Prenatal stress in the rat results in increased blood pressure responsiveness to stress and enhanced arterial reactivity to neuropeptide Y in adulthood

We have shown previously that stress in the pregnant rat leads to a heightened cardiovascular response to restraint in adult offspring. The present study was undertaken to explore further the persistent cardiovascular effects of prenatal stress, with a focus on peripheral vascular function. Sprague–Dawley female rats were exposed to restraint/bright light three times daily in the last week of pregnancy. Litters from stressed and control females were cross-fostered to control dams to eliminate possible effects of maternal stress on nursing behaviour. At 120 days, offspring cardiovascular variables were measured by radiotelemetry. Reactivity of mesenteric small arteries was assessed by myography, and responses to electrical field stimulation determined. Resting cardiovascular parameters in prenatally stressed (PS) offspring were similar to controls but PS rats showed a greater increase in systolic blood pressure following restraint stress ( P < 0.05). Recovery was also prolonged in PS animals compared with controls and was of longer duration in PS females than in PS males ( P < 0.05). Adult PS females, but not males, also had elevated basal plasma corticosterone levels in comparison with controls ( P < 0.05). Vascular reactivity to neuropeptide Y ( P < 0.05) and electrical field stimulation ( P < 0.05) in mesenteric arteries was also significantly increased in PS animals. Vascular responses to adrenergic agonists as well as endothelial dilator function did not differ between PS and controls. We conclude that prenatal stress during late gestation has long-lasting effects on cardiovascular responsiveness and vascular reactivity to neuropeptide Y in the offspring.     

Prenatal stress in rats: effects on plasma corticosterone, hippocampal glucocorticoid receptors, and maze performance

The present experiments were designed to investigate the effects of maternal stress on cognitive and endocrine parameters in the adult offspring. Pregnant rats were stressed daily during the last week of pregnancy (days 15-19) by restraint, and the performance of their offspring in the Morris water maze was recorded. Plasma corticosterone levels after swimming and the status of hippocampal glucocorticoid receptors (GRs) were determined. During acquisition of the task, prenatally stressed (PS) males - but not females - showed longer escape latencies than non-stressed controls when swimming in cold (10 degrees C) but not in warm (20 degrees C) water. This sex- and prenatal stress-specific difference was even more pronounced during reversal learning of the task. In contrast, PS females - but not males - had higher basal corticosterone levels and a lower density of hippocampal corticosteroid receptors than non-stressed controls. In all animals irrespective of treatment, swimming in the water maze causes an increase of corticosterone that was smaller on day 8 of swimming than on day 1. After swimming in cold water, the rise in corticosterone levels in females was steeper and returned faster to baseline values than after swimming in warm water. A similar pattern could be seen in PS females when compared to their non-stressed controls. The data suggest that prenatal stress impairs spatial learning in males but not in females. Basal and stress-induced increases in corticosterone levels, however, were altered in PS females and not in PS males; i.e., prenatal stress-induced changes in corticosterone secretion were not paralleled by prenatal stress-induced deficits in spatial learning.     

Alterations in stress-induced prolactin release in adult female and male rats exposed to stress, in utero

Prenatal stress alters the endocrine as well as the behavioral responses of rodents. Because of the reductions in both estradiol-induced and ether-induced prolactin (Prl) release reported in prenatally-stressed (P-S) rats, we were interested in whether prenatal stress might also modify the prolactin response of male and female rats to a moderate stressor in adulthood, viz., restraint stress. Timed-mated Sprague-Dawley females were exposed to a daily regimen of heat and restraint stress from days 15-22 of gestation. Control animals remained undisturbed throughout pregnancy. In adulthood, half of the male and female P-S and Control offspring were stressed by placing them in a Plexiglas restraint tube for 60 min (restraint stressed; S; referred to as P-SS and CS, respectively). The remaining half of the P-S and Control animals were left undisturbed (these were nonrestrained; NR; referred to as P-SNR and CNR, respectively). Blood samples (decapitation) were then collected from all animals and plasma was assayed for Prl content. P-SNR and CNR males did not differ in baseline Prl levels, nor did P-SNR and CNR females. Following the restraint stress in adulthood, P-SS males as well as PSS females exhibited significantly less of an increase in Prl relative to CS males and CS females, respectively. In addition, baseline Prl levels differed between the sexes, with females--regardless of prenatal condition--having higher plasma Prl levels than males. These sex differences were no longer evident following restraint stress. These data, in combination with other work in P-S animals in the areas of Prl release and stress responses, demonstrate that prenatal stress renders the rat less hormonally (Prl) responsive to stress, with the effect being more pronounced in the female.     

Autonomic mechanisms underpinning the stress response in borderline hypertensive rats

This study investigates blood pressure (BP) and heart rate (HR) short-term variability and spontaneous baroreflex functioning in adult borderline hypertensive rats and normotensive control animals kept on normal-salt diet. Arterial pulse pressure was recorded by radio telemetry. Systolic BP, diastolic BP and HR variabilities and baroreflex were assessed by spectral analysis and the sequence method, respectively. In all experimental conditions (baseline and stress), borderline hypertensive rats exhibited higher BP, increased baroreflex sensitivity and resetting, relative to control animals. Acute shaker stress (single exposure to 200 cycles min-1 shaking platform) increased BP in both strains, while chronic shaker stress (3-day exposure to shaking platform) increased systolic BP in borderline hypertensive rats alone. Low- and high-frequency HR variability increased only in control animals in response to acute and chronic shaker (single exposure to restrainer) stress. Acute restraint stress increased BP, HR, low- and high-frequency variability of BP and HR in both strains to a greater extent than acute shaker stress. Only normotensive rats exhibited a reduced ratio of low- to high-frequency HR variability, pointing to domination of vagal cardiac control. In borderline hypertensive rats, but not in control animals, chronic restraint stress (9-day exposure to restrainer) increased low- and high-frequency BP and HR variability and their ratio, indicating a shift towards sympathetic cardiovascular control. It is concluded that maintenance of BP in borderline hypertensive rats in basal conditions and during stress is associated with enhanced baroreflex sensitivity and resetting. Imbalance in sympathovagal control was evident only during exposure of borderline hypertensive rats to stressors.     

Psychosocial maternal stress during pregnancy: effects on reproduction for F0 and F1 generation laboratory rats

The impact of daily social maternal stress on reproduction parameters was studied in F0 and F1 generation female Long-Evans rats. Chronic maternal stress was induced in pregnant females (F0 females) by 2 h social confrontation with a dominant female throughout pregnancy. Social stress of F0 females was associated with lower maternal body mass investment in litters. While maternal stress did not cause a decline in the F0 female mass, it resulted in reduced litter sizes and lower litter masses. The individual body mass of offspring from stressed (= prenatally stressed offspring, PS) and control F0 generation mothers (= prenatal control offspring, PC) did not differ at birth. However, PS offspring grew faster during lactation and were therefore heavier than PC offspring at weaning. Reproduction parameters of F1 generation females were determined until an age of 180 days. Investigation revealed that PS females did not differ from PC females in any reproduction parameter assessed, except for higher PS offspring body mass at birth. It was also observed that a higher percentage of PS females gave birth outside the core breeding period during the light (= inactive) period. This study shows that exposure to a relatively mild social stressor during pregnancy alters female reproduction in rats. However, there was no indication of higher infant mortality which is often associated with severe laboratory stress. We argue that the reduced litter sizes in stressed F0 mothers represent an adaptive strategy from an evolutionary point of view.     

Prenatal stress reduces the effectiveness of the neurosteroid 3 alpha,5 alpha-THP to block kainic-acid-induced seizures

The effects of prenatal stress on the ability of the 5 alpha-reduced progesterone metabolite and neurosteroid 5 alpha-pregnan-3 alpha-ol-20-one (3 alpha,5 alpha-THP) to prevent seizures was examined. On gestational Day 18, pregnant rats were exposed to 20 min of restraint stress (prenatal stress condition) or no such stress (control condition). The adult, gonadectomized offspring exposed to the prenatal stress or control condition were administered 0.0, 4.0, or 8.0 mg/kg 3 alpha,5 alpha-THP 1 hr prior to testing for kainic-acid-induced (32 mg/kg SC) ictal activity. The rats exposed to prenatal stress tended to have more partial seizures and significantly more tonic clonic seizures that were of longer duration than the no prenatal stress rats. Four mg/kg 3 alpha,5 alpha-THP was sufficient to significantly reduce seizure duration of no prenatal stress females, compared to the 0.0 mg/kg dosage of 3 alpha,5 alpha-THP. Seizure duration was reduced in no prenatal stress females by a dose of 4 mg/kg 3 alpha,5 alpha-THP, whereas a dose of 8 mg/kg was required to obtain comparable seizure reduction in prenatally stressed females and males in both groups. There was attrition following kainic-acid testing; of the 18 animals in each group originally, 9 prenatally stressed males, 6 prenatally stressed females, 6 nonprenatally stressed males and 5 nonprenatally stressed females were able to be tested in the water maze and perfused. One week after seizures, there were no differences in the water maze performance of the remaining animals. There were fewer cresyl violet-stained neurons in the CA3 region of the hippocampus of prenatally stressed rats compared to the nonprenatally stressed rats. Basal plasma corticosterone was greater in prenatally stressed animals, but this was due to increases in females rather than males. Plasma 3 alpha,5 alpha-THP was not significantly different in prenatally stressed males and females compared to their no prenatal stress counterparts. These data suggest that the sensitivity to, or responsiveness of, 3 alpha,5 alpha-THP to prevent seizures is decreased after prenatal stress, particularly in females.     

Effects of prenatal stress on defensive withdrawal behavior and corticotropin releasing factor systems in rat brain

Exposure of pregnant rats to stress results in offspring that exhibit abnormally fearful behavior and have elevated neuroendocrine responses to novelty and aversive stimuli. This study examined the effects of prenatal stress on plasma corticosterone, adrenal weight, defensive withdrawal behavior, and the density of receptors for corticotropin releasing factor (CRF) in the amygdala. Pregnant Sprague-Dawley rats were stressed by daily handling and saline injection (s.c., 0.9%, 0.1 mL) during the last week of gestation. Male offspring were studied at adulthood (60-120 days of age). Adrenal hypertrophy and increased plasma corticosterone were observed in the prenatally stressed offspring. Defensive withdrawal, an ethological measure of the conflict between exploratory behavior and retreat, was quantified in naive offspring, and in offspring exposed to restraint stress (2 h). Restraint stress increased defensive withdrawal in both control and prenatally stressed offspring. Both naive and restraint-stressed prenatally stressed offspring exhibited increased defensive withdrawal compared to control offspring. There was a significant interaction between prenatal stress and restraint stress, suggesting increased vulnerability of prenatally stressed offspring. The effects of restraint in the defensive withdrawal test were reduced by intracerebroventricular administration of the CRF antagonists, alpha-helical CRF9-41 (20 microg every hour) or D-phe(12), Nle(21, 38), C(alpha)-MeLeu(37)]-CRF((12-41)) (5 microg every hour) during the restraint period. The difference between control and prenatally stressed offspring was abolished by the CRF antagonists, suggesting that increased activation of CRF receptors may be a factor in the behavioral abnormalities of prenatally stressed rats. Measurement of CRF receptors in amygdala revealed a 2.5-fold increase in binding in prenatally stressed offspring. In light of previous work from this laboratory demonstrating increased content and release of CRF in amygdala from prenatally stressed offspring, the present study suggests that the increased fearfulness of prenatally stressed rats may be a consequence of increased activity of CRFergic systems in the amygdala.     

Mild prenatal stress enhances learning performance in the non-adopted rat offspring

The present study was designed to investigate whether mild stress during pregnancy affects offspring behaviors, including learning performance. Prenatal stress was induced by short-lasting, mild restraint stress, which had previously been shown to facilitate the morphological development of fetal brain neurons. Adult offspring whose dams had been restrained in a small cage for 30min daily from gestation day 15 to 17 showed enhanced active avoidance and radial maze learning performance. In addition, the prenatally stressed rats showed weaker emotional responses than unstressed control, as indicated by decreases both in ambulation upon initial exposure to an open field and in Fos expression in the amygdala induced by physical stress. The observed effects of prenatal stress on learning performance and emotional behavior were attenuated by foster rearing by unstressed dams. Fos expression in the hypothalamic paraventricular nucleus following physical stress and corticosterone secretion during physical and psychological stress did not differ between the prenatally stressed and unstressed control rats. From these results we suggest that mild prenatal stress facilitates learning performance in the adult offspring. The enhancement of learning performance appears to be accompanied by reduced emotionality, but not by any apparent alterations in hypothalamic-pituitary-adrenal responses. In addition, the observation of differential behaviors in the adopted and non-adopted animals supports the notion that the postnatal environment modifies the behavioral effects of prenatal stress.     

Effects of anterior hypothalamic lesions on the sexual behavior of prenatally-stressed male rats

Sprague-Dawley females were exposed to the stress of heat, restraint and bright lights during the third trimester of gestation. Virtually all male offspring tested for masculine sexual behavior as adults ejaculated and copulated with lure females. Also prenatally-stressed males exhibited two to three times as many lordotic responses as did males from nonstressed mothers. Because animals were crossfostered, an in utero action of prenatal stress is supported. Anterior hypothalamic (AHA) lesions significantly reduced the number of lordotic responses observed in prenatally-stressed male rats compared to those observed in prenatally-stressed males bearing sham lesions of the AHA. The possibility is presented that prenatal stress may influence the developing male brain.     

Effects of gestational stress and neonatal handling on pain,analgesia, and stress behavior of adult mice

Stressors presented during the late prenatal and early postnatal periods can have long-term effects on offspring behavior, due to the sensitive periods in the formation of brain circuitry associated with early development. This study investigated the long-term effects of prenatal (restraint during the last week of gestation) and postnatal (daily handling for 14 days postnatal) stress, alone and in combination, on adulthood pain behavior, analgesic responses to stress and morphine, and on behavioral indices of stress reactivity. We found that all of the adult responses measured were altered by perinatal manipulations. Nociceptive thresholds were increased by prenatal or by postnatal stress in males and females; application of both stressors in combination negated these effects. Elevations in morphine analgesia were also observed in animals undergoing either perinatal stressor, but not in those who received both stressors. Behavioral and analgesic responses to stress were consistent with previous observations of reduced stress responsiveness following neonatal handling, with some sex-specific findings. Male and female handled subjects exhibited decreases in stress behavior, and both groups of female handled subjects (regardless of prenatal stress [PS] condition) exhibited decreases in stress-induced analgesia (SIA). Males, on the other hand, exhibited decreases in SIA only if they were prenatally stressed (regardless of handling condition). Thus, prenatal and postnatal stressors have differing effects on the neural circuitry underlying pain, pain inhibition, and stress behavior.     

Prenatal stress affects the rate of sexual maturation and attractiveness in bank voles

Field studies reveal that bank vole females' mobility and aggression increase during pregnancy. Here we investigated the reaction of pregnant females to social stress evoked by short but frequent meetings with another female at the same stage of pregnancy. The stress neither evoked pregnancy termination nor affected pregnancy duration but had a long-term effect on the reproductive activity of the offspring. Prenatal stress reduced the rate of sexual maturation of voles as estimated at the age of 20 days. Uterine weights of prenatally stressed females and testes weights of prenatally stressed males were significantly lower than in offspring born to nonstressed mothers. Olfactory signals are known to be important in the sexual preferences of bank voles. Adult prenatally stressed females were more attractive to other adult females than were nonstressed animals. For bank vole males, however, prenatal stress decreased the attractiveness of females; adult males selected nonstressed females over stressed partners, by odor. This study shows that prenatal conditions evoked by short but frequent encounters with another pregnant female lead to delayed puberty in females and males, and decrease sexual attractiveness in adult offspring. These two negative effects may significantly limit the reproduction of prenatally stressed offspring.     

Prenatal stress effects on exploratory activity and stress-induced analgesia in rats.

Pregnant rats were exposed three times daily to immobilization stress during gestational Days 15-19. The behavior of their offspring was compared with the behavior of offspring from unstressed control mothers. Although the stress procedure decreased the weight gain of mothers during pregnancy, it slightly but significantly increased the weight of their offspring at birth and at weaning. On postnatal Day 10, prenatally stressed pups returned to their home cage more quickly than did prenatally unstressed control pups during a nest odor discrimination task, but no differences between groups in the number of correct responses were found. On postnatal Days 70-72, prenatally stressed offspring showed increased exploratory activity in a complex tunnel maze compared with control offspring. On postnatal Day 80, analgesia induced by stress (swimming for 3 min in cold water) was determined (tail flick latency). The degree of stress-induced analgesia was smaller in prenatally stressed rats than in control rats. These data suggest that the effects of prenatal stress on behavior are most clearly discernable when such animals are confronted with a novel or stressful situation.     

Long-lasting adverse effects of prenatal hypoxia on developing autonomic nervous system and cardiovascular parameters in rats

To determine whether prenatal hypoxia increases the risk of developing cardiovascular disorders as an adult and, if so, the identity of the cell mechanisms involved in such dysfunction, we evaluated the sympathoadrenal system and central areas related to cardiovascular events during development and the cardiovascular parameters in adults. Pregnant rats were exposed to hypoxia (10% oxygen) from embryonic day (E) 5 to E20 and the offspring studied at 1, 3, 9 and 12 weeks of age for neurochemistry and at 12 weeks of age for cardiovascular analysis. In the 1-, 3- and 9-week-old offspring, the levels and utilization of catecholamines were reduced in sympathetic ganglia, in target organs, in adrenals and in the rostral part of the A2 cell group in the nucleus tractus solitarius, but were increased in the locus coeruleus. In the 12-week-old adult offspring, the lowered autonomic nervous activity was restricted to cardiac-related structures, i.e. the stellate ganglion, heart and adrenals. In adult rats, prenatal hypoxia did not affect the cardiac parameters under resting conditions but increased blood pressure and the variability of blood pressure and heart rate under stress conditions. The altered metabolic activity of the sympathoadrenal system and related central areas during development and at adulthood for most structures might be part of the potential mechanisms contributing to cardiovascular disorders in adults.     

Early emergence of increased fearful behavior in prenatally stressed rats

We have been studying the mildly prenatally stressed (PS) rat as a potentially useful animal model of anxiety disorders. Previously we have demonstrated that there are anatomical and biochemical alterations in the amygdalas of adult PS offspring and that these offspring show increased fearful behaviors. However, human data indicate that anxiety disorders often present first in early childhood and then persist throughout adolescence and adulthood. To determine if PS rats also model this characteristic of human anxiety disorders, here we asked whether behavioral indices of increased fear would be detectable at an early age. We tested the hypotheses that young PS rats would show increased behavioral fearfulness in response to an acute stressor and that this would increase with age. A mild prenatal stressor, consisting of removal of the dam from the home cage and administration of a subcutaneous injection of 0.1 ml of 0.9% saline daily, was administered during the last week of pregnancy. Offspring were tested in the defensive-withdrawal apparatus before and after exposure to restraint stress at 25, 45 and 60 days of age. PS animals showed increased defensive-withdrawal behavior following the stressor and were more fearful following restraint when compared to controls (CON). This was significant at P45 and increased to P60. Hence, fearful behaviors in PS rats emerge prior to sexual maturation and increase in magnitude thereafter, further validating our model as a means to investigate the underpinnings of anxiety disorders.     

Prenatal stress alters immune function in the offspring of rats

Pregnant rats were either exposed to restraint under bright lights for 45 min three times daily (n = 7) or were left undisturbed (n = 8) during Days 14–21 of gestation. Offspring were tested for cellular immune responses as measured by Concanavalin A-stimulated proliferation and Natural Killer (NK) cytotoxicity of splenocytes as juveniles or adults, or were tested for specific humoral immune responses to in vivo challenge with the antigen Keyhole Limpet Hemocyanin (KLH) as adults. Results indicated that: (a) Proliferation did not vary as a function of sex or prenatal treatment in either juvenile or adult offspring; (b) in juveniles NK cytotoxicity was marginally lower in males as compared to females, and was also marginally reduced by prenatal stress in males but not females, whereas in adults, NK cytotoxicity was marginally enhanced by prenatal stress in both sexes; and (c) prenatally stressed offspring of both sexes had higher levels of anti-KLH antibodies as compared to controls. © 1995 Johnv Wiley & Sons, Inc.     

Genetic predisposition to hypertension sensitizes borderline hypertensive rats to the hypertensive effects of prenatal glucocorticoid exposure

An adverse intrauterine environment can increase the incidence of hypertension and other cardiovascular disease risk factors. However, in clinical and experimental studies the magnitude of the effect is variable. Possibly, the relative influence of the prenatal environment on cardiovascular disease is determined in part by genetic factors that predispose individuals to the development of environmentally induced hypertension. We tested this hypothesis by comparing the effects of prenatal dexamethasone treatment (Dex, 300 microg kg(-1) i.p. on days 15 and 16 of gestation) in borderline hypertensive rats (BHR) and control Wistar-Kyoto (WKY) rats. Blood pressure, heart rate and plasma corticosterone values were measured at rest during the middle of the day, and during 1 h of restraint stress in the adult offspring using indwelling arterial catheters implanted at least 4 days prior to data collection. Compared with the saline (vehicle) control treatment, prenatal dexamethasone significantly (P < 0.05) increased baseline mean arterial pressure in male (123 +/- 2 versus 131 +/- 3 mmHg, saline versus Dex) and female (121 +/- 2 versus 130 +/- 2 mmHg, saline versus Dex) BHR, but not in male (108 +/- 3 versus 113 +/- 2 mmHg, saline versus Dex) or female (112 +/- 2 versus 110 +/- 2 mmHg, saline versus Dex) WKY rats. Relative to saline treatment, prenatal Dex also significantly increased baseline heart rate (328 +/- 6 versus 356 +/- 5 beats min(-1), saline versus Dex) and plasma corticosterone (5 +/- 2 versus 24 +/- 4 microg dl(-1), saline versus Dex), and prolonged the corticosterone response to acute stress, selectively in female BHR. However, prenatal Dex significantly enhanced the arterial pressure response to acute stress only in female WKY, while Dex augmented the elevation in heart rate during stress only in male rats. We conclude that prenatal dexamethasone increased baseline arterial pressure selectively in BHR, and plasma corticosterone only in female BHR. In contrast, prenatal Dex enhanced cardiovascular reactivity to stress in both BHR and WKY rats.     

The Effects of Prenatal Stress on Learning in Rats in a Morris Maze

The offspring of female Wistar rats subjected to daily stress (they were placed in an unfamiliar social group for 1 h) during the last third of pregnancy were studied. The offspring of these females were tested for the ability to perform spatial orientation in a Morris water maze at the ages of two and four months. Prenatal stress had no effect on the ability of rats to learn in the Morris maze. However, two-month-old animals subjected to prenatal stress, unlike controls, demonstrated less flexibility in their behavioral strategy in solving the spatial orientation task. These animals were characterized by a clear tendency for their behavior to perseverate. By the age of four months, the differences between the control and prenatally stressed animals had disappeared.     

Prenatal stress interacts with prepuberal social isolation to reduce male copulatory behavior

Male offspring of female rats exposed to the stress of restraint and high intensity light during Day 14–21 of gestation were weaned when 22 days old into individual cages (social isolation) or into group cages with 2 other males (social rearing). Copulatory behavior was reduced by prenatal stress or social isolation alone and was absent in males exposed to both stress and prepuberal isolation. Adult therapy consisting of living with young females restored copulatory behavior in some stressed males only if they were reared prepuberally in a social environment. Stressed isolates showed chronic deficits in sexual behavior relative to controls. The study indicates that prenatal stress and prepuberal social isolation can interact to determine adult copulatory potentials in male rats.     

Effects of prenatal stress on formalin-induced acute and persistent pain in adult male rats

Behavioral responses of 90-day-old male offspring from female Wistar rats exposed to restraint stress during the last week of pregnancy were studied in the formalin test. Specific biphasic behavioral response characterized acute (phase 1) and persistent tonic pain (phase 2). The intensity of nociceptive responses (evaluated by the number of flexions+ shakings and by the duration of paw licking) in prenatally stressed rats changed only during phase 2. During interphase, facilitation of the flexion+shakings pattern (but not the licking pattern) in response to nociceptive stimulation was seen. The response intensity during phase 1 and the duration of both phases remained unchanged. Our findings suggest that prenatal stress modulates nociceptive sensitivity in 90-day-old offspring: it affects the duration of tonic (inflammatory), but not of acute pain. It is concluded that different mechanisms are responsible for the effects of prenatal stress on acute and persistent pain in the formalin test.