Prenatal stress and subsequent exposure to chronic mild stress in rats; interdependent effects on emotional behavior and the serotonergic system

Exposure to prenatal stress (PS) can predispose individuals to the development of psychopathology later in life. We examined the effects of unpredictable chronic mild stress (CMS) exposure during adolescence on a background of PS in male and female Sprague-Dawley rats. PS induced more anxiety-like behavior in the elevated zero maze in both sexes, an effect that was normalized by subsequent exposure to CMS. Moreover, PS was associated with increased depression-like behavior in the forced swim test in males only. Conversely, sucrose intake was increased in PS males, whilst being decreased in females when consecutively exposed to PS and CMS. Hypothalamo–pituitary–adrenal (HPA) axis reactivity was affected in males only, with higher stress-induced plasma corticosterone levels after PS. Markedly, CMS normalized the effects of PS on elevated zero maze behavior as well as basal and stress-induced plasma corticosterone secretion. At the neurochemical level, both PS and CMS induced various sex-specific alterations in serotonin (5-HT) and tryptophan hydroxylase 2 (TPH2) immunoreactivity in the dorsal raphe nucleus, hippocampus and prefrontal cortex with, in line with the behavioral observations, more profound effects in male offspring. In conclusion, these findings show that prenatal maternal stress in Sprague-Dawley rats induces various anxiety- and depression-related behavioral and neuroendocrine changes, as well as alterations in central 5-HT and TPH2 function, predominantly in male offspring. Moreover, CMS exposure partially normalized the effects of previous PS experience, suggesting that the outcome of developmental stress exposure largely depends on the environmental conditions later in life and vice versa.     

Prenatal exposure to morphine in mice: enhanced responsiveness to morphine and stress

Some behavioral effects of prenatal morphine administration were studied in CD1 mice. Two sets of experiments were carried out. In a first set, which was performed during development: (a) measures of postnatal reflexes revealed only a light deficit in tests involving motor control, (b) activity measures showed a significant reduction of spontaneous activity which was evident only in the course of the first postnatal days. In a second set of experiments, in which adult mice were tested for activity, analgesia and passive avoidance learning: (a) no difference was observed, in baseline conditions, between the performances of the mice prenatally exposed to saline and those preexposed to morphine, (b) as compared with controls, enhanced responsiveness to morphine administration (for the activity and passive avoidance measures), and to morphine and stress (for the analgesic measures) were found.     

Prenatal amphetamine exposure alters behavioral reactivity to amphetamine in rats

In utero exposure to psychostimulants produces neurobehavioral alterations in the offspring of laboratory animals. Most amphetamine-related behavioral changes have been related to changes in the monoamine transmission levels, where monoamines may act as developmental regulatory substances for maturation of neuronal population. This study investigates the effect of prenatal-amphetamine exposure on the offspring's behavioral responses under amphetamine conditioning settings. Pregnant female rats were injected (subcutaneous) with amphetamine or saline during the pregnancy [gestation day (GD) 8 until parturition day]. The prenatal amphetamine exposure resulted in significantly decreased birth weights. The offspring from the saline group displayed a significantly lower number of stereotyped behaviors across the four challenge doses of amphetamine injections. Offspring from the amphetamine-treated prenatal group displayed significantly increased average startle amplitude compared to the controlled offspring. Moreover, offspring from amphetamine-treated prenatal group showed significantly less inhibition for the prepulse startle trials compared to those of the offspring from saline group. These results, taken together, indicate that the prenatally exposed rats displayed a significantly different profile of behavioral reactivity upon amphetamine challenges.     

Prenatal buprenorphine exposure decreases neurogenesis in rats

Perinatal opioid exposure has a negative effect on neurogenesis and produces neurological consequences. However, its mechanisms of action are incompletely understood. Buprenorphine, a mixed opioid agonist/antagonist, is an alternative medication for managing pregnant opioid addicts. This study provides evidence of decreased neurogenesis and depression-like consequences following prenatal exposure to buprenorphine and sheds light on mechanisms of action in a rat model involving administration of intraperitoneal injection to pregnant rats starting from gestation day 7 and lasting for 14 days and a cultured neurosphere model. Results of forced swimming test and tail suspension test showed that pups at postnatal day 21 had worse parameters of depression-like neurobehaviors, independent of gender. Neurobehavioral changes were accompanied by reduction of neuronal composition, biochemical parameters of neural stem/progenitor cells, brain-derived neurotrophic factor (BDNF) expression, tropomyosin-related kinase receptor type B phosphorylation, protein kinase A (PKA) activity, and cAMP response element-binding protein phosphorylation. Results of parallel cell studies further demonstrated a negative impact of buprenorphine on cultured neurospheres, including proliferation, differentiation, BDNF expression and signaling, and PKA activity. Taken together, our results suggest that prenatal exposure to buprenorphine might result in depression-like phenotypes associated with impaired BDNF action and decreased neurogenesis in the developing brain of weanlings.     

Prenatal exposure to zymosan results in hypertension in adult offspring rats

1. Events in utero appear to have a significant role in the development of cardiovascular dysfunction in adulthood. In the present study, we evaluated the effects of prenatal exposure to zymosan, a non-infectious and non-bacterial agent capable of inducing inflammation, on mean systolic arterial pressure (MSAP) in rat offspring at 6-66 weeks of age. 2. Pregnant rats were divided into three groups: (i) a control group, administered 0.5 mL, i.p., saline on gestation Days 8, 10 and 12; (ii) a zymosan-treated group, given 2.37 mg/kg, i.p., zymosan on gestation Days 8, 10 and 12; and (iii) a pyrrolidine dithiocarbamate (PDTC) + zymosan-treated group, which was given 100 mg/kg, i.p., PDTC 1 h before zymosan. At 6, 16, 26, 36, 56 and 66 weeks of age, MSAP was determined in rat offspring from all three groups. Serum levels of tumour necrosis factor (TNF)-alpha were determined in dams, as well as in offspring at 24 and 56 weeks of age. In addition, protein levels of nuclear factor (NF)-kappaB (p65) in the myocardium and kidney of offspring were determined at 24 weeks of age. 3. The results showed that MSAP and NF-kappaB (p65) levels in the myocardium and kidney of offspring from the zymosan-treated group were increased significantly compared with control. This increase was inhibited by concomitant treatment with PDTC. Serum TNF-alpha levels in dams exposed to zymosan and in their offspring at 56 weeks of age (but not at 24 weeks of age) were significantly increased compared with levels in the control group. Following lipopolysaccharide treatment (1 mg/kg, i.p.) of adult rat offspring at 24 weeks of age, there was a further increase in serum TNF-alpha levels in offspring in the zymosan-treated group compared with the other two groups. 4. The findings of the present study suggest that non-bacterial inflammation during gestation can lead to hypertension in offspring and that NF-kappaB signalling may play a critical role in this process.     

Oxidative stress and DNA damage in Fischer rats following acute exposure to trichloroethylene or perchloroethylene

Oxidative DNA damage is emerging as an biomarker of effect in studies assessing the health risks of occupational chemicals. Trichloroethylene (TCE) and perchloroethylene (PERC) are used in the dry cleaning industry and their metabolism can produce reactive oxygen compounds. The present study examined the potential for TCE and PERC to induce oxidative DNA damage in rats that was detectable as increased urinary excretion of 8-hydroxydeoxyguanosine (8OHdG). Thiobarbaturic acid reactive substances (TBARS) and 8-epiprostaglandin F2alpha (8epiPGF) were also measured as biomarkers of increased oxidative stress. Male Fischer rats were administered a single i.p. injection of 0, 100, 500, or 1000 mg/kg of PERC or TCE. Control rats received only vehicle (1:4 v/v of Alkamuls/water). A positive control group received 100 mg/kg 2-nitropropane (2NP). Rats were sacrificed 24 h after dosing. In rats receiving 2NP or TCE but not PERC, TBARS and the 8OHdG/dG ratios were significantly elevated in liver. Lymphocyte 8OHdG/dG was not affected significantly by 2NP, TCE or PERC. In rats receiving 2NP, urinary excretion of 8OHdG and 8epiPGF2 were significantly increased. In rats receiving TCE or PERC, significant increases in 8epiPGF2 or 8OHdG were not evident. Results indicate that a single high dose of TCE, but not PERC, can induce an increase in oxidative DNA damage in rat liver. However, the usefulness of 8OHdG as a biomarker of TCE-induced oxidative DNA damage is questionable.     

Effects of neonatal alcohol and/or cocaine exposure on stress in juvenile and adult female rats

The effects of neonatal exposure to alcohol and/or cocaine on two measures of stress were studied in juvenile and young adult female rats. After implantation with an intragastric cannula, subjects were artificially reared from postnatal days 4-10. This "brain growth spurt" period is roughly equivalent to CNS development during the third trimester of human pregnancy. There were five treatment groups: alcohol (6 g/kg/day), cocaine (60 mg/kg/day), alcohol/cocaine (6 g/kg/day alcohol and 60 mg/kg/day cocaine), stock (an artificially reared control), and sham (a suckled control). Subjects were tested in open field and forced swim tests beginning at 21 or 60-70 days of age, respectively. Compared to controls, alcohol-exposed females displayed longer latencies to become immobile in the forced swim test as juveniles and cocaine-exposed females showed increased immobility as adults. Increased immobility can be interpreted as hyporesponsiveness to stress. In contrast, very few differences were observed in the open field. Furthermore, the group exposed to alcohol and cocaine in combination did not differ from controls in either paradigm. These findings suggest that the forced swim test may be more sensitive to neonatal drug effects than open field, although these effects may not be consistent across age.     

Prenatal alcohol exposure and thermotaxic behavior in neonatal rats

The effect of prenatal alcohol exposure on thermotaxic behavior was investigated in 5-day-old rat pups. Pregnant dams were administered a liquid diet which contained 35% ethanol-derived calories (35% EDC) on days 6 to 20 of gestation. Two control groups were included: a liquid diet control which was pair-fed and had sucrose substituted for ethanol (0% EDC), and a group fed standard lab chow (LC) throughout pregnancy. Pups from each of these prenatal treatments were tested on a thermal gradient (thermocline). On each of 5 trails, pups were placed in the cool end of the thermocline and their position along the gradient was measured after 10 min. All prenatal treatment groups displayed thermotaxic behavior by moving towards the warm end. However, pups in the 35% EDC treatment group moved significantly further towards the warm end in the later trials. Despite their position on a warmer surface, their body temperature did not rise concurrently. Thermoregulatory deficits caused by prenatal alcohol exposure might account for these results.     

Prenatal lead exposure enhances methamphetamine sensitization in rats

Adult female rats were exposed to lead-free sodium acetate via gavage [0 mg (vehicle control)] or to 16 mg lead as lead acetate for 30 days prior to breeding. Following confirmation of breeding, the female animals continued to be exposed to their respective doses throughout gestation and lactation. When weaned, 16 control and 16 lead-exposed offspring were placed on regular water and food (lead-exposure was discontinued) until postnatal day (PND) 70. At this time, one-half of the control animals and one-half of the lead-treatment animals received intraperitoneal (i.p.) injections of the vehicle (saline) for 10 successive days and the remaining animals in each exposure conditions received daily injections of 1.0 mg/kg (+)-methamphetamine (METH) for 10 days (N = 8/group). Locomotion in automated chambers was monitored daily for 45 min post-injection.Subsequently, during dose-effect testing, all animals received consecutive daily i.p. injections of 0, 1.0, 2.0, and then 4.0 mg/kg METH. The results of the experiment showed that both control and lead-exposed animals exhibited heightened locomotor activity (i.e. behavioral sensitization) to the repeated administration of 1.0 mg/kg METH. More importantly, animals developmentally (perinatally) exposed to lead showed more rapid sensitization than did their control counterparts. These data indicate that early lead exposure increases sensitivity to the locomotor-stimulating effects of METH. In contrast, identically exposed lead animals exhibit diminished METH dose-effect responding when tested in an intravenous (i.v.) self-administration paradigm [Rocha A., Valles R., Bratton G.R., Nation J.R. Developmental lead exposure alters methamphetamine self-administration in the male rat: acquisition and reinstatement. Drug Alcohol Depend 2008a;95:23-29, Rocha A., Valles R., Hart N., Bratton G.R., Nation J.R. Developmental lead exposure attenuates methamphetamine dose-effect self-administration performance and progressive ratio responding in the male rat. Pharmacol Biochem Behav 2008b;89:508-514].     

Prenatal cocaine and/or nicotine exposure in rats: Preliminary findings on long-term cognitive outcome and genital development at birth

Prenatal cocaine or nicotine exposure is associated with a variety of teratogenic effects. The current study was conducted to determine their effects alone and in combination on cognitive function and sexual differentiation. Pregnant Long-Evans rats (N = 19) were exposed to either cocaine (15 mg/kg/dose b.i.d. SC on GD 8–20); nicotine (4 mg/kg/day continuous SC infusion on GD 4–20); both nicotine + cocaine; or vehicle only. Birth weight and anogenital distance (AGD) were measured in all pups at birth. Learning and memory were tested in the Morris water maze (MWM) during prepubertal and pubertal ages in five daily consecutive sessions and a sixth session 1 week later and in the radial-arm maze (RAM) during adulthood. In the RAM, a drug challenge of the β-noradrenergic antagonist propranolol (10–20 mg/kg) was given after acquisition training. Maternal weight gain was reduced 13–42% and offspring birth weight was reduced by 7–12% in all three exposure groups compared to controls. Cocaine decreased the AGD of males (2.68 mm) compared to 2.88 mm in noncocaine-exposed male pups (p < 0.025). A sex-selective cocaine effect was also seen after adjustment of AGD measurements for body weight. With this measure cocaine-treated females showed significantly (p < 0.05) greater AGD than those not exposed to cocaine. In the MWM, there were two types of trials: cued reference memory trials and uncued spatial working memory trials. On cued reference memory trials significant cocaine-induced latency deficits were seen on only the first session. On spatial working memory trials cocaine-induced latency deficits were seen throughout daily training on sessions 1–5, but not the retention session 6, 1 week later. During RAM acquisition, there were no significant differences in choice accuracy between exposure groups. Following propranolol challenge, deficits in choice accuracy were demonstrated in rats prenatally exposed to cocaine or nicotine. These rats did not show any response to propranolol, whereas the controls slightly improved their choice accuracy. The results of this study indicated that prenatal cocaine exposure altered long-term cognitive function under basal conditions in the MWM and drug challenge in the RAM, birth weight, and genital development. Cocaine-induced cognitive deficits were predominately in working memory rather than reference memory or long-term retention. Prenatal nicotine exposure was only observed to alter birth weight and cognitive function in response to propranolol challenge in the RAM.     

Prenatal cocaine exposure alters behavioral and neurochemical sensitization to amphetamine in adult rats

This study examined the neurochemical correlates of amphetamine (AMPH)-induced behavioral effects in prenatally saline (PSAL)-exposed or cocaine (PCOC)-exposed male rats. Pregnant Long-Evans rats received saline or saline containing cocaine hydrochloride (20 mg/kg s.c., b.i.d.) from gestational days 15-21. Animals were left with their biological mothers. Adult offspring were exposed to daily saline or AMPH (0.5, 1.5, or 5 mg/kg, i.p.) injections for 7 days. Behaviors were recorded in an open field during the first hour post-injection. PCOC rats did not exhibit behavioral anomalies during habituation to injection-stress or placement in the open field. PCOC rats displayed significant alterations in stereotyped responses to acute or intermittent exposure to various doses of AMPH. Within 48 h of the final testing day, striatal tissue was obtained from these animals and electrically-evoked [3H]acetylcholine (ACh) release was measured from striatal slices. Superfusion of tissue slices with various concentrations of AMPH (1-1000 nM) produced dose-dependent inhibition of ACh release in both PSAL and PCOC rats repeatedly injected with saline as adults. However, AMPH-induced inhibition of ACh release was decreased in PCOC rats repeatedly injected with AMPH as adults. At 5 mg/kg AMPH, PCOC rats exhibited increased mortality compared to PSAL rats. These data suggest that PCOC exposure produces long-lasting alterations in nigrostriatal transmission and behaviors mediated by this system.     

Prenatal exposure to cocaine disrupts cocaine-induced conditioned place preference in rats.

Cocaine-induced conditioned place preference (CPP) was tested in adult offspring of Sprague-Dawley dams that had been injected subcutaneously with 40 mg/kg/3cc cocaine HCl (C40) daily from gestational days 8-20, pair-fed (PF) dams injected with saline, and nontreated control (LC) dams. C40 and PF dams gained significantly less weight than LC dams, although offspring body weights did not differ among the three prenatal treatment groups at birth or in adulthood. Significant place conditioning was obtained in LC and PF offspring when either 2.0 or 5.0 mg/kg of cocaine was paired with the designated place. In contrast, C40 offspring did not exhibit place conditioning at either training dose. Yet, all animals exposed to 5 mg/kg of cocaine during conditioning exhibited less activity during the test (when no cocaine was given) than controls given unpaired exposures to the apparatus and cocaine and C40 offspring did not differ from LC and PF offspring in this respect. Therefore, despite their lack of a conditioned place preference for cocaine, rats that had been exposed gestationally to cocaine nevertheless revealed an effect of cocaine during conditioning in one aspect of their test behavior. Possible explanations for the lack of cocaine-induced place preference in these animals include a learning deficit or a change in cocaine's effectiveness as a reward.     

Prenatal exposure to cigarette smoke enhances oxidative stress in astrocytes of neonatal rat

Oxidative stress is involved in the pathogenesis of smoking-related disease. Protection of astrocytes from oxidative insult appears essential to maintain brain function. In this study, we have investigated the effect of gestational cigarette exposure on astrocyte survival. Pregnant female were randomly allocated to the control group or to the cigarette smoke group in which they were placed in an exposure chamber and inhale three cigarettes smoke twice a day for a period of 20 days. The control group was kept in the exposure chamber for the same duration, but without exposure to cigarette smoke. Newborn rats from both groups were weighed 24?h after birth and then cerebral hemispheres were collected for astrocyte culture. Incubation of astrocytes isolated from animals exposed to cigarette smoke with 300?μM H₂O₂ for 1?h induced a significant decrease of the proportion of surviving cells compared to cells isolated form control animals. We have observed that H₂O₂-treated astroglial cells derived from cigarette smoke exposure showed more reduced superoxide dismutase and catalase activities than H₂O₂-treated astroglial cells from control animals. In conclusion, this study indicates that astroglial cells derived from newborn rats exposed in utero to cigarette smoke are more vulnerable to oxidative assault than cultured astrocytes obtained from control animals. These results point out the existence of excitotoxic lesions in newborn exposed in utero to cigarette smoke and suggest that despite their high antioxidative activities, astrocytes cannot survive and protect neurons under massive oxidative stress.     

Prenatal chlorpyrifos exposure in rats causes persistent behavioral alterations

Use of chlorpyrifos (CPF) has been curtailed due to its developmental neurotoxicity. In rats, postnatal CPF administration produces lasting changes in cognitive performance, but less information is available about the effects of prenatal exposure. We administered CPF to pregnant rats on gestational days (GD) 17–20, a peak period of neurogenesis, using doses (1 or 5 mg/kg/day) below the threshold for fetal growth impairment. We then evaluated performance in the T-maze, Figure-8 apparatus and 16-arm radial maze, beginning in adolescence and continuing into adulthood. CPF elicited initial locomotor hyperactivity in the T-maze. Females showed slower habituation in the Fig. 8 maze; no effects were seen in males. In the radial-arm maze, females showed impaired choice accuracy for both working and reference memory and again, males were unaffected. Despite the deficits, all animals eventually learned the maze with continued training. At that point, we challenged them with the muscarinic antagonist, scopolamine, to determine the dependence of behavioral performance on cholinergic function. Whereas control females showed impairment with scopolamine, CPF-exposed females did not, implying that the delayed acquisition of the task had been accomplished through alternative mechanisms. The differences were specific to muscarinic circuits, as control and CPF groups responded similarly to the nicotinic antagonist, mecamylamine. Surprisingly, adverse effects of CPF were greater in the group receiving 1 mg/kg as compared to 5 mg/kg. Promotional effects of acetylcholine (ACh) on cell differentiation may thus help to offset CPF-induced developmental damage that occurs through other noncholinergic mechanisms. Our results indicate that late prenatal exposure to CPF induces long-term changes in cognitive performance that are distinctly gender-selective. Additional defects may be revealed by similar strategies that subject the animals to acute challenges, thus, uncovering the adaptive mechanisms that maintain basal performance.     

Prenatal TCDD exposure predisposes for mammary cancer in rats

Epidemiological data are conflicting in the link between 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure and breast cancer causation. We have hypothesized that timing of exposure to endocrine disruptors, such as TCDD, will alter breast cancer susceptibility. Using a carcinogen induced rat mammary cancer model, we have shown that prenatal exposure to TCDD alters mammary gland differentiation and increases susceptibility for mammary cancer. Investigations into imprinting via DNA methylation mechanisms showed that there were no changes in protein expression in DNA methyltransferases, ER-alpha, ER-beta, GST-pi, or MDGI. Using 2D gels and mass spectrometry, we have found seven proteins to be differentially regulated, including a decrease in superoxide dismutase 1 (SOD1). Down-regulation of SOD1 could provide an environment ill equipped to deal with subsequent free radical exposure. We conclude that prenatal TCDD can predispose for mammary cancer susceptibility in the adult offspring by altering the mammary proteome.     

Prenatal methylazoxymethanol exposure alters evoked responses in fetal rats

Although there is considerable interest in identifying methods to detect central nervous system impairment early in development, few behavioral assessment tools are available for detecting CNS deficits in the fetus. In the present study, methylazoxymethanol [MAM; Midwest Research Institute, (MRI)] was used to induce deficits in CNS development in fetal rats to assess effects on coordinated fetal behavior. Fetuses were exposed by administering MAM to pregnant rats on E17 of gestation via intraperitoneal injection and then were prepared for behavioral testing 3 days later on E20. After externalization from the uterus into a warm saline bath, fetal subjects received either an intraoral infusion of lemon extract to evoke a facial wiping response or were presented with an artificial nipple to evoke an oral grasping response. Interlimb coordination and paw-face contact during facial wiping were disrupted in MAM-exposed fetuses. Similarly, MAM exposure diminished the ability of fetuses to grasp or maintain oral contact with the artificial nipple. Although clear disruptions of movement coordination were seen in the MAM-treated subjects, there were no significant differences from saline controls in weight or anatomical measures. Together, these findings suggest that behavioral assessments of fetal motor coordination may be useful in identifying neural insult during prenatal development.     

Prenatal antiepileptic drug exposure alters seizure susceptibility in rats

An animal model is used to address the issue of prenatal exposure to certain antiepileptic drugs and seizure susceptibility in the offspring. Administration of doses established as median therapeutic doses in humans of phenobarbital, valproate and clonazepam to pregnant rats during the last third of gestation produced sexually dimorphic alterations in pentylenetetrazol (PTZ)-induced seizures as well as in non-convulsive (spontaneous alternation and cliff avoidance) behaviors in the offspring. Altered seizure susceptibility occurred in the absence of overtly recognizable morphological abnormalities and did not appear to reflect differences in the status of circulating drug-binding plasma proteins. Possible neural and/or metabolic mechanisms responsible for these behavioral changes are discussed.     

Prenatal exposure to lipopolysaccharide results in increases in blood pressure and body weight in rats

AIM: To investigate the effects of prenatal exposure to lipopolysaccharide (LPS) on blood pressure and body weight of offspring in rats. METHODS: Sixteen healthy, pregnant rats were randomly divided into 2 groups. The rats in the LPS group were injected intraperitoneally with LPS (0.79 mg/kg) on the d 8, d 10, and d 12 of gestation. Those in the control group were only treated with normal saline. After delivery, all offspring were weighed and blood pressure was measured by the tailcuff method once every 2 weeks from the 6th to the 24th week. In the 15th week, their food intake was weighed every day. At the end of the 24th week, the rats were killed by decapitation. Abdominal adipose tissues were weighed, and the serum level of leptin was detected by radioimmunoassay. RESULTS: The offspring with prenatal LPS exposure showed increased systemic arterial pressure, heavier body weight, elevated food intake, increased adipose tissue weight, and increased circulating leptin compared with the controls. CONCLUSION: Prenatal exposure to LPS leads to increases in blood pressure and body weight in rats.