Nucleus taenia of the amygdala of birds: Anatomical and functional studiesin ring doves (Streptopelia risoria) and European starlings (Sturnus vulgaris)

Nucleus taenia (Tn) in birds is a discrete component of a loosely defined a rchistriatal structure, the posterior and medial archistriatum. By virtue o f its hypothalamic projections, the posterior and medial archistriatum is t hought to be an avian homolog of the amygdala in mammals. A recent fluorogo ld (FG) study of avian hippocampus revealed backfilled labels in nucleus Tn , suggesting that this nucleus may indeed be the homolog of mammalian amygd ala. In the present study, we sought to characterize nucleus Tn in terms of its connections and function. We used the anterograde tracers Phaseolus vu lgaris leucoagglutinin (PHAL) and biotinylated dextran amine (BDA) to map t he efferent projections of Tn. The retrograde tracers FG and BDA were used to corroborate the efferent projections and to explore the pattern of affer ent inputs to Tn. Finally, we explored the role of Tn in social behavior by observing behavioral changes associated with electrolytic lesions to Tn. T he subjects of our studies were ring doves and European starlings, represen ting two avian orders. When a deposit of anterograde tracer was centered in Tn, it revealed projections to the hypothalamus, following the course of t he hypothalamic-occipitomesencephalic tract previously reported in pigeons. The projections were bilateral in ring doves and ipsilateral in starlings. The BDA injections in the archistratum intermedium, lateral to Tn, did not yield the same projectional pattern. Together with cor roborative data fro m FG retrograde experiments, these findings suggest that Tn is probably the primary origin of the hypothalamic projection. A robust projection to the hyperstriatal region was present along the lateral wall of the lateral vent ricle, continuing into the anteroventral pole of the ventricle. Highly arbo rized terminal fields were found all along this pathway, notably in the med ial parolfactory lobe (corresponding to the basal ganglia) and along the do rsal roof of the rostral hyperstriatum ventrale just ventral to the laminal frontalis superior tin ring doves) and the lamina frontalis suprema (in st arlings). Projections to the hippocampal complex were mostly restricted to the parahippocampus. The FG data suggest the presence of afferent projectio ns from the ovoidais shell and nucleus subrotundus region, the hippocampal complex in both species, and high vocal nucleus in starlings. Behavioral ef fects of Tn lesions suggest that nucleus taenia is involved in the control of social behavior through its influence on the affective state. Nucleus ta enia thus exhibits many of the structural and functional features of the am ygdaloid complex in mammals - that is, subcortical sensory inputs, hippocam pal complex connections, and a functional role in adaptive patterns of soci al behavior.