Journal of Neuroscience, Vol 4, 2303-2310, Copyright © 1984 by Society for Neuroscience
Characterization and localization of adenosine receptors in rat spinal cord
JD Geiger, FS LaBella and JI Nagy
Adenosine A1 receptors were characterized in membranes from rat dorsal and
ventral spinal cord using [3H] cyclohexyladenosine [( 3H]CHA) and compared
with those in brain. For determination of anatomical loci of adenosine A1
receptors in the dorsal and ventral spinal cord, various lesions were
employed, including kainic acid injections directly into the lumbar dorsal
spinal cord, spinal cord hemitransections, dorsal rhizotomies, and neonatal
capsaicin treatment. In control animals a single high affinity binding
component was observed in dorsal and ventral spinal cord with KD values of
2.3 and 2.6 nM and Bmax values of 170 and 123 fmol/mg of protein,
respectively. In comparison, [3H]CHA binding to whole brain membranes
exhibited KD and Bmax values of 2.3 nM and 301 fmol/mg of protein,
respectively. The IC50 values for CHA, (-)- phenylisopropyl adenosine,
adenosine-5'-ethylcarboxamide, 2- chloroadenosine, (+)-phenylisopropyl
adenosine, and theophylline to displace [3H]CHA were 3.6, 2.3, 15, 17, 21,
and 30,500 nM for dorsal horn and 5.1, 2.7, 9.8, 24, 25, and 21,000 nM for
ventral horn. The potencies of the various ligands are similar to those
found for brain tissue. Injection of kainic acid directly into the dorsal
spinal cord significantly reduced specific [3H]CHA binding by 33% in this
tissue when compared to values from saline-injected control animals. This
decrease was accompanied histologically by the depletion of intrinsic
neuronal cell bodies and extensive gliosis at the injection site. Terminals
of descending or primary afferent systems appear not to contain
[3H]CHA-binding sites since lesions which interrupt these systems failed to
alter the levels of [3H]CHA receptors in denervated spinal cord
tissue.(ABSTRACT TRUNCATED AT 250 WORDS)