Evidence for a tonic GABA-ergic inhibition of excitatory respiratory-related afferents to presympathetic neurons in the rostral ventrolateral medulla.
The effect of blockade of ionotropic GABA and glutamate receptors in the rostral ventrolateral medulla (RVLM) on the relationship between phrenic nerve, splanchnic sympathetic nerve and lumbar sympathetic nerve activities was examined in urethane anesthetized, paralyzed and vagotomized Sprague-Dawley rats. Bilateral microinjection of the GABA-A receptor antagonist, bicuculline (4 mM, 100 nl), into the RVLM dramatically, and almost exclusively, increased the post-inspiratory related discharge in both splanchnic sympathetic nerve and lumbar sympathetic nerve activities and elicited hypertension with fluctuations of arterial pressure phase locked to the discharge of the phrenic nerve. Subsequent bilateral microinjection of kynurenate, a non-selective ionotropic excitatory amino acid receptor antagonist (50 mM, 100 nl), into the RVLM significantly attenuated the sympathoexcitation and hypertension evoked by injection of bicuculline. This was accompanied by an abolition of the post-inspiratory related burst discharge of splanchnic sympathetic nerve and lumbar sympathetic nerve activities. These data suggest that the GABAergic inputs to RVLM tonically inhibit glutamatergic inputs from central respiratory neurons that normally act to increase the firing of presympathetic neurons in the RVLM. Inputs from post-inspiratory neurons appear to be an especially potent excitatory synaptic drive to the presympathetic neurons in the absence of the GABAergic inhibition.
Miyawaki
Takashi
T
Hypertension and Stroke Research Laboratories, Department of Physiology, University of Sydney, Sydney 2006, Australia.
Goodchild
Ann K
AK
Pilowsky
Paul M
PM
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000344:Afferent Pathways / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism; D007395:Interneurons / Q000187:drug effects / Q000378:metabolism*; D007736:Kynurenic Acid / Q000494:pharmacology; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects / Q000378:metabolism*; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D010791:Phrenic Nerve / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012125:Respiratory Center / Q000187:drug effects / Q000378:metabolism*; D012143:Respiratory Physiological Phenomena / Q000187:drug effects; D013153:Splanchnic Nerves / Q000187:drug effects / Q000502:physiology; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D007736:Kynurenic Acid; D001640:Bicuculline