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J I Simpson

Publications and source records attributed to J I Simpson.

At least 37 records · Page 2Linked to original sources
PubMed1994

Projections of individual Purkinje cells of identified zones in the ventral nodulus to the vestibular and cerebellar nuclei in the rabbit.

The projections of Purkinje cells from zones in the ventral nodulus of pigmented rabbits were studied with the use of extracellularly injected biocytin as an anterograde tracer. The zones were physiologically identified according to the complex spike modulation of Purkinje cells in response to optokinetic stimulation. Purkinje cells in the most medial zone do not respond to optokinetic stimulation; they project to the fastigial nucleus, the perifastigial white matter, the periinterposed white matter, and the medial vestibular nucleus. In the adjacent zone, Purkinje cells respond best to optokinetic stimulation about the vertical axis; they project to the periinterposed white matter and the medial vestibular nucleus. Purkinje cells in the next zone respond best to optokinetic stimulation about an axis approximately perpendicular to the ipsilateral anterior canal; they project to the periinterposed white matter, dorsal group y, the superior vestibular nucleus, and the medial vestibular nucleus. In the most lateral zone, Purkinje cells respond best to optokinetic stimulation about the vertical axis; they project to the periinterposed white matter, dorsal group y, and the medial vestibular nucleus. The majority of axons gave off collaterals and innervated more than one nucleus. Often, three or four different areas received terminals from a single Purkinje cell axon. The zonal projection pattern of the ventral nodulus is compared to that of the flocculus, which, with respect to the visual climbing fiber afferents, has similar zones.

Animals↗
PubMed1994

The rostral dorsal cap and ventrolateral outgrowth of the rabbit inferior olive receive a GABAergic input from dorsal group Y and the ventral dentate nucleus.

The dorsal cap and ventrolateral outgrowth of the inferior olive are involved in the control of eye movements. The caudal dorsal cap is predominantly involved in the horizontal optokinetic reflex; it receives most of its GABAergic input from the nucleus prepositus hypoglossi. In the present study, we determined the source of a major inhibitory input to the rostral dorsal cap and the ventrolateral outgrowth, which are the olivary subnuclei mainly involved in the "vertical" optokinetic reflexes. We studied these subnuclei in the rabbit with the use of retrograde tracing of horseradish peroxidase and anterograde tracing of wheat germ agglutinin-coupled horseradish peroxidase combined with postembedding immunocytochemistry. The ventral dentate nucleus of the cerebellum and dorsal group y project contralaterally to the rostral dorsal cap and ventrolateral outgrowth; this projection is entirely GABAergic. The terminals of this input form predominantly symmetric synapses with extraglomerular and intraglomerular dendrites; the remaining terminals are axosomatic. In addition, the dorsal cap and ventrolateral outgrowth contain significantly more crest synapses than any other olivary subnucleus. The terminals that form these crest synapses are derived from dorsal group y and/or the ventral dentate nucleus. None of the terminals in the dorsal cap or ventrolateral outgrowth was glycinergic.

Animals↗
PubMed1994

Functional and anatomic organization of three-dimensional eye movements in rabbit cerebellar flocculus.

1. The three-dimensional, binocular eye movements evoked by electrical microstimulation of the cerebellar flocculus of alert, pigmented rabbits were recorded using the scleral search coil technique. The components of these eye movements were obtained in reference to an orthogonal coordinate system consisting of a vertical axis and two horizontal axes at 45 degrees and 135 degrees azimuth. The azimuth coordinate was taken to increase to both sides from the 0 degrees reference in the direction of the nose. 2. Eye movements were evoked most readily by stimulation (0.2-ms pulses at 200 Hz for 1 s, intensity < or = 20 microA) at loci in the deep granular layer and the white matter. They consisted of slow (5-20 deg/s) movements. The responses were either binocular, with the eye ipsilateral to the stimulated flocculus usually having the larger amplitude, or were monocular, in which case they were restricted to the ipsilateral eye. 3. The evoked responses were classified according to the combination of the largest measured component of rotation for the two eyes and its sense of rotation (clockwise, CW, or counterclockwise, CCW). Seventy-eight percent of the evoked eye movements could be placed in one of two classes. For one of these classes the largest response component was a short-latency abduction of the ipsilateral eye about its vertical axis (19%), whereas for the other class (59%), the largest response component was a short-latency CCW rotation of the ipsilateral (left) eye about its 135 degrees axis. This response was frequently (50%) accompanied by a smaller short-latency CW rotation of the contralateral (right) eye about its 45 degrees axis. 4. The two main classes of three-dimensional eye movements are associated differentially with anatomically distinguishable compartments that are revealed by acetylcholinesterase histochemistry. Of the five anatomically distinguishable compartments in the floccular white matter, three are predominant. The middle of these three compartments is associated with the vertical axis class of movements, whereas the two adjacent compartments are associated with the 135 degrees class of eye movements. The eye movement relation of the other two, smaller compartments, was not determined. 5. The spatial orientation of the rotation axes of the two main classes of evoked eye movements closely corresponds to that of the preferred axes of the visual climbing fiber input to the flocculus. This suggests that both are organized in a similar coordinate system.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Intrathecal magnesium sulfate protects the spinal cord from ischemic injury during thoracic aortic cross-clamping.

BACKGROUND: Paraplegia is a known complication after surgery on the descending thoracic aorta. Thoracic aortic cross-clamping causes an increase in proximal aortic and cerebrospinal fluid pressures. Sodium nitroprusside, though effectively decreasing proximal aortic pressure, has been implicated in worsening the incidence of paraplegia by further increasing cerebrospinal fluid pressure and decreasing distal blood pressure, thereby reducing spinal cord perfusion pressure. Intravenous administration of magnesium sulfate has been shown to offer some spinal cord protection when used with mild hypothermia. This study investigated the effect of intrathecal magnesium on the prevention of paraplegia when sodium nitroprusside is used to control proximal hypertension during thoracic aortic cross-clamping in a dog model of spinal cord ischemia. METHODS: Two groups of eight dogs underwent thoracic aortic cross-clamping via a small thoracotomy incision for 45 min. Proximal, distal, and central venous pressures and cerebrospinal fluid pressures were monitored. Temperature was maintained at 36 degrees C. Sodium nitroprusside was used to control proximal hypertension. The control group received no magnesium sulfate, and a second group received 3 mg/kg intrathecal magnesium sulfate before thoracic aortic cross-clamping. The dogs were neurologically evaluated 24 h later by an observer blinded to the dogs' group. Spinal cord segments were obtained for histologic examination. RESULTS: Proximal mean arterial pressure, cerebrospinal fluid pressure, spinal cord perfusion pressure, and central venous pressure were not statistically different between the two groups. Neurologic outcome, however, was statistically different between the groups. None of the eight dogs in the magnesium group had any measurable neurologic injury, in contrast to the control group, in which seven of the eight dogs had severe neurologic injury (P < 0.005). Post mortem histologic data supported these findings. CONCLUSIONS: Intrathecal magnesium can prevent spinal cord injury despite markedly negative spinal cord perfusion pressure during thoracic aortic cross-clamping in a canine model of spinal cord ischemia.

Animals↗
PubMed1993

Three-dimensional organization of optokinetic responses in the rabbit.

1. Three-dimensional rotations of both eyes were measured in alert rabbits during optokinetic stimulation about axes lying in the horizontal plane or about an earth-vertical axis, with either one or both eyes viewing the stimulus. Optokinetic stimulus speed was 2 degrees /s, either continuous or alternating in polarity (triangular stimulus). In addition to the gains of the responses, the orientations of the response axes relative to the stimulus axes were determined. 2. In comparison to the response to constant-speed optokinetic stimulation about the vertical axis, the response to constant-speed optokinetic stimulation about horizontal axes was characterized by the lack of a speed buildup. In many cases, slow phase tracking was good as long as the eye was within the central oculomotor range but deteriorated when eye deviation became more eccentric and fast phases failed to be generated. These features suggest that the optokinetic reflex about horizontal axes functions as a position-control system, rather than as a velocity-control system. 3. Binocular optokinetic stimulation at constant speed (2 degrees/s) about the roll axis (0 degrees azimuth horizontal axis) elicited disconjugate responses. Although the gain of the response was not significantly different in the two eyes (0.38 for downward and 0.44 for upward stimulation), the response axes of the two eyes differed by as much as 51 degrees. 4. Monocular, horizontal axis optokinetic stimulation at constant speed elicited responses that were grossly dissociated between the two eyes. The magnitude of the responses was anisotropic in that it varied with the azimuthal orientation of the stimulus axis; the maximum gain for each eye (0.41 for the seeing and 0.33 for the covered eye) was at 135 degrees azimuth for each eye. The axis orientation and direction (sense of rotation) of the optokinetic stimulus eliciting the maximal response for each eye coincided with the optic flow normally associated with the maximal excitation of the corresponding ipsilateral anterior canal. 5. Binocular, triangular optokinetic stimulation with small excursions (+/- 10 degrees), which avoided the saturation problems of constant-speed stimulation, elicited adequate responses without systematic directional asymmetries. Gain was approximately 0.9 for all stimulus axis orientations in the horizontal plane. 6. During monocular stimulation with triangular stimuli, the response of the seeing eye showed a gain of approximately 0.5 for all orientations of the stimulus axis. In contrast, the covered eye showed anisotropic responses, with a maximum gain of approximately 0.5 during stimulation of the seeing eye about its 45 degree axis.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

The oxygen and nitrous oxide indices of flammability of endotracheal tubes determined by laser ignition.

This study determines the flammability of polyvinylchloride (PVC), red rubber (RR), and silicone (Si) endotracheal tubes in oxygen- and nitrous-oxide-enriched atmospheres. Flammability is measured by using the oxygen and nitrous oxide indices of flammability with laser ignition. The laser-ignited oxygen (O2) index of flammability of the endotracheal tubes is: PVC, 0.25; RR, 0.19; Si, 0.20. The laser-ignited nitrous oxide (N2O) index of flammability of the endotracheal tubes is: PVC, 0.45; RR, 0.37; and Si, 0.41. These results are similar to the previously reported O2 and N2O indices of flammability with propane-torch ignition. This study validates the concept that the indices of flammability are useful measures of endotracheal tube flammability and are independent of the ignition source.

Fires↗
PubMed1990

The effect of helium on endotracheal tube flammability.

The effect on endotracheal tube flammability of helium (He)-diluted oxygen and He-diluted nitrous oxide was determined with the oxidant O2 (He) and oxidant N2O (He) indices of flammability. These values then were compared with the corresponding values for nitrogen dilution, i.e., oxidant O2 (N2) and oxidant N2O (N2) indices of flammability. Four different types of endotracheal tubes were studied: polyvinylchloride (PVC), red rubber (RR), silicone (Si), and the Xomed (Xo) Lasershield tube. The oxidant O2 (He) indices are: PVC 0.274 +/- 0.0055, RR 0.194 +/- 0.0089, Si 0.194 +/- 0.0055, and Xo 0.256 +/- 0.0055. The oxidant N2O (He) indices are: PVC 0.526 +/- 0.0055, RR 0.434 +/- 0.0114, Si 0.416 +/- 0.0055, and Xo 0.456 +/- 0.0154. The oxidant O2 (N2) indices are: PVC 0.254 +/- 0.0055, RR 0.182 +/- 0.0045, Si 0.200 +/- 0, and Xo 0.230 +/- 0. The oxidant N2O (N2) indices are: PVC 0.472 +/- 0.0084, RR 0.356 +/- 0.0055, Si 0.392 +/- 0.0045, and Xo 0.444 +/- 0.0114. These differences, although statistically significant, are modest and demonstrate only a small, and probably clinically not significant, preference of He over N2 in decreasing flammability.

Fires↗
PubMed1989

Representations of ocular rotations in the cerebellar flocculus of the rabbit.

The climbing fibres (CFs) of the rabbit flocculus that respond in a speed- and direction-selective manner to retinal image slip produced by eye rotations can be divided into three classes on the basis of the orientation of the rotation axis associated with their greatest modulation (the preferred axis). The similarity of the orientations of these axes to those of the eye rotation axes of the extraocular muscles suggests that a simple geometrical correspondence may exist between the eye rotation associated with the preferred axis of a given class of CFs and the eye rotation produced by activation of the Purkinje cells upon which that class of CFs synapse. To pursue this possibility, the axes of the eye rotations evoked by electrical microstimulation of the alert rabbit's flocculus were determined simultaneously for both eyes in three dimensions using two orthogonal search coils on each eye. A limited number of slow eye movement response patterns were found, and of these, two predominated. The most common response was a counterclockwise (CCW) rotation of the ipsilateral (left) eye around an axis close to the horizontal plane and at about 140 degrees posterior to the nose. The other predominant response was abduction of the ipsilateral eye. These two response patterns, together with the smaller conjugate components for the contralateral eye, are consonant with the orientations of the preferred CF axes. In addition, a clear CCW rotation of the contralateral (right) eye about its 135 degrees axis was also evoked from some stimulation sites. This response, which occurred either alone or as a component of an upward rotation about the nasal-occipital (roll) axis, is at variance with the orientations of the preferred CF axis. However, the latencies of the CCW contralateral 135 degrees component (80-140 ms) were greater than those of the CW contralateral 45 degrees component, the CCW ipsilateral 135 degrees component and the ipsilateral abduction component (8-48 ms). These latency differences may distinguish stimulation of Purkinje cells from stimulation of other neurones.

Action Potentials↗
PubMed1988

A glycopyrrolate-ritodrine drug-drug interaction.

This is a case report of a 39-year-old patient who developed supraventricular tachycardia secondary to a ritodrine-glycopyrrolate interaction. The cardiovascular effects of ritodrine as well as the possible mechanism for this interaction are discussed. Suggested treatment for ritodrine-induced tachycardia in the parturient are presented.

Adult↗
PubMed1988

The accessory optic system of rabbit. I. Basic visual response properties.

1. The response properties of accessory optic system (AOS) neurons were assessed using single-unit extracellular recording from each of the three AOS terminal nuclei [medial, lateral, and dorsal terminal nuclei (MTN, LTN, and DTN)] in the anesthetized rabbit. 2. AOS neurons had large, monocular (contralateral) receptive fields (tens of degrees on a side) and exhibited a pronounced selectivity to the speed and direction of movement of large, textured patterns. The greatest responses occurred at slow speeds on the order of 0.5 degrees/s. 3. MTN and LTN neurons responded best to movement in near vertical directions. However, the stimulus directions corresponding to the greatest excitation and the greatest inhibition both had a posterior component and, thus, the preferred excitatory and inhibitory directions were not opposite each other. DTN neurons responded most strongly to horizontal movement and were excited by temporal to nasal movement. 4. AOS neurons were unresponsive to natural vestibular stimulation presented as sinusoidal oscillations of the rabbit about the yaw, pitch, and roll axes. 5. The response properties of AOS neurons are remarkably similar to those of the ON, direction-selective ganglion cells of the rabbit retina, and therefore this class of ganglion cell is most likely the predominant, if not the only, direct retinal input to the AOS. The local direction-selective properties of AOS neurons can be accounted for by combining the tuning curves of ON, direction-selective ganglion cells in a simple manner. 6. The low speed preference of AOS neurons, along with their large receptive fields suggests that they are suited to complement the vestibular system in detecting self-motion.

Animals↗
PubMed1988

The accessory optic system of rabbit. II. Spatial organization of direction selectivity.

1. To compare the spatial organization of the direction selectivity of neurons in the medial terminal nucleus (MTN) of the accessory optic system with that of neurons in the adjacent ventral tegmentum, extracellular single-unit recordings were made in the anesthetized rabbit. The ventral tegmental neurons were located in a region called the visual tegmental relay zone (VTRZ), which is defined by the ventral tegmental terminal field of contralaterally projecting MTN neurons. 2. Some of the present sample of MTN neurons (5 of 34) had monocular receptive fields composed of two parts distinguished by a marked difference in the orientation of their respective direction-selective tuning curves. For one part of the receptive field the preferred excitatory direction was "up," while for the other part it was "down." Such receptive fields for one eye were called bipartite, whereas the more usually encountered MTN receptive fields, which could be characterized by a single direction-selective tuning curve, were called uniform. 3. Of the 16 neurons recorded from the VTRZ, all but one were binocular. For these neurons, both uniform and bipartite receptive fields were found for each eye alone. The only monocular neuron encountered in the VTRZ had a contralateral, bipartite receptive field. 4. The spatial organization of the direction selectivity of bipartite receptive fields strongly suggests that they are suited to represent rotation of the visual field about a horizontal axis located in the vertical plane that divides the receptive field into two parts. 5. The boundary between the two parts of the bipartite receptive fields was found using handheld visual stimuli at one of two azimuthal locations, either close to 45 degrees or between 95 and 125 degrees (the 0 degree reference was rostral in the midsagittal plane). This particular structure of the bipartite receptive fields suggests that their preferred rotation axes have a close spatial relation to the best-response axes of the semicircular canals. 6. Seven VTRZ neurons were antidromically activated by electrical stimulation of the ipsilateral dorsal cap of the inferior olive. Since the receptive fields of VTRZ neurons have many of the structural features characteristic of the receptive fields of rostral dorsal cap neurons we conclude that the spatial organization of the receptive fields of dorsal cap neurons is, for the most part, synthesized prior to the inferior olive.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Spatial organization of visual messages of the rabbit's cerebellar flocculus. I. Typology of inferior olive neurons of the dorsal cap of Kooy.

1. Single-unit responses to large-field visual stimuli were recorded extracellularly from neurons in the dorsal cap of Kooy of the inferior olive in anesthetized, paralyzed rabbits. The visually modulated neurons in the dorsal cap responded optimally to slow rotation of random dot stimuli, which were produced using handheld patterns or a planetarium projector. 2. Neurons had either monocular or binocular receptive fields. For binocular receptive field neurons, monocular stimulation of one eye, called the dominant eye, elicited greater modulation than did stimulation of the other eye. Rotation about a particular axis, called the preferred axis, produced both maximal excitation and inhibition. On the basis of differences in preferred axis orientation and in eye dominance, three neuron classes called Vertical Axis, Anterior (45 degrees) Axis, and Posterior (135 degrees) Axis were distinguished. 3. Vertical Axis neurons were modulated exclusively from the eye contralateral to the inferior olive recording site. This cell type responded strongly to large-field visual stimuli rotating about the vertical axis. Excitation resulted from movement in the temporal to nasal direction, and inhibition occurred during movement in the nasal to temporal direction. 4. Two subclasses of Anterior (45 degrees) Axis neurons were distinguished according to whether the receptive field was monocular or binocular. For both subclasses, the dominant eye was ipsilateral. The receptive field organization of the dominant eye was bipartite as described in the previous paper (51) for neurons in the midbrain visual tegmental relay zone. Anterior (45 degrees) Axis neurons were maximally excited when the stimulus pattern moved upward and posterior above the horizon in the anterior quadrant of the ipsilateral visual field, from 0 degrees (nose) to approximately 45 degrees azimuth. From 45 to 180 degrees azimuth (occiput) and above the horizon, these neurons were excited by downward and posterior movement. Inhibition occurred with oppositely directed movements. For rotating stimuli presented to the dominant eye, this class of neurons responded best to rotation of the visual world about an axis oriented near the horizontal plane and approximately 45 degrees azimuth. 5. The receptive field of Posterior (135 degrees) Axis neurons was always binocular, with the dominant eye contralateral. For the contralateral receptive field, from 0 degree (nose) to 135 degrees azimuth and above the horizon, excitation occurred during upward and posterior movement.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Spatial organization of visual messages of the rabbit's cerebellar flocculus. II. Complex and simple spike responses of Purkinje cells.

1. Complex and simple spike responses of Purkinje cells were recorded in the flocculus of anesthetized, paralyzed rabbits during rotating full-field visual stimuli produced by a three-axis planetarium projector. 2. On the basis of the spatial properties of their complex spike responses, floccular Purkinje cells could be placed into three distinct classes called Vertical Axis, Anterior (45 degrees) Axis and Posterior (135 degrees) Axis. The first two classes occurred in both monocular and binocular forms; the third class was encountered only in binocular form. For the binocular response forms, stimulation through one eye, called the dominant eye, elicited a stronger modulation of the complex spike firing rate than did stimulation of the other eye. The approximate orientation of that axis about which full-field rotation elicited the deepest modulation (the preferred axis) when presented to the dominant eye served as the class label. These classes are the same as those determined qualitatively for inferior olive neurons in the previous paper (47). The present study provides a quantitative description of their spatial tuning. 3. For Vertical Axis cells, the dominant eye was ipsilateral with respect to the flocculus recording site. The preferred axis was vertical and null (no-response) axes were in the horizontal plane. For the binocular response form of Vertical Axis cells (less than 10% of this class), the direction preferences for the two eyes were synergistic with respect to rotation about the vertical axis. 4. The dominant eye for the Anterior (45 degrees) Axis cells was contralateral, with the preferred axis oriented in the horizontal plane at approximately 45 degrees contralateral azimuth. The modulation depth showed a close to cosine relation with the angle between the preferred axis and the stimulus rotation axis. The average orientation (n = 10) for the dominant eye preferred axis, determined by the best-fit sinusoid, was 47 degrees contralateral azimuth. The preferred axis orientation for the ipsilateral (nondominant) eye in the binocular response forms was between 45 and 90 degrees azimuth in the horizontal plane. A null axis for each eye was at approximately 90 degrees to the preferred axis. 5. The Posterior (135 degrees) Axis cells were encountered only in binocular response forms. The dominant eye was ipsilateral, with the preferred axis oriented at approximately 135 degrees ipsilateral azimuth close to the horizontal plane. The modulation depth showed a close to cosine relation with the angle between the preferred axis and the stimulus rotation axis.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗