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PubMed1963

THE RESPONSES TO TYRAMINE OF THE NORMAL AND DENERVATED NICTITATING MEMBRANE OF THE CAT: ANALYSIS OF THE MECHANISMS AND SITES OF ACTION.

The response to tyramine of the denervated nictitating membrane has been analysed by comparing dose/response curves obtained by injections into the femoral vein and into the carotid artery of the spinal cat while recording contractions of innervated and chronically denervated membranes and those of cats treated with reserpine. It is concluded that the effect of tyramine given by these routes is due primarily to catechol amines released from stores within the nictitating membrane itself. Higher doses of tyramine also cause contraction of the membrane by liberating catechol amines into the circulating blood from stores outside the membrane. The response to tyramine of the nictitating membrane after chronic denervation and/or prior treatment with reserpine is partially due to catechol amines released from unidentified stores within the membrane which resist depletion by reserpine and by postganglionic denervation; evidence is presented that adrenaline rather than noradrenaline is concerned. Because of the high sensitivity of the denervated nictitating membrane to adrenaline and to noradrenaline, the response to these amines released from stores outside the membrane by intravenous injections of tyramine becomes greater than that of the normal membrane. Dose/response curves obtained from responses to intravenous sympathomimetic drugs which act away from the membrane are therefore not fully representative of the effect of the drugs on the membrane itself. Tyramine probably has an affinity both for storage sites and for catechol amine receptors in the smooth muscle of the nictitating membrane, the "intrinsic activity," however, being very weak or even absent.

Amines↗
PubMed1972

The effect of bradykinin on denervated tongue.

1. The contractile response of the chronically denervated tongue of the cat to chorda stimulation, and to close arterial injections of bradykinin, acetylcholine (ACh) and other drugs was examined.2. Bradykinin in doses of 50 ng-20 mug injected close arterially always produced a contractile response of the denervated tongue. Sodium nitrite (1 mg i.a.) and isoprenaline (3-200 ng i.a.) also produced contracture; histamine (40-100 ng i.a.) evoked an increase in tension in only 2 out of 5 experiments.3. Tubocurarine in doses of 0.25-1 mg injected intra-arterially, produced a large and long-lasting contracture of the denervated tongue. When the contracture was over, the effect of bradykinin was reduced to about half; the effects of ACh and chordo-lingual nerve stimulation were markedly reduced (over 80%), and those of sodium nitrite and isoprenaline were transiently abolished. Gallamine only slightly reduced the effect of bradykinin.4. Close intra-arterial injection of physostigmine (100 mug) potentiated the effect of ACh and chordo-lingual nerve stimulation, but did not increase the response to bradykinin.5. Cocaine (1 mg/kg i.v.) deeply depressed the response to bradykinin, and moderately reduced the responses to ACh (41%) and to chorda stimulation (66%).6. In 2 out of 7 experiments, close arterial injections of bradykinin (100-500 ng) to the denervated tibialis anterior muscle of the cat, produced a contractile response. Bradykinin in small doses (200-250 ng) injected immediately before ACh potentiated its effect. On the other hand, the effect of ACh was depressed when given immediately after a big dose of bradykinin (10-15 mug).7. The possible mechanism of action of bradykinin and other substances on denervated muscle is discussed.

Acetylcholine↗
PubMed1974

Failure of chronic denervation to alter the sensitivity of the rat diaphragm to local anaesthetics of quinidine.

1 The actions of procaine, nupercaine and quinidine on the membrane resting and action potentials of the normal and chronically denervated rat diaphragm were studied in vitro.2 The degree of suppression of the rate of rise of the action potential by any of the drugs was the same in denervated as in normal muscle.3 The degree of suppression of the rate of rise of the action potential by procaine in denervated muscle was about the same in the presence and absence of tetrodotoxin.4 Three possible interpretations of the lack of effect of denervation on the response to these drugs are discussed:(a) In the sodium channel, the structural alteration that confers resistance to tetrodotoxin is quite limited and does not affect groups which interact with local anaesthetics.(b) Local anaesthetics are non-selective in their binding so that alteration in membrane structure around the channel has little influence on the efficiency of the local anaesthetic.(c) Denervation may affect the outer surface of the membrane, where acetylcholine and tetrodotoxin act, more than the intracellular surface, where local anaesthetics appear to act.5 The slope of the log concentration-effect line for quinidine was steeper than that for procaine or nupercaine.

Action Potentials↗
PubMed1981

Mechanical and electrophysiological effects of sea anemone (Anemonia sulcata) toxins on rat innervated and denervated skeletal muscle.

1 Some effects of the sea-anemone toxin ATX-II on mammalian nerve-muscle preparations have been described. 2 When ATX-II (10(-8)-10(-6) M) was applied to rat hemidiaphragm preparations, both directly and indirectly generated twitch responses were potentiated and prolonged. At the same time the resting tension of the preparations increased. 3 The increase in resting tension caused by ATX-II in innervated muscles was not prevented by curarization, but was reversed by exposure to tetrodotoxin. The increase in denervated muscles was not completely reversed by tetrodotoxin. 4 At concentrations exceeding 1 x 10(-7) M, ATX-II caused a sodium-dependent depolarization of both normal and denervated muscles. The depolarization of the denervated muscles was only partially reversed by tetrodotoxin. 5 In the presence of ATX-II repetitive endplate potentials (e.p.ps) were evoked by single shocks to the motor nerves in many fibres, and in those in which a single e.p.p. was still observed, the quantum content (m) was increased. Miniature e.p.p. frequency was not increased by ATX-II, even when muscle fibres were depolarized by 30 mV. 6 The indirectly and directly elicited action potentials of normal and denervated muscle fibres were much prolonged by ATX-II. The action potentials remained sodium-dependent. The sodium-dependent tetrodotoxin-resistant action potential of the denervated muscle fibre was also prolonged by ATX-II. 7 It is concluded that ATX-II both activates, and delays inactivation of, sodium channels in mammalian skeletal muscle fibres, probably in interacting with the channel "gate'.

Action Potentials↗
PubMed1975

Cholinergic receptors at denervated mammalian motor end-plates.

The number of acetylcholine receptors at normal and denervated end-plated in rat soleus muscles was studied using the binding of [125A] alpha-bungarotoxin as a quantitative assay. Normal end-plates bound several thousand times as much toxin as equal areas of extra-synaptic muscle membrane. After short-term denervation (up to 2.4 weeks) the extrajunctional binding increased, but there was no change in specific binding to the motor end-plate. Denervation for longer periods (up to 7 weeks) reduced binding sites at the end-plate by up to 60-70%. Direct electrical stimulation of these muscles for the entire period of denervation did not prevent the loss of junctional binding sites even though it was adequate to abolish the increase in extrajunctional toxin binding. In contrast, denervated end-plates on muscle fibres cross-innervated by a foreign nerve at a distant location continued to bind normal amounts of toxin for over four months.

Animals↗
PubMed1989

Effects of growth hormone on skeletal muscle. II. Studies on regeneration and denervation in adult rats.

The effects of human recombinant growth hormone (rhGH) on regenerating skeletal muscle after ischaemic necrosis and on denervated skeletal muscle were studied in normal adult rats. One group of rats was treated with 4 IE rhGH daily by subcutaneous injections, while control rats were injected with saline. The treatment with rhGH resulted in increased levels of insulin-like growth factor-I (IGF-I) in serum. Ischaemic necrosis was achieved in the extensor digitorum longus (EDL) muscle by cutting the supplying vessels and nerve fascicles at the entrance into the muscle. The wet weight and DNA: protein ration in the regenerating muscle were determined 2 and 4 weeks after the operation. The weight of the regenerating muscles in the rats treated with rhGH during the period of study was larger than in the control rats, while the DNA:protein ratio did not differ significantly between the groups. Denervation of the EDL and soleus muscles followed by subsequent reinnervation was obtained by freezing the sciatic nerve with a forceps chilled in liquid nitrogen. Rats treated with rhGH during the period of denervation and reinnervation, i.e. during the 4 weeks after the freezing of the sciatic nerve, revealed increased weight of both the reinnervated and normal muscles compared to corresponding muscles of control rats. Denervation of the EDL and soleus muscles without subsequent reinnervation was achieved by cutting the sciatic nerve at the level of the thigh. Four weeks after denervation the muscles showed atrophy, mainly affecting type 2 fibres in the EDL muscle and both type 1 and type 2 fibres in the soleus muscle.

Adenosine Triphosphatases↗
PubMed1986

Effects of denervation and direct electrical stimulation upon acetylcholine receptors and acetylcholinesterase accumulation in developing latissimus dorsi muscle of the chick.

The effects of denervation and of direct electrical stimulation of denervated muscle upon the acetylcholine receptor (AChR) clusters and acetylcholinesterase (AChE) spots in the fast avian muscle posterior latissimus dorsi have been investigated. Denervation at day 2 after hatching leads to a disappearance of the junctional AChR clusters and to a marked decrease of AChE spots. Direct electrical stimulation of denervated muscle allows the maintenance of AChR clusters and partly prevents the loss of AChE spots. When AChR cluster and post-synaptic AChE have disappeared in a denervated muscle, muscle activity induced by direct stimulation is unable to induce their accumulation.

Acetylcholinesterase↗
PubMed1992

Supersensitivity to morphine after chronic sympathetic denervation in guinea-pig colon.

The possible role of opioid systems in the adaptive changes which follow chronic sympathetic denervation in the guinea-pig colon has been studied by comparing the effects of the opioid agonist morphine in control animals and after chronic sympathetic denervation. Supersensitivity to the inhibitory effects of morphine on the peristaltic reflex was observed after chronic sympathetic denervation, while the potency against acetylcholine release was unmodified. Our results suggest that a modification of the opioid system occurs after sympathetic denervation in the guinea-pig colon. Supersensitivity to endogenous opioids at a site different from that regulating acetylcholine release could account for the counter-regulation of intestinal motility after chronic sympathetic denervation.

Acetylcholine↗
PubMed1969

Change of tubular reabsorption of sodium and water after renal denervation in the dog.

1. Renal function was compared in dogs before and after denervation, with normal or reduced glomerular filtration rate (GFR). GFR was reduced by one of two means, aortic clamping or injection of plastic microspheres into one renal artery.2. The data showed that the tubular rejection fraction of denervated kidneys increased at a time when the same value for the control kidney decreased, indicating that denervation diuresis is not simply a result of increased filtered load of Na and water.3. Changes in excretion after aortic clamping are not due solely to reduced filtered load. A reduction in renal blood pressure itself appears to have a direct effect on Na transport since Na excretion was significantly decreased before there were any changes in GFR, renal plasma flow and urine volume.4. When GFR in a denervated kidney was reduced by microsphere injection it was demonstrated that a significant natriuresis (U(Na) V) and diuresis (V) occurred when. GFR was reduced by as much as 40%.5. These experiments support the hypothesis that denervation diuresis does not result solely from increased filtered load, but entails altered Na transport.

Animals↗
PubMed1974

The sensitivity to glutamate of denervated muscles of the crayfish.

The effect of denervation on the sensitivity of muscle fibres to glutamate was studied in leg muscles of crayfish.1. When the motor nerve was cut close to the proximal accessory flexor muscle the distal end of the nerve degenerated. Neuromuscular transmission failed and spontaneous miniature potentials disappeared after two months. Several stages of nerve terminal degeneration were seen in muscles denervated between 1 and 3 months, and after 4 months no remains of synapses could be found.2. Following denervation for periods up to 8 months there was no significant change in sensitivity to glutamate, a substance that mimics the action of the neural transmitter. Depolarizations produced by various concentrations of glutamate in the bathing solution were the same in denervated and control muscle fibres. Moreover, the sensitivity to iontophoretically applied glutamate was localized to discrete patches as in innervated muscles.3. Supersensitivity of muscles apparently does not occur after denervation in the crayfish.

Action Potentials↗
PubMed1975

An electrophysiological and morphological study of normal and denervated chicken latissimus dorsi muscles.

1. Some electrophysiological and morphological properties of 'fast' (singly innervated) and 'slow' (multiply innervated) muscle fibres were studied in normal and denervated posterior and anterior latissimus dorsi muscles of the young chickens. 2. Normal singly and multiply innervated muscle fibres are capable of generating action potentials which in all qualitative respects are similar. 3. The action potentials of multiply innervated muscle fibres are of lower amplitude and slower maximum rate of rise than action potentials in singly innervated muscle fibres. 4. Denervation causes the resting membrane potential and the maximum rate of rise of the action potential to fall. The changes are greater in singly innervated than in multiply innervated fibres, but in neither case are as great as in mammalian skeletal muscle fibres after surgical denervation. 5. In neither singly nor multiply innervated muscle fibres do the action potentials generate any 'resistance' to tetrodotoxin as a result of denervation. 6. The diameter of multiply innervated fibres is increased after denervation, but it is reduced in singly innervated fibres. The number of myofilaments increases in multiply innervated fibres, but decreases in single innervated fibres. In both types of muscle fibre the volume fraction of myofibrils is decreased. 7. In the singly innervated muscle fibres there is an increase in the volume fraction of mitochondria. 8. In the singly innervated muscle fibres, there is some rearrangement of the membrane systems in that some of the transversely orientated triads are replaced by longitudinally orientated dyads.

Action Potentials↗
PubMed1979

Desensitization of glutamate receptors on innervated and denervated locust muscle fibres.

Depolarizations to L-glutamate, applied locally by microinophoresis to the extrajunctional membrane of locust extensor tibiae muscle fibres and measured either in current clamp or voltage clamp, increased in amplitude for equivalent doses of glutamate following chronic denervation of the muscle. 2. A two-pulse method was used to examine recovery from desentization of junctional and extrajunctional receptors. A 'response ratio', i.e. the amplitude of response to the second (test) of a pair of glutamate pulses over to the pulses. The 'response ratio' for extrajunctional depolarizations of innervated fibres increased exponentially with pulse interval, with a time constant of 15.6 +/- 4.7 sec (n = 11). Recovery of extrajunctional receptor populations from desensitization was accelerated after denervation. The recovery kinetics for responses from fibres 6-22 days after denervation were generally described by two exponential terms, with time constants in the range 0.5-10 sec which were inversely related to the glutamate sensitivity of the extrajunctional membrane. For junctional receptors on both innervated and denervated fibres the recovery kinetics were described by a single exponential with a time constant of 0.2-1 sec. 3. The results suggest that the increased extrajunctional glutamate sensitivity which occurs after denervation results from the 'appearance' of glutamate receptors with properties similar to those found at the post-junctional membrane on locust muscle fibres.

Animals↗
PubMed1980

Lifetime and conductance of acetylcholine-activated channels in normal and denervated toad sartorius muscle.

1. The average lifetime and conductance of acetylcholine-activated channels were measured in normal and denervated, voltage-clamped toad sartorius muscle fibres at 10 degrees C. 2. The null potential was -4 +/- 1 mV for subsynaptic channels in normal fibres and -6 +/- 3 mV for extrasynaptic channels in denervated fibres. 3. There was a linear relationship between variance of conductance fluctuations and mean conductance for acetylcholine-induced currents up to 50 nA, in denervated fibres clamped at -50 mV. The ratio gave a channel conductance of 14 pS. 4. At the same membrane potential, the average lifetime of extrasynaptic channels in denervated fibres was approximately double, whereas channel conductance was approximately half, that of subsynaptic channels in normal fibres: there was little difference in net charge transfer through the two types of channel under similar conditions. 5. Single channel conductance increased, whereas average channel lifetime decreased, as the membrane potential became more positive (depolarized). The effect of potential on channel lifetime and conductance was more pronounced in denervated than in normal fibres.

Acetylcholine↗
PubMed1987

Acetylcholine receptors and sodium channels in denervated and botulinum-toxin-treated adult rat muscle.

1. The number of acetylcholine (ACh) receptors and Na channels was measured in adult rat hind-limb muscles after denervation or injection of botulinum toxin type A (BoTX), using specific binding of radiolabelled neurotoxins. 2. Denervation by sciatic nerve section increased the number of [125I]iodo-alpha-bungarotoxin ([125I]BTX) binding sites from low, unmeasurable levels to 39 +/- 3 fmol of toxin bound per milligram muscle protein at 21 days. 3. Subcutaneous injection of BoTX produced complete neuromuscular blockade for 11-14 days over which time the number of [125I]BTX binding sites increased with the same time course and to the same extent as following denervation. 4. Neither denervation nor BoTX treatment significantly altered the number of tritiated saxitoxin ([3H]STX) binding sites from normal values of 7.8 fmol/mg muscle weight or 57 +/- 3 fmol/mg homogenate protein. This may, however, correspond to a lower density of [3H]STX sites in the muscle membrane. 5. It was concluded that neuromuscular blockade with BoTX is equivalent to denervation in its effects on synthesis of ACh receptors. Numbers of Na channels are more stable than ACh receptors but may also be modulated by neuromuscular activity.

Animals↗
PubMed1987

Role of sodium and potassium permeabilities in the depolarization of denervated rat muscle fibres.

1. Na+ and K+ flux measurements and membrane potential (Vm) determinations were performed on normal and denervated rat extensor digitorum longus (e.d.l.) muscles. 2. The mean Vm in normal muscle fibres was -74.6 mV. During the first week after denervation Vm fell about 20 mV following an S-shaped time course. 3. In that period the Na+ permeability (PNa) increased and the K+ permeability (PK) decreased, so that by the sixth day post-denervation, the PNa/PK ratio was increased by a factor of 2.7. 4. The decrease in PK preceded the increase in PNa. 5. No major contribution to the fall of Vm by a reduced activity of an electrogenic Na+ pump could be detected. 6. A good agreement was found between the experimental values of the depolarization and those calculated using the constant-field equation assuming Cl- is at equilibrium and no significant change of the intracellular K+ concentration ([K+]i) during the first week after denervation. 7. It is concluded that the depolarization promoted by denervation in e.d.l. rat muscle fibres can be fully explained in terms of changes in PNa and PK.

Animals↗
PubMed1987

The role of frequency in the effects of long-term intermittent stimulation of denervated slow-twitch muscle in the rat.

1. Rat soleus muscle was denervated by sciatic transection and electrically stimulated for periods of between 3 and 9 weeks with intermittent 1 s bursts of pulses. Most of the bursts were either repeated every 90 s and pulses within them had frequencies between 10 and 100 Hz, or had a frequency of 50 Hz and were repeated at intervals between 60 and 600 s. Comparisons were made with continuous stimulation at 10 Hz. 2. At the end of the period of stimulation, isometric twitches and tetani were measured and, in a proportion, also isotonic shortening velocity. 3. Isometric twitch duration (contraction and relaxation) decreased with time of stimulation. Very similar effects were seen in all animals in which intermittent stimulation had been used. There was a significant relationship between the change in twitch duration and the frequency used within the bursts of chronic stimulation, with slightly larger effects at frequencies of 40 and 60 Hz. The lowest burst repetition rate produced the largest effects. 4. It was confirmed that similar changes were found in denervated muscles that were not stimulated, although these changes were smaller and developed more slowly. 5. The extreme loss of tetanic tension induced in the muscle by denervation was reduced by chronic stimulation, with no significant difference between different regimes, although there were small differences which showed the same patterns of effectiveness described for twitch durations. 6. Continuous stimulation at 10 Hz maintained the twitch contraction and relaxation phases at the values found 3 weeks after denervation, that is it prevented secondary shortening of the twitch. Continuous stimulation reduced tension loss but was, perhaps, less effective than intermittent stimulation. 7. Twitch-tetanus ratio increased with denervation with little spontaneous reversal later. Stimulation at all frequencies reduced the ratio, but it did not reach normal values. 8. Isotonic shortening velocity was measured in many of the muscles. Maximum velocity was estimated and normalized by muscle length.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Submandibular responses to stimulation of the sympathetic innervation following parasympathetic denervation in cats.

1. The effects of continuous stimulation of the ascending cervical sympathetic nerve were compared with those of intermittent stimulation in bursts, so arranged as to deliver the same total number of impulses, in cats under chloralose anaesthesia 3 weeks after excision of the chorda tympani. 2. Parasympathetic denervation of the gland in this way enhanced the vasodilator component of the vascular response during sympathetic stimulation in bursts. During continuous stimulation this was manifested as a reduced rise in submandibular vascular resistance (SVR). It also produced a profound increase in the secretory response to sympathetic stimulation at low intensity (2 Hz continuously). 3. Enhancement of the salivary secretory responses by stimulating intermittently at relatively high frequencies resembled that which developed following parasympathetic denervation in that there was no change in the secretory capacity during maximal or supramaximal stimulation. 4. Pre-treatment with atropine substantially reduced the flow of saliva in response to sympathetic stimulation at low frequencies (2 and 5 Hz continuously) and combined pre-treatment with atropine and propranolol effectively reversed the increase in secretory sensitivity due to parasympathetic denervation indicating that beta-adrenergic and muscarinic responses are involved. Additional pre-treatment with dihydroergotamine effectively abolished the secretory response to sympathetic stimulation. 5. Stimulation in bursts was found to have a significantly greater vasodilator effect than continuous stimulation at the corresponding frequency after parasympathetic denervation. 6. Neither pre-treatment with atropine nor combined pre-treatment with atropine and propranolol had any significant effect on the changes in mean SVR at any frequency tested during or after either pattern of stimulation. Additional pretreatment with dihydroergotamine effectively abolished the vascular responses to sympathetic stimulation both continuous (5 Hz) and in bursts (50 Hz), leaving a small vasoconstrictor response that may be due to release of neuropeptide Y (NPY). 7. These results suggest that cholinergic beta-adrenergic and NPY supersensitivities are not involved in the submandibular vascular changes that result from parasympathetic denervation, but that alpha-mediated secondary vasodilator mechanisms are thereby enhanced.

Animals↗
PubMed1988

Fibre types, calcium-sequestering proteins and metabolic enzymes in denervated and chronically stimulated muscles of the rat.

1. Fibre types, Ca2+-sequestering proteins (parvalbumin, sarcoplasmic reticulum Ca2+-ATPase), enzyme activities of energy metabolism, and lactate dehydrogenase isozymes were studied in extensor digitorum longus (EDL) and soleus muscles of adult rats after denervation and direct stimulation for 45-61 days. The stimulation resembled the firing patterns of normal motor units (Hennig & Lømo, 1985) in either soleus (20 Hz, high amount) or EDL (150 Hz, low and high amount). 2. Low- and high-amount 150 Hz stimulation maintained essentially normal properties in the denervated EDL and induced many EDL-like properties in the denervated soleus, e.g. pronounced increases in Ca2+-ATPase and parvalbumin contents, a rise in the glycolytic enzyme activities, as well as a reversal of the lactate dehydrogenase H/M subunit ratio. The 150 Hz high-amount stimulation was not as efficient as the 150 Hz low amount in maintaining the fast properties of denervated EDL with the exception of the enzymes of aerobic oxidative metabolism. High-amount 20 Hz stimulation maintained essentially normal properties in the soleus but induced only moderate slow muscle characteristics in the EDL. 3. The maintenance of essentially normal properties by 'native' and the changes induced by 'foreign' stimulus patterns in the absence of the nerve indicate that evoked muscle activity plays a major role in controlling the phenotypic expression of muscle properties. However, the different responses of the denervated fast- and slow-twitch muscles to identical stimulus patterns further suggest that rat EDL and soleus muscles contain intrinsically different muscle fibres.

Animals↗