EFFERENT CONNECTIVITY OF THE HIPPOCAMPAL-FORMATION OF THE ZEBRA FINCH(TAENOPYGIA-GUTTATA) - AN ANTEROGRADE PATHWAY TRACING STUDY USING PHASEOLUS-VULGARIS LEUKOAGGLUTININ

The avian hippocampal formation (HP) is considered to be homologous to the mammalian hippocampus, being involved in memory formation and spa tial memory in particular. The subdivisions and boundaries of the pige on hippocampus have been defined previously by various morphological m ethods to detect further similarities with the mammalian homologue. We studied the efferent projections of the zebra finch hippocampus by ap plying Phaseolus vulgaris leucoagglutinin, and three main subdivisions were distinguished on the basis of the connectivity patterns. Dorsola teral injections gave rise to projections innervating the rostralmost extension of the HP, a laminar complex including the dorsal and ventra l hyperstriata and the lamina frontalis superior, the rostral lobus pa rolfactorius, the medial and ventral paleostriatal regions, the latera l septal nucleus, the nucleus of the diagonal band, the dorsolateral c orticoid area, the archistriatum posterius, and the nucleus taeniae in the telencephalon. In the diencephalon, labelled axons were seen in t he periventricular and lateral hypothalamus, including the lateral mam millary nuclei, and in the dorsolateral and the dorsomedial posterior thalamic nuclei, whereas, in the midbrain, only the area ventralis of Tsai contained hippocampal fibres. With the exception of the bilateral archistriatal efferents, all projections were ipsilateral. Dorsomedia l injections gave rise to a local fibre system that was almost complet ely restricted to the ipsilateral hippocampal formation. In addition, lectin-containing fibres continued in the dorsal septal region and a t hin band in the hyperstriatum accessorium, adjacent to the lateral ven tricle. Ventral injections gave rise to axons innervating ipsilaterall y the dorsolateral subdivision, and bilaterally the medial septal nucl ei and the contralateral ventral hippocampus. (C) 1996 Wiley-Liss, Inc .