Serotonin binding in rat brain: circadian rhythm and effect of sleep deprivation

Crude membrane fractions isolated from rat brain were used to measure specific serotonin (5-HT) binding. In untreated animals a 24 hours rhythm in 5-HT binding was evident. Sleep deprivation (SD) was applied to enhance sleep pressure. After 12, 24, and 72 hours SD the high affinity 5-HT binding, KD1 = 1-3 nM, remained unchanged, the apparent dissociation constant of the low affinity 5-HT binding, KD2 = 20-30 nM, was found to be enhanced almost by factor 2. The number of binding sites were only moderately affected by SD. If SD was followed by 1 or 4 hours recovery sleep, the dissociation constant KD2 was decreased towards control values. The brain levels of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) were not significantly changed immediately after 72 hours SD. A statistically significant increase was found only for 5-HIAA 4 hours after 72 hours SD. The results are consistent with the hypothesis that changes in the sensitivity of 5-HT binding may be involved in the regulation of the sleep-waking cycle.