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At least 1,009 records · Page 56Linked to original sources
PubMed2004

Passive movement of hip and knee joints decreases the amplitude of soleus H-reflex in stroke patients.

OBJECTIVES: The study aims to investigate the changes of the H-reflex in soleus (Sol-H-reflex) during hip and knee joint movements in stroke patients. METHODS: The experiments were carried out on five stroke patients with spastic hemiplegia (2 males and 3 females, 48 to 71 years old). Sol-H-reflexes were measured 200 times for each joint movement speed Stimulus was given at random intervals (4 to 5 seconds) during the joint movement. Two movement speeds were used to investigate the effects of movement speed. RESULTS: For both fast and slow movements, the amplitude of the Sol-H-reflex decreased in the middle flexion phase. In contrast, the amplitude of the Sol-H-reflex increased in the middle extension phase. For the fast movement, the Sol-H-reflex was smaller in only a small angle range during the flexion and extension phase in comparison to the slow movement. The Sol-H-reflex during the flexion phase was significantly smaller than during the extension phase at almost all angles for both speeds. The Sol-H-reflex for both speeds was smaller than the Sol-H-reflex at rest for the whole angle range. CONCLUSION: These results demonstrate the differential effects of Sol-H-reflex modulation in stroke patients when compared with normal subjects.

Aged↗
PubMedDate not supplied

[Clinical techniques for use in neurological physical examinations. II. Motor and reflex functions].

AIMS: The aim of this study is to highlight the chief practical aspects of the techniques used in the neurological physical examination of the motor and reflex functions. DEVELOPMENT: We recommend clinicians to carry out a brief but consistent and effective exploration in a systematic, flexible and orderly manner to check for abnormalities in the motor and reflex functions of the nervous system. Should any anomalies be detected, then a more detailed and thorough neurological exploration must be performed selectively. We present a detailed review of the practical aspects of the main techniques used in the physical examination of these neurological categories. The motor function is explored using techniques that examine muscle tone, muscle strength, muscle fatigability, hypokinesia, tremor, coordination and gait. Lastly, in this category several manoeuvres that are useful in hysterical or mimicking paralyses are also dealt with. Reflexes to examination are usually divided into: 1. Myotatic reflexes; 2. Cutaneomucous reflexes; 3. Spinal cord or defence automatism reflexes; 4. Posture and attitude reflexes. We also add the study of primitive pathological reflexes, remote reflexes, synkinesias and signs of meningeal irritation. CONCLUSIONS: We present a detailed description of the main clinical techniques used in the neurological physical examination of motility and reflexes, as well as an approach that allows them to be performed on adult patients. In addition, we underline the importance of physically examining the nervous system in contemporary medicine and the need to continually perfect the way these techniques are performed in order to achieve an efficient clinical practice.

Humans↗
PubMed1975

Reflex patters initiated by the secondary sensory fiber endings of muscle spindles: a proposal.

Muscle spindles have two kinds of sensory fibers, each with stretch-sensitive endings on the nuclear bag muscle fibers and the nuclear chain muscle fibers within the spindle. The stretch reflex responses initiated by the primary sensory fibers have been well defines. There are other stretch reflexes of poorly defined origin and distribution. Clinical studies on spastic patients indicate that these stretch reflexes show regional responses or regional synergies. Stretch of flexor muscles of proximal joints of an extremity causes slowly recruiting, prolonged, reflex flexion in that extremity, in the contralateral extremity and also in the ipsilateral extremity, producing the crossed extension-flexion reflex and long spinal reflex. Likewise, stretch of extensor muscles of the proximal joints initiates a similar extension reflex in the same distribution. Stretch of the distal flexors of an extremity reflexly spreads flexion through that extremity. Stretch of the distal extensors of an extremity spreads extension throughout that extremity. These reflexes can be abolished by intramuscular neurolysis with phenol. They have long internuncial pathways and involve both alpha and gamma motoneurons. The demonstration that these reflex patterns are initiated by stretch of the muscle and show characteristics similar to those shown in physiological studies by the secondary sensory spindle reflexes suggests that they are initiated by stretch of the endings of the secondary sensory fibers of muscle spindles.

Humans↗
PubMed1991

Measurement of anal and genitoanal reflexes in cats.

Noninvasive determination of anal and genitoanal reflexes was evaluated in clinically normal cats. Thirty adult mixed-breed cats (15 sexually intact or castrated males, 15 sexually intact or spayed females) were sedated by IV administration of ketamine, acetylpromazine, and atropine. Anal reflexes were recorded from the anal sphincter muscle after ipsilateral and contralateral electrical stimulation of the perineal skin. Genitoanal reflexes were recorded from the anal sphincter muscle after electrical stimulation of the penis or clitoris. An anal sphincter response to tibial nerve stimulation was attempted. Anal reflexes from ipsilateral and contralateral stimulations and a genitoanal reflex were detected in all cats. Anal sphincter responses to tibial nerve stimulation were inconsistent (4/30) and were not included in any analyses. Anal reflexes had response latencies of 7.5 to 12.0 ms (ipsilateral stimulation) and 6.5 to 13 ms (contralateral stimulation). Genitoanal reflexes had latencies of 9.0 to 13.0 ms (males) and 6.5 to 9.0 ms (females). Anal reflex latencies were significantly (P less than 0.05) longer for contralateral, opposed to ipsilateral, stimulation and were significantly (P less than 0.05) longer in males than in females. Genitoanal reflex latencies were also significantly (P less than 0.05) longer in males than in females, reflecting the more peripheral stimulation site in males. Anal reflex responses could be recorded in 2 feline clinic patients with such severe perineal trauma that pudendal nerve function could not be manually evaluated A potentially favorable prognosis was given in each instance on the basis of detection of the response. One cat eventually recovered.(ABSTRACT TRUNCATED AT 250 WORDS)

Anal Canal↗
PubMed1990

Noradrenergic modulation of the masseteric reflex in behaving cats. II. Physiological studies.

Studies in the preceding paper demonstrated that the amplitude of the masseteric reflex in behaving cats is augmented by pharmacological manipulations that increase norepinephrine (NE) tone in the motor trigeminal nucleus (MoV) through exogenous means. The present studies examine whether such a relationship also exists under physiological conditions, i.e., whether physiological increases in NE synaptic activity are correlated with increases in the reflex amplitude. The masseteric reflex was elicited in behaving cats by electrical stimulation of the mesencephalic trigeminal nucleus (MesV) and the response recorded via electrodes permanently placed in the masseter muscle. Following baseline measures of the reflex amplitude, the reflex was gain elicited while cats were exposed to various environmental stimuli known to activate NE neurons: 15 min of 100-dB white noise, confrontation with a dog, or auditory clicks presented repetitively at various intervals prior to MesV stimulation. Presentation of the white noise or the dog significantly facilitated the reflex response for the duration of the exposure. The clicks produced reflex facilitation at 100 and 150 msec following their presentation and reflex suppression at 20 msec. Two approaches were then employed to determine whether NE mediated, at least in part, augmentation of the reflex produced by these environmental conditions. In the first, cats were given either the alpha-1-noradrenergic antagonist prazosin (5 mg/kg, i.p.) or the serotonin antagonist methysergide (0.5 mg/kg, i.p.). In all cases, prazosin blocked the reflex augmentation whereas methysergide was without effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1990

[Reflex responses of human perioral muscles to mechanical stimulation of the vestibular oris mucosa].

To investigate the effects on perioral muscles with mechanical stimulation to the mucosa electromyograms were recorded in nine subjects. Results were as follows: 1. Tonic excitatory reflex of m. orbicularis oris and m. mentalis was evoked by the non-painful pressure stimulation to lower lip mucosa. These responses were increased, as the stimulus strength was increased. 2. Reflex responses to stimulation of the corner of the mouth and lower lip mucosa were greater than that of buccal mucosa. The response in m. orbicularis oris superior (O.O.S.) to stimulation of upper lip mucosa was greater than in m. orbicularis oris inferior (O.O.I.). And the response in O.O.I. to stimulation of lower lip mucosa was greater than the response in O.O.S. 3. Tonic excitatory reflex was abolished after local anesthesia of the stimulation area. 4. Excitatory reflex was reversed to inhibitory reflex, when background activity of three muscles was changed by voluntary lip closure. When background activity was weak, excitatory reflex was induced by pressure stimulation. On the contrary, when background activity was strong, inhibitory reflex was induced by the same stimulation. When background activity was moderate, excitatory reflex in O.O.I. and inhibitory one in O.O.S. was easily induced by lower lip stimulation. On the other hand, by upper stimulation, excitatory reflex in O.O.S. and inhibitory one in O.O.I. was easily induced. These results suggest that the orthodontic appliance placed on the vestibular oris gives mechanical stimulation to oral mucosa, which induce reflex contraction in perioral muscles.

Electromyography↗
PubMed1989

[The reflex response in the abductor pollicis brevis muscle after tapping the distal segments of the fingers, the ulnar olecranon and scapular acromion. Electromyographic study].

The author made an electromyographic investigation of reflex responses in the abductor pollicis brevis muscle abductor pollicis brevis muscle after percussion with a hammer on the dorsal, lateral, palmar, medial and distal surface of the distal digit of the thumb, on the dorsal and palmar area of the distal digits of the other fingers and also on the olecranon ulnae and acromion scapulae. The investigation was made to detect the influence of the site of percussion on the character of the reflex response. The reflex responses were examined during slight isometric contraction of the muscle. After averaging rectification and of the recorded potentials the reflex responses were identified as excitatory and inhibitory modulation of the basal muscular activity depending on the inducing stimulus. Excitatory parts of the reflex response with a short latency were recorded after percussion on the lateral, dorsal and palmar area of the distal digit of the thumb and after percussion of the dorsal area of distal digits of the other fingers and after percussion of the palmar area of the little finger. As to other sites where reflexes were evoked first the inhibitory part of the reflex response was recorded. Excitation parts of reflex responses with a medium latency were obtained from all sites where reflexes were evoked. Late-latency parts of the reflex response had an inconstant occurrence. The results of the investigation provided evidence of a short-latency proprioceptory; influence of the abductor pollicis brevis muscle from synergic muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Influence of dynorphin (1-13) on spinal reflexes in the rat.

Previously, we showed that intrathecal administration of dynorphin A (1-13) (dynorphin) in rats produced, within 5 min, a reversible inhibition of tail-shock vocalization, a reversible hind-limb paralysis and an irreversible loss of the tail-flick reflex. The selective loss of the tail-flick reflex was investigated using electrophysiologic methods and a dose of dynorphin effective in 90% of the rats. These studies revealed that intrathecal administration of dynorphin resulted in loss of the C-fiber initiated reflex when assayed 1 to 30 days after injection. On the other hand, reflexes initiated by Group I and III afferents were not obviously different from those seen in saline-injected animals. Application of dynorphin in situ on to the cord during stimulation of the dorsal root and recording of ventral root potentials demonstrated a rapid onset of peptide action. Initially the C-fiber evoked reflex was potentiated selectively with a decrease in conduction time. These responses were followed by inhibition of all reflexes for a short period of time after which the reflexes initiated by Group I and III afferents reappeared whereas the C-fiber reflex did not recover. This time course paralleled closely the time course of the loss of the tail-flick reflex suggesting that the two effects may be causally related. Furthermore, the selective N-methyl-D-aspartate antagonist DL-2-amino-5-phosphonovalerate applied directly to the spinal cord during recording resulted in a reversible inhibition of the C-fiber-initiated reflex.(ABSTRACT TRUNCATED AT 250 WORDS)

2-Amino-5-phosphonovalerate↗
PubMed1986

The nature of reverse phase reflex eye movement.

The unusual phenomenon of reverse phase reflex eye movement was first described by Ishikawa. In this study the reflex frequency response was examined by electrooculography. In typical cases a reflex was observed by repeated forced duction up to 9 Hz. As a result it was postulated that proprioception is usually involved in reverse phase reflex eye movement, because visual eye movement cannot respond to a movement beyond 1 Hz. When the lag-times between the peaks of forced duction in one eye and those of the reflex movement in the other were measured, they were almost zero or even negative at high frequencies of forced duction as 6 and 9 Hz. This phase advance of the reflex movement was explained only when the receptor of the reflex had a dynamic response, because 90 degrees phase advance results in a reflex through such a receptor. The primary ending of muscle spindle represents such a receptor. The magician's forceps phenomenon as first discovered by Mitsui in exotropia is supposed to be a blocking reflex through the tendon organ. The transmission lag-times of both reflexes can be as short as 20 msec, but must be slightly longer to consider them to be monosynaptic.

Adolescent↗
PubMed1985

Noradrenergic modulation of sensorimotor processes in intact rats: the masseteric reflex as a model system.

The masseteric jaw closure reflex was utilized as a model system with which to gauge the functional activity of central noradrenergic neurons. This system was chosen because it is a simple monosynaptic reflex the neuronal substrate of which receives a dense noradrenergic input. The modulatory effects of norepinephrine (NE) on this response in the intact, chloral hydrate-anesthetized rat were studied with a variety of pharmacological strategies. Initially, a reflex facilitation was obtained with the catecholamine precursor L-DOPA. Manipulations with greater specificity of action on the noradrenergic system were then employed. First, we used the presynaptic alpha-2 noradrenergic agonist clonidine, which acts to decrease noradrenergic transmission. Clonidine attenuated the amplitude of the reflex, and this suppression was blocked by pretreatment with the alpha-2 antagonist yohimbine. The effects of yohimbine itself were then examined, and a biphasic effect was obtained. At low doses, at which it preferentially acts as an antagonist at presynaptic alpha-2 receptors and increases noradrenergic transmission, yohimbine enhanced the reflex. At higher doses, at which it also displays postsynaptic alpha-1 antagonist activity, yohimbine depressed the reflex. This reflex modulation by yohimbine was blocked by pretreatment with the alpha-1 antagonist prazosin. The anatomical site of the observed effect was then localized to the direct noradrenergic innervation of the reflex circuitry by locally destroying, with 6-hydroxydopamine, the noradrenergic terminals in the trigeminal motor nucleus mediating the response. This significantly attenuated the reflex modulation by yohimbine, without affecting elicitation of the reflex itself.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Stapedius reflex decay in normal hearing subjects.

The fatigue of the stapedius reflex was studied in 100 normal ears. Stimulus frequencies 500 and 1000 Hz were used,and the decrement of the stapedius reflex at 5, 10, and 15 dB above the reflex threshold was estimated. No decrement at all (less than 10% decay 10 sec after the onset of a stimulus 10 dB above the reflex threshold) was present in a majority of the ears. Between 27 and 58% of the ears showed reflex decay depending on variations of different factors such as stimulus frequency, intensity of the stimulus, and the method to register the reflex. Reflex decay was more often seen at 1000 Hz than at 500 Hz stimulus frequency. Reflex decay was also more often seen 5 dB above the reflex threshold than at higher intensity levels. The reflex decay thus observed in normal ears was generally small and did only very occasionally reach values which can be regarded as pathological.

Acoustic Impedance Tests↗
PubMed1979

Interaction of cardiopulmonary chemoreceptor (Bezold-Jarisch) and somatosympathetic reflexes.

Cardiopulmonary chemoreceptor (Bezold-Jarisch) and baroreceptor reflexes produce similar overall cardiovascular effects although central integrating mechanisms are not identical. In view of recent reports emphasizing the complexity of baroreceptor mechanisms, the influence of both reflexes on spontaneous sympathetic outflow as well as their interaction with the somatosympathetic reflex were compared in anesthetized cats. The chemoreflex and the baroreceptor reflex were activated by i.v. injection of veratrine and norepinephrine, respectively, and both inhibited spontaneous efferent sympathetic nerve traffic. Stimulation of somatic nerves produces a two-component reflex potential in sympathetic nerves. Activation of cardiopulmonary chemoreceptor and baroreceptor reflexes inhibited the amplitude of the initial (spinal) phase of this somasympathetic reflex slightly and greatly attenuated the secondary (supraspinal) component. These experiments demonstrate that the cardiopulmonary chemoreceptor and baroreceptor reflexes exert similar effects on the somatosympathetic reflex and that the former two reflexes may influence sympathetic mechanisms at spinal as well as supraspinal levels.

Animals↗
PubMed1994

Direction of susceptance and conductance acoustic reflexes at high probe frequencies.

Previous investigations have shown that for low probe frequencies (220 and 660 Hz) the direction of susceptance and conductance reflexes is related to baseline transmission properties. Previously documented reflex patterns, caused by the stiffening of the ossicular chain, are characterised by decreases in both components at 220 Hz (-B-G) and increases in susceptance and decreases in conductance (+B-G) at 660 Hz. In the present study, the direction of susceptance and conductance acoustic reflexes was investigated at a probe frequency of 1000 Hz, where ears are expected to be less stiffness dominated than at the low frequencies, and for which there is little description of reflex patterns in the published literature. The pattern of ipsilateral susceptance and conductance reflexes from 30 normal ears was recorded across a wide intensity range at this probe frequency for three stimulus frequencies (0.5, 1 and 2 kHz). Reflexes were classified as either increases (+) or decreases (-) for each component, at threshold and at suprathreshold intensity levels. Ears were grouped according to transmission properties at 1000 Hz, and reflex patterns observed within each group of subjects were examined. Patterns observed in these subjects at the 1000 Hz probe frequency included: +B-G; +B+G; -B+G and -B-G. There appeared to be a relationship between baseline transmission and reflex patterns. Further, patterns appear to be consistent with theoretical models of the effect of the acoustic reflex, particularly for ears where stiffness is significant in the baseline condition. The effect of the reflex for mass dominated systems requires further investigation.

Acoustic Impedance Tests↗
PubMed1989

Diurnal rhythms in primate spinal reflexes and accompanying cortical somatosensory evoked potentials.

We recorded spinal reflexes and cortical somatosensory evoked potentials (SEPs), elicited by stretching the biceps or the triceps muscle or by electrically stimulating the posterior tibial nerve, from monkeys throughout the day. Amplitudes of the spinal stretch reflex (SSR) and of its electrically evoked analogue, the H-reflex, varied diurnally: both were greatest midway through the lights-off period and smallest during the lights-on period. Stretch-evoked and electrically evoked SEP amplitudes also varied diurnally, but were out of phase with the spinal reflex rhythms. The H-reflex is elicited by direct stimulation of the nerve and thus, unlike the SSR, bypasses the muscle spindle. The H-reflex diurnal rhythm and the phase difference between the spinal reflex and SEP diurnal rhythms indicate that these rhythms are mediated at least in part by central mechanisms. Furthermore, both the spinal reflex and SEP diurnal rhythms appeared to be entrained by the light-dark cycle, which suggests that they may be coupled to the same oscillator. Besides their theoretical importance, these rhythms have important implications for experimental and clinical studies of spinal reflexes and SEPs. These rhythms are especially pertinent to the interpretation of long-term monitoring studies, as are often carried out in the Intensive Care Unit and during lengthy neurosurgical procedures.

Animals↗
PubMed1985

Jaw, blink and corneal reflex latencies in multiple sclerosis.

Jaw, blink and corneal reflexes, which all involve the trigeminal system, were recorded in 54 patients with multiple sclerosis; thirty-seven of these patients were classified as having definite multiple sclerosis and 17 as indefinite multiple sclerosis, according to Schumacher's criteria. The jaw reflex was abnormal less frequently than either of the other two reflexes, but in four cases it was the only abnormal reflex found. Testing a combination of two or three trigeminal reflexes did not yield a higher incidence of abnormalities than testing the blink or corneal reflex alone. Nine patients showed abnormal reflexes which were unexpected on the basis of clinical symptoms. The combined recordings demonstrate at least one abnormal reflex in 74% of the patients. The various types of reflex abnormalities reflect major damage to different parts of the trigeminal system and may therefore make an important contribution to the diagnosis of multiple sclerosis.

Adult↗
PubMed1993

In vitro eye-blink reflex model: role of excitatory amino acids and labeling of network activity with sulforhodamine.

Evidence is presented suggesting that the neural correlate of the eye-blink reflex can be evoked in an in vitro brainstem-cerebellum preparation from the turtle by using electrical rather than natural stimulation of cranial nerve inputs. Abducens nerve discharge is triggered by brief electrical stimulation of the ipsilateral trigeminal nerve. This discharge corresponds behaviorally to EMG recordings of extraocular muscles and eye retraction recorded in situ, in a reduced preparation. The abducens nerve discharge has two components: a short-duration response having a latency of 3-6 ms and a duration of 50-100 ms, followed by a long-duration component having a latency of 12-20 ms and a duration of several seconds. The long-duration component of the reflex is blocked by the NMDA receptor antagonist APV, while both reflex responses are blocked by the non-NMDA glutamate receptor antagonist CNQX. To visualize the spatial distribution of activity during the abducens nerve reflex, bath application of the activity-dependent dye sulforhodamine was used. During reflex activity, neurons in the ipsilateral trigeminal nucleus, principal abducens nucleus, and presumed interneurons ventrolateral to the principal abducens nucleus, labeled with the dye, in addition to areas in the raphe nucleus and reticular formation. In conditions where the long-duration component of the reflex was suppressed, sulforhodamine label was absent in the principal abducens nucleus and in the caudal brainstem. From these data it is hypothesized that the region of interneurons and the accessory abducens nucleus participate in the short-duration component of the reflex. This response is mediated by non-NMDA receptors. The principal abducens nucleus is postulated to contribute also to the short-duration portion of the reflex, but is primarily involved in the generation of the long-duration component. This component of the reflex is mediated principally by NMDA receptors. Sustained reflex activity is further postulated to originate from recurrent excitation in pathways within the caudal brainstem, particularly the reticular formation. This interpretation is consistent with the observed patterns of sulforhodamine label, the effects of local microinjections of APV, and the elimination of sustained activity when the caudal brainstem is transected. These data have implications for pathways that may underlie conditioning of the eye-blink response.

2-Amino-5-phosphonovalerate↗
PubMed1989

Excitotoxin-induced lesions of the central but not basolateral nucleus of the amygdala modulate the baroreceptor heart rate reflex in conscious rats.

The present study has examined the influence of the central nucleus of the amygdala (Ce) and the basolateral nucleus of the amygdala (BL) on the baroreceptor heart rate (HR) reflex in conscious, unrestrained rats. Baroreceptor HR reflex activity was examined in rats with bilateral excitotoxin (N-methyl-D-aspartate; 40 nmol/side)-induced lesions of the Ce or the BL and in control rats (artificial cerebrospinal fluid). After lesioning, the reflex HR responses were recorded following intravenous bolus doses of the pressor agent phenylephrine and the depressor agent sodium nitroprusside. Baroreceptor reflex parameters were determined by sigmoidal computerized curve-fitting. Lesions of either the Ce or the BL failed to affect resting mean arterial pressure (MAP) or HR. However, the Ce lesion reduced the maximum and average gain (sensitivity) of the baroreceptor reflex, and diminished the range of the reflex by altering the minimum, but not the maximum HR plateau. The upper and lower reflex thresholds and the MAP value corresponding to the midpoint of the HR range were not affected. Bilateral lesions of the BL failed to modify any baroreceptor reflex parameters. These results suggest that despite previous evidence for the involvement of the BL in cardiovascular regulation this nucleus does not exert a tonic influence on vasomotor neurons nor does it influence the baroreceptor HR reflex. In contrast, neurons projecting from the Ce appear to provide excitatory input to medullary neurons involved in baroreceptor reflex are regulation.

Amygdala↗
PubMed2004

Modulation of the baroreceptor reflex by alpha 2A-adrenoceptors: a study in alpha 2A knockout mice.

1. Our objective was to determine whether alpha(2A)-adrenoceptors modulate the baroreceptor reflex. The efficacy of the reflex was evaluated by measuring the spontaneous blood pressure and heart rate variability at rest and the heart rate responses to evoked changes in blood pressure. Experiments were carried out in conscious, unrestrained, and anaesthetized alpha(2A)-adrenoceptor-deficient (alpha(2A)-KO) mice and WT mice. 2. In conscious alpha(2A)-KO mice, the spontaneous blood pressure variability was greater, and the spontaneous heart rate variability was lower than in conscious WT mice. This was also observed in anaesthetized animals. 3. The reflex bradycardia after intravenous injection of phenylephrine was greatly attenuated in conscious alpha(2A)-KO compared to conscious WT mice; the baroreceptor reflex gain (ratio maximal change in heart rate/maximal change in mean arterial pressure) was decreased by 40%. 4. Similar results were obtained when reflex bradycardia was elicited by intra-arterial volume loading of conscious WT and alpha(2A)-KO mice. The baroreceptor reflex gain upon volume loading was also low in anaesthetized alpha(2A)-KO mice. 5. The reflex tachycardia evoked by intravenous sodium nitroprusside injection was also significantly less in alpha(2A)-KO mice as compared to WT, conscious as well as anaesthetized; the baroreceptor reflex gains were decreased by 50 and 65%, respectively. 6. Direct stimulation of cardiac beta-adrenoceptors by the agonist isoprenaline produced similar cardioacceleration in alpha(2A)-KO and WT animals. 7. Our results show that the baroreceptor reflex function is impaired in mice lacking alpha(2A)-adrenoceptors. We conclude that central alpha(2A)-adrenoceptors facilitate the reflex response to both loading and unloading of the arterial baroreceptors.

Animals↗