{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,1]],"date-time":"2026-10-01T16:42:09Z","timestamp":1790872929327,"version":"4.1.0"},"reference-count":63,"publisher":"American Physiological Society","issue":"5","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Journal of Neurophysiology"],"published-print":{"date-parts":[[1999,11,1]]},"abstract":"<jats:p> Corneal-responsive neurons were recorded extracellularly in two regions of the spinal trigeminal nucleus, subnucleus interpolaris\/caudalis (Vi\/Vc) and subnucleus caudalis\/upper cervical cord (Vc\/C1) transition regions, from methohexital-anesthetized male rats. Thirty-nine Vi\/Vc and 26 Vc\/C1 neurons that responded to mechanical and electrical stimulation of the cornea were examined for convergent cutaneous receptive fields, responses to natural stimulation of the corneal surface by CO<jats:sub>2<\/jats:sub> pulses (0, 30, 60, 80, and 95%), effects of morphine, and projections to the contralateral thalamus. Forty-six percent of mechanically sensitive Vi\/Vc neurons and 58% of Vc\/C1 neurons were excited by CO<jats:sub>2<\/jats:sub> stimulation. The evoked activity of most cells occurred at 60% CO<jats:sub>2<\/jats:sub> after a delay of 7\u201322 s. At the Vi\/Vc transition three response patterns were seen. Type I cells ( n = 11) displayed an increase in activity with increasing CO<jats:sub>2<\/jats:sub> concentration. Type II cells ( n = 7) displayed a biphasic response, an initial inhibition followed by excitation in which the magnitude of the excitatory phase was dependent on CO<jats:sub>2<\/jats:sub> concentration. A third category of Vi\/Vc cells (type III, n = 3) responded to CO<jats:sub>2<\/jats:sub> pulses only after morphine administration (&gt;1.0 mg\/kg). At the Vc\/C1 transition, all CO<jats:sub>2<\/jats:sub>-responsive cells ( n = 15) displayed an increase in firing rates with greater CO<jats:sub>2<\/jats:sub> concentration, similar to the pattern of type I Vi\/Vc cells. Comparisons of the effects of CO<jats:sub>2<\/jats:sub> pulses on Vi\/Vc type I units, Vi\/Vc type II units, and Vc\/C1 corneal units revealed no significant differences in threshold intensity, stimulus encoding, or latency to sustained firing. Morphine (0.5\u20133.5 mg\/kg iv) enhanced the CO<jats:sub>2<\/jats:sub>-evoked activity of 50% of Vi\/Vc neurons tested, whereas all Vc\/C1 cells were inhibited in a dose-dependent, naloxone-reversible manner. Stimulation of the contralateral posterior thalamic nucleus antidromically activated 37% of Vc\/C1 corneal units; however, no effective sites were found within the ventral posteromedial thalamic nucleus or nucleus submedius. None of the Vi\/Vc corneal units tested were antidromically activated from sites within these thalamic regions. Corneal-responsive neurons in the Vi\/Vc and Vc\/C1 regions likely serve different functions in ocular nociception, a conclusion reflected more by the difference in sensitivity to analgesic drugs and efferent projection targets than by the CO<jats:sub>2<\/jats:sub> stimulus intensity encoding functions. Collectively, the properties of Vc\/C1 corneal neurons were consistent with a role in the sensory-discriminative aspects of ocular pain due to chemical irritation. The unique and heterogeneous properties of Vi\/Vc corneal neurons suggested involvement in more specialized ocular functions such as reflex control of tear formation or eye blinks or recruitment of antinociceptive control pathways. <\/jats:p>","DOI":"10.1152\/jn.1999.82.5.2092","type":"journal-article","created":{"date-parts":[[2017,12,21]],"date-time":"2017-12-21T07:53:11Z","timestamp":1513842791000},"page":"2092-2107","source":"Crossref","is-referenced-by-count":54,"title":["Responses of Medullary Dorsal Horn Neurons to Corneal Stimulation by CO<sub>2<\/sub> Pulses in the Rat"],"prefix":"10.1152","volume":"82","author":[{"given":"Harumitsu","family":"Hirata","sequence":"first","affiliation":[{"name":"Surgery, Brown University\/Rhode Island Hospital, Providence, Rhode Island 02903; and"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"James W.","family":"Hu","sequence":"additional","affiliation":[{"name":"Faculty of Dentistry, University of Toronto, Toronto, Ontario M5G 1G6, Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"David A.","family":"Bereiter","sequence":"additional","affiliation":[{"name":"Departments of Neuroscience and"},{"name":"Surgery, Brown University\/Rhode Island Hospital, Providence, Rhode Island 02903; and"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"24","reference":[{"key":"B1","first-page":"513","volume":"40","author":"Belmonte C.","year":"1999","journal-title":"Invest. 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