Journal of Neuroscience, Vol 14, 774-784, Copyright © 1994 by Society for Neuroscience
Immunocytochemical evidence that neurotensin is present in glutamatergic neurons in the superficial dorsal horn of the rat
AJ Todd, RC Spike, RF Price and M Neilson
Department of Anatomy, University of Glasgow, United Kingdom.
In order to determine whether glutamate is enriched in neurotensin-
containing axons in the superficial dorsal horn of the rat spinal cord, we
have carried out preembedding immunocytochemistry with an antiserum to
neurotensin and then used a postembedding immunogold method with antiserum
to glutamate. The immunogold label (corresponding to glutamate-like
immunoreactivity) over 40 neurotensin-immunoreactive boutons in laminae I
and II of the lumbar dorsal horn was compared with that over nearby axons
that formed asymmetrical or symmetrical synapses. In addition, for 20 of
these boutons, the labeling was compared with that over mossy and parallel
fiber terminals (both of which are thought to use glutamate as a
transmitter) from sections of cerebellum that had been processed together
with those of spinal cord. Glutamate-like immunoreactivity was consistently
high over neurotensin- immunoreactive boutons relative to most surrounding
profiles. Immunostaining over these boutons was slightly (11%) lower than
that over matched terminals that formed asymmetrical synapses, but
considerably higher than that over the terminals that formed symmetrical
synapses. The level of glutamate immunoreactivity in
neurotensin-immunoreactive boutons in dorsal horn was similar to that in
cerebellar parallel fiber terminals, but significantly lower than that in
mossy fiber terminals. These results suggest that glutamate is a
transmitter used by neurotensin-immunoreactive axons in the dorsal horn,
and since these axons are thought to be largely or entirely derived from
neurotensin-containing neurons in laminae I-III, they provide
immunocytochemical evidence for a population of excitatory glutamatergic
neurons in this region.