Primary afferent depolarization in frog spinal cord is associated with an increase in membrane conductance

1983 ◽  
Vol 61 (6) ◽  
pp. 626-631 ◽  
Author(s):  
Ante L. Padjen ◽  
Toshio Hashiguchi
Keyword(s):  
Spinal Cord ◽  
Linear Part ◽  
Membrane Conductance ◽  
Potassium Sulfate ◽  
Equilibrium Potential ◽  
Primary Afferent Depolarization ◽  
Primary Afferent ◽  
Frog Spinal Cord ◽  
Voltage Dependent ◽  
Afferent Terminals

The mechanism of primary afferent depolarization (PAD) was studied in the isolated frog spinal cord using intrafibre recording (microelectrodes filled with 0.6 M potassium sulfate) from large myelinated axons of dorsal roots. Standard current–clamp technique was used to obtain voltage–current (V–I) relationship. It was found that: (i) PAD is voltage dependent: its amplitude and rate of rise are increased with hyperpolarization; (ii) the slope of the linear part of the V–I curve obtained during PAD is decreased compared with the V–I curve at rest; (iii) the PAD equilibrium potential, estimated by extrapolation, ranged from −66 to −40 mV. These results suggest that PAD is associated with an increase in conductance of primary afferent terminals and thus seem to provide the first experimental evidence for the hypothesis that shunting of primary afferent membrane is the mechanism of presynaptic inhibition in the vertebrate nervous system.

α5GABAA receptors mediate primary afferent fiber tonic excitability in the turtle spinal cord

2013 ◽  
Vol 110 (9) ◽  
pp. 2175-2184 ◽  
Author(s):  
Emanuel Loeza-Alcocer ◽  
Martha Canto-Bustos ◽  
Justo Aguilar ◽  
Ricardo González-Ramírez ◽  
Ricardo Felix ◽  
...  
Keyword(s):  
Spinal Cord ◽  
Dorsal Root Ganglia ◽  
Dorsal Root ◽  
Afferent Fiber ◽  
Primary Afferents ◽  
Equilibrium Potential ◽  
Primary Afferent Depolarization ◽  
Primary Afferent ◽  
Dorsal Root Reflex

γ-Amino butyric acid (GABA) plays a key role in the regulation of central nervous system by activating synaptic and extrasynaptic GABAA receptors. It is acknowledged that extrasynaptic GABAA receptors located in the soma, dendrites, and axons may be activated tonically by low extracellular GABA concentrations. The activation of these receptors produces a persistent conductance that can hyperpolarize or depolarize nerve cells depending on the Cl− equilibrium potential. In an in vitro preparation of the turtle spinal cord we show that extrasynaptic α5GABAA receptors mediate the tonic state of excitability of primary afferents independently of the phasic primary afferent depolarization mediated by synaptic GABAA receptors. Blockade of α5GABAA receptors with the inverse agonist L-655,708 depressed the dorsal root reflex (DRR) without affecting the phasic increase in excitability of primary afferents. Using RT-PCR and Western blotting, we corroborated the presence of the mRNA and the α5GABAA protein in the dorsal root ganglia of the turtle spinal cord. The receptors were localized in primary afferents in dorsal root, dorsal root ganglia, and peripheral nerve terminals using immunoconfocal microscopy. Considering the implications of the DRR in neurogenic inflammation, α5GABAA receptors may serve as potential pharmacological targets for the treatment of pain.

Primary afferent depolarization of C fibres in the spinal cord of the cat

1978 ◽  
Vol 56 (1) ◽  
pp. 154-157 ◽  
Author(s):  
O. Calvillo
Keyword(s):  
Spinal Cord ◽  
Central Nervous System ◽  
Primary Afferent Depolarization ◽  
Primary Afferent ◽  
Nociceptive Information ◽  
The Central Nervous System ◽  
C Fibre ◽  
Afferent Terminals ◽  
Presynaptic Control ◽  
Terminal Excitability

The excitability of primary afferent terminals of cutaneous C fibres was tested in the spinal cord of decerebrated cats. C fibre terminal excitability was decreased in the spinal state, and increased by conditioning volleys that activated only A fibres of another cutaneous nerve and by stimulating hair mechanically. It is suggested that C fibre input and therefore nociceptive information to the central nervous system is susceptible to presynaptic control by segmental and suprasegmental mechanisms.

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