The differential distribution of AMPA-receptor subunits in the tectofugal system of the pigeon.

The tectofugal system of the pigeon was examined for the distribution of several glutamate-receptor subunits (AMPA Glu R1, Glu R2/3, Glu R4) and the calcium binding protein parvalbumin. With respect to the different antigens, a heterogeneous distribution was observed. Within the optic tectum, the Glu R1 like immunoreactivity was limited to the layers 2-5, 9, 10, and sparsely in layer 13, whereas the antibody to Glu R2/3 stained cell bodies in layers 9, 10, and very heavily in layer 13. In the rotundus only the Glu R4 antigen was expressed, while within the ectostriatal complex a large number of Glu R2/3 and a smaller contingent of Glu R4 positive neurons were stained. Quantitative analysis proved significant heterogeneities of these antigens in the mesencephalic as well as the diencephalic centre of the tectofugal pathway. The number of Glu R2/3 positive neurons undergoes a two-fold increase from the dorsal to the ventral lamina 13 of the optic tectum. Alterations in the amount of immunoreactive neurons were also observed within the rotundus, since the number of Glu R4 positive cells decreased from dorsal to ventral. Morphological differences and their correlation with functional specializations in visual information processing are discussed.