Characteristics of sympathetic reflexes evoked by electrical stimulation of phrenic nerve afferents.

In chloralose-anaesthetized cats, sympathetic reflex responses were recorded in left cardiac and renal nerve during stimulation of afferent fibres in the ipsilateral phrenic nerve. In cardiac nerve, a late reflex potential with a mean onset latency of 75.6 +/- 13.8 ms was regularly recorded which, in 20% of the experiments, was preceded by an early, very small reflex component (latency between 35 and 52 ms). In contrast, in renal nerve only a single reflex component after a mean latency of 122.1 +/- 13.1 ms was observed. Bilateral microinjections of the GABA-agonist muscimol into the rostral ventrolateral medulla oblongata resulted in a nearly complete abolition of sympathetic background activity and in an 88% reduction of the late reflex amplitude with only small effects on the latency of the evoked potentials. Under this condition, an early reflex component was never observed to appear. After subsequent high cervical spinalization, the residual small potentials which persisted after bilateral muscimol injections were completely abolished and in cardiac nerve an early reflex potential with a mean latency of 45 +/- 10 ms was observed in all but one experiment. The early reflex was therefore referred to as a spinal reflex component which, however, is suppressed in most animals with an intact neuraxis. In the renal nerve a spinal response was only observed in one experiment after spinalization. The results suggest that sympathetic reflexes evoked by stimulation of phrenic nerve afferent fibres possess similar spinal and supraspinal pathways as previously described for somato-sympathetic and viscero-sympathetic reflexes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Split medulla preparation in the cat: arterial chemoreceptor reflex and respiratory modulation of the renal sympathetic nerve activity

The study was undertaken in order to assess the changes in sympathetic output in a split medulla preparation of the cat which, as shown earlier, has impaired respiratory rhythm generation. The effects of medullary midsagittal sections on renal sympathetic nerve firing were investigated in chloralose anesthetized, paralyzed and artificially ventilated cats. Recordings of phrenic and recurrent laryngeal nerve activity served as indices of central respiratory rhythm generation. Sections, 5 mm deep from the dorsal medullary surface and extending 6 mm rostrally and 3 mm caudally to the obex, did not produce any significant changes in heart rate, blood pressure or tonic renal sympathetic nerve firing levels. They decreased or abolished, however, the respiratory rhythmicity in renal sympathetic nerve which paralleled the reduction of inspiratory discharges in phrenic and recurrent laryngeal nerves, and abolished the carotid body chemoreceptor-sympathetic reflex. The inspiratory activity remaining after the sections could still be enhanced by chemoreceptor stimulation. The inhibitory baroreceptor and pulmonary stretch receptor sympathetic reflexes, and the central excitatory effect of CO2 on renal sympathetic nerve firing were not altered. The effects of electrical stimulation within the midsagittal plane of the medulla have shown that descending pathways from the medullary inspiratory neurons (or their medullary collaterals) do not participate in the facilitation of spinal preganglionic neurons during inspiration and in relaying the pulmonary stretch receptor inhibitory sympathetic reflex. A region located close to the obex was identified from which excitatory responses in renal sympathetic nerves, compatible with the response obtained by carotid sinus nerve stimulation, could be evoked. It is concluded that a lesion in the midline of the lower medulla at the level of the obex selectively destroys cells or pathways which relay the carotid body chemoreceptor-sympathetic reflex.     

The effect of stimulation of the substantia nigra on low- and high-threshold startle reflexes in the cat

Effects of the substantia nigra (pars compacta) stimulation on two functional types of startle reflexes were studied in chloralose-anesthetized cats. The reflexes were the low-threshold ones evoked by tactile stimuli (T-reflex) and high-threshold ones evoked by intense peripheral nerve stimulation (spino-bulbo-spinal, SBS reflex). It was found that substantia nigra stimulation exerted mainly inhibitory influences on both types of reflexes. However the depression of the SBS-reflex was always more profound and long lasting (up to 8 min) than that of T-reflex. The latter reflex was sometimes facilitated.     

Influence of stimulation of the central gray matter on low- and high-threshold startle reflexes

Influences of the periaqueductal gray matter (PAG) stimulation on high-threshold jaw opening reflex (JOR) evoked by tooth pulp stimulation and on two functional types of startle reflexes were studied in chloralose anesthetized cats; the startle reflexes were high-threshold ones evoked by intense peripheral nerve stimulation (spino-bulbo-spinal, SBS, reflex) and low-threshold ones evoked by tactile stimuli (tactile spino-reticulo-spinal, TSRS, reflex). Stimulation of the majority of PAG sites induced considerable inhibition of JOR as well as profound depression of SBS-reflexes and moderate depression of TSRS-reflexes. Some PAG sites were found to exert a facilitatory action on the latter reflex. Effects of PAG stimulation were short-term (hundred ms) and/or long-lasting (minutes). Possible mechanisms of these effects are discussed.     

Effects of intravenous bicuculline and strychnine on inspiratory inhibitory responses in the cat

Single shock stimulation of the superior laryngeal nerve (SLN), intercostal nerve (ICN), phrenic nerve (PN) or within the medullary respiratory groups (DRG-VRG) produces a transient, short-latency attenuation of inspiratory motor activity. Trains of stimuli delivered to SLN and ICN cause premature termination of inspiration. This study examined involvement of glycine and GABAA receptors in these reflex inhibitions. Experiments were conducted in decerebrate, vagotomized, and paralyzed cats. Control responses of left PN activity to threshold single shock stimulation of SLN, PN, ICN and the DRG-VRG were recorded and the thresholds for SLN- and ICN-evoked inspiratory termination were determined. Five min after intravenous injection of bicuculline (1 mg/kg) or strychnine (50 micrograms/kg), the responses to stimulation were again recorded. This procedure was reiterated until the cumulative dose elicited marked convulsions. Neither drug affected the inspiratory terminating reflexes. Systemic bicuculline had no effect on transient inspiratory inhibition. However strychnine prolonged the onset latency and the duration of all four inhibitory responses. Since the degree of transient inhibition was not lessened (only delayed), it appears that these inspiratory inhibitory reflexes do not rely exclusively on actions of glycine or GABAA receptors.     

Spontaneous and reflexly evoked activity in pharyngeal, laryngeal, and phrenic motoneurons of cat

Experiments were performed on spontaneously breathing cats that were anesthetized with chloralose-urethane in order to study changing excitability in pharyngeal, laryngeal, and phrenic motoneurons. Pharyngeal constrictor motoneurons chiefly were spontaneously active during expiration; the stylopharyngeus and certain motoneurons serving the superior pharyngeal constrictors were inactive during either phase of tidal respiration. While confirming work of previous investigators that feeble glossopharyngeal (epipharyngeal branch) and superior laryngeal nerve stimulation transiently attenuated on-going phrenic nerve activity, such evoked afferent volleys excited laryngeal motoneurons independent of phases of respiration. On-going pharyngeal constrictor nerve activity (expiration) was attenuated for 20–50 msec by superior laryngeal nerve stimulation and for 100–300 msec by glosso-pharyngeal nerve stimulation. Intercostal nerve stimulation evoked occasional pharyngeal constrictor nerve discharges but more commonly attenuated its spontaneous nerve activity. Stylopharyngeus and an unknown portion of the superior pharyngeal constrictor motoneurons were excited by afferent volleys evoked in glossopharyngeal and superior laryngeal nerves. These aforementioned changes in excitability were unaffected by total neuromuscular paralysis while maintaining artificial respiration. It is concluded that certain pharyngeal constrictor motoneurons of the cat are spontaneously active during tidal expiration, are under central respiratory control, and that their intermittence along with those serving the diaphragm and larynx by modest afferent volleys in the ninth and tenth cranial nerves stage the act of swallow or expulsive reflexes, or both.     

Electro-acupuncture stimulation to a hindpaw and a hind leg produces different reflex responses in sympathoadrenal medullary function in anesthetized rats

The effects of electro-acupuncture stimulation (EAS) of two different areas of a hindlimb with different stimulus intensities on sympathoadrenal medullary functions were examined in anesthetized artificially ventilated rats. Two needles of 160 microm diameter and about 5 mm apart were inserted about 5 mm deep into a hindpaw (Chungyang, S42) or a hind leg (Tsusanli, S36) and current of various intensities passed to excite various afferent nerve fiber groups at a repetition rate of 20 Hz and pulse duration of 0.5 ms for 30-60 s. Fiber groups of afferent nerves stimulated in a hindlimb were monitored by recording evoked action potentials from the afferents innervating the areas stimulated. The sympathoadrenal medullary functions were monitored by recording adrenal sympathetic efferent nerve activity and secretion rates of catecholamines from the adrenal medulla. EAS of a hindpaw at a stimulus strength sufficient to excite the group III and IV somatic afferent fibers produced reflex increases in both adrenal sympathetic efferent nerve activity and the secretion rate of catecholamines. EAS of a hind leg at a stimulus strength sufficient to excite the group III and IV afferent fibers produced reflex responses of either increases or decreases in sympathoadrenal medullary functions. All responses of adrenal sympathetic efferent nerve activity were lost after cutting the afferent nerves ipsilateral to the stimulated areas, indicating that the responses are the reflexes whose afferents nerve pathway is composed of hindlimb somatic nerves. It is concluded that electro-acupuncture stimulation of a hindpaw causes an excitatory reflex, while that of a hind leg causes either excitatory or inhibitory reflex of sympathoadrenal medullary functions, even if both group III and IV somatic afferent fibers are stimulated.     

Inspiratory coupling to cardiac activity and to somatic afferent nerve stimulation in the anaesthetised rat

We examined the ability of somatic afferent nerve stimulation to entrain inspiratory onset in the anaesthetized spontaneously breathing rat, and compared features of this stimulus-ventilatory coupling to entrainment of inspiratory onset by cardiac activity. In 14 rats prior to stimulation, we commonly observed a constant temporal alignment between ECG R waves and inspiratory onset (cardioventilatory coupling). Stimulation of a hamstring nerve at rates close to the heart rate also caused coupling (a constant stimulus to inspiratory onset interval), although this was highly dependent upon frequency of stimulation, with small changes in frequency causing a loss of coupling. In experiments where stimuli were given at constant intervals after ECG R waves, we observed no augmentation of coupling. Our results indicate that both cardiac and somatic afferent nerve activity is able to entrain inspiratory onset. We have suggested that coupling causes respiratory frequency to increase, and it is possible that this is a general mechanism whereby non-respiratory afferents act as stimulants or pacemakers to respiratory rhythm. The role of non-respiratory activity in initiating inspiration needs to be more fully recognised and studied.     

An analysis of reflex changes in excitability of phrenic,laryngeal, and intercostal motoneurons

An investigation was carried out in anesthetized cats to ascertain whether self-excitation of phrenic motoneurons is a specific or generalized reflex mechanism for motoneurons allied to respiration. Whereas stimulation of only caudal intercostal nerves evoked discharge of phrenic motoneurons (intercostal-to-phrenic reflex), stimulation of all intercostal nerves elicited discharges in the recurrent laryngeal nerve (intercostal-to-recurrent laryngeal reflex). Weak superior laryngeal nerve stimulation provoked short-latency discharges in the recurrent laryngeal nerve but inhibited on-going inspiratory activity in phrenic and external intercostal motoneurons. In the presence of self-excitation of phrenic motoneurons (phrenophrenic system), there was concomitant excitation of laryngeal motoneurons. In contrast, when self-excitation of laryngeal motoneurons occurred (laryngolaryngeal system) there was concomitant inhibition of inspiratory activity (phrenic and external intercostal motoneurons). Paired shocks delivered to superior laryngeal and intercostal nerves while recording from phrenic, recurrent laryngeal, and intercostal nerves failed to reveal convergent interaction. It is concluded that self-excitation is a generalized reflex mechanism for certain motoneurons allied to respiration.     

Neural organization of the viscero-cardiac reflexes

The reflex responses evoked in the postganglionic nerves to the heart were tested in chloralose-anaesthetized cats. Electrical stimulation of the A delta afferent fibres from the left inferior cardiac nerve evoked spinal and supraspinal reflex responses with the onset latencies of 36 ms and 77 ms respectively. The most effective stimulus was a train of 3-4 electrical pulses with the intratrain frequency of 200-300 Hz. Electrical stimulation of the high threshold afferent fibres (C-fibres) from the left inferior cardiac nerve evoked the reflex response with the onset latency of 200 ms. The C-reflex was present in intact animals and disappeared after spinalization. The most effective stimulus to evoke this reflex was a train of electrical pulses delivered at a frequency of 1-2 Hz with an intratrain frequency of 20-30 Hz. The most prominent property of the C-reflex was its marked increase after prolonged repeated electrical stimulation. We conclude that: (1) viscero-cardiac sympathetic reflexes may be organized at the spinal and supraspinal level; (2) viscero-cardiac sympathetic reflexes evoked by stimulation of the A delta and C afferent fibres from the left inferior cardiac nerve have different central organization.     

Contribution of unmyelinated afferents from the sural nerve to spinal reflex activity

Ipsilateral ventral root reflexes evoked from electrical stimulation of the sural nerve were studied in an attempt to determine if the C or unmyelinated afferent fibers give rise to motor reflex responses because uncertainties in this area have persisted. Appropriate blocking techniques were utilized to isolate C fiber afferent barrages. Evidence was produced that a component of ipsilateral ventral root reflexes (including flexor reflexes) can be evoked solely with a C fiber afferent volley.     

Spontaneous and reflexly evoked laryngeal abductor and adductor muscle activity of cat

A study of spontaneous and reflexly evoked activity of laryngeal abductor (posterior cricoarytenoid) and adductor (thyroarytenoid and lateral cricoarytenoid) muscles was carried out in cats anesthetized with chloraloseurethane or made decerebrate and supplemented with ketamine HCl. The posterior cricoarytenoid muscle was active largely during inspiration but showed tonic activity throughout the respiratory cycle; the thyroarytenoid and lateral cricoarytenoid muscles were rhythmically active during expiration. Anesthetic amounts of pentobarbital abolished adductor rhythmicity and enhanced cyclic inspiratory activity of the abductor muscle. Hyperventilation increased the tonic adductor muscle activity while diminishing abductor muscle activity prior to resolution of apnea. Glossopharyngeal (epipharyngeal branch) and superior laryngeal nerve stimulation evoked chiefly excitatory effects on adductors and largely and attenuating effect on the abductor during inspiration. Stimulation of caudal intercostal nerves caused similar effects but to a lesser degree. Peripheral phrenic nerve stimulation during inspiration facilitated reflex abductor muscle activity whereas such stimulation during expiration facilitated reflex adductor muscle activity. The collective evidence further supports the conclusion that the larynx has a dual function: that of a respiratory organ (widening of the glottis during inspiration and its narrowing during expiration) and of a guardian of the lower respiratory tract from invading foreign matter (reflex sphincter action of contracting adductor muscles with relaxation of the abductor).     

Neuropeptide Y in the rostral ventrolateral medulla blocks somatosympathetic reflexes in anesthetized rats

The rostral ventrolateral medulla (RVLM) is a major integrative center of cardiovascular reflexes that modulate vasomotor tone. The functions of Neuropeptide Y (NPY) in the RVLM on cardiorespiratory responses remain unknown. Arterial blood pressure (AP), heart rate (HR), splanchnic sympathetic (sSNA) and phrenic nerve activities, and responsiveness to baro-, somatosympathetic, and chemoreflex stimulation were recorded before and after bilateral NPY injection (100 pmol, 200 nl/side) in the RVLM of vagotomized urethane-anesthetized rats (n=7). Responses were characterized by an initial increase in AP followed by prolonged hypotension (P<0.01). A similar biphasic effect was exerted on HR (P<0.01). NPY caused a large increase of sSNA (P<0.01), that gradually recovered towards baseline. Somatosympathetic responses evoked by tibial nerve stimulation were largely abolished following NPY microinjection (P<0.01), but sympathoexcitatory responses evoked by acute hypoxia or sympathoinhibition evoked by aortic depressor nerve stimulation were unchanged following NPY. There was no effect of NPY on phrenic nerve amplitude or frequency. We conclude that NPY exerts excitatory effects on sympathetic tone, but inhibits responses evoked by somatic inputs. We speculate that this apparent contradiction may be due to differential expression of NPY receptor subtypes on the soma of sympathetic premotor neurons in the RVLM and on the presynaptic terminals of neurons that comprise excitatory afferent pathways.     

Electrophysiological studies of a case of startle disease

A 53-year-old female with startle disease (major form) was reported. An abnormal startle response was the most prominent clinical feature. Physical examination revealed left lateral gaze palsy and left extensor plantar response. The caloric test evoked no responses bilaterally. Blood examinations including lysozomal enzymes and radiological examinations including MRI of the brain were all normal. A pathological startle reflex was elicited by the tap on the upper lip, causing the marked extension of the head with the elbow, hip, and knee joints slightly flexing. The earliest reflex activity in a surface-EMG study was recorded in the masseter muscle and the reflex then spread down the brain stem and the spinal cord. The duration of the discharge varied from 16 to 30 ms. The onset latencies of these responses from the tap were 11.2 ms, 12.7 ms, 14.5 ms, 25.7 ms, 38.5 ms, and 47.5 ms in the masseter, sternocleidomastoid, posterior-neck, biceps brachii, quadriceps femoris, and tibialis anterior muscle, respectively. An averaged electroencephalogram triggered by the taps showed no abnormal EEG activity preceding the pathological startle response, although a negative peak, which was thought as a normal early component of the trigeminal somatosensory evoked potentials, was followed by the reflex. High amplitude SEPs and long loop reflexes were observed following stimulation of the posterior tibial nerve but not of the median nerve. Blink reflexes and auditory evoked potentials were normal.(ABSTRACT TRUNCATED AT 250 WORDS)     

Area specific reflexes from normal and supernumerary hindlimbs of Xenopus laevis.

Two area specific reflexes elicited by natural stimulation of different regions of the hindlimbs of Xenopus laevis have been identified. Light or intense mechanical stimulation of the foot evokes reflex activity in the ipsilateral knee flexor nerve; moderate pressure applied to the calf evokes reflex activity predominantly in the ipsilateral knee extensor nerve. The reflex responses have been recorded electrophysiologically to overcome the limitations of behavioral observations for determining the presence of activity in particular muscles. Normal area specific reflexes are elicited in the normal ipsilateral hindlimb by stimulation of grafted supernumerary hindlimbs innervated either by hindlimb (lumbar) or by non-limb (thoracic) spinal cord segments. The area specific reflexes can be elicited only if the limb is grafted to a host younger than stage 54-55 of Nieuwkoop and Faber ('56), the stage at which reflex movements are first observed behaviorally. Abnormal reflex responses are evoked by stimulation of supernumerary limbs innervated by either thoracic or lumbar segments when the limb buds are grafted to older larvae. Supernumerary forelimbs grafted at early stages and innervated by either thoracic or lumbar spinal cord segments generally fail to elicit area specific reflex responses in the normal hindlimb. Single-unit recordings of afferent fibers supplying the normal and supernumerary hindlimbs show that each limb receives a separate nerve supply. No evidence for branched afferent fibers has been found. The implications of these results for theories of neuronal specification are discussed, particularly the hypothesis that peripheral tissues are able to specify the central actions of afferent fibers that innervate them.     

Absence of respiration modulation of carotid sinus nerve inputs to nucleus tractus solitarius neurons receiving arterial chemoreceptor inputs

The reflex responses to activation of the arterial chemoreceptors are dependent upon when in the respiratory cycle the chemoreceptor stimulus is given. To determine if the respiratory modulation of the chemoreflex occurs within the nucleus tractus solitarius (NTS), intracellular recordings were obtained in pentobarbital-anesthetized, paralyzed and mechanically ventilated cats, from 22 non-respiratory NTS cells which were depolarized following activation of the ipsilateral carotid body chemoreceptors (by close arterial injection of <100 μ1 CO₂ saturated bicarbonate). Activation of the ipsilateral carotid body chemoreceptors evoked depolarizations with amplitudes of 2.9–4.6 mV and durations of 2.1–5.9 s. Three of these cells also received a convergent excitatory input from the carotid sinus baroreceptors. Carotid sinus nerve (CSN) stimulation evoked either an excitatory post-synaptic potential (EPSPs) (n = 14, 8 monosynaptic) or an excitatory/inhibitory sequence (EPSP/IPSPs) (n = 8, 1 monosynaptic). CSN evoked PSPs were separately averaged (25–50 sweeps) during periods of phrenic nerve activity and phrenic nerve silence and during periods when the lungs were inflated and when the lungs were deflated. No parameter of the CSN evoked PSPs (latency, peak amplitude, duration) was altered during periods of phrenic nerve activity or lung inilation (all P values > 0.12, Wilxocon signed-rank test). The results suggest that there is no respiratory modulation of arterial chemoreceptor inputs by either central respiratory drive or lung stretch receptor afferent inputs at this early stage of the reflex arc.     

Studies on the respiratory control mechanism of medullary raphe nuclei and their serotonergic system

Respiratory control mechanism of the medullary raphe nuclei were studied with some references to their serotonergic mechanisms. Anesthetized, paralyzed and artificially ventilated cats were used and their phrenic nerve efferent activity was always observed as an indicator of central respiratory activity. Following results were obtained. 1) Electrical stimulation of medullary raphe nuclei, namely, nucleus raphe magnus, obscurus and pallidus, produced dominantly inhibitory responses in the phrenic nerve activity, while raphe stimulation in the pons and more rostral portion did not produce any respiratory responses. The blood pressure was depressed by raphe stimulation, too, almost in parallel to the respiratory inhibition. These inhibitory responses in respiration and blood pressure were partially antagonized by cyproheptadine (0.3-0.5 mg/kg i.v.) and methysergide (0.3-0.5 mg/kg i.v.). 2) Raphe stimulation inhibited remarkably activities of the medullary inspiratory and expiratory neurons, similarly. 3) In the experiment, where single shot stimulus was added to the raphe nuclei at the various time point in the respiratory phase, raphe stimulation showed the retardative effect of inspiratory switching, in addition to the inhibitory effect of phrenic burst activity. 4) The mechanism of respiratory inhibition produced by raphe stimulation was analyzed by evoked potentials in the averaged phrenic nerve activity. The post-stimulus averaged potentials of the phrenic nerve consist of the depolarizing potentials of about 10 msec duration and the subsequent hyperpolarizing potentials of several 10 msec duration, the duration time depending on the stimulus intensity. When stimulation was given in high frequency, the post-stimulus averaged potential became flattened, and the phrenic burst activity was inhibited almost completely. But in the case of stimulation in ventral parts of the raphe nuclei, the initial depolarizing potential was comparatively more prominent, and when high frequency stimulation was given, continuous firing was observed in the phrenic nerve activity. At the time of the continuous firing, respiratory rhythmicity was disappeared completely. 5) Propranolol (0.3-1.0 mg/kg i.v.), which have been recognized to have 5-HT1 antagonistic activity, reduced the hyperpolarizing potentials of the post-stimulus averaged potentials, and methysergide (0.3-1.0 mg/kg i.v.), 5-HT1 and 5-HT2 antagonist, reduced both depolarizing and hyperpolarizing potentials. These phenomena would suggest strongly that hyperpolarizing and depolarizing potentials are related to the 5-HT1 and 5-HT2 receptors, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Laryngeal effects of stimulation of rostral and ventral pons in the anaesthetized rat

In order to study the importance of two pontine regions modulating laryngeal resistance, electrical current or microinjections of glutamate (10-30 nl, 1-3 nmol) were made into the pontine parabrachial complex and the A5 region in spontaneously breathing anaesthetized rats. Two distinct patterns of laryngeal and respiratory responses were elicited. An increase of subglottal pressure was accompanied with an expiratory facilitatory response consisted of a decrease in both respiratory rate and phrenic nerve activity. A decrease of subglottal pressure was accompanied with an inspiratory facilitatory response consisted of an increase in both respiratory rate and phrenic nerve activity. The modification of laryngeal calibre occurred during both respiratory phases in most cases. The concomitant cardiovascular changes of these responses were also analyzed. Controls using guanethidine to block autonomic responses which might interact with respiratory control were also made. Histological analysis of stimulation sites showed a topographical organization of these responses: laryngeal constriction was evoked from K?lliker-Fuse, medial parabrachial nuclei and A5 region, whilst the laryngeal dilation was evoked from the lateral parabrachial nucleus.     

Site and action of electroacupuncture-induced effects on the rat jaw-opening reflex

The aims of the present study were to identify the specificity of the pain-relieving effects of electroacupuncture (EA) stimulation by comparing its effects on the jaw-opening reflex evoked by noxious and nonnoxious inputs, and to identify the site of action of EA in the jaw-opening reflex arc. I examined the EA effects on three responses involved in the jaw-opening reflex arc using Wistar albino rats: (i) the jaw-opening reflex to stimulation of the orofacial region, (ii) evoked responses in a secondary neuron site, and (iii) jaw-opening responses to stimulation of the secondary neuron site. EA stimulation almost suppressed the responses involved in the pathway of the jaw-opening reflex evoked by high-threshold afferent fibers, whereas it scarcely affected those in the pathway of the reflex evoked by low-threshold afferent fibers. From a comparison of the degree of suppression of the three responses, I suggest that EA suppression of the jaw-opening reflex was induced chiefly on the activity of the spinal trigeminal nucleus. In conclusion, it can be said that EA stimulation is almost selectively effective on the activity of the secondary neuron site involved in the jaw-opening reflex evoked by noxious input.     

The participation of bulbar "respiratory" and "nonrespiratory" neurons in the development of the expiration reflex

The patterns of impulse activity of medullar neurons were investigated in nembutal-anaesthetized cats during the expiration reflex elicited by electrical stimulation of the internal branch of superior laryngeal nerve. It was shown that low- and high-threshold superior laryngeal afferents caused excitatory reflex reactions of different complexity in significant number of reticular nonrespiratory neurons. Respiratory neurons exhibited systemic changes of spontaneous activity, but in 22.4 per cent of them reflex responses were recorded. These responses occurred during activation of low-threshold laryngeal afferents. Oligo- and polysynaptic excitatory connections of low-threshold laryngeal afferents are found with inspiratory beta neurons, P-cells and laryngeal motoneurons, but inhibitory ones-with inspiratory gamma neurons. Participation of investigated neurons in the mechanisms of inhibition of inspiration, vocal cords closure and rate of breathing adaptive decrease during expiration reflex is discussed.