Extending David Horrobin’s membrane phospholipid theory of schizophrenia: Overactivity of cytosolic phospholipase A2 in the brain is caused by overdrive of coupled serotonergic 5HT2A/2C receptors in response to stress

Abstract

David Horrobin’s membrane phospholipid theory of schizophrenia has held up well over time because his therapeutic prediction that dietary supplementation with eicosapentaenoic acid (EPA) would have a therapeutic effect has been partially verified and undergoes continued testing. In the final version of his theory, he hypothesized that there was hyperactivity of phosphoslipase A2 (PLA2) or a related enzyme but did not explain how the hyperactivity came about. It is known that serotonergic 5HT2A/2C receptors are coupled to PLA2, which hydrolyzes both arachidonic acid (AA) and EPA from diacylglycerides at the sn-2 position. In this paper, Horrobin’s theory is combined with a previously published theory of chronic stress in which it was hypothesized that a disinhibited dorsal raphe nucleus, the principal nucleus of the serotonergic system, can organize the neuropathology of diseases such as migraine, hypertension, and the metabolic syndrome. The new or combined theory is that schizophrenia is a disease of chronic stress in which a disinhibited DRN causes widespread serotonergic overdrive in the cerebral cortex. This in turn causes overdrive of cPLA2 and both central and peripheral depletion of AA and EPA. Because EPA is present in smaller amounts, it falls below threshold for maintaining an intracellular balance between AA-derived and EPA-derived second messenger cascades, which leads to abnormal patterns of neuronal firing. There are two causes of neuronal dysfunction: the disinhibited DRN and EPA depletion. Schizophrenia is statistically associated with metabolic syndrome, hypertension, and migraine because they form a cluster of diseases with similar pathophysiology.The theory provides an explanation for both the central and peripheral phospholipid abnormalities in schizophrenia. It also explains the role of stress in schizophrenia, elevated serum PLA2 activity in schizophrenia, the relationship between untreated schizophrenia and metabolic syndrome, and the therapeutic rationale for EPA.