Prenatal morphine exposure alters ovarian steroid hormonal regulation of seizure susceptibility

Stimulatory and inhibitory effects of morphine on pentylenetetrazol-induced epileptic activity in rat

AIMS

The present study attempts to evaluate the effects of different doses of morphine on experimental epileptiform activity caused by pentylenetetrazol (PTZ) in rats.

METHODS

Thirty adult male rats were assigned to saline (n = 5), morphine (2, 5, and 10 mg/kg, n = 15), naloxone (1 mg/kg, n = 5), and pre-treated with naloxone+morphine (1 + 10 mg/kg, n = 5) groups. The animals were anesthetized with ketamine + xylazine (80 + 8 mg/kg), and then a bipolar electrode was implanted into the CA1 (AP: -2.76 mm, ML: -1.4 mm and DV: 3 mm). To evaluate the effects of drugs on spike count and their amplitudes by elab amplifier, after drug administration for 25 min, PTZ (80 mg/kg, i.p.) was injected to induce epileptiform activity. Finally, diazepam (10 mg/kg) was used to suppress epileptic activity.

RESULTS

The results revealed that morphine at a dose of 2 mg/kg decreased, and at doses of 5 and 10 mg/kg had an increasing effect on seizure-like events (SLEs). Nevertheless, morphine at a dose of 10 mg/kg enhanced SLEs significantly (p < 0.01). Naloxone at a dose of 1 mg/kg had no significant effect on the spike count but increased amplitude of them (p < 0.001). Moreover, being pretreatment with naloxone at a dose of 1 mg/kg, the morphine group showed significantly increased in the spike count (p < 0.05).

CONCLUSIONS

Morphine has biphasic effects on PTZ-induced epileptiform activities that way at a low dose has an inhibitory effect, but if the dose is increased, it will intensify the desired event and that the stimulatory effects of morphine appear not to be via opioid receptors.

Acute and chronic effects of morphine on Low-Mg2+ ACSF-induced epileptiform activity during infancy in mice hippocampal slices

Interaction of morphine and seizure is complex. Mouse brain hippocampal slices were used to estimate how acute and chronic morphine treatment alters the low-magnesium artificial cerebrospinal fluid (LM-ACSF)-induced seizure activity. Hippocampal slices were taken from the normal and morphine-treated mice. The normal mice received saline while the other group (morphine-treated mice) received morphine daily for 5 consecutive days. Saline/morphine administration was performed subcutaneously (s.c, 0.1 mL) at postnatal days 14-18. Hippocampal slices of all animals were perfused with LM-ACSF followed by different morphine concentrations (0, 10, 100, and 1000 μM) or naloxone (10 μM). Changes in the spike count were considered as indices for quantifying the seizure activity in the slices. In hippocampus of both groups perfused with 10 or 1000 μM morphine, epileptiform activity was suppressed while it was potentiated at 100 μM morphine. The excitatory effect of morphine at 100 μM was stronger in normal mice (acute exposure) than in dependent mice (chronic exposure). Naloxone suppressed the epileptiform activities in both groups. Suppressive effect of naloxone was more significant in morphine-treated mice than in normal mice. The seizure activity in morphine-dependent mice was more labile than that of normal mice. It can be concluded that morphine had a biphasic effect on LM-ACSF-induced epileptiform activities in both groups. The occurrence of seizure was comparable in acute and chronic exposure of morphine but strength of the effect was considerably robust in normal mice. The down regulation of opioid receptors in chronic exposure is likely to be responsible for these differences.

Modeling prenatal opioid exposure in animals: Current findings and future directions

The past decade has seen a drastic rise in the number of infants exposed to opioids in utero. It is unclear what lasting effect this exposure may have on these children. Animal models of prenatal opioid exposure may provide insight into potential areas of vulnerability. The present review summarizes the findings across animal models of prenatal opioid exposure, including exposure to morphine, methadone, buprenorphine, and oxycodone. Details regarding the drug, doses, and duration of treatment, as well as key findings, are summarized in tables with associated references. Finally, significant gaps in the current preclinical literature and future directions are discussed.

Behavioral effects of perinatal opioid exposure

Opioids are among the world's oldest known drugs used mostly for pain relief, but recreational use is also widespread. A particularly important problem is opioid exposure in females, as their offspring can also be affected. Adverse intrauterine and postnatal environments can affect offspring development and may lead to various disabilities later in life. It is clear that repetitive painful experiences, such as randomly occurring invasive procedures during neonatal intensive care, can permanently alter neuronal and synaptic organization and therefore later behavior. At the same time, analgesic drugs can also be harmful, inducing neuronal apoptosis or withdrawal symptoms in the neonate and behavioral alterations in adulthood. Hence, risk-benefit ratios should be taken into consideration when pain relief is required during pregnancy or in neonates. Recreational use of opioids can also alter many aspects of life. Intrauterine opioid exposure has many toxic effects, inducing poor pregnancy outcomes due to underdevelopment, but it is believed that later negative consequences are more related to environmental factors such as a chaotic lifestyle and inadequate prenatal care. One of the crucial components is maternal care, which changes profoundly in addicted mothers. In substance-dependent mothers, pre- and postnatal care has special importance, and controlled treatment with a synthetic opioid (e.g., methadone) could be beneficial. We aimed to summarize and compare human and rodent data, as it is important to close the gap between scientific knowledge and societal policies. Special emphasis is given to gender differences in the sensitivity of offspring to perinatal opioid exposure.

Headache endocrinological aspects

In this chapter we review the current understanding of how hormones, neurohormones, and neurotransmitters participate in the pain modulation of primary headaches. Stressful conditions and hormones intimately implicated in headache neurobiology are also discussed. With the recent progress in neuroimaging techniques and the development of animal models to study headache mechanisms, the physiopathology of several of the primary headaches is starting to be better understood. Various clinical characteristics of the primary headaches, such as pain, autonomic disturbances, and behavioral changes, are linked to hypothalamic brainstem activation and hormonal influence. Headache is greatly influenced by the circadian circle. Over the millennia the nervous system has evolved to meet changing environmental conditions, including the light-dark cycle, in order to ensure survival and reproduction. The main elements for synchronization between internal biological events and the external environment are the pineal gland and its main secretory product, melatonin. Melatonin is believed to be a significant element in migraine and in other headache disorders, which has implications for treatment. A potential therapeutic use of melatonin has been considered in several headache syndromes. In short, primary headaches are strongly influenced by physiological hormonal fluctuations, when nociceptive and non-nociceptive pathways are differentially activated to modulate the perception of pain.

CNS Aspects of Prenatal Drug Exposure: Drugs of Abuse, Toxins, and Corticosteroids

Studies of the effects of prenatal exposure (to drugs or environmental factors) on postnatal brain morphology and function have an important role in assessing adverse effects of prenatal administration of corticosteroids in obstetrics, in studying the impairment of the offspring due to maternal drug abuse, as well as in studies of the influence of other environmental factors (such as toxins or stress). Timing, duration, and dose of the prenatal exposure play a significant role in the postnatal expression of the impact. However, data interpretation may be complicated by additional factors. As mixed litters of prenatally exposed subjects are evaluated, significant differences between males and females may occur. Additionally in females, cyclical changes in ovarian steroids may interfere with the effects of prenatal impact. Developmental differences may be also present, and data from infant, juvenile, prepubertal, and adult individuals cannot be simply compared. Finally, prenatal treatment is a stressful event and may present itself as prenatal stress, misguiding the interpretation. Postnatal environmental factors in raising the offspring, such as housing, maternal care, light-dark cycle, and weaning age can also change the data in such a way, which makes comparisons between different research laboratories impossible.

Actions at GABA(A) receptors in the hippocampus may mediate some antiseizure effects of progestins

Progestins can have antiseizure effects; however, the mechanisms and sites of action of these effects are not well-understood. Whether progesterone's actions at GABA(A) receptors in the hippocampus are important for its antiseizure effects was investigated. In Experiment 1, ovariectomized rats were administered sesame oil vehicle or a regimen of progesterone (500 microg sc, which produces physiological concentrations in plasma and the hippocampus), followed 2.5 hours later by administration of saline vehicle or a regimen of bicuculline (1 mg/kg, sc), a GABA(A) receptor antagonist, which does not produce any intrinsic effects on seizures. Progesterone, compared with vehicle, significantly increased the latency to, and decreased the number of, pentylenetetrazole-induced tonic seizures and increased GABA-stimulated chloride flux. Co-administration of bicuculline attenuated progesterone's antiseizure effects and decreased GABA-stimulated chloride flux in the hippocampus. Bicuculline did not alter ictal behavior compared with vehicle. In Experiment 2, ovariectomized rats were subcutaneously administered sesame oil or progesterone (500 microg), followed 2.5 hours later by bilateral infusions of bicuculline (100 ng) or vehicle (saline) into the hippocampus. Infusion of bicuculline into the hippocampus of progesterone-primed rats significantly increased ictal activity, compared with that induced by progesterone administration alone, but alone did not alter seizures compared with that produced by saline infusions into the hippocampus. These data suggest that actions of progesterone at GABA(A) receptors in the hippocampus are important for progesterone's antiseizure effects.

Attenuating 5alpha-pregnane-3alpha-ol-20-one formation in the hippocampus of female rats increases pentylenetetrazole-induced seizures

Progesterone has antiseizure effects, which may be due to the actions of its 5alpha-reduced metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP). Whether metabolism of progesterone to 3alpha,5alpha-THP in the hippocampus is essential for its antiseizure effects was investigated. In Experiment 1, ovariectomized rats were administered subcutaneous progesterone (500 microg) or vehicle (sesame oil), followed 1 hour later by subcutaneous administration of an inhibitor of the 5alpha-reductase enzyme, finasteride (50 mg/kg), or vehicle (90% sesame oil, 10% ethanol). Administration of progesterone increased the latency to, and decreased the number of, tonic seizures and increased hippocampal 3alpha,5alpha-THP levels, compared with vehicle. Administration of finasteride with progesterone attenuated progesterone's antiseizure effects and decreased levels of 3alpha,5alpha-THP in the hippocampus. Finasteride administration alone did not alter ictal behavior or 3alpha,5alpha-THP levels compared with vehicle. In Experiment 2, ovariectomized rats were administered subcutaneous progesterone (500 microg) or vehicle (sesame oil), followed 1 hour later by bilateral infusions of finasteride (10 microg) or vehicle (beta-cyclodextran) into the hippocampus. Administration of finasteride to the hippocampus of progesterone-primed rats significantly increased ictal activity and decreased hippocampal 3alpha,5alpha-THP levels, compared with progesterone administration alone. These data suggest that formation of 3alpha,5alpha-THP in the hippocampus is important for progesterone's antiseizure effects.

Effects of Seizures and Their Treatment on Fetal Brain

PURPOSE

To describe the effects of pregnancy on seizures, the effects of seizures during pregnancy on the fetus, and the effects of antiepileptic drugs (AEDs) on fetal brain and development.

METHODS

The available literature was reviewed and summarized.

RESULTS

There is a paucity of prospective studies. Retrospective studies indicate that, during pregnancy, alterations in seizure frequency can occur in an unpredictable fashion. Generalized tonic-clonic seizures may have adverse effects on the fetus. It is unclear whether complex partial seizures or absence seizures have negative consequences. AEDs may have potentially detrimental effects on the fetus and its subsequent development, but the full spectrum and clinical significance are under investigation. Monotherapy is strongly encouraged.

CONCLUSIONS

Dealing with the pregnant epileptic patient is a difficult and challenging task. Although there are several risks for the mother and the fetus, most epileptic women bear normal, healthy children.

Bicuculline seizure susceptibility and nigral GABAA alpha1 receptor mRNA is altered in adult prenatally morphine-exposed females

Prenatal morphine exposure (5-10 mg/kg twice daily on gestation days 11-18) can adversely affect neurological development, including seizure susceptibility. The present study examines the effects of prenatal morphine exposure on seizure susceptibility to the GABA antagonist and convulsant bicuculline and GABA(A) alpha(1) receptor mRNA in the substantia nigra (SN) of female rats. The results demonstrate that prenatally morphine-exposed ovariectomized (OVX) females and OVX females with estradiol benzoate (EB) replacement have an increased latency to seizure onset compared to controls. In addition, prenatal morphine exposure decreases the area covered by grains of GABA(A) alpha(1) receptor mRNA in the anterior SN in both OVX and EB+progesterone (P)-treated groups, and decreases the number of GABA(A) alpha(1) receptor mRNA-labeled cells/field in EB females. Furthermore, prenatally morphine- and saline-exposed EB and EB+P females had decreased GABA(A) alpha(1) receptor mRNA-labeled cells/field in the anterior SN compared to OVX animals of the same prenatal exposure. These results demonstrate that the long term effects of prenatal morphine exposure in female rats is dependent on their hormonal status, and suggest that seizure susceptibility may be altered via neuropharmacological changes in the GABA system in the SN.

Mu-opioid receptors in seizure-controlling brain structures are altered by prenatal morphine exposure and by male and female gonadal steroids in adult rats

The present study used autoradiography to examine the effect of prenatal morphine exposure on mu-opioid receptor density in epileptic seizure-controlling brain structures including the substantia nigra pars compacta (SNC), substantia nigra pars reticulata (SNR), superior colliculus (SC), and subthalamic nucleus (STN) of adult male and female rats. The results demonstrate that prenatal morphine exposure increases the mu-opioid receptor density in the SNC and STN, but not in the SNR or in the SC of gonadally intact adult male rats. The density of mu-opioid receptors in the SNC and STN is, however, decreased following gonadectomy in morphine-exposed males, and testosterone treatment fails to restore this decrease to the level of gonadally intact males. Further, in the SC, the density of mu receptors was lower in both saline-exposed, gonadectomized (GNX) and GNX, TP-treated males and in morphine-exposed, GNX, TP-treated males relative to gonadally intact saline- and morphine-exposed males, respectively. In ovariectomized (OVX) female rats, the same prenatal morphine exposure increases the mu-opioid receptor density in the SNC and SNR, but decreases it in the STN. The density of mu-opioid receptors is also decreased in the SNC and SC of OVX estrogen-treated females and in the SNR and SC of OVX, progesterone-treated females. Thus, the present study demonstrates that mu-opioid receptors in seizure-controlling brain structures are sex-specifically altered by prenatal morphine exposure in adult progeny. Further, prenatal morphine exposure alters gonadal hormone effects on the density of mu receptors in adult, OVX females.

Impact of maternal morphine and saline injections on behavioral responses to a cold water stressor in adult male and female progeny

The purpose of the present study was to test the effects of maternal morphine and saline injections on chronic cold water stress responses in three groups of adult male and female rats: prenatally morphine-exposed adult progeny, prenatally saline-exposed adult progeny, and control groups. All male rats were gonadally intact, and female rats were ovariectomized (OVX) in adulthood, and half of them were injected with estradiol benzoate (EB). All animals were exposed to a cold water stressor daily for 2 weeks and tested before (baseline) and after (stress effects) the chronic cold water stressor in a swim test and an open field test. In the swim test, both adult males and OVX, EB-treated adult females born to mothers injected with morphine or saline displayed more floating behavior during the swim test than their controls, both before and after the cold water stressor. Male rats exposed to morphine or saline prenatally also spent more time struggling during the swim tests than controls, and this was further increased after the cold water stressor. In the open field test, males and OVX, EB-treated females born to morphine- or saline-injected mothers were less active and displayed fewer rearings than controls. No differences were observed in OVX females as a result of prenatal injections. Thus, the present study demonstrates that maternal injections, regardless of injection content, induce long-lasting effects on stress responsiveness in adult progeny.

Prenatal morphine exposure decreases susceptibility of adult male rat offspring to bicuculline seizures

The purpose of this study was to investigate the effect of prenatal exposure to morphine (5-10 mg/kg twice daily on days 11-18 of gestation) on bicuculline seizure susceptibility and to examine the interaction of prenatal morphine exposure and hormonal background in adult male rats. The data demonstrate that prenatal morphine exposure does not affect clonic but decreases susceptibility to tonic-clonic bicuculline seizures in intact male rats. Thus, the present data support our previous work demonstrating alterations in seizure susceptibility of adult morphine-exposed animals.

Prenatal morphine exposure induces age- and sex-dependent changes in seizure susceptibility

1. Prenatal exposure to morphine induces long-term alterations in seizure susceptibility, which are age-, sex-, and seizure model-specific. 2. Adult male and female rats exposed prenatally to morphine show decreased susceptibility to GABA-regulated seizures. 3. Prenatally morphine-exposed, adult male rats are more sensitive to excitatory amino acid receptor-mediated seizures than control males, control females, or morphine-exposed females.

Estrogen differentially alters NMDA- and kainate-induced seizures in prenatally morphine- and saline-exposed adult female rats

The purpose of the present study was to investigate the effects of prenatal exposure to morphine on seizure susceptibility in adult female rats. Adult female rats, exposed to saline or morphine on prenatal days 11-18, were ovariectomized (OVX) and some were injected 48 h prior to seizure testing with estradiol benzoate (EB). To assess the latency to onset of stereotypy and seizures, females received systemic injections of N-methyl-D-aspartate (NMDA; 150, 175, 200 mg/kg) or kainic acid (KA; 10 or 15 mg/kg). Prenatal morphine exposure increased the latency to onset of wet-dog-shakes (WDS) in both OVX and OVX, EB-injected females after the higher dose of KA. However, prenatal morphine exposure increased the latency to onset of stereotypy only in OVX, EB-injected females after the highest dose of NMDA. Prenatal morphine exposure also increased the latency to onset of seizures after the lower dose of KA, but did not change the latency to onset of NMDA-induced seizures. Additionally, an EB injection increased the latency to onset of seizures in both saline- and morphine-exposed females after the lowest dose of NMDA, but decreased the latency to onset of seizures after the lower dose of KA. Thus, the present study demonstrates that prenatal morphine exposure has different effects on the estrogen regulation of the onset of seizures and stereotypy induced by NMDA or KA in adult, OVX female rats.

Neuroprotective effects of estrogens on hippocampal cells in adult female rats after status epilepticus

PURPOSE

Estrogens have neuroprotective effects in ischemia, stroke, and other conditions leading to neuronal cell death (e.g., Alzheimer's disease). The present study examined whether estrogens may have neuroprotective effects after seizures.

METHODS

The kainic acid model was used to determine if estrogens protect hippocampal cells after status epilepticus in adult female rats. Rats were ovariectomized 1 week before hormone replacement. beta-Estradiol benzoate (EB; 2 microg in 0.1 mL of oil) was injected subcutaneously 48 and 24 hours before seizure testing. We administered kainic acid (16 mg/kg intraperitoneally) and behaviorally monitored the rats for 5 hours. After this time, all rats were injected with pentobarbital (50 mg/kg intraperitoneally) irrespective of seizure severity. Some rats received two additional doses of EB, one immediately and one 24 hours after the seizures. Another group of rats received only these two doses of EB after the seizures, and yet another group of rats received pretreatment with the intracellular EB receptor antagonist tamoxifen before each of four EB injections. Control rats received oil instead of EB. Rats were killed 48 hours after seizures. Neuronal damage was evaluated in silver-impregnated and Nissl-stained sections.

RESULTS

Estrogen treatment before kainic acid administration significantly delayed the onset of kainic acid-induced clonic seizures, whereas it did not change the onset of status epilepticus compared with oil-treated controls. Furthermore, estrogen treatment significantly protected against kainic acid-induced seizure-related mortality. In control rats, examination of Nissl-stained and silver-impregnated slides revealed severe neuronal damage in the vulnerable pyramidal neurons of the hippocampal CA3 subfield and in the hilus of the dentate gyrus. Estrogen pretreatment, as well as the combination of pretreatment and posttreatment, significantly reduced the number of argyrophilic neurons in both the CA3 and the dentate gyrus. Posttreatment only had no protective effects. The data indicate that intracellular EB receptors mediate this type of neuroprotective effect, because the tamoxifen pretreatment abolished EB neuroprotection.

CONCLUSIONS

Our results suggest that estrogens can be beneficial in protecting against status epilepticus-induced hippocampal damage. Hormonal conditions may have differential effects on underlying epileptic state in some patients. Therefore, more studies are necessary to determine the prospective therapeutic advantage of hormonal treatment in seizure-related damage.

Prenatal morphine exposure alters susceptibility to bicuculline seizures in a sex- and age-specific manner

Bicuculline was used to investigate seizure susceptibility in pre- and peripubertal male and female rats exposed prenatally to morphine. Morphine-exposed males showed increased seizure susceptibility at prepubertal and decreased susceptibility at peripubertal ages. There was no difference in seizure susceptibility in morphine-exposed females at either age. Therefore, the present data suggest that males are more vulnerable than females to morphine-induced insults during prenatal brain development.

Estradiol facilitates kainic acid-induced, but not flurothyl-induced, behavioral seizure activity in adult female rats

PURPOSE

This study was designed to determine whether previously demonstrated increases in hippocampal axospinous synapse density and NMDA receptor function induced by estradiol are paralleled by increased susceptibility to limbic (kainic acid induced) or generalized (flurothyl induced) behavioral seizures.

METHODS

Kainic acid was injected systemically to ovariectomized adult female rats treated with either estradiol or oil vehicle. The latencies to each of five stages of seizure-related behaviors (staring, wet-dog shakes, head waving and chewing, forelimb clonus, rearing, and falling) were recorded for each animal. Flurothyl was administered by inhalation to ovariectomized adult female rats treated with estradiol alone, estradiol followed by short-term progesterone, or oil vehicle. The latencies to each of three stages of seizure-related behaviors (first myoclonic jerk, forelimb clonus, wild running and bouncing) were recorded for each animal.

RESULTS

Estradiol treatment decreased the latency to seizure-related behaviors induced by kainic acid, but neither estradiol alone nor estradiol followed by progesterone had any effect on flurothyl-induced seizure-related behaviors.

CONCLUSIONS

The same estradiol treatment paradigm known to induce structural and functional changes in the excitatory circuitry of the hippocampus facilitates the progression of kainic acid-induced seizures, which are known to involve the hippocampus, but has no effect on flurothyl-induced seizures. The lack of an effect of estradiol alone or estradiol followed by progesterone on flurothyl-induced seizures indicates that estradiol's effects on seizure susceptibility do not result from increased neuronal excitability throughout the brain, but rather involve action within the limbic system. The data suggest that structural and functional changes in hippocampal circuitry induced by estradiol may contribute to increased susceptibility to limbic seizure activity.

Enhanced susceptibility to cocaine- and pentylenetetrazol-induced seizures in prenatally cocaine-treated rats

We previously reported that prenatal cocaine exposure increased susceptibility to cocaine-induced seizures later in life. Here we examine whether this enhanced susceptibility to seizures generalizes to other chemoconvulsants, and whether postnatal cocaine treatment similarly increases susceptibility. Following prenatal cocaine treatment (40 mg/kg; E10-20), both male and female rats were more likely to seize to a dose of 30 mg/kg pentylenetetrazol (PTZ) at 2 months of age, although the severity of the seizures observed was increased only in females. Daily cocaine injections (10-20 mg/kg SC) during the first 10 days after birth also produced effects that were dependent on the sex of the animal. Postnatally cocaine-treated female rats showed no greater incidence of seizures in response to an acute high dose of cocaine, but did exhibit an increased susceptibility to cocaine-kindled seizures. Male, but not female, postnatally cocaine-treated rats were more susceptible to PTZ-induced seizures. The increased susceptibility to seizures induced by two different chemoconvulsants after prenatal cocaine treatment suggests that developmental cocaine exposure, particularly during the second trimester equivalent, alters the balance between excitation and inhibition in the brain.

Prenatal morphine exposure differentially alters seizure susceptibility in developing female rats

We examined the effect of prenatal morphine exposure (5-10 mg/kg on days 11-18 of gestation) on seizure susceptibility in female rats during development. The effect of morphine exposure on flurothyl-induced seizures was age-dependent. At postnatal day (PN) 15, morphine exposure decreased both clonic and tonic-clonic seizure thresholds compare to saline controls. At PN 25, morphine exposure did not alter the clonic seizure threshold but increased the threshold to tonic-clonic seizure. At PN 38, morphine exposure did not influence either threshold. The data suggest that the effects of prenatal exposure to opioids on seizures are age-related and transient.