Opiates, endorphins, and the developing organism: a comprehensive bibliography, 1982-1983

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.

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.

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.

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

The present study was designed to evaluate possible presynaptic and postsynaptic alterations in the hippocampal cholinergic innervations that account for the hippocampus-related behavioral deficits found after prenatal drug exposure. Mice were prenatally exposed to either phenobarbital or heroin. On postnatal day 50, the hippocampi were removed and protein kinase C (PkC) activity, the amounts of Gi, Go, and Gq guanosine 5'-triphosphate binding proteins (G-proteins), and choline transports were determined. Basal PkC activity was higher than control levels in both phenobarbital and heroin treated mice, by 41% and 35%, respectively. The increase of PkC activity in response to carbachol was impaired in both treatment groups: in control mice, membrane PkC activity in hippocampal slices increased by 40%-50%, while no such response, or even slight reduction in PkC activity, was observed in the drug-exposed offspring. A significant increase was found in Gi and Gq G-proteins (18%-21%) in mice exposed to phenobarbital or to heroin compared with control levels. The amount of choline transporters, determined by hemicholinium binding, increased by 70% compared with the control level in mice prenatally exposed to heroin, and increased by 71% in mice prenatally exposed to phenobarbital. The alterations in basal and carbachol-stimulated hippocampal PkC activity after prenatal drug exposure may be related to an impairment in long-term potentiation (LTP); which plays an important role in hippocampal related behavioral abilities, changes in which are caused by prenatal drug exposure.

Vicia villosa agglutinin labels a subset of neurons coexpressing both the mu opioid receptor and parvalbumin in the developing rat subiculum

Vicia villosa agglutinin (VVA), anti-parvalbumin antiserum and an affinity-purified anti-mu opioid receptor antibody were used to triple-label neurons in the postnatal rat subiculum. VVA labeled a subset of mu opioid receptor-positive neurons that were also immunoreactive for parvalbumin. The morphology of the triple-labeled neurons was heterogeneous, and included multipolar, ovoid and pyramidal-shaped neurons. Neurons single-labeled for the mu opioid receptor, VVA or parvalbumin were also morphologically heterogeneous. The postnatal development of mu opioid receptor immunoreactivity (IR), parvalbumin-IR and VVA binding was investigated using triple-labeling immunocytochemistry. Mu opioid receptor-IR appeared first and was present at postnatal day 1 (P1). Parvalbumin-IR was first observed in somata at P10, followed by proximal and distal dendrites at P15 and P20 respectively. Faint VVA labeling was seen first at P10 and surrounded a limited number of neurons. The intensity of labeling and the number of neurons labeled with VVA increased between P10 and P20; however, both measures remained below adult levels at P20. This study further illustrates the neurochemical heterogeneity of interneurons in the hippocampal formation and shows the developmentally early appearance of mu opioid receptor-IR compared to the late appearance of VVA binding and parvalbumin-IR.

Inositol phosphate formation in mice prenatally exposed to drugs: relation to muscarinic receptors and postreceptor effects

Mice were exposed to phenobarbital or heroin [diacetylmorphine (DAM)] prenatally by feeding the mother phenobarbital on gestation day 9-18; DAM was injected into the mother on gestation days 9-18. At the age of 50 days, mice exposed to phenobarbital or DAM prenatally were examined for long-term biochemical changes in the postsynaptic septohippocampal system as measured by alterations in formation of the second messenger inositol phosphate (i.p.). A significant increase in i.p. formation in response to carbachol was found after prenatal exposure to DAM. An increase in i.p. formation in response to 20 mM KCl alone or in the additional presence of 10 mM carbachol or 1mM physostigmine was found after prenatal exposure to phenobarbital or DAM. In addition, a significant increase in IP formation in response to sodium fluoride was found after prenatal exposure to phenobarbital or DAM. It is suggested that an increase in G-protein activation and in the second messenger formation accompanies the early drug-induced upregulation of the muscarinic receptors found in our previous studies.

Melanocortins and opioids modulate early postnatal growth in rats

This study was undertaken to investigate the effects of melanocortins and opioids on rat early postnatal body and organ growth. Among melanocortins tested desacetyl-alpha-melanocyte-stimulating hormone (alpha-MSH) at dosages of 0.3 and 3 micrograms/g/day was effective in stimulating neonatal growth with a weight gain of 7 and 5.6%, respectively, after 2 weeks of treatment. Likewise, a weight rise of 4.2 and 3% was obtained with 3 micrograms/g/day of both alpha-MSH and Nle4-D-Phe7 alpha-MSH. As far as opioids were concerned, while N-acetyl-beta-endorphin (beta-End) was ineffective, the activity of beta-End was dependent on dosage. Indeed, newborns treated with 0.03 microgram/g/day showed a slight, but significant, increase in weight, whereas a marked decrease in growth followed treatment with 0.3 and, mainly, 3 micrograms/g/day, with a final weight loss of 3.4 and 5.5%, respectively. All melanocortins exerted a positive action on muscular and brain trophism and, in addition, desacetyl-alpha-MSH also induced a rise of fat deposits. On the contrary, while the 0.03 microgram/g/day beta-End dose caused an increase in muscular and brain weight, the higher dosages of the opioid were detrimental, not only for muscle and brain, but also for both liver and spleen weight. A slight, although significant (P < 0.05), enhancement of serum dehydroepiandrosterone sulfate (DHEAS) level was found after the injection of 0.3 microgram/g desacetyl-alpha-MSH, whereas both the 0.3 and 3 micrograms/g doses of desacetyl-alpha-MSH and the 3 micrograms/g dose of alpha-MSH determined the rise of plasma androstenedione (P < 0.05). All tested melanocortins and opioids failed to modify the concentrations of corticosterone. Our results suggest that melanocortins and opioids can modulate early postnatal growth in rats either by direct or indirect mechanisms.

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).

Neonatal vasopressin antagonist treatment facilitates adult copulatory behavior in female rats and increases hypothalamic vasopressin content

This study confirms that i.c.v. administration of Arg-vasopressin (AVP, 20 ng) inhibits copulatory behavior in female rats (lordosis response, LR) and demonstrates that this inhibitory effect is blocked by the vasopressin antagonist (3-mercapto-3-methylbutyryl-Tyr-[Me])arginine vasopressin (dPTyr(Me)AVP, 20 ng, i.c.v.). The effects of neonatal AVP antagonist treatment on adult female copulatory behavior, hypothalamic content of AVP and AVP-like immunoreactive (AVP-ir) neurons were examined. dPTyr(Me)AVP was given to female rats 1 microgram/animal/day s.c. from day 1 through to day 7 (day 0 = day of birth). The females were ovariectomized as adults and sexual receptivity activated by submaximal doses of estradiol plus progesterone. The LR was significantly facilitated in the neonatally dPTyr(Me)AVP treated females who also showed a higher content and an increased number of AVP-ir neurons in the suprachiasmatic nucleus compared to saline controls. Functional, biochemical and immunocytochemical evidence is provided that neonatal exposure to an AVP antagonist induces persistent changes in central vasopressinergic neuronal mechanisms.

Neonatal naltrexone treatment: effects on sexual and exploratory behavior in male and female rats

The effect of neonatal naltrexone treatment (100 micrograms SC from day 1 to day 10) on copulatory and exploratory behavior in male and female rats was studied. In the female, neonatal naltrexone treatment enhanced copulatory (lordosis response) and exploratory behavior. An altered response to morphine was obtained; the effect of morphine on copulatory behavior was diminished while morphine's effect on exploratory activity was potentiated. The neonatal naltrexone treatment did not cause analogous effects in copulatory or exploratory behavior in the male rat. These data suggest that opioid mechanisms involved in the female copulatory and exploratory activity are established perinatally and can be influenced by early exposure to an opioid antagonist. It is concluded that there exist sex differences in this respect, both as to the sex-typical copulatory behavior and as to exploratory activity.

Neonatal peptides affect developing rats: beta-endorphin alters nociception and opiate receptors, corticotropin-releasing factor alters corticosterone

The dose-response relationship of neonatal (days 1-7) administration of beta-endorphin (BE) and corticotropin-releasing factor (CRF) on body weight, eye opening, response to thermal pain, and concentrations of plasma and adrenal corticosterone were measured in developing rat pups. At the highest dose (50 micrograms/pup), neonatal CRF reduced body weight, while 10 and 50 micrograms/pup accelerated eye opening. In addition, a reduction in concentration of plasma and adrenal corticosterone was correlated with the dose of neonatal CRF, whereas adrenal weights were not altered. BE produced none of these effects, but 1, 10 and 50 micrograms/pup on days 1-7 significantly reduced baseline latencies in a novel water-bath tail-flick test on day 9. These same animals showed reduced numbers of brain opiate receptors on day 14. The results indicate that peptide administration during the sensitive neonatal period can alter the development of physiological processes that will later be influenced by the peptide.

Opioid antagonist-induced modulation of cerebral and hippocampal development: histological and morphometric studies

The role of endogenous opioid systems in preweaning cerebral and hippocampal development was explored in rats utilizing naltrexone, a potent opioid antagonist. Sprague-Dawley rats were given daily injections (s.c.) of either 1 or 50 mg/kg naltrexone to invoke a temporary or complete blockade, respectively, of opioid receptors throughout the first 3 weeks of postnatal life; animals injected with sterile water served as controls. At weaning (Day 21), macroscopic, morphometric, and histological assessments were undertaken. In general, 50 mg/kg naltrexone had a stimulatory action on brain development, whereas 1 mg/kg naltrexone had an inhibitory influence. In most cases, both males and females were affected comparably. Opioid antagonist action was especially directed at cellular and tissue differentiation, with marked changes in macroscopic and areal dimensions and histotypic organization observed in the cerebrum. A prominent effect on the cerebrum of the 1 mg/kg naltrexone group was a substantial increase in packing density of the neural cells, reflecting a reduced area for accommodating neural elements. Changes in the hippocampus were largely restricted to the 1 mg/kg group. However, the number of granule cells was increased in the dentate gyrus of the 50 mg/kg group, suggesting that opioid receptor blockade affects cell types undergoing postnatal proliferation. Cellular elements derived prior to naltrexone treatment (e.g., pyramidal neurons) were capable of being influenced in only differentiative capacity. Our results show that endogenous opioids are natural trophic factors in brain development and provide evidence for the crucial role of endogenous opioid-opioid receptor interaction in neuro-ontogeny.

beta-Funaltrexamine (beta-FNA) and the regulation of body and brain development in rats

The effects of beta-FNA, a highly selective and irreversible mu opioid receptor antagonist, in altering body and brain development in preweaning rats were determined. Animals given beta-FNA did not differ from controls in body weights, brain and cerebellar weights, macroscopic dimensions of the brain, the area of the cerebellum, or in organ weight. The dosage of beta-FNA utilized (5 mg/kg) blocked morphine-induced analgesia (2 mg/kg morphine sulfate, SC) for each injection period (i.e., 48 hr). In contrast to beta-FNA treatment, rats given naltrexone (50 mg/kg SC) in a regimen which completely blocked the opioid receptor throughout ontogeny exhibited marked increases in somatic and neurobiological growth. These results suggest that, in and by themselves, mu receptors selectively antagonized by beta-FNA do not play an important role in regulating development.

Opioid antagonist-induced regulation of organ development

Naltrexone, a potent opioid antagonist, was given to preweaning rats in order to explore the influence of endogenous opioid systems on organogenesis. Sprague-Dawley rats were injected (SC) daily with either 1 or 50 mg/kg naltrexone to invoke a temporary or complete blockade, respectively, of opioid receptors; animals injected with sterile water served as controls. At weaning (Day 21), wet and dry weights, relative organ weight, and tissue water content were determined in 10 organ systems. Naltrexone's effects on growth depended on dosage, sex, and the organ system examined. In general, dosages of 1 and 50 mg/kg naltrexone caused significant decreases and increases, respectively, in organ weight. These changes in wet weight were not due to the state of hydration, but rather to dry weight, indicating that the content of cellular matter was altered. The changes in wet weight were similar to those for body weight, suggesting that a proportional increase or decrease in animal growth took place. Although the same organs in males and females within a dosage group were influenced by naltrexone, and usually to a similar degree, a dosage of 1 mg/kg naltrexone often affected different organ systems than the 50 mg/kg dosage. These results serve as the foundation for subsequent investigations directed towards delineating the role of endogenous opioid systems in developmental biology.