Figure 3.

Presynaptic T-type Ca²⁺ channels regulate neurotransmission. A. Presynaptic T-type channels in the superficial lamina of the dorsal horn of the spinal cord. a. Top: Recordings of spontaneous miniature excitatory post-synaptic currents (mEPSCs) from lamina I neurons (Control) and after application of the AMPA receptor antagonist, NBQX (left) or the T-type channel antagonist, TTA-P2 (right). Bottom: Cumulative distributions of events amplitude (left) and frequency (right) in control and TTA-P2 conditions demonstrating the presynaptic regulation by T-type channels of the spontaneous vesicular release. b. Transmission electron microscopy images from pre-embedded GFP silver staining of spinal cord dorsal horn coronal sections from knocking mice expressing GFP within an extracellular loop of the Cav3.2 channels. Red dots represent GFP antibody complexes around individual silver dot (25 mm). Areas in yellow are presynaptic regions containing dense synaptic vesicles. Green area is a postsynaptic region recognized by the postsynaptic density. Right panel is a magnification of the box in the left image. B. Presynaptic T-type channels at excitatory synapses in the entorhinal cortical layer III. a. Typical recordings of mEPSCs performed in slices from Hcn1^−/− KO mice (devoid of the type cationic h current activated upon hyperpolarization) in control condition and upon application of the T-type channel antagonist (TTA-A2, 500nM). As demonstrated by the cumulative probability graph (bottom), T-type channel blocker decreases the mEPSC frequency. b. Electron micrographs using pre-embedding double-labeling methods showing immunoreactivity for Hcn1 (peroxidase reaction product) and Cav3.2 (immunoparticles) channels in wild-type sections (WT) of entorhinal cortex. Immunogold particles for Cav3.2 were absent in Cav3.2^−/− sections. b, axon terminals; s, dendritic spines; Den, dendrite. Scale bars: 0.2μm. Modified with permission from: (A.a.)⁹¹; (A.b.)⁵⁸; (B)⁵⁷.