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B J Yates

Publications and source records attributed to B J Yates.

At least 73 records · Page 4Linked to original sources
PubMed1995

Descending pathways necessary for vestibular influences on sympathetic and inspiratory outflow.

The objective of this study was to determine which brain stem regions that have projections to sympathetic preganglionic neurons or phrenic motoneurons ae necessary for vestibulosympathetic or vestibulorespiratory responses in decerebrate cats. Bilateral kainic acid injections into the rostral ventrolateral medulla abolished splanchnic nerve responses to electrical stimulation of the vestibular nerve, suggesting that this region is critical for the production of vestibulosympathetic responses. In contrast, injections into the caudal medullary raphe nuclei had no apparent effect on the responses. Neither the dorsal nor the ventral respiratory group appears to be necessary for mediating vestibular influences on the phrenic nerve, suggesting that nonrespiratory neurons (such as vestibulospinal neurons) may be important for producing vestibulorespiratory responses.

Animals↗
PubMed1995

Ventral respiratory group bulbospinal inspiratory neurons participate in vestibular-respiratory reflexes.

1. The vestibular system responds to accelerations of the head and produces reflex responses that serve a variety of compensatory functions. The neuronal circuitry that mediates vestibulo-respiratory reflexes is largely unknown. The purpose of the present study was to investigate the possible role of bulbospinal inspiratory neurons located in the para-ambigual region of the ventral respiratory group (VRG) in mediating these reflexes. Experiments were carried out in cats that were decerebrated, paralyzed, and artificially ventilated. 2. Activation of the vestibular nerve by electrical stimulation produced prominent bilateral reflex responses recorded from the phrenic nerve, which supplies the diaphragm. The responses could be complex and consisted of a decrease and/or increase in nerve discharge. 3. Extracellular recordings were made from 35 VRG inspiratory neurons that were antidromically activated from the upper cervical spinal cord. Almost one-half of these neurons (15/35, 43%) responded to vestibular stimulation. The neuronal response patterns were consistent with VRG inspiratory neurons contributing to the vestibular reflex response simultaneously recorded from the phrenic nerve. 4. The present results indicate that approximately one-half of VRG bulbospinal inspiratory neurons contribute to vestibulo-respiratory reflexes. These findings are in contrast to our recent neuroanatomic and electrophysiological studies which revealed a paucity of vestibular inputs to the dorsal respiratory group (DRG) located in the ventrolateral nucleus of the solitary tract. Thus there appears to be a difference between inspiratory neurons in the DRG and VRG in regard to participating in vestibulo-respiratory reflexes.

Animals↗
PubMed1995

Vertical vestibular input to and projections from the caudal parts of the vestibular nuclei of the decerebrate cat.

1. To investigate the type of vestibular signals that neurons in the caudal parts of the vestibular nuclei transmit to the cerebellum and spinal cord, we studied their responses to natural vestibular stimulation in vertical planes in decerebrate cats with the caudal cerebellum removed. Most neurons were in the caudal half of the descending vestibular nucleus, the remainder at corresponding levels of the medial nucleus or the medial-descending border. 2. Dynamics of the responses of spontaneously firing neurons were studied with sinusoidal tilts delivered at 0.05-1 Hz near the plane of body rotation that produced maximal modulation of the neuron's activity (response vector orientation). For most neurons the predominant vestibular input could be identified as coming from otolith organs (46%) or vertical semicircular canals (37%). Some neurons had otolith+canal convergence (9%) and others either had such converging input or some other form of central processing (8%). 3. Gain and phase of the responses of otolith neurons were comparable with values obtained in earlier studies on Deiters' nucleus and the rostral descending nucleus. Many canal neurons had a steeper gain slope and more advanced phase than observed previously for more rostral neurons. This may be due to more irregular afferent input to many neurons or to the absence of the vestibulocerebellum. 4. Response vector orientations of canal neurons were closely bunched near the planes of the ipsilateral vertical canals. The small number of contralaterally projecting vectors showed evidence of convergence between the two contralateral vertical canals. As is the case elsewhere in the vestibular nuclei, there was no evidence of convergence from bilateral vertical canals. Response vector orientations of otolith neurons were restricted to the roll quadrants; the majority pointed ipsilaterally. 5. Antidromic stimulation with an electrode in the restiform body or with several electrodes in the dorsal half of the white matter of the upper cervical cord was used to identify neurons projecting to the cerebellum and spinal cord, respectively. A substantial number of spontaneously firing neurons projected to the cerebellum, but there were few spontaneously active vestibulospinal neurons. The properties of the vestibular input to cerebellar-projecting neurons were the same as those of the population as a whole, but the effect of tilt on vestibulospinal neurons appeared weak or absent. 6. Many neurons were inhibited by stimulation of the restiform body. We suggest that this is mainly due to stimulation of the axons of vestibulocerebellar Purkinje cells. 7. Our results demonstrate a robust vertical vestibular input to the caudal parts of the vestibular nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Organization of vestibular inputs to nucleus tractus solitarius and adjacent structures in cat brain stem.

The vestibular system is involved in maintaining stable blood pressure and respiration during changes in posture and is essential for eliciting motion sickness-related vomiting. Because the nucleus tractus solitarius (NTS) participates in the regulation of sympathetic and inspiratory outflow and the triggering of emesis, we tested the hypothesis that this region receives vestibular inputs in cats. In one set of experiments, microinjections of the tracer Phaseolus vulgaris leucoagglutinin into the medial and inferior vestibular nuclei labeled projections to the middle and lateral regions of the NTS. In electrophysiological experiments, electrical stimulation of the vestibular nerve modified the firing rates of neurons located in the same regions. Some neurons with vestibular inputs received convergent signals from the abdominal vagus nerve and could potentially mediate motion sickness-related vomiting. Others received convergent baroreceptor inputs and could act as a substrate for some components of vestibulosympathetic reflexes. In contrast, inspiratory neurons in the dorsal respiratory group received little vestibular input, suggesting that vestibulorespiratory reflexes are mediated by cells located elsewhere.

Animals↗
PubMed1994

Response of commissural and other upper cervical ventral horn neurons to vestibular stimuli in vertical planes.

1. To study their contribution to the vestibulocollic reflex, we have studied, in decerebrate paralyzed cats, the effect of sinusoidal vestibular stimulation in multiple vertical planes on the spontaneous activity of neurons in the C3 ventral horn. Antidromic microstimulation was used to identify 17/42 neurons as commissural; 10 of these were confirmed to have a projection to the contralateral ventral horn. 2. Dynamics of the responses of spontaneously firing neurons were studied with 0.05-1 Hz sinusoidal stimuli delivered near the plane of rotation that produced maximal modulation of neuron activity (response vector orientation). On the basis of their responses, we classified 38 neurons as receiving otolith, semicircular canal, or otolith + canal input. All three response types were found among commissure and nonantidromic neurons. 3. Two-thirds of neuron response vector orientations pointed contralaterally. They were either near the anterior or posterior canal planes or in the roll quadrant. In the case of neurons with input from canals, the latter indicates convergence from the vertical canals on the same side. There were almost no vectors in the pitch quadrants. The distribution of response vector orientations resembles that seen in the vestibular nuclei and pontomedullary reticular formation, suggesting that commissural neurons may not make a new contribution to spatial processing in the vertical vestibulocollic reflex. 4. It is presumed that commissural neurons are premotor. If so, some have the properties to be in the pathway between the contralateral utricle and neck motoneurons. More generally, their actions could modify the effectiveness of vestibulospinal and reticulospinal fibers that have similar spatial properties and make synapses with neck motoneurons.

4-Aminopyridine↗
PubMed1994

Properties of sympathetic reflexes elicited by natural vestibular stimulation: implications for cardiovascular control.

1. To study the properties of vestibulosympathetic reflexes we recorded outflow from the splanchnic nerve during natural vestibular stimulation in multiple vertical planes in decerebrate cats. Most of the animals were cerebellectomized, although some responses were recorded in cerebellum-intact preparations. Vestibular stimulation was produced by rotating the head in animals whose upper cervical dorsal roots were transected to remove inputs from neck receptors; a baroreceptor denervation and vagotomy were also performed to remove visceral inputs. 2. The plane of head rotation that produced maximal modulation of splanchnic nerve activity (response vector orientation) was measured at 0.2-0.5 Hz. The dynamics of the response were then studied with sinusoidal (0.05- to 1-Hz) stimuli aligned with this orientation. 3. Typically, maximal modulation of splanchnic nerve outflow was elicited by head rotations in a plane near pitch; nose-up rotations produced increased outflow and nose-down rotations reduced nerve discharges. The gains of the responses remained relatively constant across stimulus frequencies and the phases were consistently near stimulus position, like regularly firing otolith afferents. Similar response dynamics were recorded in cerebellectomized and cerebellum-intact animals. 4. The splanchnic nerve responses to head rotation could be abolished by microinjections of the excitotoxin kainic acid into the medial and inferior vestibular nuclei, which is concordant with the responses resulting from activation of vestibular receptors. 5. The properties fo vestibulosympathetic reflexes recorded from the splanchnic nerve support the hypothesis that the vestibular system participates in compensating for posturally related changes in blood pressure.

Animals↗
PubMed1993

Vestibular effects on respiratory outflow in the decerebrate cat.

Recordings were made from phrenic, abdominal and intercostal nerves following electrical stimulation of the vestibular nerve to test for the presence of vestibulo-respiratory connections in cats that were decerebrate, paralyzed, and artificially ventilated. Short stimulus trains (2 or 3 shocks) at intensities < or = 125 microA typically elicited responses bilaterally in all of the respiratory nerves; the onset latency of the evoked activity was < 15 ms from the effective shock. The mean peak-to-peak amplitudes of integrated vestibulo-respiratory responses were 15% of the average amplitude of spontaneous respiratory-related discharges in the case of the phrenic nerve and 100% in the case of the abdominal nerve. The vestibulo-respiratory reflexes, as well as vestibulo-sympathetic responses recorded from the splanchnic nerve, could be abolished by injections of the excitotoxin kainic acid confined primarily to the medial and adjacent inferior vestibular nuclei. The physiological role of vestibulo-respiratory connections is yet to be determined, but possible functions include adjustments of respiration during changes in posture, assistance in venous return to the heart during movements that might lead to orthostatic hypotension, and direct participation in the execution of specific movements and the maintenance of some postures.

Animals↗
PubMed1993

Evaluation of role of upper cervical inspiratory neurons in respiration, emesis and cough.

Upper cervical (C1-3) inspiratory (UCI) propriospinal neurons project to spinal segments containing respiratory motoneurons, but their functional significance is unknown. Bilateral kainic acid injections into this cell column in 12 decerebrate cats (11 paralyzed and artificially ventilated) had no major effect on phrenic, intercostal, and abdominal nerve discharge or EMG activity during (fictive) respiration, vomiting and coughing. Thus, UCI neurons are unessential for activation of major respiratory muscles during these behaviors.

Abdomen↗
PubMed1993

Responses of neurons in the rostral ventrolateral medulla of the cat to natural vestibular stimulation.

To investigate the neural substrate of vestibulo-sympathetic reflexes, we studied the responses of neurons in the rostral ventrolateral medulla (RVLM) of decerebrate cats to natural stimulation of the labyrinth in vertical and horizontal planes. The RVLM is a major source of excitatory inputs to sympathetic preganglionic neurons. The animals used in these studies were baroreceptor-denervated and vagotomized and had a cervical spinal transection so that inputs from tilt-sensitive receptors outside of the labyrinth did not influence the units we recorded. Of the 38 neurons whose type of vertical vestibular inputs could be classified, the majority (27) received signals mainly from otolith organs. Only 4 of the neurons received inputs predominantly from vertical semicircular canals, and 7 were classified as having convergent inputs from otoliths and canals that were spatially aligned (2 cells) or misaligned (5 cells). In addition, only 2 of 68 neurons tested responded to sinusoidal horizontal rotations in a manner typical of brainstem neurons that receive inputs from the horizontal semicircular canals. Thus, the vestibular inputs to the RVLM appear to come mainly from otolith receptors. In labyrinthectomized cats, we were unable to locate neurons with responses to tilt similar to those of cells recorded in labyrinth-intact cats, confirming that the responses attributed to vertical vestibular inputs were produced by signals from the labyrinth. In animals whose semicircular canals had been rendered dysfunctional by plugging, we only recorded responses similar to those of neurons classified as having mainly otolith inputs in canal-intact animals, indicating that the dynamic behavior of these cells does not depend upon canal inputs. The presence of otolith inputs to the RVLM is consistent with the hypothesis that this region mediates vestibulo-sympathetic reflexes involved in correcting posturally-related changes in blood pressure.

Animals↗
PubMed1993

Responses of caudal medullary raphe neurons to natural vestibular stimulation.

1. Over two thirds of caudal medullary raphespinal neurons respond to electrical stimulation of the vestibular nerve, and it has been suggested that these neurons may participate in the generation of vestibulospinal and vestibulosympathetic reflexes. The objective of the present study was to determine which vestibular endorgans (semicircular canals or otolith organs) provide inputs to these cells. 2. Experiments were conducted on decerebrate cats that were baroreceptor denervated and vagotomized, and that had a cervical spinal cord transection so that inputs from tilt-sensitive receptors outside of the labyrinth did not influence the units we recorded. 3. In most experiments, vertical vestibular stimulation was used to stimulate the anterior and posterior semicircular canals and the otolith organs. The plane of whole body rotation that produced maximal modulation of a neuron's firing rate (response vector orientation) was measured at one or more frequencies between 0.1 and 0.5 Hz. Neuron dynamics were then studied with sinusoidal (0.02-1 Hz) stimuli aligned with this orientation. Alternatively, in two animals horizontal rotations at 0.5 and 1.0 Hz were employed to stimulate the horizontal semicircular canals. 4. The properties of raphespinal neurons were similar to those of a larger sample of raphe neurons studied that either could not be antidromically activated from the cervical spinal cord or were not tested for a spinal projection. In response to vertical vestibular stimulation, > 85% of caudal medullary raphe neurons had response gains that remained relatively constant across stimulus frequencies, like regularly firing otolith afferents.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1992

Responses of neurons in the caudal medullary raphe nuclei of the cat to stimulation of the vestibular nerve.

In the decerebrate cat, recordings were made from neurons in the caudal medullary raphe nuclei to determine if they responded to electrical stimulation of the vestibular nerve and thus might participate in vestibulosympathetic reflexes. Many of these cells projected to the upper thoracic spinal cord. The majority (20/28) of raphespinal neurons with conduction velocities between 1 and 4 m/s received vestibular inputs; 13 of the 20 were inhibited, and 7 were excited. Since many raphespinal neurons with similar slow conduction velocities are involved in the control of sympathetic outflow, as well as in other functions, these cells could potentially relay vestibular signals to sympathetic preganglionic neurons. The onset latency of the vestibular effects was long (median of 15 ms), indicating the inputs were polysynaptic. In addition, 34 of 42 raphespinal neurons with more rapid conduction velocities (6-78 m/s) also received long-latency (median of 10 ms) labyrinthine inputs; 26 were excited and 8 were inhibited. Although little is known about these rapidly-conducting cells, they do not appear to be involved in autonomic control, suggesting that the function of vestibular inputs to raphe neurons is not limited to production of vestibulosympathetic reflexes. One hypothesis is that raphe neurons are also involved in modulating the gain of vestibulocollic and vestibulospinal reflexes; this possibility remains to be tested.

Animals↗
PubMed1992

Response of pontomedullary reticulospinal neurons to vestibular stimuli in vertical planes. Role in vertical vestibulospinal reflexes of the decerebrate cat.

1. To investigate the neural substrate of vestibulospinal reflexes in decerebrate cats, we studied the responses of pontomedullary reticulospinal neurons to natural stimulation of the labyrinth in vertical planes. Our principal aim was to determine whether reticulospinal neurons that terminate in, or are likely to give off collaterals to, the upper cervical segments had properties similar to those of the vestibulocollic reflex (VCR). 2. Antidromic stimulation was used to determine whether the neurons projected to the neck, lower cervical, thoracic, or lumbar levels. Dynamics of the responses of spontaneously firing neurons were studied with sinusoidal stimuli delivered at 0.05-1 Hz and aligned to the plane of body rotation, that produced maximal modulation of the neuron (response vector orientation). Each neuron was assigned a vestibular input classification of otolith, vertical canal, otolith + canal, or spatial-temporal convergence (STC). 3. We found, in agreement with previous studies, that the largest fraction of pontomedullary reticulospinal neurons projected to the lumbar cord, and that only a small number ended in the neck segments. Neurons projecting to all levels of the spinal cord had similar responses to labyrinth stimulation. 4. Reticulospinal neurons that received only vertical canal inputs were rare (1 of 67 units). Most reticulospinal neurons (48%) received predominant otolith inputs, 18% received otolith + canal input, and only 9% had STC behavior. These data are in sharp contrast to the results of our previous studies of vestibulospinal neurons. A considerable portion of vestibulospinal neurons receives vertical canal input (38%), fewer receive predominantly otolith input (22%), whereas the proportion that have otolith + canal input or STC behavior is similar to our present reticulospinal data. 5. The response vector orientations of our reticulospinal neurons, particularly those with canal inputs (canal, otolith + canal, STC) were predominantly in the roll quadrants. There was no evidence of convergence of inputs from like canals across the midline (e.g., right anterior + left anterior). 6. Two characteristics of the VCR, STC behavior and bilateral input from symmetric vertical canals (in some muscles), cannot be accounted for by the reticulospinal neurons that we studied. Because these characteristics are also not seen in vestibulocollic neurons, they are likely to be the result of the appropriate convergence of vestibular signals in the spinal cord. 7. Pontomedullary reticulospinal neurons seem particularly well suited to play a role in gravity-dependent postural reflexes of neck and limbs.

Acoustic Stimulation↗
PubMed1991

The ventrolateral medulla of the cat mediates vestibulosympathetic reflexes.

Extracellular recordings were made from 94 neurons located in the ventrolateral medulla (VLM) whose firing rate was affected by vestibular nerve (VN) stimulation; 50 of these units were in the subretrofacial (SRF) nucleus, which contains cells that make direct excitatory connections with sympathetic preganglionic neurons. The sample included 12 SRF cells which were antidromically driven from the upper thoracic spinal cord and had conduction velocities of 10 m/s or less; the effect of VN stimulation on all but one of these units was inhibition. The onset latency of the response to VN stimulation was long [20.3 +/- 3.7 (S.E.M.) ms, n = 9, for the antidromically activated neurons and 12.1 +/- 1.2 ms, n = 73, for the others], suggesting that the effects were predominantly polysynaptic. In addition, most of the spontaneously active units tested (33/36) received convergent inputs from the carotid sinus nerve (CSN), as would be expected for neurons which influence sympathetic outflow. Vestibular-elicited inhibition of SRF neurons with projections to the intermediolateral cell column could account for late, long duration inhibition of sympathetic discharges produced by labyrinth stimulation.

Afferent Pathways↗
PubMed1991

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

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.

Animals↗
PubMed1990

Convergence of cardiovascular and vestibular inputs on neurons in the medullary paramedian reticular formation.

Extracellular recordings were made from 47 neurons in the caudal medullary paramedian reticular formation of chloralose-urethan anesthetized cats. The firing rate of all of these neurons was affected by stimulation of the contralateral vestibular nerve. The onset latency of the response to vestibular nerve stimulation was accurately determined for 43 of these neurons. The large majority (36 of 43) received short-latency (onset latency less than 5 ms) inputs; 7 were driven within 2 ms and were classified as receiving disynaptic inputs. Twenty of the 47 neurons also received inputs from the ipsilateral carotid sinus nerve. The paramedian reticular formation thus appears to be an important site for the integration of cardiovascular afferent and vestibular signals. However, only a small fraction of the neurons (2 of 13 tested) which received such convergent inputs could be antidromically driven from the upper thoracic spinal cord.

Action Potentials↗
PubMed1990

Response of vestibular neurons to head rotations in vertical planes. III. Response of vestibulocollic neurons to vestibular and neck stimulation.

1. To compare the properties of the vestibulocollic reflex (VCR) with those of vestibular neurons projecting to the neck [vestibulocollic (VC) neurons], we have studied the behavior of the latter in the decerebrate cat. Neurons were identified by their antidromic responses to stimulation in C1-C2, but not C5. Responses to stimulation of vestibular and neck receptors were produced by rotation of the body and head in vertical planes. 2. We determined the plane of whole body (vestibular) or body with head counter-rotated (neck) rotation, which produced the maximal modulation of each neuron (response vector orientation). Neuron dynamics were then studied with sinusoidal (0.02-2 Hz) stimuli aligned with this orientation. 3. On the basis of dynamics and vector orientation, the neuron was assigned a vestibular input classification of otolith, vertical canal, otolith + canal, or spatial-temporal convergence (STC). 4. The properties of this sample of VC neurons are similar to those of a larger population of vestibular neurons whose projection was not identified. For example, the distributions of cells with different types of vestibular inputs were roughly the same; in particular, few cells showed STC responses. In addition, there was no evidence of significant convergence of like canals across the midline (e.g., right anterior + left anterior). 5. Also similar to the larger unidentified population, 80% of VC neurons tested for neck input received such an input. The neck and vestibular responses tended to be antagonistic; the vector orientations were usually opposite, and the response gains and phases similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Effects of muscle and cutaneous hindlimb afferents on L4 neurons whose activity is modulated by neck rotation.

We recorded extracellularly, in decerebrate, labyrinthectomized cats, from spontaneously active L4 neurons whose activity was modulated by head rotation, and studied the effects of stimulation of ipsilateral hindlimb nerves. Rotation of the head about the longitudinal (roll) axis was more effective than rotation about the transverse (pitch) axis or vertical (yaw) axis for this group of neurons. Most units received convergent excitatory or inhibitory inputs from several nerves, with excitation being more prominent. The most effective muscle nerves were quadriceps (37/43 neurons), sartorius (19/21) and tibialis anterior (17/35); stimulation of biceps posterior-semitendinosus, biceps anterior-semimembranosus, or gastrocnemius rarely influenced the firing of the neurons. Group I effects were present in only a small fraction of neurons; however, short latency (central latency less than or equal to 5 ms) group II effects were observed in almost one-third. Longer latency group II as well as group III inputs were also common. All neurons received inputs from mixed and cutaneous nerves which usually had low thresholds and central latencies greater than 5 ms. Most recording sites were in medial lamina VII or lamina VIII; some of the units were identified by antidromic stimulation as propriospinal neurons which projected to the lumbar enlargement.

Action Potentials↗