On the role of vestibulo-ocular reflex plasticity in recovery after unilateral peripheral vestibular lesions

Summary Although adaptive plasticity is a wellknown feature of the vestibulo-ocular reflex (VOR), deficits in VOR performance after unilateral labyrinthectomy are poorly compensated in a large percentage of cats. To assess whether VOR plastic capabilities are affected by labyrinthectomy, forced oscillation in front of a patterned surround was imposed in unilaterally labyrinthectomized cats. This experimental paradigm has been shown to be very effective in inducing adaptive VOR gain changes in intact animals. We demonstrate that plasticity of VOR gain is still present both in acute and chronic stages following vestibular lesions. By contrast, forced oscillation did not significantly alter the lesion-induced asymmetry of responses. We conclude that VOR gain control mechanisms are not used to their fullest possible extent in a large percentage of animals suffering unilateral vestibular damage.Supported by grants nos. 3.228.82 and 3.403.83 from the Swiss National Science Foundation and Dr. Erik Slack-Gyr FoundationProf. Precht died on March 12, 1985     

Control of upright standing posture during low-frequency linear oscillation

We examined the effects of anteroposterior movement of a sled on human upright standing. Each of six healthy men stood on the platform of a sled in the dark. The sinusoidal acceleration was provided, from 0.02 to 0.04 G, followed by 0.06 and 0.08 G, at a stroke length from 6 to 10 m and then to 14 m. Low acceleration (0.02 and 0.04 G) induced body sway, pivoting on the ankle joint. High acceleration (0.06 and 0.08 G) increased body sway, but the head-neck joint remained locked upright. The electromyographic recordings of the lower leg muscles revealed continuous tonic EMG activities of the gastrocnemius and tibialis anterior muscles at acceleration of 0.02 and 0.04 G, while reciprocal activation was observed at 0.06 and 0.08 G. During head movement, the neck muscles were slightly activated tonically at acceleration of 0.02 and 0.04 G, but they were markedly and tonically activated at 0.06 and 0.08 G. We speculate that the sled oscillation caused body sway in proportion to the acceleration, with the ankle joint playing a principal role. Analysis of neck movement also revealed that the head was held in a fixed upright position, indicating that the vestibulocollic reflex might tonically activate the neck muscles.     

Participation of Ia reciprocal inhibitory neurons in the spinal circuitry of the tonic neck reflex

Summary As part of our studies of the spinal circuitry of the tonic neck reflex, we have recorded extracellularly from Ia reciprocal inhibitory neurons of the decerebrate, labyrinthectomized cat. The activity of a majority of neurons driven by stimulation of the quadriceps nerve was modulated by sinusoidal rotation of the neck; such modulation was much less frequent in the case of neurons driven by stimulation of nerves to more distal muscles. The results suggest that some of the inhibition which is part of the tonic neck reflex is mediated by Ia reciprocal inhibitory neurons, but that other pathways must also play an important role.     

Pharmacology of spinal adrenergic systems which modulate spinal nociceptive processing

Spinopetal pathways may be activated by a variety of brainstem manipulations including microinjections of morphine which are known to modulate spinal nociceptive processing. Based on the ability of these manipulations to release spinal noradrenalin; the ability to reverse the antinociceptive effects by intrathecal adrenergic antagonists and the fact that intrathecal injections of noradrenalin mimic the antinociceptive effect, it appears that the descending modulation may be mediated by descending noradrenergic systems. Examination of the spinal receptor systems with intrathecally administered agents indicates that spinal alpha, but not beta adrenergic receptor agonists produce a powerful analgesia as measured on a variety of reflex and operant measures in mouse, rat, cat, primate and man. On the basis of agonist and antagonist structure-activity relationships it appears that a significant effect can be produced in the absence of any detectable effect on motor function by the occupation of spinal alpha 2 receptors. Distinguishable alpha 1 receptors also appear "analgetically-coupled," but their effects are uniformly contaminated by signs of cutaneous hyperreflexia at doses required to produce analgesia. The ordering of potency with which intrathecal adrenergic antagonists reverse the effects of intrathecal noradrenalin is indistinguishable from that of the reversal by these intrathecal agents of the antinociceptive effects evoked by brainstem morphine. This suggests that the population of spinal receptors acted upon by exogenously administered adrenergic agonists and endogenously released noradrenaline have indistinguishable characteristics.     

Cystometric changes in the early phase of streptozotocin-induced diabetes in rats: evidence for sensory changes not correlated to diabetic neuropathy

Summary 1. The effect of streptozotocin (STZ) induced diabetes on rat urinary bladder function was investigated by means of in vivo cystometry and in vitro recording of bladder strips contractility. A group of sucrose-fed animals was included to determine to what extent the STZ-induced changes were ascribable to the increased diuresis. 2. After 7–9 weeks from STZ injection there was a marked increase in weight of bladder and ureters. Cystometry revealed a marked increase in bladder capacity (volume threshold) although pressure threshold and amplitude of micturition contraction were unaffected. Sucrose-fed animals, having normal blood glucose levels but a similar increase in urine production exhibited cystometric changes identical to those of STZ animals. 3. In vitro experiments indicated that the response to field stimulation (0.1–20 Hz) is reduced in STZ-pretreated but increased in sucrose-fed animals, as compared to controls. 4. The content of urinary bladder and ureters in sensory neuropeptides (substance-P, neurokinin-A and calcitonin-gene related peptide-like immunoreactivity) was increased by STZ diabetes when values were corrected for the increased weight of these organs. 5. The capsaicin-induced contraction of the rat isolated bladder strips, presumably caused by neuropeptides released from intramural sensory nerves, is unaffected by STZ diabetes. 6. These findings indicate that STZ diabetes produces, at an early stage, changes similar to those reported to occur in the human disease, e. g. a greater bladder capacity with unimpaired voiding function. The increased bladder capacity of STZ-rats seems largely, if not solely, ascribable to changes in physical properties of the detrusor muscle, thereby allowing accomodation of greater than normal volumes with similar increase of intraluminal pressure. No sign of diabetic neuropathy of the capsaicin-sensitive sensory nerves can be observed at this stage (7–9 weeks) of STZ diabetes. Send offprint requests to P. Santicioli at the above address     

Different spinal effects of opioid agonists on spinal and spino-bulbo-spinal reflexes in rats

Summary The effects of morphine-HCl (MOR), methionine-enkephalin (ME) and dynorphin_1–13 (DYN) on spinal and spino-bulbo-spinal (SBS) reflexes were studied. Although spinal intrathecal administration of MOR (15g) did not produce any apparent effect on these reflexes, systemically administered MOR (3mg/kg i.v.) reduced the electrical toe stimulation-induced SBS reflex. Furthermore, MOR (3mg/kg i.v.) increased the polysynaptic reflex induced by electrical stimulation of low-threshold dorsal root afferents in intact (non-spinal) rats, but not in spinal rats. Intrathecally administred DYN (0.5 and 5 g) reduced both the electrical toe stimulation-induced spinal and SBS reflexes, while ME (15g) only reduced the SBS reflex. These results indicate the physiological multiplicity of spinal opioid receptors. MOR may affect supraspinal nuclei but not the spinal pathway which possesses MOR-sensitive opioid receptors, whereas ME and DYN affect spinal opioid peptide receptors and modulate the reflex activities in which they participate.     

Motor reflex responses elicited by cutaneous stimulation in the regenerating nerve of man: Axon reflex or ephaptic response?

In 57 of 60 nerves (29 median and 31 ulnar) sutured at the wrist, forearm and arm, we recorded motor responses in thenar or hypothenar muscles by electrical stimulation of the corresponding fingers. Recordings were made at different times during the process of regeneration, ranging from 3 months up to 11 years. The responses showed a constant shape and latency to every stimulation (simple or repetitive). The latency was shorter the more distal the level of injury and the greater the elapsed time from the reinnervation. The point of "reflexion" of the responses is at or very near the line of nerve suture. The electrophysiological behavior of the responses fits well with either the criterion of axon reflex or ephaptic response. We discuss both possibilities and conclude that it is not possible, with the electrophysiological technique that we used, to distinguish between an axon reflex and an ephaptic response.     

Effects of blood pressure changes on the catecholamine release in the locus coeruleus of cats anaesthetized with pentobarbital or chloralose

Summary Effects of carotid occlusion and drugs applied intravenously on the release of endogenous catecholamines in the locus coeruleus of cats anaesthetized with pentobarbital or chloralose were investigated. The locus coeruleus was superfused bilaterally with artificial cerebrospinal fluid through push-pull cannulae inserted stereotaxically. Dopamine, noradrenaline and in some experiments also adrenaline were determined radioenzymatically in the superfusate.Under pentobarbital anaesthesia, a bilateral carotid occlusion increased the release rate of noradrenaline in the locus coeruleus, while the release of dopamine was decreased. These changes were due to the fall of blood pressure in the carotid sinus caused by the occlusion. Loading of baroreceptors by elevating blood pressure with phenylephrine (10 g·kg^–1·min^–1, i.v. infusion) was accompanied by a decreased release of noradrenaline in the locus coeruleus. This decrease in noradrenaline release was not detected in the caudal aspect of the locus coeruleus. Under chloralose anaesthesia, phenylephrine diminished the release rate of noradrenaline to about the same extent as under pentobarbital anaesthesia. The release rate of adrenaline was also decreased. A prolonged infusion of phenylephrine led to a prolonged pressor response associated with a sustained decrease in the noradrenaline release rate. Intravenous injection of chlorisondamine (3 mg·kg^–1) did not change the release of noradrenaline, while dopamine release was reduced.It is concluded that the release of catecholamines in the locus coeruleus is influenced by signals originating from peripheral baroreceptors. The influences are similar under pentobarbital and chloralose anaesthesia. Noradrenergic neurons responding to haemodynamic signals are not uniformly distributed within the locus coeruleus. It is suggested that noradrenergic and possibly dopaminergic and adrenergic neurons of the locus coeruleus are involved in the baroreceptor reflex, thus contributing to central homeostasis of blood pressure.     

短声作为刺激声进行同侧声反射阈测定之临床价值

目的 :确定短声可代替纯音作为刺激声作同侧声反射阈测定 ,并了解探测音频率对声反射阈的影响。方法 :应用 GSI33 型中耳分析仪 ,对正常志愿者 2 3例 46耳作不同探测音频率的纯音及短声刺激率 10 0次 / s及180次 / s的同侧声反射阈测定。结果 :声反射阈 2 2 6 Hz探测音时 5 0 0 Hz、10 0 0 Hz、2 0 0 0 Hz分别为 ( 84.35±6 .96 ) d B、( 84.6 5± 5 .93) d B、( 87.96± 6 .36 ) d B;6 78Hz探测音时分别为 ( 93.13± 6 .5 4) d B、( 92 .70± 6 .33) d B、( 93.35± 5 .99) d B;10 0 0 Hz探测音时分别为 ( 86 .5 2± 4.72 ) d B、( 87.48± 5 .0 0 ) d B、( 88.30± 6 .16 ) d B。短声刺激率 10 0次 / s及 180次 / s同侧声反射阈 2 2 6 Hz探测音时分别为 ( 89.78± 6 .83) d B、( 92 .0 7± 7.42 ) d B;6 78Hz探测音时为 ( 90 .44± 6 .76 ) d B、( 90 .6 5± 6 .38) d B;10 0 0 Hz探测音时为 ( 88.0 4± 6 .87) d B、( 88.6 9± 7.49) d B。 6 78Hz探测音 ,声反射阈高于 2 2 6 Hz及 10 0 0 Hz。结论 :低刺激率的短声作为刺激声并未出现赝象 ,可作为进行同侧声反射阈测试的刺激声