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PubMed1986

Transient and delayed potassium currents in the Retzius cell of the leech, Macrobdella decora.

The properties of a quickly inactivating transient K current (IA) and a slowly inactivating delayed K current (IK) were investigated with two-electrode voltage-clamp techniques in the isolated soma of the Retzius cell of the leech, Macrobdella decora. The two currents could be pharmacologically separated according to their different sensitivities to tetraethylammonium ions (TEA) and 4-aminopyridine (4-AP). IA was totally blocked by 3 mM 4-AP but not affected by 25 mM TEA. IK was suppressed almost completely by 25 mM TEA, whereas its peak amplitude only decreased by 10-15% in 3 mM 4-AP. IA was activated at membrane potentials more positive than -35 to -30 mV, whereas the threshold for IK was at more positive potentials of approximately -20 to -15 mV. The activation of IA was rapid with a voltage-dependent time constant [tau m(A)] that varied from 6 to 2 ms for command potentials between -20 and 10 mV (at 22-24 degrees C). The inactivation, which was independent of voltage, was somewhat slower with a time constant (tau A) of approximately 90-110 ms. The time constants for activation [tau m(K)] and the early inactivation phase (tau K) of IK were both voltage dependent. In the range of potential steps from 0 to 30 mV, tau m(K) varied from 12 to 4.5 ms and tau K from 1,500 to 700 ms. The steady-state inactivation of IA varied with holding potential and was complete at potentials more positive than -30 mV. IA was fully available from potentials more negative than -70 mV. IK did not show steady-state inactivation below its threshold of activation. The time course of IA during a maintained depolarization could be reasonably described by the expression IA(t) = IA(infinity) [1-exp(-t/tau m(A))]2 exp(-t/tau A). The time course of activation of IK without allowance for inactivation was approximated by the expression IK(t) = IK(infinity) [1-exp(-t/tau m(K))]2. The reversal potentials and magnitude of both IA and IK were dependent on extra-cellular K concentration, which suggest that a substantial part of the two currents was carried by K ions.

4-Aminopyridine↗
PubMed1987

Voltage-clamp analysis of the ionic conductances in a leech neuron with a purely calcium-dependent action potential.

1. The purely calcium-dependent action potential of the anterior lateral giant (ALG) cell in the leech Haementeria was examined under voltage clamp. 2. Analysis with ion substitutions showed that the ALG cell action potential is generated by only two time- and voltage-dependent conductance systems, an inward Ca-dependent current (ICa) and an outward Ca-dependent K current IK(Ca). 3. The kinetic properties of the inward current were examined both in Cs-loaded neurons with Ca as the current carrier as well as in Ba-containing Ringer solutions with Ba as the current carrier, since Ba effectively blocked all time- and voltage-dependent outward current. 4. During a maintained depolarization, Ba and Ca currents activated with a time constant tau m, they then inactivated with the decay following a single exponential time course with a time constant tau h. The time constants for decay of both Ba and Ca currents were comparable, suggesting that the mechanism of inactivation of ICa in the ALG cell is largely voltage dependent. In the range of potentials from 5 to 45 mV, tau m varied from 8 to 2 ms and tau h varied from 250 to 125 ms. 5. The activation of currents carried by Ba, after correction for inactivation, could be described reasonably well by the expression I'Ba = I'Ba(infinity) [1--exp(-t/tau m)]. 6. The steady-state activation of the Ba-conductance mBa(infinity) increased sigmoidally with voltage and was approximated by the equation mBa(infinity) = (1 + exp[(Vh-6)/3])-1. The steady-state inactivation hBa(infinity) varied with holding potential and could be described by the equation hBa(infinity) = [1 + exp(Vh + 10/7)]-1. Recovery from inactivation of IBa was best described by the sum of two exponential time courses with time constants of 300 ms and 1.75 s, respectively. 7. The outward current IK(Ca) developed very slowly (0.5-1 s to half-maximal amplitude) and did not inactivate during a 20-s depolarizing command pulse. Tail current decay of IK(Ca) followed a single exponential time course with voltage-dependent time constants of between 360 and 960 ms. The steady-state activation n infinity of IK(Ca) increased sigmoidally with depolarization as described by the equation n infinity = [1 + exp(Vh-13.5)/-8)]-1. 8. The reversal potentials of IK(Ca) tail currents were close to the expected equilibrium potential for potassium and they varied linearly with log [K]o with a slope of 51 mV. These results suggest a high selectivity of the conductance for K ions.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1990

Mechanism of potassium uptake in neuropile glial cells in the central nervous system of the leech.

1. Ion-selective double-barreled microelectrodes (ISME) were used to measure intracellular K+ (aKi), Na+ (aNai), and Cl- (aCli) activities of neuropile glial (NG) cells in the central nervous system of the medicinal leech Hirudo medicinalis. Ion fluxes were induced by an increase in extracellular K+ concentration [( K+]o) and analyzed to elucidate the ionic mechanism of the K+ uptake occurring under such conditions. 2. In addition, the K+ concentration of the extracellular space of the nerve cell body region (NCBR) and the neuropile (N) was measured with neutral carrier K(+)-ISME. In normal saline (4 mM K+), a concentration of 4.2 mM was measured in both extracellular spaces. No differences between the K+ concentration of the bathing fluid and the extracellular spaces were found at higher (i.e., 10 and 40 mM) K+ concentrations. 3. In normal saline, the mean membrane potential (Em) was -68 mV, and the mean aKi, aNai, and aCli were found to be 77, 10, and 7 mM, respectively. The corresponding equilibrium potentials were -81, 56, and -66 mV. The chloride equilibrium potential (ECl) was similar to Em, and it is concluded that chloride is passively distributed across the NG cell membrane. 4. When [K+]o was transiently increased 10-fold (i.e., to 40 mM), aKi and a Cli increased transiently by 22 and 25 mM, respectively, and the membrane depolarized to -28 mV, which was similar to both K+ equilibrium potential (EK) and ECl. The KCl uptake was accompanied by a transient decrease in aNai to 5 mM. 5. After incubation for at least 1 h in Na(+)-free saline, NG cells accumulated K+ in the absence of extracellular Na+ to levels similar to those observed in the presence of Na+. Therefore the uptake of K+ was not dependent on external--and probably also internal--Na+. 6. Changes in cell volume induced by the increase in [K+]o were estimated by loading NG cells with choline and monitoring its intracellular concentration with Corning-K(+)-ISME. In saline containing 40 mM K+, NG cell volume increased to approximately 150% of its volume in normal saline. 7. It is concluded that the mechanism of K+ uptake in NG cells is by passive KCl and water influx, which causes cell swelling.

Animals↗
PubMed1991

Effects of ouabain on intracellular ion activities of sensory neurons of the leech central nervous system.

1. The intracellular K+, Na+, and Ca2+ of mechanosensory neurons in the central nervous system of the leech Hirudo medicinalis was measured using double-barreled ion-sensitive microelectrodes. 2. After inhibition of the Na(+)-K+ pump with 5 x 10(-4) M ouabain, the intracellular K+ activity (aKi) decreased, while the intracellular Na+ activity (aNai) increased. The input resistance decreased in the presence of ouabain. The intracellular Ca2+ increased more than one order of magnitude after ouabain addition. All changes in intracellular ion activities and membrane resistance were fully reversible. 3. When extracellular Na+ concentration ([Na+]o) was removed [replaced by tris(hydroxymethyl)aminomethane (Tris)], aNai decreased. In the absence of [Na+]o, aKi and aNai remained unchanged after inhibition of the Na(+)-K+ pump by reducing the extracellular K+ concentration ([K+]o) to 0.2 mM. The membrane resistance increased under these conditions. 4. The intracellular Ca2+ decreased or remained constant after removal of [Na+]o. Addition of ouabain in the absence of [Na+]o did not change intracellular Ca2+, which only increased after readdition of [Na+]o. 5. The relative K+ permeability (PK) measured as membrane potential change during a brief increase of the [K+]o from 4 to 10 mM, increased manyfold after addition of ouabain but only little if [Na+]o had been removed before adding ouabain. 6. The results suggest that the intracellular Na+ increase after inhibition of the Na(+)-K+ pump affects the intracellular Ca2+ level by stimulating a Nai(+)-Ca2+ exchange mechanism. The subsequent intracellular Ca2+ activity (aCai) rise may result in an increase of the membrane permeability to K+ ions.

Animals↗
PubMed1992

Analysis and modeling of the multisegmental coordination of shortening behavior in the medicinal leech. I. Motor output pattern.

1. To understand how a multisegmental animal coordinates motor activity over more than one segment, we studied shortening behavior in the medicinal leech, in which several segments contract longitudinally in response to a moderately strong mechanical stimulus. 2. We first demonstrated that the neuronal activity responsible for shortening behavior occurred in semi-intact and isolated nerve cord preparations, and then characterized the responses of motor neurons in isolated preparations. The motor output during shortening was simultaneous excitation of motor neurons innervating dorsal longitudinal muscle and of motor neurons innervating ventral longitudinal muscle. 3. The stronger the stimulus, the more segments produced the shortening motor output, with the segments nearest the stimulus recruited first. 4. Although the shortening response was produced in several segments near the site of stimulation, it was never produced in the stimulated segment, where the local bending motor output pattern was produced. The motor pattern suggests that shortening, initially considered a very simple behavior, requires the involvement of at least few segmentally iterated interneurons.

Acetates↗
PubMed1992

Analysis and modeling of the multisegmental coordination of shortening behavior in the medicinal leech. II. Role of identified interneurons.

1. Mechanical stimulation of the leech, Hirudo medicinalis, elicits withdrawal behavior that has two components: local bending in the segment stimulated and shortening in outlying segments. Local bending is characterized by excitation of longitudinal muscle on one side of the segment and inhibition on the other side. In shortening, all longitudinal muscles are excited. We wished to understand how these distinct motor patterns are produced by a nervous system with segmentally iterated neurons, a configuration that places some limitations on the complexity of connection patterns. 2. We searched for neurons in the segmental nervous system that subserved shortening behavior, expecting to find at least one interneuron in each segment that was involved in shortening behavior exclusively. We found instead that all interneurons involved in shortening are also involved in local bending, and no individual interneuron can completely account for shortening. 3. The motor output caused by individual identified interneurons is not entirely consistent with the shortening motor output pattern. For instance, one interneuron, cell 115, has the same pattern of motor effects from segment to segment, causing excitation of dorsal excitatory motor neurons and inhibition of ventral excitatory motor neurons. These effects would cause dorsal local bending, not shortening, in a few segments. Only one interneuron, cell 125, has motor effects that would cause shortening. 4. Individual interneurons were hyperpolarized while single sensory cells were stimulated, to quantify the contributions of individual interneurons to the observed motor pattern. Interneurons 115 and 125, and the inhibitory motor neuron, cell 1, were found to have significant roles in producing the shortening motor output. 5. A quantitative estimate of the role of each interneuron type showed that the identified interneurons account for most of the excitation of dorsal motor neurons, but for very little of the excitation of ventral motor neurons. This predicts that at least one additional interneuron type remains to be identified, one that would provide excitation to ventral motor neurons in several segments. 6. A back-propagation trained neural network model was constructed to predict the connections of the as yet unidentified interneurons. To match the known properties of interneurons, it was necessary to include a segmental similarity constraint in the training algorithm for segmentally iterated model neurons. The modeled networks predicted that there are at least two kinds of interneurons yet to be found. Also, the modeling showed that interneurons can have input and output patterns that differ very little from segment to segment but yet produce major differences in the motor output.

Action Potentials↗
PubMed1994

Modulation of high-threshold transmission between heart interneurons of the medicinal leech by FMRF-NH2.

1. We examined high-threshold synaptic transmission between oscillatory pairs of leech heart interneurons. Inhibitory postsynaptic currents (IPSCs) could be reliably evoked by depolarizing the presynaptic neuron in voltage clamp from a holding potential of -35 mV. At this presynaptic potential, the Ca2+ currents underlying graded transmission are completely inactivated, and we conclude that a high-threshold Ca2+ current is extant in heart interneurons. Further evidence for this was that inhibitory postsynaptic currents were blocked when Co2+ replaced Ca2+ in the saline and thus high-threshold transmission was dependent on the presence of external Ca2+. 2. When IPSCs were evoked by a 200-ms duration voltage step from a holding potential of -35 mV in the presynaptic neuron, the time course of turn-on of the IPSC consisted of a fast (time-to-peak = 17.5 +/- 1.93 (SE) ms [n = 7]) and a slow (time-to-peak = 250 +/- 28.5 ms [n = 8]) component. FMRF-NH2 reduced the amplitude of the fast component but did not affect the slow component. When the presynaptic voltage step was ended the IPSC turned off with a single exponential time course. FMRF-NH2 slowed the time course of turn-off of the IPSC. 3. When IPSCs were evoked by a 1500-ms duration voltage step from a holding potential of -35 mV in the presynaptic neuron, these IPSCs peaked around 300 ms. Following the peak, the IPSC decayed with a single exponential time course. FMRF-NH2 accelerated the time course of this decay. At potentials of 0 mV and +5 mV, FMRF-NH2 produced a significant decrease in the peak current and at potentials of -5 mV and 0 mV, produced a significant decrease in the current integral. 4. High-threshold IPSCs could also be evoked by a spike in the presynaptic neuron. Bath application of 1 microM FMRF-NH2 decreased the amplitude of the spike-evoked IPSC and slowed the time course of its falling phase. 5. We examined the effect of FMRF-NH2 on the quantal synaptic transmission. Bath-application of FMRF-NH2 increased binomial p, the probability of release, and decreased binomial n, the number of units available for release. FMRF-NH2 had no effect on q, the unit size, when calculated from the distributions of PSPs, and increased the coefficient of variation (CV). 6. The lack of a change in q and the increase in CV suggested that FMRF-NH2 acted at a presynaptic location.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

Segmental specialization of calcium-activated potassium conductances in an identified leech neuron.

1. Retzius (R) neurons of the fifth and sixth segmental ganglia of the leech, called R(5,6) neurons are specialized to innervate the adjacent reproductive organs and are morphologically and functionally distinct from R neurons of standard ganglia [R(x) cells]. In this study the electrical properties of the R(x) and R(5,6) neurons were compared under current-clamp and voltage-clamp conditions. 2. The action-potential waveforms of R(x) and R(5,6) cells were similar except for the presence in the R(5,6) cells of a long afterhyperpolarization (AHP) following action potentials arising from the resting membrane potential but not from more depolarized potentials. Its role may thus be to inhibit firing of the R(5,6) neurons at rest or in response to weak depolarizing stimuli. 3. In the presence of the Ca2+ channel blocker Cd2+, the long AHP of the R(5,6) was abolished, and the action potentials of all R cells were identical. 4. Under voltage clamp, current kinetics and densities were similar between R(x) and R(5,6) cells for Ca2+ currents, delayed and inward rectifier K+ currents, and a rapid Ca(2+)-activated K+ current (IKc) that is common to the two cell types. The R(5,6) cells, however, expressed a second Ca(2+)-activated K+ current that was not observed in the R(x) cells. This current, called IKAHP, activated and inactivated more slowly than IKC, with a time course similar to that of the AHP observed under physiological conditions. 5. Neither IKC nor IKAHP was blocked by high concentrations of charybdotoxin or apamin, which block vertebrate Ca(2+)-activated K+ channels.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1995

Segment-specific effects of FMRFamide on membrane properties of heart interneurons in the leech.

1. The effects of Phe-Met-Arg-Phe (FMRF)amide (10(-6) M) on membrane properties of heart interneurons in the third, fourth, and fifth segmental ganglia [HN(3), HN(4), and HN(5) cells, respectively] of the leech were studied using discontinuous current-clamp and single-electrode voltage-clamp techniques. FMRFamide was focally applied onto the soma of the cell under investigation. 2. Application of FMRFamide depolarized HN(3) and HN(4) cells by evoking an inward current. These responses were subject to pronounced desensitization. The inward currents evoked by application of FMRFamide were associated with an increase in membrane conductance and appeared to be voltage dependent. Currents were enhanced at more depolarized potentials. 3. The responsiveness of the HN(3) and HN(4) cells was not affected when the Ca2+ concentration in the bath saline was reduced from normal (1.8 mM) to 0.1 mM. The depolarizing response on application of FMRFamide was blocked when Co2+ was substituted for Ca2+. 4. HN(3) and HN(4) cells did not respond to FMRFamide application in Na(+)-free solution. Inward currents were largely reduced when bath saline with 30% of the normal Na+ concentration was used. When Li+ was substituted for Na+ in the saline, application of FMRFamide still evoked depolarizing responses in HN(3) and HN(4) cells. 5. We conclude that focal application of FMRFamide onto the somata of HN(3) and HN(4) cells evokes a voltage-dependent inward current, carried largely by Na+. 6. Focal application of FMRFamide onto somata of HN(5) cells hyperpolarized these cells by activating a voltage-dependent outward current. 7. HN(5) cells were loaded with Cl- until inhibitory postsynaptic potentials carried by Cl- reversed. Cl(-)-loaded cells still responded with a hyperpolarization when FMRFamide was applied onto their somata. Therefore the outward current evoked by FMRFamide appears to be mediated by a K+ conductance increase. 8. Application of FMRFamide onto the somata of HN(5) cells enhanced outward currents that were evoked by depolarizing voltage steps from a holding potential of -45 mV. 9. We conclude that the hyperpolarizing response of HN(5) cells to focal application of FMRFamide onto their somata is the result of an up-regulation of a voltage-dependent K+ current.

Animals↗
PubMed1995

Outward currents in heart motor neurons of the medicinal leech.

1. Outward currents were studied in isolation in heart motor neurons in the medicinal leech, using the single-electrode voltage-clamp technique. The currents were divided into four distinct types on the basis of their time and voltage characteristics and sensitivity to external Ca2+ concentration. 2. The four types were a fast transient current, IKA; a slow transient current. IK1; a noninactivating current, IK2, all measured in a bathing solution in which Co2+ was substituted for Ca2+; and a calcium-sensitive current. IK1Cal which was revealed in a bathing solution containing normal levels of Ca2+. 3. The outward currents in heart motor neurons studied in different ganglia possessed differences of quality. For example, heart motor neurons from ganglia 3 or 4 had significantly less IK2 and IK1 than neurons recorded from more posterior ganglia. Heart motor neurons from ganglion 3 often had little or no IK1. Soma input resistance, electrotonic length, and soma capacitance measured in heart motor neurons from both anterior and posterior ganglia exhibited no significant differences. 4. IKA started to activate near -45 mV with half-maximal activation at about -20 mV and was fully inactivated by 0 mV: IK1 started to activate near -45 mV with half-maximal activation at about -10 mV and was not fully inactivated by 0 mV; IK2 started to activate near -50 mV; IK1Cal started to activate near -35 mV. The time constant of removal of inactivation for IKA was 25 ms, measured at -80 mV, and that for IK1 was 380 ms, measured at -40 mV. 5. Tetraethylammonium acetate (TEA) allowed to diffuse from the inside of the recording microelectrode effectively blocked IKA, IK1, and IK2. Bath-applied TEA (25 mM) acted similarly but was less effective, particularly at blocking Ik2. Bath-applied 4-aminopyridine effectively blocked the transient currents IKA and IK1. A reversal potential of -65 mV was found for the outward currents, corresponding to a mix of IK1 and IK2.

4-Aminopyridine↗
PubMed1995

Widespread mechanosensory activation of the serotonergic system of the medicinal leech.

The serotonergic system of the medicinal leech comprises a small number of iterated, identified neurons, of which the Retzius (Rz) neurons are major components. Activity in pressure mechanosensory (P) cells sufficient to elicit locomotory and defensive behaviors also excites Rz neurons. We characterized the interactions between P and Rz neurons within the ganglion and at different distances along the nerve cord. 2. Within a ganglion 1) P cells excited both Rz neurons, electrically close to the site of electrical coupling between the Rz neurons; 2) each of the four P cells had similar effects on the Rz neurons; and 3) homologous contralateral P cells shared interneuronal pathways. These data show that P cells provide nearly identical bilateral information onto Rz neurons. 3. Along the nerve cord 1) every P cell excited Rz neurons in ganglia anterior and posterior to the site of stimulation; 2) the signal was carried the entire length of the nerve cord along interneuronal pathways with similar overall (but regionally different) conduction velocities in the two directions; 3) the amplitude of the Rz responses was smaller as the distance to the activated P cell increased; 4) the rate of change of the amplitude along the cord was larger when the signal traveled from front-to-back than in the opposite direction. 4. These data shows that mechanosensory input from any segment could excite Rz neurons along the cord, in proportion to the intensity of the stimulus.

Animals↗
PubMed1996

Photoinactivation of the giant neuropil glial cells in the leech Hirudo medicinalis: effects on neuronal activity and synaptic transmission.

1. We studied the effects of photoinactivation of neuropil glial (NG) cells of the leech Hirudo medicinalis on neuronal activity and synaptic transmission. Each segmental ganglion contains two of these giant glial cells, which are electrically and dye coupled. 2. One of the two NG cells in an isolated segmental ganglion was filled with the dye Lucifer yellow (LY). Subsequent irradiation of the ganglion with laser light (440 nm) to photolyze LY caused irreversible depolarization of both NG cells. The NG cells that were filled with LY depolarized from -73 +/- 1.1 (SE) mV to -22 +/- 2.4 mV within 25 +/- 2.8 min of continuous irradiation (n = 22). The other NG cell, which was not directly filled with LY, depolarized with some delay. 3. Photoinactivation of the NG cells caused an irreversible depolarization of Retzius neurons and noxious (N) sensory cells by a mean of 14 mV (n = 36) and 9 mV (n = 24), respectively. In addition, the input resistance was reduced by 54% in Retzius cells and by 34% in N cells. Spikes could not be evoked in Retzius cells after the inactivation of the NG cells, either by intracellular current injection or by electrical nerve stimulation. Similarly, anterior pagoda neurons, annulus erector neurons, and the excitor neurons of the ventrolateral circular muscles became inexcitable. However, N cells, heart interneurons, and most of the heart motor neurons, touch cells, and pressure cells could still generate spontaneous or evoked action potentials. 4. Photoinactivation of the NG cells impaired the electrical connection between the two Retzius neurons. The electrical coupling was completely eliminated in six of eight cell pairs and reduced by 66% in two others. 5. Photoinactivation of the NG cells in the 3rd and 4th segmental ganglion caused a complete block of the chemical synapse between reciprocal inhibitory heart interneurons in these ganglia; the bursting rhythm either stopped or changed to a tonic activity, whereas inhibitory postsynaptic potentials could not be recorded in either heart interneuron anymore. 6. Laser irradiation alone had no effect on neuronal activity and synaptic transmission. Addition of glutathione (10 mM) and ascorbic acid (10 mM) to the saline to bind extracellular radicals that might be produced by the irradiation did not suppress the effects caused by photoinactivation of NG cells. 7. Elevation of bath K+ concentration to 12 mM, acidification of the saline to pH 5.5, and alkalinization to pH 8.5 for 6 min each did not mimick the effects on membrane properties of Retzius cells as produced by inactivation of NG cells. The results suggest some role of glial cells in the maintenance of neuronal activity and electrical and chemical synaptic transmission.

Animals↗
PubMed1997

Functional role of Ca2+ currents in graded and spike-mediated synaptic transmission between leech heart interneurons.

We used intracellular recording and single electrode voltage-clamp techniques to explore Ca2+ currents and their relation to graded and spike-mediated synaptic transmissions in leech heart interneurons. Low-threshold Ca2+ currents (activation begins below -50 mV) consist of a rapidly inactivating component (I(CaF)) and a slowly inactivating component (I(CaS)). The apparent inactivation kinetics of I(CaF) appears to be influenced by Ca2+; both the substitution of Ca2+ (5 mM) with Ba2+ (5 mM) in the saline and the intracellular injection of the rapid Ca2+ chelator, bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA), from the recording microelectrode, significantly increase its apparent inactivation time constant. The use of saline with a high concentration of Ba2+ (37.5 mM) permitted exploration of divalent ion currents over a broader activation range, by acting as an effective charge carrier and significantly blocking outward currents. Ramp and pulse voltage-clamp protocols both reveal a rapidly activating and inactivating Ba2+ current (I(BaF)) and a less rapidly activating and slowly inactivating Ba2+ current with a broad activation range (I(BaS)). Low concentrations of Cd2+ (100-150 microM) selectively block I(BaS), without significantly diminishing I(BaF). The current that remains in Cd2+ lacks the characteristic delayed activation peak of I(BaS) and inactivates with two distinct time constants. I(BaF) appears to correspond to a combination of I(CaF) and I(CaS), i.e., to low-threshold Ca2+ currents, that can be described as T-like. I(BaS) appears to correspond to a Ca2+ current with a broad activation range, which can be described as L-like. Cd2+ (100 microM) selectively blocks spike-mediated synaptic transmission between heart interneurons without significantly interfering with low-threshold Ca2+ currents and plateau formation in or graded synaptic transmission between heart interneurons. Blockade of spike-mediated synaptic transmission between reciprocally inhibitory heart interneurons with Cd2+ (150 microM), in otherwise normal saline, prevents the expression of normal oscillations (during which activity in the two neurons consists of alternating bursts), so that the neurons fire tonically. We conclude that graded and spike-mediated synaptic transmission may be relatively independent processes in heart interneurons that are controlled predominantly by different Ca2+ currents. Moreover, spike-mediated synaptic inhibition appears to be required for normal oscillation in these neurons.

Action Potentials↗
PubMed1998

Representation of touch location by a population of leech sensory neurons.

To form accurate representations of the world, sensory systems must accurately encode stimuli in the spike trains of populations of neurons. The nature of such neuronal population codes is beginning to be understood. We characterize the entire sensory system underlying a simple withdrawal reflex in the leech, a bend directed away from the site of a light touch. Our studies show that two different populations of mechanosensory neurons each encode touch information with an accuracy that can more than account for the behavioral output. However, we found that only one of the populations, the P cells, is important for the behavior. The sensory representation of touch location is based on the spike counts in all of the four P cells. Further, fewer than three action potentials in the P cell population, occurring during the first 100 ms of a touch stimulus, may be required to process touch location information to produce the appropriately directed bend.

Action Potentials↗
PubMed2001

Mixtures of octopamine and serotonin have nonadditive effects on the CNS of the medicinal leech.

It is well established that neural networks respond to a wide variety of modulatory substances by which they can become reconfigured, yet few studies have examined the effects of neurotransmitter mixtures on such networks. In a previous study of the medicinal leech using triple intracellular recordings, we found that stimulation of identified mechanosensory neurons activated both the serotonergic cell 21 (a swimgating neuron) and the dorsal lateral octopamine (DLO) cell. Because these findings suggested that serotonin (5-HT) and octopamine (OA) may be released together, we investigated the effects of 5-HT and OA mixtures on isolated nerve cords of Hirudo medicinalis (which contained both head and tail brains). Fifty micromolar OA, 50 microM 5-HT, or a mixture of 50 microM OA and 50 microM 5-HT was bath applied to the nerve cord under constant perfusion conditions. Additional experiments were performed with combinations of either 25 or 100 microM OA and 5-HT. Neural activity was examined specifically in the segmentally repeated dorsal posterior (DP) nerve because it has been shown to contain identified swim motor units. Nonadditive effects of amine combinations were most apparent in their ability to decrease overall activity in the DP nerve and to alter patterned motor activity in the form of fictive swimming. Whereas swim burst activity has been previously shown to increase in nerve cords bathed in either 5-HT or OA solutions alone, we demonstrated that a mixture of the two amines resulted in a robust decrease in the number of swim bursts expressed and an inhibition of swim activity in preparations already swimming. Most compelling was the observation that when the amine mixture was replaced with normal saline, swim burst activity increased dramatically. We discuss that the effects of amine mixtures may be due to their interaction with descending interneurons known to trigger and inhibit swimming as the mixture-induced effects were not observed in nerve cords lacking the head and tail brains. Because the net effect of the two amines was not simply additive (i.e., 5-HT or OA is known to activate swimming, yet the mix inhibits swimming), this result reveals yet another layer of complexity inherent in "simpler" invertebrate nervous systems.

Animals↗
PubMed1975

Fibrinogenolytic substance (hementerin) of Brazilian blood-sucking leeches (Haementeria lutzi Pinto 1920).

The fibrinogenolytic activity of the salivary gland extract from the Brazilian blood-sucking leech Haementeria lutzi Pinto 1920 is characterized. The substance, named here hementerin, is stable and active at very low protein concentration, does not exhibit direct proteolytic activity on casein, fibrinogen, or fibrin, and is able to activate the human plasma fibrinolytic system in the presence of a serum cofactor and/or calcium. This indirect activation mechanism distinguishes hementerin from hirudin and shows a similarity with streptokinase. The effect on blood coagulation tests is reported.

Animals↗
PubMed1985

Eglin-c, a polypeptide derived from the medicinal leech, prevents human neutrophil elastase-induced emphysema and bronchial secretory cell metaplasia in the hamster.

Eglin-c (Eg-c), a polypeptide with a molecular mass of 8,100 daltons, was purified from the medicinal leech Hirudo medicinalis. The Eg-c was tritiated by reductive methylation for in vitro studies. Incubation of 2.1 X 10(-10) moles of human neutrophil elastase (HNE) with 3H-elastin in the presence of 8.2 X 10(-10) moles of 3H-Eg-c inhibited 98.7% of the elastolytic activity of the enzyme. Using Sephadex G 100 chromatography and 1.7 moles of 3H-Eg-c per mole of HNE, a 34,000-dalton complex (3H-Eg-c-HNE) was observed. The stability of the complex formed between 3H-Eg-c and HNE that had been inactivated with succinyl-ala2-pro-val CH2Cl was much less than that of the 3H-Eg-c-HNE complex. In vivo studies were carried out in weight-matched groups of anesthetized golden Syrian hamsters given 100, 300, 500, or 2,000 micrograms of Eg-c in 0.5 ml saline intratracheally 1 h before 300 micrograms HNE was administered intratracheally. Control animals received saline followed by HNE or 2 doses of saline 1 h apart. Eight weeks later, lung statics and dynamics were measured in anesthetized animals, followed by histologic study of lung parenchyma and the mucosa of the large intrapulmonary airways. There were no deaths, and final mean body weights were similar in all groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2005

Electrophysiological effect of beta-N-methylamino-L-alanine on retzius nerve cells of the leech Haemopis sanguisuga.

We investigated the effect of beta-N-methylamino-L-alanine (L-BMAA) on input membrane resistance of leech Retzius nerve cells and the effect of the same substance on the membrane potential in the presence of 20 mM bicarbonate. Results of our experiments show that L-BMAA significantly reduces input membrane resistance on our model. This leads to the conclusion that L-BMAA depolarizes the cell by increasing membrane permeability and conductance. The effect of L-BMAA in 20 mM bicarbonate is significantly higher than in standard Ringer solution. These results indicate that bicarbonate increases the excitatory effect of L-BMAA in our model.

Amino Acids, Diamino↗