Functional organization of the vestibulospinal system in amphibians

In experiments on the preparation of a frog perfused brain, using recording of intracellular potentials the vestibulospinal neurons were identified on the basis of excitatory postsynaptic potentials evoked by the stimulation of the ipsilateral vestibular nerve and antidromic activation from the stimulation of the cervical and lumbar enlargements of the spinal cord. The average conduction velocity determined for axons of C neurons was 10.67 m/s and for L neurons 15.84 m/s. The ratio of C and L neurons over the vestibular nuclear complex was very stimular to each other: 52% C neurons and 48% L neurons. The majority of both types of neurons were localized in the lateral vestibular nucleus (58.6%), to the lesser extent in the descending vestibular nucleus (30.7%) and very little in the medial vestibular nucleus (10.6%). Fast and slow cells were detected among the vestibulospinal neurons. The fast neurons of L cells did not prevail greatly over the slow ones, whereas the slow neurons of C cells prevailed comparatively largely over the fast neurons. Thus, it became possible to reconstruct spatial distribution of the identified vestibulospinal neurons. The results of spatial distribution of C and L vestibulospinal neurons in the frogs failed to conform to definite somatotopy, which is characteristic for mammalian vestibular nuclei. C and L neurons in the frog's vestibular nuclei as a source of vestibulospinal fibres, are scattered separately or more frequently in groups, so that they establish a "patch-like" somatotopy and do not form a distinctly designed fields as in mammals.     

Functional characteristics of the input-output correlation in the frog vestibular nuclei

Field and intracellular potentials were recorded in the vestibular nuclear complex of the frog perfused brain following stimulation of the anterior branch of the ipsilateral vestibular nerve and spinal cord. Mono- and polysynaptic EPSPs with orthodromic APs were recorded from vestibular neurones following vestibular nerve stimulation. Antidromic activation of neurones sending their axons to the labyrinth was also recorded. Antidromic APs of vestibulo-spinal neurones evoked with mean latency of 1.43 and 2.19 ms to stimulation of cervical and lumbar cords, respectively, were revealed.     

Spatial organization of inhibitory control of activity of vestibulospinal Deiters' neurons by Purkinje cells in the anterior lobe of the cerebellum

The topographical distribution of vestibulospinal neurons in Deiters' nucleus was investigated by a microelectrode method. By contrast with observations made in morphological experiments, the localization of antidromically identified vestibulocervical (C-neurons) and vestibulolumbar (L-neurons) cells was found not to be limited to the ventral middle and rostral third of the nucleus (the forelimb region) and caudodorsal part of the nucleus (hind limb region), but to include the whole of the ventral and dorsal half of the nucleus, respectively. The zones of localization of these two groups of neurons are not confined to a single layer: C-neurons are found in the dorsal half of the nucleus and L-neurons in its ventrocaudal part also. Analysis of the distribution of monosynaptic IPSPs arising in response to activation of Purkinje cells in the vestibulospinal neurons showed that C-neurons are controlled chiefly from the forelimb zone of the cerebellar cortex whereas L-neurons are controlled equally by inhibitory influences from the forelimb and hind limb zones of the anterior lobe of the cerebellar cortex.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 11, No. 1, pp. 54–64, January–February, 1979.     

Respiratory resetting induced by spinal cord stimulation in the cat

Electrical stimulation (50-150 microA, 0.5-ms duration, 3-300 Hz) was performed within three different regions (lateral, ventrolateral, and ventral) of the C2-C3 spinal cord of decerebrate, vagotomized, paralyzed, and artificially ventilated cats. Spinal cord stimulation sites were located by inserting monopolar or bipolar stimulating electrodes either at the dorsolateral sulcus or at least 1 mm medial or lateral to the sulcus. With stimulation at each site, alterations in respiratory rhythm, orthodromic phrenic nerve responses, and antidromic activation of medullary respiratory-modulated neurons were examined. Phrenic nerve responses to cervical spinal cord stimulation consisted of an early excitation (2-4 ms) and/or a late excitation (4-8 ms). Stimulation of the lateral region evoked the greatest amplitude early response and stimulation of the ventrolateral region produced the greatest late excitation. All three stimulus sites elicited antidromic activation of some respiratory-modulated neurons in the dorsal (DRG) and ventral respiratory groups (VRG). The lateral region was the least effective resetting site, and it had the highest incidence of antidromic activation of both DRG and VRG neurons. The ventrolateral region of the cervical spinal cord was the most effective resetting site, but it had the lowest incidence of antidromic activation of DRG respiratory-modulated neurons. In addition, resetting responses were observed with spinal cord stimulation at similar sites in the thoracic and lumbar spinal cord regions thought to be devoid of inspiratory bulbospinal axons.(ABSTRACT TRUNCATED AT 250 WORDS)     

Tectospinal and tectoreticular cells: their distribution and afferent connections

Experiments on chloralose-anaesthetized cats have shown that cells in the superior colliculus may be antidromically activated either from the pontomedullary reticular formation or the ventral cervical spinal cord, or from both sites. In tests on 111 units this has provided a basis for differentiating between cells of origin of the tectospinal tract and the tectoreticular system within the superior colliculus. Tectospinal cells may be activated both by spinal and pontine stimulation; tectoreticular cells cannot be activated by spinal stimulation. Both tectoreticular and tectospinal cells respond to visual and muscle afferent stimulation. The afferent connections may be strongly inhibitory as afferent input to the superior colliculus ofter prevented subsequent antidromic invasion. This was more commonly seen in tectospinal cells than tectoreticular cells. The distribution of the two cell populations within the superior colliculus was also found to be dissimilar. Evidence has also been obtained to suggest that the tectoreticular system, in part, consists of collaterals of the tectospinal tract.     

Effects of antidromic activity in gustatory nerve fibers on taste disc cells of the frog tongue

Summary Antidromic electrical stimulation of the lingual branch of the glossopharyngeal (IX) nerve of the frog was carried out while recording intracellular potentials of taste disc cells.Antidromic activation of sensory fibers resulted in depolarization of cells of the upper layer of the disc and most commonly in hyperpolarization of the cells in the lower layer. These changes in potential exhibited latencies greater than 1 s (Fig. 3), and thus cannot be due to electrotonic effects of action potentials in terminals of IX nerve fibers, which have much shorter conduction times. These cell potentials also showed summation, adaptation and post-stimulus rebound (Figs. 3, 4).Depending upon the chemical stimulus used, antidromic activity produced either depression or enhancement of gustatory fiber discharge in response to taste stimuli (Fig. 5).Alteration of the resting membrane potential by current injection did not significantly modify the antidromically evoked potentials (Fig. 8), whereas chemical stimulation of the tongue did (Fig. 7), indicating that these potential changes are not the result of passive electrical processes.These experimental results indicate that the membrane potential of taste disc cells can be modified by antidromic activity in their afferent nerves. This mechanism may be responsible for peripheral interactions among gustatory units of the frog tongue.The research was supported in part by NIH grant NS-09168.     

脑桥呼吸调整中枢向中缝大核下行投射的研究

实验在23只苯巴比妥钠麻醉(i.p.30mg/kg)的成年猫上进行。在脑桥呼吸调整中枢(NPBM-KF)共记录到67个单位放电可被电刺激中缝大核(NRM)所逆行兴奋。其中有7个单位为呼吸相关性单位(吸气性6、呼气性1),占脑桥87个呼吸相关性单位总数的8％。逆行兴奋潜伏期在0.4—2.5ms之间,平均1.2ms。中缝大核内微量注入麦角辣根过氧化酶(WGA-HRP)后在NPBM-KF区观察到大量HRP标记神经元。本实验结果表明,发自脑桥呼吸调整中枢神经元的轴突可投射到中缝大核。这一投射通路可能与呼吸及痛觉调节有关。     

Antidromic propagation of action potentials in branched axons: implications for the mechanisms of action of deep brain stimulation

Electrical stimulation of the central nervous system creates both orthodromically propagating action potentials, by stimulation of local cells and passing axons, and antidromically propagating action potentials, by stimulation of presynaptic axons and terminals. Our aim was to understand how antidromic action potentials navigate through complex arborizations, such as those of thalamic and basal ganglia afferents-sites of electrical activation during deep brain stimulation. We developed computational models to study the propagation of antidromic action potentials past the bifurcation in branched axons. In both unmyelinated and myelinated branched axons, when the diameters of each axon branch remained under a specific threshold (set by the antidromic geometric ratio), antidromic propagation occurred robustly; action potentials traveled both antidromically into the primary segment as well as "re-orthodromically" into the terminal secondary segment. Propagation occurred across a broad range of stimulation frequencies, axon segment geometries, and concentrations of extracellular potassium, but was strongly dependent on the geometry of the node of Ranvier at the axonal bifurcation. Thus, antidromic activation of axon terminals can, through axon collaterals, lead to widespread activation or inhibition of targets remote from the site of stimulation. These effects should be included when interpreting the results of functional imaging or evoked potential studies on the mechanisms of action of DBS.     

Antidromic indentification of hypothalamic neurosecretory cells in rats

Characteristics of antidromic action potentials of neurons of the paraventricular and supraoptic nuclei of the rat hypothalamus were studied during stimulation of the hypothalamo-hypophyseal tract by stimuli of varied amplitude and frequency. Step-like changes were found in spike latency in response to an increase in strength (up to 1.5–2.5 thresholds) or frequency (over 100 Hz) of stimulation, as well as cases with variation of the degree of division of the peak into A and B components. Injection of leu-enkephalin analog into the third ventricle or intravenous injection of NaCl solution (1 M) caused reversible changes in the level of excitability of antidromically activated neurons: leu-enkephalin mainly increased the latent period and threshold of action potential generation and reduced the reproducible frequency of stimulation to 10 Hz, whereas NaCl had the opposite effect. The results indicate that when the adopted criteria of antidromic identification of neurosecretory cells are used the level of their excitability must be taken into account.A. A. Ukhtomskii Physiological Research Institute, A. A. Zhdanov Leningrad State University. Translated from Neirofiziologiya, Vol. 14, No. 6, pp. 585–591, November–December, 1982.     

Neurons of upper cervical segments responding to stimulation of the bulbar locomotor strip

Synaptic responses of single neurons to stimulation of the bulbar "locomotor strip" were recorded extracellularly from superior cervical segments in mesencephalic cats. With a strength of stimulation of about 30 µA these responses usually had a latent period of 2–7 msec and they arose in neurons located at a depth of between 2 and 4 mm from the dorsal surface (Rexed's laminae V–VIII). These neurons could not be excited antidromically by stimulation of the lumbar or lower cervical segments. However, antidromic responses could be evoked by stimulation of a region located 3–5 mm caudally to the site of recording. It is suggested that neurons of segments C2 and C3 excited by stimulation of the locomotor strip are components of a cell column along which activity spreads polysynaptically in the direction of spinal stepping generators.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 11, No. 3, pp. 245–253, May–June, 1979.     

外侧臂旁核神经元对穹窿下器逆向刺激和孤束核顺向剌激的反应

Single unit discharges were extracellularly recorded from the neurons in the lateral parabrachial nucleus (LPBN) and responses of the recorded units to antidromic stimulation of the subfornical organ (SFO) and to orthodromic stimulation of the nucleus tractus solitarius (NTS) were observed in urethane-anesthetized rats. Following electrical stimulation of the SFO, 9.9% (51/151) of the LPBN units were antidromically activated. After activation of peripheral baroreceptors by raising arterial blood pressure with an intravenous injection of phenylephrine, 40.7% (22/54) of the LPBN units were inhibited and 27.8% (17/54) excited. Following orthodromic stimulation of the depressor area in the NTS, 55.6% (94/169) of the LPBN units showed an increase and 22.5% (38/169) a decrease in firing rates. Among the LPBN neurons antidromically activated by SFO stimulation, 2 units were inhibited by phenylephrine administrated i.v.; of the 8 units tested, when the NTS was stimulated, 6 were excited and 2 inhibited. The results suggest that the LPBN neurons may receive inhibitory or excitatory baroreceptive inputs from the NTS and then relay it directly to SFO.     

Morphological Study of Spatial Distribution of Vestibulospinal Neurons in the Frog Rana ridibunda

In the thew frog Rana ridibunda, local microphoretic injections of horseradish peroxidase into various parts of spinal cord were used for study of trajectory of retrograde enzyme-labeled fiber systems and topography of labeled neurons in vestibulospinal nuclei, the source of vestibulospinal fibers. The vestibulospinal tracts were shown to be formed by neurons of lateral vestibular nucleus, although descending vestibular nucleus also is partially involved, while medial vestibular nucleus contributes to even lesser degree. Besides, study of spatial distribution of C- and L-vestibulospinal neurons in the frog did not confirm the presence of the definite somatotopy that is characteristic of vestibular nuclei in mammals.     

Antidromic discharges of dorsal root afferents in the neonatal rat.

Presynaptic inhibition of primary afferents can be evoked from at least three sources in the adult animal: 1) by stimulation of several supraspinal structures; 2) by spinal reflex action from sensory inputs; or 3) by the activity of spinal locomotor networks. The depolarisation in the intraspinal afferent terminals which is due, at least partly, to the activation of GABA(A) receptors may be large enough to reach firing threshold and evoke action potentials that are antidromically conducted into peripheral nerves. Little is known about the development of presynaptic inhibition and its supraspinal control during ontogeny. This article, reviewing recent experiments performed on the in vitro brainstem/spinal cord preparation of the neonatal rat, demonstrates that a similar organisation is present, to some extent, in the new-born rat. A spontaneous activity consisting of antidromic discharges can be recorded from lumbar dorsal roots. The discharges are generated by the underlying afferent terminal depolarizations reaching firing threshold. The number of antidromic action potentials increases significantly in saline solution with chloride concentration reduced to 50% of control. Bath application of the GABA(A) receptor antagonist, bicuculline (5-10 microM) blocks the antidromic discharges almost completely. Dorsal root discharges are therefore triggered by chloride-dependent GABA(A) receptor-mediated mechanisms; 1) activation of descending pathways by stimulation delivered to the ventral funiculus (VF) of the spinal cord at the C1 level; 2) activation of sensory inputs by stimulation of a neighbouring dorsal root; or 3) pharmacological activation of the central pattern generators for locomotion evokes antidromic discharges in dorsal roots. VF stimulation also inhibited the response to dorsal root stimulation. The time course of this inhibition overlapped with that of the dorsal root discharge suggesting that part of the inhibition of the monosynaptic reflex may be exerted at a presynaptic level. The existence of GABA(A) receptor-independent mechanisms and the roles of the antidromic discharges in the neonatal rat are discussed.     

Canal and otolith inputs to single vestibular neurons in cats

Convergence of both afferents from the PC and saccular macula, and those from the PC and utricular macula on single vestibular neurons was noted by use of intercellular recording from vestibular neurons. Vestibular neurons were classified VO neurons (vestibulo-ocular proper neurons), VOS (Vestibulo-oculo-spinal neurons sending axon collaterals both to the extraocular motoneuron pools and to the spinal cord), VS neurons (vestibulospinal proper neurons) and V neurons (vestibular neurons without axons to the oculomotor nuclei or the spinal cord) on the basis of whether or not they responded antidromically to stimulation of the oculomotor nuclei and the spinal cord. Of the total 143 vestibular neurons recorded in the series of experiments on convergence of the PC and saccular afferents, 47 neurons (33%) were received inputs from both the PC and saccular nerves. Twenty-six of the 47 convergent neurons were identified as having the nature of VS neurons. Half (13/26) of those were activated monosynaptically from both the PC and saccular nerves. Only one saccular-activated neuron without PC inputs sent an axon to the oculomotor nuclei. In the other series of experiments on the convergence of the PC and utricular afferents, 41 (37%) of 111 vestibular neurons were proved to converge on inputs from both nerves. The majority (35/41) of the neurons received monosynaptic inputs from the PC nerve and polysynaptic EPSP-IPSP sequences from the utricular nerve, or vice versa. The ratio of PC-otolith convergent neurons among utricular-activated neurons (41/54, 76%) was higher than that among saccular activated neurons (47/88, 53%). The percentage of utricular alone neurons without PC inputs (13/111, 12%) was less than that of the saccular alone without PC inputs (41/145, 28%). In conclusion, the convergence of canal and otolith inputs likely contribute mainly to vestibulospinal reflexes including the vestibulocollic reflex, by sending inputs to the neck and other muscles during head inclination which creates the combined stimuli of angular and linear acceleration.     

Neuronal activity related to spontaneous and capsaicin-induced rhythmical jaw movements in the rat

Intraoral capsaicin induced rhythmical jaw movements (RJM) in anesthetized rats. Neurons in the trigeminal spinal nucleus caudalis or the cortico-peduncular (CP) axons were extracellularly recorded. Capsaicin excited dose-dependently most caudalis neurons, which were activated by stimulation of the oral cavity and/or the tooth pulp and activated during spontaneous or induced RJM. Ten of 55 CP axons were antidromically activated by stimulation of the contralateral trigeminal motor nucleus. All antidromic and 29 other CP axons discharged prior to the spontaneous RJM, but most of them did not during capsaicin-induced RJM. These neuronal activities possibly initiate spontaneous RJM although the activities of caudalis neurons are necessary for capsicin-induced RJM.     

Responses of bulbospinal and laryngeal respiratory neurons to hypercapnia and hypoxia

The purpose was to evaluate activities of medullary respiratory neurons during equivalent changes in phrenic discharge resulting from hypercapnia and hypoxia. Decerebrate, cerebellectomized, paralyzed, and ventilated cats were used. Vagi were sectioned at left midcervical and right intrathoracic levels caudal to the origin of right recurrent laryngeal nerve. Activities of phrenic nerve and single respiratory neurons were monitored. Neurons exhibiting antidromic action potentials following stimulations of the spinal cord and recurrent laryngeal nerve were designated, respectively, bulbospinal or laryngeal. The remaining neurons were not antidromically activated. Hypercapnia caused significant augmentations of discharge frequencies for all neuronal groups. Many of these neurons had no change or declines of activity in hypoxia. We conclude that central chemoreceptor afferent influences are ubiquitous, but excitatory influences from carotid chemoreceptors are more limited in distribution among medullary respiratory neurons. Hypoxia will increase activities of neurons that receive sufficient excitatory peripheral chemoreceptor afferents to overcome direct depression by brain stem hypoxia. The possibility that responses of respiratory muscles to hypoxia are programmed within the medulla is discussed.     

Neuronal mechanisms of interaction of Deiters nucleus with the cerebral cortex.

The effects of stimulation of the vestibular nerve and five different cerebral cortex areas on the neuronal activity of the lateral vestibular nucleus of Deiters were studied. Stimulation of the cerebral cortex is shown to lead to antidromic and synaptic activation of Deiters neurons. The synaptic potentials of Deiters neurons evoked from the cerebral cortex were of mono- and polysynaptic origin. In particular, stimulation of the cerebral cortex evoked in Deiters neurons mono- and polysynaptic excitatory postsynaptic potentials. Collaterals of vestibulospinal neurons reaching different cortex fields as well as convergence of influences from these cortex fields on Deiters neurons were revealed. Inhibitory effects of the cerebral cortex on Deiters neurons were of polysynaptic origin and occurred rarely. The topical correlation between Deiters nucleus and different areas of the cerebral cortex was found. The peculiarities and functional significance of the effects obtained are discussed.     

Classification of vestibulo-spinal neurons of the cat Deiters' nucleus

Antidromic excitation of neurons of the lateral vestibular nucleus of Deiters in cats in response to stimulation of the vestibulo-spinal tract in the cervical segments of the spinal cord was studied by intracellular microelectrode recording. Individual components of the antidromic action potential and accompanying after-potentials were analyzed and fast and slow neurons distinguished. The vestibulo-spinal neurons were differentiated on the basis of after-potentials accompanying the antidromic action potential. The ratio between fast and slow neurons differed in individual groups. The parameters of the depolarization after-potentials were directly proportional to the duration of the refractory period of the neurons studied. An attempt was made to correlate differences in the responsiveness of neurons with an identical conduction velocity along their axons with the characteristics of the depolarization after-potential.     

The antidromic activation of tectal neurons by electrical stimuli applied to the caudal medulla oblongata in the toad,Bufo bufo L.

In order to specify the tectal projection to the bulbar/spinal regions, the antidromic responses of the physiologically identified tectal neurons as well as the gross antidromic field responses in the optic tectum to electrical stimuli applied to the caudal medulla were examined in the paralyzed common toad, Bufo bufo. The antidromic field potential was recorded in the optic tectum in response to electrical stimuli applied to the ventral paramedian portion of the contralateral caudal medulla (where the crossed tecto-spinal pathway of Rubinson (1968) and Lázár (1969) runs), but generally not when they were applied to various parts of the ipsilateral caudal medulla. The antidromic field potential was largest at the superficial part of Layer 6 or at the border between Layers 6 and 7 of the optic tectum, indicating that neurons in these layers project to the contralateral caudal medulla. Mapping experiments of the antidromic field potential over the optic tectum showed that the antidromic field potential was recorded mainly in the lateral part of it, indicating that this part of the optic tectum is the main source of projection neurons to the contralateral caudal medulla. Various classes of tectal neurons as well as retinal ganglion neurons were identified from the characteristics of the response properties to moving visual stimuli and the properties of the receptive fields. Of these, the Class T1, T2, T3, T4, T5(1), T5(2), T5(3), and T5(4) tectal neurons were activated antidromically by stimuli applied to the contralateral caudal medulla. Only a limited proportion of the Class T5(1) neurons was activated antidromically by stimuli applied to the ipsilateral caudal medulla. On the other hand, the Class T7 and T8 neurons, as well as the Class R2, R3, and R4 retinal neurons, were not activated antidromically by stimuli applied to the caudal medulla of either side. These results suggest a possibility that these tectal neurons which project to the medullary regions form the substrate of the sensorimotor interfacing and contribute to the initiation or coordination of the visually guided behavior, such as prey-catching.     

Behavioral correlates of activity in identified hypocretin/orexin neurons

Micropipette recording with juxtacellular Neurobiotin ejection, linked micropipette-microwire recording, and antidromic and orthodromic activation from the ventral tegmental area and locus coeruleus were used to identify hypocretin (Hcrt) cells in anesthetized rats and develop criteria for identification of these cells in unanesthetized, unrestrained animals. We found that Hcrt cells have broad action potentials with elongated later positive deflections that distinguish them from adjacent antidromically identified cells. They are relatively inactive in quiet waking but are transiently activated during sensory stimulation. Hcrt cells are silent in slow wave sleep and tonic periods of REM sleep, with occasional burst discharge in phasic REM. Hcrt cells discharge in active waking and have moderate and approximately equal levels of activity during grooming and eating and maximal activity during exploratory behavior. Our findings suggest that these cells are activated during emotional and sensorimotor conditions similar to those that trigger cataplexy in narcoleptic animals.