One way of doing this is to stop the breakdown of transmitters. This is just what the MAOI antidepressants do. They block the monoamine oxidase enzyme which breaks down the transmitter, so the next time an impulse comes along, there is more transmitter, a stronger message is passed, and activity in that part of the brain is increased. The important thing to remember is that antidepressants probably mainly work by correcting the effect of having too little transmitter. They have a much more specific way of working than just stimulating you.
Some antidepressants e.g. the tricyclics, block the reuptake of serotonin and noradrenaline.
Others mainly block the reuptake of just serotonin e.g. the SSRIs. The MAOIs block the monoamine enzyme which breaks down noradrenaline, serotonin and some other transmitters. They are Monoamine Oxidase Inhibitors. Unfortunately, the MAOIs also block an enzyme in the body which breaks down other compounds. One of these is an amino acid called tyramine.