Protein kinases regulate glycine receptor binding in brain stem auditory nuclei after unilateral cochlear ablation

The contribution of synaptic input to input resistance was examined in 208 developing genioglossal motoneurons in 3 postnatal age groups (5–7 day, 13–16 day, and 18–24 day) using sharp electrode recording in a slice preparation of the rat brain stem. High magnesium (Mg2+; 6 mM) media generated significant increases (21–38%) in both the input resistance ( R n) and the first time constant (τ0) that were reversible. A large percent of the conductance blocked by high Mg2+ was also sensitive to tetrodotoxin (TTX). Little increase in resistance was attained by adding blockers of specific amino acid (glutamate, glycine, and GABA) transmission over that obtained with the high Mg2+. Comparing across age groups, there was a significantly larger percent change in R n with the addition of high Mg2+ at postnatal days 13 to 15 ( P13–15; 36%) than that found at P5–6 (21%). Spontaneous postsynaptic potentials were sensitive to the combined application of glycine receptor antagonist, strychnine, and the GABAA receptor antagonist, bicuculline. Application of either 10 μM strychnine or bicuculline separately produced a reversible increase in both R n and τ0. Addition of 10 μM bicuculline to a strychnine perfusate failed to further increase either R n or τ0. The strychnine/bicuculline-sensitive component of the total synaptic conductance increased with age so that this form of neurotransmission constituted the majority (>60%) of the observed percent decrease in R n and τ0 in the oldest age group. The proportion of change in τ0 relative to R n following strychnine or high magnesium perfusate varied widely from cell to cell and from age to age without pattern. Based on a model from the literature, this pattern indicates a nonselective distribution of the blocked synaptic conductances over the cell body and dendrites. Taken together, the fast inhibitory synapses (glycine, GABAA) play a greater role in determining cell excitability in developing brain stem motoneurons as postnatal development progresses. These findings suggest that synaptically mediated conductances effect the membrane behavior of developing motoneurons.

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Postnatal changes in cytochrome oxidase expressions in brain stem nuclei of rats: implications for sensitive periods

Journal of Applied Physiology ◽

10.1152/japplphysiol.00638.2003 ◽

2003 ◽

Vol 95 (6) ◽

pp. 2285-2291 ◽

Cited By ~ 38

Author(s):

Qiuli Liu ◽

Margaret T. T. Wong-Riley

Keyword(s):

Brain Stem ◽

Cytochrome Oxidase ◽

Vestibular Nucleus ◽

Glycine Receptor ◽

Nucleus Ambiguus ◽

Medial Vestibular Nucleus ◽

Hypoglossal Nucleus ◽

Motor Nucleus ◽

Sensitive Periods ◽

The Brain

Previously, we reported that cytochrome oxidase (CO) activity in the rat pre-Bötzinger complex (PBC) exhibited a plateau on postnatal days (P) 3–4 and a prominent decrease on P12 (Liu and Wong-Riley, J Appl Physiol 92: 923–934, 2002). These changes were correlated with a concomitant reduction in the expression of glutamate and N-methyl-d-aspartate receptor subunit 1 and an increase in GABA, GABAB, glycine receptor, and glutamate receptor 2. To determine whether changes were limited to the PBC, the present study aimed at examining the expression of CO in a number of brain stem nuclei, with or without known respiratory functions from P0 to P21 in rats: the ventrolateral subnucleus of the solitary tract nucleus, nucleus ambiguus, hypoglossal nucleus, nucleus raphe obscurus, dorsal motor nucleus of the vagus nerve, medial accessory olivary nucleus, spinal nucleus of the trigeminal nerve, and medial vestibular nucleus (MVe). Results indicated that, in all of the brain stem nuclei examined, CO activity exhibited a general increase with age from P0 to P21, with MVe having the slowest rise. Notably, in all of the nuclei examined except for MVe, there was a plateau or decrease at P3–P4 and a prominent rise-fall-rise pattern at P11–P13, similar to that observed in the PBC. In addition, there was a fall-rise-fall pattern at P15–P17 in these nuclei, instead of a plateau pattern in the PBC. Our data suggest that the two postnatal periods with reduced CO activity, P3–P4 and especially P12, may represent common sensitive periods for most of the brain stem nuclei with known or suspected respiratory control functions.

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