Embryonic development of choline acetyltransferase and nitric oxide synthase in the spinal cord of pigeons and chickens with special reference to the superficial dorsal horn

Abstract

The superficial dorsal horn of birds as well as mammals contains both cholinergic and nitrergic neuronal structures as evident from the presence of the synthesizing enzymes such as choline acetyltransferase and nitric oxide synthase, which is an NADPH diaphorase. In the rat, both systems develop only postnatally. Rats are altricial at birth whereas pigeons and chickens are semiprecocial or precocial, respectively, at the time of hatching. Immunocytochemical studies of choline acetyltransferase and nitric oxide synthase in the developing avian spinal cord (starting with embryonic day 12 of 18 in the pigeon and 14 of 21 in the chicken) showed that both systems are well developed in the superficial dorsal horn at the time of hatching in both avian species. In the pigeon, choline acetyltransferase-positive superficial dorsal horn neurons appear only on the day of hatching (E18), whereas nitric oxide synthase-positive neurons can be first detected at stage E14. In the chicken, nitric oxide synthase-positive neurons are present already at stage E14, whereas choline acetyltransferase-positive neurons appear at stage E20. Autonomic and somatic motor neurons show adult-like choline acetyltransferase-immunoreactivity and/or nitric oxide synthase-immunoreactivity at the earliest stages investigated. It is concluded that the stage of maturation at birth or hatching plays an important role in the development of superficial dorsal horn cholinergic and nitrergic systems.