Figure 5.

Immunostaining for CB₁ cannabinoid receptor is reduced in the hippocampus of epileptic patients, particularly in the inner molecular layer of the dentate gyrus (DG). A, Light micrograph illustrating profound CB₁ immunoreactivity throughout the human hippocampal formation of control subjects. By using a highly sensitive guinea pig antibody for CB₁, the immunostaining highlights the different layers and subfields of the hippocampus according to the spatial arrangements of excitatory pathways. B, C, Although the general pattern of CB₁ immunostaining is similar in the nonsclerotic and sclerotic epileptic hippocampi, the density of CB₁ immunoreactivity is reduced in several layers. D–F, The most striking differences between the control and the epileptic hippocampi are visible in the dentate gyrus. The very dense neuropil-like labeling in the inner third of stratum moleculare (str. mol.) is evident in the control sample (D), but it is less so in the nonsclerotic epileptic sample (E), and it disappears almost completely in the sclerotic epileptic samples (F). In contrast, the stratum granulosum (str. gr.) and the hilus remained similar in all three experimental groups. Scattered cell bodies of GABAergic interneurons were also stained for CB₁ (labeled by arrows), but conversely, there was no striking difference either in their distribution pattern or in their number between the control and epileptic human samples. Scale bars: A–C, 500 μm; D–F (in F), 100 μm.