In vitro electrophysiology of developing genioglossal motoneurons in the rat

Abstract

1. Experiments were performed to determine the change in membrane properties of genioglossal (GG) motoneurons during development. Intracellular recordings were made in 127 GG motoneurons from rats postnatal ages 1-30 days. 2. The input resistance (R(in)) and the membrane time constant (t(aum)) decreased between 5-6 and 13-15 days from 84.8 +/- 25.4 (SD) to 47.0 +/- 18.9 M omega (P < 0.01) and from 10.0 +/- 4.2 to 7.3 +/- 3.3 ms (P < 0.05), respectively. During this period, the rheobase (Irh) increased (P < 0.01) from 0.13 +/- 0.07 to 0.27 +/- 0.14 nA, and the percentage of cells exhibiting inward rectification increased from 5 to 40%. Voltage threshold (Vthr) of the action potential remained unchanged postnatally. 3. There was also a postnatal change in the shape of the action potential. Specifically, between 1-2 and 5-6 days, there was a decrease (P < 0.05) in the spike half-width from 2.23 +/- 0.53 to 1.45 +/- 0.44 ms, resulting, in part, from a steepening (P < 0.05) of the slope of the falling phase of the action potential from 21.6 +/- 10.1 to 32.9 +/- 13.1 mV/ms. The slope of the rising phase also increased significantly (P < 0.01) between 1-2 and 13-15 days from 68.4 +/- 31.0 to 91.4 +/- 44.3 mV/ms. 4. The average duration of the medium afterhyperpolarization (mAHPdur) decreased (P < 0.05) between 1-2 (193 +/- 53 ms) and 5-6 days (159 +/- 43 ms). Whereas the mAHPdur was found to be independent of membrane potential, there was a linear relationship between the membrane potential and the amplitude of the medium AHP (mAHPamp). From this latter relationship, a reversal potential for the mAHPamp was extrapolated to be -87 mV. No evidence for the existence of a slow AHP was found in these developing motoneurons. 5. All cells analyzed (n = 74) displayed adaptation during the first three spikes. The subsequent firing pattern was classified into two groups, adapting and nonadapting. Cells at birth were all adapting, whereas all cells but two from animals 13 days and older were nonadapting. At the intermediate age (5-6 days), the minority (27%) was adapting and the majority (73%) was nonadapting. 6. The mean slope of primary range for the first interspike interval (1st ISI) was approximately 90 Hz/nA. This value was similar for both adapting and nonadapting cells and did not change postnatally.(ABSTRACT TRUNCATED AT 400 WORDS)

GAD67-GFP+ Neurons in the Nucleus of Roller: A Possible Source of Inhibitory Input to Hypoglossal Motoneurons. I. Morphology and Firing Properties

“…5B and 7C), similar to what has been described in HMs in the rodent brain stem in previous studies (Nunez-Abades et al 1993;van Brederode and Berger 2008;Viana et al 1995). HMs in this study showed either little or no frequency adaptation or frequency acceleration due to a long first ISI.…”

Postnatal Development of Serotonergic Innervation, 5-HT1AReceptor Expression, and 5-HT Responses in Rat Motoneurons

“…Throughout this report we refer to animals ՅP8 as neonates and animals ՆP20 as juveniles. Previous reports have indicated that many of the electrophysiological properties of HMs are adult-like by this stage (Núñez-Abades et al, 1993;Bayliss et al, 1994a,c;Viana et al, 1994;Berger et al, 1996), and we consider it likely that data from these juvenile animals are representative of adults.…”

“…It is becoming increasingly apparent that integrative properties of motoneurons, as well as the neurotransmitter mechanisms by which those properties are modulated, also undergo significant changes during the early postnatal period (for review, see Berger et al, 1996). This plasticity reflects differential expression of ion channels during development (Núñez-Abades et al, 1993;Bayliss et al, 1994a;Viana et al, 1994) as well as the modulation of those ion channels by neurotransmitters at any given developmental stage (ZiskindConhaim et al, 1993;Bayliss et al, 1994c;Funk et al, 1995). Moreover, the modulatory neurochemical systems that impinge on motoneurons are not static; their chemical phenotype and projection patterns also can change throughout development (Ziskind-Conhaim et al, 1993;Bayliss et al, 1994c).…”

Pre- and postsynaptic mechanisms underlying inhibition of hypoglossal motor neuron excitability by riluzole

“…The aim of this study was to directly compare effects of riluzole at a maximal clinically relevant dose on the range of factors controlling motor neuron excitability by electrophysiological recording from HMs. Electrophysiological recordings of membrane potential, resistance, holding current, repetitive firing and single action potential properties, voltage-sensitive persistent Na ϩ and Ca 2ϩ currents, evoked, spontaneous, and miniature excitatory synaptic potentials, and postsynaptic responses to glutamate were made with whole cell patch-clamp techniques in rat HMs in in vitro brain stem slices from rats aged 10 -23 days, a period when HM morphology (Núñez-Abades et al 1994) and electrical excitability (Berger et al 1995;Núñez-Abades et al 1993) have matured sufficiently to assume or be close to their adult properties.…”