Activity‐Dependent Changes in Rat Ventral Horn Neurons in vitro; Summation of Prolonged Afferent Evoked Postsynaptic Depolarizations Produce a D‐2‐Amino‐5‐Phosphonovaleric Acid Sensitive Windup
- 30 June 1990
- journal article
- research article
- Published by Wiley in European Journal of Neuroscience
- Vol. 2 (7), 638-649
- https://doi.org/10.1111/j.1460-9568.1990.tb00453.x
Abstract
The synaptic responses of lumbar ventral horn neurons including identified flexor motoneurons, to graded stimulation of peripheral nerves have been recorded in vitro in the young rat spinal cord-hindlimb preparation. Single shock stimulation of low threshold myelinated afferents evoked short latency (< 20 ms) short duration ( 1 s) in all cells. In the majority of cells (67.4%), this depolarization exceeded 4.0 s in duration (8.01 ± 0.4 s, n = 26, maximum 14 s). In the remainder, shorter responses were evoked (< 3.0 s, mean = 1.74 ± 0.4 s, n = 18). In those cells where the postsynaptic response to a single A delta or C fibre strength stimulus exceeded 4 s, low frequency (0.5–1.0 Hz) repetitive stimulation resulted in a temporal summation of the postsynaptic depolarizations, which generated a cumulatively increasing depolarization. This incrementing depolarization was sufficient in 33% of the cells to produce a progressive increase in spike discharge (windup). On cessation of the train of stimuli the depolarization decayed slowly (65 ± 27 s). The N-methyl D-aspartic acid (NMDA) receptor antagonist D-2-amino-5-phosphonovaleric acid (d-APV) reduced the duration and amplitude of the prolonged postsynaptic depolarizations elicited by a single shock stimulation of small diameter afferents by 57% and 50% respectively. A smaller effect was produced on the low threshold afferent evoked early excitatory postsynaptic potentials (EPSP) (3% decrease in amplitude and 24% decrease in duration). In the presence of d-APV the cumulatively incrementing depolarization produced by repetitive stimulation was substantially reduced and windup failed to occur. Activity-dependent amplifications of primary afferent evoked responses in spinal neurons therefore involves a temporal summation of d-APV sensitive prolonged postsynaptic depolarizations.Keywords
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