The Journal of physiology
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The Journal of physiology · Apr 1991
Unresponsive afferent nerve fibres in the sural nerve of the rat.
1. The proportion of primary afferent nerve fibres in a skin nerve of the rat that responded or failed to respond to mechanical or thermal stimulation of the skin in the noxious and non-noxious range was analysed. 2. Activity of afferent nerve fibres was recorded from the dorsal roots. ⋯ Some of these units had mechanical thresholds as low as 64 mN (tested with calibrated von Frey hairs), or thermal thresholds down to 42 degrees C. 7. Two of the ten C units which became responsive in the course of an experiment later lost their responsiveness again. On the other hand, two of the C units which were initially responsive to noxious heat and/or noxious mechanical stimuli became completely unresponsive after repetitive stimulation, whereas one unit initially only responding to noxious heat became responsive to mechanical stimuli, suggesting that mechanical and heat responsiveness may be separately gained or lost by sensory C fibres.(ABSTRACT TRUNCATED AT 400 WORDS)
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The Journal of physiology · Mar 1991
Signalling of a step-like intensity change of noxious mechanical stimuli by dorsal horn neurones in the rat spinal cord.
1. Single-unit extracellular recordings were made from thirty-one dorsal horn neurones in the sacral spinal cord of barbiturate-anaesthetized rats. Each neurone was tested with four noxious mechanical pinches applied to its receptive field on the tail. ⋯ These results demonstrate that neurones with similar input properties and location are not necessarily a homogeneous group in terms of their processing of nociceptive stimuli. Moreover, they suggest that subgroups of both class 2 and class 3 and of superficial and deep dorsal horn neurones contribute to the different components of a nociceptive response. 7. We propose that the output and projection target of a particular dorsal horn neurone are more important than its afferent input in determining its role in nociceptive processing.
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The Journal of physiology · Jan 1991
Task-dependent changes in the responses to low-threshold cutaneous afferent volleys in the human lower limb.
1. In seven human subjects who were standing without support the sural nerves were stimulated electrically using trains of non-painful stimuli (five pulses at 300 Hz), designed to activate afferents from cutaneous mechanoreceptors. The reflex effects of the stimulus train on different muscles of the ipsilateral and contralateral legs were sought in post-stimulus averages of rectified EMG. ⋯ These changes in reflex pattern could not be explained by different levels of background contraction. 5. It is concluded that cutaneous mechanoreceptors of the foot have widespread reflex actions on muscles throughout both limbs, particularly the ipsilateral limb, and that the reflex pattern in different muscles and within a single muscle may change dependent on the task that the subject is undertaking. These task-dependent changes indicate plasticity in the expression of cutaneous reflex activity, affecting both short-latency spinal as well as long-latency pathways.
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The Journal of physiology · Jan 1991
Pairing of pre- and postsynaptic activities in cerebellar Purkinje cells induces long-term changes in synaptic efficacy in vitro.
1. An in vitro slice preparation of rat cerebellar cortex was used to analyse long-lasting modifications of synaptic transmission at parallel fibre (PF)-Purkinje cell (PC) synapses. These use-dependent changes were induced by pairing PF-mediated EPSPs evoked at low frequency (1 Hz) with different levels of membrane polarization (or bioelectrical activities) of PCs for 15 min. 2. ⋯ In contrast, pairing of PF-mediated EPSPs with calcium (Ca2+) spikes evoked by strong depolarization of PCs (n = 12) led to LTD of synaptic transmission in nearly half of the tested cells, whereas LTP was now observed in less than 20% of them. 8. In the static chamber and in the absence of PDBu, LTD of PF-mediated EPSPs was observed in most cells, whatever the pairing protocol with sodium or Ca2+ spikes. 9. This shift towards LTD was significantly reversed by PDBu in the pairing protocol using firing of sodium spikes, but not in the case of pairings with Ca2+ spikes.(ABSTRACT TRUNCATED AT 400 WORDS)
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The Journal of physiology · Nov 1990
Amino acid-mediated EPSPs at primary afferent synapses with substantia gelatinosa neurones in the rat spinal cord.
1. Fast excitatory postsynaptic potentials (EPSPs) evoked by stimulation of A delta and C fibres were examined by intracellular recording from substantia gelatinosa (SG) neurones in a transverse slice preparation of adult rat spinal cord. 2. Single low-intensity stimuli applied to the dorsal root activated A delta fibres and evoked monosynaptic EPSPs in 70% of SG neurones. ⋯ These findings suggest that A delta and C fibres use L-glutamate or a related amino acid as a transmitter at synapses with substantia gelatinosa neurones. The postsynaptic actions of this transmitter are mediated predominantly by non N-methyl-D-aspartic acid (NMDA) receptors. The failure of CNQX and APV to completely block the L-glutamate-evoked depolarization of substantia gelatinosa neurones raises the possibility that exogenously applied L-glutamate activates a non-NMDA receptor distinct from that which mediates the actions of the synaptically released afferent transmitter.