Postnatal development of [3H]flunitrazepam and [3H]strychnine binding sites in rat spinal cord localized by quantitative autoradiography.

The development of inhibitory receptors in rat spinal cord was investigated by autoradiography using [3H]flunitrazepam as a ligand for benzodiazepine receptors and [3H]strychnine as a ligand for glycine receptors. The development of benzodiazepine receptors follows a similar pattern at all levels of the spinal cord. The density of [3H]flunitrazepam binding sites is already high at birth, increases 2-fold by days 3-7 and thereafter declines to levels already present at birth. In contrast, [3H]strychnine binding sites are weakly expressed at birth and increase up to 7-fold between days 4 and 21. A craniocaudal gradient in the development of glycine receptors is not apparent. However, maturation of [3H]strychnine binding in the ventral horn precedes that in the dorsal horn for 3-4 days. In summary, the developmental expression of these two inhibitory receptors in the spinal cord appears to be regulated differently.