The Journal of physiology
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The Journal of physiology · Jul 1985
The post-natal development of cutaneous afferent fibre input and receptive field organization in the rat dorsal horn.
The responses evoked in lumbar dorsal horn cells by both natural and electrical hind-limb skin stimulation were recorded in the spinal cord of rat pups aged 0-15 days under urethane anaesthesia. The input volley was recorded on the L4 dorsal root and consisted of two separate waves from birth. Latency and threshold measurements were consistent with these two waves being immature A (myelinated fibre) waves and C (non-myelinated fibre) waves. ⋯ The duration and amplitude of these responses decreased with age. Repetitive electrical skin stimulation of the receptive fields of these cells produced 'wind-up' and prolonged after-discharge. Ipsilateral, contralateral and distant inhibitory components to receptive fields were observed from day 0.(ABSTRACT TRUNCATED AT 400 WORDS)
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The Journal of physiology · May 1985
The transport of sugars across the perfused choroid plexus of the sheep.
The blood-perfused choroid plexuses from the lateral ventricles of the sheep were used to determine the nature of sugar exchanges between blood and cerebrospinal fluid (c.s.f.). There was a net entry of sugars from blood to c.s.f. at all concentrations of sugars which were used and this net entry was seen when the sugars were measured either directly by enzymic analysis or by the use of isotopically labelled sugars. From competition experiments the order of affinity of the transporting system from both blood to c.s.f. and c.s.f. to blood was the same, i.e. 2-deoxy-D-glucose much greater than D-glucose greater than 3-O-methyl-D-glucose much greater than D-galactose. ⋯ However, the affinity of the two systems is markedly different, the blood to c.s.f. being a system of low affinity and high capacity while that of the c.s.f. to blood has a high affinity and a low capacity. The concentration of glucose in the newly formed c.s.f. was estimated from the rate of c.s.f. secretion and the net flux of glucose across the choroid plexus. The concentration of glucose in this fluid was some 45-60% of that in plasma and so the low glucose concentration observed in bulk c.s.f. would appear to be a result of the entry process and not that of cerebral metabolism.
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The Journal of physiology · Nov 1984
Efferent desensitization of auditory nerve fibre responses in the cochlea of the turtle Pseudemys scripta elegans.
Extracellular recordings were made from single auditory afferents in the isolated half-head of the turtle, and changes in their acoustic sensitivity were examined following electrical stimulation of the efferent fibres to the basilar papilla. Short trains of efferent shocks caused a prolonged elevation of the pure tone thresholds of the auditory afferents and an abolition of their spontaneous activity. These changes could be demonstrated in a majority of recordings and without antidromic firing of the afferent. ⋯ Such effects would enable the afferent to signal a wider range of sound pressures. Efferent stimulation caused a broadening of the afferent frequency-threshold curves by removal of the narrowly-tuned region around the characteristic frequency. We suggest that the loss in tuning and concomitant improvement in temporal resolution may be a functionally important consequence of efferent action.
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The Journal of physiology · Aug 1983
Sites and mechanism of action for the effects of intrathecal noradrenaline on thermoregulation in the rat.
1. In unanaesthetized rats, intrathecal injection of 0.30 mumole noradrenaline (NA) at the level of the lumbar enlargement produced a transient rise in core temperature followed by prolonged hypothermia and tail skin vasodilation.2. Studies of the distribution of [(3)H]NA injected at the lumbar enlargement revealed that at least 97% of the activity recovered from the central nervous system was located in the spinal cord, primarily within the thoracic and upper lumbar segments. ⋯ These injections produced an immediate increase in blood pressure. However, this effect was transient and, during most of the time when NA-induced vasodilation and hypothermia were present, blood pressure was normal or only slightly elevated. Thus, it is not likely that a baroreceptor-mediated reflex inhibition of sympathetic outflow contributed significantly to the vasodilatory or hypothermic action of NA.
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The rabbit's striate cortex contains a variety of receptive-field types, including concentric, uniform, simple and complex types. The spatial summation of these receptive fields was studied. Two types of linearity tests were performed: null tests and drifting grating tests. ⋯ The behaviour of nine other complex cells was difficult to describe. Generally, they were unresponsive to gratings. When they could be made to respond to gratings, they gave phase-sensitive responses like those of simple cells.