Spinal interleukin-1beta reduces inflammatory pain.

Inflammation or injury often lead to chronic pain states such as hyperalgesia where the perception of a normally painful stimulus is significantly exaggerated. Interleukin-1beta (IL-1beta) is a cytokine that is an important mediator of the inflammatory response. In addition, IL-1beta has been implicated in the modulation of pain transmission in both the peripheral and central nervous systems. We evaluated the spinal effect of this cytokine in the presence and absence of a peripheral carrageenan inflammation in rats since the spinal cord is a major region of the central nervous system in which nociceptive input is processed and modulated. Our results indicate that intrathecal IL-1beta has no effect on the latency of paw withdrawal in response to a noxious thermal stimuluation in normal rats. In contrast, we have observed that IL-1beta produces significant antinociception when administered intrathecally in rats with peripheral inflammation (carrageenan model). The IL-1beta effect appears to be selective as it is reversed when IL-1beta is administered in the presence of an IL-1beta neutralizing antibody. We evaluated some putative mechanisms of this IL-1beta-mediated antinociception and found it to be non-opioid-dependent. Collectively, these data indicate that intrathecal IL-1beta has no effect on the processing of thermal nociceptive information in the absence of a peripheral inflammation. Therefore, the response to acute pain remains normal in these rats. In contrast, IL-1beta is antinociceptive when applied spinally during inflammation. These results indicate that IL-1beta reduces inflammatory hyperalgesia while sparing the protective functions of acute pain. This study offers new insights into the role of IL-1beta and nociceptive processing at the level of the spinal cord and suggests that development of IL-1beta agonists may be an alternative to opiate based therapies in the treatment of inflammatory pain.

Biomechanics of stretch-induced beading.

To account for the beading of myelinated fibers, and axons of unmyelinated nerve fibers as well of neurites of cultured dorsal root ganglia caused by mild stretching, a model is presented. In this model, membrane tension and hydrostatic pressure are the basic factors responsible for axonal constriction, which causes the movement of axonal fluid from the constricted regions into the adjoining axon, there giving rise to the beading expansions. Beading ranges from a mild undulation, with the smallest degree of stretch, to more globular expansions and narrow intervening constrictions as stretch is increased: the degree of constriction is physically limited by the compaction of the cytoskeleton within the axons. The model is a general one, encompassing the possibility that the membrane skeleton, composed mainly of spectrin and actin associated with the inner face of the axolemma, could be involved in bringing about the constrictions and beading.

Semaphorin III can repulse and inhibit adult sensory afferents in vivo.

During development, semaphorins (collapsin, fasciclin) mediate repulsive and inhibitory guidance of neurons. Semaphorin III, a secretable member of this family, is expressed by the ventral spinal cord at the time corresponding to projection of sensory afferents from the dorsal root ganglion (DRG) into the spinal cord. The inhibitory effect of E14 ventral cord is active only on nerve growth factor (NGF)-responsive sensory afferents (small-diameter A-delta and C fibers subserving sensations of temperature and pain). Similarly, COS cells secreting recombinant semaphorin III are able to selectively repel DRG afferents whose growth is stimulated by NGF and not NT-3. However, it is not known whether these molecules can exert a functional role in the fully developed adult peripheral nervous system. In this study, we demonstrated that gene gun transfection and production of semaphorin III in corneal epithelial cells in adult rabbits in vivo can cause repulsion of established A-delta and C fiber trigeminal sensory afferents. In addition, it is shown that, following epithelial wounding and denervation, semaphorin III is able to inhibit collateral nerve sprouts from innervating the reepithelialized tissue. These findings are significant in that they provide direct evidence that small-diameter adult sensory neurons retain the ability to respond to semaphorin III. In addition, the corneal gene gun technique may be generally used to study the in vivo effects of neural growth modulators by quantifying the amount of sensory nerve growth.

Controlled gene gun delivery and expression of DNA within the cornea.

Selective delivery of genes to ocular tissues in vivo has been a long sought after goal for potential gene therapy of ocular disease. The gene gun was considered for this purpose because of its ability to focally transfer DNA to cells through gold microparticles coated with DNA. Through experimentation, we optimized a technique that allows focal delivery and expression of a plasmid encoding green fluorescent protein in the corneal epithelium 100% of the time. Though the corneal epithelium has a delicate structure, this introduction was not associated with any corneal or ocular damage and did not produce any apparent ocular irritation. These findings demonstrate the utility of gene gun delivery of DNA to selected ocular tissues for potential experimental and therapeutic purposes.

Biophysical and functional consequences of receptor-mediated nerve fiber transformation.

Stimulation of the nervous system by substance P, a G protein-coupled receptor, and subsequent receptor internalization causes dendrites to change their shape from homogeneous cylinders to a heterogeneous string of swollen varicosities (beads) connected by thin segments. In this paper we have analyzed this phenomenon and propose quantitative mechanisms to explain this type of physical shape transformation. We developed a mathematical solution to describe the relationship between the initial radius of a cylindrical nerve fiber and the average radii of the subsequently created varicosities and connecting segments, as well as the periodicity of the varicosities along the nerve fiber. Theoretical predictions are in good agreement with our own and published experimental data from dorsal root ganglion neurons, spinal cord, and brain. Modeling the electrical properties of these beaded fibers has led to an understanding of the functional biophysical consequences of nerve fiber transformation. Several hypotheses for how this shape transformation can be used to process information within the nervous system have been put forth.

Electrical double layers at the oil/water interface.

This review presents the historical development and current status of the theory of the electrical double layer at a liquid/liquid interface. It gives rigorous thermodynamic definitions of all basic concepts related to liquid interfaces and to the electrical double layer. The difference between the surface of a solid electrode and the interface of two immiscible electrolyte solutions (ITIES) is analyzed in connection to their electrical properties. The most important classical relationships for the electrical double layer are presented and critically discussed. The generalized adsorption isotherm is derived. After a short review of the classical Gouy-Chapman and Verwey-Niessen models, more recent developments of the double layer theory are presented. These include effects of variable dielectric permittivity, nonlocal electrostatics, hydration forces, the modified Poisson-Boltzmann equation and the ion-dipole plasma. The relative merits of different theories are estimated by comparing them with computer simulation of the ITIES and electrical double layer. Special attention is given to the structure of ITIES and its variation due to adsorption of ions and amphiphilic molecules.

CGRP increases the rate of corneal re-epithelialization in an in vitro whole mount preparation.

A number of studies have localized CGRP to nerves in the cornea and iris, and it is thought that CGRP, along with other neuropeptides, is involved in pain sensation. It is also possible that CGRP could mediate trophic influences between nerve endings and corneal epithelium. This investigation utilized an in vitro rabbit corneal whole mount preparation to study the effect of topical 2.5 microM CGRP application on epithelial wound healing rates of 5 mm diameter epithelial wounds. CGRP (2.5 microM) was applied topically to 5 mm epithelial wounds at 0, 4, 16, 20, 24, 28, 40, 44, 48, 52, 56, 64, 68, and 72 hours after wounding and healing was visualized with fluorescein. CGRP was found to increase the epithelial wound healing rate by 25%, from 51 +/- 3 microns/hr for the control corneas, to 64 +/- 2 microns/hr for CGRP-treated corneas (mean +/- standard error, n = 10). Histological examination of the corneas following healing showed that the epithelium of the CGRP-treated corneas healed in a similar manner as in the control corneas. These findings may have clinical utility for the understanding and treatment of corneal and other epithelial wounds.

Force-sensing microprobe for precise stimulation of mechanosensitive tissues.

Quantitative study of the transduction mechanisms in mechanically sensitive nerve terminals has been impeded by the lack of instrumentation with which to generate precisely controlled, physically localized mechanical stimuli. We have developed high-resolution force sensing mechanical microprobes for use in the characterization of such nerve terminals. This paper describes their design, fabrication, and testing. A microprobe is comprised of a 0.5- to 2-mm long silicon cantilever beam projecting from a larger supporting silicon substrate. Acting as the variable leg of a Wheatstone bridge circuit, a piezoresistive polysilicon element located at the base of the beam is used to measure the stimulation force applied at the tip. The microprobes exhibit a stable, linear relationship between the stimulation force and the resulting output voltage signal. Stimulation forces up to 3 mN have been generated with a measurement resolution of 10 microN. These microprobes have been used as the force sensing element of a closed loop feedback-controlled stimulation system capable of stimulating the mechanoreceptive nerve terminals of the rabbit corneal epithelium.

A feedback controlled silicon microprobe for quantitative mechanical stimulation of nerve and tissue.

The ability to apply and control the force and force velocity of mechanical stimulation is essential for the study of mechanoelectric transduction and adaptation processes. Silicon micromachining technology was used to produce miniature (20-70 microns wide) mechanical microprobes. Passive polysilicon, piezoresistive, force sensing elements were deposited onto the boron-doped epitaxial silicon and the individual devices were chemically etched from the bulk wafer. These microprobes display a linear force versus output voltage relationship. Stimulation forces up to 2 mN can be generated with a measurement resolution of 1.5 microN. The probes were mounted onto circuit board holders and their output sent to a proportional-integral controller which drives an electromagnetic actuator. By using this force-feedback control circuit coupled to a PC it is possible to define any stimulus wave form pattern and independently control and measure the actual stimulus force and velocity. A computer controlled 3-axis stepper motor (0.025 micron step capability) manipulator is used to position the silicon microprobe-actuator assembly relative to the mechanoreceptive field. Sensor feedback control coupled to the 3-axis stepper motor manipulator allows automatic touchdown control and/or preloading of the probe prior to stimulation. Three-dimensional topographic manipulator feedback position control allows automated receptive field mapping.

Altered thermal responsiveness during regeneration of corneal cold fibers.

1. To date, there has been no quantitative, systematic, study of the electrophysiology of regenerating cold receptors. This study, therefore, examines the changes in cold-receptor neural activity following a circular wound (5 mm dia, 200 microns deep) on the surface of the rabbit cornea. This is a well studied wounding model, in which neural regeneration has been anatomically quantified. 2. Extracellular recordings were obtained from a total of 90 single cold fibers, at 1, 3, 10, 20, or 30 days following wounding. The adapting temperature was 35 degrees C in all experiments. Thermal sensitivity for each fiber was determined by using a series of temperature steps, 0.2 degree C ranging from 35 to 34 degrees C, and 2 degrees C steps ranging from 35 to 24 degrees C. The rate of temperature change ranged from 0.2 to 1 degree C/s. 3. At the adapting temperature, the tonic activity of the regenerating cold-fibers was not significantly different from normals. Conduction velocities for regenerating cold-fibers were slower on day 1 postwounding compared with normal fibers, 0.59 +/- 0.04 and 0.75 +/- 0.04 (SE) M/s, respectively, however, were within the normal range by day 30 postwounding, 0.72 +/- 0.06 M/s. 4. On day 1, sprouting fibers showed decreased responsiveness to cooling (P < 0.05). At days 3 and 10 postwounding, action potential rates in response to cooling were enhanced by 180-200% of normal (P < 0.05) and returned to preinjury values by 20 to 30 days postwounding.(ABSTRACT TRUNCATED AT 250 WORDS)