Prenatal cocaine and cell development in rat brain regions: effects on ornithine decarboxylase and macromolecules

Neuropathology of the cerebral cortex observed in a range of animal models of prenatal cocaine exposure may reflect alterations in genes involved in the Wnt and cadherin systems

Several recent reports show that the cerebral cortex in humans and animals with altered expressions of Wnt/cadherin network-associate molecules display cytoarchitectural abnormalities reminiscent of cortical dysplasias seen in some (mouse-, rat-, and monkey-based) animal models of prenatal cocaine exposure. Therefore, we employed oligo microarrays followed by real-time RT-PCR to compare expressions of genes involved in Wnt and cadherin systems in the cerebral wall of 18-day-old (E18) fetuses from cocaine-treated (20 mg/kg cocaine, s.c., b.i.d., E8-18) and drug-naive (saline, s.c.) mice. The pregnant mice chronically treated with cocaine in the above-described manner represent one of the animal models producing offspring with widespread cortical dysplasias. Out of more than 150 relevant genes in the arrays, 32 were upregulated and 9 were downregulated in cocaine-exposed fetuses. The majority of these genes (30 out of 41) were similarly affected in the frontal and occipital regions of the cerebral wall. We also used Western immunoblotting to examine the ability of cocaine to regulate the protein levels of beta-catenin, the key functional component of both Wnt and cadherin systems. While the total cell levels of beta-catenin were increased throughout the cerebral wall of cocaine-exposed fetuses, its nuclear (gene-transcription driving) levels remained unaltered. This suggests a transcription-unrelated role for cocaine-induced upregulation of this protein. Overall, our findings point to an intriguing possibility that that cerebral cortical dysplasias observed in several animal models of prenatal cocaine exposure may be at least in part related to alterations in the Wnt/cadherin molecular network.

Prenatal cocaine administration increases glutathione and alpha-tocopherol oxidation in fetal rat brain

Recent findings suggest that prenatal cocaine exposure results in significant attenuation of uterine and placental blood flow. The extent of blood flow reduction to fetuses positively correlates with reductions in glial-derived neurotrophic factor (GDNF) and dopamine (DA). However, whether such changes in uterine blood flow are sufficient to induce oxidative stress have yet to be determined. In the following experiments, the impact of prenatal cocaine exposure on fetal brain levels of the endogenous antioxidant glutathione (GSH and its oxidized form GSSG) or the exogenous antioxidant alpha-tocopherol (alpha-T and its oxidized quinone form) was investigated. It was hypothesized that cocaine exposure would result in greater oxidation of both GSH and alpha-T. Results indicated that a single injection of cocaine to a drug-naive pregnant dam results in significant (-16.38%) reductions in the levels of GSH. GSSG can be either raised or reduced as a result of fetal uterine position: fetuses at the ovarian extremes show significant increases in GSSG in response to cocaine (+64.73%), whereas cervically situated fetuses show decreased GSSG (-47.91%). Additionally, cocaine significantly decreased the levels of alpha-T (-15.9%) and increased the levels of its oxidative product alpha-Tquinone (alpha-Tq, +34.05%). Levels of alpha-T were not affected by fetal uterine position. These data collectively suggest that cocaine exposure increases the utilization of both endogenous and exogenous anti-oxidants in the fetal rat brain. Along with previous studies, these data support the hypothesis that cocaine-induced vasoconstriction results in oxidative stress in the gestating fetus.

Prenatal cocaine exposure induces an attenuation of uterine blood flow in the rat

We have previously demonstrated that maternal cocaine injections result in a gradient of fetal brain cocaine levels that decrease as a function of the fetuses' proximity to the ovaries at embryonic (E) day 15. Our prior data suggest that cocaine-induced vasoconstriction may (1) limit cocaine's entry into the brain and (2) cause damage to DA neurons through injury associated with hypoxia or ischemia of the utero-placental junction. Therefore, using the microsphere technique (labeled with Ru(103)), the following study sought to determine whether the previously observed pattern of cocaine distribution among fetuses in the uterus were due to position-specific reductions in uterine or placental blood flow. On day 15, a single subcutaneous injection of 30 mg/kg cocaine HCl was administered to each rat. Thirty minutes after the cocaine injection, reference blood samples were drawn from the ventral tail artery. Uterine segments and placentae were removed and subjected to gamma counting. While results regarding placental blood flow were equivocal, cocaine significantly reduced average uterine blood flow by 54.6%. In addition, as one moves more proximal to the ovaries, cocaine progressively attenuates blood flow in uterine tissue segments. These data support the hypothesis that the pattern of drug distribution and subsequent brain alterations from prenatal cocaine exposure in our previous reports are likely due to differences in uterine blood flow.

Prenatal cocaine exposure produces consistent developmental alterations in dopamine-rich regions of the cerebral cortex

Administration of cocaine to pregnant rabbits produces robust and long-lasting anatomical alterations in the dopamine-rich anterior cingulate cortex of offspring. These effects include increased length and decreased bundling of layer III and V pyramidal neuron dendrites, increases in parvalbumin expression in the dendrites of interneurons, and increases in detectable GABAergic neurons. We have now examined multiple cortical regions with varying degrees of catecholaminergic innervation to investigate regional variations in the ability of prenatal cocaine exposure to elicit these permanent changes. All regions containing a high density of tyrosine hydroxylase-immunoreactive fibers, indicative of prominent dopaminergic input, exhibited alterations in GABA and parvalbumin expression by interneurons and microtubule-associated protein-2 labeling of apical dendrites of pyramidal neurons. These regions included the medial prefrontal, entorhinal, and piriform cortices. In contrast, primary somatosensory, auditory and motor cortices exhibited little tyrosine hydroxylase staining and no measurable cocaine-induced changes in cortical structure. From these data we suggest that the presence of dopaminergic afferents contributes to the marked specificity of the altered development of excitatory pyramidal neurons and inhibitory interneurons induced by low dose i.v. administration of cocaine in utero.

Ethanol inhibition of brain ornithine decarboxylase activity in the postnatal rat

The purpose of this study was to determine the relationship between ornithine decarboxylase activity (ODC; a marker for perturbed cell development), the blood alcohol level, and alcohol-induced microencephaly in the developing rat brain after binge treatment with ethanol vapour. By manipulating ethanol flow we were able to adjust vapour concentrations (24-65 mg ethanol/l air) such that an acute exposure of ethanol vapour for 3 h resulted in a range of blood alcohol levels (2.3-5.5 mg/ml). Acute studies showed that ethanol dose-dependently inhibited rat hippocampal and cerebellar ODC activity at PND4-PND10. There was a significant correlation between the blood alcohol level and degree of inhibition at all ages tested. Chronic treatment from PND4 to PND9 caused a significant decrease in both brain to body weight ratio and in hippocampal and cerebellar ODC activities at PND10. These results indicate that ethanol-induced disruption in ODC could play a significant role in ethanol's teratogenic effects during early postnatal development.

Convergent control of serotonin transporter expression by glucocorticoids and cocaine in fetal and neonatal rat brain

Serotonin plays a trophic role in brain cell differentiation. In this study, expression of the serotonin presynaptic transporter protein, which regulates the extracellular serotonin concentration, was measured with [3H]paroxetine in rats exposed to dexamethasone or cocaine prenatally. Within 24 h of a single dose of dexamethasone, significant increases were seen in fetal brain, and the effect persisted into the postnatal period. Chronic prenatal cocaine exposure elicited similar changes. These data indicate that exposures to apparently disparate drugs can elicit similar endpoints that may lead to behavioral teratogenesis.

Retinal lesions in rat fetuses prenatally exposed to cocaine

The increased use of cocaine in the United States and worldwide has created great concern about its effects on fetuses and neonates of pregnant cocaine abusers. The effects on neonates are varied: fetal growth delay, microcephaly, abnormal neurological functions, microphthalmia, and maternal obstetric complications. In this study, the effect of prenatal cocaine administration was studied microscopically in the retina of rat fetuses. Twenty-five pregnant Wistar rats were injected i.p. with an aqueous cocaine solution using a 30 mg/kg daily dose for 45 days. Control group rats (15 pregnant animals) received saline solution for the same period. Day 0 of gestation was the day after mating. Dosing began on this day. The rats were killed on gestation day 21 and fetuses were obtained for examination. The histopathological light and electron microscope studies of the retinas showed interstitial oedema, areas depleted of cells, necrosis, and hyperchromatic ganglion cells. There also was a significantly lower number of retinal cells compared to control fetuses. In four cases, teratogenic lesions of the retina were observed whereas no changes were present in control fetuses. Results indicate that development of retina in fetuses prenatally exposed to cocaine was altered by cocaine exposure.

Prenatal cocaine: effect on hypoxic ventilatory responsiveness in neonatal rats

The effects of prenatal (embryonic days 7-21) cocaine (30 mg/kg b.i.d., s.c.) exposure on postnatal respiratory and behavioral responsiveness to acute hypoxia were investigated in 5-day-old (P5) rat pups. Control and cocaine-exposed pups were subjected to 20 min of 0.21 FIO2 followed by 20 min of 0.08 FIO2. Although all pups demonstrated the characteristic biphasic response to hypoxia, cocaine-exposed pups exhibited a blunted, initial response in minute ventilation (p < 0.05) and inspiratory drive (p < 0.05) as compared with control pups who showed increases in these measures (p < 0.01 and p < 0.05, respectively). The consequence of this apparent blunted ventilatory response was reflected in blood gas data gathered after 20 min of 0.08 FIO2:PCO2 (p < 0.05) and base-excess (p < 0.05) were increased and HCO3- (p < 0.05) and SO2 (p < 0.01) were decreased relative to control pups. Cocaine-exposed pups also exhibited behavioral evidence of decreased struggling (p < 0.001) in response to the hypoxic challenge. These data in the rat confirm our previous findings of altered ventilatory responsiveness to inspired hypoxia in the rabbit and extend our observations of a decreased ability to successfully compensate and behaviorally arouse following prenatal cocaine-exposure, thus underscoring the potential vulnerability of infants so exposed.

Development of the eye after gestational exposure to cocaine. Vascular disruption in the retina of rats and humans

Clinical and basic research in the area of drugs of abuse are of utmost importance since they provide the necessary background for health programs in one of the main problems of contemporary society. The available data in this field demonstrate that acute, subacute and/or chronic abuse of illicit drugs, e.g., cocaine, alters the neurochemistry and functioning of the neural circuitries. Although recent works demonstrated that the visual system is lesioned after exposure to cocaine during the active periods of development, no studies have provided detailed information on the effects of these substances on the development of this sensory system. The present paper will report: 1) the vulnerability of the developing visual system to gestational exposure to cocaine; 2) the effects of cocaine in the visual system during the more active periods of development in humans and, as far as possible, the establishment of homologies with animal models where exposure is made in corresponding periods of human gestation, and 3) the characterization of the vascular disruption caused by ischemic/hypoxic mechanisms. The clinical study focused the ophthalmologic evaluation of newborns exposed in utero to illicit drugs. Newborns exposed to cocaine in utero showed marked vascular disruption in the retina: superficial and deep hemorrhages that, although morphologically similar to neonatal retinal hemorrhages, presented a longer reabsorption time when compared with the neonatal hemorrhagic lesions due to birth trauma in the general population. Prolonged eyelid edema was also a prominent finding. The animal study was conducted in Wistar rats exposed prenatally (gestational days 8 to 22) and postnatally (postnatal days 1-6, 1-13 and 1-29) to 60 mg/kg body weight/day and 15 mg/kg body weight/day, respectively, to cocaine hydrochloride administered subcutaneously; control groups included pair-feeding during the same experimental periods. Similar alterations to those observed in the newborns where exposure to cocaine was affirmative, were found: intraretinal hemorrhages allied to signs of chronic ischemia both in the outer retina-photoreceptor rosettes and in the inner retina-epiretinal glial membranes. Taking into consideration that the visual system is one of the more important sensory systems, the identification and characterization of these alterations, the similarity between animal and human findings, and their relation with cocaine per se, can provide a sound data base for illicit drug prevention programs.

Effects of cocaine on the rat cerebral commissure

We investigated the effects of cocaine on the corpus callosum, the nerve fibre bundle that connects the bilateral cerebral hemispheres. Our experiments in rats confirmed that, in the control group, the mid-sagittal area of the corpus callosum in the adult male was significantly larger than this area in the female. Early postnatal exposure to cocaine abolished this sexual dimorphism, that is, cocaine-treated males had a significantly smaller callosal area than the control males. Cocaine induced no significant changes in the weight of the body or brain. There were no significant sex differences in the midline sagittal area of the anterior commissure, and no apparent effects of cocaine exposure were determined in this structure. These findings suggest that early postnatal exposure to cocaine abolishes the sexual differentiation of the corpus callosum in male rats.

Prenatal cocaine produces dose-dependent suppression of prolactin and growth hormone in neonatal rats

Pregnant Long-Evans hooded rats were dosed with 5, 10, 20, or 40 mg/kg/d cocaine from GD7 through GD20; pairfed/vehicle-injected, and uninjected controls were included. At birth, representative pups from each litter were killed by decapitation and serum assayed for prolactin and growth hormone via radioimmunoassay. Prolactin levels were significantly reduced on P1 in offspring which had been dosed prenatally with 20 or 40 mg/kg/d, while growth hormone levels were significantly lower than control levels in the 5 and 10 mg/kg/d animals. Pairfed/vehicle controls did not differ from uninjected controls on levels of either hormone. These endocrine changes associated with cocaine dosing may affect subsequent development of the organism.

Effects of prenatal cocaine exposure in the photoreceptor cells of the rat retina

Despite the increasing evidence of eye abnormalities, the effects of prenatal exposure to cocaine on the visual system are still poorly understood. This study was aimed at analyzing the qualitative and quantitative organization of the retinal photoreceptor cells (PR) and outer nuclear layer (ONL) after prenatal exposure to cocaine in the rat. Pregnant Wistar rats were given sc injections of cocaine hydrochloride (60 mg/kg body wt/d) or saline or were not manipulated; analyses were performed in the 14- and 30-d-old male offspring. Radial semithin and ultrathin sections of epon-embedded flat mounts of the retina showed displaced PR-like cells in the inner nuclear layer (INL), picnotic PR nuclei in INL, and ONL, and retinal PR rosettes and outer-segment debris in the subretinal space. The quantitative study showed an increased density of PR-like nuclei in the INL in PND14 cocaine-treated rats that were within normal values at PND30; no changes were detected in the PR mean nuclear diameter and in the packing density of PR nuclei in the ONL. These data constitute the first morphological demonstration of photoreceptor damage after prenatal cocaine-exposure probably owing to a direct action of the drug and/or to the cocaine-induced ischemia/hypoxia.

Effects of prenatal cocaine exposure in the retinal ganglion cell layer of the rat. A morphometric analysis

To study the effects of prenatal cocaine-exposure on the developing retinal ganglion cell layer of the rat, female Wistar rats were administered subcutaneously (sc) cocaine hydrochloride (60 mg/kg body wt/d) or saline, or were not manipulated from gestational d 8-22. Male offspring were sacrificed at postnatal day 14 and 30. Radial semithin sections of epon-embedded flat mounts of the retinal quadrants were used to evaluate the following parameters along the centroperipheral axis: 1. Thickness of ganglion cells plus nerve fiber layer; 2. Nuclear size of ganglion cell layer neurons; and 3. Linear density (number per unit length) of ganglion cell layer neurons. To study the effects of cocaine and age on the retinal areas (temporal/nasal, dorsal/ventral), a repeated measures analysis of variance was used for each of the parameters mentioned above. All parameters were affected by prenatal exposure to cocaine. The thickness of the ganglion cell plus nerve fiber layer was reduced in cocaine-exposed rats in comparison with the saline group. Nuclear diameters were smaller in the cocaine than in the saline and control groups. The linear density was higher in the cocaine-exposed group than in the control and saline groups. The age-dependent decrease in the linear density from postnatal day 14-30 was higher in the cocaine-exposed rats than in the saline group; the decrease in the linear density along the centroperipheral axis found in both the control and saline groups was not significant in the cocaine-treated group. These morphometric findings strongly support the view that prenatal cocaine-exposure induces marked changes in the organization of the developing retina.

Cocaine inhibits central noradrenergic and dopaminergic activity during the critical developmental period in which catecholamines influence cell development

Cocaine produces neurobehavioral damage in the fetus and neonate both through its ischemic actions and through direct effects mediated by the drug within the developing brain. The replication and differentiation of catecholaminergic target cells are controlled in part by neurotransmitter input and the current study assess whether cocaine modifies the function of these neurons during the critical periods in which target cell programming occurs. Neonatal rats (1, 7, 14 and 21 days old) were given cocaine (30 mg/kg) acutely and the turnover of norepinephrine and dopamine, a measure of synaptic activity, was evaluated in vivo in three different brain regions known to be adversely affected by cocaine. For norepinephrine, cocaine suppressed transmitter turnover in the immediate postnatal period in all regions, reaching a maximal effect within the first 2 postnatal weeks; at subsequent ages, the inhibitory actions were no longer evident. For dopamine, an inhibitory effect also appeared during the first postnatal week, but by 14 to 21 days the effect was replaced by the excitatory response that is characteristic of mature brain; effects on dopamine turnover were restricted to the forebrain. The inhibitory effects of cocaine on immature brain could not be attributed to localized actions at the nerve terminal itself (blockade of reuptake, autoreceptor activation, local anesthesia), but instead are likely to represent reductions in nerve impulse activity. Brain development in the neonatal rat corresponds to fetal stages in man, and thus the transient ability of cocaine to interfere with noradrenergic and dopaminergic activity during the period in which differentiation is being patterned by neurotransmitter input, may be important in the neurobehavioral teratology of cocaine.

Long-lasting microencephaly following exposure to cocaine during the brain growth spurt in the rat

In utero exposure to cocaine has been shown to produce somatic and behavioral effects. As microencephaly is often present in children born from cocaine-addicted mothers, aim of the present study was to develop an animal model for cocaine-induced microencephaly. Rats were treated with cocaine (20, 30 or 50 mg/kg/day, s.c., each dose divided in two equal doses given 3 h apart) from postnatal day 4 through 10. None of the doses had any effect on growth, however, at 50 mg/kg, cocaine caused a significant decrease in brain weight, measured on day 12. The effect of cocaine was similar in male and female rats, and microencephaly was still present in 45-day-old animals. When the same dose of cocaine was given as a single daily injection, long-lasting microencephaly was also present, but it was accompanied by a decrease in body weight and significant toxicity. Ethanol (4 g/kg), used as a positive control, also caused microencephaly without affecting body weight, but, differently from cocaine, its effect was more pronounced in female animals. Blood and brain levels of cocaine and its metabolites norcocaine and benzoylecgonine were measured by HPLC during treatment (postnatal day 8). After administration of the 50 mg/kg dose, concentrations of cocaine were 1.92 micrograms/g in brain and 0.94 microgram/ml in blood. These levels are encountered in cases of cocaine overdoses and have been found in meconium of newborns from crack-addicted mothers.(ABSTRACT TRUNCATED AT 250 WORDS)

Prenatal cocaine eliminates the sex-dependent differences in activation observed in adult rats after cocaine challenge

In the adult rat, acute administration of cocaine results in enhanced expression of certain behaviors. This activation is often referred to as "stereotypy" because of its repetitive nature. Repeated exposure to the same dose of cocaine does not result in tolerance or a dimunition of these behavioral responses. Rather, an increased responsiveness to cocaine, termed "sensitization," is observed. Female rats, in comparison to male rats, display greater activation to a given dose of cocaine and greater sensitization with repeated exposure. As prenatal cocaine exposure can involve repeated exposure to the drug, we examined the behavioral activation induced by an acute dose of cocaine. Young adult rats of both sexes received a challenge dose of cocaine to determine the long-term effects of repeated in utero exposure to cocaine (30 mg/kg daily, SC) given between gestational days 8-20. As expected, female offspring of dams exposed to saline in utero displayed greater activation to a 20 mg/kg SC dosage of cocaine than their male counterparts. However, these sex differences were completely eliminated by prenatal exposure to cocaine. That is, female rats receiving cocaine during the prenatal period showed no more activation to an acute dose of cocaine as young adults than either control males or those males receiving cocaine in utero. Males exposed in utero to cocaine showed activation to cocaine challenge equivalent to that displayed by males exposed to saline in utero. Prenatal exposure to cocaine may alter sexual differentiation of the brain.