Sensory nerve endings of the incisive papilla of rat hard palate studied by peroxidase cytochemical methods.

This study utilized peroxidase cytochemical methods to survey and analyze the distribution, morphology, and functional relationship of the various components of sensory nerve endings in a focal region of the anterior hard palate (incisive papilla) of the rat. The studies included an anatomical survey of this relatively unknown oral structure, confirmation of the trigeminal origin (labeled by retrograde axonal transport of WGA-HRP injected into the incisive papilla) of the sensory nerve endings, and a complete analysis of the distribution of these nerve endings (labeled by anterograde axonal transport of HRP or WGA-HRP injected into the trigeminal ganglion). Three methods of fixation and two methods of cytochemical reaction were used for selection of an optimal technique for these studies. The results showed distinct patterns of peroxidase-labeled sensory nerve endings at three regions of the incisive papilla: a) dome region (ventral), where labeled nerve endings formed three parallel channels in association with three surface ridges; b) chemosensory corpuscle enriched region (medial to incisive canal), where 82% of the 30-40 chemosensory corpuscles were labeled; and c) lateral labium (lateral to incisive canal), where labeled nerve endings formed a circumscribed network guarding the orifice of incisive canal. The discrete organization of multiple sensory nerve endings in the incisive papilla of the rat may provide an easily accessible model system for various studies in sensory physiology.