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PubMedDate not supplied

Electrophysiological characteristics of crayfish inhibitory.

Parameters of IPSPs and characteristics of inhibitory neuromuscular transmission in the dactylopodite-opener muscle of the crayfish pincer at various rhythms of activity were studied by intracellular recording. The presynaptic conduction nature of high-frequency (pessimal) blockade of the inhibitory system was demonstrated. Transformation of the rhythm of stimulation correlated with a decrease in conduction velocity along the inhibitory axon and (or) its branches. At high frequencies of stimulation the mean quantum composition of IPSPs of the potentiation plateau before the beginning of rhythm transformation was lower than at lower frequencies. No signs of exhaustion of mediator reserves were found in the course of high-frequency activity. It is concluded that the mechanism of secretion of inhibitory mediator is more reliable than the function of conduction of the presynaptic nervous impulse. The possible functional significance of the comparatively low reliability of function of crustacean nerve fibers is discussed.

Animals↗
PubMed1994

Rostro-caudal distribution of reticulospinal projections from different brainstem nuclei in the lamprey.

The reticulospinal (RS) system in the lamprey is responsible for the control of locomotion, postural corrections and steering. To perform these functions, the RS system has to affect different muscular compartments along the body axis selectively. In this study, the possibility that RS neurones in different nuclei may project to different parts of the spinal cord, was investigated. The rostro-caudal extent of single RS axons was defined by stimulating them antidromically while recording from their cell body. All recorded mesencephalic RS neurones projected to the caudal tip of the spinal cord. Of the rhombencephalic RS neurones, 26% of the recorded neurones did not reach the caudalmost fourth of the spinal cord and this proportion varied between the anterior (18%), middle (17%) and posterior (36%) rhombencephalic reticular nuclei. For these RS axons, the level of termination covered the whole rostro-caudal extent of the spinal cord. No correlation was found between the length of an axon and its conduction velocity or between the length of an axon and the rostro-caudal position of its cell body in the nuclei.

Animals↗
PubMed1988

Comparisons of connectivity and conduction velocities for medial forebrain bundle fibers subserving stimulation-induced feeding and brain stimulation reward.

A behavioral adaptation of the paired-pulse collision technique was used to determine whether the same medial forebrain bundle (MFB) fibers of passage mediate brain stimulation reward (BSR) and stimulation-induced feeding (SIF) induced by lateral hypothalamic and ventral tegmental electrical stimulation. Step-functions relating second-pulse effectiveness to interpulse interval suggested connectivity between the directly activated SIF fibers at these two stimulation sites were seen in 4 animals; these data indicate that SIF, like BSR, is mediated, at least in part, by long-axon MFB fibers. In the two animals that could be tested in both paradigms, similar effects were seen in BSR tests; this suggests that either the same fibers or fibers with remarkably similar conduction velocities and medial-lateral and dorsal-ventral alignment contribute to the two behaviors.

Animals↗
PubMed1996

A comparison of the local anesthetic effects of meperidine, fentanyl, and sufentanil on dorsal root axons.

The local anesthetic effects of opioids have been demonstrated in both clinical and laboratory studies. Clinically, both meperidine and sufentanil can produce segmental sensory anesthesia. However, previous studies of the effects of opioids on nerve conduction have all made use of peripheral nerve preparations and yielded conflicting results. In the present study we describe the local anesthetic effects of phenylpiperidine opioids on individual dorsal root axons, the probable target for intrathecal local anesthetics. Dorsal roots were removed from anesthetized adult male rats and maintained in vitro. Standard single fiber recording techniques were used to isolate activity in the individual axons. Drug exposure was accomplished by perfusing the isolated dorsal root with an artificial cerebrospinal fluid containing the study drug at a clinically relevant concentration. Steady-state drug effects were measured after 15-30 min of exposure and compared to control measurements in the same preparation. Meperidine (705 microM) blocked conduction in 61.5% of 39 myelinated and unmyelinated axons, and significantly reduced conduction velocity in the remaining unblocked axons. These effects were not naloxone reversible. Fentanyl (0.6 microM and 3 microM) and sufentanil (1.04 microM) failed to affect the nerve conduction in any dorsal root axon. The discrepancy between laboratory and clinical observations is discussed. We suggest that the site of conduction block may occur at the proximal end of the dorsal root as it passes through the dorsal root entry zone, an anatomically unique segment of the primary sensory pathway with decreased conduction safety for action potential propagation.

Action Potentials↗
PubMed1983

Axon conduction failure under in vivo conditions in crayfish.

Action potential discharge in an identified axon was recorded in 'intact' crayfish, and conduction block occurred during prolonged high-frequency activity. These in vivo recordings were also used to trigger stimulation of the same axon in vitro; conduction block occurred during high-frequency bursts in small terminal branches. Quantal release was distributed in a bimodal fashion, with numerous failures, due to these occurrences of conduction block. These results indicate that conduction block may occur in intact animals and that it may also cause selective recruitment of specific nerve terminals during normal behaviour.

Action Potentials↗
PubMed1993

Uniform olivocerebellar conduction time underlies Purkinje cell complex spike synchronicity in the rat cerebellum.

1. The issue of isochronicity of olivocerebellar fibre conduction time as a basis for synchronizing complex spike activity in cerebellar Purkinje cells has been addressed by latency measurement, multiple-electrode recording and Phaseolus vulgaris leucoagglutinin (PHA-L) tracing of climbing fibres in the adult rat. 2. The conduction time of the olivocerebellar fibres was measured by recording Purkinje cell complex spike (CS) responses from various areas of the cerebellum. The CSs were evoked by stimulating the olivocerebellar fibres near the inferior olive. In spite of a difference in length, as determined directly by light microscopy, the conduction times of different climbing fibres were quite uniform, 3.98 +/- 0.36 ms (mean +/- S.D., n = 660). 3. Multiple-electrode recording of spontaneous Purkinje cell CS activity was employed to study the spatial extent of CS synchronicity in the cerebellar cortex. Recordings of CS were obtained from Purkinje cells located on the surface and along the walls of lobule crus 2a. The rostrocaudal band-like distribution of simultaneous (within 1 ms) CS activity in Purkinje cells extended down the sides of the cerebellar folia to the deepest areas recorded (1.6-2.6 mm deep). As shown in previous experiments, the distribution of simultaneous CS activity did not extend significantly (500 microns) in the mediolateral axis of the cerebellar cortex. 4. In two animals a detailed determination of the length of the olivocerebellar fibre bundles was performed by staining the fibres with PHA-L injected into the contralateral inferior olive. This measurement included fibre bundles terminating in twenty-six different areas, ranging from the tops of the various folia to the bottoms of the fissures in both the hemisphere and the vermis. There was a 47.5% difference between the length of the longest measured fibre bundle (15.8 mm, terminating in lobule 6b, zone A) and the length of the shortest measured fibre bundle (8.3 mm, terminating in the cortex at the base of the primary fissure, zone D), after correction for tissue shrinkage. To attain an isochronous conduction time the conduction velocities for these two fibre bundles were calculated to be 4.22 m/s and 2.37 m/s, respectively. 5. By interpolating between measured points a simple formula was derived to estimate the average length of olivocerebellar fibres terminating in any given area of the cerebellar cortex, excluding the paraflocculus, the flocculus and the most lateral regions of the hemisphere. 6. We investigated the most likely mechanisms by which conduction velocity variations with length could result in global isochronicity.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Effects of low-power laser irradiation on multiple unit discharges induced by noxious stimuli in the anesthetized rabbit.

This study discusses the effects of low-power laser irradiation upon multiple unit discharges within a peripheral nerve that were induced by a noxious stimulation in anesthetized rabbits. Responding to a pinch stimulation of plantar skin, transitory increase of neuronal discharges was induced in the sural nerve. This was reduced within a minute, and persistent increases, which continued during a period of the stimulation, occurred. These increases became significantly smaller than the control value during a low-power laser irradiation that was applied to the exposed sural nerve distal to the recording site. These results suggested an inhibitory effect of low-power laser irradiation on the impulse conduction within a peripheral nerve. Possible analgesic effects of low-power irradiation are discussed.

Animals↗