Min Of Electrical Stimulation Research Articles

Evaluation of ventricular repolarization features with Tp-e, Tp-e/QTc, JTc and JTd during electroconvulsive therapy

ObjectiveThe purpose of this study was to investigate the influence of electrical stimulation transmitted through the body during electroconvulsive therapy on traditional and relatively new ventricular repolarization parameters (Rate corrected QT interval (QTc), QT dispersion (QTd), rate corrected JT interval (JTc), JT dispersion (JTd), T-peak to T-end interval (Tp-e) and Tp-e/QTc ratio) under propofol anaesthesia. MethodsTwenty-two patients (aged 18–50 years) who were each scheduled for ECT for major depression, bipolar disorder or schizophrenia enrolled to the study. Electrocardiography (ECG) recordings were obtained before anaesthesia and within 3–5 min after electrical stimulus of ECT for measurements. QTc, QTd, JTc, JTd, Tp-e and Tp-e/QTc were measured as repolarization indices. ResultsThe study included twenty-two patients, 9(40.9%) females and 13(59.1%) males, and the mean age accounted for 33.57 ± 9.95 years. The comparison of the measured parameters before and after ECT, which were not statistically different, were as follows: QTc (416.52 ± 46.64 vs 430.00 ± 34.00msn; p = 0.18), JTc (308.09 ± 25.09 vs 315.47 ± 26.89msn; p = 0.30), QTd (22.27 ± 11.51 vs 20.45 ± 9.9msn; p = 0.52) and JTd (22.72 ± 11.2 vs 17.72 ± 10.20msn; p = 0.06). Also, no significant difference was detected at the following parameters Tp-e (80.0 ± 13.45 vs 78.63 ± 15.21msn; p = 0.65) and Tp-e/QTc ratio (0.19 ± 0.03 vs 0.18 ± 0.07; p = 0.08). On the other hand, HR showed a significant increase after ECT at 88.13 ± 13.74 vs 93.0 ± 15.2 bpm; p = 0.03. ConclusionQTc, QTd, JTc, JTd, Tp-e interval and Tp-e/QTc ratio, which are thought to be potential repolarisation markers for ventricular arrhythmias, did not demonstrate significant change within 3–5 min of electrical stimulation during ECT.

Contribution of the late sodium current to intracellular sodium and calcium overload in rabbit ventricular myocytes treated by anemone toxin.

Pathological enhancement of late Na(+) current (INa) can potentially modify intracellular ion homeostasis and contribute to cardiac dysfunction. We tested the hypothesis that modulation of late INa can be a source of intracellular Na(+) ([Na(+)]i) overload. Late INa was enhanced by exposing rabbit ventricular myocytes to Anemonia sulcata toxin II (ATX-II) and measured using whole cell patch-clamp technique. [Na(+)]i was determined with fluorescent dye Asante NaTRIUM Green-2 AM. Pacing-induced changes in the dye fluorescence measured at 37°C were more pronounced in ATX-II-treated cells than in control (dye washout prevented calibration). At 22-24°C, resting [Na(+)]i was 6.6 ± 0.8 mM. Treatment with 5 nM ATX-II increased late INa 8.7-fold. [Na(+)]i measured after 2 min of electrical stimulation (1 Hz) was 10.8 ± 1.5 mM and 22.1 ± 1.6 mM (P < 0.001) in the absence and presence of 5 nM ATX-II, respectively. Inhibition of late INa with GS-967 (1 μM) prevented Na(+) i accumulation. A strong positive correlation was observed between the late INa and the pacing-induced increase of [Na(+)]i (R(2) = 0.88) and between the rise in [Na(+)]i and the increases in cytosolic Ca(2+) (R(2) = 0.96). ATX-II, tetrodotoxin, or GS-967 did not affect [Na(+)]i in quiescent myocytes suggesting that late INa was solely responsible for triggering the ATX-II effect on [Na(+)]i. Experiments with pinacidil and E4031 indicate that prolongation of the action potential contributes to as much as 50% of the [Na(+)]i overload associated with the increase in late INa caused by ATX-II. Enhancement of late INa can cause intracellular Na(+) overload in ventricular myocytes.

ASIC3 Is Required for Development of Fatigue-Induced Hyperalgesia.

An acute bout of exercise can exacerbate pain, hindering participation in regular exercise and daily activities. The mechanisms underlying pain in response to acute exercise are poorly understood. We hypothesized that proton accumulation during muscle fatigue activates acid-sensing ion channel 3 (ASIC3) on muscle nociceptors to produce hyperalgesia. We investigated the role of ASIC3 using genetic and pharmacological approaches in a model of fatigue-enhanced hyperalgesia. This model uses two injections of pH 5.0 saline into muscle in combination with an electrically induced fatigue of the same muscle just prior to the second injection of acid to induce mechanical hyperalgesia. We show a significant decrease in muscle force and decrease in muscle pH after 6 min of electrical stimulation. Genetic deletion of ASIC3 using knockout mice and pharmacological blockade of ASIC3 with APETx2 in muscle prevents the fatigue-enhanced hyperalgesia. However, ASIC3(-/-) mice and APETx2 have no effect on the fatigue response. Genetic deletion of ASIC3 in primary afferents innervating muscle using an HSV-1 expressing microRNA (miRNA) to ASIC3 surprisingly had no effect on the development of the hyperalgesia. Muscle fatigue increased the number of macrophages in muscle, and removal of macrophages from muscle with clodronate liposomes prevented the development of fatigue-enhanced hyperalgesia. Thus, these data suggest that fatigue reduces pH in muscle that subsequently activates ASIC3 on macrophages to enhance hyperalgesia to muscle insult.

C-Fos induction in the brainstem following electrical stimulation of the trigeminal ganglion of chronically mandibular nerve-transected rats

Neuronal excitability in the trigeminal sensory nuclei (TSN) changes after nerve transection. We examined the effects of chronic transection of the trigeminal nerve on the c-Fos-immunoreactivity in the TSN induced 2 h after 10 min of electrical stimulation of the trigeminal ganglion (TG) at C-fiber activating condition (1.0 mA, 5 ms, 5 Hz) in urethane-anesthetized rats. In the non-transected control rats, stimulation of the TG induced c-Fos-immunoreactive cells (c-Fos-IR cells) mostly in superficial layers (VcI/II) of the nucleus caudalis (Vc) in its full extent along the dorsomedial–ventrolateral axis, but modestly in the rostral TSN above the obex, the principal, oral, and interpolar nuclei. Three days, 1, 2, or 3 weeks after transection of the inferior alveolar (IAN), infraorbital, or masseteric nerves, the stimulation of the TG induced c-Fos-IR cells in the central terminal fields of the transected nerve in the rostral TSN and magnocellular zone of the Vc. However, the number of c-Fos-IR cells in the VcI/II decreased inside the central terminal fields of the transected nerve and increased outside the fields. These results indicate that transection of the trigeminal nerve increases the excitability of TSN neurons that receive inputs from injured mechanoreceptors and uninjured nociceptors, but decreases it from injured nociceptors. The altered c-Fos responses may imply mechanisms of neuropathic pain seen after nerve injury.

Explaining Task Failure From Sustained Submaximal Isometric Contractions

Sustaining a submaximal isometric contraction leads to task failure, defined as the inability to maintain the requested force level. Both neural and muscular mechanisms contribute to the muscle fatigue associated with a sustained contraction performed with the knee extensor muscles, but the origin of task failure has not been clearly identified. PURPOSE: To determine the extent to which the knee extensor muscles themselves are limiting the endurance time (ET) of a sustained submaximal contraction. METHODS: Fourteen subjects (28±1.8 yrs, mean±SE) were asked to sustain an isometric contraction with the knee extensor muscles (dominant leg) at a target force equal to 20% of their maximal voluntary contraction force (MVC) until voluntary exhaustion (ET1). At task failure, the knee extensors were electrically stimulated (40 Hz) for 1 min aiming to develop the same target force that was not possible to develop voluntarily (20% MVC). At the end of the stimulation period, subjects were asked to again voluntarily contract the knee extensors at 20% MVC for as long as possible (ET2). Superimposed on MVC (twitch interpolation technique) and potentiated doublets were recorded before fatigue, after ET1 and after ET2. RESULTS: After task failure of ET1 (246±18s), all subjects developed 20% MVC under electrical stimulation. After the 1 min electrical stimulation period, subjects were able to resume the voluntary task and ET2 lasted 73±7s. MVC was decreased (p<0.05) by 513% after ET1 and by 573% after ET2, whereas maximal voluntary activation level was reduced (from 932% to 873% and to 89±2% after ET1 and ET2, respectively, p<0.01). Potentiated peak doublet was impaired after ET1 (-374%, p<0.001 and after ET2 (-485%, p<0.001). CONCLUSION: Although peripheral impairment is evidenced at task failure (large decrease in potentiated peak doublet), the duration of a sustained submaximal isometric knee extension performed at 20% MVC is not limited by the extensor muscles themselves but rather to mechanisms located above the neuromuscular junction, presumably involving descending motor drive.

Oxygen consumption and blood flow distribution in perfused skeletal muscle of chinook salmon

An isolated, perfused salmon tail preparation showed oxyconformance at low oxygen delivery rates. Addition of pig red blood cells to the perfusing solution at a haematocrit of 5 or 10% allowed the tail tissues to oxyregulate. Below ca. 60 ml O(2) kg(-1) h(-1) of oxygen delivery (DO(2)), VO(2) was delivery dependent. Above this value additional oxygen delivery did not increase VO(2) of resting muscle above ca. 35 ml O(2) kg(-1) h(-1). Following electrical stimulation, VO(2) increased to ca. 65 ml O(2) kg(-1) h(-1), with a critical DO(2) of ca. 150 ml O(2) kg(-1) h(-1). Dorsal aortic pressure fell to 69% of the pre-stimulation value after 5 min of stimulation and to 54% after 10 min. Microspheres were used to determine blood flow distribution (BFD) to red (RM) and white muscle (WM) within the perfused myotome. Mass specific BFD ratio at rest was found to be 4.03 +/- 0.49 (RM:WM). After 5 min of electrical stimulation the ratio did not change. Perfusion with saline containing the tetrazolium salt 3-(4,5-Dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) revealed significantly more mitochondrial activity in RM. Formazan production from MTT was directly proportional to time of perfusion in both red and WM. The mitochondrial activity ratio (RM:WM) did not change over 90 min of perfusion.

Co-release of noradrenaline and dopamine in the cerebral cortex elicited by single train and repeated train stimulation of the locus coeruleus

BackgroundPrevious studies by our group suggest that extracellular dopamine (DA) and noradrenaline (NA) may be co-released from noradrenergic nerve terminals in the cerebral cortex. We recently demonstrated that the concomitant release of DA and NA could be elicited in the cerebral cortex by electrical stimulation of the locus coeruleus (LC). This study analyses the effect of both single train and repeated electrical stimulation of LC on NA and DA release in the medial prefrontal cortex (mPFC), occipital cortex (Occ), and caudate nucleus. To rule out possible stressful effects of electrical stimulation, experiments were performed on chloral hydrate anaesthetised rats.ResultsTwenty min electrical stimulation of the LC, with burst type pattern of pulses, increased NA and DA both in the mPFC and in the Occ. NA in both cortices and DA in the mPFC returned to baseline within 20 min after the end of the stimulation period, while DA in the Occ reached a maximum increase during 20 min post-stimulation and remained higher than baseline values at 220 min post-stimulation. Local perfusion with tetrodotoxin (TTX, 10 μM) markedly reduced baseline NA and DA in the mPFC and Occ and totally suppressed the effect of electrical stimulation in both areas.A sequence of five 20 min stimulations at 20 min intervals were delivered to the LC. Each stimulus increased NA to the same extent and duration as the first stimulus, whereas DA remained elevated at the time next stimulus was delivered, so that baseline DA progressively increased in the mPFC and Occ to reach about 130 and 200% the initial level, respectively.In the presence of the NA transport (NAT) blocker desipramine (DMI, 100 μM), multiple LC stimulation still increased extracellular NA and DA levels.Electrical stimulation of the LC increased NA levels in the homolateral caudate nucleus, but failed to modify DA level.ConclusionThe results confirm and extend that LC stimulation induces a concomitant release of DA and NA in the mPFC and Occ.The different time-course of LC-induced elevation of DA and NA suggests that their co-release may be differentially controlled.

Analysis of serotonin release from single neuron soma using capillary electrophoresis and laser-induced fluorescence with a pulsed deep-UV NeCu laser.

The use of capillary electrophoresis (CE) with laser-induced fluorescence excited by ultraviolet (UV) lasers in the range 200-300 nm has been restricted by the available wavelengths and expense of UV lasers. The integration of a NeCu deep UV laser operating at 248.6 nm with a single channel CE system with post-column sheath flow detection allows detection limits for serotonin and tryptophan of 3.9x10(-8) M and 4.5x10(-8) M respectively. Single cell analysis of serotonergic metacerebral cells from the sea slug Aplysia californica yields a value of 800+/-85 fmol of serotonin in each cell soma. For the first time, serotonin is directly detected in electrically stimulated release from single metacerebral cell soma, with approximately 4% of the serotonin contained in the soma released from a semi-intact preparation with a 2 min electrical stimulation.

Morphological changes in frog mast cells induced by nerve stimulation in vivo

We investigated at both histochemical and ultrastructural levels the effects of unilateral electrical stimulation in vivo of the frog hypoglossal nerve on the mast cells (MCs) within the nerve fascicles and among the axon terminals. The right ventral root of the hypoglossal nerve in different experiments was stimulated respectively for 1, 3, 5, 10 min with over-threshold stimuli (10 Hz; 2 ms duration). The stimulations at 3, 5 and 10 min caused a progressive degranulation and histochemical and ultrastructural changes of the MCs at the stimulated side. The morphological changes consisted of the loss of Alcian Blue secretory content and of a progressive release of safranin+ secretory granules, depending upon duration of stimulation. The ultrastructural study showed that granules are discharged whole into the microenvironment or may release their content through exocytosis. A functional relationship between nerve and MCs is also suggested by the close anatomical association between MCs and pre-terminal axons observed following 10 min of hypoglossal stimulation. No changes in MC morphology occurred after 1 min of electrical stimulation. The results suggest that active cholinergic fibres can modulate MC secretion.

Alterations in neurokinin A-, substance P- and calcitonin gene-related peptide immunoreactivities in the caudal trigeminal nucleus of the rat following electrical stimulation of the trigeminal ganglion

We have carried out an immunohistochemical study on the presence of neurokinin A (NKA) and substance P (SP) in the rat caudal trigeminal nucleus (CTN) after electrical stimulation of the trigeminal ganglion (TG), used as an experimental model to induce alterations, some of which may occur during migraine attacks (release of vasoactive peptides from perivascular trigeminal axons and neurogenic inflammation). Both unilateral, 30 min electrical stimulation (5 Hz, 5 ms, 0.1–1 mA) of the TG and 5 min stimulation with a slight increase in the stimulating parameters (7.5 Hz, 5 ms, 1.4 mA) caused a significant depletion of the NKA and SP immunoreactivities (-IR) of the TG nerve central terminals in the ipsilateral CTN. Calcitonin gene-related peptide (CGRP)-IR of the ipsilateral CTN was also studied in the CTN using the increased stimulating parameters and a marked depletion of CGRP-IR was also observed following TG stimulation. Such depletion may be due to the release of neuropeptides from the trigeminal central terminals. These findings suggest that NKA, SP and CGRP could act as neurotransmitters at the first central synapses of the trigeminal nociceptive pathway to transmit the sensory stimuli to the higher brain centers.

The contribution of different types of calcium channels to electrically-evoked adenosine release from rat hippocampal slices.

The role of L-, N- and P-type voltage-dependent calcium channels (VDCCs) in the release of adenosine from rat hippocampal slices was investigated by evaluating the effect of the L-channel activator 1,4-dihydro-2,6-dimethyl-5-nitro-4-[2-(trifluoromethyl)-phenyl]-3-pyr idi ne carboxylic acid methyl ester (Bay K 8644) and of three calcium channel antagonists: the L-channel antagonist nifedipine, the N-channel blocker omega-conotoxin GVIA (omega-CgTx) and the P-channel blocker omega-agatoxin IVA (omega-Aga-IVA). Adenosine and inosine release, evoked by 5 min electrical stimulation at 10 Hz of hippocampal slices, was assayed by HPLC with ultraviolet absorbance or fluorimetric detection. Nifedipine (100 nM) did not affect adenosine and inosine release evoked by electrical stimulation. Bay K 8644 (100 nM) brought about a statistically significant increase in adenosine evoked release (70%). At a higher concentration (1 microM) Bay K 8644 had no significant effect either on adenosine or inosine release evoked by electrical stimulation. The increase in adenosine release elicited by 100 nM Bay K 8644 was abolished by nifedipine (100 nM). Both omega-CgTx (10 microM) and omega-Aga-IVA (200 nM) caused a statistically significant reduction (77-78%) in evoked release of adenosine. When the previously demonstrated glutamate-dependent component of the release of adenosine was suppressed in the presence of the NMDA and non-NMDA receptor antagonists, D(-)-2-amino-7-phosphonoheptanoic acid (D-AP7. 100 microM) and 6,7-dinitroquinoxaline-2,3-dione (DNQX, 10 microM), the remaining release of adenosine was again significantly reduced by omega-CgTx (10 microM) (60%) and omega-Aga-IVA (200 nM) (73%). These data suggest that, while L-type VDCCs are involved in the regulation of the evoked release of adenosine only when activated by Bay K 8644, both P- and N-channels play a direct role in the calcium entry involved in the coupling process between electrical stimulation and adenosine release.

Changes in pre- and postsynaptic components of noradrenergic transmission in hippocampal kindling in rats

We investigated whether modifications in noradrenergic neurotransmission occurred during the development of hippocampal kindling in rats. We measured the release of [ 3H]norepinephrine (NE) induced by field-electrical stimulation, NE-stimulation of inositol phosphates ([ 3H]IP) accumulation in the presence of LiCl and isoproterenol-induced accumulation of cAMP in hippocampal slices taken from rats electrically kindled at stages 2 and 5 in the dorsal hippocampus. One week after the last of at least 3 consecutive stage 5 seizures or 48 h after the last stage 2 stimulation, 2 min electrical stimulation of stratum pyramidale CA1–CA3 or dentate gyrus (DG) slices from kindled and contralateral hippocampi induced frequency-dependent NE release (respectively 2, 4 and 8 times spontaneous release measured at 2, 5 and 10 Hz) which did not significantly differ from that observed in shams (implanted with electrodes but not stimulated). Basal release of NE from kindled and sham-treated rats did not differe either. Isoproterenol induced a dose-dependent increase above basal cAMP concentration ranging from 40% at 0.01 μM to 180% at 10 μM ( P < 0.01, Dunnett's test) which did not differ between stages 2 and 5 and sham-hippocampi. NE (1–1000 μM) induced a dose-dependent, prazosin-sensitive increase in [ 3H]IP accumulation in the hippocampal slices. A significantly higher increase was found at stages 2 ( P < 0.05, Tukey's test) and 5 ( P < 0.05 and P < 0.01, Tukey's test) compared to shams at all doses studied. No differences were observed in the basal cAMP or [ 3H]IP concentrations in kindled versus sham animals. No differences were observed in [ 3H]IP accumulation induced by carbachol (10, 100, 1000 μM) in stage 5-kindled rats and shams. These changes have various possible implications for kindling-induced plasticity.

Control of mitochondrial ATP synthase in rat cardiomyocytes: effects of thyroid hormone

Activities of the mitochondrial ATP synthase and the electron transfer chain were investigated in cultured cardiomyocytes prepared from untreated and thyroxine-treated rats. Quiescent cells from the thyroxine-treated animals showed a 33% increase in mitochondrial ATP synthase capacity, but no change in respiratory chain capacity, relative to those from control animals. This increase was attributable largely to (a) a 25% increase in F 1 content in these mitochondria, and partly to (b) a 10% stimulation in ATPase activity due to raised intramitochondrial Ca 2+. Both types of cell showed a normal ATP content of 38–40 nmol/mg cell protein. In control cells, the mitochondrial ATP synthase responded to increased energy demand (by electrical stimulation and/or by positive inotropic agents) with an increase in its capacity of up to 2-fold. This response was absent in cells from thyroxine-treated animals. In addition, cellular ATP levels fell significantly after 2 min electrical stimulation of cells from thyroxine-treated animals, while those of control cells were constant. It was concluded that regulation of the mitochondrial ATP synthase was defective in heart cells from thyroxine treated rats, leading to an energy deficit when energy demand on the cells was increased. Animals treated with thyroxine, but allowed to recover for 17 days after treatment, showed responses indistinguishable from the control cells. Thus, the effects of thyroxine on mitochondrial activities were reversible.

Trigeminal sensory fiber stimulation induces morphological changes reflecting secretion in rat dura mater mast cells

Mast cells are involved in allergic reactions, but may also participate in neurogenic inflammation. The morphology of mast cells in rat dura mater and tongue was evaluated by histochemistry, as well as by scanning and transmission electron microscopy following unilateral trigeminal ganglion stimulation (5 min, S Hz, 5 ms, and 0.02, 0. l or l .0 mA). Mast cells in dura and tongue of normal animals were numerous, perivascular and often in close proximity to nerve fibers. After 5 min of electrical stimulation, mast cells contralateral to the stimulation showed histochemical characteristics of normal peripheral tissue mast cells (Safranin-positive), and by electron microscopy appeared homogeneous with numerous intact electron-dense granules. On the stimulated side, however, the staining characteristics of mast cells showed changes indicating progressive intracellular loss of their granular content. In addition, the total number of stainable mast cells decreased at all three stimulus intensities, but reached significance only at 0.1 and 0.02mA. Ultrastructural evidence of granule changes consistent with secretion were observed although degranulation was not observed until 20 min after stimulation. There were no mast cell changes after electrical trigeminal stimulation in adult rats treated as neonates with capsaicin to destroy small caliber sensory afferent axons. These results suggest that mast cells may secrete in response to electrical stimulation of trigeminal axons, possibly mediated by antidromic release of neuropeptides, and may participate in the development of neurogenic inflammation.

Dihydroxyphenylglycol as an index of neuronal uptake in dog saphenous vein.

Dihydroxyphenylglycol (DOPEG), the metabolite of norepinephrine (NE) that arises intraneuronally, was measured together with NE in superfusates collected before, during, and after nerve stimulation and in extracts of dog saphenous vein after superfusion and electrical stimulation (ES). Different concentrations of NE in the synaptic clefts were achieved by treating tissues with corticosterone, corticosterone and yohimbine, corticosterone and cocaine, or by omitting drugs from the superfusate. NE and DOPEG were quantitated by liquid chromatography with electrochemical detection. The time courses of NE overflow and DOPEG efflux into superfusate were followed. The amounts of DOPEG in superfusates under basal conditions were two to four times higher than the amounts of NE and progressively increased during ES except in tissues with neuronal uptake inhibited. NE overflow reached a steady state within the first 6 min of ES. Increased NE concentrations in synaptic clefts resulted in increased DOPEG production except where neuronal uptake was inhibited. The increased DOPEG production during ES appears to reflect the increased rate of neuronal uptake, which results in more NE being available for intraneuronal metabolism. No evidence was found that newly formed DOPEG was delayed in leaving the tissue. Thus the increase in DOPEG production that occurs during ES may be useful as an index of neuronal uptake of NE in dog saphenous vein.

Post-stimulatory effects of direct current stimulation of the cochlea on auditory nerve activity

Glass micro-electrode recordings from the spiral ganglion of the basal turn of the guinea pig cochlea have been obtained before, during and after negative (cathodic) current injection into scala tympani. Electrical stimulation with currents between 100 μA and 900 μA produced a marked increase in firing rate of the afferent neurons for the first 3 min of electrical stimulation. This was followed by a fall in firing rate to rates near or below the prestimulatory spontaneous rate if stimulation continued. Continuous electrical stimulation lasting 5 or 10 min reduced neural sensitivity to acoustic stimulation. Although threshold elevation was greatest for sound frequencies near the characteristic frequency of each neuron, thresholds could also be elevated at lower frequencies on the tail of the frequency-threshold tuning curve. After electrical stimulation a fall in the amplitude of the low-frequency microphonic recorded at the round window was also observed, indicating a disruption of the outer hair cell transduction. These effects were highly localized in the basal turn near the site of current injection, and were not associated with any significant structural changes in the organ of Corti, except after stimulation with very high current intensities.

Muscle action potential propagation velocity changes during activity

Fatigue from high frequency stimulation is associated with EMG signal changes, which are primarily due to a slowing of the sarcolemma conduction velocity. In the present study, in which isolated mouse soleus and extensor digitorum longus muscles have been studied, it is shown that the action potential propagation velocity is (1) decreased by an increased extracellular potassium concentration, (2) independent of extracellular pH, (3) decreased by low intracellular pH, and (4) nearly independent of moderate changes in the sodium gradient. The EDL muscle is more affected than the soleus muscle. The ion effects on propagation velocity are seen within the physiological ranges. The propagation velocity was decreased after 2 min of electrical stimulation and recovered with a time course similar to the pH recovery. The effects of extracellular potassium and internal pH are due to independent mechanisms.

Quantitative x-ray elemental imaging in stimulated single intact skeletal muscle fibers: The fate of calcium in the presence of ryanodine

We are involved in a continuing series of experiments aimed at a complete description,in terms of morphology and quantitative topochemistry, of the time course of spatial distributions of physiologically important elements during excitation-contraction coupling (ECC) at different time intervals (fractions of msec) following electrical stimulation of single, intact frog skeletal muscle fibers. In this present study wg report such distributions for Ca after 1,2 and 3 min of electrical stimulation in the presence of 2x10-4 M ryanodine, an alkaloid that, in time, causes irreversible muscle contractures.Single, intact frog skeletal muscle fibers were quick-frozen, cryosectioned, freeze-substituted and in one case freeze-fractured. The freeze-dried cryosections were subjected to electron probe X-ray microanalysis (EPXMA) in a JEOL 1200EX analytical electron microscope equipped with a Tracor Northern X-ray detector and a fully quantitative imaging system. Both, 64/64 pixel images (ambient temp.), and small raster probes (cold stage,-115 °C) for better statistics, were obtained, each from the same section.

Energy utilization and gluconeogenesis in isolated leech segmental ganglia: Quantitative studies on the control and cellular localization of endogenous glycogen

The isolated segmental ganglia of the horse leech Haemopis sanguisuga were used as a model system to study the utilization and control of glycogen stores within nervous tissue. The glycogen in the ganglia was extracted and assayed fluorimentrically and its cellular localization and turnover studied by autoradiography in conjunction with [ 3H]glucose. We measured the glycogen after various periods of electrical stimulation and after incubation with K +, Ca 2+, ouabain and glucose. The results for each experimental ganglion were compared to a paired control ganglion and the results analysed by paired t-tests. Electrical stimulation caused sequential changes in glycogen levels: a reduction of up to 67% (5–10 min); followed by an increase of up to 124% (between 15–50 min); followed by a reduction of up to 63% (60–90 min). Values were calculated for glucose utilization (e.g. 0.53 μmol glucose/gm wet weight/min after 90 min) and estimates derived for glucose consumption per action potential per neuron (e.g. 0.12 fmol at 90 min). Glucose (1.5–10 mM) increased the amount of glycogen (1.5 mM by 30% at 60 min) and attenuated the effects of electrical stimulation. Ouabain (1 mM) blocked the effect of 5 min electrical stimulation. Nine millimolar K + increased glycogen by 27% after 10 min and decreased glycogen by 34% after 60 min; 3 mM Ca 2+ had no effect after 10 or 20 min and decreased glycogen by 29% after 60 min. Other concentrations of K + and Ca 2+ reduced glycogen after 60 min. Autoradiographic analysis demonstrated that the effects of elevated K + were principally within the glial cells. We conclude that (i) the glycogen stores in the glial cells of leech segmental ganglia provide an endogenous energy source which can support sustained neuronal activity, (ii) both electrical stimulation and elevated K + can induce gluconeogenesis within the ganglia, (iii) that electrical activation of neurons produces changes in the glycogen in the glial cells which are controlled in part by changes in K +.

Electrical stimulation of the hypothalamic nucleus paraventricularis mimics the effects of light on pineal melatonin synthesis

In an attempt to clarify further the role of the hypothalamic paraventricular nuclei (PVN) in the control of pineal function, the effects of 2 min electrical stimulation of these nuclei were investigated in acutely blinded, adult, male Sprague-Dawley rats. Pineal serotonin-N-acetyltransferase (NAT) activity, melatonin content and catecholamine levels were measured by means of radio-enzymatic, radioimmunoassay and high-performance liquid-chromatography methods, respectively. All three pineal parameters underwent significant declines following brief PVN stimulation during the night time. These observations lend credence to the view that the neural pathways transmitting light information to the sympathetic innervation controlling pineal melatonin synthesis.