Developmental patterns of AMPA glutamate receptor and fos co-expression in Caudal Brainstem (CBS) of the rat during normoxia and hypoxia

AMPA glutamate receptors (GluR2/3) mediate fast excitation components of neuronal discharge, and have been implicated in cardiorespiratory regulation. Increased regional expression of fos protein occurs with hypoxia, and is also widely used as a marker for increased neuronal activation. To determine if AMPA receptor-positive neurons are recruited during hypoxia in the CBS, immunostaining for GluR2/3 and fos co-expression was performed after exposing rat pups at post-natal ages 2, 5, 10, and 20 days, and adult rats to room air or 10% O₂ for 3 hours. GluR2/3 expression increased with postnatal age in the nTS, nucleus ambiguus (NA), and particularly in the hypoglossal nucleus (XII). fos expression was enhanced by hypoxia at all post-natal ages in the nTS and NA, and also demonstrated a clear maturational pattern. However, co-localization of GluR2/3 and fos occurred in only a small proportion of neurons. We conclude that GluR2/3 expression in the CBS is developmentally regulated. Furthermore, increased neuronal recruitment within the nTS and NA during hypoxia appears unrelated to GluR2/3 expression patterns.