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 541 records · Page 30Linked to original sources
PubMed2001

Cortical representation of whole-body movement is modulated by proprioceptive discharge in humans.

Previous studies have revealed the influence of ongoing sensory discharge on modulating the central representation of muscle afferents from individual limbs. In the present study, we explored the potential for such modulatory influence on the afferent discharge arising from induced whole-body movement. Vestibular and somato-sensory inputs arise from such whole-body movement. The convergence of these two modalities is important in motor control, especially for the maintenance of postural stability. We hypothesised that transmission of proprioceptive and vestibular information to the cortex would be reduced as a result of muscle-spindle discharge in knee extensor muscles. Perturbation-evoked responses (PERs), recorded from central scalp electrodes (C3, CZ, C4), were evoked through rapid translations of subjects who were seated in a chair on a movable platform. PERs were recorded during passive linear translations alone and preceded by vibration of the patellar tendon. The PER was characterised by a slow, negative potential peaking at approximately 150 ms (N150) following displacement of the chair. The amplitude of the PER was reduced following vibration to 56% of the control. Such reduction of PERs was comparable to the attenuation of somatosensory evoked potentials and soleus H-reflex magnitudes from tibial-nerve stimulation. We conclude that muscle-spindle discharge in knee extensor muscles leads to gating of both of these afferent pathways. These results have potential implications to the understanding of the CNS control of stability during ongoing movement.

Adult↗
PubMed1992

[Effects of afferent vagal stimulation and distention of the upper digestive tract on the micturition reflex and activity of the pontine micturition center in dogs].

(1) The study was performed to elucidate the effects of afferent vagal stimulation and distension of the digestive tract on the micturition reflex in 21 acute decerebrate dogs immobilized with gallamine. Electrical stimulation of the central cut end of the cervical vagus nerve with high voltage (17.5-25 V) and moderate frequency (10-50 Hz) elicited in most cases inhibition of the periodic bladder contractions and of outflows of the pelvic vesical branch which were induced by a sustained intravesical pressure of 10-15 cmH2O. Distension of the thoracic esophagus, the stomach, and the duodenum also induced inhibition of the bladder contractions and of the pelvic outflow to the bladder. Such inhibitions were abolished after bilateral cervical vagotomies except a few cases of distension of the duodenum. (2) Another series of experiments were undertaken to clear the effect of afferent vagal stimulation on the electrical activity of the pontine micturition center in 10 acute decerebrate dogs. By means of an extracellular glass microelectrode method, unitary discharges synchronized with the grouping discharges in the pelvic vesical branch with a rhythm of 2.2-2.5 Hz were recorded from the pontine micturition center in the dorsolateral pontine tegmentum. Such a type of discharges was detected in 6 of 59 units which discharged by afferent stimulation of the pelvic vesical branch. This type of discharges was inhibited by afferent vagal stimulation at the supradiaphragmatic level. From these results, it may be concluded that the afferent pathway of the bladder relaxation reflex induced by distension of the upper digestive tract is mainly involved in the vagal nerves, but in some cases of the strong distension of the duodenum, the pathway is in splanchnic nerves, and that inhibition of the bladder contraction after stimulation of vagal nerve is induced by suppression of the pontine micturition centers.

Afferent Pathways↗
PubMed1992

Vagal and splanchnic sensory pathways mediate inhibition of gastric motility induced by duodenal distension.

Afferent pathways mediating gastric corpus relaxation after duodenal distension were studied in urethan-anesthetized rats in which the sensory neurotoxin capsaicin (1%) or its vehicle was applied directly to the cervical vagus nerve trunks or the celiac-superior mesenteric ganglia 10-20 days before experiments. Distension (0.05-0.5 ml) of a closed loop of proximal duodenum decreased gastric intraluminal pressure. Perineural capsaicin treatment to the vagus nerves decreased by 73 and 80% the response to low volumes of distension (0.05 and 0.1 ml). Perineural capsaicin treatment of the celiac-superior mesenteric ganglia significantly attenuated by 46-88% the response to all volumes of distension. Bilateral cervical vagotomy or ganglionectomy reduced the response to all volumes of duodenal distension and, in combination, abolished the response. It is concluded that the decrease in gastric corpus motility after duodenal distension is dependent on the extrinsic innervation to the upper gastrointestinal tract and is mediated by both vagal and spinal capsaicin-sensitive afferents. Capsaicin-sensitive vagal afferents mediate responses to low volumes of distension that may be physiological. Capsaicin-sensitive spinal afferents mediate the gastric response to higher volumes of distension and may be involved in mediating visceral and somatic responses to pathophysiological intestinal obstruction.

Animals↗
PubMed2001

Phasic modulation of corticomotor excitability during passive movement of the upper limb: effects of movement frequency and muscle specificity.

Modulations in the excitability of spinal reflex pathways during passive rhythmic movements of the lower limb have been demonstrated by a number of previous studies [4]. Less emphasis has been placed on the role of supraspinal pathways during passive movement, and on tasks involving the upper limb. In the present study, transcranial magnetic stimulation (TMS) was delivered to subjects while undergoing passive flexion-extension movements of the contralateral wrist. Motor evoked potentials (MEPs) of flexor carpi radialis (FCR) and abductor pollicus brevis (APB) muscles were recorded. Stimuli were delivered in eight phases of the movement cycle during three different frequencies of movement. Evidence of marked modulations in pathway excitability was found in the MEP amplitudes of the FCR muscle, with responses inhibited and facilitated from static values in the extension and flexion phases, respectively. The results indicated that at higher frequencies of movement there was greater modulation in pathway excitability. Paired-pulse TMS (sub-threshold conditioning) at short interstimulus intervals revealed modulations in the extent of inhibition in MEP amplitude at high movement frequencies. In the APB muscle, there was some evidence of phasic modulations of response amplitude, although the effects were less marked than those observed in FCR. It is speculated that these modulatory effects are mediated via Ia afferent pathways and arise as a consequence of the induced forearm muscle shortening and lengthening. Although the level at which this input influences the corticomotoneuronal pathway is difficult to discern, a contribution from cortical regions is suggested.

Adult↗
PubMed1975

Subcortical pathways involved in the mediation of andrenocortical responses following sciatic nerve stimulation.

Previous experiments from this laboratory using the hypothalamic island have demonstrated that the adrenocortical discharge following sciatic nerve stimulation is mediated by neural pathways only. With the purpose of identifying the neural structures involved, this response was studied in rats with bilateral lesions in the medial forebrain bundle (MFB), mammillary peduncle (MP), fasciculus longitudinalis dorsalis (FLD), midbrain reticular formation MRF) and the medial geniculate body (GM). Lesions in the MFB, MP and MRF have inhibited the adrenocortical response following sciatic nerve stimulation. These and other data indicate that the above structures are involved in the mediation of this response and that the afferent pathway enters the mediobasal hypothalamus anteriorly.

Adrenal Cortex↗
PubMed1979

The absence of proprioceptive nerve endings in the human periodontal ligament: the role of periodontal mechanoreceptors in the reflex control of mastication.

A review of the literature was conducted to determine the presence or absence of proprioceptive nerve endings in the human periodontal ligament. A histologic review of the periodontal ligament innervation concluded that nerve endings found were those mediating pain, pressure, or touch and that there is no histologic evidence of any "classic" proprioceptive nerve ending in the periodontal ligament. A summary is given concerning the precise role of nerve endings in the periodontal membrane, their afferent pathways, and the role of masticatory muscle proprioception, jaw reflexes, and the temporomandibular joint in the coordinated control of mastication and mandibular proprioception.

Afferent Pathways↗
PubMed1999

The stress response of critical illness.

The integrated stress response to tissue trauma is crucial for the maintenance of homeostasis. An exaggerated or prolonged response may be detrimental in compromised patients. Knowledge of the involved afferent pathways will suggest therapeutic interventions that may modulate the intensity of the stress response. Described are these concepts as they relate to perioperative medicine.

Afferent Pathways↗
PubMed1992

[Brain-stem auditory pathways: effects of atropine].

The efferent pathways exert a control action on the function of the cochlear nucleus and hair cells. Acetylcholine is the neurotransmitter of the centrifugal system and its action can be blocked by Atropine. In order to give a contribution to the knowledge of the function of the efferent bundle, Auditory Brainstem Responses (ABRs) and Acoustic Reflex Latencies (ARLs) have been examined in 10 young normal subjects there was also a decrease in latency greater than or equal to 100 microseconds by at least other two waves. The only statistically significant difference was relative to the latency mean value of the wave III recorded in contralateral derivation at 11 pps. The ARLs, after the infusion of atropine, showed a statistically significant increase in 7 of the 10 cases; no change was recorded in the AR amplitude. It can be concluded that the pharmacological block of the olivo-cochlear bundle determines a delay in the neural conduction of the acoustic impulses; this finding means that the atropine can inhibit the facilitating activity of the efferent system on the brainstem afferent pathways.

Acetylcholine↗
PubMed1984

Substantia nigra cell death from kainic acid or folic acid injections into the pontine tegmentum.

Injections of kainic acid into the rostral pontine tegmentum in rats caused not only local lesions but destruction of GABAergic and dopaminergic cells in the substantia nigra (SN), as indicated histologically and by measurements of tyrosine hydroxylase (TH) and glutamate decarboxylase (GAD). Injections of folic acid caused the nigral damage without local lesions. Pretreatment with scopolamine prevented the losses in GAD without affecting those in TH. The destruction of nigral cells is attributed to pathological stimulation of afferent pathways to the SN, some of which are cholinergic, and it is possible that a similar mechanism may be involved in some forms of Parkinsonism.

Afferent Pathways↗
PubMed1999

[Blood pressure variability in the elderly].

In the elderly, the difference in blood pressure (BP) between the day and the night is less marked than in young subjects, but it is also more unstable and more sensitive to changes in position, meals, and physical activity. A deficient cardiac baroreflex appears to be involved in this phenomenon. Mayer's oscillation, usually considered to reflect sympathetic vascular activation, is not amplified by standing, but generates slower oscillations, at lower frequencies. The sensitivity of the cardiac baroreflex is inversely correlated with age, but, after the age of 60 years, the correlation with the level of systolic blood pressure (SBP) is greater than with age and accentuation of SBP is the main determinant in problems of postural hypotension. Hypertension and alterations in the afferent pathway of the baroreflex, adrenergic receptors, structure of the arterial wall, and intravascular volume appear to participate in the changes of blood pressure variability observed in the elderly.

Adult↗
PubMed2001

A functional study of uncrossed and crossed pulmonary afferent fibres in the cervical vagus nerves of the cat.

The functional distribution of uncrossed and crossed pulmonary afferent fibres in the cervical vagus nerves has been studied in the anaesthetized cat using acute and chronic unilateral pneumonectomized preparations. The heart and lungs were sympathectomized routinely. The vagal afferent pathways of three pulmonary reflexes were investigated: the Hering-Breuer respiratory reflex, the lung inflation cardio-accelerator reflex, and the pulmonary chemoreflex. Inflation of the remaining lung caused temporary inhibition of inspiration. It also resulted in acceleration of the heart, but only when the background cardiac vagal tone was augmented. These respiratory and cardiac responses were abolished in most animals by ipsilateral cervical vagotomy; however, in some, a small response persisted and this was abolished by contralateral vagotomy. Stimulation of pulmonary C-fibre endings with right atrial injections of phenylbiguanide caused a reduction in respiration, bradycardia and systemic hypotension, responses which occurred with a latency of 2.9 +/- 0.15 s. They were mostly abolished by ipsilateral cervical vagotomy, but reduced responses persisted in a few animals. The residual responses were abolished by contralateral cervical vagotomy and by selective denervation of the lung. These results indicate that most afferent fibres subserving the three pulmonary reflexes studied run in the ipsilateral cervical vagus, representing the uncrossed pathway. Some afferent fibres, however, cross to the contralateral cervical vagus. Degenerative changes in cells of the contralateral nodose ganglion in chronic unilateral pneumonectomized animals support these findings.

Animals↗
PubMedDate not supplied

Sympathetic hyperactivity elevates blood pressure during acute cerebroventricular infusions of hypertonic salt in rats.

Hypertonic solutions of 0.3 M sodium chloride (NaCl) infused into the third ventricle (ICV) for 20 min in urethane-anesthetized rats consistently elevated mean aortic pressure by approximately 10 mm Hg. Heart rate and sympathetic nerve activity diminished slightly during the first few minutes but then accelerated to attain higher than preinfusion levels. By contrast, ICV infusions of either artificial cerebrospinal fluid alone or 0.6 M sucrose were ineffective, those of 0.6 M urea were slightly depressor, while those of 0.3 M ammonium chloride elevated blood pressure without affecting sympathetic nerve activity. In rats pretreated with a vasopressin antagonist, the early pressor effects of hypertonic NaCl were inhibited, while sympathetic nerve firing, instead of being initially inhibited, increased from the onset. Consequently, the blood pressure elevation occurring during the first 5 min of ICV infusion was considered partly due to vasoconstriction caused by increased secretion of endogenous vasopressin, and subsequent maintenance of the blood pressure elevation after the first 10 min was attributed to sympathetic overactivity. Because pressor and sympathetic nerve responses were substantially enhanced following bilateral vagotomy or sinoaortic denervation, it was considered likely that responsiveness to hypertonic NaCl in intact rats in inhibited by both cardiopulmonary and sinoaortic baroreceptor afferents. Augmentation of pressor responsiveness following interruption of baroreceptor afferent pathways suggests that increases in sympathetic activity and blood pressure produced by hypertonic NaCl could contribute to salt-induced hypertension, particularly when baroreceptor buffering becomes deficient.

Afferent Pathways↗
PubMed2002

Immunoneutralization of nerve growth factor in lumbosacral spinal cord reduces bladder hyperreflexia in spinal cord injured rats.

PURPOSE: We investigated the effects of intrathecal application of nerve growth factor (NGF) antibodies (Ab) on bladder hyperreflexia in chronic spinalized rats. MATERIALS AND METHODS: In adult female rats an intrathecal catheter was implanted at the level of the L6 to S1 spinal cord, followed by complete transection of the Th8 to 9 spinal cord. At 10 days after spinalization the intrathecal catheter was connected to an osmotic pump for continuous delivery of vehicle or NGF Ab (10 microg daily) for 2 weeks. Awake cystometry was then performed. NGF levels in the L5 to S1 dorsal root ganglia, L6 spinal cord and bladder were also measured using enzyme-linked immunosorbent assay. RESULTS: The number of uninhibited bladder contractions per voiding cycle, maximal pressure of uninhibited bladder contraction and maximal voiding pressure were significantly decreased in NGF Ab treated versus vehicle treated spinalized rats. Intercontraction interval, baseline intravesical pressure, pressure threshold for voiding and voiding efficiency were not significantly changed by NGF Ab treatment. NGF levels in the bladder, L6 spinal cord and L5 to S1 dorsal root ganglia of vehicle treated spinalized rats was 1.6 to 4.8 times higher than in spinal cord intact rats. After intrathecal NGF Ab treatment NGF levels were significantly lower in the L6 to S1 dorsal root ganglia (30% to 35%) and L6 spinal cord (53%) but not in the bladder or L5 dorsal root ganglia compared with levels in vehicle treated spinalized rats. CONCLUSIONS: Increased levels of NGF in the bladder, spinal cord and dorsal root ganglia were associated with bladder hyperreflexia after spinal cord injury. Immuno-neutralization of NGF in the spinal cord suppressed NGF levels in the L6 to S1 dorsal root ganglia, which contain bladder afferent neurons, and also suppressed bladder hyperreflexia. Thus, suppression of NGF levels in afferent pathways could be useful for treating bladder hyperreflexia associated with spinal cord injury.

Afferent Pathways↗
PubMed1998

Effects of excitation of sensory pathways on the membrane potential of cat masseter motoneurons before and during cholinergically induced motor atonia.

Electrical stimulation of the nucleus pontis oralis during wakefulness enhances somatic reflex activity; identical stimuli during the motor atonia of active (rapid eye movement) sleep induces reflex suppression. This phenomenon, which is called reticular response-reversal, is based upon the generation of excitatory postsynaptic potential activity in motoneurons during wakefulness and inhibitory postsynaptic potential activity during the motor atonia of active sleep. In the present study, instead of utilizing artificial electrical stimulation to directly excite brainstem structures, we sought to examine the effects on motoneurons of activation of sensory pathways by exogenously applied stimuli (auditory) and by stimulation of a peripheral (sciatic) nerve. Accordingly, we examined the synaptic response of masseter motoneurons prior to and during cholinergically induced motor atonia in a pharmacological model of active sleep-specific motor atonia, the alpha-chloralose-anesthetized cat, to two different types of afferent input, one of which has been previously demonstrated to elicit excitatory motor responses during wakefulness. Following the pontine injection of carbachol, auditory stimuli (95 dB clicks) elicited a hyperpolarizing potential in masseter motoneurons. Similar responses were obtained upon stimulation of the sciatic nerve. Responses of this nature were never seen prior to the injection of carbachol. Thus, stimulation of two different afferent pathways (auditory and somatosensory) that produce excitatory motor responses during wakefulness instead, during motor atonia, results in the inhibition of masseter motoneurons. The switching of the net result of the synaptic response from one of potential motor excitation to primarily inhibition in response to the activation of sensory pathways was comparable to the phenomenon of reticular response-reversal. This is the first report to examine the synaptic mechanisms whereby exogenously or peripherally applied stimuli that elicit motor excitation during wakefulness instead elicit inhibitory motor responses during the motor atonia of active sleep. Thus, not only are motoneurons tonically inhibited during active sleep, but the selective elicitation of inhibitory motor responses indicates that this inhibition can be phasically increased in response to sensory stimuli, possibly in order to maintain the state of active sleep. The data provided the foundation for the hypothesis that, during naturally occurring active sleep, there is a change in the control of motor systems so that motor suppression occurs in response to stimuli that would otherwise, if present during other behavioral states, result in the facilitation of motor activity.

Acoustic Stimulation↗
PubMed1994

Synaptic morphology of substance P terminals on catecholamine neurons in the commissural subnucleus of the nucleus tractus solitarii in the rat.

The ultrastructure of substance P-containing nerve terminals synapsing on catecholamine neurons in the rat commissural subnucleus of the nucleus tractus solitarii (NTScom) was studied using a double immunocytochemical labeling technique. Although there were numerous tyrosine hydroxylase-immunoreactive (TH-I) somata present, substance P immunoreactive (SP-I) cell bodies were only occasionally found in the NTScom. At the light microscopic level, many SP-I terminals were seen closely associated with TH-I dendrites and somata. At the electron microscopic level, SP-I terminals synapsing on TH-I structures were also readily encountered. SP-I terminals contained small, clear, and predominantly spherical vesicles (32 +/- 4 nm diameter), as well as large dense-cored vesicles approximately 100 nm in diameter. Postsynaptic TH-I dendritic profiles of various calibers and somata were encountered. These postsynaptic TH-I structures often showed postsynaptic densities. The morphological features of the SP-TH synapses in the present study, that is, the size of synaptic vesicles and the presence of postsynaptic densities, are quite different from those of central carotid sinus afferent synapses reported in our previous study [Chen et al. (1992), J. Neurocytol., 21:137-147]. Therefore, most of the SP terminals of the SP-TH synapses in the NTScom appear not to originate from the carotid sinus afferents. SP-I second-order neurons of the carotid sinus afferent pathway [Chen et al. (1991), J. Auton. Nerv. Syst., 33:97-98] may be one of the possible sources of such terminals.

Afferent Pathways↗
PubMed1993

Response time, autonomic mediation, and reversibility of hyperoxic bradycardia in conscious dogs.

Normobaric hyperoxia decreases heart rate (HR) in humans and animals. This study explored the mechanisms of hyperoxic bradycardia by examining its response time, autonomic neural mediation, and reversibility in conscious dogs. Five trained mongrel dogs breathed from a mask as the inspired gas was alternated between air and O2 for multiple cycles, and continuous time series records of HR and oxyhemoglobin saturation were recorded on a digital computer and analyzed by the technique of ensemble averaging. Hyperoxia decreased HR by 9% (P < 0.001), but only gradually, requiring 5 min to reach steady state. This delay was much longer than the time required for hyperoxic respiratory depression (10-20 s), a response known to be mediated by chemoreceptor reflexes. The bradycardia was sustained for > or = 30 min. On return to normoxia, HR gradually returned toward, but failed to reach, the baseline HR, suggesting incomplete reversibility of the response. However, in control experiments without hyperoxic challenge, HR showed a slow continuous downward trend that was sufficient to account for the apparent incomplete reversibility of hyperoxic bradycardia. Hyperoxic bradycardia was unaffected by beta-adrenergic blockade but was completely prevented by muscarinic cholinergic blockade. We conclude that 1) hyperoxia-induced bradycardia in conscious dogs is mediated by efferents of the vagus nerve; 2) its afferent pathway remains unknown, but its long response time suggests mechanisms other than chemoreceptor reflexes or other known neural reflexes; and 3) it is completely reversible.

Adrenergic beta-Antagonists↗
PubMed1985

Synaptic terminals in the ventroposterolateral nucleus of the thalamus from neurons in the dorsal column and lateral cervical nuclei: an electron microscopic study in the cat.

The afferent fibres to the ventroposterolateral nucleus (VPL) of the contralateral thalamus from neurons in the dorsal column nuclei (DCN) and the lateral cervical nucleus (LCN) were labelled by anterograde transport of wheat germ agglutinin-horseradish peroxidase conjugate and subsequent histochemical processing with tetramethyl benzidine. In accordance with the results of previous light microscopical studies using the degeneration method or autoradiographic tracing technique, the distribution of the afferents from the DCN and LCN in the VPL differed considerably. Thus the DCN terminals, which were calculated to constitute about 7-8% of the total number of boutons in the VPL, were found throughout the entire VPL, whereas the LCN terminals were mainly located in its dorsal and dorsolateral parts, where they made up about 1% of the total number of boutons. However, the morphology and synaptic organization of the terminals from the DCN and LCN were virtually identical. Thus the synaptic terminals of the two afferent pathways seemed to be represented by large boutons of a similar type, which had large, slightly oval and loosely packed synaptic vesicles and contained numerous mitochondria. Both DCN and LCN terminals synapsed preferentially on medium-sized to large dendrites, but were also presynaptic to other vesicle-containing profiles, probably of internuncial origin, which in turn were in synaptic contact with the same dendrites as the labelled ones. It is suggested that the differences in physiological properties between the somatosensory information that is transmitted to the somatosensory cortex via the dorsal column-medial lemniscus pathway and the spino-cervico-thalamic tract do not seem to have a counterpart in differences in the synaptic organization of their relay in the VPL.

Afferent Pathways↗
PubMed1984

Linear and non-linear summation of alpha-motoneuron potential changes elicited by contractions of homonymous motor units in cat medial gastrocnemius.

An analysis is made of linear and non-linear summation of the motor unit (MU) tension and motoneuron (MN) membrane potential (PSP) trajectories evoked by stimulation of MUs as previously reported. In most cases, summation of both averaged responses was linear. Seldom, PSPs summed non-linearly, then usually coinciding with non-linear summation of the responsible MU twitches. The results suggest that the afferent pathways mediating the mechanical events in muscle to MNs behave rather linearly, at least in the small-signal range of interest here.

Afferent Pathways↗