Corneal representation within the trigeminal subnucleus caudalis and adjacent bulbar lateral reticular formation of the cat.
Corneal units in the trigeminal subnucleus caudalis and adjacent bulbar lateral reticular formation were studied in urethane-chloralose anesthetized cats. Corneal units were categorized into four classes: low-threshold corneal (LTC) units, high-threshold corneal (HTC) units, wide dynamic range (WDR) units with corneal input, and subnucleus reticularis ventralis (SRV) units with corneal input. Corneal receptive fields of these four classes of corneal afferent units consisted of 3-6 spots. Mechanical thresholds of LTC units were lower than 30 mg (2.6 g/mm2) and were comparable to the sensory threshold of the human cornea measured in patients with cataract. Mechanical thresholds of the other 3 classes of corneal afferent units were well above the pain threshold in the human cornea. LTC units were located in the magnocellular layer of trigeminal subnucleus caudalis and were intermingled with cutaneous low-threshold mechanoreceptive units. HTC units were coexistent with nociceptive specific units in the marginal layer and in the outer zone of substantia gelatinosa. WDR units with corneal input were found in the lateral part of trigeminal lamina V equivalent, which corresponds to the lateral part of subnucleus reticularis dorsalis. These 3 classes of corneal units were found at a level 2.7-3.5 mm caudal to the obex. SRV units were found in the dorsolateral part of SRV along the entire length of the medulla oblongata caudal to the obex. These results support the suggestion that either nonpainful sensation or pain can be evoked from the cornea.
Nishida
Y
Y
Department of Physiology, Medical College of Shiga, Otsu, Japan.
Yokota
T
T
D000344:Afferent Pathways / Q000033:anatomy & histology / Q000502:physiology; D000818:Animals; D002415:Cats; D003315:Cornea / Q000294:innervation*; D004594:Electrophysiology; D010812:Physical Stimulation; D012154:Reticular Formation / Q000033:anatomy & histology* / Q000502:physiology; D011984:Sensory Receptor Cells / Q000033:anatomy & histology / Q000502:physiology; D012684:Sensory Thresholds / Q000502:physiology; D014275:Trigeminal Caudal Nucleus / Q000033:anatomy & histology* / Q000502:physiology