6-hydroxydopamine lesion of rat nigrostriatal dopaminergic neurons differentially affects nicotinic acetylcholine receptor subunit mRNA expression

Nicotinic acetylcholine receptor (nAChR) subunit mRNA expression in the rat substantia nigra (SN) was assayed by semiquantitative RT-PCR following 6-hydroxydopamine (6-OHDA) lesion of nigrostriatal dopaminergic neurons. Six months after unilateral injection of 6-OHDA or saline into the SN, total RNA was isolated from ipsilateral and contralateral tissue samples. RT-PCR amplifications were performed with template titration using primers specific for sequences encoding

1.	nAChR α2–α7 and β2–β4 subunits
2.	Glutamic acid decarboxylase
3.	Glyceraldehyde 3-phosphate dehydrogenase for normalization of template mass.

PCR products specific for α3, α4, α5, α6, α7, β2, β3, and glutamic acid decarboxylase were detected in the reactions containing SN RNA. This is the first evidence that α7 may be expressed in the SN. α2 and β4 PCR products were not detected in SN reactions, although they were observed in hippocampus and thalamus control reactions. A comparison of ipsilateral and contralateral SN RT-PCR reaction products showed substantial decreases in α5, α6, and β3 product yields following 6-OHDA, but not sham treatment. Neither the SN of sham-lesioned rats nor the thalamus of 6-OHDA-lesioned rats yielded similar results, indicating that the effects observed in 6-OHDA-treated SN were not caused by local mechanical damage or a nonspecific response, respectively. Effects of 6-OHDA treatment on α3, α4, α7, β2, or glutamic acid decarboxylase product yields from SN samples were small or undetectable. The results suggest that α5, β6, and β3 subunit-encoding mRNAs are expressed at substantially higher levels in dopaminergic than in nondopaminergic cell bodies in the SN.