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Abstract

The expression of ionotropic glutamate receptor subunits in the motoneuronal pools of the hypoglossal nucleus was studied using specific antibodies against subunits of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), kainate and N-methyl-D-aspartate (NMDA) subtypes. The highest numbers of intensely immunolabelled motoneurons were found in the dorsal tier and caudoventromedial part of the hypoglossal nucleus with all antibodies except that against the GluR1 AMPA subunit. Labelling for the GluR1 subunit was weak except for caudally located groups of motoneurons which innervate tongue muscles related to respiratory activity. By contrast, most motoneurons were intensely immunostained with antibodies against GluR2/3 and GluR4 subunits of the AMPA subtype. The low staining observed using an antibody specific for the GluR2 subunit (which prevents Ca(2+)-entry through AMPA channels) strongly suggests that AMPA receptors in hypoglossal motoneurons are Ca(2+)-permeable. Immunolabelling for the GluR5/6/7 kainate receptor subunits was found in many motoneuronal somata as well as in thin axon-like profiles and puncta that resembled synaptic boutons. Most motoneurons were intensely immunostained for the NMDA receptor subunit NR1. These results show that the hypoglossal nucleus contains five heterogeneous pools of motoneurons which innervate functionally defined groups of tongue muscles. The uneven expression of the different receptor subunits analysed here could reflect diverse phenotypic properties of hypoglossal motoneurons which might be expected to generate different patterns of motor responses under different physiological or pathological conditions.

Developmental Nicotine Exposure Alters AMPA Neurotransmission in the Hypoglossal Motor Nucleus and Pre-Bötzinger Complex of Neonatal Rats

“…To minimize processing variability, sections from nicotine animals were mounted with anatomically corresponding sections from a control animal on the same slide. After removal from the blocking solution, sections were incubated overnight in a mixture containing the primary antibody (rabbit anti-GluR2/GluR3, Millipore, 1:2500) (Garcia Del Cano et al, 1999) and the blocking solution. After rinsing, sections were incubated in the host-appropriate biotinylated secondary antibody solution (dilution of 1:1000) for 8 –12 h, followed by washing, and then incubation in avidin-biotin-HRP complex (Vector Laboratories, Elite kit).…”