Figure 6.

Density of glutamatergic axon terminals bearing presynaptic CB₁ cannabinoid receptors is decreased in the epileptic human hippocampus. A–C, The electron micrograph demonstrates a robust accumulation of strong CB₁ immunoreactivity within axon terminals in the inner third of the stratum moleculare of control subjects. These CB₁-positive boutons (b) form the classic asymmetric synapses (arrowheads) with an extensive postsynaptic density on dendritic spine heads. In control samples, nearly all axon terminals with asymmetric synapses are positive for CB₁, whereas in the nonsclerotic (B) and sclerotic (C) samples, the number of CB₁-positive asymmetric synapses drops noticeably. Note that a lack of staining does not necessarily mean the complete absence of CB₁ receptors, but it means that the antigen level fails to reach detection threshold in these CB₁-negative boutons (depicted by asterisks). Scale bar, 0.5 μm.