Compared effects of serotonin on cervical and hypoglossal inspiratory activities: an in vitro study in the newborn rat.

1. J Physiol. 1992;451:605-29.

Compared effects of serotonin on cervical and hypoglossal inspiratory activities:
an in vitro study in the newborn rat.

Morin D(1), Monteau R, Hilaire G.

Author information:
(1)Département de Physiologie et Neurophysiologie, URA CNRS 0205, Faculté des
Sciences et Techniques St Jérôme, Marseille, France.

1. Experiments were performed on the brain stem-spinal cord preparation of
newborn rats, in which the phrenic and hypoglossal nerves continue to show
rhythmic respiratory activity in vitro, in order to compare the effects of
serotonin (5-HT) on both activities and to analyse the mechanisms responsible for
the depression by 5-HT of the hypoglossal activity. 2. Under control conditions,
simultaneous recordings of the inspiratory discharges of hypoglossal and cervical
roots showed that the two bursts did not start simultaneously and had different
patterns (time-to-peak and peak values); this suggests that both pools of
motoneurons did not share the same central drive(s). 3. Adding 5-HT and related
agents to the bathing medium delayed and depressed the hypoglossal inspiratory
discharge via activation of 5-HT2 receptors since these effects were elicited by
5-HT2 agonists (alpha-methyl-5-HT and
1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane-HCl (DOI)) but not by 5-HT1
agonists (RU 24969 and (+/-)-8-hydroxy-2-(di-N-propylamino)tetralin hydrobromide
(8-OH-DPAT)). The 5-HT depression of the hypoglossal discharge was prevented by
applying a pretreatment with a specific 5-HT2 antagonist (ketanserin). Parallel
to the hypoglossal discharge decrease, 5-HT elicited a permanent cervical root
discharge along with a persistent inspiratory bursting. Adding the 5-HT precursor
L-tryptophan to the bathing medium depressed the hypoglossal (XII) discharge
without affecting the cervical one. 4. Local application of 5-HT within the
hypoglossal motor nucleus decreased the hypoglossal output, revealing that the
5-HT depression of the hypoglossal discharge was at least partly mediated by the
5-HT effects at the level of the motoneurons. Local application of 5-HT within
the cervical motor nucleus elicited a permanent firing in the cervical root with
a persistent inspiratory bursting. 5. Intracellular analysis confirmed the
existence of differences in central respiratory drive between cervical and
hypoglossal motoneurons under control conditions, as well as differences in
response to 5-HT. All the hypoglossal motoneurons became silent under 5-HT
bathing, and showed no change in the input membrane resistance, a moderate
depolarization, and a delayed central respiratory drive with a decreased
amplitude. The cervical motoneurons became more active during inspiration,
despite a decrease in the amplitude of the central respiratory drive, which was
compensated for by a large depolarization and an increased input membrane
resistance. Some cervical motoneurons even fired at a low rate during
expiration.(ABSTRACT TRUNCATED AT 400 WORDS)

DOI: 10.1113/jphysiol.1992.sp019181
PMCID: PMC1176178
PMID: 1403827 [Indexed for MEDLINE]

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