Immunohistochemical ultra sensitive SP method has been used to examine the expression of nerve growth factor (NGF) and its high-affinity receptor (TrkA) in developing brain, spinal cord, choroid plexuses and dorsal root ganglia of goat fetus. The histogenesis of choroid plexuses in brain ventricle and dorsal root ganglia (DRG) in goat were observed by using histological technology. The main results were summarized as follows:1. In Spinal Cord, NGF and TrkA could be detected in the gray matter at embryonic week 6, the expressional range and immunoreactive staining were gradually increased as the developmental process. NGF immunoreactivity were mainly distributed in cytoplasm and projects of neurons in ventral horn and dorsal horn. TrkA immunoreactivity were located in ventral horn and substantial gelatinosa, and could be also observed in cytoplasm and projects of neurons at later stage during development. Expression of two markers were also localized on nucleus of glial cells, myelinated axons and on the outside of accompanying Schwann cells in white substance. The results suggested that NGF functioned not only the development of sympathetic neurons and sensory neurons, but also the development of motoneurons in ventral horn.2.NGF and TrkA were extensively present in the process of development in fetal brainstem. Expression of two markers in medulla oblongata started at 6 weeks fetal, then the range and immunoreactive degree of expression increased as the process of embryo development. The Immunoreactivity of NGF and TrkA could be observed mainly at principle motor nucleus of trigeminal nerve, aducent nucleus and potine nucleus during the development of pons. The expressional pattern of two markers in medulla oblongata and pons were consistent with the developmental pattern in the two region. NGF and TrkA also could be detected in developing midbrain; their expression started at 6-week fetal, then could be found in majority nuclei of midbrain with the developmental process. Theobvious expression of TrkA occurred after embryonic weeks 14. NGF immunoreactivity (IR) were mainly localized on cytoplasm and projects of neurons, and TrkA-IR were transferred from nucleus at early stage of development to cytoplasm and cell membrane at later stage of development. The occurrence of NGF and TrkA in brainstem suggested that NGF played important role on differentiation, proliferation, development and maturation of neurons in gray matter of brainstem.3.The expression of NGF and TrkA could be detected in fetal cerebellum. The distribution and immunostaining degree of NGF in cortex and medulla were all increased as the process of embryo development, particularly after embryonic week 15, NGF were extensively distributed in cortex and medulla. Expression of NGF in Purkinje cell occurred as the formation of Purkinje cell layer at embryonic weeks 14, then strengthed gradually as the ages and maintained the trends to 21 week. The weak immunostaining of TrkA were detected in cerebellum during the development. We could also observed the expression of TrkA in Purkinje cell, but no marked change of immunostaining could be found during development. The localization of NGF and Trk A in cerebellum indicated that NGF played important neurotrophic function on growth and development in cerebellum.4. Endogenous NGF and TrkA could de detected at later developmental stage in embryonic diencephalons gray matter. NGF immunoreactivity occurred about embryonic weeks 11, and mainly distributed in habenular nuclei of superior thalamus, major nuclei of thalamus and hypothalamus, medial geniculate body and lateral geniculate body. As the embryonic development, the density of NGF positive cells dropped, but diameter of neuron body increased gradually. The lightly-stained TrkA immunoreactivity were locally distributed in some nuclei after embryonic weeks 12, the trend lasted to embryonic weeks 17, then the expressional range and immunostaining increased gradually. The cellular localization of two markers were mainly on nucleus, and ext