Cholinergic activation of a population of corneal afferent nerves.
The in vivo rabbit cornea was used to investigate the effect of acetylcholine on "free" nerve endings from A-delta and C-fibers in the long-ciliary (corneal) nerve. Extracellular electrophysiologic recordings were obtained from 67 corneal nerve fibers. Acetylcholine in concentrations of 10(-5) to 10(-3) M stimulated a specific population of these corneal afferents that were not activated by mechanical or thermal stimuli. Their conduction velocity was determined to be 1.14 +/- 0.34 m/s (mean +/- SD). The other three previously characterized corneal nerve populations (mechanical, mechano-heat, and cold) were not stimulated by the cholinergic agonists or antagonists. Acetylcholine sensitive afferents were also stimulated by carbachol (10(-5) to 10(-3) M) and nicotine (10(-6) to 10(-4) M) but not by bethanecol (10(-5) to 10(-3) M). Acetylcholine-induced activity was abolished by d-tubocurare (10(-4) M) and kappa-bungarotoxin (10(-6) M). The cAMP analog 8-bromoadenosine 3'5'-cyclic monophosphate activated the same population of chemosensitive C-fibers as acetylcholine. It is concluded that a specific population of C-fiber afferents exist in the rabbit cornea which are stimulated by acetylcholine possibly acting via a neuronal nicotinic receptor. Physiologically, these nerves may be involved in the production of pain following tissue injury or ischemia.
Tanelian
D L
DL
Department of Anesthesia, Stanford University School of Medicine, CA 94305.
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000109:Acetylcholine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000818:Animals; D003315:Cornea / Q000294:innervation*; D004594:Electrophysiology; D005071:Evoked Potentials / Q000187:drug effects; D005731:Ganglionic Stimulants / Q000494:pharmacology; D006358:Hot Temperature; D009412:Nerve Fibers / Q000187:drug effects; D009413:Nerve Fibers, Myelinated / Q000187:drug effects; D009431:Neural Conduction / Q000187:drug effects; D009475:Neurons, Afferent / Q000502:physiology*; D010275:Parasympathetic Nervous System / Q000187:drug effects / Q000502:physiology*; D010277:Parasympathomimetics / Q000494:pharmacology; D010812:Physical Stimulation; D011817:Rabbits; D013268:Stimulation, Chemical
D005731:Ganglionic Stimulants; D010277:Parasympathomimetics; D015124:8-Bromo Cyclic Adenosine Monophosphate; D000109:Acetylcholine