Retrograde tracing with
rhodamine fluorescent
microspheres combined with
fluorescein immunolabelling of
methionine-enkephalin showed the presence of
enkephalin-like material in neurons of the inferior mesenteric ganglion (sympathetic prevertebral
ganglion) projecting to the distal colon in cat. Two weeks after injecting the
microspheres into the wall of the distal colon, the inferior mesenteric
ganglion was dissected out and incubated for 24 hours in a
colchicine-containing culture medium in order to facilitate the detection of
enkephalins in the
soma of
ganglion neurons. It was observed that retrogradely labelled
ganglion cells contained
enkephalin-like immunoreactive material. These
ganglion cells corresponded to
enkephalin-like postganglionic neurons, the terminals of which were located inside the wall of the distal colon. These
enkephalin-like neurons were numerous and scattered throughout the
ganglion. Sometimes
enkephalin-like immunoreactive fibers, probably originating from spinal preganglionic neurons, ran close to immunoreactive and non-immunoreactive retrogradely labelled
ganglion cells. This suggests that
enkephalin-like immunoreactive fibers may make synaptic connections with
enkephalin-like and non-
enkephalin-like postganglionic neurons projecting to the distal colon. The present study establishes for the first time the existence of an
enkephalin-like postganglionic pathway to the digestive tract originating from a sympathetic prevertebral
ganglion. This finding indicates that the enkephalinergic innervation of the cat digestive tract may have at least two possible sources: (i) the sympathetic prevertebral ganglia; and (ii) the enteric nervous ganglia.