Laminar distribution of benzodiazepine receptors in visual cortex of adult rat

The characteristics and distribution of benzodiazepine receptors in individual layers of the visual cortex of adult rats were examined with the 3H-flunitrazepam binding technique employed on intact tissue slices. The different visual cortical layers were separated by cutting serial cryocut sections horizontally to the cortical surface and collecting the slices from each individual cortical layer under anatomical control. Highest benzodiazepine receptor densities were found in layers IV and VI. A moderate receptor density was detected in layer V (80% of highest density). The lowest receptor binding was observed in cortical layers I and II/III, still representing 66% of the highest receptor density. Binding affinities varied slightly between layers with dissociation constants somewhat higher for layers IV to VI in comparison to layers I and II/III. The distinct laminar pattern of benzodiazepine receptors in rat visual cortex suggests a differential neuromodulatory significance of these receptors in each individual cortical layer.