Dendritic spine density also reduced in bipolar disorder

By Eleanor McDermid, Senior medwireNews Reporter

Patients with bipolar disorder have significant dendritic spine loss in the dorsolateral prefrontal cortex (DLPFC), postmortem findings show.

The phenomenon has been previously reported in patients with schizophrenia. But given the differences between the two disorders, researcher Glenn Konopaske (McLean Hospital, Belmont, Massachusetts, USA) and co-workers had hypothesised that any spine loss in patients with bipolar disorder would, at the most, be intermediate between that observed in schizophrenia patients relative to control participants.

Instead, they found that bipolar disorder patients had the largest reduction in mean spine density relative to controls, at 10.5%. In schizophrenia patients, spine density was reduced by 6.5%, which just missed statistical significance.

However, the team notes that the size of the reduction in schizophrenia is markedly smaller than the 23% reported in a previous study, “suggesting variability in spine pathology” in patients with schizophrenia.

The analysis included postmortem tissue from 14 patients with schizophrenia, nine with bipolar disorder and 19 controls who were mentally healthy when they died.

Both patient groups had significant reductions in the mean number of spines per dendrite relative to controls, at 25.8% for the bipolar group and 21.6% for the schizophrenia group. They also had significantly reduced mean dendrite length, at 18.6% and 18.3%, respectively.

Although schizophrenia and bipolar disorder are often “viewed as distinct entities”, the researchers note that “they share many features, suggesting that pathophysiological commonalities exist.”

The current findings “suggest that DLPFC spine loss may be a shared pathophysiological feature of both disorders”, they write in JAMA Psychiatry.

The team believes that antipsychotic use did not explain the spine loss. There were no differences between patients who used antipsychotics in their last year of life and those who did not, and antipsychotic administration in rats did not influence spinal density. Lithium use was not related to spinal density in either patient group; however, it was associated with longer dendrites in schizophrenia patients.

“[T]he study of the mechanisms underlying the spine pathology might reveal additional similarities and differences between the 2 disorders, which could lead to the development of novel biomarkers and therapeutics”, conclude Konopaske et al.

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