The Journal of physiology
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The Journal of physiology · May 1987
Potentiation of gamma-aminobutyric-acid-activated chloride conductance by a steroid anaesthetic in cultured rat spinal neurones.
1. Intracellular recordings from cultured rat spinal cord neurones demonstrated that Cl(-)-dependent responses to GABA (gamma-aminobutyric acid) (but not glycine) were increased in amplitude and duration by the steroid anaesthetic alphaxalone (3 alpha-hydroxy-5 alpha-pregnane-11,20-dione) at submicromolar concentrations that produced little or no effect on passive electrical properties. The non-anaesthetic 3 beta-hydroxy analogue was without effect on GABA-evoked responses. 2. ⋯ Taken together, these findings indicate that the steroid anaesthetic is able to directly activate Cl- conductance normally activated by GABA in spinal neurones. 5. The actions of the steroid at GABA-receptor-Cl(-)-channel complexes are similar to those produced by the anaesthetic barbiturates (e.g. pentobarbitone), although obtained at 50-100-fold lower concentrations. These effects on the inhibitory Cl(-)-conductance mechanism may be partly responsible for the depressant actions of alphaxalone on the mammalian central nervous system.
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The Journal of physiology · May 1986
Innervation and function of hind-limb muscles in the cat after cross-union of the tibial and peroneal nerves.
Peripheral nerves to flexor (common peroneal) and extensor (tibial) nerves in a hind limb of seven 2-6 month old cats were cut and cross-united to study the plasticity in the spinal cord. The extent to which motoneurones from extensor and flexor motor pools were misdirected to their antagonistic muscles was determined by measuring the potentials generated at the spinal roots from the crossed nerves. The axons contributing to the extensor nerves normally leave the cord in the L7 and S1 ventral and dorsal roots while the axons contributing to the flexor nerves normally leave the cord in the L6 and L7 ventral and dorsal roots. ⋯ This extensor activity was more prominent when the nerve cross was less complete. We conclude that during locomotion the activity of spinal motoneurones was not substantially modified by inappropriate peripheral connexions, even when the nerve cross was carried out in young animals. This conclusion is discussed in relation to previous studies which suggested some degree of functional modification.
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The Journal of physiology · Mar 1986
Blood pressure effects of leptazol applied to the ventral surface of the brain stem of cats.
In anaesthetized cats leptazol (200 mg/ml) and sodium pentobarbitone (30 mg/ml) were applied topically to an area of the exposed ventral surface of the medulla oblongata, which lies between the rootlets of the twelfth cranial and first cervical nerve. The drugs were applied either bilaterally by means of paired Perspex rings or unilaterally by means of a single Perspex ring. Their effects on arterial blood pressure, heart rate and respiration were examined during two stages of anaesthesia, during 'surgical anaesthesia' produced by an intravenous injection of chloralose at 60 mg/kg, and during deeper anaesthesia attained by two additional intravenous injections of chloralose at 30 mg/kg. ⋯ The area from which the pressor response to leptazol was obtained lay 7-11 mm caudal to the lower border of the trapezoid bodies, i.e. about 2 mm more caudally than the 'nicotine-sensitive area' from which a depressor response to leptazol is evoked. Thus the two areas, though not identical, overlap. The result obtained with sodium pentobarbitone suggest that the area for the pressor response to leptazol plays a role in maintaining vasomotor tone during deepened anaesthesia and exerts a strong inhibitory effect on the respiratory rate during both surgical and deepened anaesthesia.
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The Journal of physiology · Jan 1986
Excitation of neurones in the rat paraventricular nucleus in vitro by vasopressin and oxytocin.
Extracellular recordings were made from ninety-seven spontaneously firing cells in the paraventricular nucleus (p.v.n.) of the rat hypothalamic slice preparation. The spontaneously firing cells tested fired at 0.1-8 spikes/s but the majority showed a slow irregular firing pattern. The average firing rate of all ninety-seven cells was 2.2 +/- 0.2 spikes/s (mean +/- S. ⋯ After blocking synaptic transmission with a low Ca2+ and high Mg2+ medium, all tested cells (AVP, n = 15; OXT, n = 14) which had responded to applications of AVP or OXT in normal medium still showed responses to the peptides, although the effect was less marked in half the cells. However, in the absence of synaptic transmission two cells showed unimpaired responses to one of the peptides but greatly depressed responses to the other. The V1-receptor antagonist [1-(beta-mercapto-, beta-cyclopentamethylenepropionic acid)], 8-D-arginine-vasopressin (d(CH2)5DAVP) or V1/V2-receptor antagonist [1-(beta-mercapto-, beta-cyclopentamethylenepropionic acid), 2-D-tyrosine,4-valine]arginine-vasopressin (d(CH2)5D-TyrVAVP) completely or partly blocked the AVP-induced responses, while the V2-receptor agonist 1-deamino-8-D-arginine-vasopressin (dDAVP) did not influence the spontaneous discharges of the cells.(ABSTRACT TRUNCATED AT 400 WORDS)
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The Journal of physiology · Oct 1985
Selective cardiovascular and neuroendocrine effects of a kappa-opioid agonist in the nucleus tractus solitarii of rats.
The cardiovascular and neuroendocrine effects of a selective kappa-opiate receptor agonist (U50488H) microinjected into the nucleus tractus solitarii have been investigated in urethane-anaesthetized rats. Comparative experiments were conducted using 8-arginine vasopressin (AVP)-deficient Brattleboro rats and an opiate agonist selective for delta receptors. Unilateral injection of U50488H elicited a significant dose-dependent increase in mean arterial pressure and a small decrease in heart rate in Sprague-Dawley rats. ⋯ An antagonist [1-(beta-mercapto-beta, beta-cyclopentamethylene-propionic acid)2-(0-methyl) tyrosine] arginine vasopressin (1,d(CH2)5Tyr(ME)AVP) specific for the vasopressor action of AVP blocked the U50488H-induced pressor response in a dose-dependent manner when administered intravenously 10 min prior to the kappa agonist, but did not significantly attenuate the response to the delta agonist. Conversely, the U50488H-induced response was not modified by pre-treatment with phenoxybenzamine whereas the delta-agonist pressor response was completely blocked by it. The results provide evidence for specific kappa-opiate cardiovascular and neuroendocrine responses in the nucleus tractus solitarii and suggest that a kappa-receptor mechanism, possibly involving a peptide of the dynorphin group as the endogenous ligand, may operate in the central control of blood pressure and AVP secretion.