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Frequency–current relationships of rat hindlimb α‐motoneurones
Author(s) -
Button Duane C.,
Gardiner Kalan,
Marqueste Tanguy,
Gardiner Phillip F.
Publication year - 2006
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2006.107292
Subject(s) - rheobase , hindlimb , decerebration , electrophysiology , chemistry , hyperpolarization (physics) , ketamine , pentobarbital , decerebrate state , neuroscience , anesthesia , medicine , anatomy , biology , central nervous system , stimulation , electric stimulation , organic chemistry , nuclear magnetic resonance spectroscopy
The purpose of this study was to describe the frequency–current ( f–I ) relationships of hindlimb α‐motoneurones (MNs) in both anaesthetized and decerebrate rats in situ . Sprague–Dawley rats (250–350 g) were anaesthetized with ketamine and xylazine (KX) or subjected to a precollicular decerebration prior to recording electrophysiological properties from sciatic nerve MNs. Motoneurones from KX‐anaesthetized rats had a significantly ( P < 0.01) hyperpolarized resting membrane potential and voltage threshold ( V th ), increased rheobase current, and a trend ( P = 0.06) for a smaller after‐hyperpolarization (AHP) amplitude compared to MNs from decerebrate rats. In response to 5 s ramp current injections, MNs could be categorized into four f–I relationship types: (1) linear; (2) adapting; (3) linear + sustained; and (4) late acceleration. Types 3 and 4 demonstrated self‐sustained firing owing to activation of persistent inward current (PIC). We estimated the PIC amplitude by subtracting the current at spike derecruitment from the current at spike recruitment. Neither estimated PIC nor f–I slopes differed between fast and slow MNs (slow MNs exhibited AHP half‐decay times > 20 ms) or between MNs from KX‐anaesthetized and decerebrate rats. Motoneurones from KX‐anaesthetized rats had significantly ( P < 0.02) hyperpolarized ramp V th values and smaller and shorter AHP amplitudes and decay times compared to MNs from decerebrate rats. Pentobarbitone decreased the estimated PIC amplitude and almost converted the f–I relationship from type 3 to type 1. In summary, MNs of animals subjected to KX anaesthesia required more current for spike initiation and rhythmic discharge but retained large PICs and self‐sustained firing. The KX‐anaesthestized preparation enables direct recording of PICs in MNs from intact animals.