Arthur M. Brown

Pressor Reflexes Produced by Stimulation of Afferent Fibers in the Cardiac Sympathetic Nerves of the Cat

Afferent fibers in cardiac sympathetic nerves were stimulated electrically in an attempt to evoke circulatory reflexes. A pressor response was always elicited during stimulation of the central end of the cut left inferior cardiac or pericoronary nerve in vagotomized intact-brain or spinal cats. The maximum blood pressure rise was 21.5 mm Hg during inferior cardiac nerve stimulation and 14.1 mm Hg during pericoronary nerve stimulation. Heart rate and respiration were unaffected by stimulation. The alpha-receptor-blocking agent phenoxybenzamine hydrochloride abolished the pressor response. Sequential sectioning of cardiac nerves arising from either the stellate ganglion or the thoracic sympathetic trunk, or of white rami 1 through 4, indicated that each branch carried afferents contributing to the pressor response. Evoked potentials revealed that excitation of Aσ fibers in the inferior cardiac nerve elicited a weak pressor response, and excitation of C fibers provoked a much stronger response. C fiber continuity between the pericoronary nerve and the inferior cardiac nerve was demonstrated.

Unified Account of the Variable Effects of Carbon Dioxide on Nerve Cells

When the abdominal ganglion of Aplysia californica is exposed to 5 percent carbon dioxide, certain neurons are depolarized, others hyperpolarized, and some are unaffected. The effect of increased carbon dioxide is due solely to the concomitant fall in extracellular pH, which causes an increase in membrane chloride conductance of responsive cells. The directional change of the membrane potential in different neurons is determined by the relative values of the chloride equilibrium and the resting potentials. The chloride equilibrium potentials are calculated after direct measurement of the intracellular chloride activity with a chloride microelectrode.

Ionic Basis of the Photoresponse of Aplysia Giant Neuron: K+ Permeability Increase

The giant neuron of the Aplysia abdominal ganglion hyperpolarizes during illumination. The light-initiated potential change is associated with an increase of membrane conductance. It reverses sign at the potassium equilibrium potential (about -83 millivolts), which was determined from direct measurements of internal potassium activity. The membrane hyperpolarization is produced entirely by a light-induced increase in potassium permeability.

Active Transport of Potassium and Chloride in an Identifiable Molluscan Neuron

Direct measurements of intracellular K+ and Cl-activities before and after blockage of cellular metabolic processes indicate that K+ is actively transported inwardly and Cl-is actively transported outwardly from the giant cell of the abdominal ganglion of Aplysia. The rewarming of cells that have been cooled to 1� � 1�C causes K+ to be taken up and Cl- to be extruded against electrochemical gradients.

Sympathetic Ganglionic Transmission and the Cardiovascular Changes of the Defense Reaction in the Cat

The effects of ganglionic blockade on the circulatory components of the defense reaction were studied in 25 anesthetized cats. Hexamethonium alone partially blocked the response; a combination of hexamethonium and atropine was necessary to block it completely. Vasodilation of skeletal muscle was reversed to vasoconstriction during hexamethonium infusion. Direct recording from pre- and postganglionic sympathetic nerves showed persisting ganglionic transmission during hexamethonium infusion that was subsequently blocked by atropine. Unit recordings showed that some ganglion cells were completely blocked by hexamethonium alone. Preganglionic discharge was unaffected. It is suggested that ganglion cells giving rise to cholinergic vasodilator fibers have fewer atropine-sensitive receptor sites than do cells from which adrenergic constrictor fibers arise.

Pulmonary Vasoconstriction Elicited by Stimulation of the Hypothalamic Integrative Area for the Defense Reaction

Changes in the pulmonary circulation evoked by stimulation of the hypothalamic integrative area for the defense reaction were studied in 22 cats anesthetized with a chloralose-urethane mixture. Pulmonary arterial pressure and flow, left and right atrial pressures, aortic pressure, arterial flow to the skinned hind limb, and heart rate were all significantly increased. The calculated pulmonary vascular resistance was also significantly increased. The rise in pulmonary vascular resistance was abolished by bilateral stellectomy or by hexamethonium infusion; it was not affected by bilateral cervical vagotomy. Therefore, the increase in pulmonary vascular resistance was mediated by the thoracic sympathetic nerves. The increase in pulmonary arterial flow was mainly caused by an increase in heart rate; a small rise in calculated stroke volume also occurred.

Carbon Dioxide Action on Neuronal Membranes

Medullary respiratory neurones of mammals are exquisitely sensitive to CO2, the excitation by this agent providing the main stimulus for respiration (VON EULER and SODERBERG [1952]). On the other hand, cortical and phrenic neurones are inhibited by CO2 (KINJEVIC, RANDIC, and SIESJO [1965]; GILL and KUNO [1963]). The mechanism whereby CO2 produced these diverse effects was unknown (LAMBERTSON [1961]), so my colleagues and I undertook a study of this problem. The results of this study have been recently published (BROWN, WALKER and SUTTON [1970]; BROWN and BERMAN [1970]) and are reported briefly here.

A Small Analog Computer for Continuous Measurement of Intracellular Ion Activities

The operation of liquid ion exchanger microelectrodes that allows measurement of internal potassium and chloride activities in identifiable neurons has been described. A computer that solves the logarithmic equation necessary for computation of these activities has been constructed and tested successfully. The great value of the computer is that it permits continuous measurement of these activities. When the internal ion activities change, such continuous measurement allows calculation of potassium and chloride permeabilities in single neurons.