A biochemical model of chronic trigeminal facial pain with elevated substance P (SP) and co-dysfunctional dopamine (DA), norepinephrine (NE) and purinergic systems is proposed. The serotonergic system is hypoactive as judged by low 5 hydroxyindoleacetic acid (5HIM). In distinction, intracerebral opioids may not be dysfunctional in facial pain as measured by normal levels of beta endorphin (BE). The neuropeptides somatostatin (SOM), cholecystokinin (CCK), met and leu-enkephalin (MENK, LENK) have very small picogram concentrations in these pain patients, but no definite conclusion can be reached on their role in trigeminal pain, alone or with monoamines, because of the small numbers, both sample size and concentrations. Interpretive obstacles to such human neurochemical studies suggest that future work might move to human clinical trials comodulating SP down, inhibitory peptides (SOM, CCK) up, and enhancing monoamine systems.
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