Organization of projections from the medial agranular cortex to the superior colliculus in the rat: a study using anterograde and retrograde tracing methods

The organization of corticotectal projections from the medial agranular cor tex (AGm). which has been considered to contain rat's frontal eye field, wa s examined using anterograde and retrograde tracing techniques. When biotin ylated dextranamine (BDA) injections were made into the rostral part of the AGm, small numbers of BDA-labeled axons were found in the rostral two-thir ds of the superior colliculus (SC) while some labeled axons were seen in th e caudal one-third of the SC. These labeled axons were distributed mainly i n the lateral part of the stratum griseum intermediate. On the other hand, after BDA injections into the caudal port of the AGm, moderate to dense ple xuses of labeled axons were found in the rostral two-thirds of the SC while some labeled axons were seen in the caudal one-third of the SC. These labe led axons were distributed in the ventromedial and dorsolateral marginal zo nes of the stratum griseum intermediate as well as in the stratum griseum p rofundum. The corticotectal projections were largely uncrossed. After combi ned injections of BDA into the caudal part of the AGm on one side and chole ra toxin B subunit (CTb) into the paramedian pontine reticular formation on the opposite side or into the interstitial nucleus of Cajal on the same si de, the overlapping distributions of BDA-labeled axons and CTb-labeled neur ons were found in the ventromedial marginal zone of the stratum griseum int ermediale ipsilateral to the site of BDA injection. These results suggest t hat the caudal part of the AGm plays a more significant role in the oculomo tor function than does the rostral part of the AGm. (C) 2001 Elsevier Scien ce B.V. All rights reserved.