The Journal of physiology
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The Journal of physiology · Jun 1983
Neuromuscular transmission and correlative morphology in young and old mice.
1. Age changes in spontaneous and evoked transmitter release, in receptor number and in ultrastructure at the neuromuscular junction were studied in the CBF-1 mouse strain, which stays physically active and relatively free of organ pathology into advanced age.2. Spontaneous miniature end-plate potentials (m.e.p.p.s) were recorded in the following young (8-12 months) and old (29-33 months) mouse muscles: extensor digitorum longus (e.d.l.), soleus (sol.), gluteus maximus (g.m.), diaphragm (diaph.) and extensor digitorum communis (e.d.c.).3. ⋯ Since no evidence of denervation was found by physiological criteria, it is concluded that in 34-month mice, nerve terminals withdraw from some synaptic gutters but do not abandon any junction entirely. The large presynaptic ultrastructural changes contrast with the physiological data showing no deficit and even increases in transmitter release. Therefore, under these conditions, these profound structural changes are either not functionally significant or are well compensated.
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The Journal of physiology · Apr 1983
Comparative StudyDifferences and similarities in the noradrenaline- and caffeine-induced mechanical responses in the rabbit mesenteric artery.
1. The properties of noradrenaline (NA)-induced and caffeine-induced contractions in the rabbit mesenteric artery were investigated and compared, using intact and skinned muscles.2. NA (> 10(-7) M) depolarized the membrane and reduced the membrane resistance. ⋯ The different mechanical responses to NA or caffeine may also relate to the behaviour of Ca; i.e. Ca may be extruded into the extracellular space in the presence of caffeine, while this ion may be extruded and to some extent, re-accumulate into the store site in the presence of NA. The oscillatory contraction evoked by treatment with NA is discussed in relation to the activation of a Ca-induced Ca-release mechanism in the store site.
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The Journal of physiology · Apr 1983
Effects of dorsal root section on spinocervical tract neurones in the cat.
1. In nine cats, dorsal roots L(6) and L(7) were sectioned under pentobarbitone anaesthesia using strict aseptic precautions. In two cats all lumbosacral roots except L(6) were sectioned under similar conditions. 27-75 days after the dorsal rhizotomies, under chloralose anaesthesia, neurones of the spinocervical tract (s.c.t.) were recorded electrophysiologically both extracellularly and intracellularly, their response properties and receptive fields were analysed, and they were injected with horseradish peroxidase (HRP). ⋯ Their dendritic trees had similar rostro-caudal, medio-lateral and dorso-ventral extents to normal cells, and appeared to exhibit similar degrees of branching. There was a suggestion that de-afferented neurones had rather more of their dorsally-directed distal dendrites invading lamina II than normal cells, but the sample size was too small to make this more than a possibility.7. It is concluded that after dorsal rhizotomy, s.c.t. neurones lose part or all of their afferent input and that within 75 days do not show any signs of new or inappropriate connexions.
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The Journal of physiology · Apr 1983
Somatic and visceral inputs to the thoracic spinal cord of the cat: effects of noxious stimulation of the biliary system.
1. Single unit electrical activity has been recorded extracellularly from 133 neurones in the grey matter of the 8th and 9th thoracic segments of the spinal cord in chloralose anaesthetized cats. The responses of these neurones to electrical stimulation of the ipsilateral splanchnic nerve, to natural stimulation of the skin and to distension of the biliary system have been studied.2. ⋯ Sixteen per cent of the neurones were found to project to supraspinal levels via crossed ventro-lateral pathways. All of these neurones were viscero-somatic with axonal conduction velocities between 12 and 68 m sec(-1).8. These results are discussed in relation to the postulates of the ;Convergence-projection' theory of referred pain.
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The Journal of physiology · Apr 1983
Effects of acute changes in blood volume on the carotid sinus baroreceptor reflex in conscious rabbits.
The control of blood pressure, heart rate, cardiac output and systemic vascular resistance by the carotid sinus baroreceptor reflex was studied in six conscious rabbits during states of acute hypervolaemia and acute hypovolaemia. These states were produced by infusing blood equal to 20% and 40%, and withdrawing blood equal to 20% and 35%, of the initial blood volume. The properties of the reflex were characterized by creating sinusoidal pressure changes across the wall of the carotid sinus at a frequency of 0.01 Hz and amplitudes of 54 and 83 mmHg. ⋯ The gain for systemic vascular resistance was reduced by hypervolaemia, and increased by 20% hypovolaemia. The gains for heart rate and blood pressure were not affected by hypervolaemia or by 20% hypovolaemia. 35% hypovolaemia reduced the gain for heart rate, but the resting value was close to the upper limit of the reflex response. It also reduced the gain for cardiac output and blood pressure, and the increase in gain for systemic vascular resistance that had been caused by 20% hypovolaemia was not sustained.