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At least 19 recordsLinked to original sources

PubMed1993

Reversal of paw preference after ablation of the preferred forelimb primary motor cortex representation of the rat depends on the size of the forelimb representation.

Animals were tested for forelimb preference in a grasp or in a force task before microstimulation mapping of the primary motor cortex contralateral to the preferred forelimb. The size and location of the preferred forelimb primary motor cortex representation was determined and ablated. Seven days later, forelimb preference was again evaluated. Reversal of the initial preference after cortical ablation depended on the size of the preferred forelimb primary motor cortex representation. The mean size of the forelimb representation of the animals that immediately reversed forelimb preference after the cortical ablation was significantly smaller than the mean size of the representation of the animals that did not reverse forelimb preference in three consecutive tests seven days after the lesion. In another experiment, the size, location, and threshold currents of the forelimb representations were evaluated bilaterally before the forelimb preference test. The mean size of the preferred representations did not differ from the mean size of the non-preferred representations. However, when the primary motor cortex representation of the preferred forelimb was ablated, reversal of the initial preference depended, as in the previous experiment, on the size of the forelimb representation. In conclusion, reversal of forelimb preference after ablation of the preferred forelimb primary motor cortex representation depends on the size of the forelimb representation. Moreover, forelimb preference in a behavioral task is not associated with a larger forelimb representation in the contralateral primary motor cortex.

Animals↗

PubMed2004

Unilateral frontal lobe contusion and forelimb function: chronic quantitative and qualitative impairments in reflexive and skilled forelimb movements in rats.

Traumatic brain injury induced by mechanical impacts of the head can be modeled in rats in order to investigate acute and chronic therapy. Because frontal lobe contusion affects the neural representation of the forelimb in both the neocortex and basal ganglia, the purpose of the present experiments was to examine the chronic changes in reflexive and skilled forelimb induced by the injury. Contusions produced a cavity in the sensorimotor cortex, accompanied by shrinkage of the pyramidal tract, loss of cells in the dorsolateral striatum, and enlargement of the lateral ventricle. There were substantial individual differences in lesion size despite use of two different contusion forces, but all rats receiving contusions displayed chronic forelimb deficits. Reflexive tests of forelimb use (limb posture, placing, and support) indicated that impairments were most pronounced in the forelimb contralateral to the lesion. Tests of limb preference indicated that the contusion rats displayed a forelimb asymmetry: they were more likely to lean on their ipsilateral-to-lesion forelimb for support when rearing in a test cylinder, and this impairment was amplified in a home cage test. They also displayed a preference for the forelimb ipsilateral to the lesion when reaching for food, although both forelimbs were equally impaired on measures of success when reaching for food from a tray and reaching for a single food pellet on a shelf. A qualitative analysis from frame-by-frame video records indicated that when reaching for single pellets, impairments in forelimb use primarily affected the contralateral-to-lesion limb, especially limb aiming, supination, and food pellet release. Impairments in the ipsilateral-to-lesion forelimb were generally, but not exclusively, secondary to postural abnormalities. The wide range of chronic impairments in forelimb use following contusion injuries are discussed in relation to the anatomical and behavioral origins of the impairments and the potential use of forelimb tests in the assessment of therapy for traumatic brain injury to the frontal cortex.

Animals↗

PubMed2005

Training the "less-affected" forelimb after unilateral cortical infarcts interferes with functional recovery of the impaired forelimb in rats.

PURPOSE: Unilateral lesions of the sensorimotor cortex (SMC) in adult rats cause major behavioral changes in the ipsilesional, "less-affected" forelimb. An increase in function and reliance on this forelimb can aid compensation for contralesional impairments, but may also promote disuse and reduced functionality of the impaired forelimb. We hypothesized that training focused on the ipsilesional forelimb following a unilateral SMC lesion would reduce the efficacy of later motor rehabilitative training of the impaired forelimb. METHODS: Rats with ischemic SMC lesions were trained on a skilled reaching task with the ipsilesional forelimb (PriorT) or received control procedures (Cont) for 10 days. Both groups were then trained with the impaired forelimb on the same reaching task for 10 days. RESULTS: In comparison with Cont, PriorT rats had little improvement on the reaching task with the impaired forelimb and had a more enduring disuse of the impaired forelimb for postural support behaviors. Lesion sizes were similar between groups. CONCLUSIONS: Behavioral experience with the less-affected forelimb early after unilateral SMC lesions has the potential to increase disuse and dysfunction of the impaired forelimb, consistent with a training-induced exacerbation of learned non-use. These findings are suggestive of competitive processes in experience-dependent neural restructuring after brain damage.

Animals↗

PubMed1995

Functional recovery of forelimb response capacity after forelimb primary motor cortex damage in the rat is due to the reorganization of adjacent areas of cortex.

Functional recovery after brain damage has been described frequently and different mechanisms have been proposed to account for the observed recovery. One possible mechanism involves the capacity of one part of the brain to take over the function of another. A possible area for this to take place is in the cerebral cortex, where a variety of reorganizational processes have been described after different manipulations. We show in the present study that the forelimb force and response capacity of the rat, which becomes highly impaired after the bilateral ablation of the forelimb primary motor cortex, is recovered when the animals receive an electrical stimulation in the ventral tegmental nucleus contingent to each forelimb response in the task. Microstimulation mapping of the cortical areas adjacent to the forelimb primary motor cortex revealed the appearance of an area located caudolaterally to the forelimb primary motor cortex, where forelimb movements could be evoked in recovered animals but to a lesser extent in non-recovered animals. A positive and significant correlation was observed between the size of the reorganized forelimb area and the behavioral performance of the animals. Ablation of the forelimb reorganized area in recovered animals reinstated the forelimb behavioral impairment, while the same lesion in normal animals had no effect on the behavioral performance. The results indicate that recovery after bilateral forelimb primary motor cortex ablation may be due to the organization of specific adjacent areas in the cortex.

Animals↗

PubMed1984

Integration in descending motor pathways controlling the forelimb in the cat. 12. Interneurones which may mediate descending feed-forward inhibition and feed-back inhibition from the forelimb to C3-C4 propriospinal neurones.

Extra- and intracellular recording was made from cells in the C3-C4 segments with the aim of finding interneurones of previously described inhibitory pathways to the C3-C4 propriospinal neurones, which may mediate descending feed-forward inhibition and feed-back inhibition from the forelimb, respectively. The lateral interneurones were found in the lateral part of lamina VII interspersed among the C3-C4 PNs and like them they receive convergent monosynaptic EPSPs and disynaptic IPSPs from the cortico-, rubro-, tecto- and reticulospinal tracts. Disynaptic IPSPs, but only rarely monosynaptic EPSPs, are evoked in them from forelimb nerves. The lateral interneurones do not project to the lateral reticular nucleus (LRN). The medial interneurones were found medially in laminae V and VI in a region where volleys in forelimb nerves evoke extracellular monosynaptic focal potentials (Rosén 1969). There is somatotopic organization of the projection from the forelimb to this region. Many neurones are strongly monosynaptically excited from group I muscle or/and cutaneous forelimb afferents. In addition, late discharges are evoked in many cells from cutaneous afferents and high threshold muscle afferents. Corticospinal volleys evoked monosynaptic excitation in the great majority of these cells and usually also late EPSPs or IPSPs. Typically, rubrospinal and tectospinal volleys evoked neither monosynaptic excitation nor late effects as those elicited from corticospinal fibres. In some of the interneurones, IPSPs were evoked from forelimb nerves. About 20% of the medial "interneurones" have an ascending projection to the caudal brain stem. Threshold mapping for antidromic stimulation revealed termination in the main cuneate nucleus, the external cuneate nucleus and/or the LRN and also a branch projecting to more rostral levels in the brain. A few of the neurones in the medial region are PNs projecting to the forelimb segments. It is postulated that interneurones both of the lateral and medial type are inhibitory and project to the C3-C4 PNs. It is further postulated that the former are intercalated in the descending feed-forward inhibitory pathway to the C3-C4 PNs and the latter in the feed-back inhibitory pathway from the forelimb to these PNs. The role of feed-forward and feed-back inhibition of transmission from the brain to forelimb motoneurones via the C3-C4 PNs is discussed.

Afferent Pathways↗

PubMed1984

Integration in descending motor pathways controlling the forelimb in the cat. 11. Inhibitory pathways from higher motor centres and forelimb afferents to C3-C4 propriospinal neurones.

Intracellular recording was made in the C3-C4 segments from cell bodies of a previously described system of propriospinal neurones (PNs), which receive convergent monosynaptic excitation from different higher motor centres and mediate disynaptic excitation and inhibition from them to forelimb motoneurones. Inhibitory effects in these PNs have now been investigated with electrical stimulation of higher motor centres and forelimb nerves. Short-latency IPSPs were evoked by volleys in the cortico-, rubro- and tectospinal tracts and from the reticular formation. Latency measurements showed that those IPSPs which required temporal summation were disynaptically mediated. After transection of the corticospinal tract in C2, only small and infrequent disynaptic IPSPs were evoked from the pyramid. It is postulated that disynaptic pyramidal IPSPs only to a small extent are evoked by monosynaptic excitation of reticulospinal inhibitory neurones known to project directly to the PNs, and that they are mainly mediated by inhibitory interneurones in the C3-C4 segments. Tests with spatial facilitation revealed monosynaptic excitatory convergence from tecto-, rubro- and probably also from reticulospinal fibres on inhibitory interneurones monosynaptically excited from corticospinal fibres (interneuronal system I). Disynaptic IPSPs were also evoked in the great majority of the PNs by volleys in forelimb muscle and skin nerves. A short train of volleys was usually required to evoke these IPSPs from group I muscle afferents. In the case of cutaneous nerves and mixed nerves single volleys were often effective, and the lack of temporal facilitation of IPSPs produced by a train of volleys showed strong linkage from these nerves. The results obtained after transection of the dorsal column at different levels show that the relay is almost entirely rostral to the forelimb segments. Test with spatial facilitation revealed that interneurones monosynaptically activated from forelimb afferents receive convergent excitation from corticospinal but not or only weakly so from tecto- or rubrospinal fibres. There was also convergence from group I muscle afferents and low threshold cutaneous afferents on common interneurones. It is postulated that the disynaptic IPSPs from forelimb afferents are mediated by inhibitory interneurones (interneuronal system II) other than those receiving convergent descending excitation. Volleys in corticospinal fibres, in addition to the disynaptic IPSPs, evoke late IPSPs in the PNs. Similar late IPSPs were evoked from the ipsilateral forelimb by stimulation of the FRA.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2004

Growth and apoptosis during larval forelimb development and adult forelimb regeneration in the newt ( Notophthalmus viridescens).

Many of the genes involved in the initial development of the limb in higher vertebrates are also expressed during regeneration of the limb in urodeles such as Notophthalmus viridescens. These similarities have led researchers to conclude that the regeneration process is a recapitulation of development, and that patterning of the regenerate mimics pattern formation in development. However, the developing limb and the regenerating limb do not look similar. In developing urodele forelimbs, digits appear sequentially as outgrowths from the limb palette. In regeneration, all the digits appear at once. In this work, we address the issue of whether regeneration and development are similar by examining growth and apoptosis patterns. In contrast to higher vertebrates, forelimb development in the newt, N. viridescens, does not use interdigital apoptosis as the method of digit separation. During adult forelimb regeneration, apoptosis seems to play an important role in wound healing and again during cartilage to bone turnover in the advanced digits and radius/ulna. However, similar to forelimb development, demarcation of the digits in adult forelimb regeneration does not involve interdigital apoptosis. Outgrowth, rather than regression of the interdigital mesenchyme, leads to the individualization of forelimb digits in both newt development and regeneration.

Animals↗

PubMed1994

Metabolic mapping of the forelimb motor system in the rat: local cerebral glucose utilization following execution of forelimb movements mainly involving proximal musculature.

The present study was undertaken to establish a metabolic map of forelimb motor pathways under conditions of physiological activation. For that purpose, we used the [14C]2-deoxy-D-glucose (2-DG) method to identify forebrain and midbrain centers showing an increase in 2-DG uptake in animals trained to execute specific lever-pressing movements with the right forelimb. Following repetitive execution of these movements, principally involving proximal (shoulder, elbow, and wrist) muscles, increases in 2-DG uptake were found contralaterally in several neocortical or subcortical centers. The largest left-right differences in local cerebral glucose utilization (LCGU) were found in a central region of the sensorimotor cortex composed of the caudal part of area 3 of the frontal cortex (Fr3; p < 0.01), the intermediate part of area 1 of Fr (Fr1; p < 0.01), and the forelimb cortical area (p < 0.04). Fr3 was the brain center with the highest differences in left-right LCGU. This central region of the sensorimotor cortex seems to correspond closely to the caudal forelimb area of Neafsey et al. (1986). Intermediate left-right differences in LCGU were found (1) in the just-adjoining rostral-medial areas of the motor cortex involving the intermediate part of area 2 of Fr (Fr2; p < 0.01) and the rostral part of Fr1 (p < 0.04), and (2) in the rostral part of area 1 of the parietal cortex (Par1; p < 0.01) and the caudal part of area 2 of Par (Par2; p < 0.05), both corresponding to forelimb representation. Weak (not statistically significant) left-right differences in LCGU were found in the rostral parts of Fr2 and Fr3, in the caudal parts of Fr2 and Fr1, in the hindlimb cortical area, and in the caudal part of Par1 and the rostral part of Par2. In the remaining cortical areas (cingulate; agranular and granular retrosplenial; temporal; and occipital), there was practically no difference in left-right 2-DG uptake. In addition, increased 2-DG uptake was present contralaterally in several subcortical motor-related centers. In those centers in which a somatomotor map has been established (caudate putamen, ventral lateral and ventral posterolateral thalamic nuclei, and red nucleus), increased 2-DG uptake was found in regions corresponding to forelimb representation.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗

PubMed1984

Integration in descending motor pathways controlling the forelimb in the cat. 10. Inhibitory pathways to forelimb motoneurones via C3-C4 propriospinal neurones.

A further analysis has been made of inhibitory pathways to motoneurones via C3-C4 propriospinal neurones (PNs). Intracellular recording was made from triceps brachi motoneurones and effects from higher centres and forelimb afferents on corticospinal IPSPs were investigated after transection of the corticospinal tract at the C5/C6 border. The shortest latencies of the IPSPs evoked by stimulation of the pyramid were as brief as those of the pyramidal EPSPs (Illert et al. 1977). It is postulated that the minimal linkage of the pyramidal IPSPs is disynaptic via inhibitory C3-C4 PNs projecting directly to motoneurones. It was confirmed that pyramidal IPSPs usually are depressed by volleys in forelimb motor axon collaterals (Illert and Tanaka 1978). A quantitative comparison was made of the recurrent depression of pyramidal IPSPs and of IPSPs caused by activation of the Ia inhibitory interneurones. The result support the hypothesis of two parallel inhibitory cortico-motoneuronal pathways via C3-C4 PNs, one disynaptic via the inhibitory PNs and the other trisynaptic via excitatory PNs and Ia inhibitory interneurones. Pyramidal volleys also evoked late IPSPs which in some cases were not depressed from forelimb motor axon collaterals. It is postulated that the late IPSPs are partly due to activation of inhibitory C3-C4 PNs. Disynaptic pyramidal IPSPs were effectively facilitated by volleys in rubro-, tecto- and reticulospinal fibres - but not from vestibulospinal fibres - showing a convergence from the former descending tracts on common inhibitory C3-C4 PNs. Projection from forelimb afferents and corticospinal fibres on common inhibitory C3-C4 PNs was revealed by strong facilitation of disynaptic pyramidal IPSPs from cutaneous forelimb afferents. No corresponding effect was evoked from C2 neck afferents. Stimulation in the lateral reticular nucleus (LRN) evoked monosynaptic IPSPs in some motoneurones. The results of threshold mapping in and around the LRN suggest that the IPSPs are caused by antidromic stimulation of ascending collaterals of inhibitory neurones also projecting to motoneurones, possibly the inhibitory C3-C4 PNs.

Animals↗

PubMed2000

Suppression of hindlimb inputs to S-I forelimb-stump representation of rats with neonatal forelimb removal: GABA receptor blockade and single-cell responses.

Neonatal forelimb removal in rats results in the development of inappropriate hindlimb inputs in the forelimb-stump representation of primary somatosensory cortex (S-I) that are revealed when GABA(A) and GABA(B) receptor activity are blocked. Experiments carried out to date have not made clear what information is being suppressed at the level of individual neurons. In this study, three potential ways in which GABA-mediated inhibition could suppress hindlimb expression in the S-I stump representation were evaluated: silencing S-I neurons with dual stump and hindlimb receptive fields, silencing neurons with receptive fields restricted to the hindlimb alone, and/or selective silencing of hindlimb inputs to neurons that normally express a stump receptive field only. These possibilities were tested using single-unit recording techniques to evaluate the receptive fields of S-I forelimb-stump neurons before, during, and after blockade of GABA receptors with bicuculline methiodide (for GABA(A)) and saclofen (for GABA(B)). Recordings were also made from normal rats for comparison. Of 92 neurons recorded from the S-I stump representation of neonatally amputated rats, only 2.2% had receptive fields that included the hindlimb prior to GABA receptor blockade. During GABA receptor blockade, 54.3% of these cells became responsive to the hindlimb, and in all but two cases, these same neurons also expressed a stump receptive field. Most of these cells (82.0%) expressed only stump receptive fields prior to GABA receptor blockade. In 71 neurons recorded from normal rats, only 5 became responsive to the hindlimb during GABA receptor blockade. GABA receptor blockade of cortical neurons, in both normal and neonatally amputated rats, resulted in significant enlargements of receptive fields as well as the emergence of receptive fields for neurons that were normally unresponsive. GABA receptor blockade also resulted in increases in both the spontaneous activity and response magnitudes of these neurons. These data support the conclusion that GABA mechanisms generally act to specifically suppress hindlimb inputs to S-I forelimb-stump neurons that normally express a receptive field on the forelimb stump only.

Amputation Stumps↗

PubMed1986

Integration in descending motor pathways controlling the forelimb in the cat. 15. Comparison of the projection from excitatory C3-C4 propriospinal neurones to different species of forelimb motoneurones.

In the preceding report (Alstermark and Sasaki 1986) it was shown that a stimulus of 500 microA applied in the lateral reticular nucleus (LRN) evokes a maximal or near monosynaptic EPSP (LRN EPSP) in forelimb motoneurones. This EPSP which is assumed to be selectively mediated by C3-C4 propriospinal neurones (PNs), was used to estimate the strength of the excitatory projection from C3-C4 PNs. A systematic comparison was made of the size and time course of the maximal LRN EPSP in various species of forelimb alpha-motoneurones innervating shoulder, elbow, wrist and digit muscles. The LRN EPSP was evoked in all investigated species of forelimb motoneurones. When either the peak amplitude or the underlying area of the LRN EPSP was compared, a three-fold range was found with some tendency for the size to vary in the order of wrist greater than shoulder approximately equal to elbow greater than digit greater than intrinsic paw motor nuclei. Generally, a positive correlation was found in each motor nucleus between the peak amplitude of the LRN EPSP versus the monosynaptic homonymous group Ia EPSP, input resistance and afterhyperpolarization duration respectively (cf. Alstermark and Sasaki 1986). It is therefore postulated, that the LRN EPSP peak amplitude is correlated with motor unit type. Comparison of the time course of the LRN EPSPs was made by measuring the time-to-peak (T-t-p) and half-width (H-w). The finding in the preceding report that the T-t-p and H-w is longer in slow than in fast motoneurones was confirmed and extended to all the investigated motor nuclei. The hypothesis that both fast slow motoneurones receive projection from a group of fast C3-C4 PNs, while slow motoneurones receive an additional projection from a group with lower conduction velocity, can therefore be applied to all forelimb motor nuclei. In addition, it is proposed that some slow shoulder, wrist and digit motoneurones receive projection from a special subpopulation of C3-C4 PNs with very slow conduction velocity.

Animals↗

PubMed1986

Functional metabolic mapping during forelimb movement in rat. II. Stimulation of forelimb muscles.

Repetitive electrical stimulation of wrist extensor muscles in rat was combined with quantitative 14C-deoxyglucose autoradiography to study sensory systems functionally activated during forelimb movement. Metabolism increased ipsilaterally in the wrist extensors, the dorsal horn of the cervical spinal cord, the cuneate nucleus and cerebellar hemisphere. The metabolic activation in cerebellum occurred in cortex surrounding the primary fissure anteriorly (lobules simplex and V), and the prepyramidal fissure posteriorly (lobules paramedian and copula pyramis). Metabolism was increased in both granule cell and molecular layers and was uniform throughout the zone of activation. Hindlimb stimulation primarily activated the medial aspect of copula pyramis, demonstrating the somatotopic specificity of changes. Forelimb stimulation also activated contralateral sites in the dorsal accessory nucleus of the inferior olive, ventrobasal thalamus, and SI and SII in cortex. Studies of the relationship between the magnitude of the response and the frequency of the stimulation revealed a positive correlation in muscle, dorsal horn and cuneate nucleus. Other activated sites only showed a significant change at the highest rates of stimulation. Comparison of the pattern of metabolic activation during forelimb movements induced centrally (Collins et al., 1986) with the pattern induced peripherally revealed overlap primarily in the paramedian zone of anterior and posterior cerebellum, and the granular cortex of SI and SII. These studies suggest that forelimb movement initiated centrally would have considerable influence on feedback sensation from the moving limb in these sites.

Animals↗

PubMed1999

Molecular cloning of the Notophthalmus viridescens radical fringe cDNA and characterization of its expression during forelimb development and adult forelimb regeneration.

Larval and adult newts provide important experimental models to study limb development and regeneration. These animals have exceptional ability to regenerate their appendages, as well as other vital structures. Our research examines the role of the fringe gene (fng) in the developing and regenerating adult newt forelimb. Fringe codes for a secretory protein. It was first discovered in Drosophila, and later homologues were isolated in Xenopus laevis, chick and mouse. This gene has been highly conserved throughout evolution, indicating its crucial role in vertebrate and invertebrate development. We have isolated, cloned, and sequenced the full length of the Notophthalmus viridescens radical fringe cDNA (nrFng) by screening a newt forelimb blastema cDNA library with a 500-bp fragment of the Xenopus lunatic fringe cDNA. The newt fringe cDNA codes for a 396 amino acid protein with a predicted N-terminal signal sequence. Newt fringe shows high homology with radical fringe homologues of many species. Whole mount mRNA in situ hybridization on several stages of newt limb development reveals that nrFng is first expressed in the limb field, with intense expression as the limb bud develops. However, gene expression diminishes with more advanced digit development. A significant role in adult forelimb regeneration is also evident, as we isolated the cDNA from a regeneration-specific library and found it highly expressed during the regenerative phases of active cell division and then down regulated at sites undergoing differentiation and morphogenesis.

Amino Acid Sequence↗

PubMed1986

Hypermetria in forelimb target-reaching after interruption of the inhibitory pathway from forelimb afferents to C3-C4 propriospinal neurones.

Forelimb target-reaching in cats with a transection at C5/6 of the cortico- and rubrospinal tracts is known to depend on C3-C4 propriospinal neurones (PNs). An additional lesion transecting the dorsal column (DC) in C5/6, caudal to the C3-C4 PNs, gave pronounced hypermetria in lifting and protraction during target-reaching. If the additional DC lesion instead was made in C2, rostral to the C3-C4 PNs, there was only small hypermetria in lifting and none in protraction. It is postulated that the hypermetria after the C5/6 DC lesion is due to interruption of the inhibitory pathway from the forelimb to the C3-C4 PNs. It is suggested that feedback control from the forelimb of the premotoneurones is an integral part of the control of normal target-reaching.

Afferent Pathways↗

PubMed2004

Effect of forelimb use on postnatal development of the forelimb motor representation in primary motor cortex of the cat.

In the cat, the motor representation in motor cortex develops between wk 8 and wk 13. Motor map development is accompanied by a decrease in the current thresholds for evoking movements with a concomitant increase in the number of effective sites, an increase in the distal representation, and the representation of multijoint synergies. In this study we used intracortical microstimulation in anesthetized cats to examine how forelimb motor experiences influence development of map characteristics. To promote skilled movements during wks 8-13, animals were engaged in daily performance of a prehension task. Forelimb movements were prevented by intramuscular botulinum toxin injection or restraint. To determine whether experience-dependent changes were permanent, we examined the map in different animals between 1 wk and 1 yr after cessation of testing. Promoting forelimb use resulted in an increase in the number of sites from which multiple joint effects were produced by stimulation and the number of joints represented at those sites. The effect was maximal at 1 wk after cessation of testing, and became progressively less at 1 mo and at 4 mo. Preventing limb use resulted in a decreased number of effective sites, an increase in current thresholds for evoking responses, and a decreased representation of joints at multijoint sites. Our findings show that the motor map can respond to novel motor demands as it is forming during development but that it reverts back to one with the properties of a map in a control animal if those demands are not maintained in the animal's behavioral repertoire.

Age Factors↗

PubMed1998

Thalamocortical and intracortical projections to the forelimb-stump SI representation of rats that sustained neonatal forelimb removal.

We previously reported the abnormal expression of hindlimb receptive fields in the stump representation of the primary somatosensory cortex (SI) in rats that sustained neonatal forelimb removal when cortical gamma-aminobutyric acid (GABA) receptors were pharmacologically blocked (Lane et al. [1997] J. Neurophysiol. 77:2723-2735). In this study, we attempted to identify the substrate for this functional modification. Three potential substrates were examined: 1) changes in intracortical connections within SI; 2) alterations in the projection pattern of thalamocortical afferents from the ventroposterior lateral (VPL) nucleus to SI; and 3) changes in the receptive fields of thalamocortical neurons. We used biotinylated dextran amine and Phaseolus vulgaris leucoagglutinin to examine the intracortical projections associated with the stump and hindlimb representations of SI. True Blue and Diamidino Yellow were used to study the organization of the VPL projections to SI. Finally, single-unit recordings from VPL neurons were made to examine the functional organization of this nucleus in neonatally amputated adult rats. Tracer studies demonstrated no significant change in the intracortical connections or VPL projections associated with the stump and hindlimb SI in neonatally amputated rats. Recordings from VPL of neonatally manipulated rats revealed a small, but significant, population of cells (19.0%) within the stump representation that had dual stump and hindlimb receptive fields. Thus, the data suggest that the functional reorganization observed in SI of neonatally amputated rats may reflect functional alterations occurring in its thalamic inputs.

Amidines↗

PubMed1978

Integration in descending motor pathways controlling the forelimb in the cat. 4. Corticospinal inhibition of forelimb motoneurones mediated by short propriospinal neurones.

A previously described inhibitory trisynaptic cortico-motoneuronal pathway (Illert et al., 1976a) was analysed in order to identify the two relay stations. Intracellular recording was made from motoneurones to elbow muscles. Corticospinal fibres were stimulated in the contralateral medullary pyramid. Pyramidal IPSPs were abolished by a transection of the corticospinal tract in C2 but remained after a corresponding lesion in C5. After a C5 lesion pyramidal volleys facilitated transmission in the Ia inhibitory pathway with a time course suggesting disynaptic excitatory action on the Ia inhibitory interneurones. The trisynaptic pyramidal IPSPs were depressed by volleys in the appropriate recurrent motor axon collaterals as would be expected if these IPSPs were mediated by Ia inhibitory interneurones. It is concluded that trisynaptic cortico-motoneuronal inhibition is evoked by consecutive activation of propriospinal neurones in C3--C4 and segmental Ia inhibitory interneurones.

Animals↗

PubMed1981

Integration in descending motor pathways controlling the forelimb in the cat. 8. Ascending projection to the lateral reticular nucleus from C3-C4 propriospinal also projecting to forelimb motoneurones.

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Afferent Pathways↗