Distribution of carbohydrate epitopes among disjoint subsets of leech sensory afferent neurons

Carbohydrate recognition plays an important role in the development of normal projections of sensory afferent neurons in the leech CNS. Four different carbohydrate epitopes are expressed by sensory afferents on their 130 kDa surface proteins: all sensory afferents share a common carbohydrate epitope (CE0) that helps them to enter and project diffusely across the synaptic neuropil; a restricted expression of three other carbohydrate epitopes (CE1, CE2, and CE3) serves to distinguish three subsets of sensory afferents. We examined the subsets of sensory afferents defined by their subset carbohydrate epitopes in the leech lip, skin, gut, and CNS. We established that the CE1, CE2, and CE3 subset epitopes define disjoint subsets of neurons by double labeling sensory afferents with monoclonal antibodies for different pairs of subset epitopes. We found that CE2 and CE3 afferents populate the lip and skin, but not the gut, and that these two subsets of sensory afferents have convergent projection patterns in the CNS. We found that CE1 afferents populate the gut and skin, but not lips; furthermore, their CNS projections diverge from those of CE2 and CE3 afferents. Our data fit the hypothesis that these carbohydrate epitopes are related to sensory modality of afferent subsets.