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Figure 9 | BMC Neuroscience

Figure 9

From: Hypocretin1/orexinA-immunoreactive axons form few synaptic contacts on rat ventral tegmental area neurons that project to the medial prefrontal cortex

Figure 9

Schematic drawing depicting the possible cellular mechanisms whereby Hcrt1/OxA activates neurons in the ventral tegmental area (VTA). Hcrt1/OxA-containing axons (Hcrt1/OxA-Ax) make asymmetric synapses (excitatory type) with VTA dendrites (Den), some of which (Fluorogold-labeled dendrite, FG-den) belong to neurons that project to the medial prefrontal cortex. In the Hcrt1/OxA axons, translucent small synaptic vesicles (ssv) release their content to the synaptic cleft, activating postsynaptic receptors, while granular vesicles (dense-cored vesicles, dcv and large dcv, ldcv) may release Hcrt1/OxA far from synaptic specializations and activate extrasynaptic receptors (Hcrt/Ox-R) by volume transmission at a distance and more slowly. Both mechanisms (synaptic and non-synaptic) are presumably involved in Hcrt/Ox actions in the VTA, thus contributing to cortical activation and wakefulness maintenance. bv, blood vessel; Hcrt/Ox-R, receptor binding Hcrt1/OxA; Hcrt1/OxA-T, Hcrt1/OxA-containing axon terminal; Hcrt1/OxA-V, Hcrt1/OxA-containing varicosity.

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