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Biomedical subjects

C J Vierck

Publications and source records attributed to C J Vierck.

At least 19 recordsLinked to original sources
PubMed1996

Anterior parietal cortical response to tactile and skin-heating stimuli applied to the same skin site.

1. The response of anterior parietal cortex to skin stimuli was evaluated with optical intrinsic signal imaging and extracellular microelectrode recording methods in anesthetized squirrel monkeys. 2. Nonnoxious mechanical stimulation (vibrotactile or skin tapping) of the contralateral radial interdigital pad was accompanied by a decrease in reflectance (at 833 nm) in sectors of cytoarchitectonic areas 3b and 1. This intrinsic signal was in register with regions shown by previous receptive field mapping studies to receive low-threshold mechanoreceptor input from the radial interdigital pad. 3. A skin-heating stimulus applied to the contralateral radial interdigital pad with a stationary probe/thermode evoked no discernable intrinsic signal in areas 3b and 1, but evoked a signal within a circumscribed part of area 3a. The region of area 3a responsive to skin heating with the stationary probe/thermode was adjacent to the areas 3b and 1 regions that developed an intrinsic signal in response to vibrotactile stimulation of the same skin site. Skin heating with a stationary probe/thermode also evoked intrinsic signal in regions of areas 4 and 2 neighboring the area 3b/1 regions activated by vibrotactile stimulation of the contralateral radial interdigital pad. 4. The intrinsic signal evoked in area 3a by a series of heating stimuli to the contralateral radial interdigital pad (applied with a stationary probe/thermode) increased progressively in magnitude with repeated stimulation (exhibited slow temporal summation) and remained above prestimulus levels for a prolonged period after termination of repetitive stimulation. 5. Brief mechanical stimuli ("taps") applied to the contralateral radial interdigital pad with a probe/thermode maintained either at 37 degrees C or at 52 degrees C were accompanied by the development of an intrinsic signal in both area 3a and areas 3b/1. For the 52 degrees C stimulus, the area 3a intrinsic signal was larger and the intrinsic signal in areas 3b/1 smaller than the corresponding signals evoked by the 37 degrees C stimulus. 6. Spike discharge activity was recorded from area 3a neurons during a repetitive heating stimulus applied with a stationary probe/ thermode to the contralateral radial interdigital pad. Like the area 3a intrinsic signal elicited by repetitive heating of the same skin site, the area 3a neuron spike discharge activity also exhibited slow temporal summation and poststimulus response persistence. 7. The experimental findings suggest 1) a leading role for area 3a in the anterior parietal cortical processing of skin-heating stimuli, and 2) the presence of inhibitory interactions between the anterior parietal responses to painful and vibrotactile stimuli consistent with those demonstrated in recent cortical imaging and psychophysical studies of human subjects.

Animals↗
PubMed1995

Comparisons of dose-dependent effects of systemic morphine on flexion reflex components and operant avoidance responses of awake non-human primates.

Electromyographic activity and the force of reflex and operant responses were recorded following administration of morphine. Low doses facilitated reflex responses to input from A-delta afferents but not from A-beta input. Higher doses inhibited A-delta responses but not A-beta responses. Operant avoidance responses to visual cues were unchanged. Thus, depending on the dose, nociceptive reflexes were facilitated or inhibited, without associated effects on non-nociceptive input or on motor output.

Animals↗
PubMed1995

Effects of anterolateral spinal lesions on escape responses of rats to hindpaw stimulation.

In order to determine the effects of spinal cord lesions on nociceptive sensitivity of rodents, methods were developed to assess the speed of operant escape responses to electrocutaneous stimulation (ES). ES was delivered across the dorsal and ventral surfaces of either hindpaw, producing a current path through deep tissues. In order to guide establishment of a range of stimulus intensities for this manner of stimulation, a preliminary human psychophysical experiment was conducted with stimulation between the dorsal and ventral surfaces of a finger. For the human subjects, detection thresholds averaged 0.13 mA, and thresholds for a sharp (but nonpainful) sensation were 0.42 mA. Levels of stimulation between these thresholds for detection and a sharp quality elicited sensations of tingle or itch. Thresholds for reports of pain averaged 0.67 mA. On the basis of these results, intensities of ES ranging from 0.05 to 1.0 mA were presented to the feet of rats that were trained to perform an escape response with one forelimb. Thresholds for escape averaged slightly less than 0.1 mA; responding was consistent at 0.4 mA; and response probability and speed were maximal at approximately 0.8 mA. Thus, the rats responded aversively at intensities below those rated as sharp or painful by the human subjects, but the speed of escape reached a plateau at intensities that were above pain threshold for the human subjects. Unilateral thoracic lesions of the lateral spinal column of rats produced a contralateral hypalgesia. Escape thresholds were elevated, and the speed of escape responses to all intensities was reduced. This effect depended upon interruption of axons in the middle and anterior portions of one lateral column, corresponding to the location of long ascending pathways for nociception, including the spinothalamic tract. The speed of escape responding increased over 20 weeks of postoperative testing of animals with the largest lesions. This confirms results obtained previously from monkeys (by means of a similar paradigm), and corresponds to clinical reports of humans who have received spinal lesions for control of intractable pain. Thus, the location and organization of nociceptive pathways in the spinal cord of rodents appear to be similar to those of primates, and similar adaptations occur following interruption of these pathways.

Adult↗
PubMed1995

A critical band filter in touch.

Separate mechanoreceptor systems in humans were isolated by varying the spectra of vibrotactile stimuli. First, the function relating threshold to frequency of a sinusoid was obtained on the fingertip for each of four subjects, and it was found to comprise two limbs: a Pacinian and a non-Pacinian limb. The peak sensitivity within the Pacinian limb (mediated by Pacinian corpuscles) was around 250 Hz and spanned the region from 65 to 400 Hz. The non-Pacinian limb showed no detectable change in sensitivity in the region between 10 and 65 Hz. These two limbs were then treated as psychophysical channels in experiments in which narrow band noise and individual sinusoids were used to excite one or both channels. In the second and third experiments, the noise stimuli varied in bandwidth from 8 to 70 Hz and varied in center frequency from 25 to 218 Hz. Masking functions were obtained for ON-frequency conditions (the sinusoidal test and noise masker occupied the same frequency region) and for OFF-frequency conditions (the test and masker occupied different frequency regions). The ON-frequency experiments were used to estimate the signal-to-noise ratio (S/N) of the Pacinian channel at threshold. The OFF-frequency masking experiments were used to infer the shape of the Pacinian channel at frequencies below 65 Hz, where thresholds for Pacinian activation were above detection threshold. The results of these three experiments predicted the findings of a fourth masking experiment with a parameter free model that treated the Pacinian channel as a filter that integrates stimulus power. The results show that the Pacinian channel is analogous to a critical band in the auditory system.

Acoustic Stimulation↗
PubMed1994

Physiological changes during recovery from a primate dorsal column lesion.

The evoked potential (EP) over primary somatosensory cortex (SI) was monitored before and after a complete lesion of the primate dorsal column (DC) pathway on one side. The EP was elicited by electrocutaneous or mechanical stimulation of either foot, and was recorded from the contralateral cortical surface for periods of up to 3 months after the lesion. The amplitudes of the three major peaks (P20, N50, and P90) of the cortical somatosensory EP were significantly reduced following interruption of the contralateral DC. Over weeks following the lesion, there was a significant increase in amplitude of the P90 component of the EP that was not evident in the other peaks. The postlesion increases in P90 amplitude were correlated with improved performance on a task that required grasping with either foot, suggesting that behavioral recovery from a DC lesion results in part from neural plasticity, as opposed to a simple relearning of the task.

Afferent Pathways↗
PubMed1993

Reduced retrograde labeling of diencephalic-projecting neurons in the gracile nucleus of the monkey following removal of dorsal column input.

As part of an anatomical investigation of neuronal responses to deafferentation of the dorsal column nuclei by transection of the dorsal spinal columns, the uptake and retrograde transport of HRP by thalamic projection cells in the dorsal column nuclei was studied. The ventrobasal thalamus of 13 macaque monkeys was injected bilaterally with HRP at periods ranging from 3 to 364 days following intended unilateral transection of fasciculus gracilis at a mid- to upper thoracic level. The density of labeled cells in the gracile nuclei ipsilateral to complete lesions of fasciculus gracilis was compared with the density of labeled cells in the contralateral gracile nuclei that were fully innervated or partially denervated by an incomplete lesion. Also, the density of labeled cells in the fully innervated cuneate nuclei was compared. In general, there was a reduction in density of labeled cells in the gracile nuclei ipsilateral to complete lesions, without a corresponding decrement in labeled cells in the cuneate nuclei on that side. This result confirms effects on spinal motoneurons and on thalamocortical projection cells in the lateral geniculate nucleus following deafferentation. However, attempts to define a time course for the reduction in transport by lemniscal projection cells revealed an effect that was dramatic in some animals, partial in others, and not demonstrable in the remainder, without a clear relationship to time after surgery. This result is related to a literature which describes a variety of morphological, biochemical, electrophysiological, and behavioral effects of deafferentation which appear to wax and wane with time after neuronal injury.

Animals↗
PubMed1993

The effect of fasciculus cuneatus lesions on finger positioning and long-latency reflexes in monkeys.

Previous studies have reported abnormalities in fine hand and finger movements following interruption of the fasciculus cuneatus (FC) in primates. We report here that many of these deficits could be caused by an inability to actively regulate the position of the finger. Three macaques were trained to maintain the index finger in one position against constant or changing loads. Periodically, torque pulses were used to elicit reflexes in finger muscles. Following unilateral FC lesions, the monkeys failed to adjust finger position during the trials, and the normal M2 long-latency response was absent in the finger muscles. Performance on the task was impaired only in monkeys with complete lesions that included the deep ventral portion of the FC. These results suggest that afferent fibers in the FC regulate finger position, and do so partly through reflexive mechanisms. When the FC is interrupted, the inability to control finger position disturbs fine motor activities.

Animals↗
PubMed1993

Population estimates for responses of cutaneous mechanoreceptors to a vertically indenting probe on the glabrous skin of monkeys.

Recordings were obtained from low-threshold mechanoreceptive afferents during stimulation with a 0.5-mm-diameter probe at the receptive field (RF) center and at different distances from the point of maximal sensitivity. At each location, force-controlled stimuli of 0.5-4.0 g were ramped on to a plateau and then off at rates of 1, 10, and 100 g/s. The properties of rapidly adapting (RA) and slowly adapting type I (SAI) mechanoreceptors, when stimulated at the RF center, were similar in many respects to those reported in previous studies. Controlled stimulation away from the RF centers revealed that RF size for RAs was primarily dependent upon ramp rate, and for SAIs the size of the RF was primarily dependent upon load (force). The action potentials from individual afferents during stimulation at each location were binned in time and assigned to spatial segments of 1 mm. These responses were multiplied by: (A) an annular area of the receptive field and (B) the innervation density for the afferent type and skin region. The calculations provided estimates of overall rates of activity among the population of cutaneous afferents that respond to indentation by a small probe. Important differences were obtained between the responses of the population of afferents activated by the trapezoidal stimulus and the responses of afferents stimulated only at the RF center. Populations of tactile afferents provide more information for rate and intensity (force) discriminations than is available from units stimulated at the RF center. For RA afferents, the exponent of the power function describing relationships between stimulus rate and the population discharge (in impulses per second) was 0.3 times greater than the exponent for responses to on-center stimulation. For SAI mechanoreceptors, the exponent of the power functions for static responses to force was 0.22 times greater for the population response than for on-center activation. Population functions for RA responses to the rate of force application and for SAI responses to static load saturated less than comparable responses to stimulation of the RF center. Thus, the coding capacity of the population extends the range of tactile discriminability. The slope and range of stimulus-response functions for populations was enhanced relative to responses to on-center stimulation. This occurs because of recruitment of afferents with RF centers adjacent to and remote from the stimulus, depending upon thresholds and receptive field sizes for different stimulus parameters. With stimulation at increasing rates and forces, there is a progressive spatial recruitment of receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1993

Relationships between touch sensations and estimated population responses of peripheral afferent mechanoreceptors.

Trapezoidal indentations of the skin by a 0.5-mm-diameter probe were presented at different rates and loads (forces) to the human fingertip, in order to compare estimates of population responses of cutaneous mechanoreceptors with the quality and magnitude of tactile sensations. The subjects were first trained to attend to and evaluate variations in the magnitude of touch sensations associated with the onset ramp, the plateau period, and the offset ramp. They examined a series of line drawings that illustrated a variety of temporal profiles for sensation magnitude. The line drawings provided a straight-forward means of describing temporal fluctuations of sensation intensity, which corresponded well to psychophysical ratios that were determined subsequently with a matching procedure. Influences of ramp rate on qualities of touch sensations were evaluated by tabulating verbal descriptions of sensory experiences. Each of three rate conditions generated a different quality of sensation during the dynamic portions of stimulation. Onsets and offsets at 100 g/s were described as "taps". During ramps at 10 g/s the quality was described as "rolling" or "moving". At 1 g/s no sense of motion was detected; instead, a "pressure" sensation was identified. Touch sensations during the plateau were always described as a pressure. The subjective magnitudes of touch sensations associated with the onset, plateau, and offset were equated by comparing different components of paired stimuli. At 100 g/s, when subjects matched the offset sensation from the first of a pair of stimuli with the onset sensation from the second, the force of the stimulus producing the offset sensation was 1.3 times greater than the intensity of the stimulus that produced the onset sensation. Matching of the plateau sensation (evaluated during the last 1.5 s of the 2.5-s plateau period) with the onset sensation required a plateau stimulus that was 1.7 times greater in force than the stimulus which produced the onset. Comparison of stimulus intensities producing a match of plateau and offset sensations with stimulus intensities predicted from the previous matches (onset versus offset and onset versus plateau) demonstrated a mean within-subject error of 4%. The mean ratio of plateau to offset forces that produced a match was 1.8:1.3. In a matching procedure in which subjects compared the subjective magnitudes of plateau sensations following onset ramps of different rates, onset ramp rate significantly influenced the magnitude of pressure sensations. The ratios of plateau forces which produced equal magnitudes of sensation following 1, 10, and 100 g/s ramps were 1.6:1.3:1.0.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1993

Lack of a proprioceptive deficit after dorsal column lesions in monkeys.

Previous psychophysical examinations of the effects of dorsal column (DC) lesions on proprioception of the lower extremity have not revealed disturbances in proprioception, and there have been no similar experiments for the upper extremity. To evaluate the effect of DC lesions on upper extremity proprioception, we tested two monkeys with a variation of the typical clinical test for position sense. This test required the monkeys to detect the direction of a passive displacement of the finger. We identified proprioceptive deficits in one monkey following a DC lesion, but only when the finger was displaced with a small (< 14 degrees), slow (< 7 degrees/sec) movement. When we included displacements of all sizes and velocities in the analysis, performance was unaffected by the DC lesions in either monkey. Since the standard test for proprioception does not specify the speed and size of movements, we conclude that this test is not a valid method for estimating damage to the DCs.

Animals↗
PubMed1993

Finger movement deficits in the stumptail macaque following lesions of the fasciculus cuneatus.

Four stumptail macaques were trained to perform a key press with the index finger without associated movement of the adjacent (third) finger. Successful performance on this task required selective control over one finger (fractionation) and differential activation of muscles producing flexion or extension at different joints (multiarticulation). Following section of the fasciculus cuneatus (FC), a number of enduring deficits in finger movement capacities were observed. Over test periods of up to 2 years, fractionated key presses with the index finger could not be made, and the combination of flexion at the proximal joint with extension at the distal joints was absent. Coarticulated flexion at all the joints of each finger was substituted for the original multiarticulated, fractionated movements. We conclude that previous failures to observe impairments of finger movements following section of the dorsal columns (DCs) have resulted from the use of tasks that permit response substitution and therefore do not isolate specific movements for observation.

Animals↗
PubMed1992

Lesions of cat sacrocaudal spinal cord: a minimally disruptive model of injury.

As part of our studies of the organization of the cat sacrocaudal spinal cord (S3-Ca7), the portion of the neuraxis that innervates the tail, we have begun to evaluate the behavioral effects of hemisection or complete transection at the level of Ca1. Clinical observations that the tail strongly deviated to the side of a hemisection indicated the presence of an ipsilateral hypertonia. After complete transection of the spinal cord, the tail became ventroflexed in a midline position and exhibited spasticity, i.e., hypertonia, hyperreflexia, and clonus. Bowel and bladder functions and hindlimb gait and reflexes remained intact following either lesion. Quantitative behavioral measures corroborated our clinical observations. With the tail tethered to a force transducer, tail muscle tone was measured after the tail was passively positioned. Following a transection, resistance to dorsiflexion of the tail was greater than resistance to ventroflexion. In addition, tonic deviation of the tail was documented with videotape analysis while cats walked on a plank. Normal cats walked with the tail sharply dorsiflexed and centered. In contrast, the tail deviated ipsilaterally in cats with a hemisection, and the tail was ventroflexed in cats with a transection. These observations indicate that the sacrocaudal spinal cord provides a model with special advantages for investigation of changes in segmental motor functions following spinal cord injury. The effects of lesions on the tail are quantifiable and can resemble that spasticity observed after spinal cord injury in humans. Importantly, minimal effects on locomotive and autonomic functions were observed following hemisection or transection of the sacrocaudal spinal cord.

Animals↗
PubMed1992

Altered precision grasping in stumptail macaques after fasciculus cuneatus lesions.

Patterns of precision grasp are described in stumptail macaques (Macaca arctoides) before and after lesions of the fasciculus cuneatus (FC). Three monkeys were videotaped while reaching for and grasping small food items. From these videotapes, records were made of the style and outcome of each grasp. Kinematic measurements were also made to describe grip formation and terminal grasp. During grip formation, grip aperture was measured as the distance between the tips of the index finger and the thumb. For terminal grasp, the joint angles of the index finger were measured. The majority of grasps by normal monkeys were of the precision type, in which the item was carried between the tips of the index finger and thumb. Each normal monkey approached objects with a highly consistent grip formation; that is, the fingertips formed a small grip aperture during the approach, and the aperture varied little on repeated grasps. To grasp an item, the forefinger moved in a multiarticular pattern, in which the proximal joint flexed and the distal joint extended. As a result of this combination of movements, the forefinger pad was placed directly onto the object. Following FC transection, the monkeys were studied for 10 months, beginning 1 month after the lesion, to allow for recovery from the acute effects of surgery. The monkeys could grasp the food items, but they rarely opposed the fingertips in precision grasp. Grip formation was altered and was characterized either by excessive grip aperture or by little to no finger opening. All of the monkeys used the table surface to help grasp items. Combined multiarticular patterns of flexion and extension were never observed postoperatively; they were replaced by flexion at all joints of the fingers. These results suggest that the FCs are more important for precision grasping than for other, less refined grasp forms (e.g., power grasps; Napier, 1956). The FCs provide critical proprioceptive feedback to cerebral areas involved in the planning and/or the execution of these movements.

Afferent Pathways↗
PubMed1992

Alterations of natural hand movements after interruption of fasciculus cuneatus in the macaque.

As part of a series of investigations on the control of fine finger movements in the macaque, spontaneous use of the hand in grooming, scratching, and manipulation was observed before and after interruption of fasciculus cuneatus (FC). Videotaped observations were made of four stumptail macaques (Macaca arctoides) living outdoors in social groups. The monkeys were followed for 1 to 3 years postoperatively. For the first 2 weeks following surgery, all monkeys neglected the affected hand and did not use it for support, locomotion, climbing, scratching, foraging, or grooming. Recovery of gross arm and hand movements occurred over a 1- to 3-month period. All the monkeys eventually used the hand for support, climbing, and object manipulation, but fine control of the fingers did not recover. Also, there was an apparent hypotonia of the fingers, imparting a "floppy" appearance to the hand. The animals coped with the loss of fine control by decreasing the frequency of some behaviors, eliminating others, and developing alternative strategies. Exploratory movements that were utilized for investigating the anogenital area or foraging for small food items were eliminated by FC interruption. There were obvious deficits in grip formation and grasp of small food objects (see Glendinning et al., this issue), but effects on similar movements during grooming only became obvious after repeated inspection of videotaped records. Self-scratching and sweeps of the hand in grooming were preserved but altered in form and frequency. The component movements in these behaviors were relatively uncoordinated, and the fingers were splayed (abducted). Often the hand was formed in a rigid posture throughout the sweeping motion, and the fingers did not stroke the skin individually. Frame-by-frame analysis of videotapes revealed that the morphology of the precision grip during grooming, in movements termed "plucks," was permanently altered. Preoperatively, the monkeys kept the index finger and thumb closely apposed and routinely made contact on the distal surfaces of the digits, as has been described for precision grip in humans. Postoperatively, this relationship was altered. The index finger frequently missed the thumb tip and made contact on the proximal part of the phalanx, or missed the thumb altogether. Thus, the dorsal column input is important for proprioceptive guidance of movements that achieve "tactile foveation," when objects or surfaces are actively contacted by the receptive areas of keenest sensitivity (on the fingertips).

Afferent Pathways↗
PubMed1991

Inspiratory resistive load detection in conscious dogs.

The physiological mechanisms mediating the detection of mechanical loads are unknown. This is, in part, due to the lack of an animal model of load detection that could be used to investigate specific sensory systems. We used American Foxhounds with tracheal stomata to behaviorally condition the detection of inspiratory occlusion and graded resistive loads. The resistive loads were presented with a loading manifold connected to the inspiratory port of a non-rebreathing valve. The dogs signaled detection of the load by lifting their front paw off a lever. Inspiratory occlusion was used as the initial training stimulus, and the dogs could reliably respond within the first or second inspiratory effort to 100% of the occlusion presentations after 13 trials. Graded resistances that spanned the 50% detection threshold were then presented. The detection threshold resistances (delta R50) were 0.96 and 1.70 cmH2O.l-1.s. Ratios of delta R50 to background resistance were 0.15 and 0.30. The near-threshold resistive loads did not significantly change expired PCO2 or breathing patterns. These results demonstrate that dogs can be conditioned to reliably and specifically signal the detection of graded inspiratory mechanical loads. Inspiration through the tracheal stoma excludes afferents in the upper extrathoracic trachea, larynx, pharynx, nasal passages, and mouth from mediating load detection in these dogs. It is unknown which remaining afferents (vagal or respiratory muscle) are responsible for load detection.

Afferent Pathways↗
PubMed1990

Long-term changes in purposive and reflexive responses to nociceptive stimulation following anterolateral chordotomy.

Macaca nemestrina monkeys received unilateral interruption of the spinothalamic tract, producing contralateral hypalgesia and a bilateral decrease in amplitude of the flexion reflex. These effects on operant escape and reflex responses to electrocutaneous stimulation (ES) were monitored for months to evaluate relationships between the extent of each lesion and the presence or absence of recovery from the early postoperative deficits. Before surgery, the animals were trained to perform an operant response that terminated ES to the lateral calf of either leg. The durations of ES tolerated by each monkey were inversely related to stimulus intensities within the pain sensitivity range of human subjects. The vigor of operant escape responses and the frequency of intertrial pulls of the manipulandum were directly related to stimulus intensity. Following anterolateral chordotomy at an upper thoracic level, these measures revealed a contralateral hypalgesia for each animal. Operant responsivity to stimulation contralateral to the lesion recovered to control levels for 7 animals (group R). Sustained contralateral recovery of operant reactivity was not observed for 8 monkeys (group U). Most of the lesions in groups R and U were similar in extent and location, involving the classical distribution of the spinothalamic tract (in the anterolateral and ventral columns). Thus, recovery was not determined solely by lesion configuration. However, when recovery did occur, it was associated with medially extensive lesions. A subgroup of 3 unrecovered animals received superficial lesions that did not substantially involve the gray matter or the ventral columns. For all animals, reflex magnitudes were initially diminished bilaterally and then increased over months of testing. Reflex recovery was greater for the animals that demonstrated recovery of intentional reactions to nociception (group R). An ipsilateral hyperreflexia became apparent for group R. Contralateral recovery to normal levels was observed for group R but not for group U. The time course of recovery for operant and reflex responses clearly differed, indicating that different processes determined changes in these spinal and supraspinal reactions to nociceptive stimulation.

Animals↗
PubMed1988

Reorganization of primary afferent nerve terminals in the spinal dorsal horn of the primate caudal to anterolateral chordotomy.

A primate model has been used to explore the possibility that anterolateral chordotomy may produce intraspinal sprouting or rearrangement of primary afferent nerve terminations that could account for delayed postoperative recovery of sensory function. Monkeys were trained to limit the duration of an electrical stimulus, and the vigor and frequency of their escape responses were used to differentiate painful from nonpainful levels of stimulation. Behavioral testing after chordotomy revealed: 1) contralateral hypalgesia in all animals, with sensory recovery in half of the group, and 2) bilateral decreases in reflexive force in all animals, with reflex recovery in the majority of monkeys. At the terminal experiment, dorsal rootlets caudal to the spinal lesion were labeled bilaterally with HRP, and the distribution of labeled synaptic complexes was determined within the dorsal horn. When compared to controls, animals undergoing chordotomy showed a loss of terminals in the superficial dorsal horn and an increase of synaptic enlargements in deeper layers. These effects were bilateral, but were most pronounced on the side contralateral to chordotomy. Animals with diffuse spinal lesions showed a completely different change in the distribution of primary afferent terminals. Animals with sensory recovery demonstrated a more normal terminal distribution pattern than persistently hypalgesic monkeys, but there was considerable variability in the data, and analysis by different statistical tests yielded varying results.

Afferent Pathways↗