Feline 'C'-type terminals possess synaptic sites associated with a hypolemmal cistern and Nissl body

Previous findings suggest that axosomatic 'C'-type terminals on rat spinal motoneurones possess 'active' synaptic sites associated with the characteristic subsynaptic cistern and postsynaptic Nissl body, but 'C'-terminals in cat do not. A re-examination of feline 'C'-terminals undertook to compare the synaptic ultrastructure in aldehyde-fixed material stained by either osmium or ethanolic phosphotungstic acid (E-PTA). In agreement with previous findings osmicated cat 'C'-terminals failed to reveal synaptic complexes in regions possessing the subsynaptic cistern ('cisternal regions'). In contrast, cisternal regions of E-PTA stained 'C'-terminals exhibited a linear array of presynaptic dense projection all opposed by a single extended postsynaptic density which abutted directly onto both postsynaptic membrane and the cistern. This close topographical relationship is suggested to be functionally significant in the trans-synaptic trophism previously demonstrated for feline 'C'-terminals.