ORIGINS AND ULTRASTRUCTURAL DISTRIBUTION OF SEROTONERGIC FIBERS OF THE SPINAL DORSAL HORN IN THE RAT——A STUDY WITH COMBINED METHOD OF HRP AND IMMUNOCYTOCHEMISTRY AND IMMUNOELECTRON MICROSCOPIC OBSERVATION / 解剖学报

ABSTRACT

Origin and ultrastructural characteristics of serotonergic fibers of the spinal dorsal horn in the rat have been confirmed by means of a combined method of HRP and immunocytochemistry and immunoelectron microscopic observation. The results showed that serotonergic axonal terminals in the spinal dorsal horn come mainly from nucleus raphe magnus and the ventral part of the reticular formation of medulla oblongata. Serotonin immunoreactive positive structures of the spinal dorsal horn have been found in lamina Ⅰ (marginal zone) and lamina Ⅱ (substantia gelatinosa) as fine myelinated and unmylinated fibers. There were mainly axo-axonic synapses between the labeled and nonlabeled terminals. The labeled terminals were presynaptic or postsynaptic element. Axo-dendritic synapses were rarely found. The non-synaptic releasing figures have not been found. Based on the ultrastructural characteristics the authors suggest that in performing analgesia role the serotonergic system in the spinal dorsal horn might influence directly or indirectly the excitability of interneurons and inhibit directly the nerve impulses of primary afferents by means of synaptic connections instead of non-synaptic releasing manner.