ISSN:0899-0220    

DOI:10.3109/08990229109144722

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

Recently, an age-related increase in the number of dorsal root ganglion (DRG) cells was reported in adult rats. This suggests neurogenesis of adult primary afferent neurons, which would be an extremely important phenomenon if it occurred. Other evidence is not compatible with this idea, however, so the issue is not settled. The primary point of contention concerns the counts of DRG cells in relation to age. In our opinion, these disagreements arise, at least in part, because different counting methods give different results for the same material. Thus, any method for determining DRG cell numbers should be calibrated. We previously calibrated some of the common methods used to count DRG cells and found that an empirical method gave accurate cell counts. In the present study, we have used this method and asked whether an age-related increase in the number of lumbar DRG cells can be demonstrated in adult rats. Our data indicate that DRG cell numbers remain essentially constant from 3 to 22 months of age. Most ancillary evidence is consistent with the hypothesis that mammalian DRG cell numbers do not change during adult life. Thus, we feel that the evidence does not support the hypothesis that there is neurogenesis of adult rat primary afferent neurons.

ISSN:0899-0220    

DOI:10.3109/08990229109144723

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

La Forte et al. (this issue) failed to find an increase in the numbers of dorsal root ganglion (DRG) neurons in rats of advancing age. However, their conclusion that our data (Devor and Govrin-Lippmann, 1985) to this effect were methodologically flawed is based on an incorrect application of our counting method. In fact, both their counting method and ours provide similar results when applied to the same tissue sections. We believe that the difference in results is biological. Specifically, DRG neurogenesis in adulthood occurs in animals in which growth continues throughout life (including the male Wistar-derived rats we used), but not in those whose body size stabilizes soon after sexual maturity (including the female Sprague-Dawley rats they used). With this caveat in mind, recent data of Schmalbruch (1987a, b) and others can be understood as corroborating our conclusions. However, an adequate, independent replication of our 1985 study has yet to be carried out.

ISSN:0899-0220    

DOI:10.3109/08990229109144724

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

The capacity of four neurologically healthy young adults to distinguish opposing directions of cutaneous motion was determined at five different sites along the proximal-distal axis of the upper limb. Constant-velocity brushing stimuli (ranging from 0.5 to 32.0 cm/sec) were delivered through an aperture in a Teflon plate that was securely positioned in light contact with the skin. In one series of experiments, directional sensitivity ind'units was assessed at each site, using an aperture length of 0.75 cm. In a second series of experiments, the aperture length required to obtain the same criterion level of directional sensitivity at each site was determined.To attain the sensitivity reached at distal sites, a proximal stimulus had to traverse a longer chord of skin. Specifically, chords 5.9 times longer on average (range = 5.4-6.2) were required on the proximal forearm than on the index finger pad. This finding suggests that relative directional sensitivity increases sixfold from the proximal forearm to the finger pad. Moreover, relative directional sensitivity on the shoulder was comparable to that observed on the proximal forearm for two of the subjects, and approximately one-half that observed on the proximal forearm for the other two subjects. In addition to such a prominent spatial gradient in relative directional sensitivity, the velocity of stimulus motion at which directional sensitivity was highest increased systematically as the test site was shifted from the finger pad to the proximal forearm. Specifically, the optimal velocity on the finger pad varied among subjects from 1.5 to 9.4 cm/sec (mean = 5.4 cm/sec), and on the proximal forearm from 11.5 to 31.2 cm/sec (mean = 18.6 cm/sec). The optimal velocity on the shoulder was not significantly different from that observed on the proximal forearm.The results suggest that effective and informed clinical testing of patients' capacity to distinguish opposing directions of motion on cutaneous regions that differ in peripheral innervation density requires appreciation of the sensitivities of different skin regions, as well as the unique velocity dependency of direction discrimination at each skin site.

ISSN:0899-0220    

DOI:10.3109/08990229109144725

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

We determined the location of 54 horseradish peroxidase (HRP)-labeled motor cortical neuron synaptic terminals on 17 parvocellular neurons in the monkey red nucleus. Synaptic terminals and their postsynaptic elements were identified and reconstructed, using light- and electron-microscopic techniques, from serial thick and thin sections. Terminals were found on proximal and distal dendrites of small and medium-sized parvocellular neurons, where they formed excitatory synapses. Some were 180μm from cell somata. Approximately half of the labeled terminals, aside from those located at dendritic origins, were situated strategically at or near dendritic branch points. Since monkey parvocellular neurons show little activity during movement, the obvious next question is this: How and in what way does motor cortex influence these cells?

ISSN:0899-0220    

DOI:10.3109/08990229109144726

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

Neuronal activity recorded from the primary motor cortex (MI) and from the supplementary motor area (SMA) was compared in two monkeys trained to perform conditioned arm movements. A handle had to be held in a central waiting position until a visual go and cueing signal indicated to the monkey to move the handle either to a medial or to a lateral target zone (choice reaction time paradigm). Unit and representative electromyographic data were analyzed in relation either to the go signal or to movement onset.In 240 penetrations, 431 SMA neurons and 353 MI neurons were found with activity related to the task. The majority of neurons (303 in MI, 290 in SMA) displayed activity changes after the go signal and before movement onset. Of these“short-lead neurons,”71% in MI and 41% in SMA were clearly related to movement execution. The distribution of lead times in MI and SMA neurons was completely overlapping without any statistical difference among subgroups.The remaining neurons were as well related to the go signal as to movement onset, or were better related to the visual go signal. The response latencies to this signal were not statistically different in SMA and MI neurons. Activity changes during the waiting period was observed more frequently in SMA (47%) than in MI (32%); modulations restricted to the waiting period occurred in 14% of SMA neurons, but were exceptional in MI neurons (3%).It is concluded from these experiments that a surprisngly large proportion of SMA neurons have“MI-like”properties, in that they are temporally recruited together with MI neurons, with similar patterns of discharges during the task. This then suggests that the two interconnected areas operate in parallel. A population of SMA neurons is involved in some processing that is not as predominantly expressed in MI. This activity could relate to sensory, timing, or other higher-order aspects of response preparation, and/or motor functions such as postural stabilization.

ISSN:0899-0220    

DOI:10.3109/08990229109144727

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

We previously described the ability to induce adult-like, coordinated airstepping following electrical stimulation of the brainstem in the hindlimb-attached,in vitrobrainstem-spinal cord preparation. These findings suggest the presence at birth of supraspinal systems capable of activating and modulating spinal locomotor mechanisms, which presumably also are present at birth. The current study employed the hindlimb-attachedin vitrobrainstem-spinal cord preparation from 0- to 4-day-old rats maintained in oxygenated artificial cerebrospinal fluid. After the control threshold-frequency relationship for eliciting airstepping was established, the dorsal roots to the attached limbs were severed and the procedure was repeated. No changes in electrical threshold or major differences in the elicited locomotor pattern were observed after deafferentation, although the amplitude of the electromyograms decreased. Themeanfrequency of alternation at threshold before deafferentation was similar to that after deafferentation. However, themaximummean frequency induced by suprathreshold stimulation was significantly higher after deafferentation than that before deafferentation. These results suggest that (1) the supraspinal modulation of spinal locomotor mechanisms is not entirely dependent on afferent input; (2) intrinsic spinal locomotor mechanisms are present in the spinal cord at birth; and (3) afferent input may limit the maximum frequency of alternation of the limbs early in development.

ISSN:0899-0220    

DOI:10.3109/08990229109144728

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

Previous studies have described the presence of alternating activity induced in left and right ventral roots of the neonate ratin vitrobrainstem-spinal cord preparation, following application of certain neuroactive substances to the bathing solution. The present findings show the presence of chemically induced, adult-like coordinated airstepping demonstrated by electromyographic recordings in the hindlimb-attachedin vitrobrainstem-spinal cord preparation. Analysis of muscular activity demonstrated alternation between antagonists of one limb and between agonists of different limbs, as well as a proximodistal delay in agonists active at different joints of the same limb. Neuroactive agents were applied independently to either the brainstem or spinal cord bath. The substances surveyed in the present studies included some of those used previously, as well as additional compounds: bicuculline and picrotoxin (γ-aminobutyric acid-ergic antagonists), N-methyl-D-aspartic acid (excitatory amino acid agonist), substance P, acetylcholine, carbachol (cholinergic agonist), and serotonin. Application of these substances to the brainstem bath produced rhythmic airstepping. Application of dopamine, aspartate, glutamate, and N-methyl-D-aspartic acid to the spinal cord bath also produced rhythmic airstepping, while application of acetylcholine produced tonic, long-lasting co-contractions. These findings reveal the presence of several neurochemical systems in the central nervous system that can be activated at birth to induce coordinated airstepping in the neonate ratin vitrobrainstem-spinal cord preparation.

ISSN:0899-0220    

DOI:10.3109/08990229109144729

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

The cortical map of adult cats that sustained spinal cord transection at T12when they were 2 weeks old is characterized by a clear duplication of the representation of the forelimb, rostral trunk, and neck. The novel representation is located in the cortical region that is, in nonoperated animals, normally devoted to the hindlimb representation. We have investigated the possibility that the reactivation of the deprived hindlimb cortex may be mediated by corticocortical projections from normal to reorganized cortex. The primary somatosensory (SI) cortex was initially mapped to determine the boundaries of the normal and reorganized cortical representations. Somatotopically corresponding regions in both normal and reorganized cortex representing the trunk, the web space, or the shoulder were more precisely mapped. Inactivation of normal cortex was achieved by the nanoinjection of a solution of lidocaine hydrochloride stained with Chicago sky blue. Two major findings are described. First, inactivation of a circumscribed region of normal cortex representing a given receptive field (RF) failed to reduce or inhibit the responsiveness of a somatotopically corresponding RF represented in reorganized cortex. Therefore, it is unlikely that intracortical connections between normal and reorganized cortex could account for the reorganizational processes observed in cats that sustained spinal cord transection at 2 weeks of age. Second, the chemical blockade of normal cortex provoked an increase of the responsiveness and of the size of the peripheral RFs represented in reorganized cortex. This finding suggests that there are corticocortical connections (possibly topographically organized) between normal and reorganized cortex, and that these connections are inhibitory.

ISSN:0899-0220    

DOI:10.3109/08990229109144730

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

Although a highly organized system of reciprocal projections exists between the cerebral cortex and the thalamus, the relationship of the thalamocortical projections to functional activity remains unclear. This study attempts to identify the correlation between thalamic relay cells and functional activity evoked in the ventroposterior nucleus (VP) of cynomolgus and squirrel monkeys. Wheatgerm agglutinin conjugated to horseradish peroxidase (WGA:HRP) was iontophoretically injected into physiologically determined sites in the somatosensory cortex, resulting in retrogradely labeled cells and anterogradely labeled terminals in corresponding somatosensory thalamic regions. In the same animals, 2-deoxyglucose (2DG) experiments were carried out 2 days later, using the somatic stimuli identified as best exciting the cortical neurons. Stimulation to the limbs produced crescent-shaped clusters of metabolic label arranged in a somatotopically organized fashion in the ventral posterior lateral nucleus (VPL). Following WGA:HRP injections into area 3b, the stimulus-evoked 2DG label was colocalized with the retrograde and anterograde tracer. This finding suggests that the location of stimulus-evoked metabolic activity can be predicted by the presence of transported WGA:HRP clusters.

ISSN:0899-0220    

DOI:10.3109/08990229109144731

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor