Pre- and postsynaptic alterations in the septohippocampal cholinergic innervations after prenatal exposure to drugs

Transgenerational influence of parental morphine exposure on pain perception, anxiety-like behavior and passive avoidance memory among male and female offspring of Wistar rats

Accumulating evidence suggests that epigenetic mechanisms play an important role in the formation and maintenance of memory within the brain. Moreover, the effect of parental drug-exposure before gestation on behavioral state of offspring has been little studied. The main objective of the current study is to evaluate the effect of parental morphine exposure on avoidance memory, morphine preference and anxiety-like behavior of offspring. The total of 32 males and 32 females were used for mating. The animals were treated with morphine. The offspring according to their parental morphine treatment was divided into four groups (n=16) including paternally treated, maternally treated, both of parents treated and naïve animals. The pain perception, anxiety-like behavior, and avoidance memory were evaluated in the offspring. In the current study, the total of 256 offspring was used for the experiments (4 tasks × 4 groups of offspring × 8 female offspring × 8 male offspring). The finding revealed that the avoidance memory and visceral pain were reduced significantly in male and female offspring with at least one morphine-treated parent. Moreover, anxiety-like behavior was reduced significantly in the male offspring with at least one morphine-treated parent. While anxiety-like behavior was increased significantly in female offspring that were treated by morphine either maternally or both of parents. The data revealed that the endogenous opioid system may be altered in the offspring of morphine-treated parent(s), and epigenetic role could be important. However, analysis of variance signified the important role of maternal inheritance.

Developmental opioid exposures: Neurobiological underpinnings, behavioral impacts, and policy implications

The devastating impact of opioid abuse and dependence on the individual, family, and society are well known but extremely difficult to combat. During pregnancy, opioid drugs and withdrawal also affect fetal brain development and newborn neural functions, in addition to maternal effects. Neonatal Abstinence Syndrome/Neonatal Opioid Withdrawal Syndrome (NAS/NOWS) rates have drastically increased in the US in the past decade. Solutions to this complex problem must be multi-faceted, which would be greatly enhanced by a translational, multidisciplinary understanding. Therefore, this mini-review incorporates biomedical, clinical, and policy aspects of opioid use during pregnancy. We review the known roles for endogenous opioids in mediating circuit formation and function in the developing brain, discuss how exogenous opioid drug use and addiction impact these processes in animal models and humans, and discuss the implications of these data on public policy. We suggest that some current policy initiatives produce unintended harm on both mothers and their children and delineate recommendations for how legislation could better contribute to addiction recovery and increase neural resilience in affected children.

Impact statement

Opioid abuse is a critical epidemic affecting individuals, families, and communities. This mini-review summarizes current literature on the impact of opioid drugs—including prescription pain relievers and illicit opioids—on neurobiological and neurobehavioral development. Using concepts related to the medical model of addiction as a brain disease, we review the public policy implications of these data and identify needs for future investigations.

Implication of protein kinase C of the left intermediate medial mesopallium in memory impairments induced by early prenatal morphine exposure in one-day old chicks

Previously we reported that prenatal morphine exposure during embryonic days 5-8 can cause cognitive deficits of one-trial passive avoidance learning (PAL) in one-day old chicks. Because protein kinase C (PKC) has been associated with memory capacity, we investigated the effects of prenatal morphine exposure on PKC isoforms expression in the left intermediate medial mesopallium (IMM) of chick brain at a time when memory tests were performed at 30, 120 and 360min respectively following training in PAL paradigm. We found that the level of PKCα in the membrane fractions in left IMM was decreased but that in the cytosol fractions showed a increased trend in prenatally morphine-exposed chicks with impaired long-term memory (120 and 360min). Moreover, the translocation of PKC δ from cytosol to membrane in left IMM was shown in prenatal morphine group which had significantly impaired long-term memory at 360min after training. Furthermore, there were no statistical differences between the two groups regarding the expressions of PKCα and PKC δ in the membrane fraction, although their levels in the cytosol fraction of prenatal morphine group which showed impaired intermediate-term memory at 30min after training, were quite different from that of prenatal saline group. Taken together, these results indicate that PKCα and PKC δ in the left IMM are differentially involved in the impairments of long-term memory induced by prenatal morphine exposure. Neither PKCα nor PKC δ in left IMM may be associated with the disruption of intermediate-term memory of chicks prenatally exposed to morphine.

Differences in morphine-induced antinociception in male and female offspring born of morphine exposed mothers

Objective:

Antinociceptive effect of morphine in offspring born of mothers that received saline or morphine during the gestation period was investigated.

Materials and Methods:

Wistar rats (200-250 g) received saline, morphine 0.5 mg/kg or 5 mg/kg during gestation days 14-16. All pups after weaning were isolated treatment/sex dependently and were allowed to fully mature. The antinociceptive effect of morphine was assessed in formalin test. Morphine (0.5-7.5 mg/kg) or saline (1 ml/kg) was injected intraperitoneally 10 min before formalin (50 μl of 2.5% solution in right hind-paw).

Results:

Male offspring born of saline-treated mothers were less morphine-sensitive than females. On the contrary, male offspring exposed prenatally to morphine (5 mg/kg) were more sensitive to morphine-induced antinociceptive response in formalin test. However, no difference in antinociceptive effect was observed amongst offspring of either sex born of mothers treated with morphine 0.5 mg/kg, identifying a lower dose effect of the opioid.

Conclusion:

The exposure to morphine during the developmental period may result in altered development of tolerance to morphine and thus involved in drug abuse.

Maternal choline supplementation improves spatial learning and adult hippocampal neurogenesis in the Ts65Dn mouse model of Down syndrome

In addition to intellectual disability, individuals with Down syndrome (DS) exhibit dementia by the third or fourth decade of life, due to the early onset of neuropathological changes typical of Alzheimer's disease (AD). Deficient ontogenetic neurogenesis contributes to the brain hypoplasia and hypocellularity evident in fetuses and children with DS. A murine model of DS and AD (the Ts65Dn mouse) exhibits key features of these disorders, notably deficient ontogenetic neurogenesis, degeneration of basal forebrain cholinergic neurons (BFCNs), and cognitive deficits. Adult hippocampal (HP) neurogenesis is also deficient in Ts65Dn mice and may contribute to the observed cognitive dysfunction. Herein, we demonstrate that supplementing the maternal diet with additional choline (approximately 4.5 times the amount in normal rodent chow) dramatically improved the performance of the adult trisomic offspring in a radial arm water maze task. Ts65Dn offspring of choline-supplemented dams performed significantly better than unsupplemented Ts65Dn mice. Furthermore, adult hippocampal neurogenesis was partially normalized in the maternal choline supplemented (MCS) trisomic offspring relative to their unsupplemented counterparts. A significant correlation was observed between adult hippocampal neurogenesis and performance in the water maze, suggesting that the increased neurogenesis seen in the supplemented trisomic mice contributed functionally to their improved spatial cognition. These findings suggest that supplementing the maternal diet with additional choline has significant translational potential for DS.

Maternal dietary loads of α-tocopherol differentially influence fear conditioning and spatial learning in adult offspring

α-Tocopherol, the main component of vitamin E, is well known to be a radical scavenger, so an increased intake of vitamin E is recommended in complicated pregnancy, to prevent possible fetus damage by free radical. In a previous work, we found that maternal α-tocopherol supplementation affects PKC-mediated cellular signaling and hippocampal synaptic plasticity in developing brain; the latter effect persists in adulthood. Here, adult rats maternally exposed to supranutritional doses of α-tocopherol were evaluated for Contextual Fear Conditioning and spatial learning in Morris Water Maze, two different hippocampus-dependent learning tasks. Moreover, anxiety, spontaneous activity, and explorative drive were also evaluated as factors potentially affecting learning performance. Treated rats showed a different behavior with respect to controls: performance in Contextual Fear Conditioning was improved, while spatial learning tested in Morris Water Maze, was impaired. The improvement of fear response was not ascribable to differences in anxiety level and/or spontaneous activity; thus it appears to be a specific effect of α-tocopherol overloading during brain development. On the contrary, the impaired performance in Morris Water Maze exhibited by treated rats can be in part explained by their enhanced explorative drive. Although extrapolation from rats to humans is difficult, a caveat in assuming supranutritional doses of vitamin E in pregnancy arises from this study.

Survival, differentiation, and reversal of heroin neurobehavioral teratogenicity in mice by transplanted neural stem cells derived from embryonic stem cells

Cell therapies in animal models of neurobehavioral defects are normally derived from neural stem cells (NSC) of the developing cortex. However, the clinical feasibility of NSC therapies would be greatly improved by deriving transplanted cells and from a tissue culture source that is self-renewing, containing cells that potentially differentiate into the desired neuronal phenotypes. These cultures can be engineered to contain the appropriate factors to support their therapeutic action and likely evoke lesser immune reactions. In the current study, we employed our model of mice neurobehaviorally impaired via prenatal exposure to heroin, to test the therapeutic efficacy of NSC derived from murine embryonic stem cells culture (ESC). The culture contained elongated bipolar cells, 90% of which are positive for nestin, the intermediate filament protein found in neural precursors. After removal of growth factors, the NSC differentiated into neurons (34.0% +/- 3.8% NF-160 positive), including cholinergic cells (ChAT positive), oligodendrocytes (29.9% +/- 4.2% O(4)), and astrocytes (36.1% +/- 4.7% GFAP positive). Reverse transcriptase polymerase chain reaction (RT-PCR) analysis confirmed the immunocytochemical findings. Mice made deficient in Morris maze behavior by prenatal heroin exposure (10 mg/kg heroin s.c. on gestational days 9-18) were transplanted into the hippocampus region on postnatal day 35 with the ES culture-derived NSC (ES-NSC) labeled with dialkylcarbocyanine (Dil) cell tracker. Dil+ and NF160+ cells were detected in the hippocampal region (50% +/- 8% survival). The transplantation completely restored maze performance to normal; e.g., on day 3, transplantation improved the behavior from the deficient level of 11.9-sec latency to the control of 5.6-sec latency (44.5% improvement).

A mechanism-based complementary screening approach for the amelioration and reversal of neurobehavioral teratogenicity

The identification of mechanisms and outcomes for neurobehavioral teratogenesis is critical to our ability to develop therapies to ameliorate or reverse the deleterious effects of exposure to developmental neurotoxicants. We established mechanistically-based complementary models for the study of cholinergic systems in the mouse and the chick, using both environmental neurotoxicants (chlorpyrifos, perfluoroalkyls) and drugs of abuse (heroin, nicotine, PCP). Behavioral evaluations were made using the Morris maze in the mouse, evaluating visuospatial memory related to hippocampal cholinergic systems, and imprinting in the chick, examining behavior dependent on cholinergic innervation of the IMHV. In both models we demonstrated the dependence of neurobehavioral deficits on impairment of cholinergic receptor-induced expression, and translocation of specific PKC isoforms. Understanding this mechanism, we were able to reverse both the synaptic and behavioral deficits with administration of neural progenitors. We discuss the prospects for clinical application of neural progenitor therapy, emphasizing protocols for reducing or eliminating immunologic rejection, as well as minimizing invasiveness of procedures through development of intravenous administration protocols.

Transplantation of neural progenitors enhances production of endogenous cells in the impaired brain

Grafting of neural progenitors has been shown to reverse a wide variety of neurobehavioral defects. While their role of replacing injured cells and restoring damaged circuitries has been shown, it is widely accepted that this cannot be the only mechanism, as therapy can occur even when an insufficient number of transplanted cells are found. We hypothesized that one major mechanism by which transplanted neural progenitors exert their therapeutic effect is by enhancing endogenous cells production. Consequently, in an allographic model of transplantation, prenatally heroin-exposed genetically heterogeneous (HS) mice were made defective in their hippocampal neurobehavioral function by exposing their mothers to heroin (10 mg kg(-1) heroin on gestation days 9-18). Hippocampal damage was confirmed by deficient performance in the Morris maze (P<0.009), and decreased production of endogenous cells in the dentate gyrus by 39% was observed. On postnatal day 35, they received an HS-derived neural progenitors transplant followed by repeated bromodeoxyuridine injections. The transplant returned endogenous cells production to normal levels (P<0.006) and reversed the behavioral defects (P<0.03), despite the fact that only 0.0334% of the transplanted neural progenitors survived and that they differentiated mainly to astrocytes. An immunological study demonstrated the presence of macrophages and T cells as a possible explanation for the paucity of the transplanted cells. This study suggests one mechanism for the therapeutic action of neural progenitors, the enhancement of the production of endogenous cells, pointing to future clinical applications in this direction by use of neural progenitors or by analogous cell-inducing techniques.

Reversal of heroin neurobehavioral teratogenicity by grafting of neural progenitors

A major objective in identifying the mechanisms underlying neurobehavioral teratogenicity in an animal model is the possibility of designing therapies that reverse or offset teratogen-induced neural damage. In our previous studies, we identified deficits in hippocampal muscarinic cholinergic receptor-induced translocation of protein kinase C (PKC) gamma as the likely central factor responsible for the adverse behavioral effects of pre-natal heroin exposure. Neural progenitors (NP) have the ability to recover behavioral deficits after focal hippocampal damage. Therefore, we explored whether behavioral and synaptic defects could be reversed in adulthood by neural progenitor grafting. Pregnant mice were injected daily with 10 mg/kg of heroin on gestational days 9-18. In adulthood, offspring showed deficits in the Morris maze, a behavior dependent on the integrity of septohippocampal cholinergic synaptic function, along with the loss of the PKCgamma and PKCbetaII responses to cholinergic stimulation. Mice that were exposed pre-natally to heroin and vehicle control mice were then grafted in adulthood with NP. Importantly, most grafted cells differentiated to astrocytes. NP reversed the behavioral deficits (p = 0.0043) and restored the normal response of hippocampal PKCgamma and PKCbetaII (p = 0.0337 and p = 0.0265 respectively) to cholinergic receptor stimulation. The effects were specific as the PKCalpha isoform, which is unrelated to the behavioral deficits, showed almost no changes. Neural progenitor grafting thus offers an animal model for reversing neurobehavioral deficits originating in septohippocampal cholinergic defects elicited by pre-natal exposure to insults.

Effect of parental morphine addiction on hippocampal long-term potentiation in rats offspring

Attention to addiction of women alone for fetus and infant's health has caused the possible role of father's status was less considered, while some developmental impairments including decrease of liter size, weight loss, congenital deficiencies, behavioral disorders, and learning and memory impairments in offspring with addicted father have been reported. In this study the effects of addiction of one or both parents to morphine on male and female offspring hippocampal long-term potentiation (LTP), were assessed. One hundred twenty female and 48 male rats (4-5 months, 250-270 g) were used. Forty females and 16 males were addicted by oral administration of morphine (32 mg/kg twice daily) for 5 days before mating. Then each two males with five females were housed (coupled) per cage as five groups for coupling: (A) addicted females+5% dextrose males (add.F); (B) addicted males+5% dextrose females (add.M); (C) addicted females+addicted males (add.MF); (D) 5% dextrose females+intact males (dex.F); (E) 5% dextrose males+intact females (dex.M). In puberty offspring LTP was induced in hippocampal dentate gyrus by stimulation of perforant path (pp). Changes of population spikes (PS) amplitude and LTP slope at 0, 5, 30, 60 and 120 min were evaluated. Slope of LTP at 30, 60 and 120 min, and amplitude of PS at 60 and 120 min in add.F and add.M offspring were significantly lower than dextrose groups (P<0.01). LTP slope and PS amplitude of male and female offspring did not different between add.F and add.M groups. Our results suggest that both parental and paternal addiction to morphine may cause memory deficiency through reduction of LTP in hippocampus.

Mechanism-Based Approaches for the Reversal of Drug Neurobehavioral Teratogenicity

Understanding the mechanism of neurobehavioral teratogenicity is the primary prerequisite for reversal of the defect. Progress in such studies can be best achieved if the investigation focuses on behaviors related to a specific brain region and innervation. Our model focused on teratogen-induced deficits in hippocampus-related eight-arm and Morris maze behaviors. Different "cholinergic" teratogens, mainly heroin, induced both pre- and postsynaptic hyperactivity in the hippocampal cholinergic innervation that terminated in desensitization of Protein Kinase C (PKC) isoforms to cholinergic receptor stimulation. Understanding this mechanism enabled its reversal with a pharmacological therapy-nicotine infusion. Studies by others provided similar findings by targeting the deficits respective to the model investigated. Consistently, destruction of the A10-septal dopaminergic pathways that downregulate the septohippocampal cholinergic innervation ameliorated maze performance. Grafting of embryonic differentiated cholinergic cells or neural progenitors similarly reversed the biochemical/molecular alterations and the resulting deficits. Reversal therapies offer a model for the understanding of neurobehavioral teratogenicity and, clinically, offer a model for potential treatment of these deficits. Whereas neural progenitor grafting appears to be the most effective treatment, pharmacological reversal with nicotine infusion seems to possess the most feasible and immediate therapy for neurobehavioral birth defects produced by various teratogens, including drugs. This is true even though the effect of pharmacological therapies is diffuse, affecting multiple areas of the brain. "Everybody is talking about the weather but nobody does anything about it." (Mark Twain).

Critical prenatal and postnatal periods for persistent effects of dexamethasone on serotonergic and dopaminergic systems

Glucocorticoid administration to preterm infants is associated with neurodevelopmental disorders. We treated developing rats with dexamethasone (Dex) at 0.05, 0.2, or 0.8 mg/kg, doses below or spanning the range in clinical use, testing the effects of administration during three different stages: gestational days 17-19, postnatal days 1-3 or postnatal days 7-9. In adulthood, we assessed the impact on synaptic biomarkers for serotonin (5-hydroxytryptamine (5HT)) systems. Across all three regimens, Dex administration evoked upregulation of cerebrocortical 5HT1A and 5HT2 receptors and the presynaptic 5HT transporter, greatest for 5HT1A receptors. The effects were fully evident even at the lowest dose. In contrast, 5HT levels in the cerebral cortex and hippocampus showed disparate patterns of temporal sensitivity, with no change after gestational treatment, an increase with the early postnatal regimen, and a decrease with the later postnatal exposure. None of the changes in 5HT concentrations were offset by adaptive changes in the fractional 5HT turnover rate. Furthermore, the critical period of sensitivity seen for 5HT levels differed from that of dopamine even within the same brain region. These findings suggest that developmental exposure to Dex during the critical neurodevelopmental period corresponding to its use in preterm infants, elicits selective changes in 5HT and dopaminergic synaptic function over and above its effects on general aspects of neural cell development, below the threshold for somatic growth impairment, and even at doses below those used clinically. Accordingly, adverse neurobehavioral consequences may be inescapable in glucocorticoid therapy of preterm infants.

Disruption of the development of cholinergic-induced translocation/activation of PKC isoforms after prenatal heroin exposure

Prenatal exposure of mice to heroin resulted in behavioral deficits present at adulthood, and related to septohippocampal cholinergic innervation accompanied by both pre- and postsynaptic cholinergic hyperactivity; including an increase in membrane PKC activity, and a desensitization of PKC to cholinergic input, which correlated highly with the behavioral performance, and was reversed by cholinergic grafting. The effect was shown in the behaviorally relevant PKCgamma and beta whereas the less behaviorally relevant PKCalpha isoform was not affected. The present study was designed to establish the effect of heroin exposure on the expression of the PKC isoforms level and on the more functionally relevant cholinergic translocation/activation of the isoforms throughout postnatal development. The hippocampi of mice pups, exposed to heroin transplacentally, were assayed after incubation with carbachol for PKC isoforms on postnatal days (PN) 1, 7, 14, 21, 30 and 50. Prenatal heroin exposure increased basal PKCgamma, beta and alpha levels. PKCgamma and alpha levels returned to control levels on PN50. While in PKCbeta, this increase lasted until PN50. Translocation/activation of the PKC isoforms gamma and beta by cholinergic receptor stimulation was present from PN1, concurrent with the presence of the isoforms. Prenatal exposure to heroin completely abolished the translocation/activation throughout the entire postnatal development. This defect was shown from the very beginning, PN1, the day when the PKC isoforms appear. The results suggest that the PKCgamma and beta isoforms are functional concurrent with their developmental appearance. Unlike findings on some other teratogens, the prenatal heroin effect on the isoforms function is similar throughout postnatal development.

Alterations in central nervous system serotonergic and dopaminergic synaptic activity in adulthood after prenatal or neonatal chlorpyrifos exposure

Exposure to chlorpyrifos (CPF) alters neuronal development of serotonin (5HT) and dopamine systems, and we recently found long-term alterations in behaviors related to 5HT function. To characterize the synaptic mechanisms underlying these effects, we exposed developing rats to CPF regimens below the threshold for systemic toxicity, in three treatment windows: gestational days (GD) 17-20, postnatal days (PN) 1-4, or PN11-14. In early adulthood (PN60), we assessed basal neurotransmitter content and synaptic activity (turnover) in brain regions containing the major 5HT and dopamine projections. CPF exposure on GD17-20 or PN1-4 evoked long-term increases in 5HT turnover across multiple regions; the effects were not secondary to changes in neurotransmitter content, which was unaffected or even decreased. When the treatment window was shifted to PN11-14, there were no long-term effects. Dopamine turnover also showed significant increases after CPF exposure on GD17-20, but only when the dose was raised above the threshold for overt toxicity; however, hippocampal dopamine content was profoundly subnormal after exposures below or above the acute, toxic threshold, suggesting outright neurotoxicity. These results indicate that, in a critical developmental period, apparently nontoxic exposures to CPF produce lasting activation of 5HT systems in association with 5HT-associated behavioral anomalies.

Altered localization of choline transporter sites in the mouse hippocampus after prenatal heroin exposure

Prenatal heroin exposure disrupts hippocampal cholinergic synaptic function and related behaviors. Biochemical studies indicate an increase in the number of presynaptic high-affinity choline transporter (HACT) sites, as assessed by [3H]hemicholinium-3 (HC-3) binding. The present study was designed to assess whether this effect involves global upregulation of the transporter, or whether disruption occurs with a specific tempero-spatial distribution. Pregnant mice were given 10mg/kg per day of heroin subcutaneously on gestational days (GD) 9-18. Autoradiographic distribution of HC-3 binding sites was evaluated in the hippocampus of the offspring at postnatal days 15, 25, and 53. These results, suggestive of hippocampal "miswiring," are likely to explain the net impairment of cholinergic synaptic function after prenatal heroin exposure, despite the simultaneous upregulation of both presynaptic cholinergic activity and postsynaptic receptors. Understanding the subregional selectivity of hippocampal defects can lead to the development of strategies that may potentially enable therapeutic interventions to offset or reverse the neurobehavioral defects.

Prenatal heroin exposure alters cholinergic receptor stimulated activation of the PKCβII and PKCγ isoforms

Prenatal exposure of mice to heroin (SC injection of 10mg/kg to the dams on gestational days 9-18) resulted at adulthood in behavioral deficits related to septohippocampal cholinergic innervation accompanied with both presynaptic and postsynaptic cholinergic hyperactivity; including an increase membrane PKC activity, and a desensitization of PKC to cholinergic input which were highly correlated with the behavioral performance and were reversed by cholinergic grafting. Therefore, we studied the receptor induced activation of the behaviorally relevant PKCgamma and PKCbetaII isoforms and the less behaviorally relevant PKCalpha isoform. Time course studies revealed peak translocation after 40 min incubation with carbachol for PKCgamma (110% increase from basal, i.e. no carbachol level, P < 0.01), 30 min for phosphorylated PKCbetaII (130%, P < 0.05) and 5 min for non-phosphorylated PKCbetaII (64%, P < 0.05) with no peak for alpha. Prenatal heroin abolished the translocation of PKCgamma and PKCbetaII while PKCalpha remained unaffected. A decrease occurred in basal phosphorylated membrane (-45%, P < 0.01) and cytosol-associated (-29%, P < 0.01) PKCbetaII, in membrane-associated non-phosphorylated PKCbetaII (-32%, P < 0.01) and PKCgamma (-25%, P < 0.01) and in cytosolic PKCalpha (-27%, P < 0.01), while membrane-associated PKCalpha was slightly increased (11%, P < 0.05). The results suggest that prenatal heroin disrupts cholinergic receptor induced PKC translocation and activation with the underlying mechanism of neuroteratogenicity potentially lying in the PKCgamma and PKCbetaII, while PKCalpha remains unaffected.

The sea urchin embryo as a model for mammalian developmental neurotoxicity: ontogenesis of the high-affinity choline transporter and its role in cholinergic trophic activity

Embryonic development in the sea urchin requires trophic actions of the same neurotransmitters that participate in mammalian brain assembly. We evaluated the development of the high-affinity choline transporter, which controls acetylcholine synthesis. A variety of developmental neurotoxicants affect this transporter in mammalian brain. [3H]Hemicholinium-3 binding to the transporter was found in the cell membrane fraction at stages from the unfertilized egg to pluteus, with a binding affinity comparable with that seen in mammalian brain. Over the course of development, the concentration of transporter sites rose more than 3-fold, achieving concentrations comparable with those of cholinergically enriched mammalian brain regions. Dimethylaminoethanol (DMAE), a competitive inhibitor of choline transport, elicited dysmorphology beginning at the mid-blastula stage, with anomalies beginning progressively later as the concentration of DMAE was lowered. Pretreatment, cotreatment, or delayed treatment with acetylcholine or choline prevented the adverse effects of DMAE. Because acetylcholine was protective at a lower threshold, the DMAE-induced defects were most likely mediated by its effects on acetylcholine synthesis. Transient removal of the hyaline layer enabled a charged transport inhibitor, hemicholinium-3, to penetrate sufficiently to elicit similar anomalies, which were again prevented by acetylcholine or choline. These results indicate that the developing sea urchin possesses a high-affinity choline transporter analogous to that found in the mammalian brain, and, as in mammals, the functioning of this transporter plays a key role in the developmental, trophic activity of acetylcholine. The sea urchin model may thus be useful in high-throughput screening of suspected developmental neurotoxicants.

Heroin neuroteratogenicity: delayed-onset deficits in catecholaminergic synaptic activity

Prenatal heroin exposure evokes neurochemical and behavioral deficits that, in part, reflect disruption of septohippocampal cholinergic function. In earlier studies, we found that cholinergic synaptic defects involve primary changes in cell signaling proteins that are shared by other transmitter systems. In the current study, we determined whether heroin also targets noradrenergic and dopaminergic inputs that operate through the same signaling cascades. Mice exposed to prenatal heroin showed significant deficits in norepinephrine and dopamine levels and much more pronounced effects on neurotransmitter turnover, an index of synaptic activity. Adverse effects were not present in the immediate postnatal period but rather emerged just before weaning and worsened subsequently. By young adulthood, the most highly-affected regions (hippocampus, cerebral cortex) displayed almost complete inactivation of noradrenergic and dopaminergic tonic activity. These effects arise after prior deficits in cell signaling are discernible, suggesting that the presynaptic effects are secondary to actions on signal transduction cascades shared by numerous neurotransmitter inputs and targeted by other neuroteratogens. These results may explain why apparently unrelated developmental neurotoxicants may ultimately produce a common set of neurochemical and behavioral anomalies.

Long-lasting CNS effects of a short-term chemical knockout of ornithine decarboxylase during development: nicotinic cholinergic receptor upregulation and subtle macromolecular changes in adulthood

Ornithine decarboxylase (ODC) and the polyamines play an essential role in brain cell replication and differentiation and polyamines also regulate the function of nicotinic acetylcholine receptors (nAChRs). We administered alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ODC, to neonatal rats on postnatal days 5-12, during the mitotic peak of the cerebellum, a treatment regimen that achieves a chemical knockout of ODC activity and polyamine depletion limited to the treatment period. Although growth inhibition and gross dysmorphology were limited to the cerebellum, both alpha7 and alpha4beta2 nAChRs were upregulated in adulthood in the frontal cortex, hippocampus and thalamus, with the largest effect in the latter region, primarily in females. Receptor upregulation was accompanied by abnormalities in macromolecular indices of cell packing density and cell membrane surface area, but the generalized cellular alterations did not share the regional or sex selectivity shown by the effects on nAChRs. Elevated DNA concentration was most notable in the hippocampus and was associated with augmented levels of glial fibrillary acidic protein, thus implying gliosis as the cause of the increased number of cells. DFMO's effects on both nAChR expression and cellular biomarkers resembled those of developmental exposure to nicotine. Accordingly, some of the effects may represent a specific alteration in nAChR signaling evoked by polyamine depletion during a critical developmental window. Alterations in polyamine gating of cholinergic synaptic signaling may thus contribute to the adverse neurobehavioral effects of numerous neuroteratogens that directly or indirectly disrupt the ODC/polyamine pathway.

Alterations in PKCgamma in the mouse hippocampus after prenatal exposure to heroin: a link from cell signaling to behavioral outcome

Administration of heroin to pregnant mice evokes neurochemical and behavioral deficits consequent to disruption of septohippocampal cholinergic innervation, notably involving desensitization of the ability of cholinergic receptors to activate PKC activity. The present study further evaluates whether desensitization occurs specifically for the PKCgamma isoform, the behaviorally relevant subtype, as compared to PKCalpha. Mice were exposed transplacentally to heroin on gestational days (GD) 9-18 via s.c. maternal injections (10 mg/kg per day). In young adulthood (50 days old), control offspring showed an increase in hippocampal cell membrane PKCgamma after incubation with the muscarinic cholinergic receptor agonist, carbachol, indicative of translocation from the cytosol. Prenatal exposure to heroin eliminated this response, whereas basal PKCgamma levels were unchanged. In contrast, PKCalpha, which is not related to heroin-induced behavioral deficits, did not show a loss of response. The present findings strongly point to abnormalities in the responsiveness of PKCgamma as a mechanism underlying the neurobehavioral teratogenicity of heroin.

Cell signaling as a target and underlying mechanism for neurobehavioral teratogenesis

A wide variety of drugs and chemicals elicit neurobehavioral teratogenesis. Surprisingly, however, despite the obvious differences among unrelated compounds, the behavioral outcomes often display striking similarities, such as cognitive and attentional deficits. Recent studies of drugs of abuse (heroin, nicotine, barbiturates) and environmental toxins (environmental tobacco smoke, pesticides, metals) suggest that, regardless of the originating mechanism for perturbation of brain development, disparate neuroteratogens converge downstream on common families of alterations, characterized by changes in the expression and/or activity of the cell-signaling molecules that are essential to neuronal differentiation and synaptic communication. Identification of these common targets may help in the design of pharmacologic interventions that, administered in adulthood, can reverse the impact of exposure to neurobehavioral teratogens.

The effects of antiepileptic drugs on spatial learning and hippocampal protein kinase C gamma in immature rats

This study was conducted to determine if alterations in hippocampal protein kinase C (PKC) gamma is one of the cellular mechanisms by which conventional antiepileptic drugs affect learning and memory. Wistar Rats (21-day-old) were divided into five groups: (1) control (no training and drugs); (2) training group (no drugs); (3) phenobarbital (PB) group; (4) carbamazepine (CBZ) group; and (5) valproate (VPA) group. A hippocampus dependent learning task (spatial changing learning) was used in the latter four groups lasting a total of 10 days. Correct responding rate of training group was significantly higher (P < 0.05) than in the PB, CBZ and VPA group. The PKC gamma staining intensity in hippocampal CA1-2 region of training group was significant greater than that of the control and PB group. There was no difference in staining intensities between the CBZ, VPA group or training group. The amount of PKC gamma located in plasma membrane of hippocampal neurons was significantly higher in the training group (P < 0.05) than the control, PB and VPA groups. No differences were found between the training and CBZ group. Lastly, the amount of PKC gamma in cytosol of hippocampus did not significantly differ between any of the five groups. These results indicate that the three antiepileptic drugs used in this study all disturbed the spatial learning of immature rats. Spatial learning was concomitant with activation of PKC gamma in hippocampal neurons. PB and VPA likely adversely affect learning and memory by interfering with PKC gamma activation, whereas CBZ may act by a different mechanism, possibly in the post-translocation process or by a PKC gamma independent pathway.

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.

Heroin neuroteratogenicity: targeting adenylyl cyclase as an underlying biochemical mechanism

Prenatal heroin exposure evokes neurochemical and behavioral deficits that in part, reflect disruption of septohippocampal cholinergic function. In earlier studies, we found that cholinergic synaptic defects involve changes in proteins, like protein kinase C, that are essential to receptor-mediated signaling. In the current study, we determined whether heroin targets another signaling protein, adenylyl cyclase (AC), which regulates the production of cAMP. Mice exposed to prenatal heroin showed subsequent postnatal elevations of AC activity that lasted into adulthood. The effect was most robust with stimulants that activate AC directly (forskolin, Mn(2+)), indicating increased expression of AC itself; we also identified shifts in catalytic properties suggestive of a change in the AC isoform. Superimposed on the overall induction of AC, there were transient deficits in the responses to stimulants working through G-proteins (NaF) or G-protein coupled receptors (isoproterenol, a beta-adrenoceptor agonist), indicating alterations at other steps in the signaling pathway. Effects on the regulation of AC activity were seen in brain regions with widely disparate maturational timetables and also occurred in regions, like the cerebellum, that are sparse in cholinergic input. These results suggest that the expression and/or function of signaling proteins distal to neurotransmitter receptors represent a major target for neurobehavioral teratogenesis by heroin; the fact that these targets are shared by otherwise unrelated neuroteratogens may account for a common set of neurochemical and behavioral anomalies in response to prenatal exposure to drugs or environmental chemicals.

Neural grafting reverses prenatal drug-induced alterations in hippocampal PKC and related behavioral deficits

Administration of heroin or phenobarbital to pregnant mice evokes neurochemical and behavioral deficits consequent to disruption of septohippocampal cholinergic innervation. The present study evaluates the relationship between the drug-induced biochemical changes and the behavioral deficits, applying two different approaches: neural grafting and within-individual correlations of biochemistry and behavior. Mice were exposed transplacentally to phenobarbital or heroin on gestational days 9-18 and tested in adulthood. Drug-exposed mice displayed impaired radial arm maze performance, increases in presynaptic choline transporter sites (monitored with [(3)H]hemicholinium-3 binding), upregulation of membrane-associated protein kinase C (PKC) activity, and desensitization of the PKC response to a cholinergic agonist, carbachol. Grafting of cholinergic cells to the impaired hippocampus reversed the behavioral deficits nearly completely and restored basal PKC activity and the PKC response to carbachol to normal; the drug effects on hemicholinium-3 binding were also slightly obtunded by neural grafting, but nevertheless remained significantly elevated. There were significant correlations between the performance in the eight-arm maze and both basal PKC activity and PKC desensitization, and to a lesser extent, between behavioral performance and hemicholinium-3 binding. Taken together, these findings indicate an inextricable link between the biochemical effects of prenatal drug exposure on the PKC signaling cascade and adverse behavioral outcomes. The ability of neural grafting to reverse both the drug-induced changes in PKC and behaviors linked to septohippocampal cholinergic function suggest a mechanistic link between this signaling pathway and neurobehavioral teratology caused by heroin or phenobarbital.

The relationship between neural alterations and behavioral deficits after prenatal exposure to heroin

The present studies employ multitudinous approaches in order to overcome the methodological obstacles in the understanding of the relationship between neurochemical alterations and behavioral deficits induced by heroin during prenatal development. Mice were exposed prenatally to heroin via daily subcutaneous injections of 10 mg/kg, on gestation days 9-18. At age 50 days, the heroin-exposed offspring displayed behavioral deficits as assessed in the eight-arm and Morris mazes, pointing to possible alteration in the septohippocampal cholinergic innervations. Biochemically there was increased presynaptic activity of these innervations as attested to by the increased [3H]hemicholinium-3 (HC-3) binding sites and by K+-stimulated inositol phosphate (IP) formation. Postsynaptically, there was global hyperactivation along the different components of the nerve conduction cascade, including an increase in M1 muscarinic receptor Bmax, a general increase in G-proteins (GP) including the most relevant, G subtype, and an increase in IP formation and in basal protein kinase C (PKC) activity. However, there was desensitization of PKC activity in response to cholinergic agonist in the heroin-exposed offspring. Transplantation of normal embryonic cholinergic cells to the impaired hippocampus reversed the behavioral deficits and both the pre- and postsynaptic hyperactivity and resensitized PKC activity. To support and further strengthen the findings of the neural grafting study, correlation of the heroin-induced behavioral deficits with the biochemical alterations, done within individuals, was applied. The results showed high r values for IP formation, basal PKC, and PKC desensitization. The r values for HC-3 binding were statistically significant but relatively low. Taken together, the findings of the neural grafting and correlation studies bring us closer to understanding the relationship between the prenatal heroin-induced biochemical and behavioral changes. However, mammalian models possess the inherent methodological hindrances, stemming from possible maternal effects. To provide a control for these confounding variables, a chick embryo model was applied in which filial imprinting, a behavior related to a specific hyperstriatal nucleus, served as an endpoint. Heroin was administered to developing chick embryos by injecting the eggs (20 mg/kg) on incubation days (ID) 0 or 5. Prehatch exposure to heroin markedly diminished the ability for filial imprinting in the hatched chicks.