Induction of nitrate reductase in needles of Scots pine seedlings by NOX and NO3−

The possibility to induce nitrate reductase (NR; EC 1.6.6.2) in needles of Scots pine ( Pinus sylvestris L.) seedlings was studied. The NR activity was measured by an in vivo assay. Although increased NR activities were found in the roots after application of NO₃⁻, no such increase could be detected in the needles. Detached seedlings placed in NO₃⁻ solution showed increasing NR activities with increasing NO₃⁻ concentrations. Exposure of seedlings to NO_x (70–80 ppb NO₂ and 8–12ppb NO) resulted in an increase of the NR activity from 10–20 nmol NO₂⁻ (g fresh weight)⁻¹ h⁻¹ to about 400 nmol NO₂⁻ (g fresh weight)⁻¹ h⁻¹. This level was reached after 2–4 days of exposure, thereafter the NR activity decreased to about 200 nmol NO₂⁻ (g fresh weight)⁻¹ h⁻¹. Analyses of free amino acids showed low concentrations of arginine and glutamine in NO_x-fumigated seedlings compared to corresponding controls.     

[3H]SCH 58261, a Selective Adenosine A2A Receptor Antagonist, Is a Useful Ligand in Autoradiographic Studies

Abstract: We have characterized the new potent and selective nonxanthine adenosine A_2A receptor antagonist SCH 58261 as a new radioligand for receptor autoradiography. In autoradiographic studies using agonist radioligands for A_2A receptors ([³H]CGS 21680) or A₁ receptors ( N ⁶-[³H]cyclohexyladenosine), it was found that SCH 58261 is close to 800-fold selective for rat brain A_2A versus A₁ receptors ( K _i values of 1.2 n M versus 0.8 µ M ). Moreover, receptor autoradiography showed that [³H]SCH 58261, in concentrations below 2 n M , binds only to the dopamine-rich regions of the rat brain, with a K _D value of 1.4 (0.8–1.8) n M . The maximal number of binding sites was 310 fmol/mg of protein in the striatum. Below concentrations of 3 n M , the nonspecific binding was <15%. Three adenosine analogues displaced all specific binding of [³H]SCH 58261 with the following estimated K _i values (n M ): 2-hex-1-ynyl-5'- N -ethylcarboxamidoadenosine, 3.9 (1.8–8.4); CGS 21680, 130 (42–405); N ⁶-cyclohexyladenosine, 9,985 (3,169–31,462). The binding of low concentrations of SCH 58261 was not influenced by either GTP (100 µ M ) or Mg²⁺ (10 m M ). The present results show that in its tritium-labeled form, SCH 58261 appears to be a good radioligand for autoradiographic studies, because it does not suffer from some of the problems encountered with the currently used agonist radioligand [³H]CGS 21680.     

Chemical and Immunological Characterization of Galactosyl-β1-3-Globoside in Bovine, Human, and Rat Brain

Abstract: Our studies of bovine brain neutral glycosphingolipids (Ngsls) have revealed the presence of several short-chain (containing -CHO 1–4) and previously uncharacterized long-chain (−CHO > 4–5) Ngsls. We reported the structural characterization of brain GgOse₄Cer (GA1) and have now purified another brain Ngsl to homogeneity. The purified Ngsl migrated close to standard GgOse₄Cer and nLcOse₅Cer on a TLC plate employing two different solvent systems. The carbohydrate molar composition indicated the presence of Gal/Glc/GalNAc in a ratio of 2.8:1.0:0.9. Five permethylated alditol acetate peaks were characterized as 2,3,4,6-OMe₄Gal, 2,4,6-OMe₃Gal, 2,3,6-OMe₃Gal, 2,3,6-OMe₃Glc, and 4,6-OMe₂GalNAcMe by gas chromatography-mass spectrometry. The anomeric carbohydrate sequence has been determined by specific exoglycosidase digestion. Six-hundred megahertz ¹H NMR spectroscopy of the oligosaccharide released by ceramide glycanase hydrolysis confirmed the structure of the Ngsl as Galβ1-3GalNAcβ1-3Galα1-4Galβ1-4Glc\1-1Cer or IV³GalGbOse₄Cer. Using the immunooverlay technique with anti-stage-specific embryonic antigen 3 antibody, it was found in bovine, rat, and normal adult human brain and bovine myelin, but not in human or rat myelin.     

Uptake of 36Cl and 22Na by the Choroid Plexus-Cerebrospinal Fluid System: Evidence for Active Chloride Transport by the Choroidal Epithelium

Abstract: Cl and Na transport by the lateral ventricle (LVCP) and fourth ventricle (4VCP) choroid plexuses were examined by kinetic analysis of ³⁶Cl and ²²Na uptake into the choroid plexus-CSF system of the adult rat. Both radioisotopes required more than 5 h to reach steady-state distribution in the in vivo choroid plexuses and CSF after intraperitoneal injection. Whereas the LVCP and 4VCP ³⁶Cl steady-state spaces were comparable (55–56%), the 4VCP ²²Na space (39%) tended to be greater than the LVCP ²²Na space (36%). No evidence for inexchangeable Cl or Na was found for the choroid plexuses; the radioisotopic and chemical spaces were not significantly different. Choroid plexus ³⁶Cl and ²²Na uptake curves were resolved into two components, a fast component ( t _1/2 0.02–0.05 h) and a slow component ( t _1/2 0.85–1.93 h). By analysis of the distribution of [³H]inulin, [³H]mannitol, and ⁵¹Cr-tagged erythrocytes within the choroid plexuses, the fast component of ³⁶Cl and ²²Na uptake was found to represent extracellular and erythrocyte contributions to the tissue radioactivity, whereas the slow component represented isotope movement into the epithelial cell compartment. The calculated cell [Cl] of LVCP and 4VCP, 67 mmol/kg cell water, was 3.9 times greater than that predicted by the membrane potential for passive distribution. It is postulated that Cl is actively transported into the choroid epithelial cell across the basolateral membrane; the energy source for active Cl transport may be the Na electrochemical potential gradient (˜90 mV), which is twice that of the Cl electrochemical potential gradient (˜45 mV).     

The State of Phosphorylation of Normal Adult Brain τ, Fetal τ, and τ from Alzheimer Paired Helical Filaments at Amino Acid Residue Ser262

Abstract: Antibody Ab262 was raised against a synthetic τ peptide (SKIGSTENLK, amino acids 258–267 of τ, termed Ser²⁶² peptide). The antibody was more reactive with Ser²⁶² peptide and unphosphorylated τ than a related phosphopeptide [SKIGS(P)TENLK, termed P-Ser²⁶² peptide] and τ phosphorylated by a partially purified kinase, glycogen synthase kinase (GSK) 3β. Ab262 reacted poorly with a peptide having the sequence DRVQSKIGSLD (amino acids 348–358). Treatment of P-Ser²⁶² peptide or GSK 3β phosphorylated τ with alkaline phosphatase increased Ab262 immunoreactivity, indicating that Ab262 is a reagent useful for studying τ phosphorylation at the Ser²⁶² residue. The Ab262 immunoreactivity was detected in τ from normal brains and Alzheimer paired helical filament (PHF-τ) and in PHFs. Alkaline phosphatase treatment had no effect on the Ab262 immunoreactivity of normal τ and PHF-τ but altered the Tau-1 and PHF-1 immunoreactivities. τ proteins from rat brains at 3 and 8 h postmortem exhibited 5 and 19%, respectively, more Ab262 immunoreactivity than τ from fresh tissues. In comparison, rat τ at 8 h postmortem was 40% more immunoreactive with Tau-1. The results suggest that Ser²⁶² is not a major phosphorylation site in vivo. Moreover, there is little or no difference between PHF-τ and normal τ in the extent of phosphorylation at Ser²⁶².     

Rate of Glutamate Synthesis from Leucine in Rat Brain Measured In Vivo by 15N NMR

Abstract: The rate of glutamate synthesis from leucine by the branched-chain aminotransferase was measured in rat brain in vivo at steady state. The rats were fed exclusively by intravenous infusion of a nutrient solution containing [¹⁵N]leucine. The rate of glutamate synthesis from leucine, determined from the rate of increase of brain [¹⁵N]glutamate measured by ¹⁵N NMR and the ¹⁵N enrichments of brain and blood leucine analyzed by gas chromatography-mass spectrometry, was 0.7–1.8 µmol/g/h at a steady-state brain leucine concentration of 0.25 µmol/g. A comparison of the observed fractional ¹⁵N enrichments of brain leucine (0.42 ± 0.03) and glutamate (0.21 ± 0.015) showed that leucine provides ∼50% of glutamate nitrogen under our experimental condition. From the observed rate (0.7–1.8 µmol/g) and the known K _m of the branched-chain aminotransferase for leucine (1.2 m M ), the rate of glutamate synthesis from leucine at physiological brain leucine concentration (0.11 µmol/g) was estimated to be 0.35–0.9 µmol/g/h, with leucine providing ∼25% of glutamate nitrogen. The results strongly suggest that plasma leucine from dietary source, transported into the brain, is an important external source of nitrogen for replenishment of brain glutamate in vivo. Implications of the results for treatment of maple-syrup urine disease patients with leucine-restricted diet are discussed.     

Effects of the Dopamine D3 Antagonist PD 58491 and Its Interaction with the Dopamine D3 Agonist PD 128907 on Brain Dopamine Synthesis in Rat

Abstract: The dopamine (DA) D₃ receptor antagonist PD 58491 {3-[4-[1-[4-[2-[4-(3-diethylaminopropoxy)phenyl]-benzoimidazol-1-yl-butyl]-1 H -benzoimidazol-2-yl]-phenoxy]propyl]diethylamine} bound with high affinity and selectivity to recombinant human DA D₃ versus D_2L and D_4.2 receptors transfected into Chinese hamster ovary cells: K _i values of 19.5 n M versus 2,362 and >3,000 n M , respectively. In contrast, the putative DA D₃ receptor antagonist (+)-AJ76 displayed low affinity and selectivity for D₃ versus D_2L and D_4.2 receptors (91 n M vs. 253 and 193 n M , respectively). In vitro, PD 58491 (1 n M −1µ M ) exhibited D₃ receptor antagonist activity, reversing the quinpirole (10 n M )-induced stimulation of [³H]thymidine uptake in D₃ CHOpro-5 cells, but did not have any significant intrinsic activity by itself in this assay. PD 58491 did not decrease the γ-butyrolactone-induced increase in DA synthesis ( l -3,4-dihydroxyphenylalanine accumulation) in rat striatum, indicating that the compound possessed no in vivo DA D₂/D₃ receptor agonist action at DA autoreceptors. PD 58491 (3–30 mg/kg, i.p.) generally did not alter DA or serotonin synthesis in either the striatum or mesolimbic region of rat brain. The D₃-preferring agonist PD 128907 decreased DA synthesis in striatum and mesolimbic regions, and this effect was attenuated by pretreatment with PD 58491. These findings support the hypothesis that DA D₃ autoreceptors may in part modulate the synthesis and release of DA in striatum and mesolimbic regions.     

Rate of 59Fe Uptake into Brain and Cerebrospinal Fluid and the Influence Thereon of Antibodies Against the Transferrin Receptor

Abstract: Uptake of ⁵⁹Fe from blood into brains of anaesthetized rats and mice has been studied by intravenous infusion of [⁵⁹Fe]ferrous ascorbate or of ⁵⁹Fe-transferrin, the results not being significantly different. Uptakes in the rat were linear with time, but increased at longer times in the mouse. Transfer constants, K _in (in ml/g/h × 10³), for cerebral hemispheres were 5.2 in the adult rat and 5.6 in the mouse. These K _in values corresponded to ⁵⁹Fe influxes of 145 and 322 pmol/g/h, respectively. ⁵⁹Fe uptake into the mouse brain occurred in the following order: cerebellum > brainstem > frontal cerebral cortex > parietal cortex > occipital cortex > hippocampus > caudate nucleus. In genetically hypotransferrinaemic mice, ⁵⁹Fe uptake into brain was 80–95 times greater than in To strain mice. Pretreatment of young rats and mice with monoclonal antibodies to transferrin receptors, i.e., the anti-rat immunoglobulin G OX 26 and the anti-mouse immunoglobulin M RI7 208, inhibited ⁵⁹Fe uptake into spleen by 94% and 98%, respectively, indicating saturation of receptors. The antibodies reduced ⁵⁹Fe uptake into rat brain by 35–60% and that into mouse brain by 65–85%. Although a major portion of iron transport across the blood-brain barrier is normally transferrin-mediated, non-transferrin-bound iron readily crosses it at low serum transferrin levels.     

Cerebral clearance of human amyloid-beta peptide (1-40) across the blood-brain barrier is reduced by self-aggregation and formation of low-density lipoprotein receptor-related protein-1 ligand complexes

Soluble amyloid-β peptide (Aβ) exists in the form of monomers and oligomers, and as complexes with Aβ-binding molecules, such as low-density lipoprotein receptor-related protein-1 (LRP-1) ligands. The present study investigated the effect of self-aggregation and LRP-1 ligands on the elimination of human Aβ(1–40) [hAβ(1–40)] from the rat brain across the blood–brain barrier. Incubation of [¹²⁵I]hAβ(1–40) monomer resulted in time-dependent and temperature-dependent dimer formation, and the apparent elimination rate of [¹²⁵I]hAβ(1–40) dimer was significantly decreased by 92.7% compared with that of [¹²⁵I]hAβ(1–40) monomer. Pre-incubation with LRP-1 ligands, such as activated α2-macroglobulin (α2M), apolipoprotein E2 (apoE2), apoE3, apoE4, and lactoferrin, reduced the elimination of [¹²⁵I]hAβ(1–40). By contrast, pre-administration of the same concentration of these molecules in the rat brain did not significantly inhibit [¹²⁵I]hAβ(1–40) monomer elimination. Purified [¹²⁵I]hAβ(1–40)/activated α2M complex and [¹²⁵I]activated α2M were not significantly eliminated from the rat brain up to 60 min. MEF-1 cells, which have LRP-1-mediated endocytosis, exhibited uptake of [¹²⁵I]activated α2M, and enhancement of [¹²⁵I]hAβ(1–40) uptake upon pre-incubation with apoE, suggesting that [¹²⁵I]activated α2M and [¹²⁵I]hAβ(1–40)/apoE complex function as LRP-1 ligands. These findings indicate that dimerization and LRP-1-ligand complex formation prevent the elimination of hAβ(1–40) from the brain across the blood–brain barrier.     

Tyrosine Hydroxylase Phosphorylation in Digitonin-Permeabilized Bovine Adrenal Chromaffin Cells: The Effect of Protein Kinase and Phosphatase Inhibitors on Ser19 and Ser40 Phosphorylation

Abstract: The protein kinases and protein phosphatases that act on tyrosine hydroxylase in vivo have not been established. Bovine adrenal chromaffin cells were permeabilized with digitonin and incubated with [γ-³²P]ATP, in the presence or absence of 10 µ M Ca²⁺, 1 µ M cyclic AMP, 1 µ M phorbol dibutyrate, or various kinase or phosphatase inhibitors. Ca²⁺ increased the phosphorylation of Ser¹⁹ and Ser⁴⁰. Cyclic AMP, and phorbol dibutyrate in the presence of Ca²⁺, increased the phosphorylation of only Ser⁴⁰. Ser³¹ and Ser⁸ were not phosphorylated. The Ca²⁺-stimulated phosphorylation of Ser¹⁹ was incompletely reduced by inhibitors of calcium/calmodulin-stimulated protein kinase II (46% with KN93 and 68% with CaM-PKII 273–302), suggesting that another protein kinase(s) was contributing to the phosphorylation of this site. The Ca²⁺-stimulated phosphorylation of Ser⁴⁰ was reduced by specific inhibitors of protein kinase A (56% with H89 and 38% with PKAi 5–22 amide) and protein kinase C (70% with Ro 31-8220 and 54% with PKCi 19–31), suggesting that protein kinases A and C contributed to most of the phosphorylation of this site. Results with okadaic acid and microcystin suggested that Ser¹⁹ and Ser⁴⁰ were dephosphorylated by PP2A.     

Causes and location of non-specific effects of SHAM on O2 uptake by wheat roots

Uptake of O₂ by whole, detached, root systems of wheat ( Triticum aestivum L. cv. Alexandria) was titrated with salicylhydroxamic acid (SHAM) in the presence and absence of cyanide. The resulting Q_all plot was non-linear indicating that SHAM was acting non-specifically. The nature of the non-specific effects was investigated in reverse titration experiments. Uptake of O₂ was titrated with KCN in the presence and absence of SHAM at 1 m M and 25 m M , which yielded Q_cy1 values of < 1 and > 1, respectively. The results suggest that at 25 m M , SHAM inhibits the cytochrome pathway, but at 1 m M it stimulates an O₂-consuming process which is likely to be a peroxidase. A SHAM-stimulated peroxidase could easily be washed from these roots. In vitro, the peroxidase was stimulated to a similar extent by low (1 m M ) and high (25 m M ) concentrations of SHAM. Failure to inhibit with high concentrations of SHAM distinguishes this peroxidase from those bitherto eluted from root tissue. Reverse titration experiments in the presence and absence of 1 m M SHAM indicated that there were no significant side effects of SHAM in root tips. These data are supported by the negligible peroxidase activity that was washed from this root fraction. In contrast, significant side effects occurred in vivo, and substantial peroxidase activity was measured in vitro, from sections 4–6 cm and 18–20 cm behind the seminal root apex. The greatest activity was found with the 4–6 cm section which may be associated with high rates of cell wall lignification. The implications of these results for measurements of root respiration are discussed.     

Acetylcholine Release in the Rat Prefrontal Cortex In Vivo: Modulation by α2-Adrenoceptor Agonists and Antagonists

Abstract: We have previously shown that the release of acetylcholine (ACh) in the medial prefrontal cortex of the conscious rat, as measured by microdialysis, is increased following intraperitoneal injection of the selective α₂-adrenoceptor antagonist (+)-efaroxan. To characterize further the receptor pharmacology of this response, the effects of other selective α₂-adrenoceptor ligands were examined. The α₂-adrenoceptor antagonists idazoxan (2.5 and 20 mg/kg), atipamezole (2.5 mg/kg), and fluparoxan (10 mg/kg) increased ACh outflow by up to 250–325% of basal levels over a 3-h period following intraperitoneal injection. The α₂-adrenoceptor agonists UK-14304 (2.5 mg/kg) and guanabenz (2.5 mg/kg) reduced ACh outflow by 80 and 60%, respectively. Clonidine (0.00063–0.16 mg/kg) had no significant depressant effect and at 2.5 mg/kg increased ACh outflow to 233% of basal levels. These results indicate a modulatory role for α₂-adrenoceptors on the release of ACh in the rat prefrontal cortex in vivo. Based on the facilitatory effects produced by the antagonists alone, this α₂-adrenoceptor modulation appears to be tonic and inhibitory. The ability of α₂-adrenoceptor antagonists to enhance ACh outflow suggests a therapeutic usefulness in disorders where cortical ACh release deficits have been implicated.     

Vasopressin-enhanced urea transport by rat inner medullary collecting duct cells in culture

Abstract. The distal inner medullary collecting duct (IMCD) is critical in the urinary concentrating process, in part because it is the site of vasopressin (AVP)-regulated permeability to urea. The purpose of these experiments was to develop a cell culture model of the IMCD on permeable structure and to characterize the responsiveness to AVP. Rat IMCD cells were grown to confluence on collagen-coated Millipore filters glued onto plastic rings. To assess the time required to achieve confluence, the transepithelial resistance was measured periodically and was found to be stable after 2 weeks, at a maximal value of 595 ± 22 ω cm². In separate monolayers the effect of AVP on inulin and urea permeability was determined. While inulin permeability was unchanged after AVP, urea permeability increased from 6.0 ± 0–4 to peak values of 16.0 ± 3–8(10nM),23.1 ± 3–9(1 μM)and28 1 ± 4–9(10μM) X 10^-6cms^-1 ( n = 24). In 10 other monolayers, after the addition of 1 mM 8-Br-cAMP, urea permeability increased from 5.1 ±0–3 to 8.1 ± 1–6 times 10^-6 cm s^-1 and, after 8-Br-cAMP +3-isobutyl-l-methylxanthine, to 12.2 ± 0–7 times 10^-6 cms^-1. We conclude that rat IMCD cells grown in culture exhibit the characteristics of a 'tight' epithelium. Inulin and urea permeability are not different in the absence of AVP, consistent with high resistance junctional complexes. Furthermore, IMCD cells retain the capacity for AVP-regulated urea permeability, a characteristic feature of this nephron segment in vivo.     

Confirmation of operative acetate, H2/CO2 and methanol methanogenic pathways in the solid-state refuse fermentation

By use of the radiolabelled substrates sodium [1–¹⁴C] acetate, sodium [2–¹⁴C] acetate, NaH¹⁴CO₃ and ¹⁴CH₃OH, three of the possible methanogenic pathways in fermenting refuse were confirmed. Due to the absence of a methanol pool, however, the relative contribution of each could not be determined. Circumstantial evidence for an operative trimethylamine pathway was gained but not confirmed whilst preliminary attempts to stimulate methanogenesis in refuse by supplementation with mono-and dimethylamine proved unsuccessful.     

Triiodothyronine Is a High-Affinity Inhibitor of Amino Acid Transport System L1 in Cultured Astrocytes

Abstract: The relationship between the transport of thyroid hormones and that of amino acids was examined by measuring the uptake of amino acids that are characteristic substrates of systems L, A, and N, and the effect of 3,3',5-triiodo-L-thyronine (T₃) on this uptake, in cultured astrocytes. Tryptophan and leucine uptakes were rapid, Na⁺-independent, and efficiently inhibited by T₃ (half-inhibition at ∼ 2 μ M ). Two Na⁺-independent L-like systems (L₁ and L₂), common to leucine and aromatic amino acids, were characterized kinetically. System L₂ had a low affinity for leucine and tryptophan ( K _m= 0.3–0.9 m M ). The high-affinity system L₁ ( K _m∼ 10 μ M for both amino acids) was competitively inhibited by T₃ with a K _i of 2–3 μ M (close to the T₃ transport K _m). Several T₃ analogues inhibited system L₁ and the T₃ transport system similarly. Glutamine uptake and α-(methylamino)isobutyric acid uptake were, respectively, two and 200 times lower than tryptophan and leucine uptakes. T₃ had little effect on the uptakes of glutamine and α-(methylamino)isobutyric acid. The results indicate that the T₃ transport system and system L₁ are related.     

Isoform-Specific Up-Regulation by Ouabain of Na+,K+-ATPase in Cultured Rat Astrocytes

Abstract: There are two α-subunit isoforms (α1 and α2) and two β-subunit isoforms (β1 and β2) of Na⁺,K⁺-ATPase in astrocytes, but the functional heterodimer composition is not known. Ouabain (0.5–1.0 m M ) increased the levels of α1 and β1 mRNAs, whereas it decreased those of α2 and β2 mRNAs in cultured rat astrocytes. The increases in α1 and β1 mRNAs were observed at 6–48 h after addition of the inhibitor. Immunochemical analyses showed that ouabain increased α1 and β1, but not α2 and β2, proteins, and that the isoforms in control and ouabain-treated cultures were of glial origin. Low extracellular K⁺ and monensin (20 µ M ) mimicked the effect of ouabain on α1 mRNA. The ouabain-induced increase in α1 mRNA was blocked by the protein synthesis inhibitor cycloheximide (10 µ M ), the intracellular Ca²⁺ chelator 1,2-bis(2-aminophenoxy)ethane- N,N,N',N' -tetraacetic acid tetraacetoxymethyl ester (30 µ M ), and the calcineurin inhibitor FK506 (1 n M ). These findings indicate that chronic inhibition of Na⁺,K⁺-ATPase up-regulates the α1 and β1, but not α2 and β2, isoforms in astrocytes, suggesting a functional coupling of α1β1 complex. They also suggest that intracellular Na⁺, Ca²⁺, and calcineurin may be involved in ouabain-induced up-regulation of the enzyme in astrocytes.     

Cloning, Characterization, and Chromosomal Localization of a Human 5-HT6 Serotonin Receptor

Abstract: We describe the cloning and characterization of a human 5-HT₆ serotonin receptor. The open reading frame is interrupted by two introns in positions corresponding to the third cytoplasmic loop and the third extracellular loop. The human 5-HT₆ cDNA encodes a 440-amino-acid polypeptide whose sequence diverges significantly from that published for the rat 5-HT₆ receptor. Resequencing of the rat cDNA revealed a sequencing error producing a frame shift within the open reading frame. The human 5-HT₆ amino acid sequence is 89% similar to the corrected rat sequence. The recombinant human 5-HT₆ receptor is positively coupled to adenylyl cyclase and has pharmacological properties similar to the rat receptor with high affinity for several typical and atypical antipsychotics, including clozapine. The receptor is expressed in several human brain regions, most prominently in the caudate nucleus. The gene for the receptor maps to the human chromosome region 1p35–p36. This localization overlaps that established for the serotonin 5-HT_1Dα receptor, suggesting that these may be closely linked. Comparison of genomic and cDNA clones for the human 5-HT₆ receptor also reveals an Rsa I restriction fragment length polymorphism within the coding region.     

Metabolism of [5-3H]Kynurenine in the Rat Brain In Vivo: Evidence for the Existence of a Functional Kynurenine Pathway

Abstract: The incorporation of tritium label into quinolinic acid (QUIN), kynurenic acid (KYNA), and other kynurenine (KYN) pathway metabolites was studied in normal and QUIN-lesioned rat striata after a focal injection of [5-³H]KYN in vivo. The time course of metabolite accumulation was examined 15 min to 4 h after injection of [5-³H]KYN, and the concentration dependence of KYN metabolism was studied in rats killed 2 h after injection of 1.5–1,500 µ M [5-³H]KYN. Labeled QUIN, KYNA, 3-hydroxykynurenine (3-HK), 3-hydroxyanthranilic acid, and xanthurenic acid (XA) were recovered from the striatum in every experiment. Following injection of 15 µ M [5-³H]KYN, a lesion-induced increase in KYN metabolism was noted. Thus, the proportional recoveries of [³H]KYNA (5.0 vs. 1.8%), [³H]3-HK (20.9 vs. 4.5%), [³H]XA (1.5 vs. 0.4%), and [³H]QUIN (3.6 vs. 0.6%) were markedly elevated in the lesioned striatum. Increases in KYN metabolism in lesioned tissue were evident at all time points and KYN concentrations used. Lesion-induced increases of the activities of kynurenine-3-hydroxylase (3.6-fold), kynureninase (7.6-fold), kynurenine aminotransferase (1.8-fold), and 3-hydroxyanthranilic acid oxygenase (4.2-fold) likely contributed to the enhanced flux through the pathway in the lesioned striatum. These data provide evidence for the existence of a functional KYN pathway in the normal rat brain and for a substantial increase in flux after neuronal ablation. This method should be of value for in vivo studies of cerebral KYN pathway function and dysfunction.     

The effect of beet cyst nematode, Heterodera schachtii, on the yield of sugar beet in organic soils

In ten experiments on commercial sugar-beet crops grown on organic soils in 1984–86, a Genstat programme was used to examine the relationship between the initial population of Heterodera schachtii and sugar-beet root yield using the equation
Y = Ymin + (Ymax - Ymin) Z^pi-T
Fixing T = 200 eggs + juveniles 100 g^-1 soil and Z^T= 0.95, estimated values of Ymax varied from 49.2–67.1 t ha^-1 (129– 155% of the national average root yield for the years in which the experiments were carried out) and estimates of Ymin varied from 14.5–53.9 t ha^-1 (27–94% of Ymax). The estimated average root yield loss caused by the nematode was 6.95 t ha^-1.