Primary Afferent Depolarization
Primary Afferent Depolarization - Related Videos
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Abnormal sensory function underlies visceral pain and other symptoms of functional and inflammatory bowel diseases. A protocol for the electrophysiological recording of the colonic afferent nerves in an ex vivo rat colorectum preparation is presented here.
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This video demonstrates an experimental protocol to investigate the prolonged depolarizing afterpotential (PDA) in white-eyed Drosophila. The fly's eye is exposed to intense blue light pulses to convert the photopigment rhodopsin to metarhodopsin, initiating a signaling cascade that opens positive ion channels and causes membrane depolarization. Because blue light prevents the reconversion of metarhodopsin to rhodopsin, the continuous influx of positive ions results in sustained depolarization,...
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Whole-cell patch-clamp recordings from auditory nerve fiber dendrites at the inner hair cell ribbon synapse in the mammalian cochlea.
10:32
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Cited by 8 •
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Mesenteric afferent nerves convey information from the gastrointestinal tract towards the brain regarding normal homeostasis as well as pathophysiology. Gastrointestinal afferent nerve activity can be assessed by mounting isolated intestinal segments with attached afferent nerves into an organ bath, isolating the nerve, and assessing basal as well as stimulated activity.
14:09
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Cited by 21 •
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This video demonstrates a protocol for conducting single-fiber electrophysiological recordings on an in vitro mouse colorectum-nerve preparation.
FAQs
The effect depends on the terminal’s unusually high intracellular chloride concentration. When GABA_A receptors open, chloride moves out of the primary afferent terminal rather than entering it, shifting the terminal membrane potential toward depolarization. This reversal of the usual inhibitory chloride response allows GABAergic axo-axonic input to regulate sensory transmission presynaptically.
Depolarization can reduce the effectiveness of excitatory currents reaching the sensory terminal by shunting them, meaning the currents are diverted through open channels. It can also reduce calcium entry into the terminal. Because calcium entry supports neurotransmitter release, these combined effects decrease transmitter output and filter the incoming sensory signal before it reaches central neurons.
PAD acts at the terminal of a primary sensory neuron, before that neuron releases neurotransmitter onto downstream spinal cells. This placement allows inhibitory control to operate selectively on incoming sensory messages rather than simply suppressing activity throughout the receiving circuit. The arrangement is therefore suited to adjusting the strength of pain, touch, and reflex-related signals.
The outcome depends particularly on chloride distribution within the primary afferent terminal and on activation of GABA_A receptors by GABAergic axo-axonic synapses. The resulting depolarization must also influence excitatory current flow and calcium entry. Together, these factors determine how strongly transmitter release is reduced and how much sensory information is filtered.
A mechanistic analysis can follow the sequence from GABAergic axo-axonic synapse activation to GABA_A receptor opening, chloride movement, terminal depolarization, altered excitatory currents, calcium entry, and neurotransmitter release. Examining this sequence connects membrane events with the final change in sensory transmission, providing a framework for interpreting presynaptic inhibition in spinal pathways.
PAD is especially relevant to spinal control of pain, touch, and reflex pathways. In each case, presynaptic regulation can alter how strongly incoming signals are conveyed to the central nervous system. Studying the mechanism helps explain how spinal circuits prevent or reduce indiscriminate transmission while preserving a controllable flow of sensory information.
Changes in this mechanism could modify how sensory inputs are filtered before entering central spinal circuits. Since those inputs contribute to pain, touch, and reflex pathways, altered presynaptic control may affect the relationship between sensation and motor responses. PAD therefore provides a useful scientific context for investigating abnormal sensorimotor processing without treating sensory input as fixed.