| Abstract
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The aim of the studies underlying this thesis was to characterize the muscarinic and adrenergic receptors expressed in rat brain oligodendrocytes' (OLs); determine if ligand binding alters second messenger levels classically associated with these families of receptors, such as inositol phosphates (InsP), intracellular calcium ( (Causd\rm\sp{2+}\rbrack\sb{i}),usd and cyclic AMP (cAMP); and the role of neurotransmitters, acetylcholine (Ach) or norepinephrine (NE) on oligodendrocyte growth. CCH (carbachol), a stable Ach analog, caused a concentration and time dependent increase in the accumulation of InsPs and the mobilization of (Causd\rm\sp{2+}\rbrack\sb{i},usd which was inhibited by atropine, a specific muscarinic antagonist, and was negatively regulated by acute activation of protein kinase C by the phorbol ester TPA. CCH also negatively regulated the usd\betausd-adrenergic-stimulated increase in cAMP levels. Using subtype m1 and m2 specific muscarinic receptor oligonucleotide primers RT-PCR confirmed the presence of, at least, these two muscarinic receptor subtypes. CCH caused a time and concentration-dependent increase in c-fos proto-oncogene mRNA levels as determined by Northern blot analysis. The CCH-stimulated c-fos increase was mediated through a non-phorbol ester sensitive PKC isozyme, and was dependent upon intra and extracellular calcium. Moreover, CCH stimulated DNA synthesis in OLPs, as measured by both (H) -thymidine and BrdU incorporation. Lastly, the NE-stimulated signal transduction pathway was characterized in developing OLPs. Using selective agonists and antagonists, we determined that NE increased the formation of InsPs through usd\alpha\sb1usd adrenoceptors. We further subclassified the usd\alpha\sb1usd receptor to the usd\rm\alpha\sbusd subtype using more selective reagents; WB4101, a selective antagonist for usd\rm\alpha\sbusd receptors blocked the response to NE, while chloroethylclonidine, an usd\rm\alpha\sb{1B}usd antagonist had no effect. Furthermore, Pertussis toxin, a bacterial toxin that ADP-ribosylates and inactivates certain G-proteins, EGTA, a calcium chelator, or CdCl2, an inorganic calcium channel blocker, all significantly blocked the NE-stimulated InsP formation. Together these results suggest that OLPs express usd\alpha\sb1usd-adrenoceptors characteristic of the usd\rm\alpha\sbusd subtype. In toto, these studies demonstrate that developing OLs express functional muscariaic and adrenergic receptors, and suggest that Ach may function as a trophic factor. These results help to define a mechanism whereby neurons, and OLs may use neurotransmitters to communicate both during development and in the mature central nervous system.
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