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B S Nail

Publications and source records attributed to B S Nail.

12 recordsLinked to original sources
PubMed1987

Laryngeal motoneurone activity in the rabbit during asphyxic gasping.

Unitary activity was recorded from 44 recurrent laryngeal nerve (RLN) and 18 external laryngeal nerve (ELN) motoneurones in anaesthetized, paralysed rabbits during the development of periods of severe asphyxia caused by temporarily interrupting artificial ventilation. Ventilation was only recommenced when a simultaneously recorded phrenic neurogram showed the animal had attempted several gasps. Inspiratory-phased fibres (17 RLN, 14 ELN) displayed brief high frequency discharges with each gasp. Some inspiratory-phased ELN motoneurones (6/14) also displayed longer tonic discharges after each of the first few gasps. In the expiratory intervals immediately following each gasp many expiratory-phased fibres (13/21 RLN, 2/4 ELN) were active and 7 RLN fibres discharged a long train of impulses with a decrementing discharge pattern. In 3 anaesthetized rabbits, breathing spontaneously through a tracheostomy, a constant airflow was directed up through the larynx; successive gasps were associated with wide swings in translaryngeal pressure which were confirmed visually as reflecting rapid dilation of the glottis during gasps and intense constriction in the intervals between gasps.

Action Potentials↗
PubMed1987

Quantitative analysis of laryngeal mechanosensitivity in the cat and rabbit.

1. Single afferent fibres in the internal branch of the superior laryngeal nerve which responded to light touch or gentle probing of discrete areas of the exposed epithelium of the opened larynx were identified in anaesthetized, paralysed cats (148 fibres) and rabbits (58 fibres). 2. A quantitative examination of the sensitivity of these laryngeal mechanoreceptors to both static (step indentations) and dynamic (vibratory) forms of mechanical stimulation was undertaken using a servo-controlled mechanical stimulator. 3. In both species two predominant classes of mechanoreceptors were observed (Boushey, Richardson, Widdicombe & Wise, 1974). One class was distinguished by a regular and continuous pattern of activity at a frequency of 10-70 Hz (tonic fibres, sixty-six in cat, thirty-five in rabbit). The other class was silent or (more rarely) irregularly active at a very low frequency (silent fibres, eighty-two in cat, twenty-three in rabbit). 4. The location of the receptive fields was determined by manual probing. Inter-species and regional variations in receptive field location were observed for the two fibre groups. 5. Conduction velocity was measured for twenty-one tonic and seven silent fibres in the rabbit by a pre-triggered averaging technique. The results obtained (tonic: range 10.8-30.0, mean +/- S.E. of mean 21.4 +/- 1.2 m/s; silent: 14.8-28.6, 20.4 +/- 1.8 m/s) were characteristic of group III afferent fibres but were not significantly different for the two classes. 6. Both classes of receptor showed a response at the onset of a step indentation of the region of the mucosa that corresponded to their receptive field. Subsequent to this brief initial response the behaviour of the two classes diverged markedly. Tonic fibres were invariably slowly adapting whereas most (forty-four out of fifty-five in cat; twenty-two out of twenty-three in rabbit) silent fibres were rapidly adapting, at least for smaller indentation amplitudes. 7. Receptors of both classes were readily entrained to discharge at the same frequency as the probe stimulator (1:1 entrainment) when this was made to vibrate upon the receptive area for test periods of 0.5 or 1.0 s. Tuning curves were constructed of the minimum amplitudes required to elicit 1:1 entrainment throughout an entire test period at various frequencies. 8. Individual fibres in the two classes could be entrained at frequencies up to 400 Hz or more at sensitive (e.g. less than 100 microns) vibratory amplitudes. However, all fibres were less sensitive at these higher frequencies than at some lower point on the frequency scale.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Respiratory muscle activity during asphyxic apnoea and opisthotonus in the rabbit.

The behaviour of submandibular, cervical, thoracic and abdominal respiratory muscles was examined in the pentobarbitone-urethane-anaesthetized rabbit during progressive asphyxia induced by rebreathing. During asphyxic hyperpnoea the external intercostal, interchondral and scalene inspiratory activities augmented until succeeded by the apnoeic period, in which all were inhibited with the diaphragm. Likewise, the genioglossus, sternohyoid and thyrohyoid muscles exhibited inspiratory augmentation during asphyxic hyperpnoea until the onset of apnoeic inhibition. However, late in the apnoea these muscles, together with the sternothyroid, sternomastoid and digastric muscles, generated an augmenting tonic discharge associated with an intense abdominal constriction, and with the extension of the limbs characteristic of opisthotonus. This intense tonic activity, which was never expressed by the diaphragm and thoracic inspiratory muscles, was immediately interrupted or terminated by the subsequent inspiratory efforts of gasping respiration, during which the abdominal muscles were inhibited but all the submandibular, cervical and thoracic inspiratory muscles greatly participated. The mylohyoid muscles presented augmenting expiratory activity during asphyxic hyperpnoea which declined during the apnoea. These muscles, however, did not exhibit the intense tonic discharge expressed by the expiratory abdominal and inspiratory submandibular and cervical muscles in late apnoea and were not active in gasping.

Animals↗
PubMed1985

Tachypnoeic response to amyl nitrite inhalation in the rabbit.

Intratracheal inhalation of amyl nitrite, a non-specific smooth muscle relaxant, in the pentobarbitone/urethane anaesthetized rabbit caused reductions in tidal volume and both inspiratory and expiratory times, without a preceding apnoea, that were independent of the associated hypotension and of reflex influences from the carotid sinus region but dependent on supra-abdominal vagal integrity. In artificially ventilated, paralyzed rabbits amyl nitrite caused a pronounced sensitization of pulmonary stretch receptors (PSRs) during the inflation phase, typically with a reduction in the level of activity during the deflation phase. The time course of the change in the pattern of PSR activity paralleled that of the tachypnoeic response. The sensitization of a small sample of rapidly adapting 'irritant' receptors was of a significantly shorter duration. A unitary analysis of non-myelinated vagal afferents was not attempted. The sensitization of these vagal afferents cannot be attributed to the smooth muscle relaxant properties of amyl nitrite since other relaxants (sodium nitrite, sodium nitroprusside, phentolamine) did not possess this capacity, and such properties would be expected to diminish their activities.

Afferent Pathways↗
PubMed1985

Diaphragmatic, thoracic and limb motor effects of amyl nitrite inhalation.

In the pentobarbitone/urethane anaesthetized rabbit and pentobarbitone anaesthetized cat intratracheal inhalation of amyl nitrite, a non-specific smooth muscle relaxant, caused a vagally dependent depression of patellar reflex and spontaneous (thermal shivering and external intercostal inspiratory) motor activities. A prolonged vagally-independent potentiation succeeded the initial inhibition. The potentiation of intercostal activity may account for the increase in tidal volume produced by amyl nitrite after vagotomy. The patellar reflex potentiation survived thoracolumbar spinal transection but could not be attributed to a direct facilitation of neuromuscular or muscular events. A correlation existed between the relative dependence of fusimotor support of a muscle and its susceptibility to the inhibitory and subsequent facilitatory affects of amyl nitrite inhalation. The diaphragm and interchondral muscles, essentially independent of the autogenetic facilitation provided by muscle spindles, demonstrated neither of these effects. Conversely, the intercostal muscles depend greatly on such facilitation, as do the pectoral and limb muscles during thermal shivering.

Amyl Nitrite↗
PubMed1985

The identification of brainstem neurones projecting to thoracic respiratory motoneurones in the cat as demonstrated by retrograde transport of HRP.

Brainstem neurones which project to the immediate vicinity of the spinal motoneurones which supply the intercostal and abdominal respiratory muscles were identified by means of the retrograde transport of horseradish peroxidase (HRP). A combined electrophysiological and histological technique was used in which recording of phasic inspiratory or expiratory motoneurone activity within upper (T3-T4) or lower (T8-T9) thoracic segments was followed by the ion-tophoretic injection of HRP at these recording sites. HRP labelled cells were concentrated in those brainstem regions known to contain phasic respiratory neurones, namely the ventrolateral nucleus of the solitary tract (vl-NTS) or dorsal respiratory group (DRG), the ambiguus complex or ventral respiratory group (VRG) and the parabrachial pontine (PB) nuclei. In 18 cats, 248 cells were labelled in these three respiratory regions of the brainstem while 668 were much more diffusely distributed in other regions of the medulla and pons. The ipsilateral and contralateral contributions within the respiratory regions were respectively; 23%:77% (DRG), 33%:67% (VRG), 95%:5% (PB). These results are considered in the general context of previous electrophysiological and histological findings, but also with particular reference to a related study of the projections from brainstem neurones to the phrenic nucleus [32].

Animals↗
PubMed1985

Cells of origin of corticospinal projections to phrenic and thoracic respiratory motoneurones in the cat as shown by retrograde transport of HRP.

A combined electrophysiological and histological approach was employed to identify neurones within the motor cortex which project to the vicinity of spinal respiratory motoneurones, and which may be involved in the alteration of the pattern of breathing under certain conditions. Recording of respiratory phased activity from phrenic, or from thoracic motoneurones within either the upper (T3-4) or lower (T8-9) segments, was followed by the iontophoretic injection of HRP at these recording sites. After injections within the cervical or thoracic ventral horn, 219 cells were retrogradely labelled in 14 experiments. The majority of these cells (88%) were labelled contralateral to the injection site. Following the injection of HRP into the phrenic nucleus, labelling was observed at two major sites within the anterior sigmoid gyrus (ASG), one along the anterolateral edge of the cruciate sulcus, and the other along the ventrolateral border of the ASG. In contrast, cells labelled after injections into the thoracic ventral grey matter were located more medially within the ASG and the posterior sigmoid gyrus (PSG). The populations of cells labelled following phrenic and thoracic injections overlapped, primarily at the lateral edge of the cruciate sulcus. The somas of labelled cells were pyramidal, round or oval. The mean diameters of cortical cells labelled after injections into the lower or upper thoracic segments were 30.5 +/- 6.2 and 31.5 +/- 5.6 respectively, which were not significantly different in size. However, they were significantly larger than the mean diameter of the cells labelled from injections into the phrenic nucleus (22.7 +/- 4.2 micron).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1978

Computerized measurement of pulmonary conductance and elastic recoil.

A system devloped for on-line measurement of transpulmonary pressure, gas flow at the mouth, change in expired volume and plethysmograph volume uses a minicomputer to control a multiplexed analog to digital converter. The computer identified samples as static or dynamic values by monitoring a voltage activating a solenoid valve, used to close the airway. Analysis of these samples by other task-specific programs yielded the static deflation pressure-volume (PV) curve, the conductance-recoil pressure, GL-Pst(L), relationship and the maximum expiratory flow-volume (MEFV) curve; the MEF-Pst(L) curve and conductance upstream from the equal pressure point were derived. The PV relationship was represented by a fourth-order polynomial and the GL-Pst(L) relationship by linear regression. In 11 subjects the results obtained using on-line data collection, compared with manual analysis of oscillograph recordings, showed small differences in static compliance and in the maximum Pst(L); but overall the two methods showed excellent agreement. Besides advantages of speed and objectivity, this system facilitates a more rigorous analytical treatment of elastic recoil and conductance.

Asthma↗
PubMed1977

Human tactile detection thresholds: modification by inputs from specific tactile receptor classes.

1. Human detection thresholds for a vibratory stimulus applied to the volar surface of the index finger were examined under conditions where afferents from specific tactile receptor classes were simultaneously activated from the thenar eminence. The experiments were designed to test whether stimuli which have been shown previously to induce afferent inhibition of ;tactile' neurones in the cuneate nucleus of the cat could modify human subjective performance in a tactile detection task. Conditioning stimuli to the thenar eminence were usually of three forms; steady indentation to engage slowly adapting tactile receptors; 300 Hz vibration to engage Pacinian corpuscles; and 30 Hz vibration to engage the intradermal, rapidly adapting tactile receptors which are thought to be Meissner's corpuscles.2. In ten subjects the mean detection threshold for a 30 Hz test stimulus in the absence of conditioning stimulation was 8.6 +/- 1.0 mum (S.E.). Detection thresholds were increased substantially in the presence of a 300 Hz, 100 mum conditioning stimulus (mean increase 11.1 +/- 2.0 mum), whereas minor or insignificant effects were seen with conditioning stimuli consisting of (a) 30 Hz, 100 mum (mean increase 1.4 +/- 0.8 mum), (b) steady indentation, 1.5 mm in amplitude (mean increase 1.3 +/- 0.7 mum) or (c) 300 Hz, 100 mum to the contralateral thenar eminence (mean increase 0.4 +/- 0.5 mum).3. The 300 Hz conditioning stimulus to the ipsilateral thenar eminence caused a marked increase in detection thresholds at all test stimulus frequencies over the range 10-450 Hz. The effects of the conditioning stimulation therefore operated on inputs from Pacinian corpuscles, which are responsible for vibration detection at 80-450 Hz, and on inputs from the intradermal, rapidly adapting receptors which are responsible for vibration detection at 10-80 Hz.4. The band width of conditioning vibratory frequencies which was effective at amplitudes of 100 mum in bringing about increases in detection threshold extended from 50-80 Hz to 300 Hz, the maximum tested.5. Whereas amplitudes of 1-2 mum produced clear increases in detection thresholds with conditioning stimuli of 300 Hz, amplitudes of > 200 mum were needed at 30 Hz.6. The observed elevations in detection threshold are consistent with an afferent-induced inhibitory action exerted at synaptic relays of the sensory pathway by tactile inputs arising exclusively or predominantly from Pacinian corpuscles.

Adult↗
PubMed1975

Central and peripheral neural respiratory activity in the mature sheep foetus and newborn lamb.

Activity from respiratory neurones in the medulla, the phrenic and intercostal nerves was recorded in 25 foetal sheep, exteriorized a few days before term from ewes given a spinal anaesthetic, and from nine newborn lambs, anaesthetized with an allobarbitone-urethane mixture. In 12 foetuses, there was little or no sustained respiratory activity, central activity consisting of tonically discharging expiratory and other neurones and silent inspiratory neurones. In the remaining 13 foetuses, respiratory activity was periodic or continuous and it was possible to confirm that the motor component of the respiratory reflex was mature, that apnoea was not due to medullary depression, that foetal respiration was unaffected by chemoreceptor stimulation, by noise, by light, by electrical stimulation of the sciatic nerve and only slightly by inflation or deflation of the lungs. All these stimuli were effective shortly after birth. Occlusion of the umbilical cord caused poorly sustained gasps in the "non-breathing" foetuses and in the "breathing" foetuses, abolition of inspiratory and expiratory activity in the medulla and the onset of gasps and flattening of the electro-corticogram. Rhythmic respiration resumed after release of the cord with a latency which varied with the duration and severity of the asphyxia. This type of respiratory depression was not reflex but due to a direct, central action of hypoxia. The sequence of respiratory events at birth is discussed.

Animals↗