Maternal cocaine treatment alters dynorphin and enkephalin mRNA expression in brains of fetal rhesus macaques

Role of Brain Modulators in Neurodevelopment: Focus on Autism Spectrum Disorder and Associated Comorbidities

Autism spectrum disorder (ASD) and associated neurodevelopmental disorders share similar pathogenesis and clinical features. Pathophysiological changes in these diseases are rooted in early neuronal stem cells in the uterus. Several genetic and environmental factors potentially perturb neurogenesis and synaptogenesis processes causing incomplete or altered maturation of the brain that precedes the symptomology later in life. In this review, the impact of several endogenous neuromodulators and pharmacological agents on the foetus during pregnancy, manifested on numerous aspects of neurodevelopment is discussed. Within this context, some possible insults that may alter these modulators and therefore alter their role in neurodevelopment are high-lighted. Sometimes, a particular insult could influence several neuromodulator systems as is supported by recent research in the field of ASD and associated disorders. Dopaminergic hy-pothesis prevailed on the table for discussion of the pathogenesis of schizophrenia (SCH), atten-tion-deficit hyperactivity disorder (ADHD) and ASD for a long time. However, recent cumulative evidence suggests otherwise. Indeed, the neuromodulators that are dysregulated in ASD and comorbid disorders are as diverse as the causes and symptoms of this disease. Additionally, these neuromodulators have roles in brain development, further complicating their involvement in comorbidity. This review will survey the current understanding of the neuromodulating systems to serve the pharmacological field during pregnancy and to minimize drug-related insults in pa-tients with ASD and associated comorbidity disorders, e.g., SCH or ADHD.

Steady-dose and escalating-dose "binge" administration of cocaine alter expression of behavioral stereotypy and striatal preprodynorphin mRNA levels in rats

This study examined the effects of chronic (14-day) steady-dose and escalating-dose "binge" pattern cocaine administration on striatal preprodynorphin (ppDyn) mRNA levels and behavioral stereotypies. Animals in the steady-state and escalating groups received cocaine in a "binge" pattern (three equal injections starting 30 min following the start of the daily light cycle, separated by 1 h). The dose of cocaine in the "steady-dose" group was 15 mg/kg/injection and remained constant throughout the study. The escalating group received 15 mg/kg/injection on days 1-3, 20 mg/kg/injection on days 4-6, 25 mg/kg/injection on days 7-9 and 30 mg/kg/injection thereafter, for a maximum daily dose of 90 mg/kg. Levels of ppDyn mRNA were determined by solution hybridization. Cocaine significantly affected body weight. Both steady-dose and escalating-dose "binge" cocaine administration resulted in expression of behavioral stereotypy and induced intense, rapid head movements which were dose- and time-dependent. Cocaine, independent of dose, increased ppDyn mRNA levels in the caudate putamen (CPu), but not in the nucleus accumbens (NAc). These data suggest that the ppDyn response to cocaine in the CPu is not dose-dependent or that it has reached a maximal level at the 45 mg/kg daily dose.

Consequences of prenatal cocaine exposure in nonhuman primates

The extent to which cocaine abuse by pregnant women can affect development of their offspring remains a matter of significant debate. In large part, this is due to difficulties in accurate determination of the type, dose, and pattern of cocaine administration by drug abusing women as well as to difficulties in controlling for a wide range of potentially confounding variables, such as other drugs used, race, socioeconomic status, and level of prenatal care. On this background, examination of the effects of prenatal cocaine exposure in highly controlled nonhuman primate models represents an important complement to the human research. The present review summarizes the data obtained in several different rhesus monkey models of cocaine exposure in utero. These data demonstrate the potential of prenatal cocaine exposure to interfere with structural and biochemical development of the brain leading to behavioral deficits at birth and/or during adulthood. However, the differences in the outcomes between individual models also suggest that the specific types and severity of cocaine effects are likely dependent on the route, dose, gestational period, and daily pattern of administration.

Prenatal exposure to cocaine decreases adenylyl cyclase activity in embryonic mouse striatum

Adenylyl cyclase activity was measured in the striatum of naive mice as a function of age and in mice exposed in utero to cocaine. In naive Swiss-Webster mice, basal and forskolin-stimulated adenylyl cyclase activity increased gradually from embryonic day 13 (E13) until 2-3 weeks of age when activity peaked before decreasing slightly to adult levels. The ability of the dopamine D1 receptor agonist, SKF 82958, to stimulate adenylyl cyclase activity also increased in magnitude until P15. In a separate study, pregnant Swiss-Webster mice were injected twice daily with cocaine (15 mg/kg, s.c.) or an equal volume of saline from E10 to E17. Adenylyl cyclase activity was measured in the striatum of E18 embryos. Basal adenylyl cyclase activity was significantly reduced following prenatal exposure to cocaine. Likewise, the ability of forskolin or SKF 82958 to stimulate adenylyl cyclase was attenuated following cocaine exposure. DeltaFosB was not induced, contrary to what is seen in adult mice. These results demonstrate a functional change in a critical signal transduction pathway following chronic in utero exposure to cocaine that might have profound effects of the development of the brain. Alterations in the cAMP system may underlie some of the deficits seen in humans exposed in utero to cocaine.

The effects of prenatal cocaine exposure on reversal learning using a simple visual discrimination task in rhesus monkeys

The purpose of this research was to determine if adult animals that were exposed to cocaine prenatally would be able to adapt to changes in the rules of reinforcement for a simple discrimination task. Treatment groups included 0.0, 1.0, and 3.0 mg cocaine/kg/day and an escalating-dose group that began treatment at 3.0 mg cocaine/kg/day, after which the dose was increased by 0.5 mg cocaine/kg/day every 2 weeks throughout the pregnancy. All animals performed a color and position discrimination task for food reinforcers for approximately 6 years before the present study. For this task, subjects were presented with colored stimuli that determined the correctness of subsequent position choices: left for red or yellow and right for blue or green. At 7 years of age, the rules for obtaining reinforcement were reversed. Animals exposed to all doses of cocaine showed impaired reversal performance. Further, animals exposed to the escalating doses of cocaine continued to show this impairment for over 285 sessions (about 21/2 years). The number of sessions required by subjects to master these contingency changes indicated that, using a task with which they have an extensive history, cocaine-exposed animals have greater difficulty in adapting to important changes in their environment.

Dopamine D1 and D2 receptor mRNA up-regulation in the caudate-putamen and nucleus accumbens of rat brains by smoking

Nicotine, the toxic substance that is exclusively absorbed from smoking, produces a wide array of behavior and collectively propels drug-seeking behaviors when abused. The neurotransmitter dopamine (DA) is important in the reward and reinforcing properties of many addictive drugs: however, the effect of nicotine by cigarette smoking itself on the expression of DA receptors in the caudate-putamen (CPu), nucleus accumbens (NAc) and olfactory tubercle (OTu) has not been elucidated completely. Hence, the effects of smoking and nicotine on DA receptors need to be defined. In this research, the effect of smoking and nicotine addiction on the DA D1 and D2 receptors in the rat CPu, NAc and OTu were studied. Adult male Spraque-Dawley (S.D., n=50) rats were administered with cigarette smoke (passive inhaled for 10 min and 1 h, 500 ml x 3 times/day, 4 weeks) and nicotine (oral, 3 mg/day). DA D1 and D2 receptor mRNA levels were determined by in situ hybridization and RNase protection assay (RPA). In the smoking groups (10 min and 1 h), DA D1 and D2 receptor mRNA greatly increased in the CPu and NAc, and most of all in the NAc. The nicotine treated group showed increased expression of DA D1 and D2 receptor mRNA too, but statistically less than in the smoking group. In the smoking group, DA D1 and D2 receptor mRNA levels were significantly higher in the CPu and NAc than in the nicotine group (P<.01). These results suggest that smoking and nicotine administration both influence DA receptor mRNAs in the CPu, NAc and OTu, in terms of up-regulation. The up-regulation was much more evident in the smoking group than in the nicotine group. In conclusion, we believe that smoking up-regulate the DA receptor mRNA expression significantly higher in rat CPu and NAc than nicotine but only a little bit higher in OTu.

Repeated prenatal cocaine increases met-enkephalin immunoreactivity in respiratory-related medulla of developing swine

Repeated prenatal exposure to cocaine is associated with attenuated respiratory and arousal responses in infants and piglets. As the normal development of these functions is influenced by medullary opioid systems, the present study explored the possible contribution of the opioid systems to the attenuation induced by cocaine. Methionine-enkephalin (met-enkephalin), an endogenous opioid peptide, was delineated by immunocytochemistry in respiratory- and arousal-related medullary regions of relatively immature (6-7-day-old) and more mature piglets (20-21-day-old). The animals were either unexposed, or exposed prenatally to 2 mg/kg cocaine four times daily administered to the pregnant sows intravenously throughout the last third of gestation. At control, met-enkephalin was found in the neurons, fibers and terminals of the respiratory- and arousal-related medullary regions throughout the age range studied. Prenatal cocaine exposure increased met-enkephalin immunoreactivity in the respiratory-related hypoglossal and solitary tract nuclei of both age groups. These findings support a modulatory role of met-enkephalin in the normal development of respiratory control, and an involvement of this peptide in the attenuation of respiration by repeated prenatal exposure to cocaine.

The distribution of dynorphinergic terminals in striatal target regions in comparison to the distribution of substance P-containing and enkephalinergic terminals in monkeys and humans

Single- and double-label immunohistochemical techniques using several different highly specific antisera against dynorphin peptides were used to examine the distribution of dynorphinergic terminals in globus pallidus and substantia nigra in rhesus monkeys and humans in comparison to substance P-containing and enkephalinergic terminals in these same regions. Similar results were observed in monkey and human tissue. Dynorphinergic fibers were very abundant in the medial half of the internal pallidal segment, but scarce in the external pallidal segment and the lateral half of the internal pallidal segment. In substantia nigra, dynorphinergic fibers were present in both the pars compacta and reticulata. Labeling of adjacent sections for enkephalin or substance P showed that the dynorphinergic terminals overlapped those for substance P in the medial half of the internal pallidal segment, but showed only slight overlap with enkephalinergic terminals in the external pallidal segment. The substance P-containing fibers were moderately abundant along the borders of the external pallidal segment, and enkephalinergic fibers were moderately abundant in parts of the internal pallidal segment. Dynorphinergic and substance P-containing terminals overlapped extensively in the nigra, and both extensively overlapped enkephalinergic fibers in medial nigra. Immunofluorescence double-labeling studies revealed that dynorphin co-localized extensively with substance P in individual fibers and terminals in the medial half of the internal pallidal segment and in substantia nigra. Thus, as has been found in non-primates, dynorphin within the striatum and its projection systems appears to be extensively localized to substance P-containing striatopallidal and striatonigral projection neurons. Nonetheless, our results also raise the possibility that a population of substance P-containing neurons that projects to the internal pallidal segment and does not contain dynorphin is present in primate striatum. Our results also suggest the possible existence of populations of striatopallidal and striatonigral projection neurons in which substance P and enkephalin or dynorphin and enkephalin, or all three, are co-localized. Thus, striatal projection neurons in primates may not consist of merely two types, one containing substance P and dynorphin and the other enkephalin.

Chronic prenatal cocaine treatment down-regulates mu-opioid receptor mRNA expression in the brain of fetal Rhesus Macaque

Ribonuclease protection assays (RPA) were performed to quantify mu-opioid receptor mRNA expression in specific brain regions of day 70 Rhesus Macaque fetuses that were exposed to cocaine (3 mg/kg) or saline from days 22-70 of gestation. The content of mu-receptor mRNA was high in the diencephalon and moderate in the mesencephalon. In contrast, mu-receptor mRNA was lightly expressed in areas such as the frontal cortex, striatum and the temporal lobe. The content of mu-opioid receptor mRNA was significantly higher in the diencephalon than in other brain regions (P < 0.001; n = 4). Cocaine exposure significantly decreased the expression of mu-receptor mRNA in the fetal diencephalon (P < 0.05; n = 4 in each group). Our data would indicate that prolonged gestational cocaine exposure causes mu-opioid receptor mRNA down-regulation in specific brain regions of the fetus.

Perinatal cocaine decreases the expression of prodynorphin mRNA in nucleus accumbens shell in the adult rat

Preprodynorphin mRNA expression in the striatal-olfactory tubercle complex was studied in adult rats exposed to cocaine (50 mg/kg) during postnatal days (PnD) 11-20. While multiple regions of the striatum and olfactory tubercle were examined, alterations were only found in the nucleus accumbens. A 50% and 20% reduction in expression within the shell region was observed at 1.2 and 1.7 mm rostral to Bregma respectively. While the core regions at these levels were unaffected, the rostral accumbens showed a trend toward an increase in expression in the cocaine-treated rats. These findings, in combination with other behavioral and neurochemical data collected on similarly treated rats, suggest that perinatal cocaine produces a long-term dampening of function in a specific population of neurons within the mesolimbic system

Cocaine exposure in fetal rhesus monkey: consequences for dopamine D1- and D2-like receptor binding densities

Previously we found that dopamine D1-, D2- and D5-receptor mRNA subtypes are significantly increased in the rostral forebrain of fetal monkeys exposed to cocaine. The purpose of the present study was to determine whether cocaine exposure during gestation also increases dopamine receptor binding densities in the fetal brain. Pregnant monkeys were treated with cocaine (3 mg/kg, i.m., n = 3) or physiological saline (n = 3), 4 times per day from day 22 of pregnancy until day 70. Quantitative receptor autoradiography of dopamine D1-like receptors was performed on day-70 fetal brain sections using [3H]SCH23390. [3H]Spiperone was used to characterize dopamine D2-like receptors. Image analysis of receptor autoradiograms revealed a high-density dopamine D1-like receptor binding in the striatum, nucleus accumbens (ACB) and the substantia nigra (SN), whereas lower binding densities were observed in the frontal cortex and the habenula (Hb). Dopamine D2-like receptor binding was also found in the frontal cortex, striatum and ACB, but was not detected in the Hb or SN. The pattern of dopamine receptor distribution was the same in both control and cocaine-treated animals. However, there was a significant increase in the density of sites for D1-like receptors in the striatum (P < 0.05) and SN (P < 0.01) and for D2-like receptors in the striatum (P < 0.01) of cocaine-treated animals versus saline-treated controls. These findings suggest that D1- and D2-like receptors are present in dopamine target neurons, whereas D2-like autoreceptors can not be detected in day-70 fetal monkey midbrain. The present results provide further support for the hypothesis that gestational cocaine exposure causes reduced synthesis and release of dopamine which leads to dopamine D1- and D2-receptor up-regulation in dopamine target neurons.