Medullary pathways mediating the parasubthalamic nucleus depressor response.
The parasubthalamic nucleus (PSTN) projects extensively to the nucleus of the solitary tract (NTS); however, the function of PSTN in cardiovascular regulation is unknown. Experiments were done in alpha-chloralose anesthetized, paralyzed, and artificially ventilated rats to investigate the effect of glutamate (10 nl, 0.25 M) activation of PSTN neurons on mean arterial pressure (MAP), heart rate (HR), and renal sympathetic nerve activity (RSNA). Glutamate stimulation of PSTN elicited depressor (-20.4 +/- 0.7 mmHg) and bradycardia (-26.0 +/- 1.0 beats/min) responses and decreases in RSNA (67 +/- 17%). Administration (intravenous) of atropine methyl bromide attenuated the bradycardia response (46%), but had no effect on the MAP response. Subsequent intravenous administration of hexamethonium bromide blocked both the remaining bradycardia and depressor responses. Bilateral microinjection of the synaptic blocker CoCl(2) into the caudal NTS region attenuated the PSTN depressor and bradycardia responses by 92% and 94%, respectively. Additionally, prior glutamate activation of neurons in the ipsilateral NTS did not alter the magnitude of the MAP response to stimulation of PSTN, but potentiated HR response by 35%. Finally, PSTN stimulation increased the magnitude of the reflex bradycardia to activation of arterial baroreceptors. These data indicate that activation of neurons in the PSTN elicits a decrease in MAP due to sympathoinhibition and a cardiac slowing that involves both vagal excitation and sympathoinhibition. In addition, these data suggest that the PSTN depressor effects on circulation are mediated in part through activation of NTS neurons involved in baroreflex function.
Ciriello
John
J
Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, Canada N6A 5C1. john.ciriello@schulich.uwo.ca
Solano-Flores
L Pastor
LP
Rosas-Arellano
M Patricia
MP
Kirouac
Gilbert J
GJ
Babic
Tanja
T
D000818:Animals; D001286:Atropine Derivatives / Q000008:administration & dosage; D017704:Baroreflex / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D001919:Bradycardia / Q000503:physiopathology; D003035:Cobalt / Q000008:administration & dosage; D018698:Glutamic Acid / Q000008:administration & dosage / Q000378:metabolism*; D006339:Heart Rate / Q000187:drug effects; D018738:Hexamethonium / Q000008:administration & dosage; D007275:Injections, Intravenous; D007668:Kidney / Q000294:innervation*; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects / Q000378:metabolism*; D008845:Microinjections; D018727:Muscarinic Antagonists / Q000008:administration & dosage; D009433:Neural Inhibition; D009434:Neural Pathways / Q000378:metabolism; D018733:Nicotinic Antagonists / Q000008:administration & dosage; D051381:Rats; D017208:Rats, Wistar; D017552:Solitary Nucleus / Q000378:metabolism; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000378:metabolism*; D013787:Thalamic Nuclei / Q000187:drug effects / Q000378:metabolism*
D001286:Atropine Derivatives; D018727:Muscarinic Antagonists; D018733:Nicotinic Antagonists; D018738:Hexamethonium; D003035:Cobalt; D018698:Glutamic Acid; C006649:methylatropine; C018021:cobaltous chloride