Amino Acids as Neurotransmitters.: A Symposium to honour Hugh McLennan on his retirement

1991 ◽  
Vol 69 (7) ◽  
pp. 1048-1048
Author(s):  
J. R. Ledsome
Keyword(s):  
Amino Acids ◽  
Spinal Cord ◽  
Amino Acid ◽  
Synaptic Transmission ◽  
Chloride Channels ◽  
Excitatory Amino Acid ◽  
Rapid Development ◽  
Long Term Potentiation ◽  
Isolation And Identification ◽  
University Of British Columbia

A meeting was held at the University of British Columbia on May 28–29, 1990 to honour the many important scientific contributions made by Dr. Hugh McLennan to our understanding of chemical neurotransmission in the brain and spinal cord. The invited speakers were those with whom Dr. McLennan has at one time or another collaborated, and their presentations reflected Hugh's early interest in GÀBA (factor I) as an inhibitory transmitter and his research over the last two decades into the physiology and pharmacology of acidic amino acid receptors.The session on GABA opened with an intriguing discussion by Professor Florey of the history of the isolation and identification of GABA as a neurotransmitter and was followed by papers dealing with the electrophysiological actions of GABA. Professor Curtis discussed its pre- and post-synaptic actions in the spinal cord, while Dr. Mathers presented data derived from GABA-gated chloride channels isolated from cultured neurones. Professor Krnjević was unfortunately unable to attend the symposium.Work presented by Professors Watkins and Lodge and Dr. Curry provided an excellent historical perspective on the birth and rapid development of excitatory amino acid pharmacology, a field to which Dr. McLennan has contributed enormously.Among the topics pertaining to the electrophysiological actions of acidic amino acids was the role of the NMDA receptor both in long-term potentiation (Dr. Collingridge) and in synaptic transmission in the kainic acid-lesioned hippocampus (Dr. Wheal), the effects of antagonists on synaptic transmission in the thalamus (Dr. Hicks), and the modulation by catecholamines of glutamate-induced neuronal excitations (Dr. Marshall).In his closing address Dr. McLennan, with characteristic grace and style, acknowledged the efforts of his co-workers in his many achievements. Those of us who have had the great pleasure of collaborating with Hugh here at UBC or within the scientific community wish him all the best in his retirement.

Involvement of excitatory amino acid receptors in long-term potentiation in the Schaffer collateral–commissural pathway of rat hippocampal slices

1991 ◽  
Vol 69 (7) ◽  
pp. 1084-1090 ◽  
Author(s):  
G. L. Collingridge ◽  
J. F. Blake ◽  
M. W. Brown ◽  
Z. I. Bashir ◽  
E. Ryan
Keyword(s):  
Amino Acid ◽  
Synaptic Transmission ◽  
Excitatory Amino Acid ◽  
Hippocampal Slices ◽  
Long Term Potentiation ◽  
Excitatory Amino Acid Receptors ◽  
Amino Acid Receptors ◽  
Term Potentiation ◽  
Commissural Pathway

The present article reviews studies from our laboratory, which have shown that excitatory amino acid receptors of the N-methyl-D-aspartate type are involved in the induction of long-term potentiation in the Schaffer collateral–commissural pathway of rat hippocampal slices. The nature of the excitatory amino acid receptors that mediate the response that is modified by the induction of long-term potentiation is also considered. The mechanism of induction of long-term potentiation is discussed, as are some possible stages that are required for the maintenance of this process. Some new data are presented concerning the ability of N-methyl-D-aspartate to potentiate synaptic transmission and to depress the amplitude of the presynaptic fibre volley. Concerning the potentiation, it is shown that brief (1–2 min) perfusion of slices with N-methyl-D-aspartate is sufficient to potentiate synaptic transmission for at least 3 h. The N-methyl-D-aspartate induced depression of the presynaptic fibre volley is shown to be transient and independent of synaptic transmission.Key words: long-term potentiation, N-methyl-D-aspartate, a-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid, synaptic plasticity, hippocampus.

Spinal cord excitatory amino acids and cardiovascular autonomic responses

1994 ◽  
Vol 267 (3) ◽  
pp. H865-H873 ◽  
Author(s):  
M. West ◽  
W. Huang
Keyword(s):  
Amino Acids ◽  
Spinal Cord ◽  
Heart Rate ◽  
Amino Acid ◽  
Excitatory Amino Acids ◽  
Excitatory Amino Acid ◽  
Intrathecal Injection ◽  
Thoracic Spinal Cord ◽  
Upper Thoracic ◽  
Intrathecal Space

The excitatory amino acid subtype receptor agonists, N-methyl-D-aspartate (NMDA) and (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA, a non-NMDA agonist), produce specific dose-related heart rate and vasoconstrictor responses when given by injection into the upper thoracic or lumbar intrathecal space of the conscious rabbit. The responses are inhibited by prior intrathecal injection of the specific excitatory amino acid subtype receptor antagonist, 2-amino-5-phosphonovaleric acid (AP-5) or 6,7-dinitroquinoxaline-2,3-dione (DNQX), respectively. Baroreceptor heart rate reflex function is inhibited by AP-5 and by DNQX applied to the upper thoracic spinal cord. In contrast baroreflex vasoconstrictor function is blocked by AP-5 but not by DNQX given in the lumbar intrathecal space. The experiments support previous evidence that spinal excitatory amino acids are important as neurotransmitters at the level of the sympathetic preganglionic neuron and as such exert tonic and reflex control of autonomic cardiovascular function. It is concluded that 1) intrathecal activation of NMDA and non-NMDA subtype receptors has similar but independent effects on heart rate and on blood pressure and 2) NMDA receptors alone participate in mediation of baroreflex vasoconstrictor function, whereas both sets of receptors determine reflex sympathetic heart rate effects.

Motor patterns for two distinct rhythmic behaviors evoked by excitatory amino acid agonists in the Xenopus embryo spinal cord

1996 ◽  
Vol 75 (5) ◽  
pp. 1815-1825 ◽  
Author(s):  
S. R. Soffe
Keyword(s):  
Amino Acids ◽  
Spinal Cord ◽  
Amino Acid ◽  
Excitatory Amino Acids ◽  
Excitatory Amino Acid ◽  
Motor Pattern ◽  
Cycle Period ◽  
Motor Patterns ◽  
Sensory Evoked ◽  
Motor Root

1. Mechanisms underlying the selective expression of different motor patterns in vertebrates are poorly understood. Immobilized, spinal Xenopus embryos are used here to examine the motor patterns evoked by various concentrations of excitatory amino acids. 2. Relatively low concentrations of N-methyl-D-aspartate (NMDA) (40-60 microM), kainate (7-8 microM), and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) (5 microM) evoked motor root discharge characteristic of swimming. Brief applications of higher concentrations of kainate (20-40 microM), AMPA (25-30 microM), quisqualate (5 microM), and glutamate (1-4 mM) evoked sequences of a different motor pattern: struggling. This is characterized by a longer cycle period, increased burst duration, and a reversed longitudinal pattern of motor root discharge. The struggling pattern was never evoked by higher concentrations of NMDA (300-500 microM), but was evoked by 30 microM AMPA or 5 microM quisqualate in the presence of 50 microM D-2-amino-5-phosphonopentanoic acid. 3. Intracellular recordings from presumed spinal motoneurons showed different patterns of activity during agonist-evoked swimming and struggling. The patterns were like those described previously during sensory-evoked behavior. 4. Caudal applications of excitatory amino acids that produced struggling discharge did so only at caudal motor roots, whereas caudal applications of NMDA evoked swimming activity throughout the spinal cord. 5. During excitatory-amino-acid-evoked struggling, sensory Rohon-Beard neurons depolarized up to 7 mV, but did not fire. 6. The results show that expression of the struggling pattern, like swimming, is not critically dependent on sensory discharge. The results are also consistent with the idea that expression of the two very different motor patterns for swimming or struggling in this simple vertebrate preparation can be controlled by the level of excitation within the spinal motor circuitry, and need not involve the activity of a specific external neuromodulator.

scholarly journals Commissural Interneurons in Rhythm Generation and Intersegmental Coupling in the Lamprey Spinal Cord

1999 ◽  
Vol 81 (5) ◽  
pp. 2037-2045 ◽  
Author(s):  
James T. Buchanan
Keyword(s):  
Spinal Cord ◽  
Amino Acid ◽  
Excitatory Amino Acid ◽  
Rhythmic Activity ◽  
Ventral Root ◽  
Rhythm Generation ◽  
Spinal Segment ◽  
Spinal Segments ◽  
Autocorrelation Method

Commissural interneurons in rhythm generation and intersegmental coupling in the lamprey spinal cord. To test the necessity of spinal commissural interneurons in the generation of the swim rhythm in lamprey, longitudinal midline cuts of the isolated spinal cord preparation were made. Fictive swimming was then induced by bath perfusion with an excitatory amino acid while recording ventral root activity. When the spinal cord preparation was cut completely along the midline into two lateral hemicords, the rhythmic activity of fictive swimming was lost, usually replaced with continuous ventral root spiking. The loss of the fictive swim rhythm was not due to nonspecific damage produced by the cut because rhythmic activity was present in split regions of spinal cord when the split region was still attached to intact cord. The quality of this persistent rhythmic activity, quantified with an autocorrelation method, declined with the distance of the split spinal segment from the remaining intact spinal cord. The deterioration of the rhythm was characterized by a lengthening of burst durations and a shortening of the interburst silent phases. This pattern of deterioration suggests a loss of rhythmic inhibitory inputs. The same pattern of rhythm deterioration was seen in preparations with the rostral end of the spinal cord cut compared with those with the caudal end cut. The results of this study indicate that commissural interneurons are necessary for the generation of the swimming rhythm in the lamprey spinal cord, and the characteristic loss of the silent interburst phases of the swimming rhythm is consistent with a loss of inhibitory commissural interneurons. The results also suggest that both descending and ascending commissural interneurons are important in the generation of the swimming rhythm. The swim rhythm that persists in the split cord while still attached to an intact portion of spinal cord is thus imposed by interneurons projecting from the intact region of cord into the split region. These projections are functionally short because rhythmic activity was lost within approximately five spinal segments from the intact region of spinal cord.

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