Early establishment of lesion-insensitive mature barrelettes correspondingto upper lip vibrissae in developing mice

Vibrissae are tactile sense organs on the face of non-human mammals, and bu ild up topographical representations in the brainstem trigeminal sensory nu cleus called barrelettes. In the present study, we examined postnatal devel opment of barrelettes corresponding to upper lip vibrissae by cytochrome ox idase (CO) histochemistry. At nuclear regions corresponding to upper lip vi brissae, a few segregated barrelettes first appeared at postnatal day 2 (P2 ), and segregation became clear for most upper lip barrelettes at P4. Compa red with major barrelettes corresponding to mystacial vibrissae on the snou t, the development of segregated pattern formation for upper lip barrelette s was retarded by 1-2 days. When vibrissa-related patterns were examined 5 days after infraorbital nerve transection, upper lip barrelettes became obs cure in all mice lesioned at P1 and P2. Lesion-insensitive upper lip barrel ettes first emerged in a few mice lesioned at P3 (33%), and the percentage attained 100% at P6. This temporal transition from lesion-sensitive to lesi on-insensitive barrelettes was 3 days ahead of mystacial barrelettes. There fore, upper lip barrelettes achieve rapid development within a narrow time frame during the first postnatal week. The early and rapid establishment of lesion-insensitive, mature barrelettes can be interpreted as suggesting th e importance of oral sensory function in neonatal life. (C) 1999 Elsevier S cience Ireland Ltd. All rights reserved.