Effects of combined lead and cadmium exposure: Changes in schedule-controlled responding and in dopamine, serotonin, and their metabolites.

Adult male rats were maintained on 1 of 4 ad-lib diets: Group Control-Diet received a normal laboratory diet that contained no added chemicals; Group Lead-Diet received a diet containing 500 ppm (parts per million) lead; Group Cadmium-Diet received a diet containing 100 ppm cadmium; and Group Lead-Cadmium Diet received a diet containing both 500 ppm lead and 100 ppm cadmium. After 60 days of exposure to their respective diets, animals were placed on restricted diets (15 g/day) of the identical food received during the exposure period. Each animal was trained to lever press on an FI 1-min schedule for 21 sessions (1 session/day). The results of schedule training showed that lead alone or cadmium alone was associated with increased lever pressing relative to control diet. However, when lead and cadmium were exposed jointly, performance was not significantly different from control performance. Similar attenuation of effects were observed for central neurotransmitter functions. Specifically, disturbances in dopamine and serotonin turnover that were produced by lead alone were attenuated by the cotreatment of cadmium and lead. Possible accounts of the apparent antagonism between cadmium and lead are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gestational exposure to cocaine or pharmacologically related compounds: effects on behavior and striatal dopamine receptors

Gestational cocaine (COC) exposure has been reported to alter behavior and possibly dopamine (DA) receptors. In this paper, we further examined the effects of prenatal COC (40 mg/kg, s.c.) on DA receptor binding and the behavioral response to quinpirole, a DA D2 receptor agonist. In an attempt to elucidate possible mechanisms of such effects, we exposed pregnant dams to specific reuptake blockers; fluoxetine 12.5 mg/kg, a serotonin reuptake blocker; desipramine 10 mg/kg, a norepinephrine reuptake blocker; GBR-12909 10 mg/kg, a DA reuptake blocker; or to a local anesthetic, lidocaine 40 mg/kg. Drugs were administered once daily over gestational days 8-20. Control dams were injected with saline (SAL) or pair-fed to the COC group. Quinpirole challenge was performed in the offspring on post natal day 19. Two pups per litter were injected (s.c.) with 0.03 or 0.09 mg/kg quinpirole-HCl on post-natal day 19. The remaining pups in each litter were sacrificed for analysis of striatal DA receptors. Results showed that only COC exposure altered the behavioral response to the quinpirole challenge by increasing quinpirole-induced stereotypy and motor activity relative to SAL controls. DA receptor analysis showed no alteration in K(D) or B(MAX) for striatal D1 or D2 sites in any group. These results suggest that prenatal COC exposure produces alterations in function of the D2 receptor complex which are not reflected in K(D) or B(MAX) and that these effects are not fully mimicked by exposure to specific monoamine reuptake blockers or a local anesthetic.     

Effects of the trichothecene mycotoxin T-2 toxin on neurotransmitters and metabolites in discrete areas of the rat brain

Systemic exposure to T-2 toxin disrupts brain biogenic monoamine metabolism. Although the mechanisms underlying these neurochemical perturbations are unclear, we have suggested that they are a reflection of increased blood-brain barrier (BBB) permeability, or altered protein synthesis that affects brain enzyme activities. Accordingly, BBB permeability, in vitro protein synthesis and in vitro monoamine oxidase (MAO) activity were examined in rats after either acute, or 7-day exposure to T-2. Membrane permeability was assessed from the recovery of systemically administered [14C]mannitol and [14C]dextran with [3H]water as the diffusible reference, either 2 hr post-intraperitoneal (i.p.) injections of 0, 0.2 and 1 mg T-2/kg body weight or following a 7-day exposure to diets containing 0 and 10 ppm T-2. Protein synthesis, determined by [14C]leucine incorporation, and MAO activity, determined by H2O2 production, were observed either 2 hr post-ip injection of 0 and 1 mg T-2/kg body weight or following a 7-day exposure to diets containing 0, 2.5 and 10 ppm T-2. Permeability increases were observed in all brain regions examined for mannitol, but not for dextran following T-2 i.p. The effect of dietary T-2 was more modest, affecting mannitol uptake in two brain regions, the cerebellum and pons plus medulla regions. Protein synthesis was significantly decreased by i.p. administration of T-2, while dietary treatment significantly reduced MAO enzyme activity. Collectively, the effect of T-2 toxin on BBB permeability, protein synthesis and MAO enzyme activity may account for the neurochemical imbalance observed in T-2 intoxication.     

Changes in serotonin level and turnover in discrete hypothalamic nuclei after pinealectomy and melatonin administration to rats

OBJECTIVE: It has previously been shown that 17 beta-oestradiol (E2) implants counteract the formation of more acidic isoforms of the gonadotrophins in post-menopausal women. A much lesser effect was observed on the charge of the gonadotrophin isoforms in women with chronic oral daily therapy with 2 mg E2 combined with a progestogen, 1 mg norethisterone acetate (NETA), in spite of similar serum levels of E2 and SHBG. The presence of the progestogen in the latter study may explain the difference observed. The present study investigated the effect of the progestogen NETA on the charge and concentration of serum FSH and LH in E2 implant treated women. DESIGN: A group of 8 post-menopausal women, mean age 65 years (range 50-80 years) treated with 20 mg E2 implants every 6 months, participated in the study. The women were given a daily oral medication of 5 mg NETA for a 4-week period starting at 4 weeks after the insertion of an E2 implant (mean serum E2 420 pmol/l). This treatment with NETA was repeated in 6 of the women starting at 18 weeks after the insertion of the E2 implant (mean serum E2 317 pmol/l). Blood samples were obtained at the start of the NETA therapy, after 2 and 4 weeks of treatment and at 4 weeks after the last NETA treatment. The effects of NETA therapy on the charge of the serum gonadotrophin isoforms was determined by electrophoresis in 0.1% agarose suspension and FSH, LH, E2, and SHBG were determined with fluoroimmunoassays. RESULTS: The NETA treatment decreased the serum FSH and LH levels after 2 weeks to 24 and 23% of the levels before NETA and after 4 weeks to 14.6 and 8.8%, which were 1.3 and 2.2% of the mean levels for non-treated post-menopausal women. Both FSH and LH isoforms became more acidic during the first 2 weeks of treatment. During the following 2 weeks of NETA treatment the isoforms of both FSH and LH became more basic again. Ten weeks later both the concentration and the charge of the gonadotrophins were similar to those before the NETA treatment. The changes in concentration and charge of the gonadotrophins during the second treatment period were similar to those during the first. All the changes were statistically significant (P < 0.05 - < 0.001). The mean SHBG level decreased (P < 0.01) from 84.5 to 70.6 nmol/l after 2 weeks and to 59.9 nmol/l after 4 weeks of NETA treatment and increased (P < 0.01) 10 weeks later to 77 nmol/l. CONCLUSION: In the oestradiol treated women, the effect of the progestogen norethisterone acetate on the charge of the gonadotrophin isoforms was time-related. The oestradiol effect on the charge was counteracted during the first 2 weeks of progestogen treatment and more acidic isoforms appeared in the circulation. During the following 2 weeks the isoforms became more basic again. The levels of the gonadotrophins were efficiently decreased after 2 weeks of progestogen treatment and further decreased after 4 weeks. The time-related effect of the progestogen on the gonadotrophin isoforms may be mediated via changes in the pattern of GnRH release from the hypothalamus. The observed gradual decrease in the SHBG level during the progestogen therapy may cause an increased oestradiol effect on the hypothalamus and pituitary.     

Effects of in utero and lactational exposure of the laboratory rat to 2,4,2'',4''- and 3,4,3'',4''-tetrachlorobiphenyl on dopamine function

We have developed a biochemical approach for identifying the components of cortical actin assembly sites in polarized yeast cells, based on a permeabilized cell assay that we established for actin assembly in vitro. Previous analysis indicated that an activity associated with the cell cortex promotes actin polymerization in the bud. After inactivation by a chemical treatment, this activity can be reconstituted back to the permeabilized cells from a cytoplasmic extract. Fractionation of the extract revealed that the reconstitution depends on two sequentially acting protein factors. Bee1, a cortical actin cytoskeletal protein with sequence homology to Wiskott-Aldrich syndrome protein, is required for the first step of the reconstitution. This finding, together with the severe defects in actin organization associated with the bee1 null mutation, indicates that Bee1 protein plays a direct role in controlling actin polymerization at the cell cortex. The factor that acts in the second step of the reconstitution has been identified by conventional chromatography. It is composed of a novel protein, Pca1. Sequence analysis suggests that Pca1 has the potential to interact with SH3 domain-containing proteins and phospholipids.     

Effects of in utero cocaine exposure on the expression of mRNAS encoding the dopamine transporter and the D1, D2 and D5 dopamine receptor subtypes in fetal rhesus monkey

The effects of in utero cocaine exposure on the development of the mRNAs encoding the dopamine transporter (DAT) and the D1, D2 and D5 dopamine receptor subtypes were determined in fetal monkey brains at day 45 and day 60 of gestation. Pregnant monkeys were treated with cocaine 3 mg/kg or saline i.m., four times a day from day 18 of gestation until the pregnancy was terminated at day 45 or day 60. The fetal brains were dissected, and tissue RNA extracted and quantified using ribonuclease protection assay analysis. In day 45 fetal monkeys, dopamine D1 and D2 receptor subtype mRNAs and DAT mRNA were found in low quantities both in control and cocaine-treated subjects. In day 60 fetal monkeys, D1 receptor mRNA levels were highest in the frontal cortex/striatal area, and low to moderate quantities were found in diencephalic and mesencephalic fetal brain regions. Dopamine D2 receptor mRNA levels were highest in the frontal cortex/striatal area, diencephalon and the midbrain, moderate in the brainstem and low in the caudal temporal lobe and surrounding cortical areas. Dopamine D5 receptor mRNA was expressed in low quantities throughout the day 60 fetal monkey brain, whereas DAT mRNA was found in the midbrain only. In utero cocaine exposure caused a significant increase in dopamine D1, D2 and D5 receptor subtype mRNAs in the frontal cortex/striatal area of day 60 fetal monkeys. These results support the hypothesis that dopamine synthesis and release may be reduced in cocaine-treated fetuses, which results in dopamine receptor up-regulation.     

Regulation of the Na+/K(+)-ATPase pump in vitro after long-term exposure to cocaine: role of serotonin

Long-term exposure to cocaine can cause persistent behavioral changes and alterations in neuronal function. One cocaine-regulated mRNA in the rat brain is the beta-1 subunit of the Na+/K(+)-ATPase pump. We examined both Na+/K(+)-ATPase function and expression after cocaine treatment of pheochromocytoma cells. One-hour exposure to cocaine did not alter Na+/K(+)-ATPase activity, as measured by the ouabain-sensitive component of rubidium uptake. Four days of cocaine resulted in an approximately 30% decrease in Na+/K(+)-ATPase activity. Western blot analyses demonstrated an approximately 25% decrease in levels of the beta-1 isoform, without changes in pump total alpha subunit levels. Treatment with dopamine type 1 or type 2 receptor agonists for the same period did not affect Na+/K(+)-ATPase activity. The serotonin-selective reuptake inhibitor paroxetine caused an approximately 45% decrease in rubidium uptake after 4 days, whereas pump function was not altered after treatment with either the dopamine-selective reuptake blocker nomifensine or the norepinephrine-selective reuptake blocker desipramine. Chronic treatment with both cocaine and LY 278,584, a serotonin type 3 receptor antagonist, did not replicate the cocaine-associated decrease in pump function. Long-term cocaine exposure regulates expression and function of the Na+/K(+)-ATPase pump in neuronal-like cells; this regulation is mediated in part via the serotonin type 3 receptor. Similar Na+/K(+)-ATPase pump regulation in vivo may selectively alter neuronal function in the mammalian brain.     

Effect of repeated immobilization on serotonin metabolism in different rat brain areas and on serum corticosterone

The effect of daily repeated 10 min immobilization on the serotoninergic neurotransmission and serum corticosterone levels was studied. Male Lewis rats were immobilized for a 10 min period daily once or on 5 consecutive days. Serotoninergic neurotransmission was followed using differential in vivo pulse voltammetry with carbon fibre electrodes measuring extracellular 5-hydroxyindoleacetic acid (5-HIAA) levels. Recordings were performed in brain areas involved in the control of behaviour, mood, and stress response such as the frontal cortex, the hippocampal CA-3 and dentate gyrus, the striatum, and the raphe nuclei dorsalis (NRD) and medialis (MRN). The first immobilization resulted in an increase of the extracellular 5-HIAA levels in all areas under study, except the striatum where no reaction was observed. The major effect was recorded in the frontal cortex, showing an increase of about 400% as compared to control, which lasted for 3h after the end of the immobilization period. Beginning on day 2 in all areas, except the striatum, a consecutive habituation to the stressor seemed to occur, since the stress-induced increase in the voltammetric signal was found to be reduced after consecutive immobilization. Serum corticosterone levels were measured directly after a single and after 5 daily immobilization periods. After single immobilization the serum corticosterone level was found to be about 270 ng/ml. After the 5th immobilization about 300 ng/ml were detected. These differences were not found to be significant. In summary, our data indicate that the serotonin metabolism shows habituation in nearly all brain areas after repeated immobilization, though the corticosterone level at the end of the immobilization period was comparable after single and repeated immobilization.     

Effect of scopolamine on the efflux of dopamine and its metabolites after clozapine, haloperidol or thioridazine

The extracellular concentrations of dopamine (DA) and its metabolites, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), in the striatum and the nucleus accumbens were measured in awake, freely-moving rats. Clozapine (20 mg/kg, i.p.) increased extracellular DA and HVA in both regions but increased DOPAC only in the striatum. Scopolamine (1 mg/kg), although it had no effect by itself in the striatum or nucleus accumbens, inhibited the ability of clozapine to increase extracellular DA, DOPAC and HVA concentrations in the striatum. The clozapine-induced increase in DA in the frontal cortex was not blocked by scopolamine. Haloperidol (1 mg/kg, i.p.) and thioridazine (10 mg/kg, i.p.) also increased extracellular DA, DOPAC and HVA in the striatum, but scopolamine pretreatment did not inhibit these increases. The results suggest that clozapine differs from haloperidol and thioridazine in that the effect of clozapine, but not that of the two neuroleptic drugs, to increase DA release in the striatum acutely depends on muscarinic receptor stimulation. These results suggest that clozapine, despite its strong muscarinic antagonist properties, does not produce full blockade of muscarinic receptors in vivo in the striatum. The interaction of clozapine with the cholinergic system in the striatum could be relevant to its lack of ability to produce extrapyramidal symptoms or tardive dyskinesia.     

Neurodevelopmental consequences of early exposure to phencyclidine and related drugs

In the early development of the central nervous system, stimulation of N-methyl-D-aspartate (NMDA) receptors may be critical for neuronal cell survival and differentiation, as well as the establishment of neural networks resulting from "experience-dependent plasticity." The trophic influence of NMDA receptor stimulation may be present only during a certain critical period of development. There are, therefore, major concerns associated with the administration of noncompetitive NMDA receptor antagonists (such as MK-801 [dizocilpine]) as neuroprotective and anticonvulsant agents to pregnant women, neonates, infants, and young children. Several studies showing disruptive effects of noncompetitive NMDA receptor antagonists on normal neurobehavioral development are reviewed in this article. This research has important public health implications because phencyclidine (PCP), a noncompetitive NMDA receptor antagonist, is a frequently-abused drug that may disrupt brain development in utero when abused by pregnant women. The article also reviews studies of neonatal blockade of the NMDA receptor complex in animals; studies that may lead to useful models of human neurodevelopmental disorders. These models may even mimic the relevant neurodevelopmental aspects of at least some forms of schizophrenia, especially the early developmental disconnection of circuits between the hippocampus and frontal cortex.     

Regional changes in dopamine and serotonin activation with various intensity of physical and psychological stress in the rat brain

The present study examined whether regional patterns of brain dopamine (DA) and serotonin (5-HT) activation after physical and psychological stress depend on the intensity of that stress. Monoamine concentrations (DA, 5-HT, and their metabolites) were measured using high-performance liquid chromatography with electrochemical detection in eight brain regions of rats exposed to two different intensities of foot shock stress for 30 min (1.5 mA or 2.5 mA) or conditioned fear stress (CFS, after single or repeated foot shock). A low level of foot shock selectively increased the DA metabolism in the medial prefrontal cortex (mPFC), whereas a high level of foot shock increased it in most of the brain regions examined in the present study. A low level of foot shock did not increase the 5-HT metabolism in any regions, but a high-intensity shock increased the 5-HT metabolism in the mPFC, nucleus accumbens, and lateral hypothalamus. Rats that received high-intensity shock displayed more freezing than those that received low-intensity shock in a conditioned fear paradigm (24 h after receiving foot shock, the animals were placed in a shock chamber without being given shock), indicating an augmentation of conditioned fear. The increased DA and 5-HT metabolism were especially marked in the mPFC after CFS following a single foot shock session (2.5 mA). Rats that were repeatedly exposed to 2.5 mA foot shock for a period of 10 days displayed a greater degree of freezing induced by CFS than those given only one foot shock session, indicating an augmentation of fear and stress intensity. CFS after repeated foot shock, like foot shock per se, increased the DA metabolism in most of the brain regions except for the striatum and increased the 5-HT metabolism in the mPFC, nucleus accumbens, and amygdala. These results suggest that regional patterns of brain DA and 5-HT activation after physical and psychological stress depend on the intensity of that stress, although there are some differences between these stress; and that the more widespread activation of DA and 5-HT after more severe stress might relate to behavioral changes that reflect the augmentation of fear.     

Changes of behavior and monoamine metabolites in the rat brain after repeated methamphetamine administration: effects of duration of repeated administration

1. The authors studied the mechanism of the reverse-tolerance phenomenon caused by long-term administration of central stimulant drugs. Methamphetamine(MAP) was chronically administered to rats, and the reverse-tolerance phenomenon was studied in terms of behavioral changes and changes in monoamine metabolites, the latter being examined by in vivo microdialysis of the extracellular compartment of the corpus-striatum. The authors also studied [3H]SCH23390 and [3H]spiperone binding to striatal membranes after chronic MAP administration. 2. MAP(4 mg/kg) or saline was administered intraperitoneally once daily to male rats. In Groups 1 and 2, 10 and 30 injections of MAP were given, respectively. In Groups 3 and 4, animals received 10 and 30 injections of saline as controls. One week after the final injection, all rats were challenged with 4 mg/kg MAP. 3. Groups 1 and 2 displayed more intense stereotypy than Groups 3 and 4, indicating that behavioral sensitization had been achieved in the former. Dopamine(DA) levels increased rapidly in response to MAP challenge in all groups, with the increases in Groups 1 and 2 being more marked than that in Groups 3 and 4. Group 1 showed greater persistence and a higher rate of DA increase than Group 2. 4. The number of D1 and D2 dopamine receptors did not change after the repeated MAP administration. 5. The rate of increase in DA release induced by MAP was dependent on the duration of repeated administration, and there was no correlation between the intensity of stereotypy and the rate of increase in DA release induced by MAP. These findings suggest that enhancement in DA release is unlikely to be the sole cause of behavioral sensitization.     

Structure-activity relationships for cocaine congeners in inhibiting dopamine uptake into rat brain synaptic vesicles and bovine chromaffin granule ghosts

Structure-activity relationships of cocaine congeners were determined in inhibiting reserpine-sensitive, Mg++/ATP-dependent uptake of [3H]dopamine into rat brain synaptic vesicles under initial velocity conditions. The C2 carbomethoxy group could be deleted without loss of activity, whereas movement of this group from axial to equatorial orientation increased the potency. There was no need for the ester linkage between the tropane and phenyl rings, nor was there need for the ethylene bridge between C1 and C5 that makes cocaine a tropane instead of a piperidine structure. The structure-activity relationships were different from those for inhibiting neuronal amine transport or blocking voltage-dependent sodium channels. There was no correlation between block of uptake and degree of lipophilicity. The equally lipophilic compounds cocaine and pseudococaine, and WIN 35,065-3 and WIN 35,140, differed in uptake-blocking potency by an order of magnitude (137 vs. 22 microM and 65 vs. 4 microM, respectively). In bovine chromaffin granules, used as a less complex model system for the vesicular uptake system, the rank order of d-amphetamine, cocaine and pseudococaine in perturbing the proton gradient and in changing the membrane potential was different from that in inhibiting uptake. The inhibition of uptake is discussed in terms of the compounds acting as weak bases, transporter substrates or transporter blockers.     

Reproductive sequelae in female rats after in utero and neonatal exposure to the phytoestrogen genistein

OBJECTIVE: To determine reproductive sequelae in female rats after in utero and lactational dietary exposure to genistein. DESIGN: Experimental animal study. SETTING: University laboratory. ANIMAL(S): Sprague Dawley rats. INTERVENTION(S): Pregnant rats were fed control rat chow or rat chow incorporated with genistein (approximately 50 microg/d) beginning on day 17 of gestation and continuing until the end of lactation (postpartum day 21). Genistein-exposed female pups were divided into two groups on day 21. One group continued to receive a genistein-added diet (G70); the other group was changed to a control diet (Ex-G). At necropsy (days 21 and 70), blood and reproductive tissues were collected. MAIN OUTCOME MEASURE(S): Serum levels of gonadotropins and gonadal steroids and histopathologic examination of the ovaries. RESULT(S): The weight of the ovaries and uterus and serum levels of E2 and progesterone in genistein-exposed rats on day 21 (G21) were significantly reduced compared with control rats. On day 70, serum levels of E2, progesterone, LH, and FSH were similar in all groups. Atretic follicles and secondary interstitial glands were more common in G70 and Ex-G rats compared with control rats. Cystic rete ovarii was observed in some G70 and Ex-G rats. CONCLUSION(S): Our data indicate that in utero and lactational exposure to dietary genistein adversely affects reproductive processes in the adult female rat.     

Effect of ketamine anaesthesia on the content of monoamines and their metabolites in the rat brain

The effects of ketamine anaesthesia (100 mg/kg i.p.) on the content of brain 5-hydroxytryptamine (5HT), 5-hydroxyindoleacetic acid (5HIAA), noradrenaline (NA), dopamine (DA) and homovanillic acid (HVA) were studied in male Wistar rats. Fifteen min after ketamine injection, when the rats were deeply anaesthetized, the 5HT content in many brain regions tended to be increased. An opposite tendency was found in the brain 5HIAA content. In rats treated with probenecid, which markedly lengthened ketamine anaesthesia, the accumulation of 5HIAA was significantly reduced by ketamine. In addition to ketamine anaesthesia, probenecid was found to lengthen thiopental anaesthesia. One hour after the ketamine administration, when the rats were no longer anaesthetized but were excited, the brain NA concentration was increased by 17% (P less than 0.02). The brain DA content was unchanged, but at 15 min and 1 hour after ketamine administration the striatal HVA content was increased by about 55% (P less than 0.05), suggesting an increased turnover of DA. The results suggest that during recovery from ketamine anaesthesia the increased NA content and the increased DA turnover may be associated with the postanaesthetic excitement of the rat, whereas the decreasamine anaesthesia.