Behavioral Effects of Pre-and Postnatal Exposure to a Mixture of Low Chlorinated PCBs in Rats

Behavioral Effects of Pre- and Postnatal Exposure to a Mixtureof Low Chlorinated PCBs in Rats. LILIENTHAL, H., NEUF, M., MUNOZ,C, AND WINNEKE, G. (1990). Fundam. Appl. Toxicol. 15, 457–467.Polychlorinated biphenyl (PCB)-treated Wistar rats were testedon three different behavioral paradigms. Animals were pre- andpostnatally exposed to a technical mixture of PCBs with a chlorinecontent of 42%. Exposure levels were 0, 5, or 30 mg/kg diet.These conditions did not affect the health of the dams, thelitter size or weight, or the physical development of the offspring.Relative liver weights in the offspring, however, were elevatedin a dose-dependent manner. Open-field ambulation, active avoidancelearning, and operant conditioning on a fixed interval 30-secschedule (FI-30-sec) were used to evaluate PCB-induced behavioralalterations. Ambulation was increased in 30-mg-treated ratsat Day 22, but not at Day 120. There were more avoidance responsesand intertrial responses in the 30-mg group than in both othergroups. On the FI-30-sec schedule slightly more reactions wereemitted by the 30-mg group during the first 10 sec of the intervalthan by the other animals. More pronounced, however, were thedifferences between groups in the temporal pattern of responseswithin the 30-sec interval. It is concluded that in rats PCBexposure causes consistent alterations in all of the testedactivity-dependent behaviors.     

Reduced levels of 1,25-dihydroxyvitamin D(3) in rat dams and offspring after exposure to a reconstituted PCB mixture.

Previous studies revealed effects of polychlorinated biphenyls (PCBs) and other polyhalogenated hydrocarbons on steroid hormone levels and hormone-dependent functions including behavior. In the present study serum concentrations of the vitamin D(3) metabolites 25-hydroxycholecalciferol (25-D) and 1,25-dihydroxycholecalciferol (1,25-D) were determined in rat dams and offspring after exposure to a PCB mixture that was reconstituted according to the congener pattern found in human breast milk. Unmated females were exposed to diets adulterated with 0; 5; 20; or 40 mg PCBs/kg diet. Exposure started 50 days prior to mating and was terminated at birth. Gestational exposure reduced serum concentrations of 1,25-D in dams in a dose-dependent manner. Concentration of 25-D was also decreased at the time of delivery, but not at weaning. Determination of 1,25-D in offspring at weaning revealed reductions in both high-exposure groups. Levels of 25-D were diminished only at the highest exposure level. Internal PCB concentrations in adipose tissue and brains exhibited a linear relation to dosages in diet. Concentrations of PCBs in brains were similar in dams and offspring at birth, but decreased at the end of lactation in dams. In offspring, values increased during this period because of continued exposure via the milk. In the adipose tissue, PCB levels were much lower in offspring than in dams. To our knowledge, this is the first report of PCB-induced effects on vitamin D(3) metabolites. In dams, reductions were seen even at the lowest exposure level used. Further studies are needed to evaluate the biological significance of these reductions in pregnant dams and possible consequences for the developing offspring.     

Behavioural disturbances in adult CD-1 mice and absence of effects on their offspring upon SO2 exposure

 Adult male and female CD-1 mice were exposed to different SO₂ concentrations (0, 5, 12, or 30 ppm) for 24 days, from 9 days before the formation of breeding pairs to pregnancy day 12–14. This exposure was near-continuous, covering about 80% of the total time indicated. The offspring of exposed dams were cross-fostered shortly after birth to dams not previously exposed. Videorecordings of the adult subjects’ activities during the first hour after the start of exposure showed marked, acute transient behavioural effects such as increase of rearing and social interactions, which were more pronounced in males than in females. Subsequent activity tests on exposure days 3, 6, and 9 showed subacute effects including a dose-dependent decrease of grooming and an increase of digging as well as changes in chamber crossing and wall-rearing which were not dose-dependent; most of these effects were more pronounced in females than in males. Food and water consumption and body weight declined in a dose-dependent fashion only after the formation of breeding pairs, when consummatory responses were enhanced in the controls. Reproductive performance as well as postnatal somatic and neurobehavioural development of the offspring (the latter assessed by an observational test battery including eight reflexes and responses) were not affected by SO₂. Passive avoidance acquisition and retention at the young adult stage (60 days) and response changes produced by repeated apparatus exposure in non-reinforced animals (habituation) were similarly unaffected. Overall, the data indicate that SO₂ produces transient, acute behavioural disturbances and more subtle subacute response changes in adult mice which may be due, at least partly, to a functional interference with olfactory modulation of mouse behaviour. The absence of effects on reproductive performance and neurobehavioural development of the offspring suggests that the risk to the developing organism from gestational SO₂ exposure is low. Received: 4 October 1995/Accepted: 27 February 1996     

Developmental exposure to brominated diphenyl ethers results in thyroid hormone disruption.

The objective of the current study was to characterize the effects of DE-71 (a commercial polybrominated diphenyl ether mixture containing mostly tetra- and penta-bromodiphenyl ethers) on thyroid hormones and hepatic enzyme activity in offspring, following perinatal maternal exposure. Primiparous Long-Evans rats were orally administered DE-71 (0, 1, 10, and 30 mg/kg/day) in corn oil from gestation day (GD) 6 to postnatal day (PND) 21. Serum and liver samples obtained from dams (GD 20 and PND 22), fetuses (GD 20), and offspring (PNDs 4, 14, 36, and 90) were analyzed for circulating total serum thyroxine (T(4)) and triiodothyronine (T(3)), or hepatic microsomal ethoxy- and pentoxy-resorufin-O-deethylase (EROD and PROD), and uridine diphosphoglucuronosyl transferase (UDPGT) activity. There were no significant effects of treatment on maternal body weight gain, litter size, or sex ratio, nor were there any effects on any measures of offspring viability or growth. Serum T(4) was reduced in a dose-dependent manner in fetuses on GD 20 (at least 15%) and offspring on PND 4 and PND 14 (50 and 64% maximal in the 10 and 30 mg/kg/day groups, respectively), but recovered to control levels by PND 36. Reduction in serum T(4) was also noted in GD 20 dams (48% at highest dose), as well as PND 22 dams (44% at highest dose). There was no significant effect of DE 71 on T(3) concentrations at any time in the dams or the offspring. Increased liver to body weight ratios in offspring were consistent with induction of EROD (maximal 95-fold), PROD (maximal 26-fold) or UDPGT (maximal 4.7-fold). Induction of PROD was similar in both dams and offspring; however, EROD and UDPGT induction were much greater in offspring compared to dams (EROD = 3.8-fold; UDPGT = 0.5-fold). These data support the conclusion that DE-71 is an endocrine disrupter in rats during development.     

Limited lactational transfer of acrylamide to rat offspring on maternal oral administration during the gestation and lactation periods

To evaluate the developmental exposure effects of acrylamide (ACR) on the nervous and male reproductive systems, pregnant Sprague-Dawley rats were given ACR at 0, 25, 50 or 100 ppm in the drinking water from gestational day 6 to postnatal day (PND) 21 and histopathological assessment was performed at PND 21. Exposure levels in offspring were examined by measurement of free ACR and hemoglobin (Hb)-ACR adducts on PND 14, and compared with maternal levels on PND 21. Additionally, a group of offspring that received ACR at 50 mg/kg by intraperitoneal injections directly three times a week from PND 2 to 21 was subjected to analysis for comparison with maternal exposure groups. Although maternal neurotoxicity was evident at 100 ppm, no changes suggestive of neurotoxicity or testicular toxicity were observed in their offspring except for growth retardation evident as lowered body weights. In contrast, offspring given ACR intraperitoneally exhibited obvious neurotoxicity, but not testicular damage. Free ACR in serum and milk was detected in neither dams nor their offspring. The level of ACR-Hb adducts in offspring was one tenth or less than that in dams. In summary, although preweaning rats have susceptibility to ACR-induced neurotoxicity, the internal level of ACR in offspring exposed through maternal oral administration is insufficient to induce neurotoxicity and testicular toxicity due to limited lactational transfer.     

Pre-exposure of rats to amphetamine sensitizes self-administration of this drug under a progressive ratio schedule

 Two groups of male rats were tested to determine whether pre-exposure to d-amphetamine would enhance the motivation to self-administer the drug under a progressive ratio schedule of reinforcement. In the first phase of the experiment, one group of rats received d-amphetamine (2 mg/kg IP), while a second group received saline on alternate days for a total of ten injections. Following a 21-day drug withdrawal period, behavioral sensitization was confirmed by a significant increase in amphetamine-induced stereotypy in the d-amphetamine-pretreated group, relative to the saline-pretreated group. In the second phase of the study, all rats were implanted with chronic jugular catheters and trained to self-administer d-amphetamine (0.2 mg/kg per infusion) under a fixed-ratio schedule of reinforcement. The progressive ratio paradigm was then imposed for 7 consecutive days; d-amphetamine-pretreated rats attained significantly higher break points than saline-pretreated animals. These data suggest that pre-exposure to d-amphetamine may enhance the motivation to self-administer this drug. Received: 16 July 1997 / Final version: 22 October 1997     

Serotonin1B receptor stimulation enhances dopamine-mediated reinforcement

The effect of 5-HT_1B receptor stimulation on dopamine-mediated reinforcement in rats was investigated using intravenous self-administration of the selective dopamine uptake inhibitor GBR-12909 on an FR5 schedule of reinforcement. Pretreatment with the 5-HT_1A/1B receptor agonist CGS-12066B (1–10 mg/kg, IP) dose-dependently reduced the self-administration of GBR-12909 (83 μg/injection) by increasing the interval between drug injections, consistent with a enhancement of the reinforcing effects of GBR-12909. Additionally, CGS-12066B pretreatment (3 mg/kg, IP) shifted the dose-effect function for GBR-12909 self-administration to the left. Pretreatment with the selective 5-HT_1A receptor agonist 8-OH-DPAT (0.03– 1.0 mg/kg, SC) had no significant effect on GBR-12909 self-administration (83 μg/injection), indicating that the effect of CGS-12066B is not mediated by the 5-HT_1A receptor. Finally, CGS-12066B pretreatment (1–10 mg/kg, IP) did not alter the self-administration of cocaine (0.03–0.5 mg/injection), suggesting that the simultaneous stimulation of multiple 5-HT receptor subtypes by the indirect 5-HT agonist properties of cocaine may mask the effect of 5-HT_1B receptor stimulation on DA-mediated reinforcement. Received: 5 February 1996/Final version: 20 June 1996     

Effects of maternal exposure to a reconstituted mixture of polychlorinated biphenyls on sex-dependent behaviors and steroid hormone concentrations in rats: dose-response relationship

In a previous experiment, maternal exposure to a polychlorinated biphenyl (PCB) mixture reconstituted according to the congener pattern found in human breast milk resulted in decreased aromatase activity in the brain of newborn male rats, together with feminization of sweet preference behavior in adult male littermates. Both mixtures led to similar reductions of serum testosterone and testes weights. The purpose of the present study was (1) to examine the dose-response relationship for the reconstituted mixture and (2) to study if the rewarding properties of testosterone are affected at levels sufficient to alter sweet preference behavior. Female rats were fed diets with 0, 5, 20, or 40 mg PCBs/kg diet, resulting in an average daily intake of 0, 0.5, 2, or 4 mg/kg body wt. Exposure started 50 days prior to mating and was continued until birth of the offspring. A dose-dependent elevation of sweet preference was found in adult male offspring, indicating feminization of this sexually dimorphic behavior. Examination of conditioned place preference revealed a preference for the testosterone-paired side at the highest exposure condition. In weanling female offspring, dose-dependent reductions of serum testosterone and estradiol concentrations were detected. In addition, testosterone concentrations were reduced in a dose-dependent manner in adult male littermates long after termination of exposure. PCB concentrations in adipose tissue from offspring of the low dose group (0.5 mg/kg body wt) were approximately 10 times higher than values at the upper margin of current human exposure. Taken together, results indicate long-lasting and dose-dependent changes in sex-dependent behaviors and levels of sex steroid hormones in rats following developmental exposure to a PCB mixture that resembles the breast milk pattern.     

Repeated in utero and lactational 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure affects male gonads in offspring, leading to sex ratio changes in F2 progeny

The effects of in utero and lactational 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the reproductive system of male rat offspring (F1) and the sex ratio of the subsequent generation (F2) were examined. Female Holtzman rats were gavaged with an initial loading dose of 400 ng/kg TCDD prior to mating, followed by weekly maintenance doses of 80 ng/kg during mating, pregnancy, and the lactation period. Maternal exposure to TCDD had no significant effects on fetus/pup (F1) mortality, litter size, or sex ratio on gestation day (GD) 20 or postnatal day (PND) 2. The TCDD concentration in maternal livers and adipose tissue on GD20 was 1.21 and 1.81 ng/kg, respectively, and decreased at weaning to 0.72 in the liver and 0.84 in the adipose tissue. In contrast, the TCDD concentration in pup livers was 1.32 ng/kg on PND2 and increased to 1.80 ng/kg at weaning. Ventral prostate weight of male offspring was significantly decreased by TCDD exposure on PND28 and 120 compared with that of controls. Weight of the testes, cauda epididymides, and seminal vesicle, and sperm number in the cauda epididymis were not changed by TCDD exposure at PND120. TCDD- or vehicle-exposed male offspring were mated with unexposed females. The sex ratio (percentage of male pups) of F2 offspring was significantly reduced in the TCDD-exposed group compared with controls. These results suggest that in utero and lactational TCDD exposures affect the development of male gonads in offspring (F1), leading to changes in the sex ratio of the subsequent generation (F2).     

Post-weaning housing conditions influence the behavioural effects of cocaine and d-amphetamine

Post-weaning social isolation can induce profound and long lasting effects on an animal’s behaviour. The present study investigated the influence of post-weaning housing conditions on the sensitivity of rats to the behavioural effects of d-amphetamine and cocaine. The locomotor stimulant effects of both drugs were compared following acute and chronic administration. The influence of post-weaning housing conditions on the effects of d-amphetamine and cocaine on responding for food and for a conditioned reinforcer were also examined. Isolated rats showed enhanced locomotor activity on exposure to a novel environment. This difference was further exaggerated following administration of d-amphetamine (0.5 mg/kg) and cocaine (5 mg/kg). Isolated, but not enriched, rats exhibited sensitisation to the locomotor activating effects of repeated administration of a dose of 0.5 mg/kg d-amphetamine, whilst both groups sensitised equally to a dose of 1.0 mg/kg d-amphetamine. Rearing conditions did not affect sensitisation to cocaine (5, 10 mg/kg). Isolated rats exhibited a higher rate of responding for a conditioned stimulus and for food on a progressive ratio schedule of reinforcement, both of which were enhanced to a greater extent in isolates following administration of cocaine (5 mg/kg) and d-amphetamine (0.5 mg/kg). These results suggest that isolation rearing induces an enhancement in sensitivity to both the locomotor stimulant and reinforcing properties of amphetamine and cocaine. Received: 12 June 1996 / Final version: 17 October 1996     

Behavioral effects of maternal exposure to an ortho-chlorinated or a coplanar PCB congener in rats

Polychlorinated biphenyls (PCBs) are still of environmental concern. Neurotoxic effects were described after developmental exposure to PCB mixtures and single congeners. The purpose of the present experiment was to compare the behavioral effects of the coplanar congener 3,4,3',4'-tetrachlorobiphenyl with the ortho-chlorinated 2,4,2',4'-tetrachlorobiphenyl. Female Wistar rats were exposed with a subtoxic dose of 1 mg/kg b.w. of 3,4,3',4'-tetrachlorobiphenyl, 2,4,2',4'-tetrachlorobiphenyl or the vehicle during gestation from day 7 to 18. There were significant lower concentrations of 3,4,3',4'-TCB than of 2,4,2',4'-TCB in dams and offspring at gestational day 19. Decreases from gestational day 19 (F 19) to postnatal day 21 (PND 21) were only observed in the adipose from dams exposed to 2,4,2',4'-TCB. The following behavioral tests were conducted in the offspring: locomotor activity in the open field, spatial learning in the radial arm maze, catalepsy induced by the dopamine receptor blocker haloperidol, and passive avoidance learning at PND 25, PND 95, PND 180, and PND 220, respectively. Significant differences to the control group were detected in the 3,4,3',4'-tetrachlorobiphenyl exposed offspring. There were increases in descent latencies in the catalepsy test and impairments of passive avoidance behavior. These behavioral effects were observed in the adult rats long after the termination of exposure when internal PCB levels were indistinguishable from those of controls. A mediation of the reported effects by alterations of dopaminergic processes or thyroid hormone levels is discussed.     

The NMDA antagonist, dizocilpine, enhances cocaine reinforcement without influencing mesoaccumbens dopamine transmission

In order to assess the role of excitatory amino acids (EAAs) in the reinforcing property of cocaine, the NMDA antagonist, dizocilpine, or the AMPA antagonist, DNQX, were administered to animals previously trained to self-administer cocaine (1.0, 0.4 or 0.16 mg/kg per infusion). The highest doses of dizocilpine (0.1 mg/kg, IP) and DNQX (30 mg/kg, IP) significantly reduced operant responding for cocaine maintained on a fixed ratio schedule of reinforcement. However, whereas dizocilpine had no influence operant responding for food, DNQX significantly decreased lever pressing for this reinforcer. These results indicate that an NMDA antagonist produces a relatively selective enhancement of cocaine reinforcement, while an AMPA antagonist decreases cocaine self-administration only at a dose that also impairs responding for an alternate reinforcer. A parallel in vivo microdialysis study performed in freely moving rats tested the effects of dizocilpine alone and in combination with cocaine on extracellular dopamine in the nucleus accumbens shell. The results revealed that dizocilpine alone (0.1 mg/kg, IP) did not alter basal extracellular dopamine levels in the nucleus accumbens or spontaneous behavior. In addition, 0.1 mg/kg dizocilpine did not alter the increase in dopamine in the accumbens shell or behavioral hyperactivity produced by cocaine (15 or 30 mg/kg). Collectively, these findings suggest that dizocilpine enhances the reinforcing effect of cocaine without influencing dopamine transmission in the nucleus accumbens shell. Received: 17 December 1996/Final version: 21 March 1997     

Developmental neurotoxicity following premating maternal exposure to hexachlorobenzene in rats.

The maternal transfer of hexachlorobenzene (HCB) may place the developing organism at risk. The present study assessed the developmental neurotoxicity of HCB using a battery of behavioral tests. Two weeks prior to breeding, maternal rats were exposed via gavage to either 10 or 100 mg HCB/kg body weight. Behaviors evaluated in pups exposed maternally to HCB included the negative geotaxic reflex on postnatal day (PND) 6, 8, and 10, olfactory discrimination (PND 9-11), and the development of exploratory behavior (PND 15-20). Significant effects in these three tests indicated hyperactivity in HCB-exposed pups. No significant effects on learning (swim T-maze) or motor activity were detected in older offspring (PND 40 and 50 respectively). The acoustic startle response (ASR) revealed apparent age-related effects of maternal HCB exposure. On PND 23 pups from the high treatment group demonstrated significantly reduced ASR amplitude, whereas these same animals, tested on PND 90 (using a reflex modification design), showed elevated ASR amplitude relative to the controls. This work demonstrates that HCB is a behavioral teratogen, and suggests that human fetuses and suckling infants may be at risk from the neurotoxic effects of HCB.     

Bioaccumulation and behavioral effects of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) in perinatally exposed mice

Polybrominated diphenyl ethers (PBDEs) are widely used flame retardants that have become pervasive environmental contaminants and may contribute to adverse health outcomes. We evaluated in mice the developmental neurotoxicity of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47), one of the most abundant PBDE congeners detected in animal and human tissues. Female C57BL/6J mice were exposed to daily doses of 0, 0.03, 0.1 or 1 mg/kg beginning 4 weeks prior to conception, continuing through gestation and lactation, and ending at weaning on postnatal day (PND) 21. Levels of BDE-47 in blood, brain, liver and adipose tissues of dams were markedly increased after 4 weeks of exposure, around the time of mating, and continued to increase through the time of parturition. Blood levels of BDE-47 in the dosed dams were within the range reported in humans. BDE-47 tissue levels in the dams decreased between parturition and weaning, possibly reflecting mobilization during lactation. Brain BDE-47 levels in the offspring at PND 1 approached those of the dams at parturition. Perinatal exposure to BDE-47 resulted in significant dose dependent growth retardation, slower motor performance in several behavioral tests, and mice exposed to 1 mg/kg/day BDE-47 showed altered performance in the Morris water maze. There were no differences between groups in the numbers of pyramidal neurons in hippocampus CA1. These results document accumulation of BDE-47 in several organ systems following exposure to low-levels of BDE-47, and provide evidence that such exposure is associated with early behavioral deficits in exposed neonates.     

Discrimination and self-administration of nicotine by inbred strains of mice

These studies aim to characterize the discriminative stimulus effects of nicotine in two inbred strains of mice that differ in many pharmacological responses, and to investigate the feasibility of IV self-administration studies with nicotine in one of the strains. For discrimination studies, three groups of C57BL/6 and one group of DBA/2 mice were trained in a two-lever operant conditioning paradigm with a tandem VI-30″ FR-10 schedule of food reinforcement. After 40 training sessions, accuracy reached 57.5, 77.5 and 90.0% in C57BL/6 mice trained with (–)-nicotine (SC) in doses of 0.4, 0.8 and 1.6 mg/kg, respectively (n = 8). DBA/2 mice trained with 0.8 mg/kg nicotine attained similar (73.3%) accuracy (n = 9). Results from extinction tests showed that all groups of mice yielded orderly dose-response curves for nicotine (0.03–1.6 mg/kg), but stimulus control remained notably weaker for the mice trained with 0.4 mg/kg nicotine than for any other group. Overall rates of responding in the undrugged state were lower for DBA/2 than for C57BL/6 mice; DBA/2 mice were also slightly less sensitive than C57BL/6 mice to the response rate-reducing effect of nicotine. The nicotine antagonist mecamylamine (1.5 mg/kg SC) blocked the discriminative stimulus effect of the training dose of nicotine in all groups. The results of the IV self-administration study suggest that nicotine (0.1 mg/kg) can serve as a positive reinforcer in drug–naive C57BL/6J mice (n = 13). Behaviour maintained by 0.1 mg/kg nicotine injections was significantly greater than behaviour maintained by vehicle injections, and it was maintained under an intermittent schedule of reinforcement (FR4). The methods described provide possible approaches for genetic analyses of strain differences in sensitivity to the discriminative and reinforcing stimulus properties of nicotine. Received: 11 April 1998/Final version: 28 June 1998     

Behavioural and neurochemical characteristics of phentermine and fenfluramine administered separately and as a mixture in rats

Clinical case studies suggest that combined administration of the serotonergic agent fenfluramine (FEN) and the weak amphetamine-like anorexic agent phentermine (PHEN) may be useful in the treatment of alcohol and cocaine addictions. The present experiment examined the nature of the interaction between the two agonists using the drug discrimination paradigm. In vivo microdialysis served to examine the neurochemical profile of dopamine and serotonin release in the nucleus accumbens. In conscious rats, acute injections of FEN (1.0–2.0 mg/kg IP) or PHEN (1.0–2.0 mg/kg IP) selectively elevated levels of serotonin and dopamine in the nucleus accumbens, respectively. A mixture (1 mg/kg of each) increased levels of both amines by similar magnitudes to those observed with each individually. Three groups of Sprague-Dawley rats were trained to discriminate (1) FEN (1.0 mg/kg IP) alone, (2) PHEN (1.0 mg/kg IP) alone or a mixture (3) PHEN+FEN (1 mg/kg of each, IP) from saline under a fixed ratio (FR-10) schedule of food reinforcement. Rats acquired the mixture discrimination rapidly, while for the other groups the training dose had to be increased to 2.0 mg/kg to attain stimulus control. The individual components of the mixture at the training dose generalized partially to the mixture, and complete generalisation was observed following 3.0 mg/kg FEN or PHEN. Rats trained to discriminate the individual components showed respective cross-generalisation profiles. Generalisation to cocaine (0.3–10.0 mg/kg IP), amphetamine (0.1–3.0 mg/kg IP) and nicotine (0.1–0.8 mg/kg SC) was greatest in the MIX-trained rats, while partial or no generalisation was observed in rats trained to discriminate the individual compounds. From the present results, it may be concluded that the two drugs given as a mixture do not produce a novel cue. Rather, these aminergics appear to interact additively. Furthermore, the dual stimulation of the amines by the mixture may be the basis for the cueing effects of the FEN+PHEN drug mixture, and its effectiveness in treating drug addictions. Received: 4 October 1996/Final version: 12 December 1996     

Developmental triclosan exposure decreases maternal, fetal, and early neonatal thyroxine: a dynamic and kinetic evaluation of a putative mode-of-action

This work tests the mode-of-action (MOA) hypothesis that maternal and developmental triclosan (TCS) exposure decreases circulating thyroxine (T4) concentrations via up-regulation of hepatic catabolism and elimination of T4. Time-pregnant Long-Evans rats received TCS po (0-300mg/kg/day) from gestational day (GD) 6 through postnatal day (PND) 21. Serum and liver were collected from dams (GD20, PND22) and offspring (GD20, PND4, PND14, PND21). Serum T4, triiodothyronine (T3), and thyroid-stimulating hormone (TSH) concentrations were measured by radioimmunoassay. Ethoxy-O-deethylase (EROD), pentoxyresorufin-O-depentylase (PROD) and uridine diphosphate glucuronyltransferase (UGT) enzyme activities were measured in liver microsomes. Custom Taqman(?) qPCR arrays were employed to measure hepatic mRNA expression of select cytochrome P450s, UGTs, sulfotransferases, transporters, and thyroid hormone-responsive genes. TCS was quantified by LC/MS/MS in serum and liver. Serum T4 decreased approximately 30% in GD20 dams and fetuses, PND4 pups and PND22 dams (300mg/kg/day). Hepatic PROD activity increased 2-3 fold in PND4 pups and PND22 dams, and UGT activity was 1.5 fold higher in PND22 dams only (300mg/kg/day). Minor up-regulation of Cyp2b and Cyp3a expression in dams was consistent with hypothesized activation of the constitutive androstane and/or pregnane X receptor. T4 reductions of 30% for dams and GD20 and PND4 offspring with concomitant increases in PROD (PND4 neonates and PND22 dams) and UGT activity (PND22 dams) suggest that up-regulated hepatic catabolism may contribute to TCS-induced hypothyroxinemia during development. Serum and liver TCS concentrations demonstrated greater fetal than postnatal internal exposure, consistent with the lack of T4 changes in PND14 and PND21 offspring. These data support the MOA hypothesis that TCS exposure leads to hypothyroxinemia via increased hepatic catabolism; however, the minor effects on thyroid hormone metabolism may reflect the low efficacy of TCS as thyroid hormone disruptor or highlight the possibility that other MOAs may also contribute to the observed maternal and early neonatal hypothyroxinemia.     

Hexachlorobenzene residues and effects on esterase activities in pre-weanling rats after a reciprocal transfer between HCB-treated and control dams

Female Wistar rats were divided into two groups. One group was fed ad libitum powdered rat chow containing 80 ppm hexachlorobenzene (HCB) and the other was fed HCB-free diet 2 weeks before mating until the termination of the experiment. Immediately after parturition, the pups were randomly culled to 10 per litter and 5 pups were reciprocally transferred between HCB and control dams. All pups within same paired litters were sacrificed on the 16th to 17th day and on the 20th to 23rd day after birth. Liver esterase activity toward indophenyl, thiophenyl, and p-nitrophenyl acetates was determined. The liver to body weight ratio, liver esterase activity and HCB resudues were significantly higher in pups nursed by HCB-fed dams than in those nursed by control dams. The HCB residue in the liver, kidney, spleen, heart and brain was analyzed by gas-liquid chromatography. At about the weaning time, the HCB residue levels in pups transferred after parturition from HCB fed to control dams were similar to those in pups which remained with the control dams. The results demonstrated that HCB in tissues at about weaning time was obtained largely through milk. In addition, transmission of HCB through milk had greater effects on esterase activities in suckling pups than placental transmission. The pups born to HCB-treated dams and nursed by the control dams were similar to the pups born and nursed by the same control dams.     

Differential effects of formamidine pesticides on fixed-interval behavior in rats

Chlordimeform (CDM), amitraz (AMZ), and formetanate (FMT) are members of the formamidine class of pesticides. To date, effects on operant behavior have been determined only for CDM. This experiment compared the effects of CDM, AMZ, and FMT on schedule-controlled responding. Nine male Long-Evans rats were trained during 1-hr sessions to lever-press under a multiple fixed-interval (FI)-1-min FI-5-min schedule of milk reinforcement. Dose-effect determinations for each compound administered ip, 20 min presession, were carried out in each subject. The dose ranges were: CDM HCl, 0.3-20 mg/kg; FMT HCl, 0.03-0.75 mg/kg; and AMZ, 5-75 mg/kg. Under baseline conditions response rates were higher under the FI-1-min than under FI-5-min, and index of curvature (IOC) values (a measure of within-interval response patterning) were generally higher under FI-5-min. All compounds produced dose-dependent decreases in response rate. CDM significantly decreased only FI-1-min response rates; a similar effect of AMZ was seen only at an intermediate dose. FMT decreased responding to the same extent in both components. CDM produced pronounced changes in the pattern of responding in both components, with IOC decreased more under FI-5-min than under FI-1-min. AMZ produced significant decreases in IOC only under FI-5-min. FMT did not appreciably decrease IOC in either component. High doses of AMZ produced general signs of poor health that persisted for several days. In addition, a greater effect on response rates and IOC in both components was obtained when AMZ (75 mg/kg) was given more than 10 days following another dose compared to when it was given 7 days or less after another dose. Formamidine pesticides produce differential effects on FI schedule-controlled behavior that are in turn modulated by the parameter value of the FI schedule.     

A high fructose diet does not affect amphetamine self-administration or spatial water maze learning and memory in female rats

High energy diets can have a detrimental effect on brain plasticity. For example, a high fructose diet impairs spatial memory in male rats. The aim of the present study was to determine whether a high fructose diet impairs another form of learning and memory: drug reinforcement learning. Female Sprague-Dawley rats were fed a high fructose diet (60%) from weaning at postnatal day (PND) 21, then allowed to acquire lever-pressing maintained by intravenous (i.v.) amphetamine at PND 68, 109, or 165. Acquisition was tested on a fixed ratio one (FR1) schedule of reinforcement (0.025 mg/kg/infusion, 1 h daily sessions, 10 sessions over 14 days), followed by testing for reinforcing efficacy on a progressive ratio (PR) schedule (0.025, 0.01, and 0.1 mg/kg/infusion), 14 days of abstinence, and within-session extinction and reinstatement tests. Subsequently, water maze acquisition and retention were tested in these subjects as well as a separate cohort tested in the water maze only. The diet had no effect on acquisition, reinforcing efficacy, extinction, or reinstatement of amphetamine seeking. Nor did the diet alter any measures of spatial memory. The high fructose diet did decrease body mass and increase relative liver and spleen mass, but did not affect plasma triglyceride concentrations consistently. Together with prior research on males, these results suggest that the metabolism of fructose and the effects of a high fructose diet on learning and memory may be sex-dependent.