Serotonergic effects on hypoglossal neural activity and reflex responses.
We determined the effects of serotonin (5HT; 6 concentrations ranging from 0.005 to 500 microM) pressure microinjection into the hypoglossal (XII) motor nucleus (100-500 nl; pH = 7.2-7.4) on XII whole nerve activity and reflex response to upper airway negative pressure in 15 decerebrated, vagotomized, paralyzed and artificially ventilated cats. Increasing 5HT concentration resulted in a concentration dependent increase in ipsilateral tonic XII activity, with no change in phasic XII activity. Threshold concentrations ranged from 0.005 to 0.5 microM, with the maximal response reached at 5 microM. Increasing 5HT concentration also increased the duration of the XII response. This ranged from 50 s with 0.5 microM, to over 10 min with 500 microM 5HT. However, 5HT did not significantly change the XII whole nerve reflex response to upper airway negative pressure (-20 cm H2O) at any 5HT concentration (n = 5). All 5HT effects were reversed by microinjection of 1.0 mM methysergide. We conclude that XII responses to 5HT are elicited at low concentrations of 5HT, which have a relatively short duration of effect, but that 5HT at the XII motor nucleus has no effect on the XII reflex response to upper airway negative pressure.
Douse
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MA
Department of Medicine, UCHSC, Denver 80220, USA. dousem@essex.hsc.colorad.edu
White
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DP
D000818:Animals; D002415:Cats; D003655:Decerebrate State; D004305:Dose-Response Relationship, Drug; D005260:Female; D007002:Hypoglossal Nerve / Q000187:drug effects*; D016014:Linear Models; D008297:Male; D008845:Microinjections; D009046:Motor Neurons / Q000187:drug effects*; D012018:Reflex / Q000187:drug effects*; D012701:Serotonin / Q000494:pharmacology*; D014132:Trachea / Q000187:drug effects*
D012701:Serotonin