Effects of square-wave gratings and diffuse light on metabolic activity in the rat visual system

The 2-deoxyglucose (2-DG) technique was used to determine the effects of pattern and diffuse light stimulation on glucose metabolism with hooded rats. Rats placed in a stimulation chamber covered with horizontal and vertical square wave gratings while wearing goggles with one of three pairings of light-occluding, diffusing, or clear lenses, allowed the assessment of the effects of different but simultaneous visual conditions on two sides of the strongly crossed visual system. Eyes covered with occluding lenses were lid-sutured shut 24 h before 2-DG. In order to assess the possibly confounding effects of this lid suture a second group of rats had one eyelid sutured for 24 h, and the other covered with an occluding lens for 20 min, before 2-DG. To further assess the effects of diffuse light a third group of rats was tested in a featureless white box with one eye occluded and the other covered by a diffusing lens. Exposure to pattern stimulation significantly increased metabolic activity in the dorsal lateral geniculate nucleus (LGNd), lateral posterior nucleus (LPN), superior colliculus (SC), and in visual cortex (VC). In contrast, diffuse light only slightly elevated LGNd activity and appeared to have little or no effect in the LPN or VC. Diffuse light, however, was as effective as patterned light in increasing ventral lateral geniculate nucleus activity and strongly suppressed SC activity to a level well below that produced by darkness. Evidently diffuse light, not just patterned light, can significantly govern the operation of central nervous system visual structures.