Journal of neurophysiology
-
1. Cutaneous reflex responses were elicited during human running (8 km/h) on a treadmill by electrical stimulation of the sural nerve at the ankle. Stimulus trains (5 pulses of 1 ms at 200 Hz) at three nonnociceptive intensities, which were 1.5, 2.0, and 2.5 times perception threshold (PT), were delivered at 16 phases of the step cycle. ⋯ These are present rather with respect to the phase of the corresponding leg than with respect to the phase of the stimulated leg. Both observations suggest that the phase-dependent reflex modulation is controlled separately in the ipsilateral and contralateral legs. 7. The response simultaneity in all investigated muscles supports the notion of a coordinated cutaneous interlimb reflex during human running.(ABSTRACT TRUNCATED AT 400 WORDS)
-
1. We recently studied the spatial representation of angular motion signals in rhesus monkeys by examining the orientation of postrotatory vestibuloocular responses during tilt of the head and body relative to gravity after constant-velocity rotation about an earth-vertical axis. We have reported that low-frequency angular motion signals in the vestibuloocular reflex (VOR) of rhesus monkeys are spatially transformed such that they remain invariant relative to gravity. ⋯ The dynamic properties of the vertical VOR in the lesioned animals, on the other hand, were indistinguishable from those in controls. 4. The cerebellar lesions affected the spatial organization of the horizontal and vertical/torsional systems in a differential way. Inertial transformation of lateral canal activity was only partially affected.(ABSTRACT TRUNCATED AT 400 WORDS)
-
1. We studied the effects of a chronic nerve constriction on the evoked responses in dorsal root fibers in the rat to norepinephrine and to thermal stimuli applied either to the dorsal root ganglion (DRG) or the site of nerve injury. We recorded a total of 59 C fibers, 15 A delta-fibers, and 46 A beta-fibers from the L5 dorsal root of the rats 11-52 days after a loose ligation of the ipsilateral sciatic nerve. ⋯ In contrast, the SA of a minority of C fibers and A beta-fibers was depressed during sympathetic stimulation. 6. After a chronic nerve constriction the DRG becomes a source of abnormal activity modulated by sympathetically released norepinephrine acting on alpha 2 receptors in DRG somata. This neuropathic activity may contribute to cutaneous pain and hyperalgesia.
-
1. The effects of culturing hypothalamic neurons in glutamate receptor antagonists were studied with fura-2 Ca2+ digital imaging of groups of synaptically coupled neurons. Removal of D-2-amino-5-phosphonovalerate (AP5) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) from cultures chronically blocked for periods of 14-188 days caused a dramatic increase in neuronal Ca2+ to abnormally high levels 5- to- 10 fold greater than the normal intracellular levels of 50-100 nM. ⋯ Relative to control cultures of the same period in vitro, chronically blocked neurons showed an enhanced Ca2+ influx when stimulated with the glutamate receptor agonists kainate (+70%), NMDA (+62%), or glutamate (+34%) in the presence of tetrodoxin. When the data from control and chronically blocked cultures stimulated with glutamate receptor agonists were pooled, without exception all the smallest responses were found in the control neurons. Compared with controls, chronically blocked neurons showed an exaggerated response to glutamate in the presence of nimodipine, indicating that Ca2+ hyperexcitability was not due to changes in voltage activated L-type Ca2+ channels.(ABSTRACT TRUNCATED AT 400 WORDS)
-
1. The effects of sympathetic stimulation and close arterial injection of norepinephrine were tested on cutaneous myelinated-fiber (A delta) mechanical nociceptors [high-threshold mechanoreceptors-(MyHTMs)] from normal and from partially transsected nerves. 2. Neither sympathetic stimulation nor close arterial injection of norepinephrine (200 ng) excited MyHTMs (18) recorded from the uninjured great auricular nerve of adult rabbits. 3. ⋯ Four MyHTMs recorded from the injured nerves were excited by sympathetic stimulation and/or norepinephrine injection but only one gave more than two impulses within 60 s to either form of stimulation. 5. The meagerness of the sympathetic and adrenergic excitation of MyHTMs after nerve injury contrasts with that observed under similar conditions for C-fiber polymodal nociceptors. Therefore, induction of adrenergic responsiveness in nociceptors after partial denervation in cutaneous MyHTMs appears to be less important for mechanisms related to pathogenic pain than alterations in certain C-fiber nociceptors.