Serotonin genotype and relations between daylight duration and brain 5-HTT binding

Objectives Daylight duration (LIGHT) is related to weight, blood pressure (BP), mood and brain 5-HTT binding. The aim of this study was to evaluate the influence of serotonin transporter genotype polymorphism (5-HTTLPR) on this interaction.

Methods We studied forty healthy young adults (25 ± 2 yrs), including fifteen monozygotic twins, who were genotyped by 5-HTTLPR (sixteen l/l, fourteen s carriers). We used 123-I-nor-beta-CIT SPECT for the evaluation of 5-HTT functions in thalamus and midbrain. Subsequent relations and genotype influence on them were studied: LIGHT (hours on the imaging day), 5-HTT binding, hip/waist, BMI, heart rate and BP.

Results In forty subjects there was significant relation between LIGHT and midbrain binding (R = -0.31, < 0.01). Apart from thalamus binding other variables did not vary significantly between the two genotype groups (p < 0.007 for thalamus, Matt-Whitney test). In the l/l group there was statistically significant relation between midbrain 5-HTT binding and LIGHT (rS = -0.56, p < 0.05; n = 16). The exclucion of subjects with abnormal BMI (> 27 kg/m2) revealed a strong association between LIGHT and midbrain 5-HTT binding in the remaining l/l group (rS = -0.82, p < 0.002; n = 11). While there were no significant relations between LIGHT and 5-HTT brain binding in s carriers, LIGHT was significantly related to systolic BP (rS = -0.62, p< 0.05), and there was tendency towards relations between both diastolic BP and hip/waist and LIGHT.

Conclusions Our preliminary findings suggested that higher midbrain 5-HTT binding was associated with less daylight in the l/l group. In s carriers less daylight was associated with higher SBP, but LIGHT and brain 5-HTT binding were not related