Relative phosphocreatine and nucleoside triphosphate concentrations in cerebral gray and white matter measured in vivo by 31P nuclear magnetic resonance

Rates of ATP metabolism generally are higher in cerebral gray matter compared to white matter. In order to study the physiology of this regional difference in vivo, the 1-dimensional chemical shift imaging technique (1D-CSI) was used to acquire 31P nuclear magnetic resonance spectra from 2.5 mm slices of 4-week old piglet brains. Spectra from predominantly gray matter slices (estimated 76% gray matter, 7 mm below the scalp) were compared to predominantly white matter slices (56% estimated white matter, 13 mm below the scalp) as assessed by magnetic resonance images. The 1D-CSI technique introduced no systematic changes in the ratio of signals from a single chamber phantom containing a phosphocreatine (PCr) and ATP solution. Gray matter slices showed a PCr/NTP ratio of 0.93 +/- 0.11 (mean +/- S.D.) using a 2 s interpulse interval, a value very close to the ratio in surface coil localized spectra. The predominantly white matter slices showed a PCr/NTP ratio of 1.32 +/- 0.18 (P < 0.02 for gray versus white matter). Using the estimated percentages of gray and white matter in the two slices and calculated concentrations from fully relaxed spectra, the gray matter PCr/NTP ratio is approximately 0.77, while the ratio in white matter is approximately 2.18. The difference in PCr/NTP measured in vivo suggests that either the total NTP concentration is higher or the steady state PCr concentration is lower in gray matter than in white matter in the piglet brain.

Nevermore: the hymen and the loss of virginity

A major milestone in a woman's life is the loss of virginity, "defloration," with the breaking of the hymen. Psychoanalysis has paid little attention to the meaning of defloration to either women or men, and virtually none to the hymen as a part of the female genitalia. The reasons for this disregard or avoidance are explored. Utilizing the few psychoanalytic writings, mythology, literature, and anthropological studies in addition to numerous clinical examples, the authors find that the unconscious meanings of the loss of virginity and the hymen emerge clearly. The common theme is that of negation, never, never again, never seen, known or named. Theoretical considerations regarding female sexuality are discussed. Technical implications for analyst-patient are presented.

Phosphocreatine and creatine kinase in piglet cerebral gray and white matter in situ

Rates of adenosine triphosphate (ATP) metabolism are higher in cerebral gray matter than in white matter. Like other excitable tissues, brain contains a phosphocreatine (PCr)/creatine kinase (CK)/ATP system including cytosolic (B-CK) and mitochondrial (Mi-CK) isozymes. High B-CK activity is present in white and gray matter while Mi-CK is mostly in gray matter. An in situ localizing 31P-NMR technique, one-dimensional chemical shift imaging (1D-CSI), has been used to study the PCr/CK/ATP system in these regions. In the metabolically mature 4-week-old piglet, the PCr/nucleoside triphosphate (NTP) ratio measured by the 1D-CSI technique is at least 50% higher in white than gray matter. Total creatine (Cr), ATP, and total NTP concentrations are the same in rapidly frozen rat white and gray matter, suggesting that PCr/Cr ratio is much higher in white matter. The PCr increases more in gray than white matter between 4 days and 4 weeks of age in piglet brain. The CK catalyzed reaction rate constant, measured by combining the saturation transfer experiment with the 1D-CSI, is also much higher in white than gray matter at both ages. The postnatal maturational increase in the CK rate constant is greater in gray matter. In summary, these differences in PCr concentration and CK reaction rates and isozymes characterize two physiologically different PCr/CK/ATP systems in gray and white matter.

'Hot spots' of creatine kinase localization in brain: cerebellum, hippocampus and choroid plexus

Creatine kinase (CK) isoenzymes, with emphasis on the mitochondrial CK isoenzymes, were characterized and localized in chicken cerebellum. Chicken cerebellum extracts analyzed by two-dimensional gels, using antipeptide antibodies specific for sarcomeric muscle-type mitochondrial CK (Mib-CK) and revealed the presence of a Mib-CK variant in avian cerebellum. This CK isoform was localized by immunofluorescence staining exclusively in the Purkinje neurons. The co-expression of this Mib-CK together with cytosolic muscle-type MM-CK, as observed in the same Purkinje neurons, may reflect the specific energy requirements associated with highly fluctuating Ca2+ levels (Ca2+ spiking) in these specialized neurons. Ubiquitous brain-type mitochondrial Mia-CK was found together with cytosolic BB-CK mainly in the glomeruli structures of the cerebellar granular layer. BB-CK, but much less so Mia-CK however, was also very prominent in Bergmann glial cells of the two mitochondrial Mi-CK isoenzymes in the chicken cerebellum is demonstrated. Other hot spots of CK localization were the granule and pyramidal cells of the hippocampus in rat. There, a developmental stage-dependent immunofluorescence staining, especially with antibodies against Mia-CK was noted. Epithelial cells of the choroid plexus were also highly enriched in CK. The possible implications of a CK/PCr circuit at these various cellular locations of the brain are discussed with respect to normal brain physiology and pathology.

Creatine and nucleoside triphosphates in rat cerebral gray and white matter

In vivo localized nuclear magnetic resonance spectroscopy has shown three-fold higher phosphocreatine/nucleoside triphosphate (PCr/NTP) ratios in cerebral white compared to gray matter. To interpret these results, total creatine (Cr) and ATP concentrations were measured enzymatically in samples taken from rapidly frozen rat cerebral cortex and corpus callosum. Total Cr (PCr plus Cr) and ATP concentrations were the same in the two regions. High performance liquid chromatography showed similar concentrations of total NTP in the two regions. These results suggest that higher in vivo PCr/NTP ratios in white compared to gray matter may be due to a higher PCr/Cr ratio in white matter and/or higher percentages of non-adenine mono- or diphosphate nucleotides in gray matter.

Parent and peer communication effects on AIDS-related behavior among U.S. high school students

Data from a 1989 national probability sample of 8,098 high school students in the United States indicate that young people's discussions about the human immunodeficiency virus (HIV) with parents and with peers are highly correlated and have opposite effects on behavior. Students who discussed HIV with their parents were less likely than those who did not to have had multiple sex partners, to have had unprotected sexual intercourse and to have ever injected drugs; on the other hand, students who discussed HIV with their peers were more likely than those who did not to have had multiple partners and to have had unprotected sexual intercourse. Subgroup analyses show that young women were influenced more by HIV discussions with parents, while young men were influenced more by discussions with peers; some communication effects differed by race and ethnicity. Students who received HIV instruction in school were more likely to have talked about HIV with both parents and peers.

Enamel hypoplasia, bilateral cataracts, and aqueductal stenosis: a new syndrome?

We report on a 12-year-old girl who presented with generalized enamel hypoplasia, cataracts, and enlargement of the cerebral ventricles secondary to aqueductal stenosis. Previously described syndromes of enamel defects with or without cataracts were excluded on the basis of clinical criteria and appearance of the dentition. Metabolic conditions which could have caused cataracts were excluded clinically and by biochemical tests. The combination of signs in this patient may represent a new syndrome.

Trends in risk behaviors for HIV infection among U.S. high school students, 1989-1991

The objective of this study was to examine trends in rates of self-reported HIV-related instruction and behaviors among high school students in the United States. Self-administered questionnaires were completed by three independent, multistage national probability samples of public and private school students in grades 9 through 12 who were surveyed in the spring of 1989, 1990, and 1991, respectively. Controlling for demographic characteristics, we used logistic regression to test for trends from 1989 to 1991. From 1989 to 1991, the proportion of students who had received HIV instruction in school significantly increased from 53.7% in 1989 to 83.3% in 1991. At the same time, the proportion of students engaging in selected sexual behaviors generally decreased. We found significant declines in the proportion of students who had engaged in sexual intercourse (58.5% in 1989 to 54.1% in 1991), had two or more sex partners during their lifetime (40.1% in 1989 to 35.2% in 1991), and had four or more lifetime sex partners (23.6% in 1989 to 18.7% in 1991). School-based HIV instruction, which is reaching greater numbers of U.S. students, may be contributing to the decline in reported risk behavior. However, because the current level of HIV-related behavior is still too high, risk-reduction efforts for adolescents should be maintained and strengthened.

pH strategies and cerebral energetics before and after circulatory arrest

The pH-stat strategy compared with the alpha-stat strategy provides more rapid recovery of brain high-energy phosphate stores and intracellular pH after 1 hour of hypothermic circulatory arrest in pigs. Possible mechanisms for this difference are (1) improved oxygen delivery and homogeneity of brain cooling before deep hypothermic circulatory arrest and (2) greater cerebral blood flow and reduced reperfusion injury owing to extracellular acidosis during the rewarming phase. To identify which of these mechanisms is predominant, we studied 49 4-week-old piglets undergoing 1 hour of deep hypothermic circulatory arrest. Four groups were defined according to cooling/rewarming strategy: alpha/alpha, alpha/pH, pH/alpha, and pH/pH. In 24 animals cerebral high-energy phosphate levels and intracellular pH were measured by magnetic resonance spectroscopy (alpha/alpha group 7, alpha/pH group 5, pH/alpha group 7, pH/pH group 5). In 25 animals cerebral blood flow was measured by labeled microspheres, cerebral metabolic rate by oxygen and glucose extraction, and the redox state of cytochrome aa3 and hemoglobin oxygenation by near infrared spectroscopy (alpha/alpha group 7, alpha/pH group 5, pH/alpha group 7, pH/pH group 6). Cerebral blood flow was greater with pH-stat than alpha-stat during cooling (56.3% +/- 3.7% versus 32.9% +/- 2.1% of normothermic baseline values, p < 0.001). Cytochrome aa3 values became more reduced during cooling with alpha-stat than with pH-stat (p = 0.049). Recovery of adenosine triphosphate levels in the initial 45 minutes of reperfusion was more rapid in group pH/pH compared with that in the other groups (p = 0.029). Recovery of cerebral intracellular pH in the initial 30 minutes was faster in group pH/pH compared with that in group alpha/alpha (p = 0.026). Intracellular pH became more acidic during early reperfusion only in group alpha/alpha, whereas it showed continuous recovery in the other groups. This study suggests that there are mechanisms in effect during both the cooling and rewarming phases before and after deep hypothermic circulatory arrest that could contribute to an improved cerebral outcome with pH-stat relative to more alkaline strategies.

Phosphocreatine and ATP regulation in the hypoxic developing rat brain

Decreased brain ATP and phosphocreatine (PCr) concentrations and intracellular pH were compared in hypoxic 4-, 10-11, and 24-25-day-old rats. Surface coil 31P-nuclear magnetic resonance (NMR) spectra were acquired in vivo every minute before, during, and after 7 min of breathing 4% O2. At all ages PCr decreased rapidly. At the two younger ages, the nucleoside triphosphate signal was still 80-85% of pre-hypoxic values, indicating 20-30% decrease in ATP, when PCr was almost fully depleted. At 24-25 days, PCr initially decreased 40-50% with an ATP loss of about 30%. Then, PCr and ATP decreased simultaneously. The decrease in brain pH was greatest at 24-25 days. More electrocortical seizure activity during hypoxia was seen at 10-11 days than at other ages. Seizure activity was seen only when ATP was less than 20% depleted and was not associated with more rapid decreases in ATP or PCr. At all ages, loss of electrocortical activity occurred when ATP was about 30% depleted. Brain creatine kinase catalyzed flux, measured by the NMR saturation transfer experiment before the hypoxic period, was 4-fold higher at 24-25 days than at 4- or 10-11 days. In conclusion, the temporally coupled depletion of PCr and ATP during hypoxia, which is characteristic of the mature brain, is seen only after the maturational increase in brain CK activity.

Reduction of cytochrome aa3 measured by near-infrared spectroscopy predicts cerebral energy loss in hypoxic piglets

Near-infrared spectroscopy is a noninvasive monitoring technique that allows quantitative measurement of changes in cerebral oxygenated Hb (HbO2), deoxygenated Hb (Hb), total Hb, and oxidized cytochrome aa3 (CytO2). Changes in cerebral Hb oxygenation and CytO2 have been measured in human neonates and infants under a variety of conditions. However, the association of these measurements with cerebral high-energy phosphate loss is not known. We studied simultaneous changes in cerebral HbO2, Hb, total Hb, and CytO2 by near-infrared spectroscopy and changes in nucleoside triphosphate (NTP, mostly ATP) and phosphocreatine (PC) concentrations and intracellular pH by in vivo 31P-labeled magnetic resonance spectroscopy. Four-wk-old piglets (n = 8) underwent sequential hypoxic episodes of increasing severity (inspired O2 concentration, 12, 8, 6, 4, and 0%). Animals were anesthetized and mechanically ventilated. At all levels of hypoxia, cerebral HbO2 decreased, and Hb increased. Loss of PC or NTP was not observed until inspired O2 concentration was decreased to less than 12%. With such severe hypoxia, hypotension, intracellular acidosis, and increasingly severe PC and NTP depletions occurred. Decreases in PC and NTP correlated closely with decreased CytO2 and arterial blood pressure (p < 0.0001) but not with changes in HbO2 and Hb. In conclusion, cerebral hypoxemia is readily detected by near-infrared spectroscopy as a decrease in HbO2 and an increase in Hb. However, relative changes in cerebral HbO2 and Hb have low predictive value for cerebral energy failure. Reduction of CytO2 is highly correlated with decreased brain energy state and may indicate impending cellular injury.

Effects of cerebroplegic solutions during hypothermic circulatory arrest and short-term recovery

Previous studies have suggested that a simple crystalloid "cerebroplegic" solution may prolong the safe duration of hypothermic circulatory arrest. We tested the hypothesis that pharmacologic modification of the cerebroplegic solution would further enhance cerebral protection. Forty-six 4-week-old miniature piglets underwent core cooling to 15 degrees C nasopharyngeal temperature and 2 hours of hypothermic circulatory arrest. Twelve animals had a 50 ml/kg dose of saline infused into the carotid artery system at the onset of hypothermic circulatory arrest and repeat doses of 10 ml/kg every 30 minutes during arrest. Eleven animals received the same initial and repeat doses of University of Wisconsin organ preservation solution and 10 received University of Wisconsin solution with 7.5 mg/L of MK-801, an excitatory neurotransmitter antagonist. In 13 control animals blood was partially drained from the piglet before 2 hours of circulatory arrest at 15 degrees C and no cerebroplegic solution was infused. All solutions were delivered at 4 degrees C. Brain temperature (n = 24) at the onset of hypothermic circulatory arrest was 15.0 degrees +/- 0.1 degrees C (mean +/- standard error). Brain temperature after cerebroplegic infusion dropped to 13.0 degrees +/- 0.3 degrees C and stayed lower than brain temperature in the control group throughout the hypothermic circulatory arrest period. Recovery of cerebral adenosine triphosphate and intracellular pH determined by phosphorus 31 magnetic resonance spectroscopy (n = 22) was significantly improved by saline infusion and was further improved with University of Wisconsin solution and University of Wisconsin solution plus MK-801 (p < 0.001). Recovery of cerebral blood flow measured by microspheres (n = 24) also was augmented by University of Wisconsin solution (p < 0.001) but not in the presence of MK-801. The vascular resistance response to acetylcholine and nitroglycerin suggested that MK-801 has a direct vasoconstrictive effect. Recovery of cerebral oxygen consumption (n = 24) was increased by University of Wisconsin solution and University of Wisconsin solution with MK-801 (p = 0.002). Brain water content (n = 46) was significantly lower in all cerebroplegia-treated groups than in controls (p < 0.001).

CONCLUSION

Cerebroplegia improves short-term recovery after 2 hours of circulatory arrest in hypothermic piglets. Pharmacologic modification with University of Wisconsin solution further improves the recovery of cerebral blood flow and metabolism. MK-801 does not augment the protective effects of University of Wisconsin solution and reduces the recovery of cerebral blood flow by a direct vascular action. Modified cerebroplegia may provide a novel approach to improved cerebral protection when prolonged hypothermic circulatory arrest is necessary.

Substance use and HIV-related sexual behaviors among US high school students: are they related?

OBJECTIVES

This study was undertaken to examine whether use of alcohol, cigarettes, marijuana, cocaine, and other illicit drugs is related to the likelihood of sexual behaviors that increase risk for human immunodeficiency virus (HIV) infection among youth.

METHODS

The 1990 national Youth Risk Behavior Survey was used to collect self-reported information about a broad range of health risk behaviors from a representative sample of 11,631 high school students in the United States.

RESULTS

Students who reported no substance use were least likely to report having had sexual intercourse, having had four or more sex partners, and not having used a condom at last sexual intercourse. Adjusted for age, sex, and race/ethnicity, odds ratios for each of these sexual risk behaviors were greatest among students who had used marijuana, cocaine, or other illicit drugs. Students who had used only alcohol or cigarettes had smaller but still significant increases in the likelihood of having had sexual intercourse and of having had four or more sex partners.

CONCLUSIONS

HIV prevention programs for youth should recognize that substance use may be an important indicator of risk for HIV infection and acquired immunodeficiency syndrome through its association with unsafe sexual behaviors.

Changes in HIV-related information sources, instruction, knowledge, and behaviors among US high school students, 1989 and 1990

OBJECTIVES

Few data have been available among adolescents to determine behavioral changes that may prevent human immunodeficiency virus (HIV) infection. This analysis examines changes in the prevalence of self-reported HIV-related information sources, instruction, knowledge, and behaviors among high school students in the United States.

METHODS

Two independent, multistage national probability samples of students in grades 9 through 12 were surveyed in 1989 (n = 8098) and 1990 (n = 11,631) with self-administered, anonymous questionnaires that included similar items.

RESULTS

Compared with students surveyed in 1989, a significantly greater proportion of students surveyed in 1990 had received HIV instruction in school. Significant decreases were found in the proportion of White and female students who reported having had sexual intercourse, in the proportion of White students reporting two or more lifetime sex partners, and in the proportion of 15- and 16-year-olds, White students, and female students who reported having had four or more lifetime sex partners. For both years, students who had a greater level of HIV knowledge were less likely to have had multiple lifetime sex partners or to have injected illicit drugs.

CONCLUSIONS

The findings suggest that school-based HIV education and knowledge may be contributing factors in reducing certain risk behaviors that can lead to HIV transmission among secondary school youth.

Effects of MK-801 and NBQX on acute recovery of piglet cerebral metabolism after hypothermic circulatory arrest

Brain protection during open heart surgery in the neonate and infant remains inadequate. Effects of the excitatory neurotransmitter antagonists MK-801 and NBQX on recovery of brain cellular energy state and metabolic rates were evaluated in 34 4-week-old piglets (10 MK-801, 10 NBQX, 14 controls) undergoing cardiopulmonary bypass and hypothermic circulatory arrest at 15 degrees C nasopharyngeal temperature for 1 h, as is used clinically for repair of congenital heart defects. MK-801 (dizocilpine) (0.75 mg/kg) or NBQX [2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline] (25 mg/kg) was given intravenously before cardiopulmonary bypass. Equivalent doses were placed in the cardiopulmonary bypass prime plus continuous infusions after reperfusion (0.15 mg kg-1h-1 and 5 mg kg-1h-1). Changes in high-energy phosphate concentrations and pH were analyzed by magnetic resonance spectroscopy in 17 animals until 225 min after reperfusion. Cerebral blood flow determined by radioactive microspheres as well as cerebral oxygen and glucose consumption were studied in 17 other animals. Cerebral blood flow and oxygen consumption were depressed relative to control by both MK-801 and NBQX at baseline. Recovery of phosphocreatine (p = 0.010), ATP (p = 0.030), and intracellular pH (p = 0.004) was accelerated by MK-801 and retarded by NBQX over the 45 min of rewarming reperfusion and the first hour of normothermic reperfusion. The final recovery of ATP at 3 h and 45 min reperfusion was significantly reduced by NBQX (46 +/- 26% baseline, mean +/- SD) versus control (81 +/- 19%) and MK-801 (75 +/- 8%) (p = 0.030). Cerebral oxygen consumption recovered to 105 +/- 30% baseline in group MK-801 and 94 +/- 31% in control but only to 61 +/- 22% in group NBQX (p = 0.070). Cerebral blood flow stayed significantly lower in group NBQX relative to control. Thus, MK-801 accelerates recovery of cerebral high-energy phosphates and metabolic rate after cardiopulmonary bypass and hypothermic circulatory arrest in the immature animal. At the dosage used NBQX exerts an adverse effect.

Recovery of cerebral blood flow and energy state in piglets after hypothermic circulatory arrest versus recovery after low-flow bypass

A miniature piglet model that replicates clinical hypothermic (14 degrees C nasopharyngeal) circulatory arrest and low-flow (50 ml/kg per minute) bypass was used to study carotid blood flow with electromagnetic flow probe, cerebral blood flow by microsphere injection, cerebral metabolic rate by arteriovenous oxygen and glucose extractions, lactate production by cerebral arteriovenous difference, and cerebral edema. Data from five animals that underwent circulatory arrest and five animals that underwent low-flow bypass (aged 28.8 +/- 0.4 [mean +/- standard error of the mean] days) were analyzed. The duration of circulatory arrest and low-flow bypass was 1 hour. In a parallel study with the same animal model, phosphorus 31 magnetic resonance spectroscopy was used to assess cerebral phosphocreatine, nucleoside triphosphate (adenosine triphosphate), and intracellular pH. Five animals (aged 31.8 +/- 1.1 days) underwent circulatory arrest, and five underwent low-flow bypass. A brief phase of hyperemic carotid blood flow was seen immediately after the onset of reperfusion in the circulatory arrest group but not in the low-flow group. In the circulatory arrest and low-flow bypass groups, cerebral blood flow (percentage of baseline 71.2% +/- 8.3% and 69.1% +/- 5.8%, respectively), cerebral oxygen consumption (45.6% +/- 10.0%, 44.5% +/- 7.6%), and cerebral glucose consumption (31.5% +/- 30.7%, 83.5% +/- 24.2%) remained depressed after 45 minutes of reperfusion and rewarming to normothermia. However, after 3 more hours of pulsatile normothermic reperfusion, cerebral oxygen consumption and cerebral glucose consumption had returned to baseline. Phosphocreatine, adenosine triphosphate, and pH were maintained at or above baseline levels throughout low-flow bypass and throughout 3 hours of normothermic reperfusion. In contrast, both phosphocreatine and adenosine triphosphate became undetectable 32 +/- 3.7 minutes after onset of circulatory arrest. During and early after circulatory arrest, pH decreased to a minimum of 6.506 +/- 0.129 at 40 minutes after reperfusion. After 3 hours of normothermic reperfusion, phosphocreatine and adenosine triphosphate recovered to 98.6% +/- 9.0% and 90.1% +/- 13.5% of baseline, respectively, and pH was 7.087 +/- 0.051, similar to baseline (7.1755 +/- 0.041). In the low-flow bypass group, the disparity between the depressed level of cerebral oxygen consumption and normal high-energy phosphate levels may reflect incomplete cerebral rewarming or decreased energy consumption. In the circulatory arrest group, the parallel recovery of oxygen consumption and high-energy phosphates eventually achieving baseline levels suggests that the degree of hypothermia used provides adequate protection for acute cerebral recovery after 1 hour of circulatory arrest.(ABSTRACT TRUNCATED AT 400 WORDS)

Profound, reversible energy loss in the hypoxic immature rat brain

The goal of this study was to compare the effects of oxygen deprivation on cellular energy state and pH in the developing and adult rat brain. Relative quantities of phosphocreatine (PC), inorganic phosphorus (P(i)), and nucleoside triphosphates (NTP), and intracellular pH, were determined using in vivo 31P NMR spectroscopy at different postnatal ages (postnatal day (P) 2-6, P9-13, P16-20, P23-27) in the hypoxic rat brain (7 min, 4% O2). While a significant increase in P(i) was seen at all ages during hypoxia, a severe but reversible reduction in concentrations of PC (80-100% decrease) and NTP (40-50% decrease) was observed only at P9-13. This dramatic response was not seen in older (> P16) or younger (< P6) animals. These latter groups responded with moderate decreases in brain PC (50-60% decrease) and NTP (20-40% decrease). In addition, the youngest animals showed much less intracellular brain acidosis than the other age groups. The transient period of development during which the brain exhibits heightened susceptibility to hypoxic energy failure coincides with known changes in brain energy production pathways and susceptibility to hypoxia-induced excitability.

Sports participation, age at smoking initiation, and the risk of smoking among US high school students

OBJECTIVE

To examine smoking patterns, smoking initiation, and the relationship of sports participation and age at smoking initiation to regular and heavy smoking among adolescents.

DESIGN

Survey.

PARTICIPANTS

A nationally representative sample of US high school students.

OUTCOME MEASURES

Prevalences of smoking patterns, prevalence and incidence of smoking initiation, and prevalences and odds of regular and heavy smoking in relation to sports participation and age at smoking initiation.

RESULTS

Seventy-two percent of students reported experimenting with, formerly, or ever smoking cigarettes, and 32% reported smoking in the past 30 days. Students who had participated in interscholastic sports were less likely to be regular and heavy smokers than were others who had not participated. Smoking initiation rates increased rapidly after age 10 years and peaked at age 13 to 14 years. Students who began smoking at age 12 years or younger were more likely to be regular and heavy smokers than were students who began smoking at older ages.

CONCLUSIONS

These data suggest that smoking initiation at a young age can increase the risk of nicotine addiction during adolescence and that sports participation may influence smoking behavior. Interventions to prevent smoking should be available before age 12 years to help combat the smoking epidemic among youth.

Creatine kinase-catalyzed reaction rate in the cyanide-poisoned mouse brain

Brain creatine kinase (CK)-catalyzed phosphorus flux from phosphocreatine (PC) to ATP was measured in vivo in young adult mice made reversibly hypoxic by injection of cyanide. Phosphorus spectra and saturation transfer measurements of CK-catalyzed flux were acquired using a high-field (8.45 T) nuclear magnetic resonance (NMR) spectrometer. After low cyanide doses (1-3 mg/kg of body weight), there were no measurable changes in brain pH or in concentrations of PC, the nucleoside triphosphates (including ATP), and Pi. The CK-catalyzed phosphorus flux increased about 75% after the low cyanide dose. Higher doses (4-6 mg/kg) produced a transient 30-40% decrease in PC concentration, doubling of Pi, and a 0.2 unit decrease in pH. The CK-catalyzed phosphorus flux decreased 50-80% after the higher cyanide doses. This decrease in phosphorus flux was present long after reactant concentrations returned to precyanide values. It is proposed that the increase in brain CK-catalyzed phosphorus flux with the lower cyanide doses is due to an increase in ADP concentration. The large, prolonged decrease in CK-catalyzed reaction rate in the moderately poisoned brain may be due to loss of activity of the mitochondrial CK isoform.

Functional maturation of creatine kinase in rat brain

The physiological role of the phosphocreatine (PCr)/creatine kinase (CK) system has been studied in rat brain by comparing maturational changes in in vivo CK-catalyzed reaction rate and activities of CK isoenzymes. The CK-catalyzed reaction rates, measured by 31P-nuclear magnetic resonance spectroscopy, increased 4-fold between 12 and 17 days of age. The mitochondrial CK (Mi-CK) isoenzyme, as a percentage of total CK, increased to the same extent over this relatively narrow age period. Cytosolic CK (B-CK) was active earlier and, with the total CK activity, increased steadily over a longer time course. An immunohistochemical study of cerebellum showed Mi-CK predominantly in gray matter, while the cytosolic CK was present in rather large concentrations in both gray and white matter. In the molecular layer, B-CK was most prominent in the Bergmann glial cells, while Mi-CK was more prominent in Purkinje neurons. During development a redistribution of Mi-CK from the Purkinje cell bodies to their processes was observed. These results point to regional differences in CK content and in isoenzyme-specific localizations. The increase in CK activity is temporally coincident with the maturational appearance of closely coupled decreases in brain PCr and ATP during hypoxia. These maturational changes suggest that the activity of the PCr/CK system, particularly the Mi-CK isoenzyme, is central in regulation of brain ATP.

Astrocyte volume regulation and ATP and phosphocreatine concentrations after exposure to salicylate, ammonium, and fatty acids

Cellular volume regulation following swelling in hypo-osmotic phosphate-buffered saline (PBS) and ATP and phosphocreatine concentrations of cells incubated in iso-osmotic or hypo-osmotic PBS were measured in primary cultured rat cerebral astrocytes exposed for 30 min to NH4Cl, salicylate, hexanoate, octanoate, and/or dodecanoate. These compounds have been implicated in the pathogenesis of cerebral edema in Reye's Syndrome. NH4Cl (0.10 - 10 mM) had no effect on astrocyte volume regulation or ATP concentration. Salicylate significantly reduced ATP concentrations at 3.0 mM and 10 mM but had no effect on volume regulation. Hexanoate (10 mM and 30 mM) decreased astrocyte ATP content by over 80% while octanoate (10 mM) reduced ATP content by more than 50%. Concentrations of these fatty acids at or below 3.0 mM had no effect on ATP content. Volume regulation was inhibited by 3.0 mM hexanoate and 3.0 mM octanoate but not lower concentrations. Dodecanoate (0.1-3.0 mM) decreased cellular ATP content by 33-51% in iso-osmotic PBS solutions. Phosphocreatine content was reduced by exposure to salicylate or octanoate at concentrations which had no effect on ATP content. These results indicate that astrocyte energy metabolism and volume regulation may be compromised by agents associated with cerebral edema in Reye's Syndrome. Analysis of the dose-dependence of these effects suggests that inhibition of astrocyte energy metabolism is not sufficient to affect volume regulation.

Synergism between occupational arsenic exposure and smoking in the induction of lung cancer

We assembled data from numerous studies to examine whether active smoking and occupational exposure to arsenic act synergistically (more than additively) to increase the risk of lung cancer. Although several smaller studies lacked the power to reject simple additive relations, the joint effect from both exposures consistently exceeded the sum of the separate effects by about 70 to 130%. The only study not showing a greater than additive effect appeared to have inadequate data to address this question. We calculated the excess fractions for the synergism; these showed that a minimum of between 30% and 54% of lung cancer cases among those with both exposures could not be attributed to either one or the other exposure alone. Previous authors addressing the synergism between arsenic exposure and smoking have evaluated deviations from a multiplicative model, which is inappropriate for this purpose. Reports of no interaction or "negative" interaction have therefore been misleading. Taken as a whole, the evidence is compelling that arsenic and smoking act in a synergistic manner to produce lung cancer. Substantial reductions in the lung cancer burden of smokers occupationally exposed to arsenic could be achieved by reductions in either exposure. The mechanism for the synergism is unclear.