Effects of soluble growth factors and contact with target cells on the development of cholinergic neurons of the rat telencephalon

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)

First Committee Member

John N. Barrett - Committee Chair


Trophic effects mediated by contact with target cells and the soluble growth factors insulin, insulin-like growth factor-1 (IGF-1), nerve growth factor (NGF), basic fibroblast growth (b-FGF) factor and a 55,000 dalton serum fraction (NSF) were studied in cultures prepared from the striatal and septal regions of embryonic day 15 rat brain. Specific questions addressed were: (1) how do these soluble neurotrophic factors affect central cholinergic neurons, (2) do the soluble factors differentially affect specific populations of neurons, (3) how is the expression of cholinergic properties of developing septal cholinergic neurons in culture affected by the presence of cells from their target region, the hippocampus, (4) do target interactions alter the response of cholinergic neurons to the soluble neurotrophic factors, (5) to what extent can a simple neuronal culture system serve as a model system for studying developmentally relevant interactions?In Chapter 1, I demonstrate that exposure to NSF, NGF or b-FGF increases choline acetyltransferase (ChAT) activity in striatal cultures. However, the pattern of increases for each growth factor was different, indicating that they act via different mechanisms. In contrast to the other growth factors, exposure to insulin decreased ChAT activity in these cultures.In Chapter 2, I demonstrate that exposure to insulin increased glutamic acid decarboxylase activity, whereas ChAT activity in the same cultures was decreased by insulin. The decrease in ChAT activity was cell density dependent, reversible and brain region specific. NGF increased ChAT but not CAD activities.In Chapter 3, I demonstrate that the expression of cholinergic properties in septal cultures is enhanced by coculture with cells from their target region, the hippocampus. Cholinergic neurons in cocultures were larger, stained more intensely for acetycholinesterase, and produced higher levels of ChAT activity than controls. The trophic effects of hippocampal cells and NGF were additive, indicating that the growth promoting effects of hippocampal cells were not due to NGF. Insulin increased ChAT activity in septal cultures but not in septal-hippocampal cocultures, indicating that contact with target cells may alter the actions of growth factors on developing neurons.These results show that a simple cell culture system may be used to study neurotrophic interactions of central cholinergic neurons.


Biology, Neuroscience; Biology, Animal Physiology

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