SYNAPTIC ARRANGEMENTS FORMED BY SEROTONIN-IMMUNOREACTIVE AXONS IN THE SUBSTANTIA GELATINOSA OF THE RAT SPINAL CORD

¹ Department of Veterinary Physiology, University of Edinburgh, Summerhall, Edinburgh EH9 1QH
² 1st Department of Anatomy, Semmelweis University Medical School, 1450 Tüzoltó utca 58, Budapest, Hungary
³ Department of Anatomy and Embryology, University of Nijmegen, P.O. Box 9101, 6500 Nijmegen, The Netherlands

Ultrastructural properties of serotonin-immunoreactive axons in the rat's substantia gelatinosa were examined in order to determine the synaptic arrangements that they form in the neuropil. Some immunoreactive varicosities formed synaptic associations with somata or dendrites suggesting that serotoninergic systems are capable of influencing the activity of these structures post-synaptically. No examples of axo-axonic synapses were found. Most varicosities, however, did not form identifiable synaptic junctions, but were closely associated with somata, dendrites or axons. Some of these associations may be functional but morphological evidence for this is lacking.