Respiratory responses to microinjection of excitatory amino acid agonists in ventrolateral regions of the lateral parabrachial nucleus in the cat.

Sites of tachypneic and hyperpneic responses to localized pressure injection of glutamate agonist were located in the small restricted regions in the ventrolateral regions of the lateral parabrachial nucleus (vlPb1) in the rostral and intermediate levels of the Pb1. The respiration-related neurons in the vlPb1 showed different sensitivity to different types of glutamate agonists. They are most sensitive, in descending order, to quisqualate, kainate, N-methyl-D-aspartate (NMDA), and glutamate. The respiratory response to kainate and NMDA was characterized by being slow and long-lasting, while the response to quisqualate and glutamate was rapid and brief. An immunocytochemical study suggested that the respiration-related neurons in the vlPb1 receive glutamatergic projections from the solitary tract nucleus, nucleus retroambigualis, nucleus para-ambigualis, para-retrofacial nucleus, subretrofacial nucleus and subfacial cell group in the medulla, Pb1 in the contralateral pons, paraventricular nucleus in the hypothalamus and central amygdaloid nucleus in the limbic system. These findings indicate that the respiration-related neurons in the vlPb1 play an important role in the modulation of respiration.