Excitatory action of a plant extract, stizolobic acid, in the isolated spinal cord of the rat

Amanita muscaria: chemistry, biology, toxicology, and ethnomycology

The fly agaric is a remarkable mushroom in many respects; these are its bearing, history, chemical components and the poisoning that it provokes when consumed. The 'pantherina' poisoning syndrome is characterized by central nervous system dysfunction. The main species responsible are Amanita muscaria and A. pantherina (Amanitaceae); however, some other species of the genus have been suspected for similar actions. Ibotenic acid and muscimol are the active components, and probably, some other substances detected in the latter species participate in the psychotropic effects. The use of the mushroom started in ancient times and is connected with mysticism. Current knowledge on the chemistry, toxicology, and biology relating to this mushroom is reviewed, together with distinctive features concerning this unique species.

Stizolobic acid on frog spinal cord; possible species dependent activation of excitatory amino acid receptors

1. We examined the effects of stizolobic acid, an amino acid isolated from a plant, Stizolobium hassjoo, on the binding of [3H]glutamic acid and [3H]kainic acid to synaptosomes from frog spinal cords and on the depolarization at the ventral roots of frog spinal cords. 2. Stizolobic acid inhibited the binding of [3H]kainic acid more potently than that of [3H]glutamic acid. 3. Among stizolobic acid derivatives, 3-Br-stizolobic acid was the most potent inhibitor of the binding of [3H]kainic acid, but the inhibitory potency was 100 times weaker than that of kainic acid. 4. Stizolobic acid and its derivatives could cause depolarization of the ventral root of frog spinal cord in a dose dependent manner, and 3-Br-stizolobic acid was a more potent inducer of depolarization than kainic acid, but the dose dependency of 3-Br-stizolobic acid was a little different from that of kainic acid. 5. The results suggest that stizolobic acid and its analogues act as a kainic acid agonist in frog spinal cord. 6. The present results and others indicate that stizolobic acid may interact with the different types of excitatory amino acid receptors dependent on the species of animals.

A metabotropic l-Glutamate receptor agonist: Pharmacological difference between rat central neurones and crayfish neuromuscular junctions

1. 2S,3S,4S-2-(carboxycyclopropyl)glycine (L-CCG-I), a conformationally restricted glutamate analogue, is a potent metabotropic L-glutamate receptor agonist in the mammalian central nervous system. 2. Depolarizing actions of L-CCG-I and trans-(+/-)-1-amino-1,3-cyclopentanedicarboxylic acid (trans-ACPD) in the newborn rat spinal motoneurone are temperature-sensitive, and are not depressed by 3-[(+/-)-2-carboxypiperazin-4-yl] propyl-1-phosphonic acid (CPP) and/or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). 3. L-CCG-I and trans-ACPD induced oscillatory responses in Xenopus oocytes injected with rat brain mRNA. Oocytes with oscillatory responses to L-CCG-I and trans-ACPD showed reversal potential of about -20 mV, which was very close to the equilibrium potential of chloride ions. 4. In rat hippocampal synaptoneurosomes, L-CCG-I stimulated phosphoinositide hydrolysis in a concentration dependent manner. L-CCG-I was less potent than quisqualate but more potent than trans-ACPD. 5. At low concentrations, L-CCG-I did not cause any depolarization of newborn rat spinal motoneurones, but reduced substantially amplitudes of monosynaptic reflexes. 6. At the crayfish neuromuscular junction L-CCG-I, acting presynaptically, reduced the amplitude of excitatory junctional potentials. This action was prevented by application of picrotoxin but not pertussis toxin. The actions of trans-ACPD differ from those of either L-CCG-I or ibotenate at the crayfish neuromuscular junction. 7. L-CCG-I has a potential to provide further useful information on metabotropic L-glutamate receptor function.

Specific lesions of rat spinal interneurons induced by systemic administration of acromelic acid, a new potent kainate analogue

A single systemic injection of acromelic acid, a potent kainate analogue, caused behavioral and pathological effects distinct from those seen after systemic kainate. There was an initial marked tonic extension of the rat hindlimb, followed often by convulsions and, in surviving rats, by a transient flaccid paralysis and, ultimately, a persistent spastic paraplegia. Pathological examination suggested specific lesions of interneurons in the lower spinal cord with little or no damage to the hippocampal neurons preferentially affected by systemic kainate.

Potent NMDA-like actions and potentiation of glutamate responses by conformational variants of a glutamate analogue in the rat spinal cord

1. Neuropharmacological actions of all possible-state isomers of alpha-(carboxycyclopropyl)glycine (CCG), conformationally restricted analogues of glutamate, were examined for electrophysiological effects in the isolated spinal cord of the newborn rat. 2. Eight CCG stereoisomers demonstrated a large variety of depolarizing activities. Among them, the (2R, 3S, 4S) isomers of CCG (D-CCG-II) showed the most potent depolarizing activity, followed by the (2S, 3R, 4S) isomer (L-CCG-IV). 3. The depolarization evoked by L-CCG-IV, D-CCG-II and other D-CCG isomers was effectively depressed by N-methyl-D-aspartate (NMDA) antagonists. D-CCG-II was about 5 times more potent than NMDA in causing a depolarization. 4. The (2S, 3S, 4S) isomer of CCG (L-CCG-I) was more potent than L-glutamate in causing a depolarization of spinal motoneurones. The depolarization was slightly depressed by NMDA antagonists, but residual amplitudes of responses to L-CCG-I in the presence of NMDA antagonists We almost insensitive to 6,7-dinitro-quinoxaline-2,3-dione (DNQX) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), suggesting that L-CCG-I might be a novel potent agonist. 5. After application of the (2S, 3S, 4R) isomer of CCG (L-CCG-III), responses to L-glutamate, D- and L-aspartate were markedly enhanced. The enhancement lasted for a period of several hours without a further application of L-CCG-III. 6. L-CCG-III also caused a depolarization, but it seemed unlikely that the potentiation of the glutamate response was directly related to the depolarization evoked by L-CCG-III. 7. The potentiation might be due to inhibition of uptake processes, but L-CCG-III was superior to L-(-)-threo-3-hydroxyaspartate, a potent uptake inhibitor of L-glutamate and L-aspartate, in enhancing the response to L-glutamate in terms of amplitude and duration of responses. 8. CCG isomers should provide useful pharmacological tools for analysis of glutamate neurotransmitter systems.