DIFFERENCE IN SENSITIVITY OF CARDIOVASCULAR AND RESPIRATORY CONTROL NEURONS IN THE SUBRETROFACIAL NUCLEUS TO GLUTAMATE RECEPTOR SUBTYPE AGONISTS IN SHR, WKY AND CATS

Using spontaneously hypertensive rats (SHR), Wistar-Kyoto rats (WKY) and cats, either glutamate or a glutamate receptor subtype agonist was injected into the subretrofacial nucleus (SRF) in the rostral ventrolateral medulla at the site where the pressor response had been evoked by electrical stimulation. The sensitivity of SRF neurons to the electrical stimulation or glutamate receptor agonist was estimated by the threshold current or dose required to evoke the pressor response. The threshold of SRF neurons to electrical stimulation was similar in the three animal groups, while that to the glutamate receptor agonist was different. The significance of the difference in threshold between WKY and SHR was calculated as was that between WKY and cats. The threshold for kainate stimulation was ten times lower for SHR (0.016 pmol, P < 0.001) and five times higher for cats (0.78 pmol, P < 0.05); that for quisqualate stimulation was fifty times lower for SHR (0.016 pmol, P < 0.001) but similar for cats; that for NMDA stimulation was twelve times lower for SHR (0.13 pmol, P < 0.001) but seven times higher for cats (11 pmol, P < 0.01); that for glutamate stimulation was ten times lower for SHR (4.2 pmol, P < 0.001) but similar for cats, The heart rate and respiratory responses associated with the pressor response were tachycardiac and hypopneic in SHR and WKY, but bradycardiac and hyperpneic in cats. These responses were less dominant than the pressor response. We suggest that the pathogenesis of hypertension in SHR may be partly due to abnormal properties of glutamate receptor subtypes acting on vasomotor control neurons in the SRF.