Cutaneous afferent fibre collaterals in the dorsal columns of the cat.

Abstract

Microelectrode recordings were made from cutaneous afferent fibre collaterals in the lumbar dorsal columns of cats, which were antidromically excited from the dorsal column at C2. The following types of cutaneous afferent unit have axon collaterals which ascend the dorsal columns to the dorsal column nuclei; hair follicle units Types G (36.4%) and T (31.8%), slowly-adapting units Types I (8.3%) and II (5.3%) pad mechanoreceptor units (8.3%) and a few high threshold units. The conduction velocities of dorsal column collaterals were measured. All collaterals had slower velocities than corresponding peripheral nerve fibres and the degree of slowing was determined by the class of afferent unit, with the pad units slowing the least and Type T hair follicle units the most. The differential slowing was confirmed by recording compound action potentials from various parts of dorsal column-peripheral nerve pathways.