[Behavioural studies during the gestational-lactation period in morphine treated rats]. / Viselkedési vizsgálatok a gesztációs-laktációs idoszakban morfin-kezelt patkányon.

UNLABELLED: Opioids impair the maternal behaviour of experimental animals. The effect of morphine on maternal behaviour in rat dams treated chronically with morphine during the whole pregnancy and lactation has not been yet analysed systematically. OBJECTIVE: The aim of our work was to investigate the behavioural effects of moderate dose morphine administered constantly in the whole perinatal period in rats. METHODS: Nulliparous female rats were treated with 10 mg/kg morphine s.c. once daily, from the day of mating. Maternal behaviour was observed, the effects of acute morphine treatment on the maternal behaviour and whether this effect could be antagonised by naloxone were also investigated. Physical and other behavioural (anxiety-like signals in elevated plus maze, changes in locomotor activity) withdrawal signs precipitated by naloxone were registered. After weaning sensitivity to the rewarding effect of morphine was measured by conditioned place preference and to the aversive effect of naloxone by conditioned place aversion tests. Antinociceptive test on tail-flick apparatus was performed to investigate the changes in morphine antinociceptive effects due to chronic morphine treatment. RESULTS: Maternal behaviour was significantly impaired in morphine-treated dams. This effect of morphine lasted c.a. 2-3 hours a day, it showed dose-dependency and was enhanced in MO-treated group (sensitisation). Only weak physical and no other behavioural (anxiety-like behaviour or hypolocomotion) withdrawal signs were precipitated by naloxone. The positive reinforcing effect of morphine and aversive effect of naloxone were markedly increased on conditioned place paradigm. Significant antinociceptive tolerance was not seen. CONCLUSION: Although human drug abuse can be hardly modelling under experimental circumstances, our constant, relatively moderate dose morphine treatment administered once daily during the whole pregnancy and lactation resulted in several subtle behavioural changes in dams. In perinatally opioid-exposed offspring short- and long-term behavioural disturbances can be detected which is well-known from literature. Besides direct pharmacological effects of morphine impaired maternal responsiveness and pup care could play a role in these disturbances.

The central versus peripheral antinociceptive effects of µ-opioid receptor agonists in the new model of rat visceral pain.

This study describes the antinociceptive effects of µ-opioid agonists, d-Ala(2),N-Me-Phe(4),Gly(5)-ol-enkephalin (DAMGO) and morphine in a model of rat visceral pain in which nociceptive responses were triggered by 2% acetic acid intraperitoneal (i.p.) injections. DAMGO and morphine were administered i.p., to the same site where acetic acid was delivered or intracerebroventricularly (i.c.v.). The antinociceptive actions of i.p. versus i.c.v. administered DAMGO or morphine were evaluated in the late phase of permanent visceral nociceptive responses. Both compounds inhibited the nociceptive responses in a dose-dependent manner and exhibited more potent agonist activity after i.c.v. than i.p. administration. DAMGO and morphine showed comparable ED(50) values after i.p. injections. However, DAMGO was much stronger than morphine after central administration. Co-administration of the peripherally restricted opioid antagonist, naloxone methiodide (NAL-M), significantly attenuated the antinociceptive effects of i.p. DAMGO or morphine. On the other hand, i.c.v. injections of NAL-M partially antagonized the antinociceptive effect of i.p. morphine and failed to affect the antinociceptive action of i.p. DAMGO indicating the partial and pure peripheral antinociceptive effects of morphine and DAMGO, respectively. These results suggest the role of either central or peripheral µ-opioid receptors (MOR) in mediating antinociceptive effects of i.p. µ-opioid agonists in the rat late permanent visceral pain model which closely resembles the clinical situation.

Effects of opioid agonist and antagonist in dams exposed to morphine during the perinatal period.

The aim of the present work was to further analyse the features of opioid dependence following chronic morphine treatment during pregnancy and lactation. Dams from the day of mating were treated either with saline or with morphine (10mg/kg) subcutaneously once daily. Physical and behavioural signs of morphine withdrawal were investigated both in the early postpartum period (maternal behaviour) and after weaning (physical signals, locomotion, anxiety-like behaviour). Maternal behaviour was evaluated after acute challenge with naloxone (3 mg/kgs.c.) or morphine (10 mg/kgs.c.) and morphine plus naloxone (10 mg/kgs.c. and 3 mg/kgs.c., respectively). After weaning sensitivity to the rewarding effect of morphine was measured by conditioned place preference and to the aversive effect of naloxone by conditioned place aversion tests. The intensity of physical and behavioural indices of dependence was also investigated by precipitation of withdrawal with naloxone (10 mg/kgs.c) after weaning. Naloxone impaired the maternal behaviour in morphine-treated dams but not in saline-ones. Acute challenge with morphine impaired maternal responsiveness both in saline and in morphine-treated dams, this effect of morphine, however could be completely antagonised by naloxone only in the saline-treated but not in the morphine-treated ones. Significantly increased sensitivity to the rewarding stimulus of morphine and more pronounced aversion to naloxone were observed in morphine-treated dams. Naloxone precipitated only moderate physical withdrawal signals in morphine-treated dams, while anxiety and locomotor activity after administration of naloxone (behavioural withdrawal) were not changed in them. In summary chronic, moderate dose morphine treatment during pregnancy and lactation resulted in only mild dependence, but it affected opioid-receptor sensitivity and presumably disrupted the functioning of endogenous opioid system.

Changes in adaptability following perinatal morphine exposure in juvenile and adult rats.

The problem of drug abuse among pregnant women causes a major concern. The aim of the present study was to examine the adaptive consequences of long term maternal morphine exposure in offspring at different postnatal ages, and to see the possibility of compensation, as well. Pregnant rats were treated daily with morphine from the day of mating (on the first two days 5mg/kgs.c. than 10mg/kg) until weaning. Male offspring of dams treated with physiological saline served as control. Behavior in the elevated plus maze (EPM; anxiety) and forced swimming test (FST; depression) as well as adrenocorticotropin and corticosterone hormone levels were measured at postpartum days 23-25 and at adult age. There was only a tendency of spending less time in the open arms of the EPM in morphine treated rats at both ages, thus, the supposed anxiogenic impact of perinatal exposure with morphine needs more focused examination. In response to 5min FST morphine exposed animals spent considerable longer time with floating and shorter time with climbing at both ages which is an expressing sign of depression-like behavior. Perinatal morphine exposure induced a hypoactivity of the stress axis (adrenocorticotropin and corticosterone elevations) to strong stimulus (FST). Our results show that perinatal morphine exposure induces long term depression-like changes. At the same time the reactivity to the stress is failed. These findings on rodents presume that the progenies of morphine users could have lifelong problems in adaptive capability and might be prone to develop psychiatric disorders.

Does the effect of morphine challenge change on maternal behaviour of dams chronically treated with morphine during gestation and further on during lactation?

Opioids impair the maternal behaviour of rats. The effect of morphine on maternal behaviour in dams treated chronically with morphine during the whole pregnancy and lactation has not been analysed systematically. The aim of the present study was to investigate the possible differences in the disruptive effect of morphine on maternal behaviour following morphine challenges between dams treated chronically with saline or morphine during gestation and postpartum. The antinociceptive action of morphine was also studied in dams. The disruptive effect of morphine on maternal behaviour was not changed as the postpartum period passed. The duration of this effect of morphine lasted for about 2h. The dose-dependent disruptive effect of acute doses of morphine on maternal behaviour was more marked in the morphine-treated dams, than in the saline-treated ones, indicating a tendency for sensitisation to this effect. A trend for tolerance was observed to the antinociceptive effect of morphine in animals treated daily with morphine during the entire gestational and lactation periods; however, this difference did not reach statistical significance. Our experimental protocol might be a predictive model of human opioid abuse. Sensitisation to the impairing effect of opiates on maternal behaviour may explain why a mother abusing heroin neglects her baby even if she does not experience euphoria.

Intermittent prenatal MDMA exposure alters physiological but not mood related parameters in adult rat offspring.

The recreational party drug "ecstasy" (3,4-methylenedioxymethamphetamine MDMA) is particularly popular among young adults who are in the childbearing age and thus there is a substantial risk of prenatal MDMA exposure. We applied an intermittent treatment protocol with an early first injection on pregnant Wistar rats (15 mg/kg MDMA s.c. on the E4, E11 and E18 days of gestation) to examine the potential physiological, endocrine and behavioral effects on adult male and female offspring. Prenatal MDMA-treatment provoked reduced body weight of offspring from the birth as far as the adulthood. Adult MDMA-offspring had a reduced blood-glucose concentration and hematocrit, altered relative spleen and thymus weight, had lower performance on wire suspension test and on the first trial of rotarod test. In contrast, no alteration in the locomotor activity was found. Anxiety and depression related behavioral parameters in elevated plus maze, sucrose preference or forced swimming tests were normal. MDMA-offspring had elevated concentration of the ACTH-precursor proopiomelanocortin and male MDMA-offspring exhibited elevated blood corticosterone concentration. No significant alteration was detected in the serotonergic marker tryptophan-hydroxylase and the catcholaminergic marker tyrosine-hydroxylase immunoreactive fiber densities in MDMA-offspring. The mothers exhibited reduced densities of serotonergic but not catecholaminergic fibers after the MDMA treatment. Our findings suggest that an intermittent prenatal MDMA exposure with an early first injection and a relatively low cumulative dose provokes mild but significant alterations in physical-physiological parameters and reduces motor skill learning in adulthood. In contrast, these adult offspring do not produce anxiety or depression like behavior.

Novel approach to demonstrate high efficacy of mu opioids in the rat vas deferens: a simple model of predictive value.

14-O-Methyloxymorphone and 14-methoxymetopon were reported as highly selective and potent micro opioid receptor agonists. The aim of this study was to demonstrate the opioid activity of these compounds in vitro and in vivo in comparison to oxymorphone, morphine and DAMGO. The micro opioid receptor efficacy, full or partial agonist nature of opioids was analyzed in the rat vas deferens (RVD) bioassay. Compared to oxymorphone, 14-O-methyloxymorphone and 14-methoxymetopon showed greater affinities to the rodent brain micro opioid receptors in receptor binding assays. In isolated organs 14-O-methyloxymorphone and 14-methoxymetopon were 3-10-fold more potent than the micro agonist opioid peptide, DAMGO. All tested compounds reached at least 70% maximum inhibition in mouse vas deferens (MVD) except morphine and oxymorphone. In the RVD, morphine could not exceed 50% inhibition of the twitches while 14-O-methyloxymorphone and 14-methoxymetopon showed inhibitory effects more than 70%. Oxymorphone reached only 4% maximal agonist effect and antagonized the inhibitory effect of DAMGO. The investigated morphinans produced dose-dependent antinociceptive activities in mice and rats. Both, 14-O-methyloxymorphone and 14-methoxymetopon are highly efficacious micro opioid receptor agonists in the RVD exhibiting full micro agonist properties. The RVD tissue contains mu receptors indicated by the comparable K(e) values of the micro antagonist naltrexone against DAMGO in the MVD. RVD may be a good alternative to assess the mu receptor efficacy of opioid agonists providing a more physiological environment for the ligand-receptor interaction than other efficacy measuring methods such as the [(35)S]GTPgammaS binding assay.

Peri, pre and postnatal morphine exposure: exposure-induced effects and sex differences in the behavioural consequences in rat offspring.

This study investigated the behavioural consequences of peri, pre and postnatal morphine (MO) exposure in rats. From gestational day 1 dams were treated with either saline or MO subcutaneously once a day (5 mg/kg on the first 2 days, 10 mg/kg subsequently). Spontaneous locomotor activity in a new environment (habituation) and antinociceptive effects of MO were measured separately in male and female pups after weaning and also in late adolescence or adulthood. The rewarding effect of MO was assessed by conditioned place preference in adult animals. Both exposure-induced and sex differences were observed. A significant delay in habituation to a new environment and decreased sensitivity to the antinociceptive effect of MO were found in male offspring of MO-treated dams. In contrast, the place preference induced by MO was enhanced in the MO-exposed adult animals and this effect was more marked in females. Prenatal exposure to MO resulted in more marked changes than the postnatal exposure through maternal milk. The results indicate that a medium MO dose administered once-daily results in long-term consequences in offspring and may make them more vulnerable to MO abuse in adulthood.