Projections from the medial agranular cortex to brain stem visuomotor centers in rats

Summary Projections from medial agranular cortex to brain stem in rat were determined by use of the anterograde tracers Phaseolus vulgaris leucoagglutinin, or wheat germ agglutinin conjugated horseradish peroxidase. Axonal trajectories were also followed by means of the Wiitanen modification of the Fink-Heimer degeneration technique. AGm was identified on the basis of its cytoarchitectonics. AGm projected to the anterior pretectal nucleus, the rostral interstitial nucleus of the medial longitudinal fasciculus, the medial accessory oculomotor nucleus of Bechterew, the interstitial nucleus of Cajal, the nucleus of Darkschewitsch, the nucleus cuneiformis and subcuneiformis, intermediate and deep superior collicular layers, the paramedian pontine reticular formation (reticularis pontis oralis and caudalis, and reticularis gigantocellularis), and raphe centralis superior. Differences in connections between rostral and caudal injections were observed: pontine and medullary projections were lighter from the rostral portion of AGm than from the more caudal portions of AGm. The heaviest projections to the anterior pretectal nucleus were from the caudal portion of AGm. The subcortical projections were very similar to those described for the frontal eye field in monkeys, and the majority of them targeted areas thought to be involved in coordination of gaze with head and neck movements. Thus AGm in rats may contain the homologue of the primate frontal eye fields.Abbreviations 3 main oculomotor nucleus - 7 facial motor nucleus; - I, II–IV, V, and VI cortical layers - III third ventricle - 7n facial nerve - AC Anterior commissure - AGm medial agranular cortex - Bec Nucleus of Bechterew - cc corpus callosum - Dark Nucleus of Darkschewitsch - Dc dorsal cochlear nucleus - DLG dorsal lateral geniculate nucleus - F fornix - fr fasciculus retroflexus - ic inferior colliculus - Me5 mesencephalic trigeminal nucleus - ml medial lemniscus - mlf medial longitudinal fasciculus - Mo5 trigeminal motor nucleus - nV trigeminal nerve - pc posterior commissure - pn pons - Po posterior thalamic nucleus - PPo pedunculo-pontine nucleus - PPRF paramedian pontine reticular formation - py pyramidal tract - R red nucleus - RaCs raphe centralis superior - RaD dorsal raphe nucleus - RCf reticularis cuneiformis - RiMLF rostral interstitial nucleus of the medial longitudinal fasciculus - RMc reticularis magnocellularis - RPc reticularis parvocellularis - RPoCa reticularis pontis caudalis pars alpha - RPoCb reticularis pontis caudalis pars beta - RPoO reticularis pontis oralis - RPoOm reticularis pontis oralis pars medialis - RScf reticularis subcuneiformis - sc superior colliculus - SCP superior cerebellar peduncle - so superior olive - Sp5 spinal trigeminal nucleus - Tz trapezoid nucleus - WGA-HRP wheat germ agglutinin- horseradish peroxidase