Prenatal cocaine exposure revealed minimal postnatal changes in rat striatal dopamine D2 receptor sites and mRNA levels in the offspring

It has been reported from this laboratory that prenatal cocaine exposure results in the postnatal transient alterations of rat striatal dopamine uptake sites examined from postnatal 0–32 wk. The present study aims to examine whether this will result in a direct/indirect stimulation of dopamine D₂ receptors. Pregnant rats were dosed orally with cocaine hydrochloride (60 mg/kg/d) from gestational day (GD) 7–21. Control animals received an equivalent volume of water. The striatum from the offspring at postnatal 0–32 wk was examined. The radioligand [³H]sulpiride was used for the Scatchard analysis of the D₂ receptors, and the changes in the levels of mRNA for the D₂ receptor were studied using Northern blot analysis. Results from the present study revealed that in the control group, there was an age-dependent increase in the number of D₂ receptor sites (B _max:44.00±2.12 to 178.00±45.10 fmol/mg protein) and in the levels of D₂ mRNA from PN0–32 wk with the most rapid increase occurring during the first 4 wk of postnatal development. Prenatal cocaine exposure resulted in only a significant decrease (p<0.001) in the number of D₂ receptor sites at PN0 wk and in a 10% increase in mRNA levels at PN3, 4, and 12 wk. It was concluded from this study that prenatal cocaine exposure resulted in minimal postnatal changes in the dopamine D₂ receptor.     

N2 fixation and nitrogen allocation to above and below ground plant parts in red clover-grasslands

Leys, used for grazing or production of forage to be conserved as silage or hay, are very important crops in northern areas. In order to measure the N₂ fixation in leys of varying ages and during different parts of the season, detailed measurements were taken of yield, N₂ fixation and the amounts of N remaining in the field after harvesting red clover (Trifolium pratense L.)-grass leys at a site in northern Sweden, where they are generally harvested twice per growing season. Entire plants, including stubble and roots, were sampled at the time of first and second harvest and, in addition, at the end of the growing season in three neighbouring fields, carrying a first, a second and a third year ley, respectively. N₂ fixation was measured by both ¹⁵N isotope dilution (ID) and ¹⁵N natural abundance (NA) methods. The proportion of clover dry matter (DM) in the stands increased from the first to the second harvest, but the grasses dominated throughout the entire season, especially below ground. The N concentrations, in both herbage and whole plants, were about twice as high in the clover as in the grasses. Seasonal variations in N concentrations were minor, and total N contents followed the same trends as DM. The clover acquired nearly all of its N from N₂ fixation: the proportion of N in clover herbage derived from N₂ fixation was often >0.8 throughout the season. The variations in the amounts of N₂ fixed during the course of the season corresponded well to the seasonal changes in clover biomass. Amounts of fixed N₂ allocated to clover herbage during the whole season were in the range 4 to 6 g N m⁻² in this unusually rainy year. Calculations of daily N allocation rates to herbage showed that N uptake rates were similar, and high, in grasses during May–June and July–August, while N₂ fixation rates in clover were about 10-fold as high in July–August as in May–June, reflecting the need for N in clover growth. The proportion of N remaining in clover stubble and roots after the first and second harvests was about 60 and 25%, respectively, while about 60% of the N in grasses remained in stubble and roots after both harvests. The considerable amounts of biomass and N that were left in field after harvesting red clover-grass leys are important for re-growth of the plants and provide substantial N fertilization for the next crop in the crop rotation.     

Heavy water labeling method for measuring the effect of genistein on mammary gland carcinogenesis

Heavy water labeling method was applied to measure the effect of genistein on mammary gland carcinogenesis by incoporating ²H from ²H₂O into the deoxyribose (dR) moiety of purine deoxyribonucleotides in dividing cells. In the present study, we followed the study design of Lamartiniere group to evaluate the efficacy of ²H₂O labeling on the measurement of mammary gland carconogenesis. Female Sprague–Dawley rats were fed estrogen-free AIN-93G diet starting 1 week before breeding and continuing through pregnancy and lactation. Female pups were assigned to the following groups on postnatal day 16 and fed AIN-93G diet: vehicle (dimethylsulfoxide) (DMSO), genistein, and estradiol benzoate (EB). On postnatal days 16, 18, and 20, female pups were injected subcutaneously with 500 μg genistein/g body wt, 500 ng EB/g body wt, or an equivalent volume of the vehicle. At day 50 postpartum, half of each group were gavaged with 60 mg dimethylbenz[a]anthracene (DMBA) in perila oil. After 1 week of DMBA treatment, all animals were labeled with ²H₂O by administration of 4% ²H₂O in drinking water after single intraperitonial bolus injection with 99.9% ²H₂O until sacrifice on postnatal day 81. The time-dependent weight gains were observed in all groups throughout the experimental period. The enrichment of body ²H₂O was attained at 1.84–2.47% through oral administration of ²H₂O. Mammary epithelial cell proliferation was measured by enrichment (EM1) of dA from rats. DMBA-treated groups showed higher fractional synthesis than DMBA non-treated groups. The group exposed only to genistein showed significantly lower EM1 (1.46 ± 0.87%) than those of control groups, i.e., the DMBA non-treated group (2.28 ± 0.29%) and the DMBA-treated group (2.32 ± 0.28%). Bromodeoxyuridine (BrdU) immunostaining of mammary tissue revealed that genistein reduced proliferation of the mammary epithelial, and the number of cells stained positive for BrdU both in DMBA-treated groups and DMBA non-treated groups. H&E staining of mammary epithelium also showed that the exposure to genistein decreased proliferation of the mammary epithelium. The epithelium in the rats treated with DMBA showed mostly multiple cell layers, in contrast to the mostly double layer shown in the DMBA non-treated rats. The exposure to genistein in the prepubertal period inhibited mammary epithelial cell proliferation. In conclusion, the ²H₂O labeling results were in good agreement with the results of BrdU incorporation and histomorphometry, which demonstrates that ²H₂O labeling can be used as a tool to measure carcinogenesis.     

An in vitro examination of intestinal iron absorption in a freshwater teleost, rainbow trout (Oncorhynchus mykiss)

This study investigated the physiological characteristics of intestinal iron absorption in a freshwater teleost, rainbow trout (Oncorhynchus mykiss). Using an in vitro gastro-intestinal sac technique, we evaluated the spatial pattern and concentration dependent profile of iron uptake, and also the influence of luminal chemistry (pH and chelation) on iron absorption. We demonstrated that the iron uptake rate in the anterior intestine is significantly higher than that in the mid and posterior intestine. Interestingly, absorption of iron in the anterior intestine occurs likely via simple diffusion, whereas a carrier-mediated pathway is apparent in the mid and posterior intestine. The uptake of ferric and ferrous iron appeared to be linear over the entire range of iron concentration tested (0–20 μM), however the uptake of ferrous iron was significantly higher than that of ferric iron at high iron concentrations (>15 μM). An increase in mucosal pH from 7.4 to 8.2 significantly reduced iron absorption in both mid and posterior intestine, implying the involvement of a Fe²⁺/H⁺ symporter. Iron chelators (nitrilotriacetic acid and desferrioxamine mesylate) had no effects on iron absorption, which suggests that fish are able to acquire chelated iron via intestine.     

Regional distribution of monoamines and dopamine D1-and D2-receptors in the striatum of the rat

Dopamine (DA) D₁-and D₂-receptor densities were determined in 18 discrete areas of the caudate-putamen-globus pallidus of male Wistar rats and compared to local DA concentrations. All three parameters were found to decrease caudally. The globus pallidus was distinguished by the low concentration of DA and its receptors and high noradrenaline, (NA) content. While there were no mediolateral differences in DA or DA D₁-receptors, a clear mediolateral gradient was observed for DA D₂-receptors which extended over several sections of the brain. The ratio of DA D₁-to D₂-receptors was significantly higher in the dorsal than in the ventral areas of the mediolateral and caudal striatum. This is the first report of clear dorsoventral differences in parameters relating to DA activity in the striatum. These findings may be of particular significance in understanding the functional dichotomy between the dorsal and ventral striatum.     

The trans labilization of cis-[PtCl2(13CH3NH2)2] by glutathione can be monitored at physiological pH by [1H,13C] HSQC NMR

In order to monitor the trans labilization of cisplatin at physiological pH we have prepared the complex cis-[PtCl₂(¹³CH₃NH₂)₂] and studied its interactions with excess glutathione in aqueous solution at neutral pH by two-dimensional [1H,13C] heteronuclear single-quantum correlation (HSQC) NMR spectroscopy. [1H,13C] HSQC spectroscopy is a good method for following the release of ¹³CH₃NH₂ but is not so good for characterizing the Pt species in solution. In the reaction of cisplatin with glutathione, Pt–S bonds are formed and Pt–NH₃ bonds are broken. The best technique for following the formation of Pt–S bonds of cisplatin is by UV spectroscopy. [1H,13C] HSQC spectroscopy is the best method for following the breaking of the Pt–N bonds. [1H,15N] HSQC spectroscopy is the best method for characterizing the different species in solution. However, the intensity of the peaks in the ¹⁵NH₃–Pt–S region, in [1H,15N] HSQC, reflects a balance between the formation of Pt–S bonds, which increases the signal intensity, and the trans labilization, which decreases the signal intensity. [1H,15N] HSQC spectroscopy and [1H,13C] HSQC spectroscopy are complementary techniques that should be used in conjunction in order to obtain the most accurate information on the interaction of platinum complexes with sulfur-containing ligands.     

Involvement of Dopamine Neurons in the Regulation of β-Adrenergic Receptor Sensitivity in Rat Prefrontal Cortex

The contribution of dopamine (DA) afferents to the regulation of beta-adrenergic receptor sensitivity (isoproterenol-stimulated adenylate cyclase activity) in the rat prefrontal cortex was investigated by comparing the effects of lesions affecting either both DA and noradrenaline (NA) or NA fibers alone. Bilateral 6-hydroxydopamine (6-OHDA) lesions made in the ventral tegmental area destroyed ascending DA and to a variable extent ascending NA fibers innervating the prefrontal cortex. Two opposite effects were observed depending on the extent of cortical NA denervation: (a) When NA denervation was complete (less than 4% of controls), a marked increase in the isoproterenol-sensitive adenylate cyclase activity (+78%) was found. The amplitude of this denervation supersensitivity was similar to that occurring following complete and selective destruction of NA innervation induced by bilateral 6-OHDA injections made into the pedunculus cerebellaris superior. (b) When 6-OHDA injections into the ventral tegmental area led to a partial destruction of cortical NA afferents (10-40% of control values), a hyposensitivity of the isoproterenol-induced adenylate cyclase activity (-30%) was observed. This effect contrasted with the moderate supersensitivity seen in rats with partial, but selective, destruction of NA innervation (pedunculus cerebellaris superior lesions). The hyposensitivity of beta-adrenergic receptors obtained in rats with partial lesions of cortical NA fibers, but devoid of cortical DA innervation, suggests that DA neurons may regulate, under certain conditions, the denervation supersensitivity of beta-adrenergic receptors.     

Radioactive synthesis and biodistribution study of β-elemene–99mTc(CO)3 conjugates

β-Elemene, (5S,7R,10S)-(−)-(1-methyl-1-vinyl-2,4-diisopropenylcyclohexane), is an anticancer agent from traditional Chinese herbal medicine. Three novel ^99mTc(CO)₃–β-elemene conjugates were synthesized successfully, and compared with β-elemene exhibited improved water solubility. A biodistribution and micro single photon emission computed tomography image study showed there is a visible accumulation in Lewis lung cancer tumors. Y. Sun and Y. Ren contributed equally to this paper.     

Effect of gonadectomy on brain catecholamines during the postnatal period

The effect produced by gonadectomy on dopamine (DA) and noradrenaline (NA) levels in the diencephalon and the rest of the brain of male and female rats during postnatal development has been studied. DA and NA metabolism or biosynthesis seems to be regulated by the ovarian hormones, directly or by means of hypophysary hormones, since both catecholamine levels rise acutely during postnatal development when ovariectomy is performed. In contrast with controls, the NA level is not stable at 45 days, but continues rising to day 60. Orchidectomy also acutely increases the level of diencephalic DA, but in contrast with females, its concentration progressively decreases, being at day 60 the same as in the controls. The reasons that cause this normalization, in the absence of testicular androgens, are unknown. In the same way, the extirpation of the testicles increases the diencephalic concentration of NA, the concentration change is similar to the control one: however, the level is higher. There is also a clear difference from the gonadectomized females, in which the diencephalic NA rises during 45-60 days. Gonadectomy does not significantly alter the level of DA or NA in the rest of the brain.     

Effects of atmospheric CO2 enrichment on δ 13C, δ 15N values and turnover times of soil organic matter pools isolated by thermal techniques

CO₂ applied for Free-Air CO₂ Enrichment (FACE) experiments is strongly depleted in ¹³C and thus provides an opportunity to study C turnover in soil organic matter (SOM) based on its δ ¹³C value. Simultaneous use of ¹⁵N labeled fertilizers allows N turnover to be studied. Various SOM fractionation approaches (fractionation by density, particle size, chemical extractability etc.) have been applied to estimate C and N turnover rates in SOM pools. The thermal stability of SOM coupled with C and N isotopic analyses has never been studied in experiments with FACE. We tested the hypothesis that the mean residence time (MRT) of SOM pools is inversely proportional to its thermal stability. Soil samples from FACE plots under ambient (380 ppm) and elevated CO₂ (540 ppm; for 3 years) treatments were analyzed by thermogravimetry coupled with differential scanning calorimetry (TG-DSC). Based on differential weight losses (TG) and energy release or consumption (DSC), five SOM pools were distinguished. Soil samples were heated up to the respective temperature and the remaining soil was analyzed for δ ¹³C and δ ¹⁵N by IRMS. Energy consumption and mass losses in the temperature range 20–200°C were mainly connected with water volatilization. The maximum weight losses occurred from 200–310°C. This pool contained the largest amount of carbon: 61% of the total soil organic carbon in soil under ambient treatment and 63% in soil under elevated CO₂, respectively. δ ¹³C values of SOM pools under elevated CO₂ treatment showed an increase from −34.3‰ of the pool decomposed between 20–200°C to −18.1‰ above 480°C. The incorporation of new C and N into SOM pools was not inversely proportional to its thermal stability. SOM pools that decomposed between 20–200 and 200–310°C contained 2 and 3% of the new C, with a MRT of 149 and 92 years, respectively. The pool decomposed between 310–400°C contained the largest proportion of new C (22%), with a MRT of 12 years. The amount of fertilizer-derived N after 2 years of application in ambient and elevated CO₂ treatments was not significantly different in SOM pools decomposed up to 480°C having MRT of about 60 years. In contrast, the pool decomposed above 480°C contained only 0.5% of new N, with a MRT of more than 400 years in soils under both treatments. Thus, the separation of SOM based on its thermal stability was not sufficient to reveal pools with contrasting turnover rates of C and N. Responsible Editor: Bernard Nicolardot.     

Brain Iron Toxicity: Differential Responses of Astrocytes,Neurons, and Endothelial Cells

Iron accumulation or iron overload in brain is commonly associated with neurodegenerative disorders such as Parkinson’s and Alzheimer’s diseases, and also plays a role in cellular damage following hemorrhagic stroke and traumatic brain injury. Despite the brain’s highly regulated system for iron utilization and metabolism, these disorders often present following disruptions within iron metabolic pathways. Such dysregulation allows saturation of proteins involved in iron transport and storage, and may cause an increase in free ferrous iron within brain leading to oxidative damage. Not only do astrocytes, neurons, and brain endothelial cells serve unique purposes within the brain, but their individual cell types are equipped with distinct protective mechanisms against iron-induced injury. This review evaluates iron metabolism within the brain under homeostatic and pathological conditions and focuses on the mechanism(s) of brain cellular iron toxicity and differential responses of astrocytes, neurons, and brain vascular endothelial cells to excessive free iron. Special issue dedicated to Dr. Moussa Youdim. An erratum to this article can be found at     

Mechanism of Activation of Caspase-9 and Caspase-3 during Hypoxia in the Cerebral Cortex of Newborn Piglets: The Role of Nuclear Ca<Superscript>2+</Superscript>-Influx

In previous studies, we have shown that cerebral hypoxia results in increased activity of caspase-9, the initiator caspase, and caspase-3, the executioner of programmed cell death. We have also shown that cerebral hypoxia results in high affinity Ca²⁺–ATPase-dependent increase in nuclear Ca²⁺-influx in the cerebral cortex of newborn piglets. The present study tests the hypothesis that inhibiting nuclear Ca²⁺-influx by pretreatment with clonidine, an inhibitor of high affinity Ca²⁺–ATPase, will prevent the hypoxia-induced increase in caspase-9 and caspase-3 activity in the cerebral cortex of newborn piglets. Thirteen newborn piglets were divided into three groups, normoxic (Nx, n = 4), hypoxic (Hx, n = 4), and hypoxic treated with clonidine (100 mg/kg) (Hx–Cl, n = 5). Anesthetized, ventilated animals were exposed to an FiO₂ of 0.21 (Nx) or 0.07 (Hx) for 60 min. Cerebral tissue hypoxia was documented biochemically by determining levels of ATP and phosphocreatine (PCr). Caspase-9 and -3 activity were determined spectrofluoro-metrically using specific fluorogenic synthetic substrates. ATP (μmoles/g brain) was 4.6 ± 0.3 in Nx, 1.7±0.4 in Hx (P < 0.05 vs. Nx), and 1.5 ± 0.2 in Hx–Cl (P < 0.05 vs. Nx). PCr (μmoles/g brain) was 3.6 ± 0.4 in Nx, 1.1 ± 0.3 in Hx (P < 0.05 vs. Nx), and 1.0 ± 0.2 in Hx–Cl (P < 0.05 vs. Nx). Caspase-9 activity (nmoles/mg protein/h) was 0.548 ± 0.0642 in Nx and increased to 0.808 ± 0.080 (P < 0.05 vs. Nx and Hx–Cl) in the Hx and 0.562 ± 0.050 in the Hx–Cl group (p = NS vs. Nx). Caspase-3 activity (nmoles/mg protein/h) was 22.0 ± 1.3 in Nx and 32 ± 6.3 in Hx (P < 0.05 vs. Nx) and 18.8 ± 3.2 in the Hx–Cl group (P < 0.05 vs. Hx). The data demonstrate that clonidine administration prior to hypoxia prevents the hypoxia-induced increase in the activity of caspase-9 and caspase-3. We conclude that the high afinity Ca²⁺–ATPase-dependent increased nuclear Ca²⁺ during hypoxia results in increased caspase-9 and caspase-3 activity.     

Iron nitrosyl complexes as models for biological nitric oxide transfer reagents

Owing to the indiscriminate reactivity of the free NO radical, intricate control mechanisms are required for storage, transport and transfer of NO to its various biological targets. Among the proposed storage components are protein-bound thionitrosyls (R_protein–SNO) and protein-bound dinitrosyl iron complexes. Current knowledge suggests the latter are derived from iron–sulfur cluster degradation in the presence of excess NO. Mobilization of protein-bound NO could involve NO or Fe(NO)₂ unit transfer to small serum molecules such as glutathione, free cysteine, or iron-porphyrins. The study reported is of a reaction model which addresses the key steps in NO transfer from a prototypal iron dinitrosyl complex. While the N,N′-bis(2-mercaptoethyl)-N,N′-diazacyclooctane (bme-daco) ligand typically binds in square-planar N₂S₂ coordination, it also serves as a bidentate dithiolate donor for tetrahedral structures in the preparation of the (H⁺bme-daco)Fe(NO)₂ derivative (Chiang et al., J. Am. Chem. Soc. 126:10867–10874, 2004). The removal of one NO produces the mononitrosyl complex, (bme-daco)Fe(NO), and simplifies studies of NO release mechanisms. We have used heme-type model complexes, Fe or Co porphyrins as NO acceptors, yielding (porphyrin)M(NO), where M is Fe or Co, and monitored reactions by ν(NO) Fourier transform IR spectroscopy. Reaction products were verified by electrospray ionization mass spectrometry. Rudimentary mechanistic studies suggest a role for HNO in the NO release from the dinitrosyl; the mononitrosyl benefits as well from acid catalysis. Other NO uptake complexes such as [(N₂S₂)Fe]₂ [N₂S₂ is bme-daco or N,N’-bis(2-mercapto-2-methylpropyl)-daco] are shown to form Fe(NO) mononitrosyls with stability and spectroscopic signatures similar to those of the porphyrins.     

Dopaminergic Agonists: Possible Neurorescue Drugs Endowed with Independent and Synergistic Multisites of Action

Dopaminergic agonists have been usually used as adjunctive therapy for the cure of Parkinson’s disease (PD). It is generally believed that treatment with these drugs is symptomatic rather then curative and does not stop or delay the progression of neuronal degeneration. However, several DA agonists of the DA D2–receptor family (including D2, D3 and D4-subtypes) have recently been shown to possess neuroprotective properties in different in vitro and in vivo experimental PD models. Here we summarize some recent data from our and other groups underlining the wide pharmacological spectrum of DA agonists currently used for treating PD patients. In particular, the mechanism of action of different DA agonists does not appear to be restricted to the stimulation of selective DA receptor subtypes being these drugs endowed with intrinsic, independent, and peculiar antioxidant effects. This activity may represent an additional pharmacological property contributing to their clinical efficacy in PD. Special issue dedicated to Dr. Moussa Youdim.     

Influence of Azolla management on the growth,yield of rice and soil fertility

A field experiment conducted at Central Rice Research Institute, Cuttack, during three successive seasons showed that with the 120-day-duration variety Ratna two dual crops ofAzolla pinnata R. Brown (Bangkok isolate) could be achieved 25 and 50 days after transplanting (DAT) by inoculating 2.0 t ha⁻¹ of fresh Azolla 10 and 30 DAT respectively. One basal crop of Azolla could also be grown using the same inoculum 20 days before transplanting (DBT) in fallow rice fields. The three crops of Azolla grown—once before transplanting and twice after transplanting—gave an average total biomass of 38–63 and 43–64 t ha⁻¹ fresh Azolla containing 64–90 and 76–94 kg N ha⁻¹ respectively in the square and rectangular spacings. Two crops of Azolla grown only as a dual crop, on the other hand, gave 26–39 and 29–41 t ha⁻¹ fresh Azolla which contained 44–61 and 43–59 kg N ha⁻¹ respectively. Growth and yield of rice were significantly higher in Azolla basal plus Azolla dual twice incorporated treatments than in the Azolla dual twice incorporation, Azolla basal plus 30 kg N ha⁻¹ urea and 60 kg N ha⁻¹ urea treatments. Azolla basal plus 30 kg N ha⁻¹ urea and 60 kg N ha⁻¹ urea showed similar yields but Azolla dual twice incorporation was significantly lower than those. The different spacing with same plant populations did not affect growth and yield significantly, whereas Azolla growth during dual cropping was 8.3 and 64% more in the rectangular spacing than in the square spacing in Azolla basal plus Azolla dual twice incorporation and Azolla dual twice incorporation treatments.     

Evaluation of N2-fixation and nitrogen economy of a maize/cowpea intercrop system using15N dilution methods

Yields of above ground biomass and total N were determined in summer-grown maize and cowpea as sole crops or intercrops, with or without supplementary N fertilizer (25 kg N ha⁻¹, urea) at an irrigated site in Waroona, Western Australia over the period 1982–1985. Good agreement was obtained between estimates of N₂ fixation of sole or intercrop cowpea (1984/85 season) based on the¹⁵N natural abundance and¹⁵N fertilizer dilution techniques, both in the field and in a glasshouse pot study. Field-grown cowpea was estimated to have received 53–69% of its N supply from N₂-fixation, with N₂-fixation onlyslightly affected by intercropping or N fertilizer application. Proportional reliance on N₂-fixation of cowpea in glasshouse culture was lower (36–66%) than in the field study and more affected by applied N. Budgets for N were drawn up for the field intercrops, based on above-ground seed yields, return of crop residues, inputs of fixed N and fertilizer N. No account was taken of possible losses of N through volatilization, denitrification and leaching or gains of N in the soil from root biomass. N₂-fixation was estimated tobe 59 kg N ha⁻¹ in the plots receiving no fertilizer N, and 73 kg N ha⁻¹ in plots receiving 25 kg N ha⁻¹ as urea. Comparable fixation by sole cowpea was higher (87 and 82 kg N ha⁻¹ respectively) but this advantage was outweighed by greater land use efficiency by the intercrop than sole crops.     

Striatal and Urinary DOPAC/DA Ratio May Indicate a Long-Lasting DA Release Enhancement by MPP+ and MPTP

The DOPAC/DA ratio in mouse striatum, in striatal synaptosomes, and in rat urine after MPP⁺ and MPTP neurotoxin administrations to the animals was followed temporally. The neurotoxins were given intraperitoneally and, in some experiments, to enhance the sensitivity, the animals were subsequently reserpinized before either sacrifice or 24 hour urine collection. MPP⁺ treatment, followed by saline, weakly lowered mouse striatal DOPAC/DA ratio up to 6 hours; in reserpinized animals, however, the neurotoxin reduced striatal ratio potently and for longer periods. Similarly, MPP⁺ reduced rat (saline treated) urinary DOPAC level and DOPAC/DA ratio in the short term (1.0 hr) while the neurotoxin effects could still be detected following longer periods up to 27 days in reserpinized animals. A single MPTP treatment (90 min.), followed by preparation of striatal synaptosomal fraction and its incubation (37°C) with or without reserpine, also led to a reduced DOPAC/DA ratio. Although mainly the pooled peripheral effect is directly indicated by urinary DOPAC/DA ratio, MPP⁺ may reduce DA oxidation in the CNS and may similarly affect the amine oxidation in the peripheral tissues. The CNS and peripheral effects differ, however, in respect to dose-sensitivity and time course. The similarities between the CNS and peripheral effects suggest that a blunted rise of urinary DOPAC/DA ratio after reserpine challenge could be utilized as a peripheral marker of MPP⁺ action in the CNS, a marker that is not currently available.     

Influence of thyroidectomy on brain catecholamines during the postnatal period

The influence of early thyroidectomy (Tx) on changes in dopamine (DA) and noradrenaline (NA) during the postnatal period (30, 45 and 60 days old) was studied in the diencephalon and the rest of the brain of male and female rats. Thyroidectomy interfered with the normal growth of the animals, decreased brain weight and markedly influenced the developmental pattern of both DA and NA in the diencephalon. When compared with control values, the DA concentration, in 45- and 60-day-old Tx male rats, was 29 and 43% lower, respectively, and 21 and 43% lower, respectively, in Tx females. Diencephalic NA levels in Tx rats were also lower than those observed in controls, 15% inferior in 45- and 60-day-old males; 27 and 22% lower, respectively, in females. Thyroidectomy does not significantly alter the level of either amine in the rest of the brain.     

Evaluation of denitrification in an urban stream receiving wastewater effluent

Urban streams often contain elevated concentrations of nitrogen (N) which can be amplified in systems receiving effluent from wastewater treatment plants (WWTP). In this study, we evaluated the importance of denitrification in a stream draining urban Greensboro, NC, USA, using two approaches: (1) natural abundance of ¹⁵N–NO₃⁻ in conjunction with background NO₃⁻–N concentrations along a 7 km transect downstream of a WWTP; and (2) C₂H₂ block experiments at three sites and at three habitat types within each site. Overall lack of a longitudinal pattern of δ¹⁵N–NO₃⁻ and NO₃⁻–N, combined with high concentrations of NO₃⁻–N suggested that other factors were controlling NO₃⁻–N flux in the study transect. However, denitrification did appear to be significant along one portion of the transect. C₂H₂ block experiments showed that denitrification rates were much higher downstream of the WWTP compared to upstream, and showed that denitrification rates were highest in erosional and depositional areas downstream of the WWTP and in erosional areas upstream of the plant. Thus, the combination of the two methods for evaluating denitrification provided more insight into the spatial dynamics of denitrification activity than either approach alone. Denitrification appeared to be a significant sink for NO₃⁻–N upstream of the WWTP, but not downstream. Approximately 46% of the total NO₃⁻–N load was removed via denitrification in the upstream, urban section of the stream, while only 2.3% of NO₃⁻–N was lost downstream of the plant. This result suggests that controlling NO₃⁻–N loading from the plant could result in considerable improvement of downstream water quality.