Biological mechanisms and perinatal exposure to abused drugs

Behavioral and social correlates of methamphetamine use in a population-based sample of early and later adolescents

This paper reports relationships between methamphetamine use and behaviors and social influences using data from a population-based survey of 8th- and 11th-grade students in Oregon for the 2001-2003 school years. We analyze methamphetamine use within a general problem behavior framework to identify malleable correlates of behavior for future prevention interventions. We specifically test two models of methamphetamine use employing logistic regression analysis: one comprised of behaviors and traits of the individual students and another focusing on peer and parental influences. This study finds adolescent methamphetamine use related to several problem behaviors. However, the specific problems vary by grade and are moderated by gender. Findings indicate the need for tailored interventions targeting gender/grade-specific behaviors or problems such as antisocial activities, risky sex, and depression, as well as social influences such as peers engaging in antisocial behaviors or using drugs and parents favoring drug use or poorly monitoring or setting limits for their children.

A “deficient environment” in prenatal life may compromise systems important for cognitive function by affecting BDNF in the hippocampus

The intrauterine environment has the capacity to mold the prenatal nervous system. Particularly, recent findings show that an adverse prenatal environment produces structural defects of the hippocampus, a critical area sub-serving learning and memory functions. These structural changes are accompanied by a disruption in the normal expression pattern of brain-derived neurotrophic factor (BDNF) and its cognate tyrosine kinase B (TrkB) receptor. The important role that the BDNF system plays in neural modeling and learning and memory processes suggests that fetal exposure to unfavorable intrauterine conditions may compromise proper cognitive function in adult life. These findings have implications for disorders that involve a dysfunction in the BDNF system and are accompanied by cognitive deficits.

The intersection of stress, drug abuse and development

Use or abuse of licit and illicit substances is often associated with environmental stress. Current clinical evidence clearly demonstrates neurobehavioral, somatic growth and developmental deficits in children born to drug-using mothers. However, the effects of environmental stress and its interaction with prenatal drug exposure on a child's development is unknown. Studies in pregnant animals under controlled conditions show drug-induced long-term alterations in brain structures and functions of the offspring. These cytoarchitecture alterations in the brain are often associated with perturbations in neurotransmitter systems that are intimately involved in the regulation of the stress responses. Similar abnormalities have been observed in the brains of animals exposed to other adverse exogenous (e.g., environmental stress) and/or endogenous (e.g., glucocorticoids) experiences during early life. The goal of this article is to: (1) provide evidence and a perspective that common neural systems are influenced during development both by perinatal drug exposure and early stress exposure; and (2) identify gaps and encourage new research examining the effects of early stress and perinatal drug exposure, in animal models, that would elucidate how stress- and drug-induced perturbations in neural systems influence later vulnerability to abused drugs in adult offspring.

Bolus maternal cocaine administration does not produce a large increase in fetal sheep cerebral cortical glutamate concentration

Human cocaine use during pregnancy may result in postnatal neurologic dysfunction and abnormal behavior. L-Glutamate, the major excitatory neurotransmitter in the brain, plays an important role in cerebral cortical development. An optimal level of glutamate is required for normal neuronal development. We tested whether acute cocaine exposure produces large increases in glutamate release in the intact cerebral cortex of the near-term fetal sheep. Cocaine 3.0 mg kg(-1) IV bolus produced the expected increase in maternal and fetal mean arterial pressure, increase in fetal heart rate, decrease in uterine blood flow, and decrease in fetal arterial blood pO2 (N = 5). The percentage increases in extracellular glutamate concentration in the fetal cerebral cortex measured by in utero microdialysis were 7%, 15%, 17%, 17%, and 43% in each fetus (upper 95% confidence bound for the median = 43%). We conclude that if cocaine increases glutamate concentration in the developing cerebral cortex, the increase in magnitude is small relative to the changes produced by other interventions such as ethanol or umbilical cord occlusion. Mechanisms other than increases in cerebral cortical glutamate concentration probably contribute to the neurologic injury associated with prenatal cocaine exposure.

Transplacental cocaine exposure. 3: Mechanisms underlying altered brain development

In a mouse model of transplacental cocaine exposure we have demonstrated alterations in brain structure and function of offspring including disturbances of brain growth, disruption of neocortical cytoarchitecture, and transient as well as persistent behavioral deficits. One mechanism by which cocaine may alter fetal brain development is through cocaine-induced alpha-adrenergic-mediated (uterine) arterial vasoconstriction. In this study pregnant Swiss Webster (SW) mice were injected with cocaine HCl (20 or 40 mg/kg, SC) without any changes evident in mean arterial blood pressure (MAP) measurements. These physiology results suggest that in our mouse model, cocaine's transplacental effects on the fetus are not due to cocaine-induced maternal vasoconstriction, nor concomitant hypoperfusion of the fetus. In a separate series of experiments, pregnant SW dams were administered cocaine HCl at 40 mg/kg/day (COC 40), 20 mg/kg/day (COC 20), or 10 mg/kg/day (COC 10) [SC, divided in two daily doses, from embryonic day (E) 8 to E17 inclusive]. Additional groups of cocaine-treated dams were administered phentolamine (5 mg/kg, SC), a short-acting alpha-adrenergic antagonist, 15 min prior to each cocaine dose (Phent COC 40, Phent COC 20, Phent COC 10). Animals born to Phent COC 40 dams demonstrated transient postnatal brain growth retardation and behavioral deficits in first-order conditioning of P9 mice comparable to mice born to COC 40 dams, which received the same regimen of cocaine injections without phentolamine pretreatment. Like COC 40 offspring, Phent COC 40 offspring also demonstrated a persistent deficit in the blocking paradigm. The behavioral and growth findings confirm and extend the physiology data, and imply that in our rodent model, alpha-adrenergic mechanisms (including maternal vasoconstriction) are unlikely to mediate these toxic effects of transplacental cocaine exposure on developing brain.

Evidence for increased seizure susceptibility in rats exposed to cocaine in utero

Clinical observations indicate that cocaine use during pregnancy is a major health concern in the United States and may result in seizure-like behavior in the offspring. In the present study, we investigated whether prenatal cocaine exposure altered seizure thresholds measured in Sprague-Dawley rats, 60-90 days postnatal. In vitro postnatal studies, focusing on hippocampal tissue, revealed a reduced threshold for both electrical stimulation- and potassium-induced epileptiform discharges in slices from cocaine-exposed animals. Modest elevation of extracellular potassium concentration from 3 to 6 mM KCl elicited spontaneous epileptiform discharges in the majority of slices from cocaine-exposed animals (13/20) but rarely in slices from saline-exposed animals (2/18). In vivo studies on awake, freely behaving adult rats indicated a significant reduction in thresholds for both flurothyl- and kainic acid-induced seizures in cocaine-exposed animals. Video-EEG monitoring during administration of kainic acid revealed reduced latencies to first 'electrographic seizure' and first 'electrographic seizure with behavior' in rats exposed to cocaine in utero compared to saline-treated controls. These studies provide strong experimental evidence that adult animals exposed to cocaine during gestation are at high risk for the development of seizure activity.

Effects of prenatal cocaine exposure on the developing hippocampus: intrinsic and synaptic physiology

A variety of neurological complications has been reported in infants exposed to cocaine during gestation. In the present study, intrinsic cell properties of hippocampal neurons from CA1, CA3, and dentate gyrus regions were measured and compared in tissue from neonatal rats exposed to saline or cocaine in utero. Synaptic properties of the CA1 pyramidal cell region were analyzed at postnatal day (P) 20 with the use of extracellular and intracellular recording techniques. In vitro intracellular recordings (n = 223) obtained at P10, P15 and P20 in tissue from cocaine- and saline-exposed animals revealed no differences in standard cell properties such as resting membrane potential, input resistance, time constant, and action potential amplitude or duration. Hippocampal slices from cocaine-exposed animals exhibited a marked reduction of spike frequency adaptation for all three types of principal hippocampal neurons (e.g., CA1, CA3, and granule cells). The amplitudes of afterhyperpolarizations following a spike train were also decreased in CA1 and CA3 cells in tissue from cocaine-exposed animals. Extracellular and intracellular recordings in the CA1 pyramidal cell region at P20 were obtained to assess and compare synaptic function in tissue from cocaine- and saline-exposed animals. In hippocampal slices from cocaine-exposed animals, synaptic responses in the CA1 region were characterized by multiple population spike activity and reduced inhibitory postsynaptic potentials. The reduction in fast inhibitory postsynaptic potential conductance was not associated with a change in reversal potential. These results suggest that gestational cocaine exposure induces significant changes in intrinsic and synaptic electrophysiological properties of hippocampal neurons in the developing animal. The cell and synaptic features are consistent with an increase in hippocampal excitability, which may contribute to the neurobehavioral deficits and epileptogenic predisposition reported in this infant population. As such, this in utero drug exposure model may provide a useful system in which to elucidate and study the basic cellular mechanisms underlying neurological complications associated with maternal cocaine abuse.