Mechanisms underlying the cardioinhibitory and pressor responses elicited from the medullary neurons in the gigantocellular tegmental field of cats.
A stimulation of the gigantocellular tegmental field (FTG) in the medulla oblongata often increases systemic arterial blood pressure (SAP) and decreases heart rate (HR). We investigated if the cardioinhibitory/depressor areas, including the nucleus ambiguus (NA), the dorsal motor nucleus of vagus (DMV) and the caudal ventrolateral medulla (CVLM), underlied the functional expression of FTG neurons in regulating cardiovascular responses. In 73 chloralose-urethane anesthetized cats, the HR, SAP and vertebral nerve activity (VNA) were recorded. Neurons in the FTG, NA, DMV and CVLM were stimulated by microinjection of sodium glutamate (25 mM Glu, 70 nl). To study if the NA, DMV, and CVLM relayed the cardioinhibitory messages from the FTG, 24 mM kainic acid (KA, 100 nl) was used as an excitotoxic agent to lesion neurons in the NA, DMV or CVLM. We found that the cardioinhibition induced by FTG stimulation was significantly reduced by KA lesioning of the ipsilateral NA or DMV. Subsequently, a bilateral KA lesion of NA or DMV abolished the cardioinhibitory responses of FTG. Compared to the consequence of KA lesion of the DMV, only a smaller bradycardia was induced by FTG stimulation after KA lesion of the NA. The pressor response induced by Glu stimulation of the FTG was reduced by the KA lesion of the CVLM. Such an effect was dominant ipsilaterally. Our findings suggested that both NA and DMV mediated the cardioinhibitory responses of FTG. The pressor message from the FTG neurons might be partly working via a disinhibitory mechanism through the depressor neurons located in the CVLM.
Hsieh
J H
JH
Institute of Biomedical Engineering, Chung Yuan Christian University, Chung Li 32o, Taiwan, ROC. jhhsieh@cycu.edu.tw
Chung
J L
JL
Su
C K
CK
Yen
C T
CT
Chai
C Y
CY
D000818:Animals; D001794:Blood Pressure / Q000502:physiology*; D002415:Cats; D005260:Female; D020546:Fourth Ventricle / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology*; D008297:Male; D008526:Medulla Oblongata / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D012970:Sodium Glutamate / Q000494:pharmacology; D013681:Tegmentum Mesencephali / Q000187:drug effects / Q000502:physiology*; D014630:Vagus Nerve / Q000502:physiology*
D012970:Sodium Glutamate