Compartmentation of the cerebellar cortex of hummingbirds (Aves: Trochilidae) revealed by the expression of zebrin II and phospholipase Cβ4

The parasagittal organization of the mammalian cerebellar cortex into zones has been well characterized by immunohistochemical, hodological and physiological studies in recent years. The pattern of these parasagittal bands across the cerebellum is highly conserved across mammals, but whether a similar conservation of immunohistochemically defined parasagittal bands occurs within birds has remained uncertain. Here, we examine the compartmentation of the cerebellar cortex of a group of birds with unique cerebellar morphology-hummingbirds (Trochilidae). Immunohistochemical techniques were used to characterize the expression of zebrin II (aldolase C) and phospholipase Cβ4 (PLCβ4) in the cerebellar cortex of two hummingbird species. A series of zebrin II immunopositive/immunonegative parasagittal stripes was apparent across most folia representing three major transverse zones: an anterior zone with a central stripe flanked by three lateral stripes on either side; a central zone of high/low immunopositive stripes; and a posterior zone with a central stripe flanked by four to six lateral stripes on either side. In addition, both folia I and X were uniformly immunopositive. The pattern of PLCβ4 immunoreactivity was largely complementary-PLCβ4 positive stripes were zebrin II negative and vice versa. The similarity of zebrin II expression between the hummingbirds and the pigeon indicates that the neurochemical compartmentation of the cerebellar cortex in birds is highly conserved, but species differences in the number and width of stripes do occur.