POSTNATAL CHANGES IN FREE AMINO ACID,DNA, RNA AND PROTEIN CONCENTRATIONS OF MINIATURE SWINE BRAIN1

Postnatal developmental characteristics of miniature swine brain were evaluated through the first 9 weeks of age. Differential growth rates of cerebrum, cerebellum and brain stem were defined in terms of DNA, RNA, protein and free amino acid concentrations at ages 5, 21, 35 and 63 days. Within the experimental conditions provided, hyperplasia ceased just prior to ages 21, 35 and 63 days for cerebellum, brain stem and cerebrum, respectively. An additional cerebral growth spurt, observed between weaning at age 35 days and sacrifice at age 63 days, may be indicative of impaired brain development due to inadequate nutrition provided by the dam's milk. Developmental changes in mean concentrations of brain free amino acids varied with anatomical area and differed somewhat from those of other species previously reported. For example, mean cerebral concentrations of aspartic acid, γ-aminobutyric acid and asparagine + glutamine decreased significantly (P < 0·05) with age and mean glutamic acid concentration was 5 times that of taurine.     

Analysis of aspartic acid and asparagine metabolism in Xenopus laevis oocytes using a simple and sensitive HPLC method

The amino acids in methanol-soluble extracts of Xenopus oocytes were measured using a method involving precolumn derivatization with phenylisothiocyanate and reverse phase HPLC of the derivatized amino acids. This technique allows the estimation of asparagine and glutamine pools in oocytes, estimated as 70 and 283 pmoles per oocyte, respectively. The pool sizes of the other amino acids were similar to previously reported results obtained using conventional ion exchange chromatography and postcolumn derivatization with ninhydrin. The advantages of the method developed here include picomolar sensitivity and the enhanced resolution of asparagine and glutamine from other amino acids. The kinetics of aspartic acid and asparagine utilization were monitored following microinjection of oocytes with [³H]aspartic acid and [¹⁴C]asparagine. The aspartic acid pool turned over rapidly with a half-time of <30 min. The asparagine pool was metabolized much more slowly and appeared to be utilized almost completely for protein synthesis. The absolute rate of protein synthesis in oocytes was calculated from the incorporation data and chemical pool measurements as ～25 ng/hr-oocyte. The methodology developed here may be useful in experimental situations involving limited amounts of biological material. © 1994 Wiley-Liss, Inc.     

Solid-phase synthesis of larger peptides by a new strategy of detachment from the resin

Attachment of the side-chain carboxyl of the protected aspartic or glutamic acid ester to the resin support has been established for the solid-phase synthesis of the asparagine or glutamine peptide. After further elongation of the α-amino deprotected resin-bound peptide ester with protected peptide fragments and the final detachment from the resin support by ammonolysis, the larger peptides containing, or preferably C-terminated with, asparagine or glutamine could be obtained. Thus, the C-peptide of human proinsulin was prepared by coupling to the resin-bound dipeptide derivative, Leu-Glu(OCH₂Ph®)·OtBu, with six fragments consecutively. It was obtained in an overall yield of 36% after detaching from the resin with alcoholic ammonia, followed by mild acidolysis, DEAE cellulose chromatography, and gel filtration. This procedure has now been applied to the synthesis of the C-terminal fragment of the insulin A chain ending in asparagine, and also to the synthesis of the threonine or serine peptide, where the anchorage to the resin was designed by the reaction of the sidechain hydroxyl with succinic anhydride in the presence of 4-dimethylaminopyridine to form the hemiester of succinic acid, which in turn was condensed to the aminomethyl resin by the DCC-HOBt procedure. Model experiments on the synthesis of the Z-Thr(CO-CH₂CH₂CONHCH₂Ph®)·OtBu and Bpoc-Lys(Boc)-Thr(COCH₂CH₂CONHCH₂Ph®)·OtBu, as well as their detachment from the resin by amminolysis or hydrazinolysis, have shown the potential for a milder process in the solid-phase synthesis of larger peptides.     

Organic Nutrients in the Media for Propagation of Cymbidium in vitro

Protocorms of Cymbidium (Orchidaceae) were grown on media containing different organic nutrients. Of the sugars tested sucrose was better than maltose, glucose and fructose, and sucrose had an optimum concentration of 3 to 4 %. D-Mannose was significantly less effective than the other sugars. The amino acid mixtures casamino acids (casein hydrolysate) and tryptone increased growth while yeast extract was inhibitory and malt extract without effect. Optimal concentrations were 2 to 3 g · l^-1 casamino acids and 3 to 4 g · l^-1 tryptone. It was to some extent possible to substitute the amino acid mixtures with a single amino acid (glutamine at 300 mg · l^-1). Arginine was inhibitory and asparagine was without any effect. Vitamins proved to be unnecessary although there was a tendency towards increased growth with nicotinic acid and meso-inositol. Purines and pyrimidines were added to the medium but with no effect. Liquid endosperm from coconuts (10 to 15%) increased growth while the liquid endosperm from Aesculus hippocastanum was inhibitory. On the basis of these results a revised medium is proposed for the in vitro propagation of Cymbidium.     

INFLUX OF GLUTAMIC ACID IN PERIPHERAL NERVE—CHARACTERISTICS OF INFLUX1

Abstract— —The influx of glutamic acid in frog sciatic nerve has been studied by monitoring the disappearance of ¹⁴C labelled compound from the bathing medium. After 5hr of incubation in 10 ⁻⁶m non-labelled l -glutamic acid and 0·01, μc/ml labelled isotope, the intracellular concentration of labelled glutamic acid is about 15 times the concentration in the bathing medium; however, there appears to be a net loss of non-labelled compound with incubation. Uptake of L,-glutamic acid is accompanied by conversion of significant amounts of labelled E-glutamic acid to carbon dioxide and glutamine; small amounts of γ-aminobutyric acid and aspartic acid are also formed. The rate of disappearance of labelled l -glutamic acid decreases with increasing concentration of non-labelled isotope in the bathing medium. Construction of a Lineweaver-Burk plot from initial velocities of influx yields an average V_m of 4·02 × 10⁻⁹ moles/g/min and an average K_m. of 3·23 × 10 ⁻⁵ moles/l. The influx of glutamic acid is highly specific with regard to molecular structure; of the compounds tested, only l -glutamine, l -glutamic acid, GABA, l -lysine, and l -aspartic acid are taken up, and only l -aspartic acid will compete with l -glutamic acid for uptake.     

Influence of Several Growth Regulators and Amino Acids on in vitro Organogenesis of Torenia fournieri Lind.

The effects of several growth regulators and amino acids onin vitro organogenesis of Torenia fournieri Lind. were determinedusing internodal segments. Treatment with 2,4-D¹ resulted innodular callus formation, while NAA and IAA induced roots constantlybut much less frequently shoot buds. Individually BA, zeatin,and 4-PU induced bud formation, but these shoot buds did notdevelop further. Formation of buds by cytokinin was influencedby a simultaneous application of NAA or 2,4-D, but not of IAA,its degree being reduced when BA was simultaneously appliedwith NAA or 2,4-D. When zeatin or kinetin was added with NAA,numerous roots were induced. The effects of various L-amino acids on in vitro organogenesiswere also investigated using the defined medium in which KNO₃was a principal source of nitrogen. The formation of buds wasconsiderably stimulated by alanine and asparagine, and slightlyby glutamic acid in the medium containing both NAA and BA, inwhich bud formation was easily induced. On the other hand, allamino acids except for glutamic acid and aspartic acid inhibitedroom formation in this medium. Root formation was greatly stimulated by proline, alanine, glutamine,glutamic acid, and aspartic acid, and slightly by arginine andtryptophan in the medium containing NAA but no BA. Glutamicacid and aspartic acid also enhanced bud formation in this medium.     

EFFECTS OF SODIUM FLUOROACETATE ON THE METABOLISM OF N-ACETYLASPARTATE AND ASPARTATE IN MOUSE BRAIN

A subconvulsant dose of sodium fluoroacetate inhibited the metabolic utilization of intracerebrally-administered N-acetyl-l -[U-¹⁴C]asparticacid and the labelling of glutamine from this precursor in mouse brain, but not the labelling of glutamate or aspartate. A convulsant dose also inhibited the utilization of l -[U-¹⁴C]aspartic acid. When intraperitoneal injection of a convulsant dose of sodium fluoroacetate was followed by intracerebral injection of N-acetyl-l -[U-¹⁴C]asparticacid, the levels of N-acetylaspartate, aspartate and glutamate in brain were lowered, while the glutamine content was increased. The specific radioactivity of glutamine relative to that of glutamate was much lower when these compounds were labelled from l -[U-¹⁴C]aspartic acid than when N-acetyl-l -[U-¹⁴C]aspartic acid was used as the precursor. Intracerebral injection of tracer amounts of l -[U-¹⁴C]aspartic acid reduced the content of N-acetylaspartate in brain and raised the glutamine content. Sodium fluoroacetate had no additional effect on the relative specific radioactivity of glutamine or the content of N-acetylaspartate, aspartate, glutamate or glutamine when l -[U-¹⁴C]aspartic acid was the precursor. We consider the results to be consistent with a selective inhibition both by sodium fluoroacetate and by exogenous aspartic acid of the tricarboxylic acid cycle in brain associated with the biosynthesis of glutamine. We suggest that the activity of this pathway may regulate the metabolism of N-acetylaspartate and aspartate.     

A comparison of amide and ureide nitrogen sources in tissue culture of tree legume Prosopis alba clone B2 V50

The effects of medium nitrogen sources on the recalcitrant nature of Prosopis alba clone B2V50 in tissue culture were compared involving shoot development using axillary bud explants from 2 to 4-year-old greenhouse-grown trees. A significant difference (P<0.05) was found between the amino acids aspartic acid and glutamic acid and their corresponding amide-containing compounds asparagine and glutamine. A comparison between amide and ureide nitrogen sources showed that allantoin, a ureide, was an acceptable replacement for asparagine or glutamine. Allantoin, asparagine, and glutamine could be used as the sole nitrogen sources. Allantoin at a concentration of 20 mM was adopted for use in future research. Although shoots were consistently induced, all explants showed complete shoot-tip necrosis after 12 weeks of in vitro culture.     

UPTAKE AND METABOLISM OF GLUTAMATE BY ISOLATED TOAD BRAINS CONTAINING DIFFERENT LEVELS OF ENDOGENOUS AMINO ACIDS

—The uptake of [U-¹⁴C]glutamate into the amphibian brain was studied in vitro using brains from toads (Bufo boreas) adapted either to a fresh water (FWA) or an hyperosmotic saline (HOA) environment. Initial rates of ¹⁴C-glutamate uptake showed a single apparent K_m of about 0·2 mm . Uptake by HOA brains was slower than that by FWA brains, reflecting perhaps a non-competitive type of inhibition by the higher content of glutamate in the HOA brains. Although the glutamate content of HOA brains was maintained during prolonged incubation at twice the level found in FWA toads, other metabolic parameters measured in the two types of brain preparations were surprisingly similar. Tissue to medium concentration ratios of greater than 3000:1 were generated by both FWA and HOA brains. In both brain systems the clearance of glutamate from the medium was accompanied by a rapid conversion of the amino acid to glutamine and its release into the medium. In both the FWA and HOA toad brain systems some [U-¹⁴C]glutamate was metabolized to aspartate and GABA; in both systems the specific radioactivity (SA) of glutamine in the tissue was from two to four times greater than that of glutamate; also the SA of glutamine released into the medium was higher by several orders of magnitude than the SA of glutamine in brain tissues. These and other findings support the concept that, in both the FWA and HOA toad brains, transport processes are instrumental in preserving low extracellular levels of glutamate but that mechanisms other than transport are responsible for the maintenance of different levels of glutamate in the FWA and HOA toad brains.     

Amino-acid profiles in red algae

Free protein amino acids have been quantitatively determined in 30 red algae. In most of the species, aspartic acid (asparagine), glutamic acid (glutamine), alanine, glycine and serine dominate, while massive accumulation of proline (up to 80·5%) was observed in six species, all belonging to the family Rhodomelaceae.     

Variations in the content of free and bound amino acids during dormancy and the first cell cycle in Helianthus tuberosus tuber explants

Abstract

Qualitative and quantitative analysis of free and bound amino acids and amides during dormancy and the most important phases of the first cell cycle was carried out in tubers of Helianthus tuberosus.

In the dormant tuber arginine was confirmed to be the most abundant amino acid. A high amount of asparagine was also present; on the contrary glutamine was found in very low concentrations. During the progression of dormancy, all the free amino acids and amides declined while aspartic and glutamic acid increased.

During the G₁ phase of the first cell cycle induced by 2,4-D, all the free amino acids and amides decreased with the exception of glutamic acid.

At 18, 20, 24 h of activation with 2,4-D, corresponding to the S phase and the beginning of mitosis, bound amino acids were also determined. In these phases of the cell cycle they increased reaching a maximum at 20 h; on the other hand the free amino acid and amide content, especially aspartic acid, asparagine and arginine, decreased with the exception of glutamic acid, alanine and phenylalanine.     

Amino Acid metabolism of pea leaves: labeling studies on utilization of amides

Short term (2-hour) incorporation of nitrogen from nitrate, glutamine, or asparagine was studied by supplying them as unlabeled (¹⁴N) tracers to growing pea (Pisum sativum L.) leaves, which were previously labeled with ¹⁵N, and then following the elimination of ¹⁵N from various amino components of the tissue. Most components had active and inactive pools. Ammonia produced from nitrate was assimilated through the amide group of glutamine. When glutamine was supplied, its nitrogen was rapidly transferred to glutamic acid, asparagine, and other products, and there was some transfer to ammonia. Nitrogen from asparagine was widely distributed into ammonia and amino compounds. There was a rapid direct transfer to glutamine, which did not appear to involve free ammonia. Alanine nitrogen could be derived directly from asparagine, probably by transamination. Homoserine was synthesized in substantial amounts from all three nitrogen sources. Homoserine appears to derive nitrogen more readily from asparagine than from free aspartic acid. A large proportion of the pool of γ-aminobutyric acid turned over, and was replenished with nitrogen from all three supplied sources.     

The fine structure of peritrophic membranes of the blowfly, Calliphora erythrocephala, grown in vitro under different conditions.

The formation of peritrophic membranes (PM) in vitro was studied in a flow chamber in order to avoid the accumulation of metabolic substances during prolonged incubation. During the first 8 to 10 hr of incubation the production of PM was nearly constant—3·5 ± 1·4 mm PM/hr. After about 10 hr it decreased and stopped after about 35 hr. Between 1 and 8 hr after the beginning of incubation the width of the periodic crossband pattern reached or nearly reached the values found in PM which had formed in vivo; afterwards it decreased more and more. During the first 20 min of incubation a ‘disturbed zone’ of PM without any regular crossband pattern is formed.In the cardia of adult Calliphora erythrocephala there are three formation zones forming three PM of different fine structures. The fine structure of PM 1 to 3 formed in vitro during the first 6 to 8 hr of incubation in Leloup's medium 1, with an osmolarity of 340 mOsmol, a pH of 6·8, and a temperature of 27°C, does not differ from the PM grown in vivo. PM 1–3 grown in vitro in Tyrode's solution with added glutamine or in Leloup's medium with added β-ecdysone show a considerable increase in thickness and a disturbed formation of the electron dense layer of PM 1.     

Effect of plant secondary compounds on in vitro methane,ammonia production and ruminal protozoa population

Aims

The objective of this study was to evaluate the potential of secondary plant metabolites from 38 sources to serve as antimethanogenic additives in ruminant diets. The effect of leaf tannins from these different plant sources on rumen fermentation, protozoal populations and methanogenesis was also studied.

Methods and Results

Samples (200 mg dry matter, DM) were incubated without and with polyethylene glycol (PEG)‐6000 (400 mg DM) as a tannin binder during 24‐h incubation in the in vitro Hohenheim gas system. In the leaf samples, total phenol (g kg^?1 DM) was maximum in Pimenta officinalis (312) followed by Oenothera lamarckiana (185) and Lawsonia inermis (105). Of the 38 samples, condensed tannins exceeded 4·0 g kg^?1 in only Alpinia galanga (7·50), Cinnamomum verum (4·58), Pelargonium graveolens (18·7) and Pimenta officinalis (23·2) and were not detected in seven samples. When the bioactivity of the leaf samples was assessed using the tannin bioassay, the percentage increase in the amount of gas produced during incubation of samples with the tannin‐binding agent PEG‐6000 over the amount produced during incubation without the tannin binder ranged from nil (zero) to 367%, with the highest being recorded with A. galanga leaves. The ratio of methane reduction per ml of total gas reduction was maximum with Rauvolfia serpentina (131·8) leaves, followed by Indigofera tinctoria (16·8) and Withania somnifera (10·2) leaves. Total and differential protozoal counts increased with added PEG in twenty‐two samples, maximum being in Pimenta officinalis. Increased accumulation of total volatile fatty acids during incubation with added PEG‐6000 was recorded, and the values ranged from zero to 61%. However, the increase was significant in only 11 of the 38 tannin sources tested indicating noninterference of tannin on in vitro fermentation of carbohydrates by the majority of samples tested. Conversely, in 26 of 38 plant sources, the leaf tannins reduced N‐digestibility as evidenced by increased accumulation of NH₃‐N with added PEG.

Conclusions

Our study unequivocally demonstrated that plants containing secondary metabolites such as Rauvolfia serpentine, Indigofera tinctoria and Withania somnifera have great potential to suppress methanogenesis with minimal adverse effect of feedstuff fermentation.

Significance and Impact of the Study

It was established that methanogenesis was not essentially related to the density of protozoa population in vitro. The tannins contained in these plants could be of interest in the development of new additives in ruminant nutrition.     

The influence of different nitrogen sources on the production of volatile compounds by Dipodascus aggregatus

Summary The yeast fungus Dipodascus aggregatus was grown aerobically on 9 different nitrogen sources and the production of volatile compounds determined by a gas chromatographic head-space technique. Excellent growth was supported by glutamine, aspartic acid, asparagine, (NH₄)₂-tartrate and NH₄H₂PO₄. Valine, leucine, and particularly isoleucine were utilized with a somewhat lower growth rate. Lysine was rapidly utilized after a prolonged lag phase.The highest production of volatile compounds was obtained from leucine and isoleucine. At least 20 volatile compounds were formed from each of them and many products were detected in high concentrations. Intermediate amounts of volatile compounds were produced from asparagine, the ammonium salts and valine, and low amounts from lysine, glutamine and aspartic acid.Ethyl acetate was a major product irrespective of the nitrogen source used. Regarding the pattern of volatile compounds produced, leucine, isoleucine and valine had much in common. Most of the volatile products formed from these amino acids contained a branched carbon chain and at least three high-boiling components eluted later than n-amyl acetate from the gas chromatographic column. The other six nitrogen sources could be grouped together. In general the same volatile compounds were formed from these sources, but the quantities of the individual compounds differed. Only one component eluted later than n-amyl acetate. No basic difference in production of volatile compounds was observed between the ammonium salts and -amino compounds like lysine and asparagine.     

Uptake and release of possible false transmitter amino acids by rat brain tissue

—The uptake of l [¹⁴C]glutamine by a crude isolated nerve ending fraction of rat brain was found to be linear with time for at least 5 min, profoundly temperature-dependent, apparently half-saturated at a substrate concentration of 0·26 mm , partially inhibited by dinitrophenol and ouabain and elevated [K⁺], weakly Na⁺-dependent, poorly inhibited by drugs which block uptake of biogenic amines and more strongly inhibited by glutamic acid (IC₅₀= 0·5mm ) than by aspartic acid, GABA, glycine or methionine. The [¹⁴C]glutamine taken up appeared to be associated with nerve endings and was released by membrane-disruption; about 20 per cent was associated with free mitochondria. Glutamine, δ-aminolevulinic acid and several other amino acids were poor inhibitors of [³H]GABA-uptake; δ-aminolevulinic acid was a poor inhibitor of [³H]glutamine-uptake, whereas glutamine was a moderately effective competitive inhibitor (K_i= 1 mm ). [¹⁴C]glutamine and [³H]GABA were released from brain slices by electrical stimulation or 50 mm K⁺, while labeled δ-aminolevulinic acid, leucine, urea, amphetamine and tyramine were poorly released. [¹⁴C]glutamine was not released by unlabeled glutamate or several aromatic amines. We conclude that the neuropsychiatric features of porphyria are not likely due to a ‘false transmitter’ role for δ-aminolevulinic acid although such a role for glutamine in hepatic encephalopathy or other neuropsychiatric diseases should be considered.     

Changes in the Free Amino Compounds in Young Tomato Plants in Light and Darkness with particular Reference to {gamma}-Aminobutyric Acid

Tomato plants were grown to the five-leaf stage under uniformconditions in a growth room with a daily light period of 15h. Plants were sampled at intervals through 24 h periods andthe free ninhydrin-positive compounds determined in roots, bleedingsap, stems and shoots (mainly leaves), using ion-exchange columnchromatography and a lithium-buffer separation system. The compoundspresent and their range of concentrations are given for twooccasions: after illumination for 8 hand after 5 h of darkness. Data for -aminobutyric acid (GAB), glutamic acid, glutamine,alanine, aspartic acid and ammonia are summarized graphicallyfor all occasions and for all parts of the plant; asparaginefor sap only. The data were examined for correlations betweenthese substances for both light and dark conditions. Relative amounts of free acids were: root glutamine> glutamicand GAB > aspartic > alanine; bleeding sap glutamine >asparagine > GAB > aspartic> alanine; stem glutamine> glutamic > GAB and aspartic > alanine; shoot (leaf)GAB and glutamine > aspartic > alanine and glutamic. Patternsof change were as follows: in the root GAB and glutamic weresimilar and unlike glutamine; alanine did not change;sap ammonia,GAB and alanine were parallel, glutamine was similar to theseonly in light; in the stem glutamine and glutamic tended toaccumulate in parallel in light, but GAB did not; in the shoot(leaf) GAB and glutamine were similar except that the formeraccumulated more rapidly in the initial light period; glutamicacid and alanine were similar to each other but distinct fromGAB and glutamine. The relatively large amounts of GAB in tomato plants and themagnitude of the changes occurring in light and darkness seemindicative of its importance as a temporary storage productfor protein amino acids, but the factors controlling accumulationand utilization in different parts of the plant are unknown.     

Ammonium and amino acid metabolism in excised leaves of wheat (Triticum aestivum) senescing in the dark

Several parameters of amino acid metabolism were studied in detached primary leaves of wheat (Triticum aestivum L. cv. Castell) during a 14 day incubation period in the dark. Protein loss was accompanied by a 5-fold increase in the total amount of free amino acids during the first 4 days of the incubation period with asparagine being the most important. Beyond this stage a pronounced intracellular accumulation of ammonium occured. A gradual decrease in the levels of free amino acids and ammonium at the later stages of senescence could in part be accounted for by leakage from the leaves. Additionally, some nitrogen was lost due to ammonia volatilization. The rapid decay of the glutamine synthetase (GS; EC 6.3.1.2)-glutamate synthase (Fd-GOGAT; EC 1.4.7.1) system and the fast decline of glutamate-pyruvate transaminase (GPT; EC 2.6.1.2) activity appear to be predominant features of senescence in the dark. Decreasing Fd-GOGAT activity was slightly compensated by a small and temporary increase in the activity of NADH-GOGAT (EC 1.4.1.14). Glutamateoxalocetate transaminase (GOT: EC 2.6.1.1) activity, although declining continuously, proved to be much more persistent. Changes in glutamate dehydrogenase (GDH; EC 1.4.1.3) activity closely resembled the profile of ammonium evolution in the leaves and NADP-isocitrate dehydrogenase (IDH; EC 1.1.1.42) activity revealed a temporary maximum during the period of rapid increase in GDH activity. Increased activity of GDH could also be induced by exogenous ammonium. Ammonium accumulation could, at least partly, be caused by increased asparaginase (EC 3.5.1.1) activity which accompanied the rapid conversion of asparagine to aspartic acid. Asparagine aminotransferase (EC 2.6.1.14) activity declined sharply from the beginning of the senescence period. Although the activity profile of glutaminase (EC 3.5.1.2) was similar to that of asparaginase, glutamine was of little importance quantitatively and an analogous relationship between glutamine and glutamic acid could not be detected.     

Somatic embryogenesis and plant regeneration in Triticum aestivum x Leymus angustus F1 hybrids and the parental lines

Somatic embryos and plants were produced from cultured inflorescence and leaf segments of Triticum aestivum X Leymus anaustus F₁ hybrids and the parental lines. Inflorescences showed a better capacity for somatic embryogenesis and plant regeneration than leaves. Leymus anaustus produced the highest number of embryogenic calli, while the hybrids were intermediate between this species and Triticum aestivum. Presence of 2,4-D was shown to be essential for induction and maintenance of somatic embryogenesis. Addition of five amino acids (glutamine, proline, asparagine, aspartic acid and glutamic acid) did not have any marked effect when they were used in the callus induction medium. The regenerated plants had the same morphology as the original plants. No cytological modification was observed in the examined plants.     

Amino acid concentrations in hypothalamic and caudate nuclei during microwave-induced thermal stress: Analysis by microdialysis

Exposure to radiofrequency radiation (RFR) may produce thermal responses. Extracellular amino acid concentrations in the hypothalamus (Hyp) and caudate nucleus (CN) were measured by using in vivo microdialysis before and during exposure to RFR. Under urethane anesthetic, each rat was implanted stereotaxically with a nonmetallic microdialysis probe and temperature probe guides and then placed in the exposure chamber. The rat laid on its right side with its head and neck placed directly under the wave guide. Temperature probes were placed in the left brain, right brain, face (subcutaneously), left tympanum, and rectum. Each microdialysis sample was collected over a 20 min period. The microdialysis probe was perfused for 2 h before the rat was exposed to 5.02 GHz radiation (10 μs pulse width, 1000 pulses/s). The right and left sides of the brain were maintained at approximately 41.2 and 41.7 °C, respectively, throughout a 40 min exposure period. Initially when the brain was being heated to these temperatures, the time-averaged specific absorption rates (SARs) for the right and left sides of the brain were 29 and 40 W/kg, respectively. Concentrations of aspartic acid, glutamic acid, serine, glutamine, and glycine in dialysate were determined by using high-pressure liquid chromatography with electrochemical detection. In the Hyp and CN, the concentrations of aspartic acid, serine, and glycine increased significantly during RFR exposure (P < .05). These results indicate that RFR-induced thermal stress produces a general change in the amino acid concentrations that is not restricted to thermoregulatory centers. Changes in the concentrations of glutamic acid (Hyp, P = .16; CN, P = .34) and glutamine (Hyp, P = .13; CN, P = .10) were not statistically significant. Altered amino acid concentrations may reveal which brain regions are susceptible to damage in response to RFR-induced thermal stress. Bioelectromagnetics 18:277–283, 1997. © 1997 Wiley-Liss, Inc.