The trigemino-pupillary reflex: a model of sensory-vegetative integration.
Trigeminal stimulation can induce pupillary changes. In vivo and in vitro studies have demonstrated that electrical impulses applied at the trigeminal level can provoke a miotic response, whose nature has been ascribed to the anti-dromic release of neuropeptides (substance P in particular). In order to better define the pupil response to trigeminal stimulation, we investigated the human pupil response to quantified (painless and painful) corneal stimuli by means of a combined (neurophysiological and pharmacological) technique. The response to corneal stimulation was bilateral, direct and consensual. It had a biphasic progression with an initial mydriasis (which directly correlated with the stimulus intensity), followed by a miotic phase. The mydriatic phase disappeared after thymoxamine application, while homatropine pre-treatment prevented occurrence of the miotic phase. The data obtained indicate that the pupillary response to corneal stimulation (trigemino-pupillary reflex) is a multisynaptic reflex with an afferent branch involving the trigeminal system, and an afferent branch involving both the sympathetic and the parasympathetic system. Other pathways, such as the SP-mediated release of acetylcholine, cannot be excluded. Thus the reflex appears to be a potentially useful tool for investigating pain/vegetative interactions in various clinical conditions. In turn, the description of its changes in pathologies characterized by a sympathetic/parasympathetic deficit or by a SP-ergic imbalance will allow us to better describe its inner mechanisms.
Micieli
G
G
Department of Neurology, C. Mondino Foundation, University of Pavia, Italy.
Tassorelli
C
C
Sandrini
G
G
Antonaci
F
F
Nappi
G
G
D000328:Adult; D001341:Autonomic Nervous System / Q000502:physiology*; D003315:Cornea; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D008297:Male; D008916:Miotics; D009184:Mydriatics; D012025:Reflex, Pupillary / Q000502:physiology*; D014276:Trigeminal Nerve / Q000502:physiology*
D008916:Miotics; D009184:Mydriatics