Seasonal Independence of Low Prolactin Concentration and High Spontaneous Eye Blink Rates in Unipolar and Bipolar II Seasonal Affective Disorder

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Abstract
• Twenty-four subjects with seasonal affective disorder (SAD: bipolar II, n = 14; unipolar, n = 10) and 20 normal controls were assessed for early follicular basal serum prolactin (PRL) concentration in winter and summer. Luteal basal PRL concentration was assessed in winter. The PRL values represented the mean of three values derived during a 45-minute period. A subset of 17 subjects with SAD and 11 controls were also assessed for spontaneous eye blinking via a polygraphic recording in winter and summer. In winter, compared with controls, subjects with SAD were characterized by significantly lower follicular (10.1 vs 4.5 μg/L, respectively)and luteal (14.4 vs 7.4 μg/L, respectively) PRL values and by significantly higher eye blink rates (30 vs 61 blinks per 3 minutes, respectively). In summer, controls and subjects with SAD showed similar significant differences in follicular PRL values (9.3 vs 3.9 μg/L, respectively) and eye blink rates (25 vs 67 blinks per 3 minutes, respectively). No significant differences in PRL values or eye blink rates were found between the bipolar II and unipolar forms of SAD in either season. Results were discussed in terms of dopamine functioning.