α1B receptors are the main postsynaptic mediators of adrenergic excitation in brainstem motoneurons, a single-cell RT-PCR study

Abstract Norepinephrine (NE) is an important modulator of brainstem motoneurons. It is released at high levels during wakefulness, whereas its reduced release during sleep may contribute to motor suppression, including upper airway hypotonia. To identify the receptors that mediate postsynaptic effects of NE in brainstem motoneurons of juvenile and adult rats, we determined the pattern of adrenoceptor mRNA expression and co-expression in retrogradely labeled and acutely dissociated hypoglossal (XII) motoneurons ( n =121) using single-cell, real-time reverse transcription-polymerase chain reaction (RT-PCR). The α 1B receptor mRNA was present in most motoneurons (33/39 or 85%). The remaining six adrenoceptor mRNA species investigated were consistently present in micropunches of tissue extracted from the XII nucleus, but were either rarely expressed in individual motoneurons (α 1A mRNA in 15%, α 1D in 14%, α 2B/C in 2% of cells) or absent (α 2A , β 1 and β 2 ). When present, the α 1A and α 1D mRNAs were co-expressed with α 1B mRNA. The adrenoceptor mRNA expression profiles in dissociated locus coeruleus and inferior olive neurons were significantly different. We conclude that postsynaptic effects of NE in XII motoneurons are primarily mediated by α 1B receptors; the effects ascribed to α 2 and/or β adrenoceptors may be exerted presynaptically.