The trigemino-pupillary reflex: a model of sensory-vegetative integration

Giuseppe Micieli, Cristina Tassorelli, Giorgio Sandrini, Fabio Antonaci, Giuseppe Nappi

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish
Pages (from-to)179-185
Number of pages7
JournalJournal of the Autonomic Nervous System
Issue number3
Publication statusPublished - 1992


  • Homatropine
  • Pain
  • Pupil
  • Substance P
  • Thymoxamine
  • Trigeminal stimulation

ASJC Scopus subject areas

  • Physiology
  • Clinical Neurology
  • Neuroscience(all)


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