Functional postnatal changes in avian brain regions responsive to retinal slip: a 2-deoxy-D-glucose study

The postnatal development of two avian brain areas, the nucleus of the basal optic root (nBOR) and the lentiform nucleus of the mesencephalon (LM), was studied using the 2-deoxy-D-glucose (2-DG) method. Previous studies have shown that these nuclei respond to whole field visual motion, which is used for optokinetic eye movements. In the present study vertical whole field visual motion presented to one eye resulted in the accumulation of 2-DG label in the contralateral nBOR in both hatchlings and 3-week or older chicks. In hatchlings the nBOR was diffusely labeled whether upward or downward motion was used as the test stimulus, whereas in older birds the label was localized within different subdivisions of the nBOR depending on the direction of vertical motion: upward motion resulted in concentration of 2-DG label in the dorsal nBOR, whereas downward motion resulted in label in the ventral nBOR. Horizontal whole field visual motion presented to one eye resulted in 2-DG label in the contralateral LM and in the lateral portion of the contralateral nBOR in animals of both ages. In hatchlings, visual motion in both temporal-to-nasal and nasal-to-temporal directions resulted in labeling of both subdivisions of the LM, LM magnocellularis (LMmc) and LM parvocellularis. In older birds, temporal-to-nasal motion resulted in labeling of only the LMmc, whereas nasal-to-temporal motion produced labeling in both subdivisions. These results strongly suggest that the nBOR and LM continue to develop their response properties postnatally and that different functional units become separated within particular subdivisions of the nuclei. Conceivably, the functional segregation within the nBOR is due to an intrinsic reorganization, whereas functional changes in the LM may be due to the postnatal development of a projection from the telencephalon.