It is really not possible to discuss how many drugs work for symptoms of neuropathy, without understanding how neurons work and their anatomy.

This Wiki article is very good, and I suggest readers here read this before I get into the various types of drugs.

http://en.wikipedia.org/wiki/Neuron

Damage to the axon, can occur in PN. This can be autoimmune antibodies that attack the insulation, or a toxin. Some inflammatory cytokines produced by the body, may attack axons. There is a nice diagram on the Wiki link showing what an axon is. There are some very LONG axons in the body, so damage can happen anywhere along it. It can be severed or compressed. Sciatica is one common example.
This link explains the myelin sheath, how it may be injured and how it may regenerate:
http://en.wikipedia.org/wiki/Myelin

Statin drugs that are used to lower cholesterol, affect they myelin production in the body and the repair of myelin in nerves.
This article by Dr. Graveline MD explains this:
http://www.spacedoc.com/neuropathy_statins.htm
And this explanation explains why this family of drugs can lead to nerve damage both in the periphery and brain.

Also this article explains "inhibitory" actions some nerves have and this concept is important to understand. Inhibitory nerves are affected by benzodiazepines-- drugs like Xanax and Valium.
This link explains inhibitory functions of neurons.
http://en.wikipedia.org/wiki/GABAA_receptor

This is one reason why benzodiazepines work for PN pain in some patients. And why when discontinued, the inhibition is removed and activity is restored, often with very uncomfortable results. Benzos also are given following seizures, to reduce hyperexcitable neurons from starting up again. They can also be used to prevent certain types of seizures. When patients are taking them for anxiety or psychiatric reasons, and suddenly discontinue, a seizure may result. Hence, discontinuance of Benzos should be montiored carefully by a doctor. I have read in some places that it can take weeks to months to successfully wean off them. Klonopin is the worst offender in this regard.

While PNers here are mostly concerned about peripheral nerves, there are nerves in the brain too, that participate in the perception of pain. Some of the drugs used to treat symptoms of PN work in the brain mostly, and are the antidepressants.
One older drug, amitriptyline (and nortriptyline) have shown in a recent study to help peripheral nerve growth factors. But the newer SSRIs and SSNIs work mostly in the brain to affect the perception of pain. The pain loop in the brain is quite large and covers a large area while it is working.

This Medscape article illustrates this:
http://www.medscape.com/viewarticle/568704_9
If you are not a member of Medscape you can join easily for free. There are some wonderful articles there on many medical topics.
The SSRI drugs therefore work on this complex pain loop and may reduce pain for some patients. Cymbalta is the newest, and Lilly did studies with it to prove this effect so the FDA would approve it for pain. It however, is not the only one that works.
The antidepressants with dual actions like Cymbalta are Effexor and Savella. These seem to work better than the old SSRIs like Prozac.

I will be attending the big pain conference this spring that is given every year... and any new information on central pain research I typically pick up there. I'll bring that to this board when that conference is held. It is usually in April or May.(Michigan Head-Pain and Neurological Institute sponsors it)

Edit -- This Medscape link describes the various treatments for neuropathic pain.
http://www.medscape.org/viewarticle/754961
You may have to join which is free, to view this video, and you may have to pause the video when the slides come up, as they don't remain on the screen for long. But the graphics are very good and illustrate the pain pathways in the dorsal roots and spinal cord.