Drugs of abuse modulate the phosphorylation of ARPP-21, a cyclic AMP-regulated phosphoprotein enriched in the basal ganglia

ARPP-21 is a cyclic AMP-regulated phosphoprotein of M(r) 21 kDa that is enriched in the cell bodies and terminals of medium-sized spiny neurons in the basal ganglia. Using a new phosphorylation state-specific antibody selective for the detection of ARPP-21 phosphorylated on Ser(55), we have demonstrated that activation of dopamine D1 receptors increased the level of ARPP-21 phosphorylation in mouse striatal slices. Conversely, activation of D2 receptors caused a large decrease in ARPP-21 phosphorylation. Treatment of mice with either methamphetamine or cocaine resulted in increased ARPP-21 phosphorylation in vivo. Studies using specific inhibitors of protein phosphatases and experiments in mice bearing a targeted deletion of the gene for DARPP-32, a dopamine-activated inhibitor of protein phosphatase-1, indicated that protein phosphatase-2A is primarily responsible for dephosphorylation of ARPP-21 in mouse striatum. These results demonstrate that phosphorylation and dephosphorylation of ARPP-21 are tightly regulated in the striatum. We speculate that ARPP-21 might mediate some of the physiologic effects of dopamine and certain drugs of abuse in the basal ganglia.     

Cytochrome P450 enzymes in aquatic invertebrates: recent advances and future directions

A variety of enzymes and other proteins are produced by organisms in response to xenobiotic exposures. Cytochrome P450s (CYP) are one of the major phase I-type classes of detoxification enzymes found in terrestrial and aquatic organisms ranging from bacteria to vertebrates. These enzymes metabolize a wide variety of substrates including endogenous molecules (e.g. fatty acids, eicosenoids, steroids) and xenobiotics (e.g. hydrocarbons, pesticides, drugs). Aquatic invertebrates, especially those in marine habitats, occupy every aspect of the environment, from above the surface (intertidal) to below the sediments. In turn, they have extremely diverse physiologies and are exposed to a vast array of potential toxicants. Aspects of aquatic invertebrate cytochrome P450 enzymes have been studied for the last 25 years. In a few phyla, P450 activities have been measured and are responsive to xenobiotic exposures. Until the last several years, little progress had occurred in the identification of P450 gene diversity in aquatic invertebrates. Molecular biology tools have greatly aided this search, and are likely to identify as much diversity for this protein superfamily as is present in higher marine and terrestrial organisms. Recent work has expanded our knowledge of the CYP superfamily, and new developments will rapidly advance the usefulness of these genes into such fields as biomarker research. Advances of the last decade are reviewed and insights are presented from related insect studies.     

Protection by cyclosporin A of cultured hepatocytes from the toxic consequences of the loss of mitochondrial energization produced by 1-methyl-4-phenylpyridinium.

Cyclosporin A prevented the killing of cultured rat hepatocytes by 1-methyl-4-phenylpyridinium (MPP+). However, in the presence of both cyclosporin and atractyloside, there was no protection. Cyclosporin had no effect on the depletion of ATP or the loss of mitochondrial energization by MPP+. Cyclosporin, however, did prevent the increase in the molecular order of hepatocyte membranes produced by MPP+. These data suggest that mitochondrial de-energization produced by MPP+ is accompanied by a "permeability transition" analogous to that which occurs in vitro in the presence of calcium. By preventing this transition, cyclosporin protects the cells. By antagonizing this action of cyclosporin, atractyloside restores the cell killing. The mitochondrial transition is causally linked to cell killing by a mechanism that increases the molecular order of the hepatocyte plasma membrane.     

Morphine-induced metabolic changes in human brain. Studies with positron emission tomography and [fluorine 18]fluorodeoxyglucose

Morphine sulfate effects (30 mg, intramuscularly) on cerebral glucose utilization and subjective self-reports were examined in 12 polydrug abusers by positron emission tomography and [fluorine 18]fluorodeoxyglucose in a double-blind placebo-controlled crossover study. During testing, subjects sat with eyes covered, listening to white noise and "beep" prompts. Morphine significantly reduced glucose utilization by 10% in whole brain and by about 5% to 15% in telencephalic areas and the cerebellar cortex, assuming no contribution of hypercapnia. When the contribution of PaCO2 (45 minutes after morphine was administered) was partialled out, significant morphine-induced reductions persisted in whole brain and six cortical areas. Irrespective of morphine, left-greater-than-right asymmetry occurred in the temporal cortex, and an interaction between hemisphere and drug was noted in the postcentral gyrus. In most cases, effects on glucose utilization were not significantly related to measures of euphoria.     

"Crack smoke" is a respirable aerosol of cocaine base

The smoking of cocaine base [corrected] ("crack") has emerged as a significant substance abuse problem. A detailed characterization of cocaine smoke is a prerequisite for studies of its pharmacokinetics, abuse potential and toxicity. Model pipes were used to generate cocaine smoke analogous to that inhaled by human "crack" abusers. Using procedures to minimize pyrolysis, cocaine base smoke was determined to be 93.5% cocaine particles with the remainder being cocaine vapor. The average particle size generated from all model pipes was 2.3 mu which is small enough to ensure deposition into the alveolar region of the human lung. Although this particle size is eminently respirable [corrected] by primates, a much smaller fraction will reach the alveolar region of rodents. Special generating procedures would therefore be required to expose rodents to meaningful doses of airborne cocaine that mimic the rapid absorption achieved by "crack" smokers.     

Abnormalities of cerebral oxidative metabolism in animal models of Parkinson disease

Abnormalities of cerebral oxidative metabolism were investigated in "animal models" of Parkinson disease by in situ optical measurements of local cerebral blood volume and cytochrome oxidase redox shifts in rats two weeks after unilateral 6-hydroxydopamine lesions of the substantia nigra with or without interruption of ascending noradrenergic pathways. The data demonstrate oxidative metabolic dysfunction of ipsilateral cerebral hemispheres caused by lesions that involve both dopaminergic and noradrenergic systems but not when dopaminergic neurons only are affected. We speculate that the dementia of Parkinson disease may be more prevalent when degeneration of catecholaminergic systems is widespread and not restricted to the dopaminergic system.     

The use of a computer to select optimized conditions for high-performance liquid chromatography separation.

Computer simulation allows the convenient prediction and optimization of HPLC separation as a function of various separation conditions. The use of retention and bandwidth relationships that have been validated for a broad range of chromatographic systems minimizes the number of experimental runs needed, especially for the new technique of restricted multi-parameter optimization. The chromatographer is free to use these procedures in a trial-and-error mode, or alternatively use can be made of resolution maps and other data summaries. "Gridding" experiments, based on the automated collection of chromatographic data, can be used to supplement predictions obtained from computer simulation.     

Simulation of blood flow in microgravity.

Knowledge of venous, capillary, and arterial blood flow in microgravity is required to modify hemostatic techniques for control of bleeding in traumatic injuries or surgical procedures in space. To simulate human arterial, venous, and capillary bleeding, fresh whole bovine blood was injected by two operators at calculated flow rates (3.5, 7, and 14 mL for venous and 14 and 28 mL for arterial) in 10 seconds with empirical controls in a lucent glove box during zero gravity parabolic flight on NASA's KC-135 aircraft. A pig's foot was used to mimic capillary bleeding. Hemostasis with sponges and laerdal suction was evaluated by video and still photography. Evaluations of the arterial and venous bleeding were conducted at 3 rates x 3 parabolas, and capillary bleeding was evaluated with 5 parabolas x 2 methods (pig's foot and sponge). Influenced by surface tension, the slow venous bleeding coated syringe surfaces and formed a dome over the skin laceration bleeding site. Arterial and venous bleeders broke into uniform spheres with low-velocity spheres bouncing off an absorbent pad and suction tip. Conventional dabbing with gauze fragmented blood into small spheres. Capillary oozing was better controlled by "wicking" up blood with gauze. Repeated arterial bleeding opacified the glove box wall. This stimulation demonstrated unique characteristics of extracorporeal blood flow and inadequacies of common methods of hemostasis in microgravity.     

A novel neuronal messenger molecule in brain: the free radical, nitric oxide.

Understanding of the organization and function of a newly identified neuronal messenger molecule, nitric oxide, has progressed rapidly. Nitric oxide synthase has been purified and molecularly cloned from brain. Its localization is exclusively neuronal and endothelial. The catalytic activity of nitric oxide synthase accounts for the NADPH diaphorase staining of neurons that are uniquely resistant to toxic insults and neurodegenerative disorders. Nitric oxide has diverse functions. In platelets it inhibits their aggregation, in macrophages it mediates cytotoxicity, and in blood vessels it acts as a vasodilator. In the nervous system nitric oxide may be the retrograde transmitter in long-term potentiation. It is the "neurotransmitter" of cerebral vasodilator nerves and the inhibitory "neurotransmitter" of the motor neurons of the intestines. Nitric oxide in situations of excessive production may function as a neurotoxin, suggesting a role for nitric oxide in neurodegenerative disorders.