title: Transection of the infraorbital nerve in newborn hamsters alters the somatosensory but not the visual representation in the superior colliculus.
abstract: The experiments described in this report were designed to determine whether changing the somatosensory representation in the deep laminae of the hamster's superior colliculus would result in a corresponding reorganization in the visual map in the overlying superficial layers. The somatosensory representation was altered by transecting the infraorbital (IO) nerve on the day of birth. This trigeminal branch supplies, among other targets, the snout and mystacial vibrissa follicles. These peripheral structures compose a major portion of the somatosensory representation in the deep collicular laminae. The effects of these lesions were assessed in anatomical and physiological experiments when the animals reached adulthood. Retrograde tracing with true blue demonstrated a 48% reduction in the number of trigeminocollicular neurons in the partially deafferented subnucleus interpolaris (the main source of trigeminal input to the rodent colliculus--e.g., Killackey and Erzurumlu: J. Comp. Neurol. 201:221-242, '81), but anterograde tracing with horseradish peroxidase (HRP) and wheat germ agglutinin-conjugated HRP showed that the terminal field of the trigeminocollicular projection from the deafferented subnucleus was essentially normal. This pathway terminated as a series of patches along the border between the stratum griseum intermediale and stratum album intermedium and encompassed approximately 75% of the rostrocaudal extent of the colliculus. The electrophysiological experiments revealed a marked change in somatosensory collicular topography. There was an under-representation of the vibrissae and the entire IO peripheral field in the deep laminae of the nerve-damaged animals, and neurons with trigeminal ophthalmic and mandibular receptive fields were recorded from portions of the colliculus in which only whisker-sensitive neurons would be normally isolated. There were no corresponding changes in the organization of the visual representation. These results support the conclusion that the organization of the visual representation in the superficial laminae and the organization of the somatosensory map in the deep layers of the mammalian superior colliculus follow independent developmental programs.
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001370:Axonal Transport; D006224:Cricetinae; D004558:Electric Stimulation; D006735:Horseradish Peroxidase; D013003:Somatosensory Cortex / Q000502:physiology*; D013477:Superior Colliculi / Q000502:physiology*; D014276:Trigeminal Nerve / Q000502:physiology*; D014785:Vision, Ocular; D014795:Visual Pathways / Q000502:physiology; D014796:Visual Perception
chemical_list: D006735:Horseradish Peroxidase