Stimulatory effectiveness of amino acids on the olfactory response in an algivorous marine teleost, the rabbitfish Siganus fuscescens Houttuyn

The detection of threshold concentrations and relative stimulatory effectiveness (RSE) for 19 amino acids were studied by olfactory bulbar electroencephalogram (EEG) in the algivorous rabbitfish. The threshold concentrations for 19 amino acids ranged from 10⁻¹⁰ to 10⁻⁵ M. l -Alanine was the most effective amino acid, and the threshold concentration was estimated to be from 10⁻¹⁰ to 10⁻⁹M. These results were compared with the olfactory response in herbivorous and carnivorous fishes previously reported. The comparison of RSE for rabbitfish with those for other fishes showed correlation coefficients ranging from r = 0.97 to r = 0.50, but high similarities did not correspond with difference in feeding habits for herbivores and carnivores. The role of amino acids in fish chemosensory behaviour and the olfactory response of the rabbitfish was compared with the gustatory response reported previously. It was found that l -serine was the most potent stimulant in both chemoreceptors, l -proline and l -glutaminic acid were the most potent gustatory stimulants, and l -alanine, l -glutamine, l -arginine and l -lysine were the most potent olfactory stimulants.     

Olfactory sensitivity of the herbivorous grass carp, Ctenopharyngodon idella, to amino acids

The olfactory sensitivity of a herbivore, the grass carp, Ctenopharyngodon idella , to ten amino acids was investigated using electrophysiological recording techniques. Underwater electroolfactogram recordings increased exponentially with logarithmic increases of stimulus concentration from threshold to 1 × 10⁻³ m. Calculated detection thresholds ranged from 1 × 10^−7.15 m to 1 × 10^−8.7 M and are similar to those previously reported for carnivorous fish species. The relative stimulatory efficacy (RSE) of the ten amino acids determined at 1 × 10⁻⁴ M revealed five groups of stimuli, with cysteine the most stimulatory and proline the least. Measures of amino acid RSE did not differ significantly from those of previously studied carnivores, except for arginine. Grass carp showed strong responses to this compound, whereas it has produced only limited responses in carnivores. Differences in the responsiveness of herbivores and carnivores were not observed, suggesting that feeding niche segregation is probably not facilitated by differential olfactory sensitivities to feeding stimuli.     

Emission rate of amino acids and ammonia and their role in olfactory preference behaviour of juvenile Arctic charr, Salvelinus alpinus (L.)

The behaviour of juvenile Arctic charr, Salvelinus alpinus (L.) , to an abrupt concentration step of L-amino acids, L-alanine and ammonium chloride was studied by fluviarium technique. The emission rates of these substances were studied. Juvenile Arctic charr emit 8.0 × 10⁻⁴ mol total ammonia-N kg⁻¹ h⁻¹ and 3.3 × I0⁻⁵ mol amino acids kg⁻¹ h⁻¹. In behaviour tests the charr avoided 5.6x 10⁻⁶and 5.6 × 10⁻⁷ M ammonium chloride. The 17 L-amino acid mixture, ranked as observed in the analysis of emission, was avoided at 4.6 × 10⁻⁷ M, while 100 times dilution of this value gave neither avoidance nor attraction. The charr avoided L-alanine tested alone at the concentration of 4.6 × 10 ⁻⁷ M. Anosmic charr showed neither avoidance nor attraction to the mixture of 17 amino acids tested at 4.6 × 10⁻⁷ M. The results indicate that ammonia as well as emitted amino acids are not responsible for the olfactory mediated attraction to conspecific odour shown earlier in Arctic charr. On the contrary, these substances may have a negative effect by reducing the strength of attraction.     

Feeding behaviour in some teleosts is triggered by single amino acids primarily through olfaction

The present study investigated behavioural responses of naïve rainbow trout Oncorhynchus mykiss , lake charr Salvelinus namaycush , lake whitefish Coregonus clupeaformis and goldfish Carassius auratus to food extracts as well as selected amino acids (at 10⁻⁶ M) and related chemicals in a flow‐through behaviour trough. Cysteine, the most potent olfactory stimulating amino acid determined electrophysiologically, enhanced locomotor activity, an initial arousal behaviour, in all species examined, in exactly the same fashion as did food extracts. The increased locomotor activity was followed by distinct species‐specific search behavioural patterns: 1) bottom searching in rainbow trout; 2) surfacing and jumping in lake charr; 3) exploratory behaviour against the trough window in lake whitefish; 4) gravel pecking in goldfish. Olfactory‐stimulating neutral amino acids alanine and serine and gustatory‐stimulating imino acid proline were effective, to varying degrees, in eliciting feeding behaviour. Arginine and glutamate suppressed the locomotor activity in rainbow trout, but triggered feeding behaviour in the other species. Agmatine, a decarboxylated arginine, stimulated feeding behaviour in all species tested, except rainbow trout. The observed behavioural responses were in close accordance with the electrophysiological threshold and specificity. Together, the present data demonstrate that single amino acids and closely related chemicals initiate feeding behaviour primarily by olfaction, and interchangeably and complemented by gustation, in naive fishes.     

Electroencephalogram recordings from the olfactory bulb of juvenile (0 year) Atlantic cod in response to amino acids

Olfactory sensitivity of juvenile (0 year) Atlantic cod Gadus morhua to 20 L‐amino acids was studied by recording electroencephalograms (EEG) from the olfactory bulb. Leucine, methionine, asparagine, glutamine, alanine and threonine were highly stimulatory; proline, phenylalanine, aspartic acid and tryptophan were the least stimulatory. Threshold concentrations determined for four amino acids were 10⁻⁸ M for alanine, 10⁻⁷ M for arginine and leucine and 10⁻⁶ M for glutamic acid.     

Effects of phenolic acids on ammonia oxidation by terrestrial autotrophic nitrifying microorganisms

Abstract It has been hypothesized that vegetation in certain ecosystems inhibits nitrification in soil by producing phenolic compounds that inhibit oxidation of ammonia by nitrifying microorganisms. This hypothesis is based largely on a report that very low concentrations (10⁻⁶ M–10⁻⁸ M) of several phenolic acids (notably ferulic acid) completely inhibited NO₂⁻ production in an aqueous suspension of soil treated with (NH₄)₂SO₄ and a nutrient solution suitable for growth of Nitrosomonas and other autotrophic nitrifying microorganisms. To evaluate this hypothesis, we determined the effects of three ohenolic acids (ferulic acid, caffeic acid, and p -coumaric on nitrite production by representatives of three genera of terrestrial autotrophic nitrifying microorganisms ( Nitrosospira, Nitrosomonas , or Nitrosolubos ) grown on a defined medium containing NH₄⁺. We found that nitrite production by the Nitrososspira was not inhibited by ferulic acid, caffeic acid, or p -coumaric acid at concentrations of 10⁻⁶ or 10⁻⁵ M and was only slightly inhibited when these acids were at a concentration of 10⁻⁴ M. We also found that ferulic acid did not markedly inhibit nitrite production by the three genera of nitrifying microorganisms studied, even when its concentration was as high as 10⁻³ M. These observations invalidate the hypothesis tested because the phenolic acids studied did not significantly retard ammonia oxidation by autotrophic microorganisms even when their concentration in cultures of these microorganisms greatly exceeded their concentrations in soils.     

Gustatory responses to feeding‐ and non‐feeding‐stimulant chemicals, with an emphasis on amino acids, in rainbow trout

Specific receptor and fibre types of rainbow trout Oncorhynchus mykiss involved in the detection and discrimination of amino acids and a heterogeneous collection of compounds were investigated by recording the electrical activity of the maxillary branch of the facial nerve innervating taste buds inside the upper jaw. Proline (Pro), alanine (Ala), leucine (Leu), betaine (Bet) and 2‐amino‐3‐guanidinopropionic acid (Agp) were the major amino acids detected by the gustatory system. The two experimental approaches, concentration‐response curves and cross‐adaptations, showed that all amino acids were detected by three independent receptor types: Pro ‐, Agp/Bet ‐ and Leu ‐receptors. Bile acids, the most potent stimulants recorded, were detected by a single receptor type independent of those for amino acids, with threshold concentrations of 10⁻¹² M. Strychnine, quinine and tetrodotoxin may have partially shared a single receptor mechanism. The gustatory sensibility narrowly tuned towards the amino acid spectrum compared to those for a diverse array of non‐feeding stimulant chemicals, combined with feeding behaviour triggered primarily by vision and olfaction, suggest that in rainbow trout, and possibly other salmonid species, gustatory chemical cues, in addition to food finding and intake, play an important role in detecting poisonous prey and substances.     

Gustatory sensitivity of the herbivore Tilapia zillii to amino acids

The gustatory sensitivity of the herbivorous fish Tilapia zillii was investigated using electrophysiological techniques. Integrated responses from facial taste nerves were recorded during stimulation by l l amino acids. All compounds proved to be effective stimuli. The relative stimulatory efficacy (RSE) determined at 1 × 10 ⁻³ m indicated that stimuli can be organized into three groups on the basis of similarity of efficacy. Effects of pH which altered the RSE of some amino acids are documented. Amino acid RSE differed to some extent from those of previously studied carnivorous fish. There was concordance between the composition of preferred food, effective feeding stimuli and the peripheral receptor responses. These observations support the hypothesis that peripheral chemosensitivity might serve as a mechanism of feeding specialization in some fish.     

Amino Acids as Nitrogen Sources for the Growth of Euglena gracilis and Astasia longa

SYNOPSIS. Euglena gracilis (bacillaris variety, strain SM-L1, streptomycin-bleached) used the following amino adds (10⁻³ M) as sole nitrogen source for growth on a defined medium: glycine, alanine, valine, leucine, isoleucine, serine, threonine, and glutamic acid. Aspartic acid was used at 10⁻² M. Glutamine and asparagine were used at 10⁻³ M and were better N sources than their parent dicarboxylic amino acids. Not used as sole N source for growth were phenylalanine, tyrosine, tryptophan, cysteine, cystine, methionine, proline, hydroxyproline, histidine, arginine, lysine, and taurine. Astasia longa (Jahn strain) was more restricted than Euglena and used only asparagine and glutamine as N sources for growth.     

The role of F-series prostaglandins as reproductive priming pheromones in the brown trout

Electrophysiological studies demonstrated that the olfactory epithelium of mature male brown trout Salmo trutta parr was acutely sensitive to F-series prostaglandins (PGFs) PGF_1α and PGF_2α, with detection threshold concentrations of 10⁻¹¹ M. The olfactory epithelium was also sensitive to the PGF metabolite 15-ketoPGF_2α (threshold 10⁻⁸ m), but did not detect a further metabolite, 13,14,-dihydro-15-ketoPGF_2α Immature brown trout did not detect any of the prostaglandins tested. Exposure of mature male brown trout parr to waterborne PGF_1α and PGF_2α (concentration 10⁻⁸ m), resulted in significant increases in levels of expressible milt and the plasma concentrations of 17,20β-dihydroxy-4-pregnen-3-one, testosterone and 11-ketotestosterone. The olfactory epithelium of both immature and mature male brown trout parr was sensitive to the urine and ovarian fluid from ovulated female brown trout. Exposure of mature male brown trout parr to ovarian fluid resulted in an increase in the levels of plasma 17,20β-dihydroxy-4-pregnen-3-one whilst exposure to urine increased the levels of expressible milt. In addition, PGF_2α was found to be present within both the urine and ovarian fluid of mature female brown trout. It is suggested that the F-series prostaglandins have a role as priming pheromones in male brown trout.     

Resistance to cadmium by pretreated rainbow trout alevins

A toxicity test with cadmium concentrations ranging from 0·1 to 100·0 mg Cd 1⁻¹ was used to assess the effect of cadmium pretreatment on rainbow trout ( Salmo gairdneri Richardson) alevins. The median period of survival for fish pretreated at 0·01 mg Cd 1⁻¹ was found to be increased at test concentrations up to 10mg Cd 1⁻¹ compared with alevins pretreated with dilution water. However, at concentrations above 10mg Cd 1⁻¹ pretreatment at 0·01 mg Cd 1⁻¹ reduced the median period of survival.     

Protein Synthesis in a Cell-free System from Rat Brain Sensitive to ACTH-like Peptides

Abstract: Protein synthesis was measured using a cell-free system obtained from subcortical rat brain tissue. The concentrations of Mg²⁺ and K⁺ and the amount of tissue, during both the preparation and the final assay, were critical to the incorporation of amino acids as expressed per milligram protein. Even under optimal conditions mainly elongation of growing peptide chains was measured. Behaviorally active fragments of ACTH modulated the activity of the system in a biphasic manner; i.e., at a low concentration (10⁻⁸ M) of ACTH a stimulation of between 10 and 70% was found; a high concentration (10⁻⁴ M) was inhibitory (50 to 70%). Structure-activity studies revealed that the stimulatory effect was confined to the N-terminus of the peptide (1–24), whereas the C-terminal sequence was responsible for the inhibition. The stimulation by ACTH_1–24 was dependent on Ca²⁺ and Mg²⁺. Cyclic AMP (10⁻⁵ M) stimulated the amino acid incorporation too. When a similar cell-free extract was prepared from brain tissue of hypophysectomized rats, the lower in vivo protein synthesis in these animals was preserved in the present cell-free system. The data are discussed in terms of a possible direct intracellular effect of ACTH on brain protein synthesis.     

Effect of rearing density on thyroid and interrenal gland activity and plasma and hepatic metabolite levels in rainbow trout, Salmo gairdneri Richardson

There were significant inverse correlations between rearing density of rainbow trout, Salmo gairdneri Richardson, and final body weight, plasma L-thyroxine (T₄), trüodo-L-tryronine (T₃), cortisol and protein concentrations, plasma T₄/T₃ ratios and thyroid epithelial cell height. In addition, hepatosomatic indices and plasma free fatty acid concentrations were higher in fish reared at low (134 g 1⁻¹) density compared with groups reared at medium (210g1⁻¹) or high density (299g 1⁻¹), and the post-feeding (3.5-4h) elevation in plasma glucose and triglyceride levels evident in trout maintained at low rearing density was not found in those fish reared at higher densities. There were no significant effects of rearing density on hematocrit, carcass composition, hepatic glycogen and lipid levels and interregnal nucleus size.     

Behavioural and electrophysiological responses to F-prostaglandins, putative spawning pheromones, in three salmonid fishes

Behavioural and electro-olfactogram (EOG) responses to synthetic F-prostaglandins (PGFs) were recorded in the three salmonids: brown trout Salmo trutta , lake whitefish Coregonus clupeaformis and rainbow trout Oncorhynchus mykiss . Exposure to 10⁻⁸ M PGF_2α and 13, 14-dihydro-PGF_2α increased swimming activity in individually exposed brown trout in a flow-through tank. Digging and nest probing behaviours were further observed in brown trout females exposed to PGF_2α. Lake whitefish exposed to 10⁻⁸ M PGF_2α and 15-keto-PGF_2α also increased their locomotion. In rainbow trout, the absence of behavioural responses to PGFs correlates with a lack of olfactory sensitivity to these chemicals. PGFs triggered behavioural responses distinct from the feeding stimulant in brown trout. EOG measurements demonstrated that brown trout were most sensitive to PGF_2α, with a threshold concentration of 10⁻¹¹ M. Lake whitefish were most sensitive to both 15-keto-PGF_2α and 13, 14-dihydro-PGF_2α. Cross-adaptation and binary mixture experiments suggest that only one olfactory receptive mechanism is involved in PGFs detection. The behavioural and olfactory responses observed with exposure to PGF_2α and its metabolites suggest these compounds function as reproductive pheromones in brown trout and lake whitefish.     

Identification of jasmonic acid in Mimosa pudica and its inhibitory effect on auxin- and light-induced opening of the pulvinules

Jasmonic acid was identified from Mimosa pudica L. plants by mass spectrometry, high performance liquid chromatography and thin layer chromatography. Effects of authentic jasmonic acid on pulvinule movement and transpiration of the pinnae were compared with those of abscisic acid. Jasmonic acid and abscisic acid each at 10⁻⁵ M inhibited both auxin- and light-induced opening of the pulvinules. A closure-inducing activity of jasmonic acid at 10⁻⁴ M was greater than that of abscisic acid at 10⁻⁴ M. Pinnae transpiration was reduced by 10⁻⁵ M abscisic acid but not by 10⁻⁴ M jasmonic acid.     

Identification of Strychnine Binding Sites in the Rat Retina

Abstract: [³H]Strychnine specifically binds to membrane fractions isolated from rat retinae. The binding is saturable, with an apparent dissociation constant, K _D, of 14.3 × 10⁻⁹ M and 205 fmol bound/mg protein. Specific binding is time-dependent and proportional to protein concentration. Glycine and taurine are equally potent inhibitors of [³H]strychnine binding ( K _i= 4 × 10⁻⁵ M); no other amino acids endogenously present in the retina inhibited [³H]strychnine binding.     

Effects of Arachidonic Acid on Dopamine Synthesis, Spontaneous Release, and Uptake in Striatal Synaptosomes from the Rat

Abstract: Arachidonic acid (AA) markedly stimulated, in a dose-dependent manner, the spontaneous release of [³H]dopamine ([³H]DA) continuously synthesized from [³H]tyrosine in purified synaptosomes from the rat striatum. As estimated by simultaneous measurement of the rate of [³H]H₂O formation (an index of [³H]tyrosine conversion into [³H]DOPA), the AA response was associated with a progressive and dose-dependent reduction of [³H]DA synthesis. In contrast to AA, arachidic acid, oleic acid, and the methyl ester of AA (all at 10⁻⁴ M ) did not modify [³H]DA release. The AA (3 × 10⁻⁵ M )-evoked release of [³H]DA was not affected by inhibiting AA metabolism, with either 5,8,11,14-eicosatetraynoic acid or metyrapone, suggesting that AA acts directly and not through one of its metabolites. AA also inhibited in a dose-dependent manner [³H]DA uptake into synaptosomes, with a complete blockade observed at 10⁻⁴ M . However, AA (10⁻⁴ M ) still stimulated [³H]DA spontaneous release in the presence of either nomifensine or other DA uptake inhibitors, indicating that AA both inhibits DA reuptake and facilitates its release process. Finally, the AA (10⁻⁴ M )-evoked release of [³H]DA was not affected by protein kinase A inhibitors (H-89 or Rp -8-Br-cAMPS) but was markedly reduced in the presence of protein kinase C inhibitors (Ro 31-7549 or chelerythrine).     

The rooting ability of shoots raised 'in vitro' from the apple rootstock A2 in juvenile and in adult growth phase

The apple rootstock A2 can be readily propagated in vitro both in the juvenile and in the adult growth phase. Shoots were produced by meristem tip culture from the apple rootstock A2 in different growth phases. The influence of growth phases and different concentrations of PG and IBA was investigated as to rooting percentage, survival percentage, number of roots per rooted shoot, root length, shoot length and formation of callus. IBA at 15 μ M without PG gave a significantly lower rooting percentage than 5 and 10 μ M IBA. PG together with IBA stimulated rooting, the optimum concentrations of PG being, however, not the same for the different growth phases. For the adult growth phase, 10⁻⁴ M PG promoted rooting, whereas 10⁻³ M PG markedly inhibited rooting. In the juvenile growth phases, both 10⁻⁴ and 10⁻³ M PG stimulated rooting. PG at 10⁻⁴ M also increased the number of roots. The longest roots were obtained at 10⁻³ M PG and 5 μ M IBA. PG at 10⁻³ M reduced callus formation at all IBA concentrations used. Neither shoot length nor root length influenced the survival percentage.     

Behavioural responses of fishes to chemical cues: results from a new bioassay

A new behavioural bioassay for determining the locomotor response by fish to chemical cues is described. The assay combines a behavioural trough, capable of delivering up to 10 discrete plumes of treated water, together with a digital method for quantifying the movements of single fish. Sample responses of two whitefish, Coregonus clupeaformis , one to an attractant (a food extract) and one to a repellant (quinine monohydrochloride), are provided. Their locomotor responses are analyzed in terms of such parameters as total distance travelled, average velocity, number of turns, average excursion distance, and the number of times specific boundaries are crossed. The assay's sensitivity is demonstrated through concentration-response curves by Arctic char, Salvelinus alpinus , to the bile acid, taurocholic acid, and the amino acids, L-serine and L-alanine. Behavioural response threshold concentrations for these three substances were estimated to be 10⁻¹⁵, 10⁻ⁿ, and 10⁻⁹ m, respectively.     

Use-Dependent Suppression of the Nicotinic Acetylcholine Receptor Response by the Proadrenomedullin N-Terminal 20-Amino Acid Peptide in Rat Locus Coeruleus Neurons

Abstract: The effects of the proadrenomedullin N-terminal 20-amino acid peptide (PAMP) on the nicotinic acetylcholine (ACh) receptor (nAChR)-mediated inward current were investigated in neurons acutely dissociated from the rat locus coeruleus using whole-cell recording under voltage clamp. Nicotine and cytidine mimicked the ACh response, whereas the maximal response to dimethyl-phenylpiperazinium was lower in amplitude compared with that to ACh. Nicotine-induced current ( I _nic) was suppressed more effectively by mecamylamine than by hexamethonium. In addition, neither atropine nor α-bungarotoxin affected the I _nic. PAMP reversibly and noncompetitively suppressed the peak amplitude of 10⁻⁴ M I _nic. PAMP concentrations for the threshold, half-maximal inhibition, and maximal inhibition of 10⁻⁴ M I _nic were 10⁻⁸, 2.6 × 10⁻⁷, and 10⁻⁵ M , respectively. The peak amplitudes of 10⁻⁴ M I _nic elicited at 2-min intervals showed a gradual decline in the presence of 10⁻⁷ M PAMP. This decline in the I _nic was independent of the period of PAMP pretreatment. The suppression of I _nic by PAMP did not show any voltage dependency at a holding potential ( V _H) of <0 mV, although the inhibitory effect was masked by the marked inward rectification of I _nic at a V _H of 0 mV. These results suggest that PAMP could thus be a unique endogenous peptide that antagonizes the nAChR in the CNS.