Jean-Michel Macron

Somatotopy in the phrenic motor nucleus of the cat as revealed by retrograde transport of horseradish peroxidase

Cats received unilateral or bilateral horseradish peroxidase (HRP) injections into various portions of the diaphragm. In two experiments one of the cut cervical roots of the phrenic nerve was immersed in HRP. The phrenic motoneurons located in the fifth and occasionally the fourth cervical segment send their axons, via the upper phrenic root, to pars sternalis and pars costalis of the diaphragmatic dome whereas the neurons of the sixth segment innervate preferentially the dorsal portion both crura and dome. No evidence of contralateral innervation of the diaphragm was obtained.

Influence of trigeminal nasal afferents on bulbar respiratory neuronal activity.

This study examined the influence of nasal trigeminal afferents, the anterior ethmoidal nerve (AEN) and posterior nasal nerves (PNN) on the spike discharges of respiratory-related neurons recorded in the ventral respiratory group (VRG) (2.6-3.5 mm lateral to the midline, from 1 mm rostral to 3 mm caudal to the obex and at depth of 2-4 mm below the dorsal surface). Electrical stimulations to the AEN and PNN were administered to 10 pentobarbital anaesthetized cats and to 8 ketamine anaesthetized, vagotomized, curarized and ventilated cats. Single shock stimulations of either nerve evoked transient and total inhibition of inspiratory activities. Expiratory-related neurons of the VRG presented three patterns of activity in response to stimulation:excitation, inhibition or inhibition followed by excitation. More generally, expiratory units are activated with a short latency. In the course of repetitive stimulation of the AEN and PNN we observed a prolongation of the spontaneous inspiratory discharge which presented transient, short inhibition in response to each shock. Most expiratory units presented a short activation which was synchronous with the transient inhibition of inspiratory activities. When repetitive stimulation provoked a sneeze-like response, we observed a progressive increase in the duration of transient inspiratory inhibition first, associated with a progressive reinforcement of transient expiratory activation. Secondarily, just before the expiratory thrust, we noted a stronger inhibition of the inspiratory activity which preceded a high-frequency (400 Hz) expiratory discharge. Nasal afferents exert a forceful excitatory effect on bulbospinal (BS) and non-bulbospinal-non-vagal (NBS-NV) expiratory cells of the VRG. The effects due to vagotomy and curarization are discussed.

Segmental motor innervation of the cat diaphragm

In ten anaesthetized adult cats, bipolar recording electrodes were inserted in different muscular bundles of each hemi-diaphragm. Both stimulation and section of the phrenic cervical branches were made. The upper phrenic cervical branch innervates both the sternal and lateral portions of the diaphragm whereas the lower phrenic cervical branch innervates both the lateral and dorso-caudal portions.

Projection of phrenic afferents to the external cuneate nucleus in the cat

The present study, performed on anesthetized, spontaneously breathing cats, deals with the projection of group I and II muscle afferents of the phrenic nerve (PN) to the external cuneate nucleus (ECN). Stimulation of the central end of the PN evoked a complex response in the ipsilateral ECN. Two principal components could be distinguished in this potential from the respective absolute refractory periods (ARP) and from the effect of antidromic stimulation in the ECN. Thus, the early group of waves may correspond to recordings of direct fibers and the later group to postsynaptic activations within the ECN. Similar to the forelimb nerves and intercostal nerves of the upper intercostal spaces, the larger muscle afferents of the PN project to the ECN.

Role of respiratory and non-respiratory neurones in the region of the NTS in the elaboration of the sneeze reflex in cat.

Extracellular recordings were made in the dorsal respiratory group (DRG) and adjacent reticular formation following single-shock stimulation of the anterior ethmoidal nerve (AEN) and during sneeze evoked by repetitive stimulation of the AEN in nembutal-anaesthetized, curarized and ventilated cats. These neurones were characterised according to (i) their activity during the respiratory cycle (as inspiratory augmenting or decrementing (I Aug or I Dec), expiratory augmenting or decrementing (E Aug or E Dec), silent or tonic), and (ii) their axonal projection (bulbospinal or non-bulbospinal-non-vagal (BS or NBS-NV)). Following single-shock stimulation of the AEN, most of the inspiratory neurones were transiently inhibited, whereas E Aug neurones were activated and E Dec neurones were activated and then inhibited. Silent neurones responded with a multispike or a paucispike pattern. Following repetitive stimulation of the AEN and during the resulting sneeze reflex, I Aug neurones increased their activity in parallel with the phrenic activity, I Dec neurones fired at the onset and at the end of the inspiration, E Dec and some silent neurones fired either during the compressive phase or after the expulsive phase, whereas E Aug and some silent neurones fired during the expulsive phase. We conclude that sneeze involves a reconfiguration of the central respiratory drive which uses, at least partly, the respiratory network to trigger a non-ventilatory defensive motor act.

Phrenic afferent input to the lateral medullary reticular formation of the cat

The afferent inputs from phrenic nerve stimulation to the lateral reticular formation of the lower brain stem were studied in anesthetized spontaneously breathing cats. The activity of reticular neurons was recorded by means of extracellular tungsten microelectrodes. Electrical stimulation of the central end of the right phrenic nerve evoked excitatory or inhibitory responses in the lateral reticular nucleus (LRN), in the nucleus ambiguus (AMB) and in a region dorsal to the AMB of ipsi- and contralateral sides. Phrenic afferents belonging to the flexor reflex afferent group were involved in these responses. The discharge pattern of the respiratory related units (RRU) of the AMB were exceptionally affected by phrenic nerve stimulations. It is concluded that high threshold phrenic afferents relay in the LRN before projecting to the cerebellar cortex. The overlapping of respiratory and non-respiratory afferents in the reticular formation may participate to the adaptations of respiratory and somatomotor functions during specific behaviors.

Nasal air puff stimulations and laryngeal, thoracic and abdominal muscle activities

In cats, we studied the activity of laryngeal, thoracic and abdominal muscles and the variations in oesophageal pressure in response to air puff stimulations of the nasal mucosa. Following single stimulations, inspiratory and laryngeal dilator muscles were transiently inhibited. During inspiratory inhibition, expiratory muscles and laryngeal constrictor were transiently activated. Repetitive air puff stimulations, which induced sneeze, evoked a similar pattern of transient activities during the inspiratory preparation of sneeze. This resulted in transient fluctuations of the oesophageal pressure, whose mean value became more negative as the preparatory inspiration enhanced. Our results suggest that the entire pool of respiratory neurons (bulbospinal, vagal and facial) works together in the sneeze reflex. Study of transient inspiratory inhibition demonstrates two periods during the preparatory inspiration phase of sneeze. In the first period transient effects are related to each shock of the stimulation. The second period is characterized by a diminution or a lack of transient effects associated with the stimulation. At the end of the expulsive phase, the diaphragm and the glottal dilator were further activated.

Influence of vagal afferents in the sneeze reflex in cats

We studied the effects of bilateral vagotomy and step pulmonary inflations (5, 10, 15 mmHg, i.e., 0.66, 1.33, 2 kKPa) on sneeze reflex in ketamine-anaesthetized cats. Bilateral vagotomy lengthens the duration of preparatory inspiration and diminishes the amplitude of expiratory activities in sneeze. In contrast, 5 mmHg pulmonary inflation facilitates the sneeze. It shortens the inspiratory preparation and increases the frequency of sneeze attacks. At 10 mmHg pulmonary inflations, inspiration is inhibited and only expiratory thrust occurs. At 15 mmHg pulmonary inflations, vagal afferent stimulations inhibit the sneeze.

Projections of phrenic afferences to the cat cerebellar cortex

Evoked phrenic potentials were recorded on the cerebellar cortex of anesthetized adult cats after electrical stimulation of both cervical branches (C5 and C6) of the right phrenic nerve. In this case phrenic stimulation evoked a surface positive response with a mean amplitude (+/- S.D.) of 13.4 +/- 5.2 microV. The mean latency and the mean duration of this phase were, respectively, 9.5 +/- 1.2 ms and 19.4 +/- 2.1 ms. This response was found only in the ipsilateral intermediate cortex and in the ipsilateral and, to a less extent, in the contralateral vermis of the posterior part of the anterior lobe (Larsells lobule V); these areas corresponding to the forelimb projection zones. The phrenic afferences projecting to the cerebellar cortex were essentially conducted in the contralateral ventro-lateral spinal tracts.

Effects of ipsilateral and contralateral cervical phrenic afferents stimulation on phrenic motor unit activity in the cat

The phrenic-to-phrenic inhibitory reflex has been analyzed using recordings of activity of single C5-phrenic motor units (PMUs). After ipsilateral or contralateral stimulation of the C6-phrenic root, early and late PMUs exhibit a similar inhibition. After contralateral stimulation, the duration of the inhibition is smaller and the threshold stimulus is higher than the corresponding values observed after ipsilateral stimulation. The latency of the inhibition is similar for both stimulations. Hemispinalization, contralateral to the recording site, affects weakly the phrenic-to-phrenic reflex. We conclude that early and late PMUs receive a similar inhibitory input from phrenic afferents and that the inhibition observed after cervical phrenic nerve stimulation may involve spinal cord circuits.