Australian Frog Pseudophryne Research Articles

Further evidence that the tachykinin PG-KII is a potent agonist at central NK-3, but not NK-1, receptors.

Intracerebroventricular (i.c.v.) injection of tachykinins (TKs) inhibits ethanol intake and angiotensin II-induced water intake; the effects are apparently mediated by NK-3 and NK-1 receptors, respectively. The present study evaluated the effect of the TK PG-KII, a novel kassinin-like peptide isolated from the skin of the Australian frog Pseudophryne güntheri, in these in vivo tests for central activity. PG-KII, given by i.c.v. injection, potently inhibited alcohol intake in genetically selected alcohol-preferring rats, being about 3 times more potent than the selective NK-3 receptor agonist NH2-SENK. The dose of 100 ng/rat, that markedly inhibited ethanol intake, did not inhibit food intake and prandial drinking in food deprived rats, providing evidence that the effect of PG-KII on ethanol intake is behaviorally selective. The effect on ethanol intake was inhibited by i.c.v. injection of the NK-3 receptor antagonist R820, but was not modified by the NK-1 receptor antagonist SR 140333. PG-KII inhibited drinking induced by angiotensin II only at doses of 300 or 1000 ng/rat, being about 5 times less potent than the selective NK-1 receptor agonist [Sar9, Met(O2)11] substance P. These doses of PG-KII produced also marked increase in competing behaviors, such as grooming and locomotion. The dose of 1000 ng/rat evoked a general inhibition of the ingestive behavior, reducing also food intake. The i.c.v. injection of the NK-1 receptor antagonist SR 140,333 only slightly inhibited the effect of PG-KII on angiotensin II-induced drinking, while it markedly reduced that of [Sar9, Met(O2)11] substance P. These findings, in accordance with those of previous studies, indicate that PG-KII is endowed with marked activity at central NK-3 receptors, and low activity at NK-1 receptors.

The chemistry of cyclic tautomers of tryptophan: Total synthesis of (+)-(ent)-pseudophrynaminol

A diastereoselective synthesis of the unnatural (+)-enantiomer of the hexahydropyrroloindole alkaloid (-)-pseudophrynaminol ( 3), isolated from the skin of the Australian frog Pseudophryne coriacea, from a cyclic tautomer ( 1) of l-tryptophan, is described. The CD spectrum of the synthetic 3 is opposite in sign to that of the natural material enabling the configuration of the natural product to be established as 3aS,8aR.

Electrophysiological effects of a neurotoxin extracted from the skin of the Australian frog Pseudophryne coriacea

1. The electrophysiological effects of a pumiliotoxin-B-like alkaloid extracted from the skin of the Australian frog Pseudophryine coriacea (PsC) have been studied in rat superior cervical ganglia at 37°C. 2. PsC (50 mg/ml) elicits a broadening of the evoked compound action potential and, at rest, the appearance of spontaneous spike discharge at 10–20 Hz. Action potentials presumably originate far away from the soma, which is invaded in a typical ISSD sequence. 3. The toxin effect is not related to any direct action on the preganglionic fibers of the sympathetic trunk, and does not involve synaptic mechanisms. 4. Two-electrode voltage-clamp experiments showed that the main properties of the major voltage-dependent ionic currents are apparently unaffected by the toxin, while the cell input resistance is considerably reduced. 5. The data are consistent with the hypothesis that PsC elicits a cationic permeability increase generating a pacemaker current in a region close to the cell soma.

A tonic inhibitory control of rat pepsin secretion is mediated by central GABA-A receptors

Polidori, C., I. Panocka, R. Ciccocioppo, M. Broccardo, G. Improta, D. Regoli and M. Massi. Further evidence that the tachykinin Pg-Kii is a potent agonist at central Nk-3, but not Nk-1, receptors. Peptides 18(6) 825–833, 1997.—Intracerebroventricular (ICV) injection of tachykinins (TKs) inhibits ethanol intake and angiotensin II-induced water intake; the effects are apparently mediated by NK-3 and NK-1 receptors, respectively. The present study evaluated the effect of the TK PG-KII, a novel kassinin-like peptide isolated from the skin of the Australian frog Pseudophryne güntheri, in these in vivo tests for central activity. PG-KII, given by ICV injection, potently inhibited alcohol intake in genetically selected alcohol-preferring rats, being about 3 times more potent than the selective NK-3 receptor agonist NH2-SENK. The dose of 100 ng/rat, that markedly inhibited ethanol intake, did not inhibit food intake and prandial drinking in food deprived rats, providing evidence that the effect of PG-KII on ethanol intake is behaviorally selective. The effect on ethanol intake was inhibited by ICV injection of the NK-3 receptor antagonist R820, but was not modified by the NK-1 receptor antagonist SR 140333. PG-KII inhibited drinking induced by angiotensin II only at doses of 300 or 1000 ng/rat, being about 5 times less potent than the selective NK-1 receptor agonist [Sar9,Met(O2)11]substance P. These doses of PG-KII produced also marked increase in competing behaviors, such as grooming and locomotion. The dose of 1000 ng/rat evoked a general inhibition of the ingestive behavior, reducing also food intake. The ICV injection of the NK-1 receptor antagonist SR 140333 only slightly inhibited the effect of PG-KII on angiotensin II-induced drinking, while it markedly reduced that of [Sar9,Met(O2)11]substance P. These findings, in accordance with those of previous studies, indicate that PG-KII is endowed with marked activity at central NK-3 receptors, and low activity at NK-1 receptors.

Epileptogenic effects of skin extracts from the Australian frog Pseudophryne coriacea after intracerebral microinfusion in rats

The behavioural and electrocortical (ECoG) effects induced by a methanol extract of the skin of the Australian frog Pseudophryne coriacea, directly microinjected into several areas of the brain, were studied in freely moving rats. Administration of the P. coriacea extract (5, 10, 15 and 20 μg) into the dorsal hippocampus produced a dose-dependent and reversible behavioural stimulation and ECoG spikes lasting 20–140 min. Similar but less intense effects were elicited in rats receiving injections into the III cerebral ventricle, amygdala and caudate nucleus. In conclusion, the present experiments show that the skin extract of P. coriacea produces behavioural stimulation and ECoG spikes when injected into the rat brain, the most sensitive area being the hippocampus.

Electrophysiological effects of a pumiliotoxin-B-like alkaloid derived from the skin of the Australian frog Pseudophryne coriacea

Skin extracts of the Australian frog Pseudophryne coriacea (PsC) potentiate and prolong the bioelectric activity of various excitable tissues. When studied by electrophysiological means in a preparation of mouse diaphragm, PsC skin extracts did not affect the spontaneous acetylcholine (ACh) release. However, the indirect stimulation of the preparation in the presence of PsC skin extracts gave rise to a different profile of rhythmic activity showing afterpotentials and variable oscillatory activity. The action potential and the total sodium current recorded in the muscle fibre with the loose patch clamp method were not modified significantly by the alkaloid. Concentrations of PsC skin extract that did not cause repetitive activity, seemed to reduce slightly the quantal content of the evoked release of ACh. The resting potential of muscle fibres was not modified even by the highest PsC skin extract concentrations. These results suggest that the facilitation effects of PsC skin extracts could be due to intracellular mechanisms probably related to the control of the cytosolic calcium concentrations or to an increased excitability of the presynaptic biomembranes.

Six novel tachykinin- and bombesin-related peptides from the skin of the Australian frog Pseudophryne güntheri

Six novel peptides belonging to the tachykinin and bombesin families were isolated and sequenced from extracts of the skin of the Australian myobatrachid frog Pseudophryne güntheri. One of these peptides (PG-L) was of the bombesin family and may be considered an N-elongation of the litorin/ranatensin molecule, with which it shares an identical spectrum of activity on isolated smooth muscle preparations. The other five peptides were of the tachykinin family with two of these peptides (PG-SPI and PG-SPII) related to substance P and three (PG-KI, PG-KII and PG-KIII) to kassinin. In contrast to the basic nature of substance P, the PG-SP peptides showed a clear acidic character and displayed a more potent and sustained action on isolated smooth muscle preparations and rat blood pressure than did substance P. Two of the three PG-K peptides were more potent than kassinin; PG-KIII was considerably less potent. PG-KI and PG-KII were also present in a deamidated, poorly active, form.

Total synthesis of ( [formula omitted]) pseudophrynaminol

The first synthesis of ( + ) pseudophrynaminol, a unique pyrrolo [2,3b] indole recently isolated from the Australian frog Pseudophryne coriacea, is described.

Facilitation of [ 3H]acetylcholine and [ 3H]5-hydroxytryptamine release from rat cerebral cortex synaptosomes by a factor extracted from the skin of the Australian frog Pseudophryne coriacea

A partly purified extract of the skin of the Australian frog Pseudophryne coriacea (PsC) evoked the release of [ 3H]acetylcholine ([ 3H]ACh) and of [ 3H]5-hydroxytryptamine ([ 3H]5-HT) from superfused rat cerebral cortex synaptosomes prelabeled with [ 3H]choline or [ 3H]5-HT, respectively. The PsC-evoked release of both transmitters was sensitive to tetrodotoxin and was strictly Ca 2+-dependent. The release of [ 3H]5-HT caused by PsC was unaffected by the 5-HT uptake inhibitor citalopram. Activation of muscarinic autoreceptors by ACh or of serotonin autoreceptors by 5-HT depressed the PsC-evoked release of [ 3H]ACh or of [ 3H]5-HT, respectively. It is concluded that PsC elicits a Ca 2+-dependent exocytotic-like transmitter release, possibly by opening Na + channels in the presynaptic membrane.

Implications of tooth root hypercementosis in a Barbados slave skeletal collection

J. W. Daly, R. J. Highet and C. W. Myers. Occurrence of skin alkaloids in non-dendrobatid frogs from Brazil (Bufonidae), Australia (Myobatrachidae) and Madagascar (Mantellinae). Toxicon22, 905 – 919, 1984.—Several taxa of small frogs from the southern hemisphere contain alkaloids similar or identical to compounds previously known only from neotropical poison frogs of the family Dendrobatidae. Skin of the Brazilian toad Melanophryniscus moreirae (family Bufonidae) contains a new alkaloid 8-hydroxy-8-methyl-6-(5′-hydroxy-2′-methyl-hexylidene)-1- azabicyclo-[4.3.0]nonane (C16H29NO2), which is designated pumiliotoxin 267C. Such a structure is typical of the pumiliotoxin-A class of dendrobatid alkaloids. Melanophryniscus moreirae contains smaller quantities of an alkaloid (C19H33NO3) identical in chromatographic and mass spectral properties to the dendrobatid alkaloid allopumiliotoxin 323B. Allopumiliotoxin 323B and an isomer of 267C occur with unidentified alkaloids in skin of the Australian frog Pseudophryne semimarmorata (family Myobatrachidae) and also in the skin of the Madagascan frog Mantella aurantiaca (family Ranidae, subfamily Mantellinae). In addition to new compounds, Mantella aurantiaca and M. madagascariensis also contain other alkaloids (e.g. histrionicotoxin and pumiliotoxin B) that were known previously only in dendrobatid frogs. Such alkaloids have not been detected in a phylogenetically wide array of other anuran amphibians, and the dendrobatid alkaloids thus become an evolutionary enigma. Certain of these compounds may have arisen convergently from new biosynthetic pathways in several families of frogs, or these alkaloids may represent parallel expression of shared-primitive pathways that are unexpressed or lost in related frogs.

A potent factor in extracts of the skin of the Australian frog, PSeudophryne coriacea—III : Potentiation of contractions elicited in avian and mammalian isolated skeletal muscle preparations by direct and indirect electrical stimulation

Extracts of the skin of the Australian frog Pseudophryne coriacea displayed a striking potentiating effect on contractions evoked in isolated skeletal muscle preparations of mammals (phrenic nerve diaphragm) and birds (chick biventer cervicis and semispinalis muscles) by indirect and direct electrical stimulation. There was both a conspicuous increase in the amplitude of the twitch, up to 10-fold, and a remarkable prolongation of the duration of the twitch. The effect was dose- and frequency-dependent. In the presence of the extract, fusion of twitches after tetanic stimulation occurred earlier. No tachyphylaxis upon repeated stimulation by the extract was observed and the response to large doses persisted, declining slowly, for hours. These effects must be ascribed to an alkaloid related in structure to pumiliotoxin B. Response to the extract of Pseudophryne coriacea by indirectly-stimulated preparations was potentiated by physostigmine and blocked by tubocurarine and α-bungarotoxin, demonstrating that in these preparations the extract acted pre-synaptically to facilitate the release of acetylcholine from motor nerve endings. However, the extract of Pseudophryne coriacea displayed equally potent effects in directly stimulated preparations, insensitive to physostigmine and to blockers of nicotinic acetylcholine receptors, indicating a direct action on the skeletal muscle. It is suggested that, like pumiliotoxin B, the Pseudophryne coriacea alkaloid may interfere in the regulation of calcium channels in both nerve and muscle fibres.

A potent factor in extracts of the skin of the Australian frog, Pseudophryne coriacea: Apparent facilitation of transmitter release in isolated smooth muscle preparations

Extracts of the skin of the Australian frog Pseudophryne coriacea (PsC) displayed potent stimulant effects on isolated smooth muscle preparations of intestine and similar effects on electrically-stimulated vas deferens preparations. These effects must be ascribed to an alkaloid, related in structure to the pumiliotoxins, a class of alkaloid compounds occurring in the skin of neotropical poison frogs. On the basis of results obtained with antagonists and blocking agents, it is suggested that the extract has a pre-synaptic, neurogenic point of attack and that it acts to facilitate the release of transmitters from nerve endings. Acetylcholine is the most important agent involved in the response to the extract by the intestinal muscle and noradrenaline in the response by vas deferens preparations. However, release of other aminergic or peptidergic transmitters may participate, positively or negatively, in the response.

Occurrence of skin alkaloids in non-dendrobatid frogs from Brazil (Bufonidae), Australia (Myobatrachidae) and Madagascar (Mantellinae)

J. W. Daly, R. J. Highet and C. W. Myers. Occurrence of skin alkaloids in non-dendrobatid frogs from Brazil (Bufonidae), Australia (Myobatrachidae) and Madagascar (Mantellinae). Toxicon 22, 905 – 919, 1984.—Several taxa of small frogs from the southern hemisphere contain alkaloids similar or identical to compounds previously known only from neotropical poison frogs of the family Dendrobatidae. Skin of the Brazilian toad Melanophryniscus moreirae (family Bufonidae) contains a new alkaloid 8-hydroxy-8-methyl-6-(5′-hydroxy-2′-methyl-hexylidene)-1- azabicyclo-[4.3.0]nonane (C 16H 29NO 2), which is designated pumiliotoxin 267C. Such a structure is typical of the pumiliotoxin-A class of dendrobatid alkaloids. Melanophryniscus moreirae contains smaller quantities of an alkaloid (C 19H 33NO 3) identical in chromatographic and mass spectral properties to the dendrobatid alkaloid allopumiliotoxin 323B. Allopumiliotoxin 323B and an isomer of 267C occur with unidentified alkaloids in skin of the Australian frog Pseudophryne semimarmorata (family Myobatrachidae) and also in the skin of the Madagascan frog Mantella aurantiaca (family Ranidae, subfamily Mantellinae). In addition to new compounds, Mantella aurantiaca and M. madagascariensis also contain other alkaloids (e.g. histrionicotoxin and pumiliotoxin B) that were known previously only in dendrobatid frogs. Such alkaloids have not been detected in a phylogenetically wide array of other anuran amphibians, and the dendrobatid alkaloids thus become an evolutionary enigma. Certain of these compounds may have arisen convergently from new biosynthetic pathways in several families of frogs, or these alkaloids may represent parallel expression of shared-primitive pathways that are unexpressed or lost in related frogs.