Compare and contrast classic, retrograde and volume neurotransmission. Note any specific neurotransmitters that are produced each way. Classic neurotransmission involves an electrical process in which electrical impulses sent by neurons travel from one part of a cell to another part of the cell through their axons; classic neurotransmission occurs when a neuron carries a neurotransmitter to the receptor of a second neuron (Stahl, 2013). Retrograde neurotransmission occurs when postsynaptic neurons communicate with presynaptic neurons from the bottom to top. Neurotransmitters that are produced specifically as retrograde neurotransmitters include endocannabinoids, nitric oxide, and nerve growth factor. Volume neurotransmission occurs when neurons send chemical messengers to other neurons, and they may spill over to sites distant from its own synapse through diffusion. Neurotransmitters that are produced specifically in volume neurotransmission include dopamine and monoamine autoreceptors. Provide a brief overview of signal transduction cascades. Chemical neurotransmission triggers signal transduction cascades, which starts with numerous molecules being passed on to the first neurotransmitter messenger, and moves on to second, third, fourth and more messengers (Stahl, 2013). Specific molecules carry specific messages to the next specialized molecule, until the message reaches its destination. Four of the most important signal transduction cascades in the brain include G-protein-linked systems, ion-channel-linked systems, hormone-linked systems, and neurotrophin-linked systems. Signal transduction begins with binding of a first messenger, leading to enzymatic formation of second messengers. This can cause activation of third and fourth messengers, often phosphoproteins. Genes may be activated, causing a synthesis of new proteins, ultimately altering the neuron’s functions. The balance between neurotransmitter activity determines the degree of chemical activity that plays a role in forming gene expression and synaptogenesis. Discuss whether or not you think drug companies should be permitted to advertise their products (prescription medication).