Perspective Graphics as a Means of Portraying the Distribution of Radiolabelled Ligands in the Spinal Cord — A Pilot Study Using Intrathecally Administered ³H Morphine

Abstract

Tritium-labelled morphine sulphate was injected into the lumbar (L4-5) subarachnoid space of an adult male baboon. Three hours after injection, the animal was sacrificed. Using quantitative light microscopic autoradiographic mapping techniques, contour and perspective diagrams were prepared that described the position of radiolabel and by inference the distribution of morphine binding sites within the spinal cord. High concentrations of 3 H was found in the medial regions of laminae I, II (substantia gelatinosa) and III of the dorsal horns. Smaller, but significant levels were seen bilaterally in the spinal anterolateral quadrant. Minimal 3 H activity was seen in the remainder of the spinal cord with the lowest level being recorded in the spinal canal. Perspective graphics proved a precise and attractive method for locating the position and quantifying the concentration of radio la bel in baboon spinal cord.

Differential antinociceptive effects of spinal opioids on foot withdrawal responses evoked by C fibre or Aδ nociceptor activation

“…This potency distinction may be due simply to differential access of the drug to receptors at various depths in the spinal cord. With intrathecal injection, a concentration gradient is established from the cerbrospinal fluid (CSF) toward the centre of the cord (Gregory et al , 1986). In addition, the distribution, and hence part of the potency of drugs within the spinal cord will depend on its lipid solubility and the local lipophilicity/hydrophylicity (McQuay et al , 1989).…”