, hippocampus or striatum. However, significant decreases in nicotinic binding sites, labelled by [( 3H]acetylcholine), were observed in the frontal cortex of nucleus basalis treated animals; scatchard plot analysis indicated a significant decrease in the number, but not affinity, of nicotinic binding sites. Colchicine injected into the nucleus basalis had no effect on the binding of [3H]acetylcholine in the hippocampus, but decreased binding of [3H]acetylcholine in the striatum. Subsequent experiments, in which colchicine was administered into the striatum at a site above the nucleus basalis had no significant effect on nicotinic binding in the striatum or frontal cortex. These results support the hypothesis that degeneration of the nucleus-basalis-cortical cholinergic pathway results in a loss of presynaptic nicotinic binding sites in the cortex as well as in the striatum (through transsynaptic degeneration of the cortico-striatal pathway).

Neurochemical and neurohistological alterations in the rat and monkey produced by orally administered methylenedioxymethamphetamine (MDMA)

MDMA is an amphetamine analog prescribed by some health professionals in the field of psychotherapy and used as a recreational drug by the general public. In recent reports, investigators have suggested that MDMA produces acute neurotoxicity when administered by subcutaneous injection. In order to determine if MDMA produces lasting neurochemical alterations after oral administration, groups of six rats (adult male Sprague-Dawley) were dosed by gavage with either 40 or 80 mg/kg of MDMA or saline vehicle once every 12 hr for 4 days. These rats were terminated 2 weeks after the first dose along with an additional group of rats (80 mg/kg) terminated 4 weeks after the first dose. Brain regions including the hippocampus (H), caudate nucleus (CN), hypothalamus (HY), frontal cortex (FC), and brain stem (BS) were analyzed by HPLC with electrochemical detection for concentrations of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), and norepinephrine (NE). In the CN, 40 mg/kg MDMA produced no change in DA, DOPAC, or HVA, but a 50-60% decrease in 5-HT and 5-HIAA concentrations was observed at 2 weeks. Similar effects were observed at 80 mg/kg at both 2 weeks and 4 weeks. A temporary decrease was also seen in DA (21%) and in HVA (34%) 2 weeks but not 4 weeks after the 80 mg/kg dose regimen. In the H, MDMA (40 or 80 mg/kg) produced no change in NE, but a 50-60% decrease was seen in 5-HT and 5-HIAA concentrations at 2 weeks. Concentrations of 5-HT and 5-HIAA were significantly decreased in the HY and FC by all MDMA treatments, but DA and DOPAC concentrations were not altered as compared to vehicle controls. BS was least affected by treatment with no change in DA, DOPAC, or 5-HIAA concentrations and only a slight decrease in 5-HT (19-33%) concentrations at 2 weeks but not at 4 weeks. To determine the sensitivity of the nonhuman primate to MDMA, a total of nine rhesus monkeys were dosed with vehicle or 5 or 10 mg/kg MDMA (n = 3) by gastric intubation twice per day for 4 days. One month after MDMA dosing, a dose-related reduction from vehicle control values for 5-HT and 5-HIAA was observed. These results indicate that the monkey may be more sensitive than the rat to the persistent serotonergic neurotoxicity of MDMA.(ABSTRACT TRUNCATED AT 400 WORDS)

Gestational exposure to phencyclidine (PCP) in rats decreases PCP binding sites in term fetal brain

Pregnant Sprague-Dawley rats were treated with 5 mg/kg body weight of phencyclidine (PCP) injected at 1 ml/kg subcutaneously on three consecutive days at four different stages of gestation. Within 10-30 min after treatment, dams showed some lack of motor coordination and became lethargic. On gestational day 21, all rats were killed by decapitation and brains were dissected and stored from mother and fetus for neurochemical analysis. PCP, dopamine and muscarinic cholinergic receptor binding was measured in membranes prepared from maternal and fetal whole brain. Neurotransmitter concentrations were also measured in the fetal brain homogenates. There was a significant decrease in PCP binding sites in fetal but not maternal brains after maternal PCP injection at gestational days 12-14, 15-17 and 18-20, but not at 9-11 days. Dopamine and muscarinic cholinergic receptor binding was not significantly altered in fetal or maternal brain when compared with vehicle control animals. The whole brain dopamine, 3,4-dihydroxyphenylacetic acid, serotonin, and 5-hydroxyindoleacetic acid concentrations did not show significant change in any group studied. These data indicate that gestational exposure to PCP decreases high affinity binding of PCP in term fetal brain at doses which do not alter maternal PCP receptor binding.

Morphometric studies of the rat hippocampus following chronic delta-9-tetrahydrocannabinol (THC)

Persistent behavioral effects resembling those of hippocampal brain lesions have been reported following chronic administration of marijuana or its major psychoactive constituent, delta-9-tetrahydrocannabinol (THC) to rats. We used morphometric techniques to investigate the effects of chronic THC on the anatomical integrity of the hippocampus. Rats dosed orally for 90 days with 10 to 60 mg/kg THC or vehicle were evaluated by light and electron microscopy up to 7 months after their last dose of drug. Electron micrographs revealed a striking ultrastructural appearance and statistically significant decreases in mean volume of neurons and their nuclei sampled from the hippocampal CA3 region of rats treated with the highest doses of THC. A 44% reduction in the number of synapses per unit volume was demonstrated in these same rats. Golgi impregnation studies of additional groups of rats treated with 10 or 20 mg/kg/day THC and sacrificed 2 months after their last treatment with THC revealed a reduction in the dendritic length of CA3 pyramidal neurons, despite normal appearing ultrastructure and no changes in synaptic density. The hippocampal changes reported here may constitute a morphological basis for behavioral effects after chronic exposure to marijuana.

Effect of trimethyltin on ornithine decarboxylase in various regions of the mouse brain

Male C57B1/6N mice, 8-10 weeks old were given a single oral dose of 0, 1.0 or 3.0 mg/kg body weight of trimethyltin hydroxide (TMT). Levels of ornithine decarboxylase (ODC) activity were measured in several brain areas, 1, 2 and 7 days later. The lower dose of TMT produced a decrease of ODC in the caudate nucleus and hippocampus at all time points studied. Hypothalamus, cerebellum and brain stem levels of this enzyme were unaltered. At the higher dose of TMT, ODC activity in hippocampus, cerebellum and brain stem were increased relative to controls at 1 and 2 days after treatment, while other regions were not significantly affected. These elevated ODC levels returned to control values within 7 days. Thus, trimethyltin treatment causes changes in ODC activity in a region and dose-specific manner.