A stereotaxic headholder for small birds.

MOST groups working on avian brains use head holders adapted to their needs from conventions available ones such as the Kopf and Wells stereotaxic devices. One example is the so-called Revzin-adaptor described by Karten and Hodos [l]. An advantage of their modification is the more accurate placement of the head in an exactly defined angle to the vertical, but this hinders free access to the lateral parts of the brain and restricts heavily the visual field of the bird. Another device is described by Vowles et al. [4] which is only slightly modified from the Kopf and Wells stereotaxic apparatus. It also accurately fixates the head of the bird, but does not seem to be appropriate for small birds, as the second fixating point, the lachrymal duct, is too tiny and fragile in these animals. The most important ~~onve~ence of these headholders is the difficulty in accurately centering the head in the apparatus, as one has to adjust two different earbars. The procudure which has to be accomplished to fix the head in the correct angle by adjusting the mouth bar is also difficult and time consuming. The device described below avoids these two disadvantages. It was originally developed for experiments with zebra finches (~~e~~o~yg~u gtlttafa castanotis Gould). The head holder is made from aluminum, which is stable enough for the small animals. It is mounted on an aluminum plate of 20 x 8 cm. This plate can in turn be affixed to a solid steel plate which has a rail for the stereotaxic microdrive (Fig. 1). The const~ction of ths headholder is demonstrated in Fig. 2. The rotatable two earbars (E) are inserted into the main block (M) of the device. They can be moved like a pair of tongs by turning a spindle drive (S) located under the main block. The up-down movement of the spindle block is transferred to the earbars by two levers which connect block and earbars by articulated joints. The tip of the bird’s beak was chosen as the second fixating point. It was fixed by the beak holder (B) which is also movable. The movable part is inserted into a hole in the main block which is drilled in a direction so that its axis meets the imaginary line between the two earbars and builds an angle