PACAP and glutamate are co-stored in the retinohypothalamic tract

The retinohypothalamic tract (RHT) relays photic information from the eyes to the suprachiasmatic nucleus (SCN). Activation of this pathway plays a ro le in adjusting circadian timing to the light/dark environment. Two transmi tters, glutamate and pituitary adenylate cyclase activating polypeptide (PA CAP) having phase shifting capacity during the night and day, respectively, are located in the RHT. Using double staining immunohistochemistry at the light and electron microscopic level, we showed that PACAP was co-stored wi th glutamate in a subset of retinal ganglion cells and in nerve terminals i n the retino-recipient area of the SCN. These findings provide an anatomica l basis for the recent demonstration of the interaction between these two t ransmitters on the SCN phase response at night. (C) 2000 Wiley-Liss, Inc.