Spinal mechanisms
In addition to peripheral mechanisms, spinal mechanisms are thought to have an influencing role in phantom pains. Peripheral nerve injury can lead to the degeneration of C fibers in the dorsal horn of the spinal cord, and terminating A fibers may subsequently branch into the same lamina. If this occurs, A fiber inputs could be reported as noxious stimuli. Substance P, involved in the transmission of pain signals, is usually expressed by Aδ and C fibers, but following peripheral nerve damage, substance P is expressed by Aβ fibers. This leads to hyperexcitability of the spinal cord, which usually occurs only in the presence of noxious stimuli. Because patients with complete spinal cord injury have experienced phantom pains, there must be an underlying central mechanism responsible for the generation of phantom pains. Central mechanisms
Under ordinary circumstances, the genetically determined circuitry in the brain remains largely stable throughout life. For much of the twentieth century, it was believed that no new neural circuits could be formed in the adult mammalian brain, but experiments from the 1980s onward cast this into doubt. For instance, functional MRI studies in amputees have shown that almost all patients have experienced motor cortical remapping. The majority of motor reorganization has occurred as a downward shift of the hand area of the cortex onto the area of face representation, especially the lips. Sometimes there is a side shift of the hand motor cortex to the ipsilateral cortex.
Amitriptyline/perphenazine (Duo-Vil, Etrafon, Triavil, Triptafen) is a formulation that contains the tricyclic antidepressant amitriptyline and the medium-potency typical (first-generation) antipsychotic, perphenazine. In the United States amitriptyline/perphenazine is marketed by Mylan Pharmaceuticals Inc. and Remedy Repack Inc.

Medical uses
In the United States amitriptyline/perphenazine is indicated for the treatment of patients with:
Moderate-severe anxiety and/or agitation and depression
Depression and anxiety in association with chronic physical disease
Schizophrenia with prominent depressive symptoms

Adverse effects
Common (>1% incidence) adverse effects include
Sedation
Hypertension — high blood pressure. Neurological impairments (such as extrapyramidal side effects which include dystonia, akathisia, parkinsonism, muscle rigidity, etc.) Anticholinergic side effects such as:- Blurred vision
- Constipation
- Dry mouth
- Nasal congestionIncreased appetite
Weight gain
Nausea
Dizziness
Headache
VomitingUnknown frequency adverse effects include
Diarrhoea
Alopecia — hair loss
Photophobia
Pigmentation
Eczema up to exfoliative dermatitis
Urticaria
Erythema
Itching
Photosensitivity (increased sensitivity of affected skin to sunlight)
Hypersalivation — excessive salivation. Hyperprolactinaemia — elevated blood prolactin levels. This may present with the following symptoms:- Galactorrhea — the release of milk that is not associated with pregnancy or breastfeeding
- Gynaecomastia — the development of breast tissue in males
- Disturbances in menstrual cycle
- Sexual dysfunctionPigmentation of the cornea and lens
Hyperglycaemia — elevated blood glucose (sugar) levels. Hypoglycaemia — low blood glucose (sugar) levels. Disturbed concentration
Excitement
Anxiety
Insomnia
Restlessness
Nightmares
Weakness
Fatigue
Diaphoresis — excessive/abnormal sweating.Uncommon/Rare adverse effects include
Tardive dyskinesia, an often irreversible adverse effect that usually results from chronic use antipsychotic medications, especially the high-potency first-generation antipsychotics. It is characterised by slow (hence tardive), involuntary, repetitive, purposeless muscle movements. Neuroleptic malignant syndrome, a potentially fatal complication of antipsychotic drug use. It is characterised by the following symptoms:- Muscle rigidity
- Tremors
- Mental status change (e.g. hallucinations, agitation, stupor, confusion, etc.)