Localization of neurotrophin-3-like immunoreactivity in the rat central nervous system

Abstract

Neurotrophin-3 (NT3) is a nerve growth factor (NGF) homologue whose function is presently unknown. The factor promotes the survival of a subpopulation of sensory and sympathetic neurons in vitro. NT3 mRNA is widely distributed in both the peripheral and central nervous system but the distribution of NT3 has not yet been examined. In the present study we have determined the regional distribution and cellular localization of NT3-like immunoreactivity (-IR) in the central nervous system by immunohistochemistry. Both glia and neurons were stained. NT3-IR glia were distributed in corpus callosum, substantia nigra, fimbria of hippocampus, subependymal areas of the ventricles and cerebellum. In the forebrain, NT3-IR was detected in a number of neuronal cells, including pyramidal cells in the fifth layer of the cerebral cortices, subpopulations of neurons in the septal nuclei, diagonal bands of Broca, olfactory primary cortex, amygdala and islands of Calleja. In the hippocampus, pyramidal cells in the CA1, CA2 and lateral regions of CA3 and granular cells in dorsal dentate gyrus were labelled with different intensities. Neurons in the bed nuclei of the striatum terminalis, mesencephalic trigeminal nuclei and motoneurons in the brain stem and spinal cord were intensively labelled. A subpopulation of neurons in the reticular thalamic nuclei and midbrain were moderately labelled. Finally, in the cerebellum, NT3-IR was also found in Purkinje cell sand neurons in the deep cerebellar nuclei. In some brain regions such as hippocampus, the distribution of NT3-IR correlates with that of mRNA NT3 as described by others. In contrast in other regions such as spinal cord and brain stem, little correlation was found between protein and mRNA. The results suggest that some NT3 immunoreactive neurons in the central nervous system accumulate NT3 in accord with a neurotrophic role for their maintenance or survival, while others may synthesize and secrete the factor to provide support for innervating neurons.