Modulation of the sensitivity of the retina by circadian clocks and efferent input for the brains is the main focus of the project. Circadian clocks in the Limulus brain and Japanese quail's eye modulate the structure and sensitivity of retinas in both animals. Noncircadian efferent inputs from the quail brain further modulate retinal sensitivity. Our long range goal is to understand how such modulatory inputs adapt vision for essential tasks. We propose to investigate the circadian modulations of the Japanese quail retina by putative neurotransmitters, dopamine and melatonin (Aim 1), that circadian modulation of the Limulus retina by multiple neurotransmitters (Aim 2), and the efferent modulation of the spatial and temporal response properties of the Japanese quail (Aim 3) and Limulus (Aim 4) retinas. We plan parallel studies with Japanese quail and Limulus involving methods of anatomy, physiology, pharmacology and molecular biology. Our physiological techniques allow long-term recordings of retinal responses in situ from both Limulus (-5 days) and Japanese quail (-2 days) as well as precise control of efferent inputs to both retinas. We can recorded clock activity from isolated Limulus brains (-2 days) and analyze properties of isolated Limulus photoreceptors (-12 hours). Our pharmacological techniques allow manipulation of the putative circadian signals (dopamine and melatonin) in the quail eye and the manipulation of the efferent neurotransmitters (octopamine, 2kD neuropeptide, and light-adapting hormone) in the Limulus eye. These experimental techniques are well suited for investigating the efferent and circadian modulation of retinal sensitivity and establish Limulus and Japanese quail as appropriate models for this research. The primary tenet of the project is that comprehensive studies of these animal models will yield new insights on basic mechanisms of retinal function.