- Homer-1 mRNA in the rat suprachiasmatic nucleus is regulated differentially by the retinohypothalamic tract transmitters pituitary adenylate cyclase activating polypeptide and glutamate at time points where light phase-shifts the endogenous rhythm. Nielsen, H.S., Georg, B., Hannibal, J., Fahrenkrug, J. Brain Res. Mol. Brain Res. (2002)