1,721,012 research outputs found
Only minor spinal motor reflex effects from feline group IV muscle nociceptors
No full textThe contribution of group III and IV muscle nociceptors activated by injection of KCl or bradykinin into the muscle artery (i.a.) of the gastrocnemius-soleus muscle to spinal motor reflex pathways was investigated in high spinal cats. Group I-III fibres were completely blocked by TTX, leaving group IV-fibre conduction intact. Thus, effects from i.a. KCl or bradykinin injection persisting after TTX were attributed to TTX resistant group IV fibres while the contribution of group III fibres was approximately defined by the difference between those effects and the control effects before TTX. Confirming former findings the chemical activation of group III and IV muscle afferents induced distinct reflex facilitation of the flexor posterior biceps semitendinosus and inhibition of the extensor quadriceps. After the block of all myelinated fibres by TTX the same stimuli induced only minor reflex effects mediated by the persistently conducting TTX resistant group IV afferents. It is concluded that the main functional meaning of group IV muscle afferents, which respond preferentially with a higher threshold to mechanical stimuli, is probably less related to reflex motor control than that of group III afferents. (C) 2002 Elsevier Science Ireland Ltd. and the Japan Neuroscience Society. All rights reserved
Changes in Tetrodotoxin-Resistant C-Fibre Activity during Fatiguing Isometric Contractions in the Rat
No full textIt is by now well established that tetrodotoxin-resistant (TTX-R) afferent fibres from muscle in the rat exhibit a multisensitive profile, including nociception. TTX-R afferent fibres play an important role in motor control, via spinal and supraspinal loops, but their activation and function during muscle exercise and fatigue are still unknown. Therefore, the specific effect of isometric fatiguing muscle contraction on the responsiveness of TTX-R C-fibres has been investigated in this study. To quantify the TTX-R afferent input we recorded the cord dorsum potential (CDP), which is the result of the electrical fields set up within the spinal cord by the depolarisation of the interneurons located in the dorsal horn, activated by an incoming volley of TTX-R muscle afferents. The changes in TTX-R CDP size before, during and after fatiguing electrical stimulation of the gastrocnemius-soleus (GS) muscle have been taken as a measure of TTX-R C-unit activation. At the end of the fatiguing protocol, following an exponential drop in force, TTX-R CDP area decreased in the majority of trials (9/14) to 0.75 +/- 0.03% (mean +/- SEM) of the pre-fatigue value. Recovery to the control size of the TTX-R CDP was incomplete after 10 min. Furthermore, fatiguing trials could sensitise a fraction of the TTX-R C-fibres responding to muscle pinch. The results suggest a long-lasting activation of the TTX-R muscle afferents after fatiguing stimulation. The role of this behaviour in chronic muscle fatigue in connection with pain development is discussed. Accumulation of metabolites released into the interstitium during fatiguing stimulation might be one of the reasons underlying the C-fibres' long-lasting activation
Rhythmic phrenic, intercostal and sympathetic activity in relation to limb and trunk motor activity in spinal cats
No full textDuring L-DOPA-induced fictive spinal locomotion rhythmic activities in nerves to internal intercostal and external oblique abdominal muscles and in phrenic and sympathetic nerves were observed which were always coordinated with locomotor activity in forelimb and hindlimb muscle nerves. A periodicity with longer lasting tonic phases could be induced by cutaneous nerve stimulation or asphyxia. This activity was observed in limb motor nerves as well as in respiratory motor and sympathetic nerves. A slow independent activity of the phrenic and intercostal nerves or the sympathetic nerves, which could be related to a normal respiratory rhythm or independent sympathetic rhythms was not observed. The findings indicate that during fictive spinal locomotion the activity of spinal rhythm generators for locomotion also projects onto respiratory and sympathetic spinal neurotics. (C) 2003 Elsevier Science Ireland Ltd and the Japan Neuroscience Society. All rights reserved
In Vivo Measurement of Conduction Velocities in Afferent and Efferent Nerve Fibre Groups in Mice
No full textElectrophysiological investigations in mice, particularly with altered myelination, require reference data of the nerve conduction velocity (CV). CVs of different fibre groups were determined in the hindlimb of anaesthetized adult mice. Differentiation between afferent and efferent fibres was performed by recording at dorsal roots and stimulating at ventral roots, respectively. Correspondingly, recording or stimulation was performed at peripheral hindlimb nerves. Stimulation was performed with graded strength to differentiate between fibre groups. CVs of the same fibre groups were different in different nerves of the hindlimb. CVs for motor fibres were for the tibial nerve (Tib) 38.5 +/- 4.0 m/s (A gamma: 16.7 +/- 3.0 m/s), the sural nerve (Sur) 39.3 +/- 3.1 m/s (12.0 +/- 0.8 m/s) and the common peroneal nerve (Per) 46.7 +/- 4.7 m/s (22.2 +/- 4.4 m/s). CVs for group I afferents were 47.4 +/- 3.1 m/s (Tib), 43.8 +/- 3.8 m/s (Sur), 55.2 +/- 6.1 m/s (Per) and 42.9 +/- 4.3 m/s for the posterior biceps (PB). CVs of higher threshold afferents, presumably muscle and cutaneous, cover a broad range and do not really exhibit nerve specific differences. Ranges are for group II 22-38 m/s, for group III 9-19 m/s, and for group IV 0.8-0.9 m/s. Incontrovertible evidence was found for the presence of motor fibres in the sural nerve. The results are useful as references for further electrophysiological investigations particularly in genetically modified mice with myelination changes.Deutsche Forschungsgemeinschaft [SCHO 37/16
In Vivo Measurement of Conduction Velocities in Afferent and Efferent Nerve Fibre Groups in Mice
No full textElectrophysiological investigations in mice, particularly with altered myelination, require reference data of the nerve conduction velocity (CV). CVs of different fibre groups were determined in the hindlimb of anaesthetized adult mice. Differentiation between afferent and efferent fibres was performed by recording at dorsal roots and stimulating at ventral roots, respectively. Correspondingly, recording or stimulation was performed at peripheral hindlimb nerves. Stimulation was performed with graded strength to differentiate between fibre groups. CVs of the same fibre groups were different in different nerves of the hindlimb. CVs for motor fibres were for the tibial nerve (Tib) 38.5 +/- 4.0 m/s (A gamma: 16.7 +/- 3.0 m/s), the sural nerve (Sur) 39.3 +/- 3.1 m/s (12.0 +/- 0.8 m/s) and the common peroneal nerve (Per) 46.7 +/- 4.7 m/s (22.2 +/- 4.4 m/s). CVs for group I afferents were 47.4 +/- 3.1 m/s (Tib), 43.8 +/- 3.8 m/s (Sur), 55.2 +/- 6.1 m/s (Per) and 42.9 +/- 4.3 m/s for the posterior biceps (PB). CVs of higher threshold afferents, presumably muscle and cutaneous, cover a broad range and do not really exhibit nerve specific differences. Ranges are for group II 22-38 m/s, for group III 9-19 m/s, and for group IV 0.8-0.9 m/s. Incontrovertible evidence was found for the presence of motor fibres in the sural nerve. The results are useful as references for further electrophysiological investigations particularly in genetically modified mice with myelination changes.Deutsche Forschungsgemeinschaft [SCHO 37/16
Opioidergic action on nociceptive reflex components evoked by TTX-resistant C-fibres in the cat
No full textRole of L-DOPA in Spinal Nociceptive Reflex Activity: Higher Sensitivity of A delta Versus C Fibre-Evoked Nociceptive Reflexes to L-DOPA
No full textThe role of L-DOPA in spinal nociceptive reflex activity has been re-evaluated. In high spinal cats, with supraspinal loops being excluded, the onset of reflex facilitation induced by noxious radiant heat is delayed after injection of L-DOPA by 4 to 10 s, i.e. the early component of nociceptive reflex facilitation is blocked, while the late component persisted. Further investigations have shown that the early component of reflex facilitation induced by noxious radiant heat is mediated by A delta-fibres and the late component by C-fibres. Therefore, it can be assumed that L-DOPA, like opioids, preferentially blocks the transmission in nociceptive reflex pathways from A delta-fibres.Deutsche Forschungsgemeinschaft [SCHO 37/16
Opioidergic action on nociceptive reflex components evoked by TTX-resistant C-fibres in the cat
No full textRole of L-DOPA in Spinal Nociceptive Reflex Activity: Higher Sensitivity of A delta Versus C Fibre-Evoked Nociceptive Reflexes to L-DOPA
No full textThe role of L-DOPA in spinal nociceptive reflex activity has been re-evaluated. In high spinal cats, with supraspinal loops being excluded, the onset of reflex facilitation induced by noxious radiant heat is delayed after injection of L-DOPA by 4 to 10 s, i.e. the early component of nociceptive reflex facilitation is blocked, while the late component persisted. Further investigations have shown that the early component of reflex facilitation induced by noxious radiant heat is mediated by A delta-fibres and the late component by C-fibres. Therefore, it can be assumed that L-DOPA, like opioids, preferentially blocks the transmission in nociceptive reflex pathways from A delta-fibres.Deutsche Forschungsgemeinschaft [SCHO 37/16
Spinal motor actions of the μ-opioid receptor agonist DAMGO in the cat
No full textFor further evaluation of opioidergic spinal motor functions the action of the mu-opioid receptor agonist DAMGO was tested on transmission in different non-nociceptive and nociceptive spinal reflex pathways from flexor reflex afferents (FRA), and in non-FRA reflex pathways in spinal cats. The action of DAMGO was complex, not following a simple pattern with selective depression of nociceptive pathways compared to non-nociceptive ones. Monosynaptic reflexes of the flexor posterior biceps semitendinosus (PBSt) and transmission in nociceptive as well as non-nociceptive excitatory FRA pathways to PBSt were depressed, while the specific excitatory nociceptive non-FRA pathway from the central foot pad to foot extensors was mainly not depressed but rather facilitated by DAMGO. DAMGO caused a facilitation of monosynaptic reflexes to the extensor gastrocnemius soleus (GS) and partly a reversal of inhibitory to excitatory conditioning effects from cutaneous afferents to GS. FRA interneurones could show either an increase or a cessation of their spontaneous activity, but responsiveness to nociceptive and non-nociceptive afferent activation was blocked by DAMGO. The main DAMGO action is generated via interneuronal systems rather than on motoneurones themselves. The results indicate that opioidergic spinal functions are extensively involved in spinal motor control exceeding a mere suppression of nociceptive motor withdrawal reactions. (C) 2011 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.Deutsche Forschungsgemeinschaft [SCHO 37/16
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