Spinal integration of segmental, cortical and breathing inputs to thoracic respiratory motoneurones

Abstract

SUMMARY1. The spinal integration of cortical, segmental and breathing inputs to thoracic motoneurones was studied in anaesthetized, paralysed cats: the breathing input was intensified by underventilation or abolished by hyperventilation.2. In apnoeic animals, low intensity stimulation of an internal intercostal nerve evoked a brief latency polysynaptic reflex discharge of expiratory motoneurones (direct response) in several adjacent segments with no or little response of the inspiratory motoneurones.3. A similar direct response of expiratory motoneurones occurred with brief tetanic stimulation of the trunk area in the contralateral sensorimotor cortex.4. Conditioning of an intercostal-intercostal test reflex by a prior stimulus to an intercostal nerve or to the cortex gave conditioning curves showing facilitation of transmission to expiratory motoneurones at short intervals (5-25 msec) and inhibition at long intervals (25-200 msec).5. The direct response of expiratory motoneurones to the cortical or' segmental inputs was depressed during the inspiratory phase when the animal was underventilated; conversely the spontaneous activity of the inspiratory motoneurones was inhibited for a period that corresponded with the direct response or to the phase of facilitated transmission to expiratory motoneurones. During the expiratory phase, the cortically or segmentally induced direct response was facilitated but the inhibition of inspiratory motoneurone activity was concealed by the absence of spontaneous activity.6

Variations in the time course of the synchronization of intercostal motoneurones in the cat

“…The thoracic dorsal roots contain afferents that excite motoneurones monosynaptically in the same and adjacent segments (Sears, 1964b;Kirkwood & Sears, 1982 a, b) and polysynaptically with a wider distribution (Downman, 1955;Aminoff & Sears, 1971 However, our principal evidence concerning the influence of dorsal root afferents is that many of the experiments described above were performed with the ipsilateral dorsal roots cut in up to five segments, always including the ones used for efferent recordings a, b; Kirkwood et al 1981b). An approximately equal number of the experiments were performed with the roots intact.…”

“…Sumi, 1963b;Guilbaud, Benelli & Besson, 1977) although there is plentiful evidence for interneuronal pathway (Downman, 1955, Sumi, 1963 Aminoff & Sears, 1971) and in particular for their release by spinal cord section (Downman, 1955;Downmann & Hussain, 1958). The upper lesions we used include the dorsolateral quandrant which Downman & Hussain (1958) found to be critical in the release of splanchnic to intercostal and intercostal to intercostal reflexes.…”

“…The interneurones may be part of a descending polysynaptic pathway transmitting the respiratory drive in parallel with the monosynaptic pathway so as to allow for integration with segmental and other inputs (Aminoff & Sears, 1971) and thus be excited by the respiratory drive. Alternatively they may be inhibited by the respiratory drive.…”

A bilateral cortico-bulbar network associated with breath holding in humans, determined by functional magnetic resonance imaging

“…possibly by a 'direct' corticospinal pathway, demonstrated both by electrophysiological studies in animals (Aminoff and Sears, 1971) and clinical observations in humans (Corfield et al, 1998;Nathan, 1963;Severinghaus and Mitchell, 1962); or by an 'indirect' pathway via the brain stem respiratory centres and their associated bulbospinal neurones (Orem and Netick, 1986).…”

Are the neurophysiological techniques useful for the diagnosis of diaphragmatic impairment in multiple sclerosis (MS)?

“…The voluntary respiratory pathway operates during wakefulness, allows behavioural modulation of respiration and the performance of volitional respiratory movement (Plum, 1970;Newson-Davis, 1974). The system depends on willed activity from the cerebral cortex through the corticospinal tracts and descending in the dorsolateral columns of the spinal cord (Plum, 1970;Aminoff and Sears, 1971;Howard et al, 1992).…”