On the central pattern generator for the basic breathing rhythmicity

Abstract

Recent advances in several laboratories concerning the respiration-related medullary neurons, their locations, projections, interconnections, morphological and physiological properties, and patterns of inhibitory postsynaptic potentials, excitatory postsynaptic potentials, and discharge rate, on the one hand, and the "systems behavior," on the other, have provided the basis for new hypothesis concerning the neural mechanisms underlying the central pattern generator (CPG) for breathing and its different parts. The onset of the "ramp"-like increase in inspiratory activity is due to an abrupt release of inhibition and a subsequent progressively increasing synaptic excitation of inspiratory premotor neurons. The integration of the excitatory "drive" inputs underlying the ramp inspiratory activity seems to depend on structures in the ventrorostral medulla, including nucleus paragigantocellularis. The termination of this activity by the off-switch mechanisms is actuated when a critical threshold is attained by the excitatory inputs of 1) a slowly increasing inspiration-related activity and 2) the afferent input from the pulmonary stretch receptors. The nature of the former activity is discussed. During the expiratory phase, an inhibitory activity suppresses inspiration-facilitating inputs with a slowly decaying power that controls the expiratory duration. The postinspiration activity, which brakes the rate of exhalation during the first part of the expiratory phase, depends on mechanisms separate from those responsible for the inspiratory ramp activity. The respiratory CPG seems to be organized with considerable amount of redundancy, or "degeneracity."

Modification by chemical stimuli of temporal difference in the onset of inspiratory activity between vagal (superior laryngeal) or hypoglossal and phrenic nerves of the rat.

“…JOHN et al (1981) found that during eupnea and apneusis the onset of recurrent laryngeal nerve inspiratory activity is earlier than that of Phr burst, whereas in gasping the Phr activity begins before recurrent laryngeal activity. These differences in onset of inspiratory discharges in eupnea have been explained on the basis of 1) differences in threshold of the recruiting motoneurons, 2) differences in depolarizing input drive to the motoneurons or drive influences from the chemosensors, and 3) differences in reflex influence from the pulmonary stretch receptors (CoHEN, 1975;EULER, 1983EULER, , 1986. The third possibility may not account for the present results because experiments were performed in the vagotomized animal.…”

The Midbrain Periaqueductal Gray Control of Respiration

“…Cell groups in the medullary and pontine lateral tegmental field are thought to control respiration (von Euler, 1983;Feldman, 1986;Long and Duffin, 1986). The inspiration-related cell groups differ from those related to expiration.…”

“…Expiration-related nuclei contain interneurons projecting to the internal intercostal and abdominal muscle motoneurons in the thoracic and upper-lumbar spinal cord (Holstege and Kuypers, 1982;Miller et al, 1989;Holstege, 1991b). Together, these premotor respiration-related centers regulate cyclic breathing (or eupnea) on the basis of afferent information from the pulmonary mechanoreceptors (lung volume, stretch, and airway receptors) and from peripheral chemoreceptors in the carotid arteries measuring pCO 2 and pO 2 levels in the blood (von Euler, 1983;Feldman, 1986;Long and Duffin, 1986). Most of this information enters the brainstem via the vagal nerve.…”

Reconfiguration of respiratory-related population activity in a rostrally tilted transversal slice preparation following blockade of inhibitory neurotransmission in neonatal rats

“…Numerous studies and reviews have addressed the question of how the mammalian respiratory rhythm and motor pattern is generated, modulated, and transmitted to the respiratory muscles [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Despite the growing knowledge in this field the models for respiratory rhythm generation are still being discussed controversially [17][18][19].…”

“…Nevertheless, synaptic inhibition is required from birth on to generate a physiological threephase motor pattern [22]. The generation of this threephase motor pattern of breathing (inspiration, postinspiration and late expiration) requires the functional and structural integrity of a pontomedullary respiratory network [3,4,14,15,23,24]. Nevertheless, the network can be separated anatomically and functionally into compartments.…”