Papers by Graham Johnston
GABA-containing tea has gained popularity as an accessible intervention to reduce the impact of c... more GABA-containing tea has gained popularity as an accessible intervention to reduce the impact of chronic stress-induced autonomic imbalance and increased risk for cardiovascular disease despite a lack of evidence concerning the γ-aminobutyric acid (GABA) content in a cup of the tea and its effects on physiological and psychological stress as measures of cognitive function. We aimed to measure the effects of GABA-fortified tea consumption on heart rate variability (HRV) and stress in 30 participants using a pre-post cohort study design. Ten minute lead II ECG recordings were analyzed with Kubios software. Frequency domain parameters including total power, high and low frequency power, along with heart rate, were determined. A control group that consumed a non-fortified tea was included in the research. Statistical analysis was by two-way ANOVA for two-group comparison with time as an interaction and a significance level of p<0.05. Oolong tea consumption led to a significant decrease in the immediate stress score and a significant improvement in HRV. We conclude that autonomic imbalance and heart rate variability in people with acute stress is significantly reduced following a cup of GABA fortified oolong tea and highlights the complex interaction between autonomic nervous system function and mood.
Flavonoids, both naturally occurring and synthetic, are known to have multiple effects on the act... more Flavonoids, both naturally occurring and synthetic, are known to have multiple effects on the activation of ionotropic receptors for γ-aminobutyric acid (GABA), the major inhibi-tory neurotransmitter in our brains. They can act as positive or negative allosteric modu-lators, enhancing or reducing the effect of GABA. They can elicit a direct activation of the receptors. They can also act to modulate the action of other modulators. This ability to influence function via their actions on GABA receptors permits a range of effects of flavonoids, including relief of anxiety, anticonvulsant, analgesic and sedative actions.
The terpenoid lactones from Ginkgo biloba, bilobalide and ginkgolides, have been shown to act as ... more The terpenoid lactones from Ginkgo biloba, bilobalide and ginkgolides, have been shown to act as negative modulators at α 1 β 2 γ 2L GABA A receptors. They have structural features similar to those of the chloride channel blocker picrotoxinin. Unlike picrotoxinin, however they are not known to produce convulsant effects. Using two-electrode voltage clamp electrophysiology, this study compared the effect of mutation of 2′, 6′ and 15′ pore facing M2 domain residues to cysteine on the action of picrotoxinin, bilobalide and ginkgolides at α 1 β 2 γ 2L GABA A receptors expressed in Xenopus oocytes. Picrotoxinin was affected by mutation differently from the ginkgo terpenoid lactones. Although some of these compounds were affected by the mutation at same position and/or subunit, the changes in their potency were found to be dissimilar. The results suggest that the intracellular pore binding site for picrotoxinin, bilobalide, ginkgolide A, ginkgolide B and ginkgolide C is comprised of 2′β-6′β6′γ, 2′α2′β-6′α6′β, 2′α2′β2′γ-6′β6′γ, 2′α, 2′β2′γ-6′β and 2′α2′β, respectively. Unlike bilobalide and ginkgolides, the inhibitory action of pi-crotoxinin was not affected by mutations at 15′ position. It is proposed that 15′α15′β, 15′β, 15′α15′β and 15′α15′β15′γ forms an extracellular pore binding site for bilobalide, ginkgolide A, ginkgolide B and ginkgolide C, respectively. The lack of convulsant effects of bilobalide, and ginkgolide A and B may be associated in part with their different binding locations within the chloride channel.
Neurochemistry International, 1987
The activity of adenosine deaminase (ADA) has been measured in the hypothalamus, pons medulla and... more The activity of adenosine deaminase (ADA) has been measured in the hypothalamus, pons medulla and cerebral cortex from 30-day-old and 100-day-old spontaneously-hypertensive rats (SHR) and age-matched WKY controls. At I00 days there was a significant reduction in ADA activity in the hypothalamus (18.0%), pons medulla (20.6%) and cerebral cortex (14.7%). In 30-day-old SHR animals (prior to the development of significant hypertension) no significant changes were seen in the cerebral cortex or pons medulla but there was a small but significant reduction in ADA activity in the hypothalamus (9.2%). There was no significant reduction in the ADA activity in heart or kidney. Extracts of 100-day-old pons medulla which had been briefly heated to destroy endogenous ADA activity did not differentially affect the activity of exogenous purified ADA.
Neuroscience Letters, Nov 11, 1988
The actions of convulsant barbiturates were studied on dorsal root ganglion (DRG) cells in vitro ... more The actions of convulsant barbiturates were studied on dorsal root ganglion (DRG) cells in vitro using intracellular recording techniques. Only the convulsant barbiturates (+)-DMBB and CHEB produced a concentration-dependent depression in the responses to 7-aminobutyric acid (GABA). All convulsan! barbiturates were found to produce a direct depolarization of the DRG cell membrane which was accompanied by a decrease in the inpul resistance of the cell and a reduction in the orthodromic action potential. A sub-population of DRG cells were found to be refractory to these actions but there was no relationship between the cell type (Aft, A6 and C) and ability to respond to the convulsant barbiturates.
Neuroscience Letters, 1987
Neonatal administration of monosodium glutamate (MSG) failed to alter blood pressure (BP) develop... more Neonatal administration of monosodium glutamate (MSG) failed to alter blood pressure (BP) development in either SHR or WKY rats. Hypothalamic disturbance relevant to hypertension in the SHR is not contributed to by neonatal MSG treatment. All normotensive WKY animals show a transient rise in BP corresponding to the time at which BP peaks in SHR.
Neuropharmacology, 2004
Mutations of the proline residue at the 2′ position (P2′) within the second transmembrane (M2) do... more Mutations of the proline residue at the 2′ position (P2′) within the second transmembrane (M2) domain of the γ-aminobutyric acidC (GABAC) ρ1 subunit are known to produce receptors with altered pharmacology. In the present study, P2′ was mutated to alanine (ρ1P2′A), phenylalanine (ρ1P2′F), glycine (ρ1P2′G) and serine (ρ1P2′S). Mutant receptors were characterized using a range of agonists, partial agonists and antagonists.ρ1P2′A, ρ1P2′G and ρ1P2′S receptors were less susceptible than wild-type receptors to agonist activation. Most notably, the partial agonists, (±)-trans-2-(aminomethyl)cyclopropanoic acid ((±)-TAMP) and imidazole-4-acetic acid (I4AA) were converted to antagonists at ρ1P2′G and ρ1P2′S receptors and the partial agonist CACA acted as an antagonist at ρ1P2′S receptors. In contrast, ρ1P2′F receptors were more prone to activation by agonists. A correlation was observed between the pharmacological properties of the mutant receptors and the hydrophobicity of each residue.Unlike the agonists or partial agonists, the affinity of competitive antagonists, (1,2,5,6-tetrahydropyridine-4-yl)methylphosphinic acid (TPMPA) and 4,5,6,7-tetrahydroisoxazole[4,5-c]pyridine-3-ol (THIP), did not change significantly between wild-type and mutant receptors. Thus, the results suggest that the agonist/competitive antagonist binding site(s) were not significantly affected by the mutations, but that receptor activation properties altered such that the more hydrophobic the residue at the 2′ position, the more prone the receptor is to agonist activation.
Molecular Pharmacology, May 1, 1997
We have investigated the mechanism of action of a series of glutamate derivatives on the cloned e... more We have investigated the mechanism of action of a series of glutamate derivatives on the cloned excitatory amino acid transporters 1 and 2 (EAAT1 and EAAT2), expressed in Xenopus laevis oocytes. The compounds were tested as substrates and competitive blockers of the glutamate transporters. A number of compounds showed contrasting mechanisms of action on EAAT1 compared with EAAT2. In particular, (2S,4R)-4-methylglutamate and 4-methylene-glutamate were transported by EAAT1, with K m values of 54 M and 391 M, respectively, but potently blocked glutamate transport by EAAT2, with K b values of 3.4 M and 39 M, respectively. Indeed, (2S,4R)-4-methylglutamate is the most potent blocker of EAAT2 yet described. (Ϯ)-Threo-3-methylglutamate also potently blocked glutamate
Metab Brain Dis, 1992
The pharmacological profile and binding characteristics of the non-NMDA antagonist of glutamate r... more The pharmacological profile and binding characteristics of the non-NMDA antagonist of glutamate receptors [3H]6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX), were investigated in triton-washed crude synaptosomal membranes prepared from canine cerebral cortex. [3H]CNQX binding was inhibited by various glutamate agonists and antagonists, the rank order of potency being CNQX greater than alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) = quisqualate = kainate greater than glutamate. Two binding sites for [3H]CNQX were apparent when non-specific binding (NSB) was defined with unlabelled CNQX. In contrast, when NSB was defined with saturating concentrations of unlabelled AMPA and kainate, only one binding site was identified which corresponded to the high affinity site identified when CNQX was used to define NSB. No physiologically relevant differences were found in binding parameters for [3H]CNQX membranes from dogs with congenital portosystemic encephalopathy (PSE) when compared with control dogs. The affinity constant (Ki) of AMPA displacement of [3H]CNQX binding was not significantly different in PSE dogs compared with control dogs. These results suggest that the antagonist site on cortical non-NMDA receptors is not perturbed in dogs with congenital PSE.
Neuropharmacology, 2011
Extracts from the Ginkgo biloba tree are widely used as herbal medicines, and include bilobalide ... more Extracts from the Ginkgo biloba tree are widely used as herbal medicines, and include bilobalide (BB) and ginkgolides A and B (GA and GB). Here we examine their effects on human 5-HT 3 A and 5-HT 3 AB receptors, and compare these to the effects of the structurally related compounds picrotin (PTN) and picrotoxinin (PXN), the two components of picrotoxin (PTX), a known channel blocker of 5-HT 3 , nACh and GABA A receptors. The compounds inhibited 5-HT-induced responses of 5-HT 3 receptors expressed in Xenopus oocytes, with IC 50 values of 470 mM (BB), 730 mM (GB), 470 mM (PTN), 11 mM (PXN) and >1 mM (GA) in 5-HT 3 A receptors, and 3.1 mM (BB), 3.9 mM (GB), 2.7 mM (PTN), 62 mM (PXN) and >1 mM (GA) in 5-HT 3 AB receptors. Radioligand binding on receptors expressed in HEK 293 cells showed none of the compounds displaced the specific 5-HT 3 receptor antagonist [ 3 H]granisetron, confirming that they do not act at the agonist binding site. Inhibition by GB at 5-HT 3 A receptors is weakly use-dependent, and recovery is activity dependent, indicating channel block. To further probe their site of action at 5-HT 3 A receptors, BB and GB were applied alone or in combination with PXN, and the results fitted to a mathematical model; the data revealed partially overlapping sites of action. We conclude that BB and GB block the channel of the 5-HT 3 A receptor. Thus these compounds have comparable, although less potent, behaviour than at some other Cys-loop receptors, demonstrating their actions are conserved across the family.
International Symposium on the Chemistry of Natural Products, Jul 23, 2006
Journal of the Chemical Society
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Journal of the Chemical Society
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Journal of the Chemical Society
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Australian journal of biological sciences
Helvetica physiologica et pharmacologica acta
Journal of Neurochemistry
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Papers by Graham Johnston