bluuebunny/crossref_metadata_2025 huggingface dataset:
CYCLIC NUCLEOTIDE METABOLISM IN ELECTROPLAX OF ELECTROPHORUS ELECTRICUS
Authors: Childers S. R. , Siegel F. L.
Published: December 2006

Abstract— In order to describe the regulation of cyclic nucleotide metabolism in a cholinergic tissue, the properties of cyclic nucleotide phosphodiesterase were determined in electroplax of Electrophorus electricus and compared to those of mammalian brain. Electroplax phosphodiesterase was Mg2+ ‐dependent. localized in the soluble fraction and displayed normal linear Lineweaver‐Burk kinetics (Km: cyclic AMP. 1.4 μm; cyclic GMP, 0.54 μm). No low affinity (i.e. high Km) activity was detected. These results were correlated with comparatively low tissue levels of cyclic AMP (67 pmol/g) and cyclic GMP (3.2 pmol/g). Attempts were made to detect calcium‐dependent phosphodiesterase because of the presence of large amounts of the calcium‐dependent regulator protein (CDR) in electroplax, as this protein has been shown to activate brain phosphodiesterase. Assay with EGTA under a variety of conditions revealed that no calcium‐dependent activity could be detected. Preparation of CDR‐deficient phosphodiesterase also failed to produce calcium‐dependent activity. Assay of phosphodiesterase in other cholinergic tissues revealed calcium‐dependent activity in Electrophorus muscle and rat diaphragm but not in Torpedo electroplax. The results suggest that calcium‐dependent activity is not a significant portion of phosphodiesterase in electroplax and indicate alternate roles for CDR in electric tissue.
MALNUTRITION AND BRAIN DEVELOPMENT: CEREBELLAR WEIGHT, DNA, RNA, PROTEIN AND HISTOLOGICAL CORRELATIONS
Authors: Griffin W. S. T. , Woodward D. J. , Chanda R.
Published: December 2006

Abstract— Rat pups were reared in litters of 20 and litters of 6 to study effects of malnutrition on cerebellar development. Cell production and cell content were determined by assaying for DNA, as a measure of cell number, and RNA and protein, as indicators of cell constituents. By comparing DNA contents at 3, 4, 8, 11, 14, 17, 21, and 28 days after birth, we concluded that (a) there is little nutritional reserve at birth since significant differences appear by day 4, (b) most relative differences between groups appeared by day 8, with absolute differences increasing to day 21, and (c) there is partial recovery of cell number and cell constituents in the malnourished rats between 21 and 28 days.

Areal measurements of histological preparations showed that malnutrition resulted in less total area in cerebellar midsagittal sections at days 8, 11. and 14. In malnourished animals, the germinal matrix area of the cerebellum, the external granular layer, was smaller on the 8th postnatal day, the same on the eleventh day, and larger on the fourteenth day when compared with that of well fed animals. At all three ages alterations could be discerned in the distribution of cells between the mitotic external mantle and nonmitotic internal matrix portions of the external granular layer.

Further studies involving exchanging animals between large and small litters at various ages indicated that the time around days 4 to 8 is most sensitive to malnutrition. The results suggest a process in which malnutrition exerts its maximum effect by a slowing of cell production in the external granular layer in the initial exponential growth phase. It is likely that an adaptation occurs immediately in the external granular layer which subsequently permits a partial recovery of cerebellar growth between days 21 and 28.
EFFECTS OF OXYGEN INDUCED CONVULSIONS ON THE UPTAKE OF ACETATE INTO RAT BRAIN LIPIDS1,2
Authors: VanRollins M. , Velazquez‐Ortiz J. , Moran J. V. , Frattali V.
Published: December 2006

Abstract— Rats were exposed to 5 atmospheres absolute of oxygen, and [1‐14C]acetate was injected into the jugular vein either before or at the onset of electroencephalogram‐defined convulsions. Levels of 14C observed 2.2 min after the injection were reduced in the total lipids of brain and elevated in the blood of convulsed rats when compared to the nonconvulsed controls. These differences between convulsed and nonconvulsed animals were less pronounced when measured 15 and 60 min after injection. Convulsions did not change the amount of 14C incorporated into the total lipids of plasma during the 60 min period studied. Six fractions obtained from total lipid extracts of brain by TEAE‐cellulose showed similar 14C distributions in convulsed and control animals. The results suggest that oxygen‐induced convulsions cause an impaired utilization of systemically administered acetate for fatty acid incorporation into the lipids of brain.
POLYAMINES OF THE HUMAN BRAIN DURING NORMAL FETAL AND POSTNATAL GROWTH AND DURING POSTNATAL MALNUTRITION
Authors: McAnulty P. A. , Yusuf H. K. M. , Dickerson. J. W. T. , Hey E. N. , Waterlow J. C.
Published: December 2006

Abstract— The concentrations of the polyamines and putrescine were measured in the brains of human infants during fetal and early postnatal development. The concentrations of the amines were also measured in the brains of children who were malnourished during the first 2 years of life. In the brains of the adequately‐nourished infants there were differences in the developmental profiles of the amines between different regions of the brain, and the changes in polyamine concentrations paralleled changes in nucleic acid accumulation. The concentration of putrescine was much higher than that of the polyamines in all regions of the brain, and in the brain stem there were marked increases in putrescine concentration at the time of most rapid rate of myelination. Putrescine also increased markedly in the forebrain at the time of neuroblast multiplication in the fetus. In children malnourished during the first year of life there were reductions in the concentrations of spermidine and putrescine in the forebrain and brainstem, but spermine was unaffected. Malnutrition had no effect on the concentration of any of the amines in the cerebellum.
THE SPECIFIC INTERACTION OF S‐100 PROTEIN WITH SYNAPTOSOMAL PARTICULATE FRACTIONS. SITE‐SITE INTERACTIONS AMONG S‐100 BINDING SITES1
Authors: Donato R.
Published: December 2006

Abstract— The Scatchard plot of the specific binding of the brain‐specific S‐100 protein to synaptosomal particulate fractions (SYN) is curvilinear, concave upwards. This could indicate the existence either of multiple classes of sites with different but fixed affinities, or of site‐site interactions of the type defined as negative cooperativity among a single class of sites. To discriminate between these possibilities, the dissociation test described by De Meyts et al. (1976) for demonstrating negative cooperativity among insulin binding sites of human lymphocytes or liver membranes, was applied to the interaction of S‐100 with SYN. The results show that the dissociation of the 125I‐labelled S‐100‐site complex is faster due to an ‘infinite’(100‐fold) dilution of the complex plus an excess of unlabelled S‐100 than due to dilution only, the effect of unlabelled S‐100 being specific and dose‐dependent. 125I‐IabeIIed S‐100 dissociation is time, temperature, and Ca2 +‐dependent. The effect of unlabelled S‐100 is more evident at a low site occupancy than at a high one, suggesting that at high site occupancies 125I‐labelled S‐100 binding sites could be already negatively cooperating. It can be reasonably excluded that the effect of unlabelled S‐100 is due to inhibition of rebinding of the dissociated tracer. Na+ and K+ stimulate the dissociation even at physiological concentrations. At low pH 125I‐labelled S‐100 dissociates very little, while at high pH dissociation is greatly stimulated. Finally, the protein denaturating reagent urea accelerates the dissociation even at concentrations as low as 1m. These data suggest that negative cooperativity occurs among S‐100 binding sites, but do not exclude other possibilities. Together with previously reported findings, they further support the view that S‐100 binds to highly specific sites in nervous membranes.
DOPAMINE‐SENSITIVE ADENYLATE CYCLASE FROM THE RAT CAUDATE NUCLEUS: REGULATION BY GUANYL NUCLEOTIDES AND THE INTERACTION OF MAGNESIUM AND MAGNESIUM ATP1
Authors: Clement‐Cormier Yvonne C. , Rudolph Frederick B. , Robison G. Alan
Published: December 2006

Abstract— An adenylate cyclase present in the caudate nucleus of the rat brain, which is selectively stimulated by low concentrations of dopamine and which is believed to mediate dopaminergic synaptic transmission has been characterized with respect to interactions with guanyl nucleotides and magnesium ions. The addition of GTP (10−5 M) or GMPPNP (10−5 M) did not alter the linear increase in cyclic AMP as a function of time in the presence and absence of dopamine. GTP did, however, inhibit basal adenylate cyclase activity in homogenates of the caudate but the dopamine‐stimulated enzyme activity was not affected, thus increasing the percent stimulation produced by dopamine. This ability of GTP to increase responsiveness to dopamine was not dependent on the level of added Mg2+ in the assay medium. Conversely, GMPPNP (10−5 M) markedly lowered the basal as well as the dopamine stimulated activity as a function of magnesium in the caudate. These results suggest an important role for GTP and Mg2+ in the regulation of caudate adenylate cyclase and its activation by dopamine. In homogenates of the cortex the most dramatic effect of GTP and GMPPNP was on the potentiation of the norepinephrine effect. The guanyl nucleotides studied in the cortex did not have the inhibitory effect on basal enzyme activity as observed in homogenates of the caudate.

Interactions between Mg2+ and MgATP2‐ and the dopamine‐sensitive adenylate cyclase from the rat caudate nucleus have also been studied. The data are consistent with a bireactant sequential mechanism where Mg2+ is a required activator and free ATP4 is not a significant inhibitor of the reaction. The data show that dopamine lowered the apparent Km for free Mg2+ about 2‐fold without significantly changing the Vmax. GTP and GMPPNP did not alter the apparent Km for Mg2+ but did lower the Vmax both in the presence and absence of dopamine. GMPPNP was more potent than GTP in producing these effects in the striatal enzyme. The data presented herein implicate an important role for guanyl nucleotides and Mg2+ in the regulation of brain adenylate cyclase and its activation by various neurotransmitters. Furthermore, the results also suggest that although the role for guanyl nucleotides may be equally important in various areas of the brain, the mechanisms of action of guanyl nucleotides in these areas may differ.
BIOSYNTHESIS OF PHOSPHATIDIC ACID IN RAT BRAIN VIA ACYL DIHYDROXYACETONE PHOSPHATE
Authors: Hajra Amiya K. , Burke Caryl
Published: December 2006

Abstract— The enzymes for the biosynthesis of phosphatidic acid from acyl dihydroxyacetone phosphate were shown to be present in rat brain. These enzymes were mainly localized in the microsomal fraction of 12–14 day old rat brains. The brain microsomal acyl CoA: dihydroxyacetone phosphate acyl transferase (EC 2.3.1.42), exhibited a broad pH optimum between pH 5 and 9 with maximum activity at pH 5.4. Km for DHAP at pH 5.4 was 0.1 mm and Vmax was 0.86nmol/min/mg of microsomal protein. The corresponding microsomal enzyme for the glycerophosphate pathway (acyl CoA: sn‐glycerol‐3‐phosphate acyl transferase EC 2.3.1.15) was shown to have a different pH optimum (pH 7.6). On the basis of the differences in pH optima, differential effects of sodium cholate in the enzymes and a common substrate competition study, these acyl transferases were postulated to be two different microsomal enzymes.

Acyl DHAP:NADPH oxidoreductase (EC 1.1.1.101) in brain microsomes was found to be quite specific for NADPH as cofactor, being able to utilize NADH only at very high concentrations. This enzyme exhibited a Km of 8.6 μm with NADPH and Vmx of 0.81 nmol/min/mg protein. The presence of these two enzymes and the known presence of l‐acyl‐sn‐glycerol‐3‐phosphate: acyl CoA acyl transferase in brain (Fleming & Hajra, 1977) demonstrated the biosynthesis of phosphatidic acid in brain via acyl dihydroxyacetone phosphate. Phosphatidic acid was shown to form when dihydroxyacetone phosphate, acyl CoA, NADPH and other cofactors were incubated together with brain microsomes. Further properties of the enzymes and the probable importance of the presence of this pathway in brain were discussed.
THE CATECHOL ESTROGEN, 2‐HYDROXYESTRADIOL, INHIBITS CATECHOL‐O‐METHYLTRANSFERASE ACTIVITY IN NEUROBLASTOMA CELLS
Authors: Lloyd Tom , Weisz Judith , Breakefield Xandra O.
Published: December 2006

Abstract— The hydroxylation of estrone and estradiol at C2 to their respective catechol estrogens has been demonstrated by others with in vitro preparations from rat hypothalamic tissue. The subsequent methylation of these catechol estrogens by catechol‐O‐methyltransferase (COMT) in rat brain extracts has also been observed. Therefore, in specific sites in brain, 2‐hydroxylation of estrogens could play a significant role in the regulation of catecholamine metabolism. To evaluate the potential physiological significance of these interactions, we studied cultured murine neuroblastoma cells where the effect of 2‐hydroxyestradiol on COMT activity could be investigated in living cells and in cell homogenates. The addition of 2‐hydroxyestradiol to the cultures caused a specific dose‐dependent reduction in the formation of methylated products from the catecholamine, dopamine. The properties of COMT activity in the cell homogenates were examined and optimized with respect to the substrate, pH, concentrations of Mg2+, and the co‐factor, S‐adenosylmethionine. The catechol substrate. 3, 4‐dihydroxybenzoic acid, and 2‐hydroxyestradiol were both methylated by the cell homogenates. Inhibitor studies confirmed that both methylations were due to COMT. Furthermore, the catechol estrogen inhibited catechol methylation competitively at micromolar levels. These findings are consistent with the hypothesis that catechol estrogens are endogenous modulators of catecholamine metabolism.
EFFECT OF CORTISONE AND THYROXINE ON ACID GLYCOSIDASES IN RAT FOREBRAIN AND CEREBELLUM DURING EARLY POSTNATAL DEVELOPMENT
Authors: Lau Herbert C. , Horowitz Carolyn , Jumawan Jocelyn , Koldovsky Otakar
Published: December 2006

Abstract— l‐Thyroxine (200 μg/100 g B.W.) or cortisone‐acetate (5 mg/100 g B.W.), administered for 4 consecutive days, affected several lysosomal enzymes in forebrain and cerebellum of rats during various periods of the first month of postnatal development; their effect was age dependent as well as organ specific. Extending thyroxine or cortisone treatment to 7 days (from day 2 to 9) affected enzyme activity more than the 4‐day treatment period.
Tyrosine Hydroxylase Regulation: Apparent Kinetic Alterations Following Incubation of Brain Slices in a Sodium‐free Medium
Authors: Bustos Gonzalo , Simon Jay , Roth Robert H.
Published: December 2006

Abstract: In an attempt to determine if alterations in intraneuronal Ca2+ may regulate tyrosine hydroxylase activity, brain slices were subjected to experimental manipulations known to increase the intraneuronal concentration of free Ca2+ ions. Incubation of either striatal or olfactory tubercle slices in a Na+‐free medium for 15 min at 37° resulted in a marked increase in the activity of tyrosine hydroxylase present in the 20,000 g supernatant fraction of homog‐enates prepared from the slices. Tyrosine hydroxylase isolated from slices previously incubated in a Na+‐free, choline‐enriched medium or in a Na+‐free, sucrose‐enriched medium exhibited maximal activities when assayed at pH 6.0 and 7.0, respectively. However, the percentage stimulation of enzyme activity induced by incubation of the slices in a Na+‐free medium was maximal when the enzyme assays were performed at pH 7.0. The observed increase in enzyme activity seems to be mediated by a decrease in the apparent Km of the enzyme for pteridine cofactor, regardless of whether the kinetic enzyme analyses were conducted at pH 6.0 or 7.0, and by an increase in the K1 of the enzyme for end‐product inhibitor dopamine. The apparent kinetic changes in the enzyme do not seem to result from alterations in the endogenous dopamine content of the slices, and they are independent of any increase in dopamine release that might have occurred as a response to the augmented intraneuronal Ca2+ concentration. Furthermore, the activation of tyrosine hydroxylase produced by incubating slices in a Na+‐free medium is observed even in slices depleted of dopamine by pretreatment of rats with reserpine 90 min before preparation of brain slices. The activation of tyrosine hydroxylase observed under these experimental conditions does not seem to be mediated by cAMP or by a cAMP‐dependent phosphorylation process. It is suggested that the changes in tyrosine hydroxylase reported are mediated primarily by a rise in the free Ca2+ concentration within the nerve tissue. These observations are consistent with the hypothesis that the kinetic activation of tyrosine hydroxylase produced after depolarization of central dopaminergic neurons may occur through a Ca2+‐dependent event other than transmitter release.
Protein Turnover in Retina
Authors: III A. Ames , Parks J. M. , Nesbett F. B.
Published: December 2006

Abstract: Rabbit retinas were exposed in vitro to 0.5‐h pulses of [3H]leucine or [14C]Ieucine. Some retinas were harvested promptly after labeling to measure synthesis. These were combined, in double‐labeling experiments, with retinas that had been returned to unlabeled medium for a subsequent 1 h or 3.75 h to measure degradation. All of the proteins were solubilized, and separated according to size by gel electrophoresis. The gels were cut into 95 slices, and each slice was differentially counted. The amount of protein in the slice was estimated from the Coomassie blue staining, and its molecular weight from the distribution of molecular weight (MW) standards. Turnover rates of the various sizes of proteins were calculated from these data using certain well‐defined assumptions. Retinal protein contained about 32 ± 103 nmol of polypeptide per g, with a median MW of 27,000. Total synthesis was at the rate of 103 nmol/g of protein/h, with the most rapid synthesis in the 33,000–43,000 MW range, at 2 nmol/g/h for every 1000 increment in MW. Protein renewal averaged 0.52%/h, but varied directly (p < 0.0001) with MW, so that proteins of 10,000 MW were being renewed at about 0.1%/h and proteins of 140,000 MW at about 1.4%/h. Taken together, the measurements of fractional renewal and the measurements of degradation of the newly synthesized proteins demonstrated that each slice contained proteins with markedly different breakdown coefficients, and provided enough information to characterize the proteins in the slice in terms of a fast and a slow subgroup. This analysis indicated that: breakdown coefficients varied much more than rates of synthesis and were therefore the prime determinant of the amount of each protein that was present; as MW increased, breakdown coefficients of the long‐lived proteins increased (p < 0.0001), accounting in major part for the correlation between size and turnover; most staining bands were due to proteins with peculiarly long lifespans; the proteins with the slowest turnover of all appeared to be histones: there was an unusually rapid synthesis of a 138,000 MW polypeptide with a moderately short half‐life (about 3 h).
Topographical Distribution of γ‐Aminobutyric Acid Within the Cat Thalamus in Relation to the Basal Ganglia, as Determined by Mass Fragmentometry
Authors: Yoshida Mitsuo , Ariga Toshio , Kanazawa Ichiro , Miyatake Tadashi
Published: December 2006

Abstract: Chemical ionization mass spectrometry was introduced for the assay of GABA in the cat brain. The method is quite simple, sensitive, and specific for quantitative analysis. Study of the regional distribution of the GABA content within the thalamus disclosed that the ventromedial nucleus (VM) of the thalamus had a high concentration of GABA. The VM receives the afferent projection from the zona reticulata of the substantia nigra. The result, together with the results obtained by physiological as well as pharmacological studies, supports the hypothesis that the transmitter substance of the nigrothalamic pathway is GABA.
Cysteine and Cystine Transport at the Blood‐Brain Barrier
Authors: Wade Lester A. , Brady Helen M.
Published: December 2006

Abstract: The nature of cysteine and cystine uptake from the cerebral capillary lumen was studied in the rat using the carotid injection technique. [35S]‐Cysteine uptake was readily inhibited by the synthetic amino acid 2‐amino‐bicyclo(2,2,1)heptane‐2‐carboxylic acid (BCH), the defining substrate for the leucine‐preferring (L) system in the Ehrlich ascites cell. The addition of non‐radioactive alanine or serine, representatives of the alanine, serine, and cysteine‐preferring (ASC) system, produced no significant decrease in the uptake of cysteine after cysteine transport by the L system was blocked with BCH. This indicated that the major component of cysteine's transport from the brain capillary lumen was by the L system with no detectable uptake of cysteine by the ASC system. No carrier‐mediated transport of cystine, the disulfide form of the amino acid, was detected, nor was there any inhibition by cystine of the transport of the neutral amino acid methionine or the basic amino acid arginine. These results suggest that the ASC system, if present, is not quantitatively important for the transport of neutral amino acids from the brain capillary lumen.
P‐31 Nuclear Magnetic Resonance Analysis of Brain: The Perchloric Acid Extract Spectrum
Authors: Glonek Thomas , Kopp Stephen J. , Kot Eva , Pettegrew Jay W. , Harrison William H. , Cohen Maynard M.
Published: December 2006

Abstract: Perchloric acid (PCA) extracts were prepared from liquid‐N2‐frozen guinea pig brains and their organophosphate profiles examined by P‐31 nuclear magnetic resonance (NMR) spectroscopy. Thirty‐two phosphorus‐containing brain metabolites were characterized and quantitated. A distinctive feature of brain tissue metabolism relative to that of other tissues probed by P‐31 NMR is its pronounced ribose 5‐phosphate content. Comparison of brain metabolite levels following control or sublethal cyanide treatment (4 mg/kg) revealed specific cyanide‐induced changes in brain metabolism. Brains from cyanidetreated animals were characterized by a reduced phosphocreatine content and elevated α‐glycerolphosphate and inorganic orthophosphate contents relative to control. P‐31 NMR spectra of brain PCA extracts at pH 7.2 were also obtained under conditions that approximate those used for in vivo and intact tissue in vitro P‐31 spectroscopic analyses. The spectra reveal nine separate resonance bands corresponding to: sugar phosphates, principally ribose 5‐phosphate (3.7δ); inorganic orthophosphate (2.2δ); glycerol 3‐phosphorylethanolamine (0.3δ); glycerol 3‐phosphorylcholine (−0.1δ); phosphocreatine (−3.2δ); adenosine tri‐(β‐ATP) and di‐(β‐ADP) phosphate ionized end‐groups (−6.2δ); α‐ATP, α‐ADP, and nicotinamide adenine dinucleotides esterified end‐groups (−11.1δ); uridine diphosphohexose, hexose esterified end‐groups (−13.0δ); and β‐ATP ionized middle group (−21.6δ). Knowledge of the phosphatic molecules that contribute resonances to the brain P‐31 NMR spectrum as well as understanding their magnetic resonance properties is essential for the interpretation of in vivo brain spectroscopic data as well as brain extract data, since these same compounds contribute to the intact brain P‐31 spectrum.
Glycine Antagonists Structurally Related to Muscimol, THIP, or Isoguvacine
Authors: Krogsgaard‐Larsen P. , Hjeds H. , Curtis D. R. , Leah J. D. , Peet M. J.
Published: December 2006

Abstract: Microelectrophoretic methods were used to study the effects on cat spinal neurones of a number of compounds structurally related to the ‐γ‐Aminobutyric acid (GABA) agonists muscimol, THIP, and isoguvacine. While N‐methylmuscimol was an agonist at bicuculline methochloride‐sensitive GABA receptors, somewhat weaker than GABA and THIP, neither N, N‐dimethylmuscimol nor N‐methyl‐THIP interfered significantly with GABA receptors in vivo or binding sites in vitro. Both N, N‐dimethylmuscimol and N‐methyl‐THIP, however, reversibly antagonized the depressant action of glycine. The seven‐membered ring analogues of THIP, namely THIA (5,6,7,8‐tetrahydro‐4H‐isoxazolo[5,4‐c]azepin‐3‐ol), THAZ (5,6,7,8‐tetrahydro‐4H‐isoxazolo[4,5‐d]azepin‐3‐ol) and iso‐THAZ (5,6,7,8‐tetra‐hydro‐4H‐isoxazolo[3,4‐d]azepin‐3‐ol), also blocked neuronal inhibition by glycine, iso‐THAZ being the most potent compound. The conformationally mobile isomer of THAZ and iso‐THAZ, 3‐PYOL (5‐(3‐pyrrolidinyl)‐3‐isoxazolol), was a much less selective glycine antagonist, being also an antagonist of GABA. 3,4‐TAZA (2,5,6,7‐tetrahydro‐lH‐azepine‐4‐carboxylic acid) and 4,5‐TAZA (2,3,6,7‐tetrahydro‐lH‐azepine‐4‐carboxylic acid), which are amino acid analogues of THIA and THAZ, respectively, and ring homologues of isoguvacine, were also shown to be glycine antagonists. The mechanism of action of the present class of zwitterionic glycine antagonists is unknown. The compounds are much less potent than strychnine.
Distribution and Localization of Estrogen‐Sensitive Dopamine Receptors in the Rat Brain
Authors: Hruska Robert E. , Pitman Karen T.
Published: December 2006

Abstract: Administration of estrogen to adult male rats increases the density of striatal dopamine receptors. The densities of the dopamine receptors in the nucleus accumbens and cortex are not altered, while the density of those in the hippocampus is decreased. In the pituitary the density, on a whole pituitary basis, is not changed. The increased density of striatal dopamine receptors normally observed after estrogen treatment is prevented by prior injection into the striatum of kainic acid, which destroys the intrinsic neurons in the striatum. In addition, the benzodiazepine receptors in the striatum, cortex, hippocampus, and cerebellum are not altered by estrogen treatment, showing the specificity of the estrogen treatment and suggesting that the effects of estrogen are not mediated through benzodiazepine receptors.
High‐Affinity Choline Uptake in the Hippocampus: Its Relationship to the Physiological State Produced by Administration of Barbiturates and Other Treatments
Authors: Richter Judith A. , Gormley Joanne M. , Holtman Joseph R. , Simon Jay R.
Published: December 2006

Abstract: Choline uptake in hippocampal synaptosomes was not inhibited by pentobarbital administration when rats were decapitated immediately upon loss of the righting reflex (3–4 min) even though it was inhibited at later times post‐injection, when the rats were still unable to right themselves. Choline uptake was increased when the animals were decapitated at convulsion after an injection of picrotoxin, high doses of bicuculline, or one of the convulsant barbiturates. However, another convulsant barbiturate, as well as strychnine and lower doses of bicuculline, did not increase choline uptake even though the animals also convulsed. Thus loss of righting reflex or convulsion is not directly correlated with changes in choline uptake. At 7 min after injection, levels of pentobarbital in the hippocampus (and other brain regions) were correlated with the degree of inhibition of choline uptake up to about 50% inhibition; however, greater inhibition could not be achieved with much higher brain levels of the drug. Although hippocampal uptake was partially inhibited at 1 h after septal lesions, 3 h after the lesion the inhibition was no longer apparent. Inhibition was almost complete 10–12 days after the lesion. These results suggest that other factors in addition to impulse flow influence choline uptake.
Neurochemical Studies of the Mesolimbic Dopaminergic Pathway: [3H]Spiperone Labels Two Binding Sites in Homogenates of the Nucleus Accumbens of Rat Brain
Authors: Beart P. M. , McDonald Danielle
Published: December 2006

Abstract: The binding of [3H]spiperone to membranes of the nucleus accumbens of the rat brain was studied in vitro and found to be of high affinity, rapid, saturable, reversible and stereospecific. Dissociation and saturation experiments indicated the presence of two specific binding sites with apparent dissociation constants of 70 pM and >1 nM. Specific binding with 25 pM [3H]spiperone represented >90% of total binding and was displaced by dopaminergic agonists, neuroleptic drugs and ergot derivatives. The rank order of potency for the ergot derivatives was bromocryptine > pergolide > lergo‐trile, and that for D‐2 antagonists was domperidone > sulpiride > molindone > metoclopramide. Noradrenergic, histaminergic and serotonergic components of the binding were not detected. [3H]Spiperone binds to high‐affinity sites in homogenates of nucleus accumbens, which are likely to be D‐2 receptors.
Cerebral Glutamic Acid Decarboxylase Activity and γ‐Aminobutyric Acid Concentrations in Mice Susceptible or Resistant to Audiogenic Seizures
Authors: Sykes C. C. , Horton R. W.
Published: December 2006

Abstract: DBA/2 mice between 21 and 28 days of age are highly susceptible to sound‐induced seizures. Drug studies suggest a possible deficit of γ‐Aminobutyric acid (GABA)‐mediated neurotransmission may be involved. We have measured the whole brain GABA concentration and glutamic acid decar‐boxylase activity in DBA/2 mice at various ages before, during, and after the period of maximal susceptibility to audiogenic seizures. Corresponding determinations were carried out on age‐matched TO mice, a strain much less susceptible to audiogenic seizures than DBA/2 mice at all ages. No significant differences in GABA concentration or glutamic acid decarboxylase activity were found between strains at any age. The susceptibility of DBA/2 mice to audiogenic seizures does not result from a gross inability to synthesise or store GABA.
Glycine Uptake by Cultured Human Y79 Retinoblastoma Cells: Effect of Changes in Phospholipid Fatty Acid Unsaturation
Authors: Yorek Mark A. , Hyman Bradley T. , Spector Arthur A.
Published: December 2006

Abstract: Glycine uptake was investigated in cultured Y79 retinoblastoma cells containing different degrees of phospholipid fatty acid unsaturation. The modifications were produced by growing the retinoblastoma cells in medium supplemented with various unsaturated fatty acids. Glycine was taken up by the retinoblastoma cells through two kinetically distinguishable processes. The high‐affinity system is totally dependent upon extracellular Na+ and partially dependent upon Ca2+. Of the glycine taken up by retinoblastoma cells, 85–90% remains as free intracellular glycine and less than 3% is incorporated into cellular protein. When the cells are grown in a medium containing 10% fetal bovine serum as the only source of fatty acids, the phospholipids contained 23% polyunsaturated fatty acids. Under these conditions the high‐affinity system has a K′m of 34.2 ± 3.7 μM and a V′max of 91.2 ± 16.2 pmol min−1 mg protein−1. The low‐affinity system has a K′m of 2.7 ± 0.4 mM and a V′max of 4.1 ± 0.5 nmol min−1 mg protein−1. When the polyunsaturated fatty acid content of the phospholipids was increased by supplementing the medium with linolenic or docosahexaenoic acids (n‐3 polyunsaturates) or linoleic or arachidonic acids (n‐6 polyunsaturates), the K′m and V′max of the high‐affinity glycine uptake system were increased three‐ to fourfold. By contrast, supplementing the medium with oleic acid, an n‐9 monounsaturate, did not significantly alter the K′m or K′maxfor glycine uptake. The results with this model system suggest that one of the effects of the high polyunsaturated fatty acid content normally present in neural cell membranes may be a modulation of the high‐affinity transport system so that it functions more efficiently in regulating glycine uptake.
Bovine Brain S100 Proteins: Separation and Characterization of a New S100 Protein Species
Authors: Baudier Jacques , Mandel Paul , Gérard Dominique
Published: December 2006

Abstract: Three S100 protein species (S100a, S100b, S100a′) have been purified from bovine brain using a modification of standard preparative methods. A higher yield for each protein was obtained at the last separation step. Characterization by urea/sodium dodecyl sulfate/polyacrylamide gel electrophoresis, UV absorption spectra, and fluorescence parameters provided evidence of anew tryptophan‐containing S100 protein called S100a′, which exhibits, as S100a and S100b, the properties of a Ca2+ binding protein.
Kinetics of Transport and Phosphorylation of 2‐Fluoro‐2‐Deoxy‐d‐Glucose in Rat Brain
Authors: Crane Paul D. , Pardridge William M. , Braun Leon D. , Oldendorf W. H.
Published: December 2006

Abstract: The kinetics of transport across the blood‐brain barrier and metabolism in brain (hemisphere) of [14C]2‐fluoro‐2‐deoxy‐d‐glucose (FDG) were compared to that of [3H]2‐deoxy‐d‐glucose (DG) and d‐glucose in the pentobarbital‐anesthetized adult rat. Saturation kinetics of transport were measured with the brain uptake index (BUI) method. The BUI for FDG was 54.3 ± 5.6. Nonlinear regression analysis gave a Km of 6.9 ± 1.1 mM and a Vmax of 1.70 ± 0.32 μmol/min/g. The K1 for glucose inhibition of FDG transport was 10.7 ± 4.4 mM. The kinetic constants of influx (k1) and efflux (K2) for FDG were calculated from the Km, Vmax, and glucose concentrations of the hemisphere and plasma (2.3 ± 0.2 μmol/g and 9.9 ± 0.4 mM, respectively). The transport coefficient (k1 FDG/k1glucose) was 1.67 ± 0.07 and the phosphorylation constant was 0.55 ± 0.16. The predicted lumped constant for FDG was 0.89, whereas the measured hexose utilization index for FDG was 0.85 ± 0.16. Conclusion: The value for the lumped constant can be predicted on the basis of the known kinetic constants of FDG and glucose transport and metabolism, as well as brain and plasma glucose levels. Knowledge of the lumped constant is crucial in interpreting data obtained from 18FDG analysis of regional glucose utilization in human brain in pathological states. We propose that the lumped constant will rise to a maximum equal to the transport coefficient for FDG under conditions of transport limitation (hypoglycemia) or elevated glycolysis (ischemia, seizures), and will fall to a minimum equal to the phosphorylation coefficient during phosphorylation limitation (extreme hyperglycemia).
Induction of Brain Ornithine Decarboxylase During Recovery from Metabolic, Mechanical, Thermal, or Chemical Injury
Authors: Dienel Gerald A. , Cruz Nancy F.
Published: December 2006

Abstract: Metabolic, mechanical, thermal, and chemical injury induced ornithine decarboxylase (ODC) activity in rat brain. A two‐ to sixfold increase in ODC activity was measured at 5‐9 h after different modes of injury to the brain. During the early phase of recovery from transient ischemia, when average protein synthesis was <50% of control, ODC activity was increased nearly fivefold. The rise in activity could be blocked by anisomycin, or reduced by intracerebral injections of actinomycin D. Drilling burr holes into the skull, injection of the vehicle for actinomycin D, hyperthermia, and freezing lesions all caused increased ODC activity. Neurotoxic chemicals (ammonia, methionine sulfoximine, acrylamide, carbon tetrachloride, and anisomycin) also increased brain ODC activity, whereas other chemicals (mannitol and valine) did not. Treatments known to stimulate the synthesis of heat shock proteins (carotid occlusion, hyperthermia, Cd2+, canavanine, and ethanol) induced ODC activity in the liver, whereas only hyperthermia and ethanol caused significant increases in spleen ODC activity. All increases in ODC activity were blocked by difluoromethylornithine, an irreversible inhibitor of ODC. The cellular response to noxious or stressful stimuli includes the synthesis of a small number of proteins of unknown functions; ODC may be one of these “heat shock” or “trauma” proteins.
Decreased Uptake and Release of D‐Aspartate in the Guinea Pig Spinal Cord After Dorsal Root Section
Authors: Potashner S. J. , Tran P. L.
Published: December 2006

Abstract: This study attempts to determine if L‐gluta‐mate and/or L‐aspartate may be transmitters of dorsal sensory neurons. The uptake and the electrically evoked release of D‐[3H]aspartate, a putative marker for L‐glu‐tamate and L‐aspartate, were measured in the cervical enlargement (segments C4‐T1) of the guinea pig spinal cord before and after cutting dorsal roots C5‐T1 on the right side. The uptake and the release of γ‐aminobutyric acid (GABA) also were measured as indices of the integrity of GABAergic neurons in the spinal cord. The cervical enlargement was excised and divided into left and right halves, then into dorsal and ventral quadrants. Quadrants from unlesioned animals took up D‐aspartate and GABA, achieving concentrations in the tissues which were 14‐25 times that in the medium. Subsequently, electrical stimulation evoked a Ca2+‐dependent release of D‐aspartate and of GABA. The uptake and release of D‐aspartate and GABA were similar in tissues taken from intact and sham‐operated animals. However, dorsal rhi‐zotomy, without damage to dorsal radicular or spinal blood vessels, depressed the uptake (by 22‐29%) and the release (by 50%) of D‐aspartate only in quadrants ipsilat‐eral to the lesion. The uptake and the release of GABA were unchanged. In transverse sections of the cervical enlargement, stained to reveal degenerating fibers, by far the heaviest loss of axons occurred in the cuneate fasciculus and in the gray matter ipsilateral to the cut dorsal roots. These findings suggest that the synaptic endings of dorsal sensory neurons probably mediate the uptake and the release of D‐aspartate and, therefore, may use L‐glu‐tamate or L‐aspartate as a transmitter. When spinal blood vessels were damaged during dorsal rhizotomy, the deficits in D‐aspartate uptake and release were larger than those in the absence of vascular damage and were accompanied by deficits in GABA uptake and release. These findings imply that vascular damage results in the loss of intraspinal neurons, some of which probably mediate the uptake and release of D‐aspartate and, therefore, may use L‐glutamate and/or L‐aspartate as a transmitter.
Stimulation of [3H]γ‐Aminobutyric Acid Release by Calcium Chelators in Synaptosomes
Authors: Arias Clorinda , Sitges Maria , Tapia Ricardo
Published: December 2006

Abstract: The effect of EGTA on the release of labeled γ‐aminobutyric acid (GABA), glutamate, acetylcholine, and dopamine was studied in superfused synaptosomes from mouse brain. In the absence of both Ca2+ and Mg2+, EGTA and also EDTA at 50 μM or higher concentrations induced a 2.5‐5‐fold stimulation of [3H]GABA release, similar to that produced by potassium depolarization, whereas only a slight effect, or no effect at all, was observed on the release of the other transmitters studied. The GABA‐releasing action of EGTA was practically abolished in the presence of Mg2+. In contrast, the effect of EDTA was also observed when the medium contained Mg2+. Studies on the ionic dependence showed that the stimulation of GABA release by EGTA was abolished in a Na+‐free medium. Li+ did not substitute Na+ for the EGTA effect, which was also independent of chloride. This Na+ dependence does not seem to involve voltage‐sensitive channels, since tetrodotoxin did not affect the GABA‐releasing action of EGTA, whereas in parallel su‐perfusion chambers it blocked over 80% the stimulation of GABA release by veratridine. In contrast, two calcium channel blockers in synaptosomes, La3+ and the cationic dye ruthenium red, greatly inhibited the GABA‐releasing effect of EGTA. L‐2,4‐Diaminobutyric acid, an inhibitor of the Na+‐dependent GABA carrier, did not affect the releasing action of EGTA, whereas in a parallel experiment this drug inhibited by more than 90% the exchange of labeled GABA with unlabeled GABA. It is concluded that the Na+‐dependent releasing action of EGTA and EDTA on GABA is probably due to a destabilization of the synaptosomal membrane by chelation of endogenous membranal Ca2+, which can be prevented by Mg2+. Such destabilization results in Na+ influx through Ca2+ channels, and the consequent increase in the intrater‐minal Na+ concentration induces the release of GABA by a mechanism probably not involving the amino acid carrier. The possible participation of mitochondrial Na+ ‐Ca2+ exchange is considered improbable in view of the lack of effect of EGTA on the release of other neurotrans‐mitters.
Cerebrospinal Fluid Measurements Suggest Precursor Availability and Sex Are Involved in the Control of Biogenic Amine Metabolism in a Primate
Authors: Young Simon N. , Ervin Frank R.
Published: December 2006

Abstract: Biogenic amine precursors and metabolites were measured in cisternal cerebrospinal fluid from 83 female and 55 male vervet monkeys. The results indicate that mean rates of 5‐hydroxytryptamine, dopamine, and noradrenaline metabolism in the brain are higher in females than in males. They also suggest that under physiological circumstances tryptophan availability is involved in the control of brain 5‐hydroxytryptamine synthesis while tyrosine availability is involved in control of both dopamine and noradrenaline metabolism. The similarities seen between our results on vervets and those seen with human cerebrospinal fluid suggest that the vervet is a useful primate to study.
Effect of Folate Deficiency on Local Cerebral Glucose Utilization in the Rat
Authors: Hakim Antoine M. , Arrieta Marie J. , Cooper Bernard A. , Pappius Hanna M.
Published: December 2006

Abstract: There is considerable debate on the role of folate in CNS function. Recent work indicates that folate deficiency may affect CNS serotonin metabolism, and clinical studies describe many consequences of such a deficiency. On the other hand some workers maintain that folate deficiency alone causes CNS abnormalities. We maintained rats, through dietary deprivation, at folate levels below 4 ng/ml for more than 6 weeks and showed that at that time both their liver and brain folate levels were significantly reduced. We then studied their local cerebral glucose utilization (LCGU) using the [14C]deoxyglucose technique. This method assesses cerebral function by measuring regional metabolic activity. We also determined LCGU in rats given the same diet but replenished with folate (folate control) and in others given free access to commercially available food (normal controls). Our results show that this degree of folate deficiency has no effect on cerebral function. This contrasts with the focal suppression of LCGU we previously reported in a model of vitamin B12 deficiency.
Microsomal Opiate Receptors: Characterization of Smooth Microsomal and Synaptic Membrane Opiate Receptors
Authors: Roth Bryan L. , Coscia Carmine J.
Published: December 2006

Abstract: In continuing studies on smooth microsomal and synaptic membranes from rat forebrain, we compared the binding properties of opiate receptors in these two discrete subcellular populations. Receptors in both preparations were saturable and stereospecific. Scatchard and Hill plots of [3H]naloxone binding to microsomes and synaptic membranes were similar to plots for crude membranes. Both synaptic membranes and smooth microsomes contained similar enrichments of low‐ and high‐affinity [3H]naloxone binding sites. No change in the affinity of the receptors was observed. When [3H]D‐ala2‐D‐leu5‐enkephalin was used as ligand, microsomes possessed 60% fewer high‐affinity sites than did synaptic membranes, and a large number of low‐affinity sites. In competition binding experiments microsomal opiate receptors lacked the sensitivity to (guanyl‐5′‐yl)imidodiphosphate [Gpp(NH)p] shown by synaptic and crude membrane preparations. In this respect microsomal opiate receptors resembled membranes that were experimentally guanosine triphosphate (GTP)‐uncoupled with N‐ethylmaleimide (NEM). Agonist binding to microsomal and synaptic membrane opiate receptors was decreased by 100 mM NaCl. Like NEM‐treated crude membranes, microsomal receptors were capable of differentiating agonist and antagonists in the presence of 100 mM NaCl. MnCl2 (50–100 μM) reversed the effects of 100 mM NaCl and 50 μM GTP on binding of the μ‐specific agonist [3H]dihydromorphine in both membrane populations. Since microsomal receptors are unable to distinguish agonists from antagonists in the presence of Gpp(NH)p, they are a convenient source of guanine nucleotide‐uncoupled opiate receptors.
Effects of Methotrexate on Biopterin Levels and Synthesis in Rat Cultured Pineal Glands
Authors: Culvenor Anne J. , Miller Leonard P. , Levine Robert A. , Lovenberg Walter
Published: December 2006

Abstract: Culture of rat pineal glands in methotrexate (0.5, 5, or 10 μM) for 6 or 24 h did not alter pineal tetrahydrobiopterin (85–90% of total biopterin in cultured glands), except for a decrease of 30% after 24 h culture in 10 μM methotrexate. However, pineal dihydrobiopterin and/or biopterin (10–15% of total biopterin) was increased by methotrexate up to 2.5‐fold. Biopterin detected in the culture medium following pineal culture was also increased to a similar extent after methotrexate treatment and appeared to represent leakage of pineal dihydrobiopterin and/or biopterin. Culture of glands in 5 μM methotrexate did not alter the conversion of [U‐14C]‐guanosine to [14C]biopterin, suggesting that pineal tetrahydrobiopterin synthesis was not altered by methotrexate. Complete inhibition of dihydrofolate reductase activity measured in pineal homogenates was obtained following culture of glands in all concentrations of methotrexate studied. Therefore, dihydrofolate reductase and dihydrobiopterin do not appear to be involved in a major biosynthetic pathway for pineal tetrahydrobiopterin from GTP, although they may have a minor role in tetrahydrobiopterin synthesis.
Basic and Regulatory Mechanisms of In Vitro Release of Met‐Enkephalin from the Dorsal Zone of the Rat Spinal Cord
Authors: Cesselin F. , Bourgoin S. , Artaud F. , Hamon M.
Published: December 2006

Abstract: Under control conditions, superfused slices of the dorsal half of the lumbar enlargement from adult rats released Met‐enkephalin‐like material (MELM) that behaved as authentic Met‐enkephalin under two different chromatographic procedures (Bio‐gel filtration, HPLC). MELM release increased markedly on exposure of slices to batrachotoxin (0.5 μM) or to an excess of K+ (28 and 56 mM instead of 5.6 mM). The K + ‐evoked release was totally dependent on the presence of Ca2+ in the super‐fusing fluid whereas the spontaneous efflux of MELM was only partially Ca2+‐dependent. Further experiments performed with tissues of polyarthritic rats indicated that the increase in their MELM levels was associated with a lower fractional rate constant of MELM release, therefore suggesting that spinal Met‐enkephalin turnover might be reduced in chronically suffering animals. Examination of the possible modulation of MELM release by various neuroactive compounds present within the dorsal horn revealed that cholecystokinin (10 μM), but not its desulphated derivative, substance P‐sulphoxide (10 μM), and to a lesser extent substance P, enhanced the K+‐evoked MELM release. In contrast, γ‐aminobutyric acid (10 μM) and (–)‐baclofen (1 μM) partially prevented the stimulatory effect of K+ on MELM release. Other compounds such as serotonin, somatostatin, and neurotensin altered neither the spontaneous nor the K+‐evoked release of MELM.
Inhibition of a Membrane‐Bound Enkephalin‐Degrading Aminopeptidase by Bestatin Analogs
Authors: Shimamura Mariko , Hazato Tadahiko , Hachisu Mitsugu , Katayama Takashi
Published: December 2006

Abstract: A variety of bestatin analogs were examined as potent inhibitors of a membrane‐bound enkephalin‐degrading aminopeptidase that was purified from monkey brain. Bestatinyl amino acid derivatives showed strong inhibition of this enzyme. The most effective was bestatin‐l‐Arg AcOH, with a Ki value of 0.21 × 10−8M with Leu‐enkephalin as substrate. It exhibited competitive kinetics and was about 100‐fold more potent than bestatin. This compound seems to be useful for pharmacological and other studies.