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Discharge properties of cat cervical motoneurons innervating distal forelimb muscles were investigated by intracellular current injection. Values for rheobase current, afterhyperpolarization duration and several measures of repetitive discharge characteristics were in most respects similar to those obtained for hindlimb motoneurons.
The activity of C3-C4 propriospinal neurons was recorded during fictitious forelimb locomotion in immobilized decerebrated cats with the spinal cord transected at the lower thoracic level. The discharge frequency of most neurons was rhythmically modulated in relation to the cycle of fictitious stepping in spite of the absence of any rhythmic signals from the limb receptors. Thus, the intraspinal mechanisms present a powerful input to the C3-C4 propriospinal neurons.
Premotor neurones mediating skin reflex actions onto cat forelimb motoneurones at T1 were identified by observing their monosynaptic effects on motoneurones by means of spike-triggered averaging. Both excitatory and inhibitory premotor neurones, with mono- or polysynaptic inputs from skin afferents, were identified at C7 to rostral C8, and were found mostly in laminae V-VI. They received excitatory inputs from corticospinal and rubrospinal tract fibres.
During cat forelimb fictive locomotion, short-latency reflex pathways were examined by recording nerve discharges and intracellularly from motoneurones. Stimulation of cutaneous afferents, superficial radial nerves, evoked trisynaptic excitation of the elbow flexors, biceps brachii and brachialis, and stimulation of muscle afferents, deep radial nerves, evoked oligosynaptic, i.e. monosynaptic and disynaptic excitation of the flexors. The short-latency excitatory postsynaptic potentials (EPSPs) evoked from both nerves were rhythmically modulated; they were facilitated during the flexion phase and suppressed during the extension phase. Stimulation of high threshold muscle afferents evoked EPSPs with a central delay of ca. 4.2 ms, which were depressed throughout episodes of fictive locomotion. Since the short-latency EPSPs and longer-latency EPSPs in the same motoneurone were differently influenced during fictive locomotion, the effects observed could not be explained by changes occurring at only the motoneuronal level but they probably occurred at the premotoneuronal level. In addition, short-latency cutaneous excitation of the distal muscles, innervated by the median and ulnar nerves, was little modulated during fictive locomotion.
The spinal cord projections of the 3 main forelimb nerves-median, radial and ulnar, were studied in the rat dorsal horn with transganglionic transport of wheat germ agglutinin-horseradish peroxidase (WGA-HRP), or using the disappearance of fluoride resistant acid phosphatase (FRAP) after nerve section. The projection patterns in lamina II were similar following the two procedures. The median and the radial nerve fibers projected to the medial and the intermediate thirds, respectively, of the dorsal horn lamina II in spinal cord segments C4-C8. The ulnar nerve projected to segments C6-C8 between the areas occupied by the other two nerves. The FRAP method also showed that the lateral part of lamina II, which was not filled by radial nerve fibers, received the projections from the dorsal cutaneous branches of cervical spinal nerves. In addition, FRAP disappeared from the medial end of segment T1 after skin incisions extending from the medial brachium to the axilla, which seemed due to severance of the cutaneous branchlets of the lateral anterior thoracic nerve. The FRAP procedure is thus sensitive enough to detect fibers in lamina II arising from small peripheral nerves, and may be used as an alternative to the anterograde tracing methods whenever there are no overlapping projections.
Prolyl hydroxylase activity was measured to obtain insight into changes in collagen metabolism during forelimb regeneration in the adult newt, Notophthalmus viridescens. Activity increased markedly during the redifferentiative stages, remained elevated during digit formation, and decreased as regeneration neared completion. The greatest activity, seen during early digit formation, represents a 20-fold increase in activity over the level seen in nonregenerating limbs. The profile of enzyme activity correlates with the rate of collagen synthesis and the soluble collagen content of the regenerating tissue. Enzyme extracted from limbs in the early stages of regeneration can be activated in vitro upon preincubation with cofactors; however, preincubation has little, if any, effect on enzyme extracted from limbs at the later digit-forming stages.
Cells of amputated, denervated larval Ambystoma forelimbs dedifferentiate and enter the cell cycle but do not subsequently proliferate sufficiently to form a blastema. The denervated limb stump resorbs slowly until reinnervation stimulates regeneration. We used this system to investigate the fate of cells in denervated limbs which undergo early but limited cycling in response to amputation. In Experiment 1, cells were labeled with [3H]thymidine (3H-T) on Day 4 postamputation (PA)/Day 3 postdenervation (PD). Labeled cells were still present on Day 7 PA, but were less frequently observed on Day 13 PA when the limbs were reinnervated and beginning to regenerate. In Experiment 2 we denervated 1 day preamputation to obtain earlier reinnervation and prevent loss of Day 4 PA labeled cells. Cells labeled with 3H-T on Day 4 PA/Day 5 PD were present throughout the denervation period and most were still present on Day 13 PA. Little or no mitotic activity was found among the labeled cells after the initial round of cycling. The apparent cell cycle block was released upon reinnervation on Days 12 and 13 PA when cycling resumed. Labeled mitotic figures were present on Day 13 PA, and the mitotic index of the labeled population increased as a result of reinnervation. These results demonstrate that blocked cells are rescued by nerves, re-enter the cell cycle, and thus contribute to the reinnervation blastema.
It seems a paradox that more primary sensory neurons are lost but recovery is better after peripheral nerve injury in neonates as compared to adult mammals. A possible explanation is that surviving neurons sprout in the neonate. To test this, forelimbs in neonatal rats were amputated, which caused the death of many primary sensory neurons. The number of neurons in the dorsal root ganglia, and the number of myelinated and unmyelinated fibers in the dorsal and ventral roots were determined on the amputated and contralateral normal sides. On the amputated side, soma loss in the ganglia was 30%, and the fiber numbers were decreased by 16% in the dorsal root and increased by 20% in the ventral root. These data are compatible with the hypothesis that there is axonal branching or sprouting from surviving sensory neurons. In addition, morphometric analyses showed a changed myelin-axon relationship for central processes of sensory cells whose distal processes have been cut.
Our results showed that hypoglossal neurons localized in the mediocaudal part of the XIIth nucleus modulate their firing in relation to somatosensory information travelling along the forelimb nerves. Large evoked potentials and responses of single hypoglossal units were recorded during electrical stimulation of the common radial nerve of both sides. A spinohypoglossal pathway has not been described before, but our results indicate this possibility. The latencies of the hypoglossal responses to somatosensory stimulation suggest that somatic afferent volleys may stop at the reticular level and contact the XIIth nucleus through a spinoreticulohypoglossal pathway. Previous work showed that visual and vestibular input contact the same mediocaudal region of the hypoglossal nucleus. Thus it is possible that the postural arrangement of the tongue is subject to a complex control depending on the vestibular, visual, and somatosensory system.
Longitudinal stresses acting in the cranial and caudal cortices of the radius and the dorsal and palmar cortices of the metacarpus in the horse were determined using two independent methods simultaneously. One approach involved the use of rosette strain gauges to record in vivo bone strain; the other involved filming the position of the horse's forelimb as it passed over a force plate. Agreement between the two analyses was better for the radius than for the metacarpus. Both methods showed the radius to be loaded primarily in sagittal bending, acting to place the caudal cortex in compression and the cranial cortex in tension. At each gait the magnitude of peak stress in each cortex based on the film/force analysis was 1.5-2 times higher than that determined from the bone strain recordings. In the metacarpus, the magnitude of stress in each cortex calculated from the film/force method was 2-3 times greater at each gait than that shown by the bone strain recordings. However, whereas the film/force analysis indicated that the metacarpus was loaded in sagittal bending (acting to place the palmar cortex in compression and the dorsal cortex in tension), the bone strain recordings showed the metacarpus to be loaded primarily in axial compression at each gait. Because the film/force method depends on an accurate measure of limb segment orientation relative to the direction of ground reaction force, comparatively small errors in calculations of bending moments may lead to a significant difference in the level and distribution of stress determined to act in the bone's cortices. The discrepancy in metacarpal loading obtained by the two methods may be explained in part by the simplicity of the biomechanical model which, for instance, neglected the force exerted by the sesamoids on the distal end of the metacarpus. The records of stress determined from the in vivo bone strain recordings showed that each bone was subjected to a consistent loading regime despite changes of gait. Such a consistent strain distribution should allow these bones to maximize economy in the use of tissue required to support the dynamic loads applied. Peak stresses measured from the bone strain recordings in the radius during locomotion at constant speed (-40.8 +/- 4.1 MN m-2) were significantly larger than those in the metacarpus (-25.1 +/- 2.8 MN m-2), regardless of speed and gait. During acceleration and deceleration, however, peak stress rose dramatically in the metacarpus (-40.6 +/- 3.4 MN m-2) but remained constant in the radius (-37.8 +/- 5.8 MN m-2).(ABSTRACT TRUNCATED AT 400 WORDS)
We have previously reported that training rats to reach for bits of cookies resulted in an increase in dendritic length and branching complexity in the apical branches of layer V pyramidal cells within the motor-sensory forelimb cortex. In this paper, we describe the effects of reach training upon the basilar branches of two subpopulations of pyramidal cells in layers II and III. The two subpopulations of pyramids are distinguishable by morphological characteristics and location within layers II and III. The basilar dendrites of one subtype, the forked apical pyramid, are selectively altered in size and complexity during reach training; whereas the other subtype, the single shaft apical cells, do not measurably change during training. Based upon these findings, we postulate that these cells may have different roles in governing the reaching behavior.
Depletion of caudate-putamen dopamine (DA) was produced by intraventricular injection of 6-hydroxydopamine (6-OHDA) in three day old rats. When adult, the rats were given cognitive and motor tasks sensitive to adult dopamine depletion, including: tests of cue and place spatial navigation in a swimming pool, a test of skilled forelimb use, requiring reaching for small pellets of food, a test of tongue protrusion, requiring tongue extension to lick mash from a spatula, a test of limb posture, sensorimotor tests of orienting to tactile stimulation and catalepsy. Despite apparent normal physical appearance and locomotor behavior, the rats were impaired on all tasks except orienting to tactile stimulation and catalepsy. There was a significant positive correlation between the degree of impairment on the behavioral tasks and the extent of caudate-putamen dopamine depletion. The results show that sparing of function following neonatal dopamine depletion is selective and incomplete. The results are discussed with respect to the questions of sparing of function following neonatal lesions, the heterogeneous nature of the neonatal depletions and the contributions of dopamine to complex spatial and motor behavior in the rat.
Transgenic embryos were generated carrying a Hoxb-8 transgene under control of the mouse RAR beta 2 promoter, which extends the normal expression domain to more anterior regions of the embryo. These embryos showed mirror-image duplications in the forelimb, analogous to the duplications observed in chick in response to transplantation of a ZPA to the anterior margin of the limb bud. Examination of Sonic hedgehog, Fgf-4, and Hoxd-11 gene expression confirmed that a second ZPA had been generated at the anterior side of the limb bud. Besides other alterations, posterior homeotic transformations of axial structures were observed, involving the first spinal (Froriep's) ganglion and several cervical vertebrae.
Eight rats were trained to use their left paw to rapidly press the right lever of an operant chamber once and the left lever twice to obtain a food reward. Between-levers interresponse times and same lever interresponse times were measured daily for several weeks before and after bilateral removal of frontal motor/sensory cortex. This surgery resulted in a permanent deficit in most rats' ability to rapidly alternate between levers, but resulted in only a temporary deficit in their ability to rapidly press the same lever. Sham surgery and removal of hindlimb motor cortex had little immediate effect on interresponse times. The data demonstrate that sequential motor behavior tested in the between-levers tasks is chronically affected by cortical lesions, but the speed of the same repetitive movement tested in the same lever task is not. Measuring the time to rapidly alternate between two different levers, therefore, provides a quantitative method for measuring acute and chronic forelimb motor deficits due to motor cortex injury in rats which could be applied to any mammal.
The movements of rats trained to reach through an aperture for food pellets, located on a shelf, were videorecorded and filmed from lateral and ventral perspectives for analysis using Eshkol-Wachman Movement Notation (EWMN). Reaching was subdivided into phases of locating the food and advancing the limb to grasp the food, bringing the food to the mouth, and returning to the starting position. Further analysis of the movements comprising these acts revealed a number of novel findings. (1) Most of the first phase of the movement is produced proximally, with the limb lifted, aimed, and advanced from the shoulder. (2) After the limb is lifted from the substrate to initiate reaching, it is carried to a parasagittal position so that the long axis of the forearm is aligned along the midline of the body. This aspect of the movement 'aims' the limb toward the target. (3) The digits are opened as the limb is advanced from the aiming position toward the food. As the paw approaches the food, pronation of the palm is accomplished by abduction of the upper arm. (4) As the limb is retracted, the digits are closed to grasp the food. As retraction ends, the paw is supinated by a rotatory movement at the wrist. This is the only distal rotatory movement. (5) The position taken by the second forelimb, as it is adducted to aid in holding the food pellet for eating, resembles the 'aiming' posture. The results are discussed in reference to the kinematics, neural control, and the evolutionary origins of reaching in the rat and other animals. Additionally, the results provide a framework for analysis of changes in movements produced by physiological manipulations.
After ablation of the motor cortex contralateral to the preferred limb, rats were forced to use this limb in grasping food out of a horizontal tube by restraining the non-preferred foreleg with a bracelet. In a right-handed rat the motor behaviour is less impaired and the recovery is better after a left hemisphere lesion in comparison with a left-handed rat after a right hemisphere lesion. This difference is primarily the time needed to use the limb in reaching for seed (testperiod 3) and the total time needed for 10 successive seizings of seed (testperiod 5). Surprisingly, the differences in the course of recovery do not correlate with the degree of preoperative limb preference: the initially ambidextrous rate also show the same differences in results of the motor cortex ablation in left and right hemisphere. However, in the group of initially consistent ambidextrous rats, after 10 weeks of tests with a restrained forelimb, the testing under unrestrained free conditions shows a gradual decrease in the induced limb preference and a shift to the use of the foreleg contralateral to the intact hemisphere, while in contrast the initially consistent left- or right-handed rats preserve the limb preference under the unrestrained testing conditions. Therefore the degree of initial preference still influences the choice of limb after motor cortex ablation and intensive training to use the 'damaged' limb.
This study describes how rats use their paws and digits when handling a wide range of foodstuffs, including food pellets, grapes, sunflower seeds, shelled and unshelled peanuts, and different sized pastas, etc. Analysis of videorecordings show that the rats display digit postures that include variations in the spacing of the digits, differences in the relative use of different digits, and interlimb differences in paw and digit posture. The rats also display limb preferences in that one paw is used in a supporting function while the other rotates, flips, or pushes the food as is required by the shape of the item. There is a significant correlation between the paw used for manipulation and food items of similar shape but no correlation between the limb used for manipulation and that used for skilled reaching. Small unilateral lesions to the forepaw area of somatic sensorimotor cortex produced impairments in use of the paw contralateral to the lesions. These results: (1) reveal a surprising complexity in the way in which rats use their paws and digits in manipulating food; (2) show that rats have limb preferences in spontaneous food handling; and (3) show that manipulatory dexterity is dependent upon the integrity of the forelimb area of motor cortex. The results are discussed in relation to the evolution of motor skill, the use of rats for investigating questions of motor system organization, neural plasticity, and recovery of function after brain damage.
This study characterizes physiological, histological and behavioral effects of traumatic brain injury (TBI) produced by a controlled pneumatic impactor striking the entire right sensorimotor cortex of the anesthetized rat. Damage to both the fore- and hindlimb sensorimotor areas resulted in a hemiparetic animal which allowed us to use four sensitive behavioral/neurological tests to track the recovery sequelae after injury. Initial experiments measured cardiovascular and respiratory effects after cortical impact which depressed the dura to varying depths. Both 0.5 mm and 1 mm cortical depressions produced a momentary decrease (P < 0.05) in mean arterial blood pressure (MABP) while cortical impacts to depths of 2 mm or 3 mm produced a momentary increase (P < 0.05) in MABP. Normotension was re-established within 30 s after the initial response at all injury levels. Respiratory rate was affected only following 3 mm cortical depressions. A 1 mm cortical depression appeared ideal in terms of minimal cardiorespiratory effects, low mortality and lasting behavioral effects. For behavioral and histologic studies, therefore, additional rats were injured by a 1 mm cortical impact and tested for 8 weeks after TBI using four behavioral tests. Injured rats displayed both fore- and hindlimb deficits up to 56 days while traversing a narrow beam (P < 0.001) and up to 28 days when crossing a pegged beam (P < 0.05). Forelimb deficits evaluated on a wire grid platform were evident for 28 days (P < 0.05). Forepaw preference measured in a non-test setting indicated a bias to use the unaffected forepaw for 35 days (P < 0.05). A biphasic pattern of functional recovery was seen on all tests. A period of rapid functional recovery lasting 7 to 10 days was followed by a slower period of functional recovery lasting many weeks. Possible meanings of this biphasic recovery are discussed as issues of behavioral compensation/adaptation versus true neural recovery. Eight weeks after TBI histological analyses indicated that axonal degeneration was present in the areas adjacent to the ipsilateral cortical injury site. Degenerating fibers also extended across the corpus callosum into the homologous area in the contralateral cortex and were seen in the ipsilateral striatum, somatosensory and motor thalamic nuclei and substantia nigra. Significant axonal degeneration occurred bilaterally around the deep cerebellar nuclei. Degenerating fibers extended into the folia and terminated in the cerebellar granule cell layer. Thus the entire sensorimotor control system appeared to have been affected by a cortical injury.