Alteration of brain cell membrane function following cocaine exposure in the fetal guinea pig

Neurochemistry of drug action: insights from proton magnetic resonance spectroscopic imaging and their relevance to addiction

Proton magnetic resonance spectroscopy ((1)H MRS) is a noninvasive imaging technique that permits measurement of particular compounds or metabolites within the tissue of interest. In the brain, (1)H MRS provides a snapshot of the neurochemical environment within a defined volume of interest. A search of the literature demonstrates the widespread utility of this technique for characterizing tumors, tracking the progress of neurodegenerative disease, and for understanding the neurobiological basis of psychiatric disorders. As of relatively recently, (1)H MRS has found its way into substance abuse research, and it is beginning to become recognized as a valuable complement in the brain imaging toolbox that also contains positron emission tomography, single-photon-emission computed tomography, and functional magnetic resonance imaging. Drug abuse studies using (1)H MRS have identified several biochemical changes in the brain. The most consistent alterations across drug class were reductions in N-acetylaspartate and elevations in myo-inositol, whereas changes in choline, creatine, and amino acid transmitters also were abundant. Together, the studies discussed herein provide evidence that drugs of abuse may have a profound effect on neuronal health, energy metabolism and maintenance, inflammatory processes, cell membrane turnover, and neurotransmission, and these biochemical changes may underlie the neuropathology within brain tissue that subsequently gives rise to the cognitive and behavioral impairments associated with drug addiction.

Nitric Oxide and Oxidative Stress in the Brain of Rats Exposed In Utero to Cocaine

The role of nitric oxide (NO) and lipid peroxidation (LPO) processes in the physiological deficits induced by in utero cocaine exposure was examined in rats. NO generation in the hippocampus and cortex was detected using the electron paramagnetic resonance and LPO products were measured as thiobarbituric acid reactive species (TBARS). Pregnant Sprague-Dawley rats received a daily intraperitoneal injection of 20 mg/kg cocaine (IUC) or saline solution for control dams (IUV) between E17-E20. NO level was lower in the brain of IUC rats at postnatal day 1 and 2, but not 4, as compared with IUV rats. TBARS content was increased at day 1-4. Animals were used for behavioral testing at 25 days of age. Both NO and TBARS were elevated in the hippocampus of IUC rats as compared with IUV rats. Juvenile IUC rats developed significant learning impairments in the water-maze, as revealed by probe test retrieval deficits. Behavioral sessions resulted in a significant increase of TBARS levels only in IUV animals. Therefore, IUC rats showed a significant oxidative stress in basal conditions that may be related to their impaired learning ability. We did not find direct correlation between the changes in NO generation and intensity of LPO processes. It may probably mean that changes in intensity of LPO processes observed during prenatal cocaine exposure are not directly linked to NO pathway activation.

Memory impairments and oxidative stress in the hippocampus of in-utero cocaine-exposed rats

We examined whether significant oxidative stress is induced in the brain of juvenile rats exposed in utero to cocaine, and contributes to their mnesic difficulties. We measured nitric oxide generation, using electron paramagnetic resonance, and the thiobarbituric acid reactive species as specific indexes of lipid peroxidation. Both nitric oxide and lipid peroxidation were elevated in the hippocampus of in-utero cocaine-exposed rats as compared with control animals. In-utero cocaine-exposed rats developed significant learning impairments in the water-maze, shown by probe test retrieval deficits. In parallel, behavioural sessions resulted in increases of thiobarbituric acid reactive species levels only in control animals. Therefore, in-utero cocaine exposure resulted in a significant oxidative stress in basal conditions, which may be related to impaired learning ability.

Oral methylphenidate challenge selectively decreases putaminal T2 in healthy subjects

Despite the recent rise in oral methylphenidate (MPH) abuse, few studies have characterized the time course of oral MPH brain effects in human subjects. Accordingly, this study assessed the hemodynamic effects of oral MPH effects in 11 healthy young adults (six women), by measuring brain transverse relaxation times (T2). T2 can be interpreted as a surrogate marker for, and inversely correlated with, steady-state cerebral blood volume (CBV). Data were acquired from the caudate nucleus, putamen, and thalamus, using a 1.5 T MRI scanner at baseline and serially for 2 h following oral MPH administration (0.5 mg/kg). Physiological and subjective measures and plasma MPH levels also were examined. MPH induced a selective T2 decrease (-1.65+/-0.53 ms) in the putamen (F(6,54)=2.68, P<0.03). Heartrate, blood pressure and plasma MPH levels increased significantly after drug administration, as well as subjective ratings of "feeling drug effect". T2 decreases may reflect MPH-induced increases in putaminal blood volume. These data suggest that T2 relaxometry can be used to study the time course of regional cerebral blood volume responses to MPH and perhaps to other stimulant drugs.

Proton magnetic resonance spectroscopy of human basal ganglia: response to cocaine administration

BACKGROUND

Proton magnetic resonance spectroscopy was used to determine the effects of intravenous cocaine or placebo administration on human basal ganglia water and metabolite resonances.

METHODS

Long echo time, proton magnetic resonance spectra of water and intracellular metabolites were continuously acquired from an 8-cm(3) voxel centered on the left caudate and putamen nuclei before, during, and after the intravenous administration of cocaine or a placebo in a double-blind manner.

RESULTS

Cocaine, at both 0.2 and 0.4 mg/kg, did not alter the peak area for water. Cocaine at 0.2 mg/kg induced small and reversible increases in choline-containing compounds and N-acetylaspartate peak areas. Cocaine at 0.4 mg/kg induced larger and more sustained increases in choline-containing compounds and N-acetylaspartate peak areas. No changes in either water or metabolite resonances were noted following placebo administration.

CONCLUSIONS

These increases in choline-containing compounds and N-acetylaspartate peak areas may reflect increases in metabolite T2 relaxation times secondary to osmotic stress and/or increased phospholipid signaling within the basal ganglia following cocaine administration. This is the first report of acute, drug-induced changes in the intensity of human brain proton magnetic resonance spectroscopy resonance areas.

Amphetamine increases the extracellular concentration of glutamate in striatum of the awake rat: involvement of high affinity transporter mechanisms

Using microdialysis it was found that intracerebral infusions of amphetamine increase the extracellular concentration of glutamate, and also of dopamine, aspartate, GABA, and taurine. The increases in glutamate produced by amphetamine was independent of calcium in the perfusion medium but was significantly attenuated by specific blockers of the high affinity transporters of this neurotransmitter. Amphetamine infusions also produced a decrease in the extracellular concentration of Na+, an increase in the extracellular concentration of lactate, and a decrease in haemoglobin in the area of perfusion. All these data suggest that amphetamine increases the extracellular concentration of glutamate and other neurotransmitters through a hypoxic mediated process. This study also shows that an alpha-noradrenergic receptor antagonist is able to attenuate the effects of amphetamine on the release of glutamate, dopamine, GABA and taurine, which further suggests a vasoconstrictor effect of amphetamine as a result of which hypoxia could develop.

A circuitry model of the expression of behavioral sensitization to amphetamine-like psychostimulants

Repeated exposure to psychostimulants such as cocaine and amphetamine produces behavioral sensitization, which is characterized by an augmented locomotor response to a subsequent psychostimulant challenge injection. Experimentation focused on the neural underpinnings of behavioral sensitization has progressed from a singular focus on dopamine transmission in the nucleus accumbens and striatum to the study of cellular and molecular mechanisms that occur throughout the neural circuitry in which the mesocorticolimbic dopamine projections are embedded. This research effort has yielded a conglomerate of data that has resisted simple interpretations, primarily because no single neuronal effect is likely to be responsible for the expression of behavioral sensitization. The present review examines the literature and critically evaluates the extent to which the neural consequences of repeated psychostimulant administration are associated with the expression of behavioral sensitization. The neural alterations found to contribute to the long-term expression of behavioral sensitization are centered in a collection of interconnected limbic nuclei, which are termed the 'motive' circuit. This neural circuit is used as a template to organize the relevant biochemical and molecular findings into a model of the expression of behavioral sensitization.