Blockade of glutamate receptors in CVLM and NTS attenuates airway dilation evoked from parabrachial region

Previous work from our laboratory has shown that stimulation of cell bodies and dendrites in the medial and lateral parabrachial nuclei dilates the airways. The sites participating in the pathway mediating this airway response are not known. Two likely candidates are the caudal ventrolateral medulla (CVLM) and the nucleus tractus solitarii (NTS). Using chloralose- anesthetized cats, we assessed the airway dilation evoked from the parabrachial region before and during bilateral blockade of the NTS or the CVLM. The airway dilation arising from stimulation of the parabrachial region was evoked by microinjection of DL-homocysteic acid (25 nl, 100 mM). Bilateral blockade of the NTS or CVLM, achieved by microinjection of kynurenic acid (50 nl, 100 mM), reversibly attenuated the airway dilation in every cat tested. On average, kynurenic acid-induced blockade of the NTS caused a more complete attenuation of the dilation evoked from the parabrachial region than did blockade of the CVLM. Bilateral microinjection of cobalt chloride (50 nl, 50 mM) into the CVLM gave inconclusive results, attenuating the airway dilation evoked from the parabrachial region in six cats and potentiating it in three others. We conclude that the CVLM and the NTS participate in the airway dilation arising from the parabrachial region.