Brain stem mechanisms in the regulation of blood pressure in the rabbit

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Abstract
1. Blood pressure responses were evoked by electrical stimulation of the brain stem of the conscious, immobilised rabbit, front hypothalamus to medulla, before and after application of pentobarbitone. 2. After injection of the drug, many pressor points showed mixed depressor-pressor responses or pure hypotensive reactions, while others exhibited only a reduction of the blood pressure elevation under the influence of the barbiturate. Depressor points however never showed a reversal. 3. The percentage of mixed plus depressor points increased from 17 to 58% after application of the barbiturate. 4. Both types of vasomotor points are randomly distributed throughout the whole brain stem, with the greatest density of depressor elements in the posterior medulla. 5. The present results make anatomical definitions of circumscribed, antagonistic vasomotor centers untenable.