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PubMed1987

Morphology and distribution of the projection neurons in the cerebellum in a teleost, Sebastiscus marmoratus.

Cerebellar efferent neurons in a teleost, Sebastiscus marmoratus, were studied by means of the horseradish peroxidase (HRP) tracing and Golgi impregnation methods. The cerebellar efferents or eurydendroid neurons are classified into two types (A and B) on the basis of the morphology of the dendrites, intracerebellar distribution, and other afferent connections. Type A neurons form a cell cluster in the lobus caudalis and have one thick primary dendrite from which several branches with sparse but long spines extend into the molecular layer of the lobus caudalis. Type B neurons, observed in both the valvula and corpus cerebelli, have two or three primary dendrites running along the ganglion cell layer, and the distal dendritic branches are distributed in molecular layer perpendicularly to the cerebellar surface. Small spines are densely studded on the dendrites of type B neurons. Somata of type A and B neurons are located in and just beneath the ganglion cell layer. The cerebellum projects to the ipsilateral nucleus lateralis valvulae and torus longitudinalis and bilaterally, but mostly contralaterally to the nucleus ventromedialis thalami of Schnitzlein ('62), nucleus ruber, the vicinity of the oculomotor complex, torus semicircularis, and brainstem reticular formation. Type A neurons send axons primarily to the vicinity of the oculomotor complex and partly to the nucleus ventromedialis thalami and the nucleus ruber, whereas type B cells project to all main cerebellar targets. In addition, type B cells are organized topographically in the cerebellum in relation to the efferent targets in the brainstem.

Animals↗
PubMed1989

Descending projections to the mammillary nuclei in the rat, as studied by retrograde and anterograde transport of wheat germ agglutinin-horseradish peroxidase.

The cells of origin and projection fields of the descending afferents to the mammillary nuclei were studied in the rat with retrograde and anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase. The subiculum projects bilaterally to the entire medial mammillary nucleus (MM) in a topographic fashion along the two axes: 1) the proximal part of the subiculum along the presubiculo-CA1 axis projects to the caudal and lateral regions of the MM whereas the more distal part of the subiculum projects to the medial region; 2) the septal part of the subiculum projects to the caudodorsal region of the MM whereas the more temporal part projects progressively to the more rostroventral regions. The ventral subiculum also projects ipsilaterally to the ventral and lateral margin of the lateral mammillary nucleus (LM). The presubiculum projects bilaterally to the dorsolateral region of the pars posterior of the MM and ipsilaterally to the LM. The infra-limbic cortex projects bilaterally to the rostrodorsal region of the MM, whereas the retrosplenial cortex (areas 29a and 29b) projects bilaterally to the medial region at the midrostrocaudal and middorsoventral levels of the MM. The nucleus of the diagonal band projects bilaterally to the caudomedial region of the MM, whereas the lateral septal nucleus projects bilaterally to the pars mediana and the mammillary fiber capsule. A part of the anterior hypothalamic area ventromedial to the fornix projects predominantly ipsilaterally to the rostroventral part of the MM, whereas other basal forebrain regions such as the bed nucleus of the stria terminalis, the medial preoptic and anterior hypothalamic areas, and the area of the tuber cinereum send fibers predominantly ipsilaterally to the mammillary fiber capsule. The results reveal a complex organization of the descending projections to the mammillary nuclei, which may reflect the complex functions of these nuclei within the limbic circuitry.

Afferent Pathways↗
PubMed1992

Pathway from the zona incerta to the superior colliculus in the rat.

In order to test the proposal that the zona incerta contributes to the generation of orienting movements, we examined the synaptic relationships between the incertotectal pathway and the cells of origin of the predorsal bundle. The predorsal bundle cells give rise to the major premotor pathway from the superior colliculus to the brainstem gaze centers. First, cytochrome oxidase histochemistry, gamma-aminobutyric acid (GABA), and glutamic acid decarboxylase (GAD) immunocytochemistry, and the axonal transport of markers were used to define the borders of a ventral subdivision of the zona incerta. This subdivision projects topographically to the same sublamina of the intermediate grey layer of the superior colliculus that contains the vast majority of the predorsal bundle cells. Experiments in which incertotectal cells were labeled by both retrograde transport and immunocytochemistry showed that this pathway is GABAergic. Retrograde and anterograde experiments also showed that this pathway is reciprocated by a pathway from the intermediate grey layer of the superior colliculus to the same ventral subdivision of the zona incerta. Finally, experiments combining axonal transport and electron microscopic methods showed that the incertotectal pathway is the source of a monosynaptic GABAergic input to the cells of origin of the predorsal bundle. The ventral subdivision of the zona incerta is contrasted with a second source of GABAergic input to the predorsal bundle cells, the substantia nigra pars reticulata.

Afferent Pathways↗
PubMed1992

Connections between the retrosplenial cortex and the hippocampal formation in the rat: a review.

The retrosplenial cortex is situated at the crossroads between the hippocampal formation and many areas of the neocortex, but few studies have examined the connections between the hippocampal formation and the retrosplenial cortex in detail. Each subdivision of the retrosplenial cortex projects to a discrete terminal field in the hippocampal formation. The retrosplenial dysgranular cortex (Rdg) projects to the postsubiculum, caudal parts of parasubiculum, caudal and lateral parts of the entorhinal cortex, and the perirhinal cortex. The retrosplenial granular b cortex (Rgb) projects only to the postsubiculum, but the retrosplenial granular a cortex (Rga) projects to the postsubiculu, rostral presubiculum, parasubiculum, and caudal medial entorhinal cortex. Reciprocating projections from the hippocampal formation to Rdg originate in septal parts of CA1, postsubiculum, and caudal parts of the entorhinal cortex, but these are only sparse projections. In contrast, Rgb and Rga receive dense projections from the hippocampal formation. The hippocampal projection to Rgb originates in area CA1, dorsal (septal) subiculum, and post-subiculum. Conversely, Rga is innervated by ventral (temporal) subiculum and postsubiculum. Further, the connections between the retrosplenial cortex and the hippocampal formation are topographically organized. Rostral retrosplenial cortex is connected primarily to the septal (rostrodorsal) hippocampal formation, while caudal parts of the retrosplenial cortex are connected with temporal (caudoventral) areas of the hippocampal formation. Together, the elaborate connections between the retrosplenial cortex and the hippocampal formation suggest that this projection provides an important pathway by which the hippocampus affects learning, memory, and emotional behavior.

Afferent Pathways↗
PubMed2004

Pressor effects of electrical stimulation of medial prefrontal cortex in unanesthetized rats.

The medial prefrontal cortex (MPFC) is involved in central nervous system (CNS)-mediated cardiovascular modulation. We compared the cardiovascular effects of electrical stimulation (EE) of the MPFC in unanesthetized rats to those observed after stimulation of the same area in urethane-anesthetized rats. Electrical stimulation (35, 106, 177, 247, 318, and 389 microA rms/10 sec, 60-Hz sine wave) of the MPFC of urethane-anesthetized rats caused depressor responses of stimulus-related intensity. The cardiovascular response to electrical stimulation of the MPFC in unanesthetized rats was characterized by stimulus-related pressor responses. No significant heart rate changes were observed during the EE period in any case. The pressor response to electrical stimulation (106 microA rms/10 sec, 60-Hz sine wave) of the MPFC was not affected by intravenous pretreatment with the vasopressin antagonist dTyr(CH(2))(5)(Me)AVP (50 microg/kg, intravenously), by hypophysectomy, or by intravenous pretreatment with the angiotensin II antagonist losartan (1 mg/kg, intravenously). The pressor response was blocked by intravenous pretreatment with the ganglionic blocker mecamylamine (2 mg/kg, intravenously) but was not affected by adrenal demedullation, thus suggesting involvement of the neural component of the sympathetic nervous system without a major involvement of its hormonal component. Our results confirmed the occurrence of depressor responses after electrical stimulation of the MPFC in urethane-anesthetized rats and evidenced that only pressor responses are observed after its stimulation in unanesthetized rats. The fact that the pressor response to the stimulation of the MPFC was blocked by a ganglioplegic suggests that the MPFC has functional excitatory actions over the sympathetic nervous system.

Adrenal Medulla↗
PubMed1995

AAEM case report #2: the carpal tunnel syndrome.

The symptoms and signs which constitute the carpal tunnel syndrome (CTS) result from entrapment or compression of the median nerve within the carpal tunnel. Electrodiagnostic studies may objectively document the presence of median neuropathy within the carpal tunnel and help distinguish CTS from other disorders such as cervical radiculopathy, neurogenic thoracic outlet syndrome, proximal median nerve compression syndromes, and polyneuropathy which may either mimic or occasionally coexist with CTS. Recording median nerve responses with wrist and palm stimulation allows determination of the wrist segment conduction velocity which is a more sensitive nerve conduction parameter than wrist latency measurements. Electrodiagnostic testing permits estimation of severity and relative contribution of axonal versus demyelinative nerve injury. This information can provide prognostic information and help guide therapeutic decisions.

Action Potentials↗
PubMed2005

Sacral neuromodulation in lower urinary tract dysfunction.

Vesico-urethral dysfunction is a major problem in daily medical practice due to its psychological disturbances, its social costs and its high impact on quality of life. Recently, sacral neuromodulation, namely the electrical stimulation of the sacral nerves, appears to have become an alternative for radical bladder surgery particularly in cases of idiopathic bladder overactivity. The mechanism of action is only partially understood but it seems to involve a modulation in the spinal cord due to stimulation of inhibitory interneurons. Temporary sacral nerve stimulation is the first step. It comprises the temporary application of neuromodulation as a diagnostic test to determine the best location for the implant and to control the integrity of the sacral root. If test stimulation is successful, a permanent device is implanted. This procedure is safe in experienced hands. So-called idiopathic bladder overactivity still the major indication for this technique. Patients not likely to benefit from the procedure were those with complete or almost complete spinal lesions, but incomplete spinal lesions seemed to be a potential indication. This technique is now also indicated in the case of idiopathic chronic retention and chronic pelvic pain syndrome. When selection is performed, more than three-quarters of the patients showed a clinically significant response with 50% or more reduction in the frequency of incontinent episodes, but the results vary according to the author's mode of evaluation. From the economic point of view, the initial investment in the device is amortized in the mid-term by savings related to lower urinary tract dysfunction. Finally, this technique requires an attentive follow-up and adjustments to the electric parameters so as to optimize the equilibrium between the neurological systems.

Afferent Pathways↗
PubMed1990

Identification of motoneurons in the spinal cord of the zebrafish (Brachydanio rerio), with special reference to motoneurons that innervate intermediate muscle fibers.

We investigated the location and size distribution of motoneurons that innervate red, intermediate and white muscle fibers in the axial musculature of the zebrafish (Brachydanio rerio). Motoneurons were identified by retrograde labeling from the respective myotomal compartments with horseradish peroxidase applied either in small polyacrylamide gel fragments or as pure crystals. We found a spatial relationship between the three myotomal muscle fiber types and the corresponding motoneurons. The white motoneurons are grouped in the dorsal part of the motorcolumn, near the central canal. Motoneurons of the red and intermediate muscle are clustered in the ventral part of the motorcolumn. The average position of the red motoneurons is ventral to that of the intermediate motoneurons. Some sizes are distributed over wide overlapping ranges, spanning from 41 to 352 microns 2 for red and intermediate and from 56 to 894 microns 2 for white motoneurons. These data are discussed in relation to the recruitment order of myotomal muscle fibers of different types as revealed by electromyographic recordings in fish, and the so called "size principle" for motoneuron recruitment.

Animals↗
PubMed1991

Nigrotectal projections in the primate Galago crassicaudatus.

The pattern of the nigrotectal projection in Galago crassicaudatus was determined using retrograde and anterograde transport methods. These experiments revealed that pars reticulata and pars lateralis of the substantia nigra project to all layers of the ipsilateral and contralateral superior colliculus, except to layer I. The nigrotectal projection is not homogeneous, but is concentrated in particular collicular layers and sublayers, and the intensity and laminar distribution of the projection varies along the rostral-caudal dimension of the superior colliculus. The ipsilateral and contralateral nigrotectal projections are generally similar, except that a tier of dense label which is prominent in the ventral part of much of the ipsilateral layer IV is not obvious contralaterally; moreover, the contralateral projection is much sparser than the ipsilateral. Deposits of tracers at different medial-lateral locations within the substantia nigra did not result in different laminar patterns of anterogradely transported label in the superior colliculus. Based on the known connections and functions of the collicular layers and sublayers, the pattern and distribution of the nigrotectal projection suggests that the substantia nigra may use this pathway to gain access to particular components of vision- and visuomotor-related networks.

Afferent Pathways↗
PubMed1977

Descending connections between superior olivary and cochlear nuclear complexes in the cat studied by autoradiographic and horseradish peroxidase methods.

The descending pathways from the superior olivary complex (SO) to the cochlear nuclear complex (CN) were investigated in 58 cats using labelled aminoacid and horseradish peroxidase transport techniques. Descending connections were found coursing bilaterally through the trapezoid body (TB) and ipsilaterally in the intermediate and dorsal acoustic striae. The dorsolateral periolivary nucleus (DLPO) sends fibres through both the intermediate and dorsal striae, which are joined by others from the lateral preolivary nucleus (LPO). Both the latter nucleus and the medial preolivary nucleus (MPO) give rise to a bilateral descending projection which traverses TB. The distribution of these descending pathways within CN is described (although the technique did not permit precise synaptic identification). The possible implications of these pathways for response patterns at the level of CN are discussed.

Animals↗
PubMed1977

The distribution of degenerating axons after small lesions in the intact and isolated visual cortex of the cat.

The extent of the spread of axonal degeneration was investigated in the visual cortex of the cat after making small lesions restricted to the grey matter. Two series of experiments were undertaken. In the first, normal adult cats were used, and in the second, the cortex of the postlateral gyrus was isolated from its extrinsic afferents by surgical undercutting 3 months before making the lesions. The results were similar in the two series in most respects. 1. Horizontal fibres extended in considerable numbers for some 500 micrometer from the lesion, mainly in layers I, III/IV and V, a few reaching 2/3 mm. These fibres were better seen in the intact than in the isolated cortex. Their spread was usually asymmetrical, being greater posteromedially than anterolaterally. 2. Oblique axons ran downwards from the middle layers into layers V and VI, or upwards into layers I and II. 3. Axons arising from layers II to VI descended vertically into the white matter. Degeneration patterns after lesions in areas 17 and 18 were compared.

Afferent Pathways↗
PubMed1980

Sequential output-input maturation of kitten motor cortex.

Average response histograms of the responses of single cortical neurons to imposed forelimb displacements in the kitten were utilized to quantify: (1) Background activity, (2) excitatory response latency, (3) percentage responding neurons, and (4) synaptic effectiveness. Motor cortical neuronal responses to the input did not attain adult values until 55--65 days of age, while adult-like responses were found in somatosensory cortical neurons as early as 9 days postnatally. Motor cortical output to alpha-motoneurons innervating triceps brachii, as tested by intracortical and subcortical microstimulation, first appeared over an interval ranging from 37--45 days postnatally. Thus, motor cortical responses to forelimb mechanoreceptors develop after completion of the output linkages from motor cortex to forelimb motoneurons and, though the motor cortex can output at 45 days, motor cortical functions requiring somatosensory feedback cannot be operative until about 60 days. This system provides a discrete and "late" maturing model in which to study the postnatal development of neuronal networks underlying normal and abnormal motor behavior.

Afferent Pathways↗
PubMed1977

Descending inputs to the cat dorsal cochlear nucleus: an electron microscopic study.

This experimental study provides identification of several types of terminals in the fusiform cell layer (FCL) of the cat dorsal cochlear nucleus (DCN). Eight types of synaptic terminal were defined in control animals. 22 experimental cats were then subjected to unilateral lesions of the superior olivary complex or SOC (Groups I and II), the inferior colliculus or IC (Groups III and IV), or the IC plus the dorsal nucleus of the lateral lemniscus or DNLL (Groups V and VI). After one to 14 days, animals were killed by perfusion-fixation and brain stems prepared for light and electron microscopic study of degeneration. After SOC lesions, the ipsilateral FCL showed degeneration of small (type 2a) endings on small dendritic shafts; the contralateral FCL showed degeneration of larger (type 5) endings mostly on fusiform cell somata and on some primary dendrites. Both sides showed mild degeneration of large, glomerular (type 1a) endings. After small IC lesions, the ipsilateral FCL demonstrated degenerating type 1a glomerular endings but the contralateral FCL showed severe degeneration of type 5a terminals (axodendritic to fusiform cells) and mild degeneration of both glomerular (type 1a) and axosomatic (type 5) endings. Combined IC-DNLL lesions caused extensive degeneration in a pattern similar to that following IC lesions. In addition retrograde degeneration of fusiform cells occurred bilaterally. These studies showed that: (1) type 2a endings originate in the ipsilateral SOC; (2) type 5 endings on fusiform cell bodies originate from the contralateral SOC; (3) type 5a endings on fusiform cell dendrites originate from the contralateral IC; and (4) type 1a glomerular endings probably arise from several sources, including the IC, the SOC and (possibly) the DNLL of both sides.

Animals↗
PubMed1992

Effects of dorsal root entry zone lesion on spinal cord potentials evoked by segmental, ascending and descending volleys.

The spinal cord potentials (SCPs) were recorded from the dorsal root entry zone (DREZ) and posterior epidural space in patients before and after dorsal root entry zone lesion (DREZL) during general anaesthesia. The SCPs from the DREZ activated by segmental, ascending and descending volleys were basically the same in fundamental waveform as those recorded from the posterior epidural space. Segmentally activated slow negative (N1) wave, reflecting synchronized activities of dorsal horn neurones, and positive (P2) wave, thought to indicate primary afferent depolarization, were affected by DREZL in all 4 subjects tested, even by contralateral stimulation, suggesting that these components of the segmental SCPs in man partly reflect the activities of the contralateral dorsal horn. The spike-like potentials activated by ascending volleys were not affected by DREZL, while the subsequent slow components were decreased in the lesioned level. This may indicate that ascending spinal cord tracts are not affected by the operation, and suggests that the origin of the slow components by ascending volleys lies at least in part in the segmental dorsal horn. The slow negative and positive components, recorded at a remote segment from DREZL, in response to the descending volleys, were augmented after DREZL, suggesting that activation of ascending or descending inhibition through a feedback loop via the supraspinal structures might occur at least transiently following DREZL. All components of the SCPs activated by descending volleys were decreased or disappeared in recording from the lesioned level, as expected. Thus, intra-operative recording of the SCPs during DREZL might be beneficial for monitoring and studying human spinal cord function.

Afferent Pathways↗
PubMed2001

Can proprioception really be improved by exercises?

There is little question that ankle disc training can improve ankle muscle motor performance in a unipedal balance task, most likely through improved strength and coordination [62] and possibly endurance. How much of the observed improvement in motor performance is due to improved ankle proprioception remains unknown. We have reviewed a number of theoretical ways in which training might improve proprioception for moderately challenging weight-bearing situations such as balancing on one leg. Although the relevant experiments have yet to be performed to test this hypothesis, any improvement would theoretically help to reduce injuries at these moderate levels of challenge. We question, however, whether these exercises can ever improve the reactive response required to prevent injury under the most challenging time-critical situations. If confirmed, this limitation needs to be acknowledged by authors and practitioners alike. Alternative protective strategies for the most challenging time-critical situations should be sought. We conclude that, despite their widespread acceptance, current exercises aimed at "improving proprioception" have not been demonstrated to achieve that goal. We have outlined theoretical scenarios by which proprioception might be improved, but these are speculative. The relevant experiments remain to be conducted. We argue that even if they were proven to improve proprioception, under the best circumstances such exercises could only prevent injury under slow to intermediate rate provocations to the joint musculoligamentous complex in question.

Afferent Pathways↗
PubMed2003

Arm-trunk coordination in the absence of proprioception.

During trunk-assisted reaching to targets placed within arm's length, the influence of trunk motion on the hand trajectory is compensated for by changes in the arm configuration. The role of proprioception in this compensation was investigated by analyzing the movements of 2 deafferented and 12 healthy subjects. Subjects reached to remembered targets (placed approximately 80 degrees ipsilateral or approximately 45 degrees contralateral to the sagittal midline) with an active forward movement of the trunk produced by hip flexion. In 40% of randomly selected trials, trunk motion was mechanically blocked. No visual feedback was provided during the experiment. The hand trajectory and velocity profiles of healthy subjects remained invariant whether or not the trunk was blocked. The invariance was achieved by changes in arm interjoint coordination that, for reaches toward the ipsilateral target, started as early as 50 ms after the perturbation. Both deafferented subjects exhibited considerable, though incomplete, compensation for the effects of the perturbation. Compensation was more successful for reaches to the ipsilateral target. Both deafferented subjects showed invariance between conditions (unobstructed or blocked trunk motion) in their hand paths to the ipsilateral target, and one did to the contralateral target. For the other deafferented subject, hand paths in the two types of trials began to deviate after about 50% into the movement, because of excessive elbow extension. In movements to the ipsilateral target, when deafferented subjects compensated successfully, the changes in arm joint angles were initiated as early as 50 ms after the trunk perturbation, similar to healthy subjects. Although the deafferented subjects showed less than ideal compensatory control, they compensated to a remarkably large extent given their complete loss of proprioception. The presence of partial compensation in the absence of vision and proprioception points to the likelihood that not only proprioception but also vestibulospinal pathways help mediate this compensation.

Adaptation, Physiological↗
PubMed2004

Long-lasting body leanings following neck muscle isometric contractions.

Our objective was to investigate the neural mechanisms and the functional relevance of motor effects that develop involuntarily following the release of a sustained isometric muscle contraction. The few data available in the literature deal only with post-contractions occurring in a body segment. Although these data emphasise the role of proprioceptive input, the question as to whether this phenomenon is of central or peripheral origin remains unclear. Given the leading role of neck muscle proprioceptive input in body orientation and posture regulation, we designed two experiments to test for postural posteffects after voluntary and involuntary neck muscle contraction. The spatiotemporal characteristics of the posteffects were analysed by means of stabilometric recordings following 30-s isometric contraction of splenius, trapezius and levator muscle groups, and 30-s electrically-induced contraction of the levator muscle group. Results show that a postural response occurred after voluntary contraction of each muscle group tested, which was oriented in the plane of action of the muscle, and lasted 14 min at least. In contrast, no clearly oriented body leanings were found after electrical stimulation of the levator muscle, except for a slight increase in natural postural instability. Data are interpreted as a change in the postural reference resulting from an increase in proprioceptive inflow accompanying mainly the voluntary muscle contraction.

Adult↗