ULTRASTRUCTURAL-STUDY ON NOS-IMMUNOREACTIVE NERVE-TERMINALS IN THE RAT CELIAC GANGLION

NERVE terminals immunoreactive for nitric oxide synthase (NOS) were st udied in the rat coeliac-superior mesenteric ganglion by electron micr oscopy using a preembedding immunostaining method. The immunoreactive material was distributed in the axoplasmic matrix and was not specific ally associated with any subcellular organelle. In most NOS-immunoreac tive axon terminals numerous small clear vesicles (35-50 nm) were seen , and in some terminals a small number of large granular vesicles (70- 120 nm) were intermingled with small clear vesicles. Most NOS-immunore active axon terminals formed axodendritic as well as axe-somatic synap ses with non-immunoreactive ganglion neurones, and axo-axonic contacts were very scarce. These results suggest that NO may be released at th e synaptic sites from the axon terminals and may affect ganglion neuro nes.