Figure 4.

Transcription pathway for melatonin biosynthetic enzymes. The axon terminal of the neuron originating from the superior cervical ganglion releases norepinephrine (NE) into the synapse when stimulated. NE binds to beta-1 (β1) and alpha-1 (α1) receptors on the cell membrane of pineal gland cells (pinealocytes). β1 receptor stimulation leads to activation of downstream signaling of Gαs, adenylate cyclase (AC), and phosphorylated protein kinase A (PKA-P) to stimulate the transcription of AA-NAT RNA which will be transcribed into biosynthetic enzymes to synthesize melatonin.