title: GABAergic mechanisms in the ventrolateral medulla alter vasopressor responses from the anterior hypothalamus.
abstract: The facilitatory and inhibitory roles of the ventrolateral medulla in modulating cardiovascular responses elicited from the anterior hypothalamus were studied in urethane-anesthetized rats. Control pressor responses (35-50 mm Hg) were consistently evoked by electrically stimulating the anterior hypothalamic medial preoptic area (AH/POA). The ventrolateral medulla is divided into two functionally distinct neuron pools, namely a rostral ventrolateral vasopressor area ( VLPA ) and a caudal ventrolateral vasodepressor area ( VLDA ). In each experiment neuron pools in the VLDA or VLPA were identified with bilateral microinjections of the neuroexcitatory amino acid L-glutamate, and changes in AH/POA responses were determined before and after alterations in ventrolateral neuronal activity. Inhibition or excitation of neuronal activity was accomplished by bilaterally stimulating or blocking gamma-aminobutyric acid (GABA) receptors, respectively, in the VLPA or VLDA . Inhibition of neuronal activity by microinjecting the GABA agonist muscimol into the VLPA decreased the AH/POA response by 64 +/- 10% and, in the VLDA , increased the AH/POA response by 57 +/- 4%. Blockade of GABA receptors by microinjecting the GABA antagonist bicuculline methiodide into the VLPA caused a 68 +/- 7% increase in the AH/POA response. Most surprising was a reversal of the AH/POA pressor response to a depressor response (150 + 2% decrease) following bicuculline microinjections in the VLDA . This finding suggests that GABA is released in the VLDA following AH/POA stimulation. It was concluded that neuron pools in the VLPA and VLDA determine the magnitude and direction of blood pressure responses elicited by electrical stimulation of the AH/POA. GABAergic mechanisms in the VLPA and the VLDA may modulate blood pressure changes relayed from the hypothalamus. A hypothetical pathway is proposed.
mesh_terms: D000818:Animals; D007025:Anterior Hypothalamic Nucleus / Q000502:physiology*; D001640:Bicuculline / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects*; D004558:Electric Stimulation; D006339:Heart Rate / Q000187:drug effects; D007033:Hypothalamus, Middle / Q000502:physiology*; D008297:Male; D008845:Microinjections; D009118:Muscimol / Q000494:pharmacology*; D009474:Neurons / Q000502:physiology; D010080:Oxazoles / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000502:physiology*; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
chemical_list: D010080:Oxazoles; D011956:Receptors, Cell Surface; D011963:Receptors, GABA-A; D009118:Muscimol; D005680:gamma-Aminobutyric Acid; D001640:Bicuculline