Attenuation of cocaine-induced genomic and functional responses in prenatal cocaine-exposed rabbits

Cocaine-induced neurodevelopmental deficits and underlying mechanisms

Exposure to drugs early in life has complex and long-lasting implications for brain structure and function. This review summarizes work to date on the immediate and long-term effects of prenatal exposure to cocaine. In utero cocaine exposure produces disruptions in brain monoamines, particularly dopamine, during sensitive periods of brain development, and leads to permanent changes in specific brain circuits, molecules, and behavior. Here, we integrate clinical studies and significance with mechanistic preclinical studies, to define our current knowledge base and identify gaps for future investigation. Birth Defects Research (Part C) 108:147-173, 2016. © 2016 Wiley Periodicals, Inc.

Gestational exposure to cocaine alters cocaine reward

Exposure of the developing foetus to drugs of abuse during pregnancy may lead to persistent abnormalities of brain systems involved in drug addiction. Mice prenatally exposed to cocaine (25 mg/kg), physiological saline or non-treated during the last 7 days of pregnancy were evaluated in adulthood for the rewarding properties of cocaine (3, 25 and 50 mg/kg), using the conditioned place preference procedure. Dams treated with physiological saline gained significantly less weight over the course of gestation than controls; no other differences were observed in the maternal and offspring data. All the animals developed preference to 3 and 25 mg/kg of cocaine, but those treated prenatally with cocaine did not develop preference after receiving the highest cocaine dose. In these mice, the motor activity in response to 50 mg/kg showed a small decrease. Although a reduced response to the highest cocaine dose can be argued, we suggest that the lack of preference obtained is more likely attributable to an increased sensitivity to the environmental cues associated during training to an aversive effect of this cocaine dose. The aversive properties of cocaine seem to be more apparent and to prevail over the rewarding action of the highest dose in exposed animals. These findings indicate that recurrent gestational cocaine exposure results in permanent (mal)adaptations of the structure and function of brain reward systems.

Dopamine transporters in the cerebellum of mutant mice

In the central nervous system, dopamine is known to play a critical role in motor and cognitive functions. Although the cerebellum plays a role in the control of movement and posture and in cognitive functions, it has not been considered to be a dopaminergic region and the dopamine present was thought to represent a precursor of noradrenaline. However, recent evidence suggests that in the cerebellum there is a small dopaminergic element, whose properties are similar to the well characterized system of striatum. In order to better understand the functional role of this system and to delineate its specific interactions within the cerebellum, the distribution and properties of dopamine transporter (DAT) in the cerebellum of reeler and Purkinje cell degeneration (Nna1pcd) mutant mice, which are characterized by severe loss of different cell populations and abnormalities in synapse formation, have been studied. Kinetic studies revealed that [3H]dopamine is transported into cerebellar synaptosomes prepared from normal mice with affinities similar to that into striatal synaptosomes but with much lower maximal velocities. In reeler cerebellar synaptosomes the number of transport sites is significantly reduced. In Nna1pcd cerebellar synaptosomes the kinetic properties of transport of [3H]dopamine are similar to the normal. However, in vitro quantitative DAT autoradiography revealed a significantly increased binding in cerebellar nuclei, a decreased binding in molecular layer and an unaltered binding in the granule cell layer. These observations confirm a dopaminergic innervation of the cerebellum and contribute to our understanding of the intracerebellar distribution of the dopaminergic system.

Anatomical abnormalities in dopaminoceptive regions of the cerebral cortex of dopamine D1 receptor mutant mice

Alteration of dopamine neurotransmission during development can induce specific changes in neuronal structure and function. Here, we report specific morphological and neurochemical changes of projection neurons and interneurons of the medial frontal cortex of the dopamine D(1) receptor null mouse. Using immunostaining of cytoskeletal proteins and a crossbred D(1) receptor null:YFP transgenic reporter line, we demonstrate that the apical dendrites of pyramidal cells are abnormally organized in the prefrontal and anterior cingulate cortices of mice lacking the D(1) receptor. Neuronal processes exhibit a decrease in bundling and an increase in irregular, tortuous patterning as they weave a course towards the pial surface. In addition, there is increased parvalbumin staining of the dendrites of cortical interneurons in D(1) receptor null mice. Both pyramidal and interneuron alterations are evident by the early postnatal period and persist into adulthood. The alterations show regional specificity, in that dendritic profiles of projection neurons and interneurons in somatosensory and visual cortices develop normally. The abnormalities are reminiscent of those induced by prenatal exposure to cocaine in rabbits, an insult which has been shown to produce an attenuation of D(1) receptor-mediated responses through G(salpha). These results suggest that loss of D(1) receptor-mediated signaling during development produces permanent alterations in the cellular organization of specific cortical areas involved in attention, cognition, and emotion. Pharmacological and behavioral studies in the D(1) null mouse should be interpreted in the context of possible altered circuitry, given the presence of these developmental defects in the organization of dopaminoceptive regions of the cerebral cortex.

Cocaine effects on the developing brain: current status

The present paper reports on the results obtained in a rabbit model of prenatal cocaine exposure that mimics the pharmacokinetics of crack cocaine in humans, and relates these findings to studies in other species including humans. A general finding is that prenatal exposure to cocaine during neurogenesis produces dysfunctions in signal transduction via the dopamine D(1) receptor and alterations in cortical neuronal development leading to permanent morphological abnormalities in frontocingulate cortex and other brain structures. Differences in the precise effects obtained appear to be due to the dose, route and time of cocaine administration. Related to these effects of in utero cocaine exposure, animals demonstrate permanent deficits in cognitive processes related to attentional focus that have been correlated with impairment of stimulus processing in the anterior cingulate cortex. The long-term cognitive deficits observed in various species are in agreement with recent reports indicating that persistent attentional and other cognitive deficits are evident in cocaine-exposed children as they grow older and are challenged to master more complex cognitive tasks.

Does drug abuse beget drug abuse? Behavioral analysis of addiction liability in animal models of prenatal drug exposure

Prenatal exposure to drugs of abuse is the single largest preventable cause of developmental compromise of American children today. In the clinical population, it is difficult to determine the independent effects of gestational exposure to a single drug on brain development, in part due to the confounding effects of additional risk factors that are encountered in the substance-abusing population. The enormous clinical and societal problem of gestational toxicity of drugs of abuse, both legal and illegal, has driven the need to develop and investigate animal models of gestational drug exposure in which these variables can be controlled. More specifically, as clinical data are gathered suggesting an increased liability to substance abuse among children of drug-abusing mothers, a mechanistic understanding of the lasting effects of early drug exposure on the developing brain and the behavioral repertoire of the developing animal is crucial. In this review we summarize experimental animal research that investigates the role of drug exposure in utero on the functional development of specific brain circuits that are involved in the reinforcing effects of drugs of abuse, and on the behaviors that are mediated by these brain reward systems.

Immediate-early gene expression in concurrent prenatal ethanol- and/or cocaine-exposed rat pups: intrauterine differences in cocaine levels and Fos expression

Concurrent use of cocaine and ethanol is a common mode of abuse. Cocaine and ethanol have distinctive pharmacologies but both have been shown to cause uterine vasoconstriction and fetal hypoxia. We developed a paradigm of chronic ethanol exposure via liquid diet coupled with binge cocaine exposure on the last day of gestation. Lipton et al. demonstrated unequal segregation of cocaine in rat fetuses as a function of proximal-distal location in the uterus, indicating a differential vasoconstriction of the two main arteries supplying the uterus in rats receiving cocaine. By performing C-sections after exposure to cocaine, we were able to measure the cocaine content and immediate-early gene (IEG) induction in the brains of fetuses according to their intrauterine position and assess the potentially vasoconstrictive effect of ethanol. HPLC analysis of fetal brains exposed to cocaine supported the study of Lipton et al.: fetuses from the proximal (lower) end of the uterus had more cocaine than fetuses from the distal (upper) end. Concurrent ethanol decreased the amount of cocaine reaching the fetuses and diminished the proximal-distal gradient. There were increased numbers of Fos-immunoreactive cells in fetuses exposed to both ethanol and cocaine compared to cocaine binge only. Additionally, the gradient of c-fos induction observed as a function of intrauterine position in cocaine-treated rats was in the opposite direction: most distal fetuses generally had the most Fos-immunoreactive cells. These results indicate that IEG induction in fetal brains exposed to cocaine and ethanol may be more related to hypoxic consequences of prenatal drug exposure.