DIFFERENTIAL DISTRIBUTION OF A 2ND TYPE OF TYROSINE-HYDROXYLASE IMMUNOREACTIVE AMACRINE CELL IN THE CHICK RETINA

A second population of tyrosine hydroxylase-immunoreactive amacrine ce lls was demonstrated in embryonic and adult chicken retinas by immunoh istochemistry techniques in whole flat-mount preparations. The populat ions were differentiated on a basis of different immunostaining intens ities, levels of stratification in the inner plexiform layer, and topo graphical distributions. Cells of one type were similar to the previou sly described dopaminergic amacrine cells, denoted here as tyrosine hy droxylase type 1 cells. Immunoreactive neurons of the second type obse rved in the present work had relatively smaller somata size, and weake r immunostaining than type 1 cells, and were located preferentially in the ventral retina. These tyrosine hydroxylase type 2 cells could be visualized from embryonic day 14 to 21 days after hatching animals. Th e distribution of the second population was coincident with that of th e targets of centrifugal fibres and with cells involved in long propri oretinal connections. We propose that the tyrosine hydroxylase type 2 amacrine cells found in the ventral retina could mediate an important pathway to the upper half of the visual field so as to aid in the dete ction of predators.