Alterations of phrenic nerve activity caused by stimulation of neuronal structures in rostral area of ventral surface of the medulla oblongata

Abstract

Electrical stimulation of neuronal structures in a rostral area of the ventral bulbar surface alters central inspiratory activity in anesthetized rats, augmenting the amplitude and velocity of this activity during the periods of its increase and plateau. The reactions are more pronounced in rats with transected vagal nerves. Blockade of pulmonary mechanoreceptors eliminates the influence of rostral neuronal structures only on the temporal" parameters of the plateau. Bilateral cooling of neuronal structures to 20~ results in complete block of central inspiratory activity. Key Words: rostral region of ventral bulbar structure; central inspiratory activity; respiratory centerCentral inspiratory activity (CIA) of the respiratory center forms under the influence of specific afferent pulses from chemo-and mechanoreceptors [6,71. The role of central chemoreceptors in this activity remains unclear because these receptors have not been identified. Recent studies have shown that neuronal structures located in the rostral region of the ventral surface of medulla oblongata (ventral bulbar surface, VBS) probably fulfil a chemosensory function and exert a complex effect on the respiratory center [2,4]. The mechanism of this effect is poorly understood. The purpose of the present study was to evaluate the role of the rostral region of the VBS in the mechanisms through which the CIA of the respiratory center is formed. MATERIALS AND METHODSThe study was carried out on 58 Nembutal-anesthetized (35 mg/kg) rats (body weight 200-250 g) with intact (n=36) or cut (n=22) vagal nerves. The VBS was exposed from the C1 level to the level of Department of Normal Physiolo9% State Medical University, Samara exit of roots of cranial nerves VI-VII and 4.0-4.5 mm lateral to the midline. Rostral neuronal structures of the VBS were stimulated via bipolar electrodes (interelectrode distance 100 g) with square pulses (100 Hz, 1 msec, 0.5-20 gA) delivered by an ESU-2 electrostimulator. Neuronal structures were cooled to 20~ unilaterally or bilaterally with a thermode. Electrical activity of the phrenic nerve was measured with bipolar silver electrodes, amplified, and integrated using standard equipment [1]. Arterial blood pressure was recorded with an ID-2I apparatus. The results were statistically analyzed by Student's t test with comparison of the means. RESULTSNeuronal structures of the VBS were electrically stimulated, with a step of 1 mm, at levels from the middle of cranial nerve XII roots to the exit of nerve VI roots (Fig. 1). A neurogram with its envelope showing variations of the phrenic nerve activity (PNA) before and after electrical stimulation is shown in Fig. 2. This activity changed, upon stimulation of a limited zone within the rostral region of the VBS.

Nitric Oxide in the A5 Region Modulates Reaction of the Respiratory Center and Blood Pressure to Hypoxia in Rats

“…The diaphragmatic nerve was prepared at a distance of 4-6 mm. The peripheral nerve segment was transected and put to bipolar sliver electrodes connected to an amplifier-integrator system [1]. Electrical activity of the diaphragmatic nerve was digitized and recorded.…”

NMDA Receptors of A5 Area in the Regulation of Blood Pressure and Respiratory Activity during Hypoxia in Rats

“…Ventral surface of the brainstem was opened from the fi rst cervical vertebra to cranial nerve VI orifi ce and 4.0-4.5 mm lateral to midline. Surgical approach to ventral surface of the brainstem was described previously [2][3][4].…”

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Role of NMDA- and non-NMDA Subtypes of Glutamate Receptors in A5 Neuronal Structures in the Regulation of Respiration and Circulation during Thermal Nociceptive Stimulation in Rats

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