The Journal of physiology
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The Journal of physiology · Nov 1972
Properties and distribution of peripherally evoked presynaptic hyperpolarization in cat lumbar spinal cord.
1. The action of peripheral nerve volleys on the polarization of presynaptic terminals of inactive sensory fibres in cat lumbar spinal cord has been investigated by recording (a) the dorsal root potential (DRP), (b) intracellular changes in polarization of single preterminal axons (PAD or PAH), and (c) changes in excitability of populations of preterminal axons.2. Presynaptic hyperpolarization (positive DRP-PAH) can be evoked by stimulation of muscle group III afferents as well as by volleys in cutaneous Abeta, Adelta and C afferents. ⋯ Intracellular recording from single axons reveals that the same stimuli evoke widely varying ratios of PAD and PAH.8. Stimulation of FRA evokes PAH > PAD in PBST group I afferents, PAD > PAH in sural A fibres and intermediate effects in G-S group I units.9. It is suggested that activation of flexor reflex afferents may selectively potentiate the synaptic efficacy of large muscle afferents mediating the flexor reflex rather than large skin afferents or large afferents from extensor muscles.
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The Journal of physiology · Jul 1972
Comparison of receptive-field organization of the superior colliculus in Siamese and normal cats.
1. The superior colliculus has been studied in Siamese and normal cats by recording the responses of single tectal units to visual stimuli.2. The retinotopic organization of the superior colliculus has been compared in the two breeds. ⋯ The squint commonly exhibited by Siamese cats is regarded as a compensation for the anomalous retinotectal topography. It is suggested that, in the absence of an adaptive modification, the anomalous retinotectal projection would lead to mislocalization in Siamese cats just as it does in frogs and hamsters whose retinotectal projection has been experimentally altered. The convergent strabismus which Siamese cats commonly exhibit may be a cure for the abnormal retinal projections rather than a disease.
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The Journal of physiology · Jun 1971
The imprecision arising from the application of the Henderson-Hasselbalch relationship to the blood of anesthetized dogs.
1. Arterial blood samples were obtained from anaesthetized dogs in which either a respiratory alkalaemia, a respiratory acidaemia or a non-respiratory acidaemia was produced and from animals in which no deliberate changes in acid-base balance were produced. The samples were analysed for pH, carbon dioxide tension and concentration, oxygen tension and concentration and haematocrit. ⋯ The values of pK' increased with an alkalaemia and decreased with an acidaemia.4. In addition to the variation of pK' with pH there was a considerable residual scatter of pK' values at any one pH value.5. It was concluded that in these experimental conditions the use of the Henderson-Hasselbalch equation in a form not dealing with activities was unacceptable and could lead to much larger errors than has hitherto been thought.
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The Journal of physiology · Apr 1971
Presynaptic depolarization of myelinated afferent fibres evoked by stimulation of cutaneous C fibres.
1. The origin of the dorsal root potential observed following a volley in cutaneous unmyelinated or C fibres (C-DRP) has been investigated by several assays.2. Measurements of the spatial decrement of the C-DRP along the dorsal roots indicate that mainly the thick myelinated primary afferent fibres contribute to this C-DRP.3. ⋯ These findings and direct measurements of the interactions between A- and C-DRPs indicate that the pathways involved in A- and C-PAD exhibit convergence.6. C-DRPs were also recorded from contralateral rootlets.7. Some functional aspects of the PAD produced by an afferent volley in C fibres are discussed.
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1. Pressures have been measured in the thoracic duct of anaesthetized and conscious dogs to ascertain the mean pressures, the nature of the pressure waves and the pressure gradients along the duct and between it and the great veins.2. The average mean pressure in the thoracic duct of ten anaesthetized dogs was 1.4 mm Hg. ⋯ They were increased by panting and by drinking.4. The pressure gradients along the duct were small, no more than 0.5-2.0 mm Hg along its whole length.5. No evidence was found of spontaneous contractions of the duct.