Abnormal melatonin secretion not linked to pineal volume in BD patients
MedWire News: Results from a French study suggest that abnormal melatonin secretion in patients with bipolar disorder (BD) is not associated with abnormal volume of the pineal gland.
"Abnormalities of melatonin secretion, and in particular hypersensitivity to light (nocturnal bright light suppression of melatonin), have been proposed as a heritable trait marker of BD," observe Josselin Houenou (University Paris-East) and colleagues in the Journal of Affective Disorders.
As BD patients often show reduced levels of melatonin, which is secreted by the pineal gland, the researchers investigated whether BD patients have smaller pineal glands than individuals without the condition.
They recruited 20 outpatients with bipolar I or II disorder, aged 18-65 years, and 20 mentally healthy individuals (controls) who were matched for age, gender, and laterality. None of the participants had a history of alcohol abuse or dependence.
Three-dimensional (3D) magnetic resonance imaging was used to assess total pineal volume. As a reference value, the team also estimated total pineal volume using the classical Hasegawa method, with the formula 0.5 × H × L × W, where H is the maximum height, L the maximum length, and W the maximum width of the gland.
As large asymptomatic pineal cysts (type 3) might impair the estimation of true parenchymal pineal volume, four BD patients and four controls with this type of cyst were excluded from the analysis.
Among the remaining participants, the researchers found no significant differences in total pineal volume between BD patients and controls using 3D MRI, at 115.3 and 110.4 mm3, respectively.
There were also no significant differences between BD patients and controls when total pineal volume was estimated using the Hasegawa method, at 93.4 and 106.7 mm3, respectively.
The lack of any significant difference in total pineal volume between the groups remained after accounting for total intracranial volume, the researchers note.
Houenou and team conclude: "These results indicate that the putative dysfunction of the pineal gland in BD could be not directly related to an abnormal volume of the pineal gland; any such dysfunction is thus not correlated with the parenchymatous volume but presumably with some other functional aspect of the gland."
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By Mark Cowen