Figure 4.

Effect of β-adrenergic signaling on nocturnal 5-HT synthesis and release. (A) Blockade of β-adrenergic receptors leads to elevated 5-HT secretion. β-Adrenergic receptor blocker propranolol (PROP, 10 μM) was infused directly into the pineal through the microdialysis probe between 11 p.m. and 1 p.m. at day 5 (D5). Secretion profiles of 5-HT (Upper) and melatonin (Lower) were measured before, during, and after the drug treatment with in vivo pineal microdialysis. Identical results were seen in all rats tested (n = 4). (B) 5-HT content during early night is reduced in the absence of β-adrenergic signaling. Rats injected with propranolol (PROP, 30 mg/kg, i.p.) were killed at the indicated times 4 h after the injections and analyzed for their pineal 5-HT levels by using HPLC-FD. Each data point represents the mean of five rats at the indicated times.