Neurotransmission
A similar process occurs in retrograde neurotransmission, where the dendrites of the postsynaptic neuron release retrograde neurotransmitters (e.g., endocannabinoids; synthesized in response to a rise in intracellular calcium levels) that signal through receptors that are located on the axon terminal of the presynaptic neuron, mainly at GABAergic and glutamatergic synapses.
Neurons form complex biological neural networks through which nerve impulses (action potentials) travel.
Neurotransmitters are spontaneously packed in vesicles and released in individual quanta-packets independently of presynaptic action potentials.
The vesicle exocytosis is thought to be driven by a protein complex called SNARE, that is the target for botulinum toxins.
The main model involves a receptor composed of multiple subunits that allow for coordination of ion preference.
[10] Action potential generation is proportionate to the probability and pattern of neurotransmitter release, and to postsynaptic receptor sensitization.
To release neurotransmitters, the synaptic vesicles transiently dock and fuse at the base of specialized 10–15 nm cup-shaped lipoprotein structures at the presynaptic membrane called porosomes.
[15] The neuronal porosome proteome has been solved, providing the molecular architecture and the complete composition of the machinery.
Some neurons can release at least two neurotransmitters at the same time, the other being a cotransmitter, in order to provide the stabilizing negative feedback required for meaningful encoding, in the absence of inhibitory interneurons.
It is found that the endocannabinoid anadamide and the cannabinoid WIN 55,212-2 can modify the overall response to sympathetic nerve stimulation, and indicate that prejunctional CB1 receptors mediate the sympatho-inhibitory action.
[19] One unusual pair of co-transmitters is GABA and glutamate which are released from the same axon terminals of neurons originating from the ventral tegmental area (VTA), internal globus pallidus, and supramammillary nucleus.
For example, enrichment analyses of different signaling pathways led to the discovery of a genetic association with intracranial volume.
