Two- rather than three-dimensional representation of saccades in monkey superior colliculus.

Saccades are controlled by neurons in the brainstem reticular formation that receive input from the superior colliculus and cortex. Recently two quantitative models have been proposed for the role of the colliculus in the generation of three-dimensional eye movements. In order to test these models, three-dimensional eye movements were measured in the alert monkey to investigate whether the saccadic motor map of the superior colliculus is two-dimensional, representing retinal target vectors, or three-dimensional, representing three-dimensional motor error for the rotation of the eye. Electrical stimulation of the superior colliculus produced two-dimensional, not three-dimensional, eye movements. It is therefore concluded that the collicular motor map is two-dimensional.

Ht31: the first protein kinase A anchoring protein to integrate protein kinase A and Rho signaling.

In an attempt to isolate protein kinase A anchoring proteins (AKAPs) involved in vasopressin-mediated water reabsorbtion, the complete sequence of the human AKAP Ht31 was determined and a partial cDNA of its rat orthologue (Rt31) was cloned. The Ht31 cDNA includes the estrogen receptor cofactor Brx and the RhoA GDP/GTP exchange factor proto-lymphoid blast crisis (Lbc) sequences. The Ht31 gene was assigned to chromosome 15 (region q24-q25). It encodes Ht31 and the smaller splice variants Brx and proto-Lbc. A protein of the predicted size of Ht31 (309 kDa) was detected in human mammary carcinoma and HeLa cells. Anti-Ht31/Rt31 antibodies immunoprecipitated RhoA from primary cultured rat renal inner medullary collecting duct cells, indicating an interaction between the AKAP and RhoA in vivo. These results suggest that Ht31/Rt31 represent a new type of AKAP, containing both an anchoring and a catalytic domain, which appears to be capable of modulating the activity of an interacting partner. Ht31/Rt31 have the potential to integrate Rho and protein kinase A signaling pathways, and thus, are prime candidates to regulate vasopressin-mediated water reabsorbtion.

Projections from the superior colliculus motor map to omnipause neurons in monkey.

Descending projections from the superior colliculus (SC) motor map to the saccadic omnipause neurons (OPNs) were examined in monkeys by using anterograde transport of tritiated leucine. The SC was divided into three zones: the rostral pole of the motor map, a small horizontal saccade zone in central SC, and a large horizontal saccade zone in caudal SC. Tracer injections into the intermediate layers of the three zones led to different patterns of silver grain deposits in and around nucleus raphe interpositus (RIP), which contains the OPNs: 1) From the rostral pole of the motor map, coarse axon branches of the crossed predorsal bundle spread medially into the RIP, branched, and terminated predominantly unilaterally over cells on the same side. 2) From the small horizontal saccade zone, the axon branches were of a finer caliber and terminated diffusely in the RIP, mainly on the same side. 3) From the large horizontal saccade zone, no terminal labeling was found within the RIP. 4) From the rostral pole of the motor map and small horizontal saccade zone, fiber branches from the ipsilateral descending pathway terminated diffusely over RIP. 5) In addition, terminal labeling in reticulospinal areas of the pons and medulla increased in parallel with the size of the saccade according to the SC motor map. The results suggest that there are multiple projections directly onto OPNs from the rostral SC but not from the caudal SC associated with large gaze shifts. The efferents from the rostral pole of the motor map may subserve the suppression of saccades during visual fixation, and those from the small horizontal saccade zone could inhibit anatagonist premotor circuits.

Histological identification of premotor neurons for horizontal saccades in monkey and man by parvalbumin immunostaining.

The premotor excitatory and inhibitory burst neurons are essential for horizontal saccades. In the monkey, excitatory burst neurons lie in the ipsilateral paramedian pontine reticular formation, and the inhibitory burst neurons lie more caudally in the contralateral nucleus paragigantocellularis dorsalis. For a neuropathological analysis of degenerative changes in saccadic disorders of patients, the histological identification of the burst neuron areas in man is important. Here, we show that this is possible with parvalbumin immunostaining as a histological marker. First, in monkeys, the premotor burst neurons were backlabeled by injections of wheat germ agglutinin-horseradish peroxidase or cholera toxin subunit B into the abducens nucleus or tetanus toxin fragment C into the lateral rectus muscle and shown by double labeling to contain parvalbumin. Then, human brainstem sections were immunoreacted for parvalbumin, and, by comparing the resulting staining pattern to that in the monkey, the homologous burst neuron areas were defined in man. In the monkey, excitatory burst neurons were confirmed to the nucleus reticularis pontis caudalis and did not extend farther rostrally into the nucleus reticularis pontis oralis. All retrogradely labeled cells in both burst neuron areas were parvalbumin positive, and approximately 70% of the parvalbumin-positive cells were retrogradely labeled. Both burst neuron areas were highlighted by their parvalbumin staining pattern and could be outlined in man as well. The putative excitatory burst neuron area in man is in the medial part of the nucleus reticularis pontis caudalis (extending 2.5 mm mediolaterally), immediately rostral (250 microns) to the omnipause neurons and extending 2.2 mm rostrally, and the putative inhibitory burst neuron area lies in the medial part of the paragigantocellular nucleus caudal to the abducens nucleus, extending 1.8 mm caudally. The location of the burst neuron areas, including the burst neurons themselves, via parvalbumin immunostaining will help in the analysis of clinical cases with slow saccades.

Vestibular stimulation affects dichotic lexical decision performance.

We report an experimental attempt to shift, by vestibular stimulation, healthy subjects' right ear advantage (REA) in a dichotic listening (DL) task with words and nonwords as stimuli. Forty right-handed men performed the task under two different conditions, once while sitting in a stationary turning chair (baseline) and once during sinusoidal rotation. In this latter condition, every other stimulation was received during maximal left-to-right (i.e., clockwise), every other during maximal right-to-left (i.e., counterclockwise) acceleration. There was a reliable REA for lexical decision accuracy in the baseline and right-to-left trials but not during left-to-right rotation. While right ear performance was unaffected by rotation, there were more correct lexical decisions to left ear targets exclusively during left-to-right turns (one-tailed P = 0.05). Since there were no parallel shifts in auditory thresholds under the different conditions, this effect is not due to any hypothetical auditory-vestibular interactions on a primary sensory level. The improvement in left ear DL performance, although small in our study, is comparable to the symptom-alleviating effect of caloric vestibular stimulation in patients with left-sided hemispatial neglect and interpreted as a consequence of a rotation-induced attentional shift towards the left hemispace.

Activated platelets induce tissue factor expression on human umbilical vein endothelial cells by ligation of CD40.

CD40 is a type I member of the tumour necrosis factor (TNF) receptor superfamily of proteins, and is present on a wide variety of cells including vascular endothelial cells. Ligation of this receptor on endothelial cells is known to increase expression of inflammatory adhesion molecules. We have recently demonstrated that platelets express the ligand of CD40 (CD154) within seconds of exposure to agonist, and interact with endothelial cells to participate directly in the induction of an inflammatory response. Here we show that activated platelets induce tissue factor (TF) expression on endothelial cells in a CD40/CD154-dependent manner, and that the magnitude of this response can equal that induced by TNFe. Moreover, CD40 ligation on endothelial cells downregulates the expression of thrombomodulin. We also show that CD40-mediated TF expression is less sensitive to inhibition with the oxidative radical scavenger pyrrolidine dithiocarbamate than is that mediated by TNFalpha, indicating that CD40 has a distinct signalling pathway. Tissue factor is a cell membrane protein which functions as the main trigger of the extrinsic pathway of blood coagulation, and its expression on endothelial cells is implicated in wound healing and angiogenesis. Since platelets are among the first cells involved in haemostasis following tissue injury, our data showing that ligation of CD40 by CD154 induces a procoagulant phenotype on vascular endothelial cells suggests that platelets may play an important role in the induction of wound healing.

Circularvection: psychophysics and single-unit recordings in the monkey.

In psychophysical experiments, human subjects indicated the amount of circularvection (CV) that experienced during sinusoidal rotation (0.01-5 Hz) of the visual surround. Accelerations varied between 5 and 160 degrees/second2; maximal velocities did not exceed 160 degrees/second. Below 0.1 Hz and 20 degrees/second2, most subjects experienced full CV; above, CV was only partial. Subjects then perceived a combination of CV and object motion. All subjects still had some CV at 2 Hz. The upper frequency limit seemed to occur around 5 Hz. In related neurophysiological studies, single units were investigated in the vestibular cortex (area 2v) of the alert monkey. Neurons responded to animal rotation in the dark as well as to sinusoidal rotation of the visual surround (0.01-1 Hz). Units responded to the visual stimulus in the high-frequency range with a gain increase. These experiments demonstrate the prominent influence of the visual system on vestibular neurons even at high frequencies.

Vestibular habituation in man and monkey during sinusoidal rotation.

Habituation of the vestibular system by repeated steps of angular velocity leads to a shortening of nystagmus. These steps can be broken down into different frequency sinusoids. High-frequency sinusoidal rotation (above 0.1 Hz) generally was found to be ineffective, while low-frequency stimulation (0.0015-0.05 Hz) led to a dramatic shortening of time constants after only a few cycles of stimulation. In the alert monkey, time constants of vestibular nystagmus and single units, recorded from the vestibular nuclei, are always similar and covary together. Experiments in humans, with measurement of nystagmus and subjective velocity sensation, suggest similar processes for habituation.

Input-output activity of the primate flocculus during visual-vestibular interaction.

In the primate flocculus, unit activity was recorded during vestibular (rotation of the monkey about the vertical axis in complete darkness), optokinetic (rotation of the visual surround around the stationary monkey), and conflicting (rotation of the visual surround and the turntable fixed together) stimulation. Activity indicating two different mossy fiber inputs was recorded. One carried a signal that was similar to that in the vestibular nuclei: during optokinetic stimulation, neurons saturated at a velocity of 60 degrees/second; and during conflicting stimulation, neuronal activity was attenuated only at low accelerations. This input combines vestibular, visual, and oculomotor information. Another mossy fiber input carried information about visual image slip only. This input indicates instances when nystagmus is not compensatory. Purkinje cells were modulated in their simple spike activity during optokinetic stimulation only at high stimulus velocities of 40-60 degrees/second and above, and during conflicting stimulation at high accelerations. This suggests a complementary information processing of the flocculus and the vestibular nuclei during visual-vestibular stimulation. The findings are corroborated by lesion studies in primates.

Canal and otolith afferent activity underlying eye velocity responses to pitching while rotating.

Pitching the head while rotating (PWR) combines periodic activation of the semicircular canals and the otoliths to generate pitch and roll eye deviations and continuous horizontal nystagmus. Monkeys were tested after individual pairs of semicircular canals were plugged and single units were recorded in the vestibular nerve while the animals were sinusoidally pitched 20-40 deg about a spatial horizontal axis with 5- and 16-s periods and simultaneously rotated about a spatial vertical axis at 30-120 deg/s. As previously shown, the steady-state horizontal response disappeared after plugging the vertical semicircular canals, but was maintained when the lateral canals were plugged. When the left anterior and right posterior canal (LARP) pair was left intact, the steady-state response depended on the axis about which the pitching took place. When the axis was normal to the LARP plane, there was no steady-state response. When the pitching axis was perpendicular to the LARP normal, the response was maximal. Firing rates of otolith units were approximately in phase with pitch position, and the addition of rotation about a vertical axis did not change the response. Lateral canal units did not have a steady-state modulation during pitch or constant velocity rotation. During PWR, they oscillated at twice the pitch frequency. This corresponded to the frequency at which the canal was maximally activated as it aligned with the plane of rotation. The amplitude of modulation increased proportionally to rotational velocity, but the phase remained the same. These characteristics were unchanged during roll while rotating (RWR), which induces little continuous nystagmus. Anterior and posterior canal units were maximally excited near pitch-velocity maxima and minima, respectively, during pure pitching. During PWR, however, the phases of both components simultaneously shifted toward each other and toward being in phase with otolith units. The peak excitation tended toward a forward-pitch position when the rotation was to the ipsilateral side, and toward a backward pitch position when the rotation was to the contralateral side. With 120-deg/s rotation during a 16-s pitch period, the phase difference between anterior and posterior canal units was as small as 17 deg. These data support the postulate that the correlation between vertical canal and otolith units is the critical factor in generating continuous unidirectional horizontal nystagmus during PWR.

Coding of information about rapid eye movements in the pontine reticular formation of alert monkeys.

Neurons in the rostral paramedian zone of the pontine reticular formation (PRF) have distinct frequency changes prior to and during quick eye movements, but generally little or no tonic activity associated with eye position. Evidence indicates that horizontal saccades and quick phases of nystagmus are generated in this region. Firing of units activated with eye movements (burst units) and of units which are inhibited (pause units) was analyzed. Eye movements were described by a vector having an amplitude (A) and an angle (a). These parameters were related to position changes in certain planes by the equation delta pos = A - cos alpha. In each of 80 cells in the PRF which were encountered, the activity could be related to some parameter of the above equation: change of position (delta pos), amplitude (A), or the cosine of the angle between the direction of movement and a reference direction (cos alpha). Units coding amplitude of eye movement or change in position in a particular plane conveyed the information by number of spikes. Units coding direction of movement did so by frequency. In many units, the information coding was precise so that the direction or amplitude of single eye movements could be predicted from the frequency changes of single units. In other units, this could be determined from averages of the frequency changes. Cells coding direction or change in position had frequency maxima only in planes corresponding to the pulling direction of the eye muscles. The results suggest that a vector description is not only a convenient mathematical tool, but is the way eye movements are coded in the PRF and possibly elsewhere in the central nervous system.

Horizontal and vertical vestibulo-ocular and cervico-ocular reflexes in the monkey during high frequency rotation.

In the alert monkey the horizontal vestibulo-ocular reflex (VOR) is basically compensatory over the range of 0.5 to 6 Hz with a gain near unity, and with the phase of the compensatory eye position having a minimal lag with respect to head position. Typical frequency-dependent eye movement patterns were observed. Vertical VOR is also compensatory having the same phase relations but with a reduced gain (-2.5 to -3.7 dB). In this range, vestibular input appears to be the predominant sensory influence on reflex eye movements. Additional optokinetic reflexes do not improve the VOR above 0.5 Hz. The horizontal cervico-ocular reflex (COR) is minimal or absent in normal monkeys.

Vestibulo-ocular reflexes after selective plugging of the semicircular canals in the monkey--response plane determinations.

The contribution from different pairs of semicircular canals to the generation of horizontal vestibular nystagmus was examined in monkeys. Animals with different pairs of semicircular canals surgically plugged were accelerated sinusoidally at 1 Hz (a predictive stimulus) or with steps of angular velocity (a non-predictive stimulus) about an earth vertical axis while the head was placed in various static pitch positions. In normal animals, and in animals with only the lateral canals intact, horizontal nystagmus elicited with angular velocity steps is maximal at a static pitch angle of 15 degrees nose-down (relative to the horizontal stereotaxic plane). The response follows a cosine function of the pitch angle, approaches zero at an angle of 90 degrees to the optimal orientation, and finally reverses. In animals with only the vertical canals operating, direction specific horizontal nystagmus can still be elicited. Using velocity steps, a null plane at which nystagmus reverses can be determined. It is found at about 32 degrees nose-down and thus is different from the optimal plane of the lateral canals. Consequently, it is not possible to stimulate the lateral canals maximally without stimulating the vertical canals simultaneously. Using sinusoidal rotation, nystagmus is attenuated at the static pitch position of 32 degrees nose-down, but does not reverse direction with further pitching.

Vertical eye movement related unit activity in the rostral mesencephalic reticular formation of the alert monkey.

Eye movement related unit activity was recorded in the rostral mesencephalic reticular formation (MRF) of the alert monkey. Most units (78 out of 117) were activated with a short activity burst starting before the eye movement and were otherwise silent. The activity was the same whether movements occurred spontaneously in the light or dark, or were fast phases of vestibular or optokinetic nystagmus, and could be related to parameters of a vector representing the eye movement such as amplitude, position changes along certain planes or direction of movements. Units coding position changes or direction of movement had their preferred direction always close to the vertical. Other units (18 out of 117) showed some tonic activity, which was also only related to vertical eye position. It is suggested that this region of the rostral MRF acts an an immediate supranuclear structure, mediating eye movements in the vertical plane.

Frontal eye field projection to the paramedian pontine reticular formation traced with wheat germ agglutinin in the monkey.

Injections of the retrograde tracer [125I]wheat germ agglutinin have been placed in different areas of the paramedian pontine reticular formation (PPRF), a well known premotor center for gaze control. Experiments in 5 monkeys revealed 3 major sources of input: (1) bilateral projections from the so-called frontal eye field (FEF), which is situated in the frontal cortex around the arcuate sulcus; (2) the intermediate and deep layers of mainly the contralateral superior colliculus; and (3) ipsilateral projections from brainstem structures such as the accessory oculomotor nuclei (nucleus interstitialis of Cajal, nucleus of Darkschewitsch, and nucleus of the posterior commissure), the mesencephalic reticular formation, the vestibular nuclei, the nucleus prepositus hypoglossi, and the cerebellar fastigial nucleus. The results are compared with previous anatomical investigations and confirm the electrophysiologically demonstrated FEF-PPRF-abducens disynaptic pathway.

Nystagmus generated by sinusoidal pitch while rotating.

Sinusoidal pitch while rotating about a vertical axis in darkness causes continuous horizontal compensatory nystagmus in the monkey which persists for the duration of stimulation. The steady-state velocity sums with post-rotatory nystagmus to reduce or cancel it, suggesting involvement of the velocity storage mechanism. Analysis of the labyrinthine excitation during pitch while rotating suggests that the vertical canals play a predominant role in generating the response. Effects of selective labyrinthine lesions are in agreement with this hypothesis. Plugging the lateral canals, leaving the vertical canals intact, blocked the initial rapid response at the onset of rotation, but did not interrupt the continuous nystagmus induced by pitch while rotating. On the other hand, plugging the vertical canals abolished the response. If the lateral canal nerves were cut so that the velocity storage mechanism was inactivated, the continuous response to pitch while rotating also disappeared. The dominant labyrinth activation responsible for the nystagmus during pitching while rotating appears to arise in the vertical semicircular canals and to couple to the oculomotor system through the velocity storage mechanism.

ISO-frequency curves of oculomotor neurons in the rhesus monkey.

Static firing frequencies have been determined in extraocular motoneuronal discharge patterns for different eye positions within +/- 30 deg around the primary position. From these data iso-frequency curves were plotted stating all possible eye positions for a given firing rate. Such curves have been constructed for the lateral, medial, and inferior recti, the superior oblique and for the upward pulling muscles (without distinguishing superior rectus and inferior oblique). Fixation of eye position always involved natural synergistic action of all muscles. The iso-frequency curves of individual motoneurons are a family of almost parallel curves with mainly horizontal or vertical gradients. Especially for the superior oblique, the innervation gradients depend strongly on eye position. Motoneurons subserving the same muscle can have different innervation gradients at the same eye position.

Chameleon eye position obeys Listing's law.

Listing's law (LL) states that 3D-eye positions lie in a plane, when they are described as single-axis rotations from the primary position. This implies that the degrees of freedom of eye movements are reduced from three to two. Various hypotheses exist, regarding the implementation of LL. These include facilitation of binocular vision, optimization of oculomotor control, and mechanical constraints in the orbit. We recorded the 3D-eye position during saccadic scanning in the chameleon, to investigate whether LL is valid in an animal with different anatomical and behavioral characteristics compared to primates. We show that in chameleons, the eye position obeys LL with a high precision. Since the anatomical arrangement of the orbit in chameleons is very different from that in primates, and binocular fused vision is virtually absent, we suggest that in the chameleon, LL mainly optimizes oculomotor control.

Static roll and pitch in the monkey: shift and rotation of Listing's plane.

In three rhesus monkeys three-dimensional eye positions were measured with the dual search coil technique. Recordings of spontaneous eye movements were made in the light and in the dark, with the monkeys in different static roll or pitch positions. Eye positions were expressed as rotation vectors. In all static positions eye rotation vectors were confined to a plane, i.e. Listing's plane was conserved. Tilt about the roll axis shifted the plane along this axis, i.e. a constant torsional component was added to all eye positions. Tilt about the pitch axis changed the pitch angle of Listing's plane.

Visual suppression of torsional vestibular nystagmus in rhesus monkeys.

Juvenile rhesus monkeys, placed on a motorized turntable, were rotated at constant velocity and then decelerated about an Earth-vertical axis. The animals were implanted with dual search coils to measure eye movements in three dimensions. By changing the monkey's body position (upright, ear-down, supine), postrotatory nystagmus was elicited in the horizontal, vertical, or torsional direction. Peak slow phase eye velocity and time constant of velocity decay were compared between decelerations in the dark and in the light. In all nystagmus directions, illumination reduced the time constant (Tc) to values around 5 sec. Peak velocity (Vp) was markedly attenuated in the horizontal and vertical directions (around 50%), but the effect of light on Vp in the torsional direction was small (less than 20%). These findings were independent of the velocity step size. Our hypothesis is that the two dynamic components of optokinetic nystagmus, as they interact with postrotatory nystagmus during visual suppression, differ in their dimensionality: the early component (fast component, direct pathway, pursuit system) is mainly activated in the horizontal and vertical directions, while the late component (slow component, indirect pathway, optokinetic system) effectively operates in all three dimensions.