Morphine analgesia is potentiated in adult rats prenatally exposed to ethanol

Early exposure to environmental enrichment modulates the effects of prenatal ethanol exposure upon opioid gene expression and adolescent ethanol intake

Prenatal ethanol exposure (PEE) promotes ethanol consumption in the adolescent offspring accompanied by the transcriptional regulation of kappa opioid receptor (KOR) system genes. This study analysed if environmental enrichment (EE, from gestational day 20 to postnatal day 26) exerts protective effects upon PEE-modulation of gene expression, ethanol intake and anxiety responses. Pregnant rats were exposed to PEE (0.0 or 2.0 g/kg ethanol, gestational days 17-20) and subsequently the dam and offspring were reared under EE or standard conditions. PEE upregulated KOR mRNA levels in amygdala (AMY) and prodynorphin (PDYN) mRNA levels in ventral tegmental area (VTA) with the latter effect associated with lower DNA methylation at the gene promoter. These effects were normalized by exposure to EE. PEE modulated BDNF mRNA levels in VTA and Nucleus accumbens (AcbN), and EE mitigated the changes in AcbN. EE induced a protective effect on ethanol intake and preference, an effect more noticeable in males than in females, and in prenatal vehicle-treated (PV) than in PEE rats. The male offspring drank significantly less ethanol than the female offspring. The latter result suggests that the protective effect of EE on ethanol drinking may only emerge at lower levels of drinking. In the dams, PEE induced an upregulation of PDYN and KOR in AcbN. PDYN gene expression was normalized by exposure to EE. These results suggest that EE is a promising treatment to inhibit the effects of PEE. The results confirm that PEE effects are mediated by alterations in the transcriptional regulation of KOR system genes.

Perinatal alcohol exposure enhances nocistatin levels in adulthood

In earlier experiments perinatal hormonal imprinting by alcohol decreased the hormone content of immune cells for life. In the present study, both a single day (15% on the third postnatal day) and a long-term treatment schedule of alcohol exposure (3% for 21 days) of dams during lactation significantly (P < 0.01) enhanced endogenous levels of nocistatin in the blood plasma as well as in the cerebrospinal fluid of the offspring, measured in 3-month-old rats. Our data suggest that alcohol consumption during lactation can cause a life-long influence on nocistatin levels in the offspring and most likely modify nocistatin-related functions such as pain tolerance.

Long-term effects of neonatal surgery on adulthood pain behavior

The long-term consequences of neonatal noxious stimulation on adulthood pain behavior were investigated in male and female mice. On the day of birth, mouse pups were exposed to a laparotomy under cold anesthesia followed by an analgesic dose of morphine (10 mg/kg) post-operatively, or a saline control. An additional group of subjects was exposed to the non-noxious aspects of the surgical procedure (cold exposure, separation from the dam, injection) comprising a 'sham' surgery control group, whereas another group of control subjects was administered an injection of saline or morphine, but was otherwise undisturbed. Behavioral observations of the pups immediately following the procedure indicated that the laparotomy produced increased distress vocalizations in the ultrasonic range (40 kHz) compared to both groups of control subjects. During 90 min observations periods following the surgery and 1-week later, maternal care did not vary among treatment conditions. In adulthood, offspring were tested for nociceptive sensitivity on the hot-plate (HP; 53 degrees C), tail-withdrawal (TW; 50 degrees C) and acetic acid abdominal constriction test (AC). On both the TW and the AC tests, neonatal surgery decreased pain behavior relative to both groups of control subjects, an effect that was reversed by post-operative morphine treatment. On the HP test, both groups of subjects exposed to the stressful aspects of neonatal surgery (laparotomy or sham surgery) exhibited decreased pain behavior in adulthood. These findings suggest that early exposure to noxious and/or stressful stimuli may induce long-lasting changes in pain behavior, perhaps mediated by alterations in the stress-axis and antinociceptive circuitry.

Neonatal ethanol exposure produces a hyperalgesia that extends into adolescence, and is associated with increased analgesic and rewarding properties of nicotine in rats

RATIONALE

Drug exposure during CNS development may alter subsequent dependence liability. We postulated that early alcohol exposure might produce persistent alterations in responses to noxious stimuli. Because relief of physical discomfort may be negatively reinforcing, changes in responses to noxious stimuli produced by early alcohol exposure may increase the rewarding properties of nicotine, a potent analgesic. Such factors may contribute to the high level of alcohol and nicotine co-abuse in humans.

OBJECTIVES

The purpose of this study was to determine whether neonatal ethanol exposure in rats altered responses to noxious stimuli, and whether nicotine would then be more rewarding to the alcohol-exposed offspring, perhaps via its analgesic actions.

METHODS

Neonatal rats received ethanol by gavage (5.0 or 6.5 g/kg) on postnatal days (PND) 9-13. An iso-caloric control group was also included. Rats were then tested to assess responsiveness to a mild noxious heat stimulus, as measured in the tail-flick assay (PND 14 and PND 28), for their response to acute analgesic injections of either nicotine or ethanol (PND 28), and for nicotine induced conditioned place preference (CPP) (PND 36).

RESULTS

Neonatal ethanol exposure produced hyperalgesia during the first 24 h after alcohol withdrawal (PND 14) that continued through PND 28. The analgesic effects of 12.5 microg/kg nicotine were enhanced approximately 2-fold in adolescent rats with previous ethanol histories, relative to controls. These ethanol-exposed rats also showed a significant CPP to nicotine, whereas controls showed no CPP.

CONCLUSIONS

Persistent decreases in tail-flick response latencies suggestive of hyperalgesia were observed following neonatal ethanol exposure in the rat. These changes were accompanied by increases in the analgesic and place-conditioning effects of nicotine in adolescence. If similar effects occur in humans, prenatal alcohol exposure may play a role in an increased risk for the rewarding effects and dependence liability of nicotine later in life.

Effect of prenatal ethanol and stress on levels of beta-endorphin in different brain regions of the rat

The combination of prenatal ethanol exposure and footshock stress was investigated for its effects on brain beta-endorphin levels. Subjects were offspring of rats that received 1 of 3 prenatal dietary treatments: an ethanol-containing liquid diet, a identical liquid diet with ethanol substituted isocalorically with maltose-dextrin (pair-fed group), and standard laboratory rat chow (chow-fed group). Two different stress paradigms were used: a short (30-sec) footshock stress paradigm and a prolonged (180-sec) footshock stress paradigm. Levels of beta-endorphin were measured with radioimmunoassay in eight brain regions of unstressed (baseline) rats, and of stressed rats at 3 and 30 min following termination of the stress. Seven brain regions containing high densities of beta-endorphin axons and terminals were chosen, as well as the arcuate region of the hypothalamus, the only brain region where both beta-endorphin perikarya and terminals are located. Following the short footshock stress paradigm, there were no changes in beta-endorphin levels, except for a trend toward increased levels in the pair-fed group. After the prolonged stress paradigm, levels of beta-endorphin in both the pair-fed and chow-fed groups tended to be decreased in several brain regions, including the arcuate region, at 3 min after termination of the stress. In contrast, for the prenatally ethanol-exposed group, beta-endorphin levels were increased significantly in the arcuate region, and moderately increased in the septal/preoptic region and medulla/pons at 3 min after the prolonged stress paradigm.(ABSTRACT TRUNCATED AT 250 WORDS)

Prenatal ethanol exposure: susceptibility to convulsions and ethanol's anticonvulsant effect in amygdala-kindled rats

The present experiments assessed the effects of prenatal ethanol exposure on the susceptibility to convulsions and on the anticonvulsant effect of ethanol using the electrical kindling model of epilepsy in rats. Adult male Sprague-Dawley rats from prenatal ethanol (E), pair-fed (PF), and ad libitum-fed control (C) treatment groups were tested following the implantation of a stimulation electrode in the left amygdala complex. The same rats were tested in four consecutive experiments. Both E and PF rats showed a slightly slower rate of kindling than C rats, as measured by convulsion class but not as measured by forelimb clonus duration (experiment 1). However, the groups did not differ significantly in the electrical stimulation threshold for kindled convulsions (experiment 2). Furthermore, prenatal ethanol exposure had no significant effect on the dose-response curve for ethanol's (0, 0.9, 1.1, 1.3, and 1.5 g/kg, ip) anticonvulsant effect (experiment 3), or on the rate of tolerance development to ethanol's (1.5 g/kg, ip) anticonvulsant effect (experiment 4) on kindled convulsions. Thus, prenatal exposure to ethanol does not appear to have long-term effects on the susceptibility to convulsions or on the anticonvulsant effect of ethanol in adult male rats in the kindling model as used in the present experiments.

Effects of prenatal ethanol exposure on later sensitivity to the low-dose stimulant actions of ethanol in mouse offspring: possible role of catecholamines

The purpose of this study was to examine whether prenatal ethanol (EtOH) exposure alters later sensitivity to the low-dose stimulant effects of EtOH. Because the locomotor stimulant effects of EtOH are thought to be mediated, at least in part, by activation of brain monoamine systems, and because prenatal EtOH exposure has been shown to alter brain monoamine activity, it was hypothesized that prenatal EtOH exposure may alter sensitivity to the stimulant actions of EtOH. To test this hypothesis, sensitivity to the locomotor stimulant effects of various challenge doses of EtOH was examined in male and female offspring from prenatal alcohol (A), pair-fed (PF), and lab chow (LC) groups at different ages. In addition, to address the hypothesis further, sensitivity to the catecholamine synthesis inhibitor alpha-methyl-p-tyrosine (AMPT) was examined in these offspring, as well. Results indicated that male offspring prenatally exposed to EtOH exhibited reduced baseline activity and a blunted stimulant response to all challenge doses of EtOH (0.75-1.5 g/kg) in comparison with control offspring at 30 days of age, but these effects appeared to "normalize" at 70 days of age. Female EtOH-exposed offspring also exhibited a reduced baseline level of activity relative to control offspring, as well as a blunted stimulant response to the lowest challenge dose of EtOH (0.75 g/kg) at 30 days of age, and these effects persisted into adulthood. The stimulant response to higher doses of EtOH did not significantly differ among prenatal treatment groups in young or adult female offspring. However, because baseline activity was significantly lower in female EtOH-exposed offspring than control offspring, the stimulant response to these doses of EtOH (1.125 and 1.5 g/kg) was relatively greater than that for PF and LC offspring. Importantly, none of the differences in performance among the prenatal treatment groups could be attributed to an alteration in EtOH pharmacokinetics, because blood EtOH levels measured immediately following the 10-min test session were similar for all prenatal treatment groups across all of the EtOH test doses. Further, a similar response profile as that observed following EtOH challenge at 70 days of age was obtained following phenobarbital challenge (10-40 mg/kg). Finally, whereas AMPT (50-400 mg/kg) dose-dependently antagonized the stimulant effects of EtOH in all prenatal treatment groups, this effect of AMPT was significantly greater in mice prenatally exposed to EtOH in comparison with control offspring.(ABSTRACT TRUNCATED AT 400 WORDS)

Opioid-dependent behaviors in infant rats: effects of prenatal exposure to ethanol

Pregnant rats were given diets containing either 5% ethanol, an isocaloric (pair-fed) diet, or casein pellets. Offspring were tested at postnatal day 10 for isolation-induced ultrasonic vocalizations and subsequent stress-induced analgesia. Rats prenatally exposed to ethanol vocalized significantly less in the five minutes during isolation. The opiate, morphine, caused a greater suppression of vocalizations in alcohol-exposed pups compared to controls, while the increased calling normally seen with the opiate antagonist, naltrexone, was attenuated. In a test in which the pup withdraws a paw from a hot plate (48 degrees C), prenatal alcohol offspring demonstrated baseline latencies (no isolation) similar to controls but had greatly attenuated responses in their isolation-induced analgesia. Since both vocalization and analgesia responses have been determined to be modulated by the endogenous opioid system, the aberrant responses of the prenatal-ethanol-exposed offspring can be interpreted as failures to respond by opioid release/secretion to appropriate stimuli.

Indices of stress in rats: effects of sex, perinatal alcohol and artificial rearing

Three groups of rats were normally reared by dams, artificially reared but not exposed to alcohol or artificially reared and exposed to 6.6 g/kg/day of ethanol condensed into 8 h of each 24-h period. Alcohol exposure was given from postnatal day 4 through 9 and artificial rearing was conducted from postnatal day 4 to 12. In adulthood, approximately half of the rats were fitted with a chronic jugular catheter and were exposed to swim stress for 1 min in 21 degrees C water. Alcohol exposure augmented the corticosteroid stress response to the swim stress in female rats but not in male rats. The other half of the animals were tested for acquisition and extinction of a conditioned emotional response (CER). While alcohol exposure had no effects on the CER, extinction of CER was greatly accelerated by artificial rearing alone in female rats but not in male rats. Taken together, these findings suggest that some aspects of the stress response in female rats are more vulnerable to insults during the early postnatal period than those in male rats and that the insult-induced alterations can affect hormonal and behavioral measures differentially.

Opioids and the developing organism: a comprehensive bibliography, 1984-1988

A comprehensive bibliography of the literature concerned with opioids and the developing organism for 1984-1988 is presented. Utilized with companion papers (Neurosci. Biobehav. Rev. 6:439-479; 1982; 8:387-403; 1984), these articles cover the clinical and laboratory references beginning in 1875. For the years 1984, 1985, 1986, 1987, and 1988, a total of 877 citations were recorded. A series of indexes accompanies the citations in order to make the literature more accessible. These indexes are divided into clinical and laboratory topics, and subdivided into such topics as the type of opioid explored and the general area of biological interest (e.g., physiology).