Evidence that large myelinated primary afferent fibers make synaptic contacts in lamina II of neonatal rats

Abstract

Choleragenoid horseradish peroxidase (B-HRP) is a retrogradely transported marker that selectively labels large cutaneous myelinated primary afferent fibers. In adults, B-HRP labelled large afferent fibers are seen to enter laminae III-V, and to a lesser extent lamina I, whereas lamina II, which is the major termination site of unmyelinated primary afferents, remains unlabelled. In the neonate, however, there is extensive B-HRP label in lamina II. The present study shows that the B-HRP labelled fibers in the neonate make many synaptic contacts in lamina II. This supports the idea that large primary afferent fibers in neonatal animals make synaptic contact with post-synaptic targets that pres..