The Journal of Neuroscience, May 1, 1999, 19(9):3545-3555
NK-1 Receptor Immunoreactivity in Distinct Morphological
Types of Lamina I Neurons of the Primate Spinal Cord
X. H.
Yu1,
E.-T.
Zhang3,
A. D.
Craig3,
R.
Shigemoto4,
A.
Ribeiro-da-Silva1, 2, and
Y.
De
Koninck1
1 Department of Pharmacology and Therapeutics, and
2 Anatomy and Cell Biology, McGill University,
Montréal, Quebec, H3G 1Y6 Canada, 3 Division of
Neurobiology, Barrow Neurological Institute, Phoenix, Arizona 85013, and 4 National Institute for Physiological Sciences,
Okazaki 444-8585, Japan
In cat and monkey, lamina I cells can be classified into three
basic morphological types (fusiform, pyramidal, and multipolar), and
recent intracellular labeling evidence in the cat indicates that
fusiform and multipolar lamina I cells are two different types of
nociceptive cells, whereas pyramidal cells are innocuous thermoreceptive-specific. Because earlier observations indicated that
only nociceptive dorsal horn neurons respond to substance P (SP), we
examined which morphological types of lamina I neurons express
receptors for SP (NK-1r).
We categorized NK-1r-immunoreactive (IR) lamina I neurons in serial
horizontal sections from the cervical and lumbar enlargements of four
monkeys. Consistent results were obtained by two independent teams of
observers. Nearly all NK-1r-IR cells were fusiform (42%) or multipolar
(43%), but only 6% were pyramidal (with 9% unclassified). We
obtained similar findings in three monkeys in which we used double-labeling immunocytochemistry to identify NK-1r-IR and
spinothalamic lamina I neurons retrogradely labeled with cholera toxin
subunit b from the thalamus; most NK-1r-IR lamina I spinothalamic
neurons were fusiform (48%) or multipolar (33%), and only 10% were
pyramidal. In contrast, most (~75%) pyramidal and some (~25%)
fusiform and multipolar lamina I spinothalamic neurons did not display
NK-1r immunoreactivity.
These data indicate that most fusiform and multipolar lamina I neurons
in the monkey can express NK-1r, consistent with the idea that both
types are nociceptive, whereas only a small proportion of lamina I
pyramidal cells express this receptor, consistent with the previous
finding that they are non-nociceptive. However, these findings also
indicate that not all nociceptive lamina I neurons express receptors
for SP.
Key words:
dorsal horn; spinothalamic; nociception; substance P; monkey; functional specialization
Copyright © 1999 Society for Neuroscience 0270-6474/99/1993545-11$05.00/0