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At least 811 records · Page 45Linked to original sources

PubMed2005

Ipsi- and contralateral exteroceptive EMG modulation in uni- and bilaterally activated thenar muscles.

OBJECTIVE: The cutaneous silent period (CSP) is a spinal inhibitory reflex mediated by A-delta fibers. The exact underlying neural pathway, however, is unknown. This study was undertaken to investigate whether the neural circuitry mediating CSPs is wired unilaterally or whether there is evidence of influence from or upon the contralateral side. METHODS: Fifteen healthy subjects underwent bilateral CSP testing following unilateral nociceptive digit II stimulation. Surface electromyographic (EMG) recordings were obtained bilaterally from thenar muscles following unilateral recurrent nociceptive digit II stimulation while activating the ipsilateral or the contralateral or both thenar muscles against resistance. RESULTS: Nociceptive digit II stimulation evoked consistent CSPs in ipsilateral thenar muscles during voluntary contraction, while there was no consistent influence on EMG activity in contralateral thenar muscles at rest. Furthermore, nociceptive digit II stimulation did neither consistently affect EMG activity in ipsilateral thenar muscles at rest nor in contralateral thenar muscles during voluntary contraction. Finally, there was no significant difference between any CSP parameters obtained during unilateral versus bilateral muscle contraction. Occasional late excitatory EMG activity in relaxed or contracted thenar muscles resembled startle reflexes, which seem to contribute to the post-inhibition EMG-rebound. CONCLUSIONS: The present findings are consistent with unilateral wiring of the spinal circuitry mediating CSPs. SIGNIFICANCE: The essential lack of a crossed inhibitory influence of nociceptive digit II stimulation underscores the utility of CSP testing in the assessment of the A-delta fiber system in healthy subjects and patients with various pathologies.

Adult↗

PubMed1977

Ventral root mapping of cardiac nerves in the canine using evoked potentials.

The sympathetic efferent contribution of left ventral roots T2, T3, and T4 to some cardiac nerves was studied using evoked potentials in mongrel dogs anesthetized with sodium pentobarbital. Electrical stimulation of the ventral roots while recording evoked potentials from the sympathetic chain, anterior ansa subclavia, posterior ansa, ventrolateral cervical cardiac nerve, ventromedial cervical cardiac nerve, and the vagosympathetic trunk demonstrated that A-, B-, and C-type fibers exist in these efferent neural pathways. The range of conduction velocities observed was 0.7-104 m/s. T2 contributed the largest number of A-type fibers, and T2 and T3 contributed C-type fibers equally, while T4 had the least number of fibers coursing through the cardiac nerves.

Animals↗

PubMed1996

Acute and chronic angiotensin hypertension: neural and nonneural components, time course, and dose dependency.

We examined the mechanisms mediating hypertension in conscious rats during acute and chronic infusion of angiotensin II (ANG II) at pressor doses (50, 100, and 200 ng.kg-1.min-1). Trimethaphan-induced blood pressure reduction was inversely related to the acute dose of ANG II, consistent with a constrictor action of ANG II on vascular smooth muscle and withdrawal of sympathetic tone. During chronic ANG II infusion, the entire increase in mean arterial pressure (MAP) was inhibited by trimethaphan, consistent with neural mediation. During acute ANG II hypertension, the AT1-specific receptor blocker losartan induced a large fall in MAP (64 +/- 4 mmHg) in ganglion-blocked (chlorisondamine) rats, whereas, during chronic ANG II hypertension, losartan had only a small hypotensive effect (11 +/- 3 mmHg). To determine the time course of the change from vascular smooth muscle action to neural action, we measured MAP in response to trimethaphan during the first 24 h of ANG II infusion. After 5 h, the minimal MAP in response to trimethaphan was significantly higher than that before ANG II. After 10 h of infusion, trimethaphan decreased MAP to pre-ANG II levels. That is, the neural component was fully active after only 10 h of infusion in rats. Finally, chronic administration of ANG II resulted in a dose-related increase in MAP that, at all doses, was completely inhibited by trimethaphan. These findings are consistent with ANG II acting primarily on vascular smooth muscle during acute infusion and via neural pathways during chronic treatment. The transition from direct smooth muscle to indirect neural action is rapid in rats (< 10 h), and the MAP and neural responses to ANG II are dose related during chronic hypertension.

Acute Disease↗

PubMedDate not supplied

Effect of docosahexaenoic acid content of maternal diet on auditory brainstem conduction times in rat pups.

Previous studies of dietary docosahexaenoic acid (DHA; 22:6n-3) effects on neurodevelopment have focused mainly on effects on the visual system; these studies may be confounded by effects on the retina rather than on neural pathways. Auditory brainstem conduction times (ABCTs) provide an alternate measure of central neural development. We conducted a dose-response study in which ABCTs were measured in pups whose dams were fed diets containing one of three levels of DHA (2, 4 or 6% of total fatty acids) from a single cell oil. Diets were fed during pregnancy and lactation, and pups were randomly cross-fostered on postnatal day 3 to minimize litter effects. ABCTs showed a dose-response effect, with higher levels of dietary DHA being associated with longer conduction times on postnatal day 31 (p < 0.05). Higher dietary DHA was reflected in pup cerebrums collected on postnatal days 3 and 31, and levels of arachidonic acid (AA, 20:4n-6) were inversely related to levels of DHA. This study demonstrated that the auditory brainstem response is sensitive for identifying effects of diet on neurodevelopment, and that supplementing the maternal diet with high levels of DHA may negatively impact development of the central auditory system of offspring.

Animals↗

PubMed1992

Anatomy and fine structure of neurons in the deutocerebral projection pathway of the crayfish olfactory system.

Golgi impregnation and neurobiotin injection were used to examine details of the neural pathways in the olfactory system of the freshwater crayfish, Procambarus clarkii. Deutocerebral projection neurons (globuli cells) were directly injected with neurobiotin. These neurons have dendritic arborizations in the ipsilateral olfactory and accessory lobes, and they project axons to the lateral protocerebrum, where they terminate in microglomeruli of the hemi-ellipsoid body. The axons of the deutocerebral projection neurons are readily impregnated by Golgi procedures, and they terminate as an expanded membranous knot about 5 microns in diameter. Electron microscopy on Golgi-stained terminals has revealed that each knot makes several hundred synapses with small spine-like or shaft-like processes of postsynaptic neurons. Injection of neurobiotin into local interneurons of the hemi-ellipsoid body and subsequent examination of stained preparations with the electron microscope reveals that these cells are a major postsynaptic target of the deutocerebral projection neurons. Furthermore, the local interneurons make extensive efferent synaptic connections with unidentified neurons in the terminal medulla.

Animals↗

PubMed1998

Delivery of Nerve Growth Factor to the Brain via the Olfactory Pathway.

Purpose: To assess the potential of delivering nerve growth factor (NGF) to the brain along the olfactory neural pathway for the treatment of Alzheimer's disease. Methods: Recombinant human NGF (rhNGF) was given as nose drops to anesthetized rats. The rhNGF concentrations in the brain were determined by enzyme-linked immunosorbent assay (ELISA). Results: Following olfactory administration, rhNGF reached the brain within an hour, achieving a concentration of 3400 pM in the olfactory bulb, 660–2200 pM in other brain regions and, 240 pM and 180 pM in the hippocampus and the amygdala, respectively. In contrast, little or no rhNGF was found in the brain following intravenous administration. Conclusions: A significant amount of rhNGF can be delivered to the brain via the olfactory pathway. The detection of rhNGF by ELISA indicates that rhNGF is delivered to the brain relatively intact. The rapid appearance of rhNGF in the brain suggests that it may be transported by an extraneuronal route into the brain via intercellular clefts in the olfactory epithelium. Further work to clarify the transport mechanism is underway. The olfactory pathway is a promising, non-invasive route for drug delivery to the brain, which has potential for the treatment of neurodegenerative diseases including Alzheimer's disease.

Journal Article↗

PubMed1999

Bladder afferent pathway and spinal cord injury: possible mechanisms inducing hyperreflexia of the urinary bladder.

Lower urinary tract dysfunction is a common problem in patients with spinal cord injury (SCI). Since the coordination of the urinary bladder and urethra is controlled by the complex mechanisms in spinal and supraspinal neural pathways, SCI rostral to the lumbosacral level disrupts voluntary and supraspinal control of voiding and induces a considerable reorganization of the micturition reflex pathway. Following SCI, the urinary bladder is initially areflexic. but then becomes hyperreflexic because of the emergence of a spinal micturition reflex pathway. Recent electrophysiologic and histologic studies in rats have revealed that chronic SCI induces various phenotypic changes in bladder afferent neurons such as: (1) somal hypertrophy along with increased expression of neurofilament protein; and (2) increased excitability due to the plasticity of Na+ and K+ ion channels. These results have now provided detailed information to support the previous notion that capsaicin-sensitive, unmyelinated C-fiber afferents innervating the urinary bladder change their properties after SCI and are responsible for inducing bladder hyperreflexia in both humans and animals. It is also suggested that the changes in bladder reflex pathways following SCI are influenced by neural-target organ interactions probably mediated by neurotrophic signals originating in the hypertrophied bladder. Thus, increased knowledge of the plasticity in bladder afferent pathways may help to explain the pathogenesis of lower urinary tract dysfunctions after SCI and may provide valuable insights into new therapeutic strategies for urinary symptoms in spinal cord-injured patients.

Afferent Pathways↗

PubMed2004

Mechanisms determining cholinergic neural responses in airways of young and mature rabbits.

Neural pathways help control airway caliber and responsiveness. Yet little is known of how neural control changes as a function of development. In rabbits, we found electrical field stimulation (EFS) of airway nerves led to more marked contractile responses in 2- vs. 13-week-old animals. This enhanced response to EFS may be due to prejunctional, junctional, and/or postjunctional neural mechanisms. We assessed these mechanisms in airways of 2- and 13-week-old rabbits. The contractile responses to methacholine did not differ in the groups, suggesting postjunctional neural events are not primarily responsible for differing responses to EFS. To address junctional events, acetylcholinesterase (AChE) was measured (spectrophotometry). AChE was elevated in 2-week-olds. However, this should lead to less and not greater responses. Prejunctionally, EFS-induced acetylcholine (ACh) release was assessed by HPLC. Airways of 2-week-old rabbits released significantly more ACh than airways from mature rabbits. Choline acetyltransferase, a marker of cholinergic nerves, was not different between groups, suggesting that more ACh release in young rabbits was not due to increased nerve density. ACh release in the presence of polyarginine increased significantly in both groups, supporting the presence of functional muscarinic autoreceptors (M2) at both ages. Because substance P (SP) increases release of ACh, SP was measured by ELISA. This neuropeptide was significantly elevated in airways of younger rabbits. Nerve growth factor (NGF) increased SP and was also significantly increased in airways from younger rabbits. This work suggests that increases in EFS-induced responsiveness in young rabbits are likely due to prejunctional events with enhanced release of ACh. Increases in NGF and SP early in life may contribute to this increased responsiveness.

Acetylcholine↗

PubMed1994

Isolation and developmental expression of retinoic-acid-induced genes.

The vitamin A derivative retinoic acid (RA) is involved in vertebrate anteroposterior axis formation and cellular differentiation and has been shown to modulate the expression of a number of genes implicated in the control of early embryonal development. Under defined culture conditions, all-trans-RA induces differentiation of P19 embryonal carcinoma cells into neural derivatives. In this report, we describe the isolation and partial characterization of 14 RA-regulated genes from P19 cells committed to differentiate along the neural pathway. In addition to the previously recognized genes encoding vimentin, heat stable antigen, neural cadherin, Hox-B2, F52/MacMARCKS, thymosin beta 4b, and the murine homolog of COUP-TF1, we identified 7 novel genes, 5 of which are predominantly expressed in developing neural tissues as shown by in situ hybridization. The results confirm the usefulness of the P19 system in the isolation and study of the regulation of developmentally expressed genes.

Amino Acid Sequence↗

PubMed2005

The cholinergic anti-inflammatory pathway.

The regulation of the innate immune response is critical for controlling inflammation and for the prevention and treatment of diseases. We recently demonstrated that the efferent vagus nerve inhibits pro-inflammatory cytokine release and protects against systemic inflammation, and termed this vagal function "the cholinergic anti-inflammatory pathway." The discovery that the innate immune response is regulated partially through this neural pathway provides a new understanding of the mechanisms that control inflammation. In this review, we outline the cholinergic anti-inflammatory pathway and summarize the current insights into the mechanisms of cholinergic modulation of inflammation. We also discuss possible clinical implications of vagus nerve stimulation and cholinergic modalities in the treatment of inflammatory diseases.

Animals↗

PubMed2005

Bilateral oculosympathetic paresis associated with loss of nocturnal melatonin secretion in patients with spinal cord injury.

BACKGROUND: Lesions along the sympathetic pathway to the eye produce oculosympathetic paresis (OSP, Horner's syndrome). The oculosympathetic pathway descends from the hypothalamus through the cervical spinal cord and ascends to the superior cervical ganglion (SCG), which innervates sympathetic targets in the ipsilateral face and eye. This pathway appears to closely co-localize with a similar retino-pineal neural pathway from the hypothalamus through the cervical spinal cord and SCG to the pineal gland. As such, lesions along this shared pathway, such as occur in neurologically complete injury to the cervical spinal cord (tetraplegia), would be predicted to result in simultaneous OSP and loss of pineal melatonin production. Loss of melatonin production may contribute to the pervasive sleep disruption observed in patients with tetraplegia. METHODS: We assessed the presence of OSP by photographic documentation of ptosis and pupillary dilation response to cocaine eye drops in 5 individuals with neurologically complete damage to their upper thoracic or lower cervical spinal cord. We correlated these results with an analysis of the pattern of melatonin production in these same individuals. RESULTS: Bilateral OSP was present in individuals with cervical spinal cord injury; each also lacked significant production of melatonin. No evidence of OSP was observed in the 2 individuals with thoracic spinal cord injury below the level of the oculosympathetic pathway. Both had normal circadian rhythms of melatonin production, with timing and amplitude of the rhythm within normal parameters. CONCLUSION: The presence of bilateral oculosympathetic paresis can be predictive of the complete loss of the nocturnal production of melatonin.

Adult↗

PubMed2006

Behavioral guides for sensory neurophysiology.

The study of natural behavior is important for understanding the coding schemes of sensory systems. The jamming avoidance response of the weakly electric fish Eigenmannia is an excellent example of a bottom-up approach, in which behavioral analyses guided neurophysiological studies. These studies started from the electroreceptive sense organs to the motor output consisting of pacemaker neurons. Going in the opposite direction, from the central nervous system to lower centers, is the characteristic of the top-down approach. Although this approach is perhaps more difficult than the bottom-up approach, it was successfully employed in the neuroethological analysis of sound localization in the barn owl. In the latter studies, high-order neurons selective for complex natural stimuli led to the discovery of neural pathways and networks responsible for the genesis of the stimulus selectivity. Comparison of Eigenmannia and barn owls, and their neural systems, has revealed similarities in network designs, such as parallel pathways and their convergence to produce stimulus selectivity necessary for detection of natural stimuli.

Animals↗

PubMed2000

Flicker sensitivity as a function of target area with and without temporal noise.

Flicker sensitivities (1-30 Hz) in foveal, photopic vision were measured as functions of stimulus area with and without strong external white temporal noise. Stimuli were circular, sinusoidally flickering sharp-edged spots of variable diameters (0.25-4 degrees ) but constant duration (2 s), surrounded by a uniform equiluminant field. The data was described with a model comprising (i) low-pass filtering in the retina (R), with a modulation transfer function (MTF) of a form derived from responses of cones; (ii) normalisation of the temporal luminance distribution by the average luminance; (iii) high-pass filtering by postreceptoral neural pathways (P), with an MTF proportional to temporal frequency; (iv) addition of internal white neural noise (N(i)); (v) integration over a spatial window; and (vi) detection by a suboptimal temporal matched filter of efficiency eta. In strong external noise, flicker sensitivity was independent of spot area. Without external noise, sensitivity increased with the square root of stimulus area (Piper's law) up to a critical area (A(c)), where it reaches a maximum level (S(max)). Both A(c) and eta were monotonic functions of temporal frequency (f), such that log A(c) increased and log eta decreased linearly with log f. Remarkably, the increase in spatial integration area and the decrease in efficiency were just balanced, so A(c)(f)eta(f) was invariant against f. Thus the bandpass characteristics of S(max)(f) directly reflected the composite effect of the distal filters R(f) and P(f). The temporal equivalent (N(it)) of internal neural noise (N(i)) decreased in inverse proportion to spot area up to A(c) and then stayed constant indicating that spatially homogeneous signals and noise are integrated over the same area.

Adult↗

PubMed2000

Vagal immune-to-brain communication: a visceral chemosensory pathway.

The immune system operates as a diffuse sensory system, detecting the presence of specific chemical constituents associated with dangerous micro-organisms, and then signalling the brain. In this way, immunosensation constitutes a chemosensory system. Several submodalities of this sensory system function as pathways conveying immune-related information, and can be classified as either primarily brain barrier associated or neural. The vagus nerve provides the major neural pathway identified to date. The initial chemosensory transduction events occur in immune cells, which respond to specific chemical components expressed by dangerous micro-organisms. These immune chemosensory cells release mediators, such as cytokines, to activate neural elements, including primary afferent neurons of the vagal sensory ganglia. Primary afferent activation initiates local reflexes (e.g. cardiovascular and gastrointestinal) that support host defense. In addition, at least three parallel pathways of ascending immune-related information activate specific components of the illness response. In this way, immunosensory systems represent highly organized and coherent pathways for activating host defense against infection.

Animals↗

PubMed1985

Effects of different fragments of the fibronectin molecule on latex bead translocation along neural crest migratory pathways.

Previous studies from this laboratory have utilized latex beads as probes of embryonic migratory pathways. After microinjection into embryos at the time of neural crest migration, uncoated latex polystyrene beads were found to translocate to ventral sites and to settle in the vicinity of endogenous neural crest derivatives. However, latex beads coated with fibronectin did not translocate ventrally, but remained associated with cells surrounding the implantation site. Fibronectin is a large glycoprotein with a variety of biological activities and multiple binding domains. Here, the binding activities which might be responsible for immobilization of the fibronectin-coated beads are examined. Latex beads were coated with three types of fragments of the fibronectin molecule representing different functional domains: (i) a 66-kDa fragment containing collagen-binding activity; (ii) a mixture of 45- and 32-kDa fragments containing heparin-binding activity; and (iii) a 120-kDa fragment containing cell-binding activity. The beads coated with fibronectin fragments were injected into the newly formed trunk somites of avian embryos. After injection, beads coated with either the heparin- or the collagen-binding domain translocated ventrally and distributed analogously to uncoated latex beads. In contrast, the majority of beads coated with the fibronectin cell-binding domain did not translocate but remained associated with dermamyotomal cells surrounding the injection site. The cell-binding fragment, however, was not as effective as the intact fibronectin molecule in preventing translocation of the beads. The results suggest that the cell-binding domain is primarily responsible for restriction of fibronectin beads from the ventral neural crest pathway. Because intact fibronectin is more effective at immobilizing beads than is the cell-binding fragment, other binding domains of fibronectin, more efficient coating with intact fibronectin, or crosslinking of intact fibronectin molecules may also play some role in immobilization of the beads at the implantation site.

Animals↗

PubMed2002

Visualising microglial activation in vivo.

In health, microglia reside as quiescent guardian cells ubiquitously, but isolated without any cell-cell contacts amongst themselves, throughout the normal CNS. In disease, however, they act as swift "sensors" for pathological events, including subtle ones without any obvious structural damage. Once activated, microglia show a territorially highly restricted involvement in the disease process. This property, peculiar to microglia, confers to them diagnostic value for the accurate spatial localisation of any active disease process, acute or chronic. In the brain, the isoquinoline PK11195, a ligand for the peripheral benzodiazepine binding site (PBBS), binds with relative cellular selectivity to activated, but not resting, microglia. Labelled with carbon-11, (R)-PK11195 and positron emission tomography (PET) have been used for the study of inflammatory and neurodegenerative brain disease in vivo. These studies demonstrate meaningfully distributed patterns of regional [(11)C](R)-PK11195 signal increases that correlate with clinically observed loss of function. Increased [(11)C](R)-PK11195 binding closely mirrors the histologically well-described activation of microglia in the penumbra of focal lesions, as well as in the distant, anterograde, and retrograde projection areas of the lesioned neural pathway. There is also some indication that in long-standing alterations of a neural network with persistent abnormal input, additional signals of glial activation may also emerge in transsynaptic areas. These data suggest that the injured brain is less static than commonly thought and shows subtle glial responses even in macroanatomically stable appearing regions. This implies that glial activation is not solely a sign of tissue destruction, but possibly of disease-induced adaptation or plasticity as well. Whilst further technological and methodological advances are necessary to achieve routine clinical value and feasibility, a systematic attempt to image glial cells in vivo is likely to furnish valuable information on the cellular pathology of CNS diseases and their progression within the distributed neural architecture of the brain.

Animals↗

PubMed2001

The glossopharyngeal nerve as a novel pathway in immune-to-brain communication: relevance to neuroimmune surveillance of the oral cavity.

Glossopharyngeal afferents may be the neural channel by which immune challenge of the posterior oral cavity conveys information to the brain. If this is the case, then bilateral transection of the glossopharyngeal nerves (GLOx) should disrupt this communication. Injection of lipopolysaccharide (LPS) or interleukin (IL)-1beta into the soft palate (ISP) of sham-operated rats induced a dose-related febrile response. GLOx significantly attenuated the febrile response induced by ISP injection of both LPS and IL-1beta. In contrast, GLOx did not affect the febrile response when LPS or IL-1beta were injected intraperitoneally, indicating that the effect of GLOx is not systemic. These results provide experimental evidence for a novel neural pathway for immune-to-brain communication.

Afferent Pathways↗

PubMed1975

The septum: neural systems involved in eating, drinking, irritability, nuricide, copulation, and activity in rats.

Eating, drinking, irritability, muricide, and copulation were measured in 45 male rats before and after one of three coronal knife cuts in the septal region or a control operation; in addition, activity was measured postoperatively. (a) Cuts posteroventral to the septum resulted in slight hypophagia, marked hyperdipsia, irritability, asexuality, and decrease in activity. (b) Cuts of the fornix resulted only in slight decrease in activity. (c) Cuts through the anterior septum resulted in irritability, slight hyposexuality, and slight decrease in activity. No significant correlations between the various behavioral effects were found. It was suggested that the neural pathways mediating eating, drinking, irritability, muricide, copulation, and activity are relatively distinct and that neural activity in the septal region probably does not influence behavior in any unitary fashion.

Aggression↗