Glycine-mediated neurotransmission results from activation of the inhibitory glycine receptor (GR). Our present knowledge on the biological role of central GRs is in part based on results from anatomical distribution studies in rodents and humans, whereas distribution studies in other mammals are lacking. The aim of the present study was to provide a detailed anatomical distribution of GR binding sites in the cat CNS. Appropriate autoradiographic assays conditions were established in saturation binding experiments performed on slide-mounted spinal cord sections incubated with increasing concentrations of [3H]strychnine. Nonspecific binding was determined with glycine (10mM). [3H]strychnine (10 nM) binds with high affinity (KD= 7.3±0.6 nM; Bmax= 149±9 fmol/mg tissue) to cats spinal cord sections. Analysis of the autoradiographic data reveals a discrete localization of glycine binding sites in the cat CNS. Examination of the gross regional distribution shows that the density of GRs decreases progressively as one ascends in the neuraxis. High density of sites were detected in the gray matter of the spinal cord, medullary nuclei (i.e., cuneatus and gracilis nuclei) and in the pons. Lower levels of binding were seem in the diencephalon (i.e., nucleus centralis thalami) and still lower levels in the telencephalon (i.e., amygdala). This distribution seems to correspond well with that found in rat, mouse and human brain in previous studies.

In conclusion, under the conditions described [3H]strychnine labels a population of binding sites with a distribution in the cat CNS closely resembling that previously described for GR in other mammals. Supported by MEC (BFU2006-06598).