The efferent connections to the thalamus and brainstem of the physiologically defined eye field in the rat medial frontal cortex

The anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) was injected into sites of the rat frontal eye field (FEF) located in the medial frontal cortex. After a single iontophoretic injection of PHA-L into a FEF site where intracortical microstimulation elicited eye movements, anterogradely labelled fibres and terminal-like elements were found in the thalamus in the anterior nuclei, intralaminar nuclei, lateral portion of the mediodorsal nucleus and posterior nuclear group. In the midbrain and pons, labelled fibres were located in the anterior pretectal area, Darkschewitsch nucleus, superior colliculus and dorsolateral portion of the central gray. When the tracer was injected at the FEF periphery, at a site the stimulation of which evoked both eye and whisker movements, labelling distribution in the thalamus differed from that observed after FEF injections, while a similar distribution was observed in the brainstem. In the thalamus, anterograde labelling was observed in these latter cases in the anterior nuclei, ventral nuclei, medial portion of the laterodorsal nucleus. The present findings point out that the FEF and FEF periphery are connected with numerous subcortical structures of the thalamus and brainstem. In addition, the connections of FEF and FEF periphery with the thalamus differ, whereas the midbrain and pons connections of the two subdivisions share common targets.