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Glutamate sensitivity of the presynaptic membrane in the crustacean neuromuscular synapse
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22 Neurotransmitters I SELECTIVE RAT SPINAL KOICHI Nagoya 06510,
Amino acids
A N T A G O N I S M OF S Y N A P T I C A N D A M I N O C O R D BY G L U T A M A T E A N T A G O N I S T S
Y O S H I O K A * a n d # C R A I G E. 466 a n d # Sect. Molec. USA
ACID-EVOKED
JAHR* Dept. Neurobiol.,
EXCITATION
IN THE
NEWBORN
P h a r m a c o l . , N a g o y a Univ. Sch. Med., Y a l e Univ. Sch. Med., N e w Haven, CT
The s p e c i f i c i t y of t h e a c t i o n of s e v e r a l g l u t a m a t e r e c e p t o r a n t a g o n i s t s w a s s t u d i e d in o r d e r to d e t e r m i n e w h i c h r e c e p t o r t y p e s are l i k e l y to m e d i a t e s y n a p t i c t r a n s m i s s i o n e v o k e d b y p r i m a r y a f f e r e n t i n p u t in t h e in v i t r o n e w b o r n rat spinal cord. Kynurenate antagonized N-methyl-D-aspartate (NMDA), quisqualate, kainate, L-aspartate and L-glutamate-induced depolarizatioms recored from the ventral root, b u t h a d no e f f e c t on r e s p o n s e s to o t h e r p u t a t i v e t r a n s m i t t e r s . Kynurenate also d e p r e s s e d b o t h m o n o - a n d p o l y s y n a p t i c c o m p o n e n t s of v e D t r s l root potential (VRP). In c o n t r a s t , 2-aminophosphonovalerate, a specific NMDA antagonist, was quite s e l e c t i v e in a n t a g o n i z i n g the p o l y s y n a p t i c c o m p o n e n t of the VRP , while having l i t t l e e f f e c t on the m o n o s y n a p t i c p o r t i o n . Intracellular recordings from motoneurons confirmed that kynurenate antagonized the Ia epsp evoked by stimulation of homonymous muscle nerves. T h e s i t e of a c t i o n of k y n u r e n a t e was examined by observing its e f f e c t on s y n a p t i c d e p e s s i o n and was found to be consistent with a postsynaptic mechanism. T h e s e r e s u l t s s u g g e s t t h a t the Ia e p s p is mediated by excitatory a m i n o a c i d r e c e p t o r s of the non-NMDA type. L-2aminophosphonobutyrate (L-APB) w a s a l s o a p o t e n t d e p r e s s a n t of Ia epsp. However, the effect of L - A P B on s y n a p t i c d e p r e s s i o n i n d i c a t e d a postsynaptic site of action, s u g g e s t i n g the e x i s t e n c e of p r e s y n a p t i c L - A P B s e n s i t i v e r e c e p t o r s on t h e t e r m i n a l s of g r o u p Ia a f f e r e n t s .
A MORE POWERFUL EXCITATORY AMINO ACID THAN KAINIC ACID, ACROMELIC ACID, FROM A POISONOUS MUSHROOM HARUHIKO SHINOZAKI, MICMIKO ISHIDA and TSUKASA OKAMOTO*, The Tokyo Metropolitan Institute of Medical Science, Bunkyo-ku, Tokyo 113, Japan The ingestion of a poisonous mushroom, Clitocybe acromelalsa, causes a sharp pain and marked reddish edema in the foot and finger about a week later. The mechanisms of the action of the poisonous principle are not yet known clearly, although axonal damages in the patient with the poisoning by the mushroom have been suggested. Clithloneine, clitidine and acromelic acid have so far been isolated from the mushroom, and recently Shirahama and his colleagues succeeded in the synthesis of acromelie acid to provide a sample for biological assay. The structural similarity of this amino acid to glutamic or kainic acid prompted us to investigate its possible action on the glutamatergic system in both the invertebrate and vertebrate. Intracellular recordings were made at the invertebrate neuromuscular Junction, and the spike discharges were extracellularly recorded from the rat cortical neurones. Acromelic acid markedly depolarized the crayfish opener muscle fibre in a dose dependent manner and its potency was much greater than that of kainic acid and domoic acid. Acromellc acid markedly potentiated the glutamate response of the muscle fibre even at concentrations lower than the threshold concentration for depolarization. When acromelic acid was iontophoretically applied to a glutamate sensitive spot, a large depolarization was induced, presenting a strong contrast with kainic acid or domoic acid, which did not produce such a large depolarization when applied iontophoretically at the crayfish neuromuscular junction; and the distribution of the acromelate sensitive spot almost coincided with that of the L-glutamate sensitive spot. Cross desensitization of the receptor between glutamate and acromelate was observed. Like kainic acid, acromelic acid significantly depressed the quisqualate response in a dose dependent manner, but its potency was much greater than that of kainate. When acromelic acid was iontophoretically applied to the rat cortical neurone (anaesthetized with 500 mg urethane/kg and 40 mg chloralose/kg), significant spike discharges were induced by this amino acid in most neurones which responded to iontophoretically applied glutamate. When large amounts of acromellc acid were applied, the amplitude of the spike discharges decreased and then were abolished, presumably by excessive depolarization. The cessation of discharges evoked by acromelic acid was much more delayed than by glutamate. Acromellc acid was shown to be a very useful tool in the field of neuroscience research.
22 Neurotransmitters I SELECTIVE RAT SPINAL KOICHI Nagoya 06510,
Amino acids
A N T A G O N I S M OF S Y N A P T I C A N D A M I N O C O R D BY G L U T A M A T E A N T A G O N I S T S
Y O S H I O K A * a n d # C R A I G E. 466 a n d # Sect. Molec. USA
ACID-EVOKED
JAHR* Dept. Neurobiol.,
EXCITATION
IN THE
NEWBORN
P h a r m a c o l . , N a g o y a Univ. Sch. Med., Y a l e Univ. Sch. Med., N e w Haven, CT
The s p e c i f i c i t y of t h e a c t i o n of s e v e r a l g l u t a m a t e r e c e p t o r a n t a g o n i s t s w a s s t u d i e d in o r d e r to d e t e r m i n e w h i c h r e c e p t o r t y p e s are l i k e l y to m e d i a t e s y n a p t i c t r a n s m i s s i o n e v o k e d b y p r i m a r y a f f e r e n t i n p u t in t h e in v i t r o n e w b o r n rat spinal cord. Kynurenate antagonized N-methyl-D-aspartate (NMDA), quisqualate, kainate, L-aspartate and L-glutamate-induced depolarizatioms recored from the ventral root, b u t h a d no e f f e c t on r e s p o n s e s to o t h e r p u t a t i v e t r a n s m i t t e r s . Kynurenate also d e p r e s s e d b o t h m o n o - a n d p o l y s y n a p t i c c o m p o n e n t s of v e D t r s l root potential (VRP). In c o n t r a s t , 2-aminophosphonovalerate, a specific NMDA antagonist, was quite s e l e c t i v e in a n t a g o n i z i n g the p o l y s y n a p t i c c o m p o n e n t of the VRP , while having l i t t l e e f f e c t on the m o n o s y n a p t i c p o r t i o n . Intracellular recordings from motoneurons confirmed that kynurenate antagonized the Ia epsp evoked by stimulation of homonymous muscle nerves. T h e s i t e of a c t i o n of k y n u r e n a t e was examined by observing its e f f e c t on s y n a p t i c d e p e s s i o n and was found to be consistent with a postsynaptic mechanism. T h e s e r e s u l t s s u g g e s t t h a t the Ia e p s p is mediated by excitatory a m i n o a c i d r e c e p t o r s of the non-NMDA type. L-2aminophosphonobutyrate (L-APB) w a s a l s o a p o t e n t d e p r e s s a n t of Ia epsp. However, the effect of L - A P B on s y n a p t i c d e p r e s s i o n i n d i c a t e d a postsynaptic site of action, s u g g e s t i n g the e x i s t e n c e of p r e s y n a p t i c L - A P B s e n s i t i v e r e c e p t o r s on t h e t e r m i n a l s of g r o u p Ia a f f e r e n t s .
A MORE POWERFUL EXCITATORY AMINO ACID THAN KAINIC ACID, ACROMELIC ACID, FROM A POISONOUS MUSHROOM HARUHIKO SHINOZAKI, MICMIKO ISHIDA and TSUKASA OKAMOTO*, The Tokyo Metropolitan Institute of Medical Science, Bunkyo-ku, Tokyo 113, Japan The ingestion of a poisonous mushroom, Clitocybe acromelalsa, causes a sharp pain and marked reddish edema in the foot and finger about a week later. The mechanisms of the action of the poisonous principle are not yet known clearly, although axonal damages in the patient with the poisoning by the mushroom have been suggested. Clithloneine, clitidine and acromelic acid have so far been isolated from the mushroom, and recently Shirahama and his colleagues succeeded in the synthesis of acromelie acid to provide a sample for biological assay. The structural similarity of this amino acid to glutamic or kainic acid prompted us to investigate its possible action on the glutamatergic system in both the invertebrate and vertebrate. Intracellular recordings were made at the invertebrate neuromuscular Junction, and the spike discharges were extracellularly recorded from the rat cortical neurones. Acromelic acid markedly depolarized the crayfish opener muscle fibre in a dose dependent manner and its potency was much greater than that of kainic acid and domoic acid. Acromellc acid markedly potentiated the glutamate response of the muscle fibre even at concentrations lower than the threshold concentration for depolarization. When acromelic acid was iontophoretically applied to a glutamate sensitive spot, a large depolarization was induced, presenting a strong contrast with kainic acid or domoic acid, which did not produce such a large depolarization when applied iontophoretically at the crayfish neuromuscular junction; and the distribution of the acromelate sensitive spot almost coincided with that of the L-glutamate sensitive spot. Cross desensitization of the receptor between glutamate and acromelate was observed. Like kainic acid, acromelic acid significantly depressed the quisqualate response in a dose dependent manner, but its potency was much greater than that of kainate. When acromelic acid was iontophoretically applied to the rat cortical neurone (anaesthetized with 500 mg urethane/kg and 40 mg chloralose/kg), significant spike discharges were induced by this amino acid in most neurones which responded to iontophoretically applied glutamate. When large amounts of acromellc acid were applied, the amplitude of the spike discharges decreased and then were abolished, presumably by excessive depolarization. The cessation of discharges evoked by acromelic acid was much more delayed than by glutamate. Acromellc acid was shown to be a very useful tool in the field of neuroscience research.