The Journal of physiology
-
The Journal of physiology · Mar 1992
Pain, hyperalgesia and activity in nociceptive C units in humans after intradermal injection of capsaicin.
1. Capsaicin, the potent algesic substance in chilli peppers, was applied topically to, or injected intradermally into or outside, the receptive fields of 14 C mechanoheat (polymodal) nociceptor units in awake humans. The nociceptor discharges were recorded using microelectrodes inserted into the peroneal nerve. ⋯ The after-effects of capsaicin on C nociceptor excitability depend on concentration: high concentration (by injection) leads to desensitization, whereas low concentration (by topical application) leads to sensitization. On-going discharges and lowered response thresholds to heat in these units after topical application of capsaicin correlates with background pain as well as lowered pain thresholds to heat of the affected skin (primary hyperalgesia). The unchanged responsiveness of C nociceptors in the skin well outside the injection area indicates that central rather than peripheral sensitization accounts for the observed mechanical hyperalgesia in this region (secondary hyperalgesia).
-
The Journal of physiology · Mar 1992
Central changes in processing of mechanoreceptive input in capsaicin-induced secondary hyperalgesia in humans.
1. Capsaicin, the algesic substance in chilli peppers, was injected intradermally in healthy human subjects. A dose of 100 micrograms given in a volume of 10 microliters caused intense pain lasting for a few minutes after injection and resulted in a narrow area of hyperalgesia to heat and a wide surrounding area of hyperalgesia to mechanical stimuli (stroking) lasting for 1-2 h. 2. ⋯ Electrical intraneural microstimulation normally eliciting non-painful tactile sensations was accompanied by pain when the sensation was projected to skin areas within the region of mechanical hyperalgesia induced by capsaicin injection. 4. The threshold for pain evoked by intraneural microstimulation was reversibly lowered and pain from suprathreshold stimulation was exaggerated during the period of mechanical hyperalgesia, regardless of lidocaine anaesthesia of the cutaneous innervation territory of the stimulated fibres. 5. The results indicate that hyperalgesia to stroking on a skin area surrounding a painful intradermal injection of capsaicin is due to reversible changes in the central processing of mechanoreceptive input from myelinated fibres which normally evoke non-painful tactile sensations.
-
The Journal of physiology · Mar 1992
Regulation of single quantal efficacy at the snake neuromuscular junction.
1. Postsynaptic responses to spontaneous quantal transmitter release have been compared among neuromuscular junctions in a thin snake muscle. For each junction the type, diameter, and input conductance, G(in) of the postsynaptic muscle fibre were determined. ⋯ Assuming that quantal content is proportional to synaptic size, this relation was sufficient to account for the observed increase in quantal content with increasing G(in) among fibres in the muscle, but was not alone sufficient to account for the observed regulation of evoked current. 8. It is concluded that the efficacy of individual transmitter quanta released at the snake neuromuscular junction is regulated such that large muscle fibres receive larger single quantal currents. Regulation of single quantal current contributes substantially to overall regulation of synaptic strength in the muscle.
-
The Journal of physiology · Mar 1992
Cl- and Na+ homeostasis during anoxia in rat hypoglossal neurons: intracellular and extracellular in vitro studies.
1. To understand the mechanisms which lead to acute neuronal swelling during anoxia, we studied the ionic movements of Cl- and Na+ during O2 deprivation in the hypoglossal (XII) neurons of rat brain slices using double-barrelled ion-selective microelectrodes. 2. Baseline extracellular Cl- and Na+ activities ([Cl-]o, [Na+]o) were 128.3 +/- 7.4 and 150.0 +/- 3.4 mM respectively (n = 12) in the adult. ⋯ Prolonged anoxia (6-12 min) in the neonate led to a more substantial increase in [Cl-]i, an observation consistent with the decrease in [Cl-]o after prolonged O2 deprivation. 7. We conclude that during anoxia: (1) intracellular [Cl-] increases in the adult and this most likely occurs because of entry of extracellular Cl- into the cytosol and (2) there is a major maturational difference in mechanisms regulating Cl- and Na+ homeostasis between newborn and adult brain tissue. We speculate that these mechanisms may account, at least partially, for the relative tolerance to anoxia in the newly born.