Fig. 2.

Percentages of IRt cells expressing mRNA for choline acetyltransferase (ChAT) and different cholinergic receptors among the 37 cells retrogradely labeled from the XII nucleus (XII premotor) and 29 nonretrogradely labeled from the XII nucleus neurons dissociated from the medullary IRt region. Each cell was tested for the presence of all 7 mRNA species. Over half (57%) of XII premotor neurons expressed ChAT mRNA, whereas only 14% of nonretrogradely labeled IRt cells expressed this message (P < 0.0008). The percentage of XII premotor neurons expressing type 2 muscarinic receptor mRNA (M2; 35%) was also higher than for nonretrogradely labeled IRt cells (10%; P < 0.04). The percentages of cells expressing other muscarinic receptor mRNAs (M1, M3, M4, and M5) were relatively low and not significantly different between XII premotor neurons and nonretrogradely labeled IRt cells. Over 60% of IRt cells expressed mRNA for the α₄ nicotinic receptor subunit (Nα₄), a dominant nicotinic subunit in the brain stem (17, 36), but the percentages were not different between XII premotor neurons and nonretrogradely labeled IRt cells. Error bars represent SE of the estimated proportions, as determined by the size of each population and the assumption of a random bimodal distribution (Analyse-It Software, Leeds, UK).