Bone and non-contractile soft tissue changes following open kinetic chain resistance training and testosterone treatment in spinal cord injury: an exploratory study.

Twenty men with spinal cord injury (SCI) were randomized into two 16-week intervention groups receiving testosterone treatment (TT) or TT combined with resistance training (TT + RT). TT + RT appears to hold the potential to reverse or slow down bone loss following SCI if provided over a longer period. INTRODUCTION: Persons with SCI experience bone loss below the level of injury. The combined effects of resistance training and TT on bone quality following SCI remain unknown. METHODS: Men with SCI were randomized into 16-week treatments receiving TT or TT + RT. Magnetic resonance imaging (MRI) of the right lower extremity before participation and post-intervention was used to visualize the proximal, middle, and distal femoral shaft, the quadriceps tendon, and the intermuscular fascia of the quadriceps. For the TT + RT group, MRI microarchitecture techniques were utilized to elucidate trabecular changes around the knee. Individual mixed models were used to estimate effect sizes. RESULTS: Twenty participants completed the pilot trial. A small effect for yellow marrow in the distal femur was indicated as increases following TT and decreases following TT + RT were observed. Another small effect was observed as the TT + RT group displayed greater increases in intermuscular fascia length than the TT arm. Distal femur trabecular changes for the TT + RT group were generally small in effect (decreased trabecular thickness variability, spacing, and spacing variability; increased network area). Medium effects were generally observed in the proximal tibia (increased plate width, trabecular thickness, and network area; decreased trabecular spacing and spacing variability). CONCLUSIONS: This pilot suggests longer TT + RT interventions may be a viable rehabilitation technique to combat bone loss following SCI. CLINICAL TRIAL REGISTRATION: Registered with clinicaltrials.gov : NCT01652040 (07/27/2012).

Spontaneous and evoked inhibitory junction potentials in the circular muscle layer of mouse colon.

Intracellular microelectrodes were used to record spontaneous and evoked inhibitory junction potentials (IJPs) from the circular muscle layer of an in vitro preparation of whole mouse colon. Membrane potential recordings were made from cells of the mid to distal region of colon at 36 +/- 1 degrees C in a modified Krebs' solution that contained atropine (1 microM) and nifedipine (1-2 microM). Spontaneously occurring hyperpolarisations of irregular amplitude and frequency (range: up to 20 mV and 2 Hz) were recorded that were resistant to N(G)-nitro-L-arginine (NOLA, 100 microM), but were abolished by tetrodotoxin (TTX, 1.6 microM) or apamin (250 nM). These were considered to be spontaneous IJPs as a consequence of activity in inhibitory motor neurons. Single electrical stimuli (0.6 ms, 15 V), elicited a fast IJP, whose time course could be superimposed on spontaneous IJPs of similar amplitude. The amplitude of evoked IJPs was not depressed by NOLA (100 microM). However, in NOLA (100 microM), further addition of apamin (250 nM) significantly depressed the amplitudes of the evoked IJPs by 44%. NOLA- and apamin-resistant evoked IJPs were abolished by TTX (1.6 microM). It is suggested, that in the circular muscle layer of mouse colon, NO does not mediate the fast hyperpolarisations associated with spontaneous or evoked IJPs. Apamin abolished spontaneous IJPs, but electrical stimuli evoked an IJP with apamin-sensitive and resistant components both of which were non-nitrergic in origin.

Inhibitory neurotransmission in the circular muscle layer of mouse colon.

Intracellular electrophysiological techniques were used to record the spontaneous myoelectric activity in the circular muscle layer of an in vitro preparation of whole mouse colon. In 34 out of 58 preparations, spontaneous depolarisations (myoelectric complexes, MCs) were recorded cyclically, about every 4 min. In these preparations, apamin (250 nM) and NG-nitro-L-arginine (NOLA, 100 microM) depolarised the membrane potential between MCs by 8 mV or 13 mV, respectively. Tetrodotoxin (1.6 microM) abolished MCs and also induced depolarisation (17 mV). In the remaining 24 preparations, MCs were not recorded and the membrane potential was significantly depolarised compared to the membrane potential between MCs. NOLA (100 microM), apamin (250 nM) and tetrodotoxin (1.6 microM) were without significant effect on membrane potential. It is suggested that in preparations that exhibit MC cycling, membrane potential between MCs is maintained in a state of tonic inhibition, predominantly mediated by nitrergic mechanisms generated via spontaneously active inhibitory neurons. Apamin-sensitive channels may also be involved in the inhibition.

Muscarinic receptor activation in guinea-pig chromaffin cells causes decreased membrane conductance and depolarization.

Membrane potentials were recorded with conventional intracellular microelectrodes from chromaffin cells in isolated, bisected adrenal glands from guinea-pigs. The local pressure ejection of muscarinic agonists, acetylcholine (in the presence of hexamethonium) or bethanecol, caused a transient depolarization that was relatively slow (1-2 s) in onset compared with the depolarization associated with the activation of nicotinic receptors. Muscarinic receptor-induced depolarization was associated with an increase in input resistance and the firing of action potentials. Repetitive stimulation of splanchnic nerve fibers within the gland, in the presence of hexamethonium, caused a maintained depolarization that was slow in both onset and decay and in many cells caused the repetitive firing of action potentials. It is suggested that, in this species, the exocytosis of catecholamines caused by the activation of muscarinic receptors, described by others, may be due to the initiation of tetrodotoxin-sensitive action potentials and consequent opening of voltage sensitive Ca2+ channels.

Tetrodotoxin-sensitive action potentials in smooth muscle of mouse vas deferens.

Action potentials were recorded during impalements of some but not all smooth muscle cells of mouse vas deferens in response to both nerve stimulation and intracellular current injection. They were resistant to blockade by nifedipine (0.1-1.0 microM) but were blocked by tetrodotoxin (TTX, 0.2-1.0 microM) when this was added in the presence of nifedipine. It is suggested that voltage-dependent sodium (Na+) channels are present in mouse vas deferens that function to amplify calcium (Ca2+) influx through voltage-dependent Ca2+ channels.

Currents caused by the spontaneous release of quanta of acetylcholine onto chromaffin cells in guinea-pig adrenal medulla.

Membrane potentials were recorded from chromaffin cells in isolated bisected adrenal glands from guinea-pigs. Spontaneous excitatory synaptic potentials (SESPs) were recorded whose frequency was increased following brief (up to 10 s) periods of presynaptic nerve stimulation at 10-30 Hz. The single electrode voltage-clamp method was used to record the currents underlying all but the largest SESPs. Spontaneous excitatory synaptic currents (SESCs) decayed according to a single exponential with a time constant of about 8 ms at 30 degrees C. Thus the neuronal nicotinic receptor-channels giving rise to SESCs in chromaffin cells are probably very similar to those that are opened by quanta of acetylcholine in sympathetic ganglion cells.

Synaptic transmission from splanchnic nerves to the adrenal medulla of guinea-pigs.

1. Membrane potentials were recorded with conventional intracellular microelectrodes from chromaffin cells in isolated, bisected adrenal glands from guinea-pigs. 2. All cells were electrically excitable and responded to depolarizing current with all-or-nothing action potentials that were blocked by tetrodotoxin. 3. Input resistance was 180 +/- 14 M omega and this was lower than that reported for isolated chromaffin cells using patch electrodes. 4. All cells responded to transmural stimulation with action potentials that arose from excitatory synaptic potentials in response to the excitation of one or more preganglionic fibres, many having strong synaptic action. Other fibres had weaker synaptic action but in all cases, maximal transmural stimulation caused depolarization well above threshold for action potential initiation. 5. Spontaneous excitatory synaptic potentials were observed whose frequency was greatly increased by repetitive stimulation at 10 or 30 Hz. 6. No evidence was found for the desensitization of nicotinic receptors in response to acetylcholine released from presynaptic nerve terminals. 7. These experiments show that there are many similarities between the responses to splanchnic nerve stimulation of guinea-pig chromaffin cells in situ and sympathetic ganglion cells from the same species.

Membrane properties of rabbit basilar arteries and their responses to transmural stimulation.

Changes in membrane potential of rabbit basilar arteries were recorded in response to transmural stimuli applied by means of a suction electrode. Responses to current pulses of long duration and low intensity showed that the passive electrical properties of basilar arteries were similar to those of other vascular smooth muscles. In contrast to peripheral arteries, action potentials were readily evoked by depolarizing currents. Action potentials were graded in amplitude from 17-60 mV according to stimulus strength. Amplitudes and rates of rise of the directly evoked action potentials increased with increasing external calcium and were abolished by cobalt, manganese and magnesium. Brief electrical stimuli which might have been expected to activate perivascular nerves produced slow depolarizing responses whose amplitude and duration increased with increasing stimulus intensity. These responses were not blocked by tetrodotoxin, lowered external calcium, or sympathetic denervation. They do not appear to be due to the release of a conventional neurotransmitter.

Effects of nifedipine on nerve-evoked action potentials and consequent contractions in rat tail artery.

The effects of nifedipine on the electrical and mechanical activity recorded from the rat tail artery were examined. Intracellular recordings were obtained from the smooth muscle and vessel diameter monitored during nerve stimulation. Nifedipine (0.1-10 microM) depressed contractions elicited by single and repetitive (2 Hz) stimulation by 32-100% but was ineffective in decreasing the amplitude of the associated action potentials. Concentrations greater than or equal to 10 microM caused a slowly developing membrane depolarization. No change in the amplitude of subthreshold excitatory junction potentials was observed at concentrations of nifedipine less than 50 microM when the membrane depolarization was less than 8 mV. At all concentrations examined nifedipine lowered the stimulus intensity required to initiate an action potential. The amplitude of the nerve-evoked action potential recorded in lowered external Ca2+ (1 mM) was slightly increased (5-10%) by nifedipine. However, nifedipine readily reversed the increased amplitudes of the nerve-evoked action potentials and contractions caused by the addition of 20 mM tetraethylammonium chloride in the tail artery. The action potential recorded in normal solution from the guinea pig vas deferens was selectively abolished by nifedipine.

Atropine-resistant depolarization in the guinea-pig small intestine.

1. Junction potentials were recorded from the circular muscle cells of the guinea-pig ileum following transmural stimulation in the presence of atropine at 30 degrees C.2. Single stimuli produced a transient hyperpolarization, the inhibitory junction potential (i.j.p.). At high stimulus strengths the i.j.p. was followed by a post-stimulus depolarization (PSD).3. During repetitive stimulation the magnitude of the hyperpolarization decreased; however, at the end of the stimulus period the PSD was enhanced and often reached threshold for the generation of action potentials. Thus, the size of the PSD was not directly related to the degree of the preceding hyperpolarization.4. Hyperpolarization of the circular muscle cells was produced by the application of anodal current using large external electrodes. Rapid cessation of the applied current produced a transient after-depolarization which was shorter in time course than the PSD following the i.j.p. If the applied anodal current was reduced slowly (at a rate which mimicked the decrease in the hyperpolarization during repetitive nerve stimulation) no after-depolarization was observed.5. Conditioning hyperpolarization of the circular muscle cells reduced the amplitude of the i.j.p. The i.j.p. was reversed at membrane potentials greater than approximately -90 mV.6. The PSD did not appear to be due to the extracellular accumulation of potassium ions following the i.j.p. since the PSD persisted even when the i.j.p. was reversed.7. The neurotoxin apamin reversibly abolished the i.j.p. and unmasked a transient excitatory junction potential (e.j.p.) with a variable latency (350-900 ms).

Effects of tetraethylammonium chloride on sympathetic neuromuscular transmission in saphenous artery of young rabbits.

1. Excitatory junction potentials and electrotonic potentials were recorded from the smooth muscle of the rabbit saphenous artery using intracellular electrodes. 2. Tetraethylammonium chloride (TEA) in concentrations greater than 3.5 mM caused depolarization. Concentrations greater than 5 mM caused spontaneous electrical activity in the form of excitatory junction potentials (e.j.p.s) and all-or-nothing action potentials which were associated with spontaneous mechanical activity. 3. Concentrations of TEA less than 2.5 mM did not alter the resting potential nor the passive membrane properties of the smooth muscle over a range of +/- 15 mV. 4. The following effects were observed in 2.0 mM-TEA. (a) The minimum stimulus strength required for the initiation of an e.j.p. fell by three to fivefold. (b) Single stimuli that elicited only a small e.j.p. in normal solution evoked an all-or-nothing action potential of up to 70 mV amplitude. (c) Whereas in normal solution e.j.p.s could only be recorded up to 7 mm away from the perivascular stimulating electrode e.j.p.s could be recorded at distances of up to 13 mm. (d) The duration of the e.j.p. was prolonged. 5. Based on these results and the effects of TEA reported for other synapses it is proposed that TEA may act to increase the amount of transmitter released per axon, to increase the duration of release and to cause an increased invasion throughout the autonomic ground plexus by nerve impulses. This would imply that in normal solution, in vitro, the action potential may not propagate throughout the whole length of the terminal axon and its many branches due to failure of conduction at one or more points along the terminal portion of the axon.

An electrophysiological analysis of the effects of noradrenaline and alpha-receptor antagonists on neuromuscular transmission in mammalian muscular arteries.

1 The effects of exogenously applied noradrenaline (NA) and alpha-adrenoceptor antagonists on the mechanical and intracellularly recorded responses to perivascular nerve stimulation were examined in the rabbit ear artery, rabbit saphenous artery and rat tail artery. 2 Excitatory junction potentials (e.j.ps) and action potentials recorded from these smooth muscles were not blocked or depressed by phentolamine, phenoxybenzamine, prazosin, or labetolol in concentrations as high as 10 microgram/ml. Phentolamine (1 to 10 microgram/ml) depressed neurally-evoked contractions of the ear and saphenous, but not the tail artery, and also depressed the contractions produced by direct muscle stimulation in the ear and saphenous arteries. Prazosin and labetolol (0.1 to 10 microgram/ml) had no effect on the neurally evoked contractile response in any of the arteries examined. 3 The amplitude of the steady-state e.j.p. during repetitive stimulation at 0.45 to 2 Hz was increased by phentolamine or phenoxybenzamine but not by prazosin or labetolol. Phentolamine and phenoxybenzamine also increased the amplitude of the e.j.p. evoked by a single stimulus in the majority of the preparations. 4 Concentrations of NA greater than or equal to 1 microgram/ml depolarized the smooth muscle while concentrations greater than or equal to 0.5 microgram/ml depressed the amplitude of the e.j.ps recorded from these arteries. alpha-Antagonists did not suppress either the NA-induced membrane depolarization or depression of e.j.ps. 5 These observations call into question the physiological relevance of both pre- and postsynaptic alpha-receptors in regard to adrenergic neuromuscular transmission in muscular arteries.

Some properties of the excitatory junction potentials recorded from saphenous arteries of rabbits.

1. Excitatory junction potentials (e.j.p.s) were recorded from smooth muscle cells of the saphenous arteries of young rabbits. 2. The amplitudes of e.j.p.s recorded from different preparations, in response to a single maximal stimulus, were small and variable (5--14 mV). They decayed exponentially with a time constant of about 200 msec. 3. At frequencies greater than 1 Hz the shape of those e.j.p.s which exceeded 12--15 mV in amplitude was changed. The early part of the e.j.p.s became faster in time course. 4. Trains of up to five stimuli, at frequencies greater than 4 Hz, caused summation of e.j.p.s; 'active responses' were superimposed on this depolarization. Peak amplitude of the response to repetitive stimulation was 50 mV. 5. In normal solution, contraction appeared to be associated with a change in the configuration of e.j.p.s. 6. No action potentials resembling those recorded from most visceral smooth muscles were observed in normal solutions although these could be evoked in the presence of TEA (2.5--10 mM). 7. The method of Abe & Tomita (1968) was used to determine the values of the length constant (lambda) and time constant (tau) of the smooth muscle of intact arteries. The value of lambda (0.6 mm) was about half that found for circular strips cut from larger arteries. 8. The time constant of decay of single e.j.p.s of less than 12 mV in amplitude was indistinguishable from the membrane time constant. 9. Noradrenaline caused contraction of the artery in the absence of a change in membrane potential. 10. It is tentatively suggested that there may be two different populations of receptors in this smooth muscle membrane.

Can nonadrenergic inhibitory varicosities be identified structurally.

The distribution of vesicles in axon varicosities was examined in rabbit jejunum and opossum esophagus. Circular muscle cells of both rabbit jejunum and opossum esophagus responded to stimulation of intrinsic nerves with inhibitory junction potential in nearly all cases. Inhibitory junction potentials were rare and small in longitudinal muscle cells of rabbit jejunum. There were few axon varicosities with a predominance of large opaque vesicles or large dense-cored vesicle in any muscle layer of rabbit or opossum or in the plexuses of rabbit jejunum. There were almost as high a proportion of such varicosities in longitudinal as in circular muscle of rabbit jejunum, and there were almost none in circular muscle of opossum esophagus. The distribution of vesicles in varicosities was found often to be heterogeneous and could account for the observed occurrence of a small proportion of varicosities with a predominance of large vesicles. It is suggested that there is no structural distinction in vertebrates between axons which are cholinergic and axons which are nonadrenergic inhibitory.