Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Afferent Pathways”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 487 records · Page 27Linked to original sources
PubMed2006

Dissociation of thalamic high frequency oscillations and slow component of sensory evoked potentials following damage to ascending pathways.

OBJECTIVE: Somatosensory evoked potentials (SEPs) recorded from the thalamus have a slow component and high frequency (approximately 1000 Hz) oscillations (HFOs). In this study, we examined how lesions in the sensory afferent pathway affect these components. METHODS: Thalamic SEPs to contralateral median nerve stimulation were recorded from deep brain stimulation electrodes in two patients. Patient 1 had spinal cord injury at the C4/5 level. Patient 2 had multiple sclerosis with mid brain lesions. Seven patients with no brain or cervical spinal cord lesions served as controls. RESULTS: In both patients, the low frequency component of the SEP (LF SEP) was delayed and/or prolonged and greatly decreased in amplitude compared with controls. HFOs were recorded in both patients. The latencies of onset and peak of the HFOs were approximately the same as those of the LF SEPs and their amplitudes were similarly reduced. However, their frequency was similar to that of the control group. Cortical SEPs were absent in both patients. CONCLUSIONS: Normal frequencies of thalamic HFOs in association with increased peak latencies, and decreased amplitudes provide further evidence that the HFOs are likely due to intrinsic oscillations in the thalamus rather than high frequency synchronous inputs. SIGNIFICANCE: Thalamic HFOs are closely associated with the LF SEP but are generated by a different mechanism.

Adult↗
PubMed1995

Fos expression within regions of the preoptic area, hypothalamus and brainstem during pregnancy and parturition.

Vaginocervical stimulation, that occurs during mating or with the birth of pups, is believed to induce specific sexual and maternal behaviours in the rat as well as stimulating a number of neuroendocrine responses including the secretion of oxytocin, prolactin and luteinizing hormone. Since the medial preoptic area has been implicated in the induction of maternal behaviour, the expression of the immediate-early gene product Fos was compared between non-pregnant, late pregnant and parturient rats. Although no difference was detected in the number of Fos-positive neuronal profiles in the preoptic area of non-pregnant and late-pregnant rats, a large increase was observed in the medial preoptic nucleus and the anteroventral periventricular region, as well as in the hypothalamic supraoptic nucleus, of parturient rats. Double labelling for Fos and tyrosine hydroxylase immunoreactivity in the brainstem of parturient rats showed the activation of catecholaminergic neurons in both the nucleus of the tractus solitarius and in the ventrolateral medulla that may form part of the afferent pathway from the uterus and cervix to the preoptic area and hypothalamus.

Afferent Pathways↗
PubMed1991

Laryngeal afferent activity and reflexes in the guinea pig.

We have investigated the various sensory modalities represented in the laryngeal nerves of the guinea pig. In addition, we have examined the defensive responses to mechanical stimuli and capsaicin instillation into the laryngeal lumen of the same species. Recording from both the whole superior laryngeal nerve and from single units of the same nerve revealed the presence of afferent activity related (1) to the contraction of laryngeal muscles and/or the 'tracheal tug', (2) to transmural pressure changes, either positive or negative and (3) to mechanical and chemical irritants. The irritant type receptors of this species, when challenged with water solutions, show two distinct patterns of activation: some behave as osmoreceptors, some respond to the lack of chloride ions. Challenges with capsaicin solutions activated one ending with the characteristics of a C-fiber receptor that failed to respond to a subsequent trial. This behavior is consistent with the reflex apnea, dependent on an intact laryngeal innervation, induced by capsaicin instillation that was not elicitable on repeating the challenge. Cough to mechanical probing of the supraglottic area depended on an intact SLN, whereas cough elicited from the subglottic area depended on an intact RLN. Cough to mechanical stimulation could not be desensitized by capsaicin. These findings suggest the presence of two independent afferent pathways for defensive responses.

Afferent Pathways↗
PubMedDate not supplied

Somatosensory evoked potentials in lacunar syndromes of pure motor and ataxic hemiparesis.

Syndromes of hemiparetic lacunar infarction include pure motor hemiparesis and ataxic hemiparesis. Twelve such patients were evaluated with somatosensory evoked potentials. Potentials were delayed or absent in all 4 patients with ataxic hemiparesis and in 1 of 8 patients with pure motor hemiparesis. Unlike pure motor hemiparesis, ataxic hemiparesis appears to be associated with abnormal somatosensory evoked potentials. These abnormalities suggest that disturbance of afferent pathways are important in ataxic hemiparesis.

Afferent Pathways↗
PubMed1986

Respiratory myoclonus. Report of a case with electromyographic study.

A case of respiratory myoclonus in a 45 year-old male was studied by electromyography. He complained of anorexia, involuntary swinging movement of the thorax and trunk, and epigastric pulsation. Electromyographic studies showed synchronous rhythmic grouped discharges at the of 2 to 3 Hz from the bilateral 8th to 10th intercostal muscles, the right iliocostalis lumborum muscle, and the left hemidiaphragm only during the expiratory phase. They disappeared on inspiration and forced expiration. Anesthetic block of the left phrenic nerve abolished both the voluntary and myoclonic movements of the left hemidiaphragm. Abnormal excitation of the central nervous system and possible irritation of the afferent pathways were postulated.

Afferent Pathways↗
PubMed1984

Sensory consequences of commissural myelotomy. A challenge to traditional anatomical concepts.

Twenty-five cases of commissural myelotomy were studied. Representative cases are reported, including a histological examination of the lesion in one. Although the purpose of the operation is to produce a cuirass of loss of pain sensibility by dividing the spinothalamic and spinoreticulothalamic fibres as they decussate in the anterior commissure of the cord, this result is not always obtained. Whether or not the expected sensory loss is obtained, the chronic pain for which the operation is performed can be relieved. Sensibility tends to return towards normal after myelotomy. Even with substantial recovery of sensory loss, the pain for which the operation was performed can remain absent. Asymmetrical sensory loss may be produced by the operation; reasons for this are suggested. Differences between the results of commissural myelotomy and anterolateral cordotomy are discussed. Unlike the results of anterolateral cordotomy, which can be accounted for on the basis of known anatomy, the results of commissural myelotomy are inexplicable on present anatomical knowledge. Attention is drawn to the results of myelotomy reported originally by Hitchcock and confirmed by other neurosurgeons in which a short myelotomy incision in the upper cervical cord caused loss of pain over a vast region of the body. The difficulty in explaining the patterns of sensory loss in these cases is discussed. The literature on pathways alternative to the spinothalamic and spinoreticulothalamic is reviewed. It is argued that the central incision cannot cause relief of pain merely by cutting an afferent pathway, and it is suggested that this lesion blocks impulses entering into, in, or leaving the spinothalamic complex. The accurate localization of pinprick and thermal stimuli via the spinothalamic tract is demonstrated.

Afferent Pathways↗
PubMed1982

A contribution to the study of the afferents to the pigeon optic tectum.

The origins of several afferent pathways to the pigeon's tectum were studied using the horseradish peroxidase tracing technique. The results confirm the presence of several previously described afferents, and add further data on intertectal and hyperstriatofugal projections. Two new sources of afferents to the tectum, located in the hypothalamus and the septum, were identified. The latter is described in greater detail.

Afferent Pathways↗
PubMed2002

Disruption of early events in thalamocortical tract formation in mice lacking the transcription factors Pax6 or Foxg1.

Early events in the formation of the thalamocortical tract remain poorly understood. Recent work has suggested that thalamocortical axons follow a path pioneered by transient thalamic afferents originating from the medial part of the ventral telencephalon. We studied the development of these transient afferents and the thalamocortical tract in mutant mice lacking transcription factors normally expressed in the dorsal thalamus or ventral telencephalon. Pax6 is expressed in the dorsal thalamus, but not in the medial part of the ventral telencephalon, and the thalamocortical tract fails to form in Pax6(-/-) embryos. We found that transient thalamic afferents from the ventral telencephalon do not form in Pax6(-/-) embryos; this may contribute to the failure of their thalamocortical development. The distribution of Pax6(-/-) cells in Pax6(-/-)<--> Pax6(+/+) chimeras supports conclusions drawn from forebrain marker gene expression that Pax6 is not required for the normal development of the medial part of the ventral telencephalon but is required in the dorsal thalamus. Failure of the transient afferent pathway to develop is therefore likely a cell nonautonomous defect reflecting primary defects in the thalamus. We then examined the formation of thalamic afferents and efferents in Foxg1(-/-) embryos, which lack recognizable ventral telencephalic structures. In these embryos thalamic efferents navigate correctly through the thalamus but fail to turn laterally into the telencephalon, whereas other axons are able to cross the diencephalic/telencephalic boundary. Our results support a role for the ventral telencephalon in guiding the early development of the thalamocortical tract and identify a new role for the transcription factor Pax6 in regulating the ability of the thalamus to attract ventral telencephalic afferents.

Afferent Pathways↗
PubMed2002

Pathways involved in synchronization of sympathetic nerve discharge to lung inflation.

In urethane-anesthetized cats, we tested the hypothesis that sympathetic nerve discharge (SND) is synchronized to lung inflation, in part, over a vagal afferent pathway that bypasses the central respiratory oscillator. For this purpose, partial coherence analysis was used to mathematically remove the portion of the relationship between intratracheal pressure (ITP; index of lung inflation) and inferior cardiac SND that was common to that between ITP and phrenic nerve activity (PNA; index of central respiratory cycle). ITP-SND partial coherence (PNA-related component removed) at the frequency of breathing should be significantly different from zero if a bypass pathway exists. This was found to be the case in paralyzed, artificially ventilated cats when lung inflation and rhythmic PNA were coupled in various ratios (e.g. 1:1, 3:1) and in spontaneously breathing cats. As expected, surgical vagotomy eliminated ITP-SND coherence in artificially ventilated cats. These findings support the view that a portion of the relationship between ITP and SND is independent of the influences of pulmonary stretch receptors on central respiratory networks.

Afferent Pathways↗
PubMed1982

Effect of electrical stimulation of the testis on the nucleus praeopticus pars magnocellularis of the frog, Rana tigrina.

The changes in the nucleus praeopticus (NPO) pars magnocellularis of the frog Rana tigrina were studied after electrical stimulation of the left testis. After a 3-min stimulation, the neurones of the nucleus showed a statistically significant increase in the nuclear and cellular diameters. The lateral neurones in particular showed a complete loss of Nissl substance and other acute chromatolytic changes. In the aldehyde fuchsin stained preparations, however, the perikarya appeared filled with clumps of intensely stained neurosecretory material (NSM) and disintegrating cell nuclei. The NSM was discharged in the axons, resulting in an increase in number and size of the Herring bodies. These changes were abolished in frogs whose testes had been pre-anaesthetized with xylocaine. Based on these observations, the possible existence of an afferent pathway from the testis to the NPO pars magnocellularis is suggested.

Afferent Pathways↗
PubMed1995

Early and late stretch responses of human foot muscles induced by perturbation of stance.

In eight subjects standing on a movable platform, surface EMG activity was recorded from the foot muscles extensor digitorum brevis (EDB) and flexor digitorum brevis (FDB) and from the leg muscles soleus (Sol) and tibialis anterior (TA) during perturbations of upright stance. Perturbations inducing foot dorsiflexion (upward tilt and backward translation) evoked a short-latency response (SLR) and a medium-latency response (MLR) to stretch in the physiological extensors FDB and Sol, and a long-latency response (LLR) in the physiological flexors EDB and TA. Perturbations inducing plantar-flexion (downward tilt and forward translation) evoked the MLR in EDB and TA, and the LLR in FDB and Sol. The latency of the FDB and Sol SLR was compared to that of the H and T reflexes evoked in the same muscles by electrical or mechanical stimulation, respectively. In both muscles, the T reflex and the SLR followed the H reflex at delays accounted for by the different stimulation mode, indicating that the SLR induced in both muscles by upward tilt and backward translation was a true autogenetic stretch reflex from spindle primaries. The time interval between the onset of SLR and of MLR was significantly greater for the FDB than the Sol muscle, suggesting that MLR is a spinal reflex travelling through slower peripheral afferent pathways than SLR. From these latency differences and from the distance between the muscles, we calculated in four subjects the conduction velocity of the afferent fibres presumably responsible for the MLR in FDB. This was about 29 m/s. LLRs were evoked in TA and EDB during upward tilt and backward translation, and in Sol and FDB during downward tilt, but not forward translation. LLRs did not adhere to a proximal-to-distal pattern, since these could appear earlier in the foot than in the leg muscles. All responses were modulated by perturbation type (tilt vs translation) and body posture (normal stance vs forward leaning). Both the large amplitude of the foot muscle responses and their temporal pattern indicate that the muscles acting on the toes play a major role in stabilising posture. Their action increases in amplitude and extends in time the foot-ground reaction force, thereby improving the efficiency of the superimposed action of the leg muscle responses.

Adult↗
PubMed1983

Inhibition and excitation of thoracic spinoreticular neurons by electrical stimulation of vagal afferent nerves.

Neurons in spinal segments T1-T3 of cats projecting to the region of the nucleus reticularis gigantocellularis were tested for their responses to electrical stimulation of the vagus nerve. The effects of vagal efferent activity were blocked with methylatropine, thereby limiting vagal input to the effects of afferent fibers. Seventeen spinoreticular (SR) neurons were inhibited by vagal stimulation; one was excited; four were both inhibited and excited, and nine were unaffected. Half of the SR neurons were not spontaneously active; they were excited by somatic stimuli for 20- to 30-s periods in order to test for vagal inhibition. Vagal stimuli sometimes were sufficiently potent to completely suppress neuronal discharge during and just after 10-s periods of stimulation. Parameters of stimulus duration and frequency suggest activation of both A delta and C fibers in the vagus nerves. Vagal stimulation could inhibit increased firing from cardiac stimuli, such as coronary artery occlusion and injection of bradykinin into the heart. Two-thirds of the SR neurons so tested responded to bilateral sympathetic stimuli, whereas about one-half had excitatory somatic receptive fields restricted to the left foreleg and upper left side. The other half had bilateral, widespread, and complex somatic fields, including inhibitory responses. Such multiple inputs suggest an integrative role for spinoreticular neurons in sensory processing. Vagal inhibition and excitation of SR neurons probably operates via well known descending inhibitory systems from the nucleus raphe magnus and other medullary centers. The vagi are the only peripheral afferent pathway into this descending system that has been described to date.

Afferent Pathways↗
PubMed1990

Adrenalectomy decreases neuropeptide Y mRNA levels in the arcuate nucleus.

Recent studies suggest that glucocorticoids may increase NPY and NPY mRNA levels. To determine if endogenous corticosterone affects the level of NPY mRNA in areas that control NPY levels in the paraventricular nucleus, we examined the effects of adrenalectomy and corticosterone replacement on NPY mRNA levels in the arcuate nucleus and brainstem. Rats were either adrenalectomized, adrenalectomized and corticosterone replaced, or sham-operated. The arcuate nucleus, hypothalamus (excluding arcuate nucleus), and brainstem were collected and the RNA isolated. Dot blots were made of each tissue and the NPY mRNA quantitated by densitometry. Adrenalectomy significantly reduced NPY mRNA levels in the arcuate nucleus, while corticosterone replacement restored the NPY mRNA levels. NPY mRNA levels in the remainder of the hypothalamus were not affected by adrenalectomy. Adrenalectomy also had no affect on NPY mRNA levels in the brainstem. These data suggest that the paraventricular nucleus may be affected by glucocorticoids via an NPY pathway and that the two major afferent pathways of NPY-containing neurons to the paraventricular nucleus may be regulated by different mechanisms.

Adrenal Glands↗
PubMed1997

Hippocampal interneurons express a novel form of synaptic plasticity.

Individual GABAergic interneurons in hippocampus can powerfully inhibit more than a thousand excitatory pyramidal neurons. Therefore, control of interneuron excitability provides control over hippocampal networks. We have identified a novel mechanism in hippocampus that weakens excitatory synapses onto GABAergic interneurons. Following stimulation that elicits long-term potentiation at neighboring synapses onto excitatory cells, excitatory synapses onto inhibitory interneurons undergo a long-term synaptic depression (interneuron LTD; iLTD). Unlike most other forms of hippocampal synaptic plasticity, iLTD is not synapse specific: stimulation of an afferent pathway triggers depression not only of activated synapses but also of inactive excitatory synapses onto the same interneuron. These results suggest that high frequency afferent activity increases hippocampal excitability through a dual mechanism, simultaneously potentiating synapses onto excitatory neurons and depressing synapses onto inhibitory neurons.

Afferent Pathways↗
PubMed1991

Localization of [125I]endothelin binding sites in the region of the carotid bifurcation and brainstem of the cat: possible baro- and chemoreceptor involvement.

We have demonstrated by autoradiography, displaceable binding for [125I]endothelin-1 ([125I]ET-1), [125I]endothelin-2 ([125I]ET-2), and [125I]endothelin-3 ([125I]ET-3) in the cat carotid bifurcation as well as in the nucleus of the tractus solitarius, where baroreceptor and chemoreceptor afferents from the carotid body and sinus terminate. There was also significant binding in the nodose and superior cervical ganglia. Barosensory and chemosensory discharge was recorded from filaments of the carotid sinus nerve in cats anesthetized with pentobarbitone. Intra-carotid injection of ET-1 or ET-3 (4-402 pmoles) caused transient dose-related depression of baroreceptor discharge without any immediate effects on systemic blood pressure (BP) or heart rate; there was a delayed biphasic effect on BP. ET-1 had little effect on chemosensory discharge during the first 15 s post-injection, but there was a delayed (45-90 s) dose-related increase in discharge. The effects of all three ETs were qualitatively similar, and ET enhanced chemoexcitation evoked by either acetylcholine or sodium cyanide. Our results show that (a) ET binding sites are located in the baroreceptor and chemoreceptor afferent pathways and (b) ETs can influence afferent activity of baroreceptors and chemoreceptors. Further studies are needed to determine the significance of these findings, particularly with regard to reflex control of the cardiovascular system.

Animals↗
PubMed1976

Computer mapping of brain-stem sensory centers in man.

A computer program is described for use on-line with a two--stage stereotaxic technique in man. It has four capabilities. It transposes coordinates between a brain atlas and a stereotaxic frame, simultaneously adjusting for variations in individual brain dimensions. Corrections for electrode trajectories, and for any irregularities of placement of the stereotaxic frame in the head are also made. It plots an operative template that shows electrode trajectories and the sites from which physiological data are collected appropriately oriented upon a sagittal diagram of the brain. It graphically displays physiological data in the form of a Woolsey-type figurine chart that indicates threshold in milliamperes and, through the use of coded symbols, the quality of response and certain other data. It stores all this data in a tape library together with the locations of any lesions made. This makes it possible to replot any individual patient's operative data at any time. It also permits scanning of the stored protocols from all patients for any particular type of data either by itself or in combination with other data. This retrieved information is plotted on appropriate sagittal brain diagrams corrected for individual variations in brain size. Illustrations of the capabilities of the program are presented particularly with reference to the primary afferent pathways of the upper brain stem.

Afferent Pathways↗
PubMed1991

Pathological changes in dendrites of substantia nigra neurons in Parkinson's disease: a Golgi study.

Neurons of the substantia nigra show severe morphological changes in Parkinson's disease. Pathological alterations of cell bodies have been described, whereas those of neuronal processes have hardly been investigated. Golgi impregnation has been the chosen method for demonstrating neuronal processes and dendritic and somatic spines. We therefore used the Golgi-Braitenberg method to qualitatively and semi-quantitatively study the substantia nigra of eight patients with Parkinson's disease compared with eight control cases. Golgi impregnation of substantia nigra neurons was good in all control cases. In full agreement with the analysis of Braak and Braak (1986) three neuronal types within the substantia nigra were found. In cases of Parkinson's disease, severe pathological changes such as decrease of dendritic length, loss of dendritic spines and several types of dendritic varicosities were found only in the melanin-containing pars compacta neurons. Pars reticulata nerve cells were intact. These findings support the predominant role played by the dopaminergic efferent pathway in the degenerative process. The afferent pathway was not affected. This suggests that the substantia nigra lesion is primary in Parkinson's disease. Loss of neurons found in H & E sections corresponded to a lesser amount of impregnated pars compacta neurons in cases with Parkinson's disease when compared to controls. Evidences exist that the duration of the disease may be related to the extent of pathologically altered Golgi-impregnated pars compacta cells. The amount of Lewy bodies in H & E sections corresponded to the quantity of round varicosities in impregnated pars compacta neurons. These round dendritic varicosities were considered to be Lewy body inclusions.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1990

Neurological involvement in group iv HIV-positive patients. Neurophysiological and clinical data.

Spinal and cortical SEP responses were recorded during tibial and median nerve stimulation in 58 HIV+ subjects (8 IV/C1, 24 IV/C2 & IV/A, 11 III and 15 II), all asymptomatic from a neurological point of view. The electrophysiological features were compared with clinical assessment and serum HIV markers for purposes of prognosis and therapy. In group IV we observed a slowing of conduction along the afferent pathway in the spinal tracts and afferent ways to the cortex. The major part of the delay occurred in the mid and lower medullary tract. These results agree with neuropathological finding from post-mortem examination in AIDS pts.

Acquired Immunodeficiency Syndrome↗