Schizophrenia and bipolar disorder are both associated with dendritic spine loss in the brain, suggesting the two distinct disorders may share common pathophysiological features.
A dendritic spine is a small membranous protrusion from a neuron's dendrite that typically receives input from a single synapse of an axon. They act as storage sites for synaptic strength and help transmit electrical signals to the neuron's cell body.
Researchers at the McLean Hospital in Massachusetts and Harvard Medical School found the spines play a role in a variety of brain functions.
Previous studies have observed spine loss in the dorsolateral prefrontal cortices from individuals with schizophrenia.
To determine whether spine pathology happens in individuals with a disorder distinct from schizophrenia, the authors included patients with bipolar disorder in their study. Although the two conditions differ clinically, they share many features.
The authors analysed post-mortem human brain tissue from 14 individuals with schizophrenia, nine individuals with bipolar disorder and 19 unaffected control group individuals.
Average spine density was reduced in individuals with bipolar disorder by 10.5% and in individuals with schizophrenia by 6.5% compared with control patients.
There was a significant reduction in the average number of spines per dendrite in both individuals with schizophrenia, with 72.8 spines per dendrite, and individuals with bipolar disorder, with 68.9 spines per dendrite.
The control group individuals had 92.8 spines per dendrite, in comparison. Individuals with both conditions also had reduced average dendrite length compared with the control group.
"The current study suggests that spine pathology is common to both schizophrenia and bipolar disorder," said study author Glenn Konopaske.
"Moreover, the study of the mechanisms underlying the spine pathology might reveal additional similarities and differences between the two disorders, which could lead to the development of novel biomarkers and therapeutics."
Around one in 100 people will experience schizophrenia or bipolar disorder in their lifetime in the UK. Schizophrenia affects around 1% of the general population of the US.
The research was published in Jama Psychiatry.