The focus of this project is investigation of the biology of neurotrophic factors in the central nervous system (CNS). Specifically, we are studying the fibroblast growth factor (FGF) family of neurotrophic factors and, more recently, a newly identified factor, glial cell-line-derived neurotrophic factor (GDNF). Much of the information currently available regarding the neurotrophic activities of these molecules has been obtained through studies of their activity in primary neuronal cultures. Little is known about the distribution and function of these trophic factors in vivo . The objective of the current project is to describe the precise anatomical distribution of the mRNA for each of the FGF and GDNF proteins in the normal adult rat brain using in situ hybridization. Further, through the use of well characterized animal models of neurodegeneration, we are studying in vivo regulation of mRNAs for GDNF and the FGFs in response to injury and pharmacological manipulation. Using radiolabeled cRNA probes which recognize each of these trophic factor and receptor mRNAs, in situ hybridization is being performed on serially cut, slide mounted tissue sections from rodent brain. The radiolabeled sections are exposed to x-ray film or liquid emulsion and the resulting autoradiograms are analyzed using computer assisted image analysis. In addition, to facilitate dual labeling of section for both mRNA and protein, we are currently setting up the technique of non-isotopic in situ hybridization. Results to date show localization of acidic FGF in spinal cord motor neurons as well as numerous brainstem and mid-brain nuclei including substantia nigra, locus coeruleus and the facial motor nucleus. Reports from other labs suggest that acidic FGF and GDNF are trophic for these same groups of neurons. For acidic FGF, this effect may be indirect. We hypothesize that acidic FGF may be released from neurons in these regions after injury and act indirectly as trophic factors by inducing synthesis and secretion of additional trophic factors (such GDNF) from surrounding glia which in turn act directly to support the injured neuronal population.
