Brainstem serotonin (5-HT)-containing cells are remarkable for their w
idespread axonal projections and having their highest activity during
wakefulness and lowest during rapid eye movement sleep. One important
site of action of 5-HT is on upper airway motoneurons. However, which
of the 14 known 5-HT receptors mediate the effects is uncertain. We us
ed the reverse transcriptase/polymerase chain reaction to detect mRNA
for six distinct 5-HT receptors (1A, 1B, 2A, 2C, 3 and 7) in 50 nl mic
ro-punches collected from the hypoglossal (XII) motor nucleus and, for
comparison, from the viscerosensory nucleus of the solitary tract (NT
S) in adult rats. The relative abundance of the distinct mRNAs was cha
racterized by the minimal number of amplification cycles (25-40) neces
sary to detect a given mRNA. In the XII nucleus, mRNA for type 1B, 2A
and 2C receptors was detectable after 29-31 cycles, detection of type
3 and 7 receptor mRNA required 33-35 cycles; and type 1A receptor mRNA
was not detected. In the NTS, detection of mRNA for type 1B, 2C and 7
receptors required 31-33 cycles; type 1A receptor mRNA required 39 cy
cles; and type 2A receptor mRNA was not detected. The data from the XI
I nucleus demonstrate that not only the previously recognized type 1B,
2A and 2C receptors, but also type 3 and 7 receptors have the potenti
al to mediate serotonergic effects in XII motoneurons. (C) 1997 Elsevi
er Science B.V.