Rat brain oligodendrocytes express muscarinic and adrenergic receptors

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 ( (Ca$ rm sp{2+} rbrack sb{i}),$ 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 (Ca$ rm sp{2+} rbrack sb{i},$ 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 $ beta$-adrenergic-stimulated increase in cAMP levels. Using subtype m1 and m2 specific muscarinic receptor oligonucleotide primers RT-PCR confirmed the presence of, at least, these two muscarinic receptor subtypes. CCH caused a time and concentration-dependent increase in c-fos proto-oncogene mRNA levels as determined by Northern blot analysis. The CCH-stimulated c-fos increase was mediated through a non-phorbol ester sensitive PKC isozyme, and was dependent upon intra and extracellular calcium. Moreover, CCH stimulated DNA synthesis in OLPs, as measured by both ($ sp3$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 $ alpha sb1$ adrenoceptors. We further subclassified the $ alpha sb1$ receptor to the $ rm alpha sb{1A}$ subtype using more selective reagents; WB4101, a selective antagonist for $ rm alpha sb{1A}$ receptors blocked the response to NE, while chloroethylclonidine, an $ rm alpha sb{1B}$ antagonist had no effect. Furthermore, Pertussis toxin, a bacterial toxin that ADP-ribosylates and inactivates certain G-proteins, EGTA, a calcium chelator, or CdCl$ sb2,$ an inorganic calcium channel blocker, all significantly blocked the NE-stimulated InsP formation. Together these results suggest that OLPs express $ alpha sb1$-adrenoceptors characteristic of the $ rm alpha sb{1A}$ 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