In mammals, circadian rhythms are controlled by the central clock, suprachiasmatic nuclei (SCN) in the hypothalamus. The external light signal could entrain SCN through intrinsically photosensitive retinal ganglion cells (ipRGCs), a type of neuron in the retinal of mammalian eyes, by releasing glutamate. The innervation of ipRGCs to SCN has been revealed by using genetic tracing techniques and contributes to the synchronization of the circadian rhythm. SCN is a heterogenous structure that contains different neurons, while AVP and VIP neurons are critical for the networking of circadian rhythm. In single ipRGC tracing study suggested that ipRGCs innervation does not limit to VIP neurons specifically but throughout the whole SCN. To know whether ipRGC and AVP neurons in SCN are a monosynaptic pathway, we use GCaMP7f, a calcium sensor, to image the neural activity in SCN under optogenetic stimulation. Using in vitro calcium imaging, here we showed that AVP neurons in the SCN could be activated by ipRGCs under bath application of TTX and 4AP to block multi-synaptic activation. Our results suggested that AVP neurons may receive direct ipRGC input from the retina for circadian clock regulation.