Showing papers on "Reflex published in 1969"

Diminished Baroreflex Sensitivity in High Blood Pressure

Abstract: Sudden intravenous injections of small amounts of angiotensin or phenylephrine were given to 30 subjects to produce modest, brief increases in directly measured systemic arterial pressure. A plot of each systolic pressure against the second succeeding cardiac cycle length produced a linear distribution, the slope of which was expressed as the millisecond increase in cycle length per mm Hg rise in systolic pressure. The slope is an index of baroreflex sensitivity and was found to have an average value of 12.8 in 18 subjects without hypertension and 2.8 in 12 others with hypertension. When all results were pooled, there was an inverse relationship between the resting mean arterial pressure and slope of the baroreflex regression lines. The findings demonstrate reduced sensitivity of the baroreflexes in hypertension, with respect to control of heart rate. A distinction is made between this change in sensitivity and simple resetting of the reflex.

An electromyographic analysis of muscular activity in the hindlimb of the cat during unrestrained locomotion.

Abstract: During walking in unrestrained cats the electromyographic activity in many hindlimb muscles has been correlated with the angular movement in the hip, knee and ankle joints. The activity is rather uniform in the extensors but individual in different functional groups of flexor muscles. Observations on the precise timing of the onset of the main extensor activity suggest that it is not a reflex effect produced by stimulation of receptors (from muscle or skin) in the limb. It is assumed that the basic activity is a centrally programmed alternating activation of extensors and flexors. A possible reflex regulation mainly from la afferents of this basic activity is discussed with special attention given to factors that may elucidate the difference in movement at the hip on one side and the knee and ankle on the other.

Muscular, bronchomotor and cardiovascular reflexes elicited by mechanical stimulation of the respiratory tract

Abstract: 1. The effects of mechanical stimulation in the nose, epipharynx, laryngopharynx and tracheobronchial tree, and of chemical irritation of the nasal mucosa, were studied on various somatic and autonomic functions in cats.2. Action potentials were recorded from the diaphragm and rectus abdominis muscles of spontaneously breathing cats, and from the phrenic and lumbar nerves of paralysed, artificially ventilated cats. Expulsive processes such as sneezing and coughing evoked from the nasal, laryngopharyngeal and tracheobronchial mucosae were characterized by strong diaphragmatic and abdominal expiratory discharges; synchronous discharges in these antagonistic respiratory muscles and their motoneurones often occurred especially during laryngopharyngeal stimulation of coughing.3. The ;aspiration reflex' elicited from the epipharynx was characterized by brief bursts of high-frequency activity in the phrenic nerve and diaphragm, and was usually not followed by any expiratory activity in the rectus abdominis or its motoneurones.4. In paralysed, artificially ventilated cats stimulation of the laryngeal and tracheobronchial regions caused large increases both in total lung resistance and in tracheal constrictor nerve fibre activity, indicating reflex tracheo-bronchoconstriction; similar stimulation of the epipharyngeal and nasal mucosae decreased both total lung resistance and tracheal constrictor nerve fibre activity, indicating reflex bronchodilation.5. In paralysed cats, stimulation of each of the four sites in the respiratory tract caused a reflex increase in systemic blood pressure, the largest hypertensive response coming from the epipharynx. Nervous activity in cervical sympathetic efferent fibres was increased by the stimulations, especially those of the epipharyngeal and laryngopharyngeal regions.6. There was good correlation in time and magnitude between the changes in total lung resistance and in bronchoconstrictor fibre activity, and also between the changes in blood pressure and in efferent sympathetic discharge, although the mechanical changes lagged behind the nervous ones.7. In anaesthetized, spontaneously breathing cats stimulation of the respiratory tract evoked large variations in blood pressure accompanying the spasmodic respiratory efforts, probably by mechanical effects.

The rubrospinal tract. II. Facilitation of interneuronal transmission in reflex paths to motoneurones

Abstract: Summary. 1. The effect of stimulation of the red nucleus on transmission of synaptie actions from different systems of primary afferents to alpha motoneurones has been invest/gated in cats, mainly with intracellular recording from motoneurones. 2. The dominating effect is facilitation, presumably caused by excitatory action exerted from the rubrospinal tract on interneurones of reflex arcs. The time course of facilitation suggests that the minimal linkage from the rubrospinal tract to these interneurones is monosynaptic. 3. Interneuronal transmission in reflex pathways from the following afferent systems is facilitated : a) Ia inhibitory between flexors and extensors, l~ubrospina] facilitation did not reveal Ia inhibitory pathways between adductors and abductors at the hip. b) Ib excitatory and inhibitory. There is marked facilitation of the reciprocal effects evoked by Ib afferents from extensors but also of other Ib pathways, for example inhibitory from extensors to flexor nuclei and from flexors to extensor nuclei and excitatory from flexors to extensor nuclei, e) Low threshold joint, inhibitory and excitatory, presumably from afferents with Ruffini endings. d) Low threshold cutaneous, excitatory and inhibitory. Since transmission from these afferents could be facilitated under conditions when there was no effect on transmission from high threshold muscle afferents it is postulated that the effect is exerted on pathways which are not part of the common pathways from the flexor reflex afferents, e) Flexor reflex afferents, excitatory and inhibitory. Facilitation of these pathways is not found regularly, in some eases there was no effect and in others inhibition. 4. The effeets are discussed in relation to the complex effects evoked from the rnbro spinal tract in motoneurones and to supraspinal regulation of proprioceptive reflexes. 5. It is postulated that in complex movements alternative Ib patterns may be mobilized, whereas flexion-extension movements are subserved by the Ib pattern found in the spinal eat. 6. Facilitation of the Ia inhibitory pathway is taken to indicate "a-y-linkage" in reciprocal inhibition. It is pointed out that convergence from Ia and descending impulses on a common inhibitory interneurone may play an important role in the regulation of a-y-linked flexion-extension movements.

Eye movements from single utricular nerve stimulation in the cat.

Abstract: Single utricular nerves were electrically stimulated in the cat. The induced eye movements were almost pure rotation in both eyes. In addition to rotation, there were upward shifts in the ipsilateral eye and downward shifts in the contralateral eye. Slight contralateral horizontal shifts occurred in both eyes. Tension increases in extraocular muscles were strongest in the ipsilateral superior oblique and contralateral inferior oblique. They were weaker in the ipsilateral superior rectus and contralateral inferior rectus, and were weakest in the ipsilateral medial rectus and contralateral lateral rectus muscles. The tension increase in the contralateral inferior oblique and the lateral rectus was studied by changing the frequency of stimulation. The utricular-ocular reflex reacted from very low to very high frequencies, as high as 1600 cps. In comparison, the cupulo-ocular reflex arc did not respond well to high frequencies. The temporal summation in the vestibulo-ocular reflexes appeared different between...

Reflexes to sacral parasympathetic neurones concerned with micturition in the cat

Abstract: 1 Reflexes to sacral parasympathetic neurones were studied by electrophysiological techniques in decerebrate, in chloralose-anaesthetized, and in chronic spinal cats2 Excitatory reflexes from pelvic nerve and sacral somatic afferent nerve fibres were present before and after chronic transection of the spinal cord, but the latencies differed markedly It was concluded that the long-latency reflexes observed when the spinal cord was intact involved long-loop reflexes to the brain-stem The weak, short-latency reflexes in the chronic spinal cat were never observed when the spinal cord was intact and could be due to reorganized spinal connexions The short-latency reflexes are probably unimportant in normal micturition3 Stimulation of afferent fibres in the pelvic or sacral somatic nerves produced short-latency inhibitory post-synaptic potentials (IPSPs) and inhibition of discharges in parasympathetic neurones This inhibition was due to a spinal reflex4 A local reflex was demonstrated in the pelvic plexus This was probably a cholinergic axon reflex, but the remote possibility that it was a local cholinergic reflex involving sensory neurones in the bladder wall has not been excluded

Presynaptic inhibition of the monosynaptic reflex by vibration

Abstract: In cats, the monosynaptic reflex (MSR) elicited from L7 or S1 dorsal roots, or from the tibial nerve (H reflex) was suppressed by vibration at 50-500 c/s of the hind limb with innervation intact. The MSR was not suppressed by selective vibration of cutaneous receptors, and suppression was still observed after the hind limb was skinned. In contrast, the phenomenon disappeared when all muscle nerves were crushed. Suppression of the MSR by vibration was shown to be mediated by presynaptic inhibition by the following methods: correlation with onset of the dorsal root potential (DRP) evoked by vibration, and abolition of both DRP and reflex suppression by picrotoxin; demonstration of primary afferent depolarization and normal excitability of motoneurones to direct stimulation. Reasons are given for deducing that the muscle afferent fibres responsible for the presynaptic inhibition induced by vibration are group Ia rather than groups Ib or II, or afferent fibres from Pacinian corpuscles.

Neuronal Controls of a Behavioral Response Mediated by the Abdominal Ganglion of Aplysia

Abstract: Tactile stimulation of the siphon and mantle shelf in Aplysia causes a characteristic withdrawal response of the external organs of the mantle cavity. A similar response also occurs spontaneously. Both responses are mediated by the abdominal ganglion and therefore provide an opportunity for correlating cellular functioning and behavior in a relatively simple and well-studied neuronal system. The withdrawal responses are controlled by five identified motor cells which receive two types of synaptic inputs. One set of excitatory connections, activated by tactile stimulation of the siphon and mantle shelf, mediates the defensive withdrawal reflex. A second set of connections is activated by a spontaneous burst of activity in a group of closely coupled interneurons which are excitatory to some of the motor cells and inhibitory to the others. This second set of connections mediates the spontaneous withdrawal response. These two inputs can therefore switch the same population of motor cells from a simple reflex to a more complex, internally organized response.

Evidence that the secondary as well as the primary endings of the muscle spindles may be responsible for the tonic stretch reflex of the decerebrate cat

Abstract: 1. The size of the tonic stretch reflex of the soleus or gastrocnemius muscle of the decerebrate cat has been compared with the size of the reflex contraction elicited in the same muscle by high-frequency vibration applied to its tendon. 2. On the assumption that vibration preferentially excites the primary endings of the muscle spindles it may be used to estimate the relation between the reflex response and the frequency of the Ia input to the spinal cord. On this basis, the increase in tension evoked by increasing extension is too great to be explained by the increase in Ia input with extension previously found on single fibre recording in comparable preparations. 3. When vibration was superimposed on stretch reflexes elicited by different extensions, the size of the additional contraction elicited by the vibration remained approximately constant. If the stretch and vibration reflexes both depended entirely upon the Ia pathway, then occlusion between them would have been expected instead of the simple summation which was found. 4. The absence of occlusion was not due to variation of the contractile strength of the muscle with its extension. This was shown by finding that the reflex contraction of soleus produced by stimulating the medial gastrocnemius nerve also remained the same size when elicited at different lengths of the muscle. 5. The reflex effects were studied of superimposing alternate stretches and releases of 0·2 mm, on extensions of several mm. The small stretches elicited responses which were larger than expected from the response to large stretches, and which were approximately the same size at different mean lengths of the muscle. 6. It is concluded that the tonic stretch reflex of the decerebrate cat cannot readily be explained solely by the increase in Ia discharge produced by stretching, as usually believed. Instead, it is suggested that the group II afferent fibres from the secondary endings of the muscle spindle also play an important part in its production.

Cardiovascular responses in apnoeic asphyxia: role of arterial chemoreceptors and the modification of their effects by a pulmonary vagal inflation reflex.

Abstract: 1. In the spontaneously breathing anaesthetized dog, the systemic circulation was perfused at constant blood flow; there was no pulmonary blood flow and the systemic arterial blood P(O2) and P(CO2) were controlled independently by an extracorporeal isolated pump-perfused donor lung preparation. The carotid and aortic bodies were separately perfused at constant pressure with blood of the same composition as perfused the systemic circulation.2. Apnoeic asphyxia, produced by stopping the recipient animal's lung movements and, at the same time, making the blood perfusing the systemic circulation and the arterial chemoreceptors hypoxic and hypercapnic by reducing the ventilation of the isolated perfused donor lungs, caused an increase in systemic vascular resistance.3. While the systemic arterial blood was still hypoxic and hypercapnic, withdrawal of the carotid and aortic body ;drive' resulted in a striking reduction in systemic vascular resistance. Re-establishing the chemoreceptor ;drive' immediately increased the vascular resistance again.4. Apnoeic asphyxia carried out while the carotid and aortic bodies were continuously perfused with oxygenated blood of normal P(CO2) had little or no effect on systemic vascular resistance.5. The systemic vasoconstrictor response produced by apnoeic asphyxia was reduced or abolished by re-establishing the recipient animal's lung movements, and this effect occurred in the absence of changes in the composition of the blood perfusing the systemic circulation and arterial chemoreceptors. This abolition of the vasoconstriction was due to a pulmonary reflex.6. Apnoeic asphyxia slowed the rate of the beating atria due to excitation of the carotid and aortic body chemoreceptors. This response can be over-ridden by an inflation reflex arising from the lungs.7. It is concluded that the cardiovascular responses observed in apnoeic asphyxia are due, at least in part, to primary reflexes from the carotid and aortic body chemoreceptors engendered by arterial hypoxia and hypercapnia. The appearance of these responses is, however, dependent upon there being no excitation of a pulmonary (inflation) vagal reflex.

Reflex Response of Orbicularis Oculi Muscle to Supraorbital Nerve Stimulation: Study in Normal Subjects and in Peripheral Facial Paresis

Abstract: A REFLEX blink was first described by Overend 1 in 1896. Wartenberg 2 in 1945 recognized that blink reflexes evoked with different maneuvers were probably identical and proposed the term "orbicularis oculi reflex." Kugelberg 3 studied the response of the orbicularis oculi muscle to a tap over the brow. He recognized two different responses, an early ipsilateral reflex (latency: 12 msec) and a late bilateral reflex (latency: 21 to 40 msec). From a comparison with the masseter reflex (latency: 7.5 msec), he postulated that the early reflex was transmitted through a simple arc compatible with a myotatic reflex. However, the nature and pathway of this arc is still in dispute. On the basis of animal experiments, Tokunaga et al 4 suggested that the early reflex was relayed through the main sensory nucleus of the trigeminal nerve rather than through the mesencephalic nucleus. The late bilateral reflex is probably transmitted through

The activity of lung irritant receptors during pneumothorax, hyperpnoea and pulmonary vascular congestion

Abstract: 1. The activity of lung irritant receptors during pneumothorax, hyperpnoea and pulmonary congestion has been studied by recording from single vagal nerve fibres from the receptors in rabbits. 2. The receptors were stimulated during induction and during removal of pneumothorax. 3. Pneumothorax caused a greater depression of minute volume in bilaterally vagotomized rabbits, compared with those with intact vagus nerves. 4. Hyperpnoea due to breathing through an added dead space increased the discharge of the receptors. Experiments on paralysed and artificially ventilated rabbits showed that this was not a direct action of the asphyxial changes in blood gas tensions. 5. Pulmonary congestion, induced by inflating a balloon in the left atrium, stimulated the receptors in paralysed artificially ventilated rabbits. 6. The evidence that the receptors cause vagal reflex hyperpnoea and bronchoconstriction is discussed, together with their role in the reflex ventilatory and bronchomotor changes in the conditions studied.

Descending Monosynaptic and Reflex Control of γ-Motoneurones

Abstract: The supraspinal and reflex control of γ-motoneurones has been studied with intra- and extracellular recording from lumbosacral γ-motoneurones in the cat. Monosynaptic EPSPs were recorded in some γ-motoneurones on stimulation of the brain stem. These effects were evoked from the Deiters' nucleus and from fibres descending in the medial longitudinal fascicle probably originating in the pontine reticular formation. Previous investigations have revealed monosynaptic connections to α-motoneurones from these regions and our results suggest parallel effects to α- and part of the γ-motoneurone population supplying one muscle. Indirect evidence suggests that this monosynaptic effect is exerted only on static γ-motoneurones, thus implying a linkage between the descending monosynaptic control of α- and static γ-motoneurones via these pathways. The reflex effects to γ-motoneurones have been studied with graded electrical stimulation of ipsi- and contralateral hindlimb nerves. Five γ-motoneurones, presumably all belonging to extensor motor nuclei, were found to receive IPSPs from group I afferents and it is suggested that only static γ-motoneurones are influenced. It has not been possible to decide if these IPSPs are evoked from Ib or Ia afferents. The reflex effects from group II and III muscular afferents, joint and cutaneous afferents seem to conform to the effects evoked in α-motoneurones from these afferents.

An analysis of possible nervous mechanisms involved in the peristaltic reflex

Abstract: 1. The effects of drugs on peristalsis and on the contractions of the two muscle coats of the isolated guinea-pig ileum in response to co-axial electrical stimulation have been studied. 2. Co-axial stimulation (0·1 msec pulses) never produces simultaneous contraction of both muscle coats. When one muscle contracts, the other either relaxes or remains quiescent. 3. The circular muscle contraction has two components. The first is reflex in origin and is brought about either by distension of the gut with increasing intraluminal filling or by the contraction of the longitudinal muscle in response to electrical stimulation at low frequency (1/sec), provided this raises the intraluminal pressure to the threshold for eliciting the circular muscle contraction. As the circular muscle contracts, the longitudinal muscle relaxes although stimulation continues. If the circular muscle contraction is prevented by reducing the intraluminal filling, or by adding a ganglion-blocking drug, the longitudinal muscle remains contracted until withdrawal of the stimulus. 4. In the presence of hyoscine, the reflex contraction of the circular muscle is unimpaired but, since the longitudinal muscle contraction is abolished, a higher intraluminal pressure is required to elicit the reflex. 5. The second component of the circular muscle contraction appears in response to electrical stimulation at high frequency (3-10/sec), upon withdrawal of electrical stimulation. This delay indicates the simultaneous stimulation of a dominant inhibitory innervation. 6. The excitatory nerves to the circular muscle require a higher frequency of stimulation than those to the longitudinal muscle, which respond to single shocks. 7. Cholinergic blocking agents (hyoscine, morphine, hemicholinium and botulinum toxin) antagonize the responses of the longitudinal muscle to co-axial stimulation without affecting those of the circular muscle, thus suggesting that the excitatory fibres to the circular muscle are not cholinergic. Prostaglandins (E1 and E2) selectively antagonize the circular muscle contractions evoked by co-axial stimulation. Tetrodotoxin blocks both longitudinal and circular muscle responses. 8. Dimethylphenylpiperazinium (DMPP) and 5-hydroxytryptamine (5-HT) stimulate ganglia but have no direct action on the smooth muscle of guinea-pig ileum. 9. During a maintained contraction of the longitudinal muscle in the presence of high concentrations of acetylcholine (2·5 × 10−7 to 10−6 g/ml.) a contraction of the circular muscle accompanied by a relaxation of the longitudinal muscle is elicited by distension of the gut, and by co-axial stimulation. Similar reciprocal responses are produced by 5-HT or by DMPP and they are finally blocked by DMPP. 10. These results are consistent with the hypothesis that in the myenteric plexus there exists an arrangement of nerves which ensures that the two muscle coats of the intestine do not contract simultaneously but are activated reciprocally so that when one muscle layer contracts the other relaxes or is prevented from contracting.

The Influence of DOPA on the Static and the Dynamic Fusimotor Activity to the Triceps Surae of the Spinal Cat

Abstract: The influence of descending “noradrenergic” fibres on the stretch reflex and the discharge of γ-motoneurones to the triceps surae has been analysed by injecting DOPA i.v. in the acute spinal unanesthetized cat. After DOPA, a tonic stretch reflex develops in the soleus muscle as revealed by an increased electromyographical activity on extension of the muscle. In parallel, static γ-motoneurones aqcuire a resting discharge, which can be inferred from the finding that secondary endings have an elevated discharge rate after DOPA. The discharge in single γ-efferents could be influenced through short latency reflex paths from afferent fibres including group II afferents; further, the γ-efferents were found to participate in the late and long-lasting reflex effects that can be evoked after DOPA. On the basis of their resting discharge and reflex effects, the γ-efferents recorded could tentatively be identified as static or dynamic. Both static and dynamic γ-motoneurones to extensors have a higher resting discharge after DOPA. Hence in contrast to previous findings on flexor γ-motoneurones no reciprocal control on the resting discharge in the two types of efferents is exerted. Only γ-motoneurones classified as static received monosynaptic activation from fast descending fibres, presumably vestihulospinal.

Intercostal-to-phrenic reflexes in the spinal cat.

Abstract: The diaphragm, which previously has been shown to contain relatively few proprioceptors and to lack autogenetic facilitation, was found to be under reflex control from intercostal afferents. Electrical stimulation of the intercostal nerves of the lowest thoracic segments elicited a polysynaptic reflex excitation of phrenic motoneurones followed by a depression of ‘spontaneous’ phrenic motor activity. No phrenic responses were elicited from the upper thoracic segments. Increased phrenic activity was also elicited by mechanical stimulation of the trunk wall; the receptive area of these effects was similarly limited to the region of the insertion of the diphragm. Alike reflex effects were obtained from both the internal and the external intercostal nerves. In the internal nerve both group Ib and II afferents were found to contribute to the reflex whereas in the external nerve it was mainly the secondary muscle spindle endings which gave rise to the response. In contrast to the intercostal-to-intercostal reflexes cutaneous afferents proved to be without effect in the intercostal-to-phrenic reflex.

Neonatal startles, smiles, erections, and reflex sucks as related to state, sex, and individuality.

Abstract: Frequencies of startles, reflex smiles, erections, and reflex sucks were recorded in the context of the state in which they occurred in 32, 2- to 3-dayold healthy neonates. States were monitored for each infant during 2 hours and 20 minutes divided in 6 observation periods. Observer agreements ranged from 80 percent to 100 percent on the infants' states and from 93 to 100 percent on the spontaneous behaviors. Results confirm Wolff's findings (1966) that there is a highly significant relation between state and the type and frequency of the spontaneous behaviors. The frequencies are highest during regular sleep when the infant is most deafferented and they diminish in direct proportion to the infant's closeness to wakefulness. Results on sex differences reflect a consistent trend that males startle more in all states and females engage more frequently in reflex smiles and bursts of rhythmical mouthing. Since the mean rate of the spontaneous behaviors is almost identical for males and females when erections are excluded, it appears that females make up in smiles and reflex sucks what they lack in startles. The data also suggest that erections are spontaneous behaviors which occur over and above the other discharge behaviors. Rank correlations showed that individual infants tend to rely heavily on specific discharge channels over states (e.g., .77 for erections, .53 for rhythmical mouthing). The discussion focuses on the possible function of the spontaneous behaviors for providing endogenous afferent stimulation under conditions of deafferentation, during a period when such stimulation may be critical for the developing central nervous system, and on the potential significance of these behaviors for later development.

Elicitation of Reflex Vagal Relaxation of the Stomach from Pharynx and Esophagus in the Cat

Abstract: Distension of different parts of the esophagus in chloralosed cats caused prompt and pronounced relaxation of the stomach. Even slight distension was sufficient to elicit gastric relaxation, and the degree of relaxation vaned with that of the esophageal distension. The gastric relaxatory response was shown to be due to elicitation of a vago-vagal reflex to the stomach. The response could be elicited also after exclusion of spinal connections, but disappeared after vagotomy. It could not be blocked by atropine or guanethidine. It thus resembled the gastric relaxation obtained by direct electric stimulation of the vagal “relaxatory” fibres to the stomach. It is concluded that these fibres constitute the efferent pathway of the observed esophageo-gastric vago-vagal relaxatory reflex.—Furthermore, a similar gastric relaxation, mediated via the vagal efferent relaxatory fibres, was recorded in connection with pharyngeally elicited swallowing. It is assumed that the gastric relaxation pattern described plays an essential role in “receptive relaxation” of the stomach during deglutition.

Renal receptors evoking a spinal vasometer reflex.

Abstract: 1. Certain afferent fibres in the renal nerves show an increased rate of discharge in response to small increases in renal vein pressure and to substantial increases of ureteral pressure. Such fibres enter the spinal cord largely through the upper lumbar dorsal roots. 2. In spinal cats, stimuli exciting these afferent fibres evoke a reflex discharge in sympathetic nerves to the kidney and a fall in systemic arterial pressure. Change in flow or peripheral resistance, independent of arterial pressure, could not be demonstrated for the renal vascular bed. In spite of a lack of evidence for a renal vasomotor effect, the existence of the reflex fall in arterial pressure following excitation of receptors sensitive to venous pressure strongly implies that there is a form of circulatory regulation at the spinal cord level.

Cardiac Sympathetic Nerve Activity: Changes Induced by Ouabain and Propranolol

Abstract: A study of the effects of ouabain and propranolol on the spontaneous activity in the preganglionic sympathetic nerves to the cat heart showed that ouabain can produce both an inhibition and a stimulation of the spontaneous activity in sympathetic nerves. The inhibition appears to be reflex in nature and is not present when the buffer nerves are sectioned. The stimulation is correlated with the development of cardiac arrhythmias and is antagonized by propranolol.

Reflex Cardiovascular Depression Produced By Stimulation Of Pulmonary Stretch Receptors In The Dog

Abstract: To study the possible reflex effects of stimulation of pulmonary stretch receptors on the cardiovascular system, experiments were designed that would allow separate assessment of the responses of the heart, the total peripheral vascular resistance, and the resistance of the innervated hindlimb that was perfused at a constant flow rate. In every experiment, inflation of the lungs to a positive pressure of 20 mm Hg produced significant negative inotropic and chronotropic effects. Heart rate fell an average of 22.3±3.8% (SEM) (P < 0.01), pressure recorded from within an isovolumic balloon in animals on total cardiopulmonary bypass fell an average of 14.3±4.6% (P < 0.05), dp/dt recorded from within the balloon declined an average of 31.4 ± 6.0% (P < 0.01), and contractile force measured with a Walton-Brodie strain gauge arch fell an average of 18.6 ±2.2% (P < 0.01). Similarly, a depressor response to inflation of the lungs was noted in the periphery as manifested by an average decrease in total peripheral vascular resistance of 21.9±2.5% in the animals on total cardiopulmonary bypass (P < 0.01), and by an average decrease in perfusion pressure in the isolated hindlimb of 26.0 ±3.8% (P < 0.01). After bilateral cervical vagotomy, the cardiovascular responses to inflation of the lungs were either abolished or markedly lessened. Thus, sudden expansion of the lungs activates the afferent arm of a depressor reflex, which produces negative inotropic and chronotropic responses, in addition to arterial vasodilation. The receptors are sensitive to stretch and the afferent pathway runs predominantly in the vagus nerves.

Late motor neuron degeneration following poliomyelitis.

Abstract: A RELATIONSHIP between preceding acute anterior poliomyelitis and the later development of motor neuron disease has only occasionally been suggested since it was first postulated by Charcot in 1875. The clinical differentiation between “chronic spinal atrophy,” “chronic poliomyelitis,” and amyotrophic lateral sclerosis was not made clear in the earlier case reports and, except in a few instances, only one or two cases were reported and there is no record of the natural history of the disease. We therefore report five cases of disease of the motor neuron system developing many years after poliomyelitis in early life, and also emphasize the benign nature of this condition, in contrast to the very bad prognosis of classical motor neuron disease, where death usually occurs within four years of the onset.

Conditional Reflex Activation of the Sympathetic Cholinergic Vasodilator Nerves in the Dog

Abstract: Sympathetic, cholinergic kasodilatation in skeletal muscle was induced as orienting and conditional reflex responses in conscious dogs. A sound stimulus elicited an orienting reflex accompanied by an atropine-sensitive vasodilatation in the skeletal muscles of the hind limb. Further, a tachycardia and a slight blood pressure rise were noticed. The orienting reflex response disappeared gradually on repetition of the sound stimulus. The same cardiovascular events were obtained as conditional reflexes to both electrical cutaneous stimulation and exercise on a treadmill. The conditional responses were not diminished if the conditional reflexes were reinforced by training. Graded conditional responses were obtained when the intensities of the unconditional stimuli were varied. The increase in blood flow to the hind limb following treadmill exercise was not influenced by atropine. Our findings indicate that the sympathetic vasodilator system is activated prior to situations when an increased muscle blood flow is suddenly required. The results also suggest that activation of the dilator nerves takes place not only in emotionally charged situations, such as the defence reaction, but also in anticipation of exercise when the emotional involvement is less prominent.