Abstract
Abstract A morphological description is given of a small, but well defined, collection of neurons in the frog medulla located at the rostral end of the dorsal column. Anatomical and electrophysiological data reveal that collaterals of primary afferent fibers terminate in this area which can be defined as a primordial dorsal column nucleus (DCN). Thus, ascending dorsal column axons come into close apposition with neurons in the DCN and afferent volleys from cutaneous and mixed nerves evoke a large negative (N-) wave on the surface of the medulla corresponding to the anatomically defined DCN. The N-wave reached its greatest amplitude within the depth of the nucleus. The existence of primary afferent depolarization (PAD) in the frog DCN was demonstrated by means of a surface positive (P-) wave and more directly by increased excitability of dorsal column terminals. Depression of DCN synaptic activity as manifested by the ability of an afferent volley to reduce the effectiveness of a succeeding volley to produce thalamic potentials was correlated with PAD. It is concluded that synaptic mechanisms exist in the frog DCN which are similar to those present in the mammalian dorsal column nuclei.
Published Version
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