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At least 811 records · Page 45Linked to original sources
PubMed1992

Bicarbonate-dependent changes of intracellular sodium and pH in identified leech glial cells.

A new triple-barrelled ion-sensitive microelectrode was used to investigate the importance of bicarbonate for the regulation of intracellular Na+ and pH (Nai and pHi, respectively) of neuropile glial cells in the central nervous system of the leech Hirudo medicinalis. Addition of CO2/HCO3- produced an increase of the Nai activity and an intracellular alkalinization, indicating bicarbonate accumulation in the glial cells. Changes of external pH (from 7.4 to 7.0 and 7.8) produced large and rapid shifts of pHi and Nai and of the membrane potential in the presence, but not in the absence, of bicarbonate. Thus, acid/base transport and Na+ movements across the glial membrane into and out of the cells were accelerated severalfold in CO2/HCO3(-)-buffered saline as compared to a CO2/HCO3(-)-free, HEPES-buffered saline. The results suggest that the electrogenic, reversible, cotransport of Na+ and HCO3- in the glial cell membrane [3,9] can produce significant changes in intraglial pH and Na activity, and can carry a significant fraction of the total Na+ flux across the cell membrane.

Animals↗
PubMed1976

Studies on the host-parasite interaction and role of esterases during biting of the Indian cattle leech, Poecilobdella granulosa.

Histochemical localization of acetylcholinesterase and butyrylcholinesterase in the salivary glands has unfolded the significant fact that salivary glands are of two types, one being enzymatically negative and the other showing positive activity. Activity of these enzymes has been linked with the operation of glandular dynamics, particularly concerning the synthetic and secretory processes. The enzymes have been seen localized in the core of jaw. Contrary to it they are absent in the papillary and interpapillary zones of the jaw. Absence of esterases in the papillary and interpapillary ductules has been correlated with its possible non-involvement in the synthesis of vasodilating and anticoagulating materials. The experiments on effect of biting on host tissue give a faint indication of vascular dilation due to bite. Likewise, experiments on enzymatic state of a salivary gland after leech-bite reveal that the diminution of the reactive coverage area in the salivary glands reaches its maximum in the case of ATPase, indicating thereby its more involvement in salivary functions than those of esterases and acid phosphatase.

Acid Phosphatase↗
PubMed1976

Studies on the fine structure of invertebrate blood vessels. II. The valves of the lateral sinus of the leech, Hirudo medicinalis L.

The position, structure and function of the valves within the lateral sinus of the medical leech, Hirudo medicinalis, are described on the basis of vital, light- and electron microscopy. In this species the valvular apparatus consists of multiple elongated fir cone-shaped fibrous villi surrounding the orifices of the latero-lateral and latero-dorsal vessel like a tentacular crest. Each villus is covered by a thin sheet of a continuous endothelium. The valves prevent the backflow of hemolymph during systolic contraction of the lateral sinus. The endothelium contains many small mitochondria and polyribosomes in the perinuclear cytoplasm and it develops deep projections into the underlying connective tissue. Each of these consists of a multilayered system of closely interwoven thin endothelial membranes. The endothelium is anchored to its basement membrane by means of a great number of poorly defined hemidesmosomes. The fibrous tissue of the villi consists mainly of a homogeneous vitreous matrix in which few cellular components and very fine filaments are dispersed. Close to the endothelium this matrix appears to be condensed to form a multilayered framework made out of a basement membrane-like material. Though the valves themselves are devoid of muscle cells, those situated at their base and thus belonging to the vascular wall proper, display some specific morphological features: in particular the nuclei of these cells show a distinct fibrous lamina. Moreover, these muscle cells seem to be innervated only by one type of axon, containing both small, lucent synaptic vesicles as well as some of the dense-core variety. These findings are compared with data from earlier works and are discussed in relation to the hemodynamic functions of this valvular apparatus.

Animals↗
PubMed1988

Effects of procaine on intracellular pH and its regulation: measurements with pH-selective micro-electrodes in Retzius neurones of the leech.

The experiments were performed with double-barelled micro-electrodes in Retzius neurones of the leech in order to see if the tertiary amine local anesthetic procaine affects intracellular pH (pHi) and its regulation. Lasting about 20 min, exposures to procaine (3 mM) saline caused an intracellular alkalosis of about 0.2 pH units which gradually degradated; its removal initiated a fast decrease of pHi resulting in an acidosis, fron which the cells recovered. Detailed studies, involving CO2 or NH4+ acid loaded cells as well as inhibition of the pHi regulating exchange mechanism by various drugs or exposures to Na-free salines suggest, that neither the Na+ -H+, nor a probably Na+ -dependent HCO3-(-)Cl- exchange are affected by procaine. We propose a model for procaine action on pHi assuming that neutral procaine passes the membrane easily through lipophilic pathways. The degradation of alkalinity during procaine exposure hints on an entry of loaded procaine, some possible transport paths of which are discussed.

Animals↗
PubMed1983

Intracellular Na+ and Ca2+ in leech Retzius neurones during inhibition of the Na+-K+ pump.

The intracellular Na activity, aNai, and the intracellular Ca activity, aCai, were measured with double-barrelled neutral carrier Na+- and Ca2+-sensitive microelectrodes in Retzius neurones in the central nervous system of the leech Hirudo medicinalis. The aNai was measured to be 8.0 mM (corrected for Ca interference), which corresponds to a cytoplasmic Na+ concentration of 10.7 mM, assuming a Na activity coefficient of 0.75. The calculated Na+ equilibrium potential was 59 mV, giving a total Na+ electrochemical gradient of approximately 102 mV. The aCai was found to range between 1 and 5 X 10(-7) M, from which a Ca2+ equilibrium potential near + 120 mV was estimated. When the Na+-K+ pump was inhibited by lowering the external K+ concentration or by adding the glycoside ouabain (5 X 10(-4) M), the aNai reversibly increased severalfold. When aNai increased to high levels following complete pump inhibition, the aCai increased above 10(-6) M, and the membrane input resistance decreased. After removal of ouabain, aNai, aCai and the membrane resistance recovered within 30 min after a delay of 20-40 min. Our results suggest that a large increase of aNai produces a rise in aCai, possibly by means of a Na+-Ca2+ exchange across the cell membrane. The elevation of the aCai may be responsible for the decrease in membrane resistance, and may also be related to the uncoupling of the paired Retzius neurones observed in the presence of Na+-K+ pump inhibitors.

Animals↗
PubMed1987

Neural mechanisms generating the leech swimming rhythm: swim-initiator neurons excite the network of swim oscillator neurons.

This paper describes newly identified excitatory connections linking the segmentally iterated swim-initiator interneurons with the network of oscillator neurons that generates the leech swimming rhythm. Apparently monosynaptic excitatory chemical connections are made from one class of swim-initiator neurons (cells 204/205) to several members of the swim oscillator network, including cells 28, 115 and, as described by Weeks (1982c), cell 208. A second class of swim-initiator neurons, cells 21 and 61, also excites this subset of the oscillator neurons. The unpaired swim oscillator neuron, cell 208, also chemically excites cells 28 and 115, apparently directly. Thus, in addition to its role as a member of the swim oscillator, the excitatory output from cell 208 to the swim oscillator adds to that provided by the swim-initiator neurons. The results of this paper enlarge the subset of identified swim oscillator neurons synaptically excited by the swim-initiator neurons. These newly described targets of the swim-initiators strengthen the hypotheses that: 1) the swim-initiator neurons supply much of the tonic excitatory drive responsible for activation and maintenance of the swim central motor program, and 2) the two classes of swim-initiators, cells 204/205 and cells 21/61, act synergistically to initiate and maintain swimming.

Animals↗
PubMed1986

Initiation of swimming activity by trigger neurons in the leech subesophageal ganglion. I. Output connections of Tr1 and Tr2.

The aim of this study was to identify neurons in the subesophageal ganglion of the medicinal leech which initiate swimming activity and to determine their output connections. We found two bilaterally symmetrical pairs of interneurons, Tr1 and Tr2, located in the first division of the subesophageal ganglion which initiate swimming activity in the isolated nervous system when depolarized with brief (1-3 s) current pulses. Tr1 and Tr2 are considered trigger neurons because elicited swimming episodes outlast the stimulus duration, and because the length of elicited swim episodes is nearly independent of the intensity with which Tr1 and Tr2 are stimulated. Tr1 and Tr2 have similar morphologies. The neurites of both cells cross contralaterally in the subesophageal ganglion, project posteriorly, and exit the subesophageal ganglion in the contralateral connective. The axons of Tr1 and Tr2 extend as far posterior as segmental ganglion 18 of the ventral nerve cord. Tr1 provides direct excitatory drive to three groups of segmental neurons which are capable of initiating swimming: swim-initiating interneurons (cells 204 and 205), serotonin-containing interneurons (cells 61 and 21), and the serotonergic Retzius cells. In addition, all Retzius cells in the subesophageal ganglion are excited directly by Tr1. These three groups of neurons are excited even if Tr1 stimulation is subthreshold for swim initiation. In contrast to Tr1, Tr2 stimulation evokes transient inhibition in swim-initiating and serotonin-containing interneurons, and has little immediate effect on Retzius cells. In addition, Tr2 indirectly inhibits several oscillator neurons, including cells 208, 33, and 60. When Tr1 is stimulated during a swimming episode the swim period decreases for several cycles, while stimulation of Tr2 during swimming episodes reliably resets the ongoing swimming rhythm. Our findings indicate that Tr1 and Tr2 are trigger neurons which initiate swimming activity by different pathways. These neurons also have functional interactions with the swim oscillator network since either Tr1 or Tr2 stimulation during swimming can modulate the ongoing swimming rhythm.

Animals↗
PubMed1986

Initiation of swimming activity by trigger neurons in the leech subesophageal ganglion. II. Role of segmental swim-initiating interneurons.

Cell Tr1, a trigger neuron found in the subesophageal ganglion of the leech, Hirudo medicinalis, is part of a network of subesophageal ganglion neurons which control swimming activity, and makes apparently direct connections to swim-initiating interneurons (SIIs; cells 204 and 205). In this study, we investigated the role of SIIs in swim initiation by cell Tr1. We also examined how brief Tr1 activity controls swim initiation at the levels of the SIIs and of the oscillator neurons. We found: In shortened nerve cord preparations consisting of the head ganglion (supra- and subesophageal ganglia) through segmental ganglia 11 or 12, the effectiveness of swim initiation by Tr1 stimulation was highly correlated with the concurrent injection of depolarizing or hyperpolarizing current into a single cell 204. Tr1 stimulation causes sustained excitation in SIIs, serotonin-containing interneurons and Retzius cells, independent of whether or not swimming is initiated. A short, depolarizing current pulse injected simultaneously into as many as three 204 cells does not replicate the sustained excitation evoked in these cells by Tr1 stimulation. An oscillator neuron, cell 208, is inhibited when Tr1 stimulation fails to elicit swimming, but receives excitatory input from Tr1 otherwise. In another oscillator neuron, cell 115, stimulation of Tr1 suppressed an unidentified source of inhibitory synaptic potentials only on trials which resulted in swim initiation. We conclude that Tr1 stimulation triggers swimming by activating a long-lasting ramp depolarization in the SIIs which, in turn, provide excitatory drive to the swim oscillator. Moreover, Tr1 initiates swimming only when inhibitory inputs to the swim oscillator are suppressed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Intracellular stimulation of sensory cells elicits swimming activity in the medicinal leech.

Intracellular stimulation of each of three different types of mechanoreceptors, the T, P and N cells, evokes swimming behavior in leech preparations. Stimulation of an individual N cell or P cell evoked swimming in 75% and 53% respectively, of the preparations tested. Stimulation of an individual T cell was ineffective in eliciting swimming; however, simultaneous stimulation of two T cells evoked swimming in 59% of our preparations. Stimulation of mechanosensory neurons elicited swimming activity for a limited number of trials; i.e. the response habituated. The number of swim episodes evoked before habituation to criterion did not differ significantly for the different types of mechanoreceptors. The duration of swim episodes declined significantly over the course of N cell stimulation. The tendency for swim length to decline with repeated stimulation was present as well for swim episodes elicited by P or T cell stimulation. Swim initiation recovered spontaneously following habituation resulting from T cell stimulation. Spontaneous recovery following N cell stimulation was not demonstrated. However, N cell stimulation evoked swimming again after DP nerve shock or to a limited extent, after cell 204 stimulation. Spontaneous recovery of swim initiation to P cell stimulation was not investigated. A previous study detailed habituation of swimming activity to mechanical stimulation of the body wall (Debski and Friesen 1985). Only the T cells are activated significantly by this stimulus. Stimulation of sensory receptors other than mechanoreceptors was not effective in eliciting swimming in our preparation. We conclude that T cells mediate swim initiation elicited by stroking of the body wall and that the cessation of swimming to this stimulus is not due to sensory adaptation.

Action Potentials↗
PubMed1985

Superelongation in helical muscles of leeches.

The fine structure of leech body wall muscles, has been analysed under great length variations. All the measurable parameters of the fibre (distance between thick filaments, sarcomere and A band width, percentage of actin crowns around myosin filaments, fibre radius) at different elongations were tested with equations describing the geometrical model of helical fibres. Anaesthetized and nonanaesthetized worms behave in different ways and can be utilized to verify the 'changing partner hypothesis'. The fit between theoretical and experimental data suggests that a double change of partner actually takes place in extremely stretched fibres.

Actin Cytoskeleton↗
PubMed1995

Modeling the leech heartbeat elemental oscillator. I. Interactions of intrinsic and synaptic currents.

We have developed a biophysical model of a pair of reciprocally inhibitory interneurons comprising an elemental heartbeat oscillator of the leech. We incorporate various intrinsic and synaptic ionic currents based on voltage-clamp data. Synaptic transmission between the interneurons consists of both a graded and a spike-mediated component. By using maximal conductances as parameters, we have constructed a canonical model whose activity appears close to the real neurons. Oscillations in the model arise from interactions between synaptic and intrinsic currents. The inhibitory synaptic currents hyperpolarize the cell, resulting in activation of a hyperpolarization-activated inward current Ih and the removal of inactivation from regenerative inward currents. These inward currents depolarize the cell to produce spiking and inhibit the opposite cell. Spike-mediated IPSPs in the inhibited neuron cause inactivation of low-threshold Ca++ currents that are responsible for generating the graded synaptic inhibition in the opposite cell. Thus, although the model cells can potentially generate large graded IPSPs, synaptic inhibition during canonical oscillations is dominated by the spike-mediated component.

Animals↗
PubMed1995

Modeling the leech heartbeat elemental oscillator. II. Exploring the parameter space.

In the previous paper, we described a model of the elemental heartbeat oscillator in the leech. Here, the parameters of our model are explored around the baseline canonical model. The maximal conductances of the currents and the reversal potential of the leak current are varied to reveal the effects of individual currents and the interaction between synaptic and intrinsic currents in the model. The model produces two distinct modes of oscillation as the parameters are varied, S-mode and G-mode. These two modes are defined, their origin is identified, and the parameter space is mapped into S-mode and G-mode oscillation and no oscillation. Finally, we will make predictions for how the period can be modulated in heart interneurons.

Animals↗
PubMed1976

Divalent cations and the action potential of leech Retzius cells.

The effects of Sr, Ba, Mn, La and Co on the action potential of the leech Retzius cell were examined using intracellular recording techniques. A previous paper showed that these cells could fire Ca-dependent action potentials in Na-free solution provided TEA was present (Kleinhaus and Prichard, 1975). Under the same conditions Sr 1.5--20 mM was capable of substituting as a current carrier. Ba 2--25mM added to normal Ringer prolonged the duration and increased the amplitude of the action potential of the Retzius cell, and supported action potentials without requiring TEA in Na-free solutions. The overshoots of the Sr- and Ba-dependent action potentials varied with a slope of 40 mM and 75 mV, respectively per 10-fold change in divalent cation concentration. Mn and La selectively blocked that portion of the action potential resulting from an inward movement of Ca, Sr or Ba without affecting the Na-dependent depolarization. The actions of Ca 1 mM on Sr-dependent action potentials were compatible with reversible competitive antagonism. In conclusion the findings: 1. support the proposition that outward K current must be blocked in order for divalent cations to dominate the Retzius cell's behavior during excitation. 2. characterize the divalent cation conductance channel as pharmacologically distinct from the Na conductance channel in the Retzius cell and similar to those described in several other excitable membranes. 3. suggest that the current carrying divalent cations probably flow through the same channel.

Action Potentials↗
PubMedDate not supplied

An investigation of the effect of amtizol on the plastic properties of the membrane of the Retzius neuron of the leech.

The effect of amtizol, a blocker of the inactivation of calcium-dependent potassium channels of the outward current, on the spontaneous and evoked impulse activity of these cells was investigated in experiments on Retzius neurons of the leech. It was demonstrated that the extracellular application of amtizol induces a decrease in the amplitude and an increase in the duration of evoked AP, while not exerting a perceptible influence on the form of the spontaneous AP. In addition, disruption of the development of the process of habituation that develops in the norm during high-frequency synaptic activation of the neuron is observed in a solution containing amtizol.

Action Potentials↗
PubMed1988

Multifunctional interneurons in behavioral circuits of the medicinal leech.

We are using the medicinal leech to study the neuronal basis of behavioral choice. In particular, we are recording from neurons, both extracellularly and intracellularly, in preparations that can express three different behaviors: the shortening reflex, crawling and swimming. We have found that particular mechanosensory neurons can elicit any of the behaviors, and that the movements are produced by just four sets of muscles, each controlled by a small number of motor neurons. Hence, there must be three different pattern-generating neuronal circuits, each of which can be activated by the same set of sensory neurons. We are studying how the choice is made among the three behaviors by recording, while one behavior is being performed, from neurons known to be involved in the initiation of the other two. We have found that an interneuron, cell 204, which is known to initiate and maintain swimming, is also active during shortening and crawling. The activity level in this interneuron can influence whether a mechanosensory stimulus produces shortening or swimming. The neuronal mechanisms by which this choice is normally effected awaits further elucidation of the circuits that elicit and generate shortening and crawling.

Animals↗
PubMed1992

Presence of a partial urea cycle in the leech, Poecilobdella granulosa.

Ornithine carbamoyltransferase (OCT) and arginase, but not arginine synthetase (AS), were detected in the body wall and gut tissues of the leech. The activities of these enzymes were not altered by starvation. The high activity of arginase in body wall is probably due to the association of the latter with botryoidal tissue. Hirudineans, which evolved from oligochaete ancestors, appear to have lost the citrulline-arginine segment of the urea cycle due to their ammonotelic mode of nitrogen excretion.

Animals↗
PubMed1996

Modulation and selection of neurotransmitter responses during synapse formation between identified leech neurons.

1. Serotonin (5-HT) modulates two different responses in the pressure sensitive neurons (P) of the leech: an inhibitory, Cl- dependent synaptic response and a depolarizing extrasynaptic response. 2. Serotonergic Retzius cells (R) in vivo and in culture elicit inhibitory Cl- dependent responses in P neurons. Moreover, at discrete sites of contact between R and P cells, the excitatory response to 5-HT is gradually lost prior to synapse formation. This phenomenon is specifically mediated by R cells. 3. The extrasynaptic response is mediated by cation channels sensitive to protein kinase C (PKC). Cation channels are present at the sites of contact but they become insensitive to PKC. Moreover, cation channels from single P cells are no longer modulated by PKC if they are inserted (by cramming the patch pipette) into the cytoplasm of a P cell in contact with an R cell. 4. Blockers of tyrosine kinases prevent the uncoupling of cation channel modulation and inhibit synapse formation between the R and the P neurons. 5. We suggest that cell contact induces an intracellular, tyrosine kinase-dependent signal as part of the mechanism of neuronal recognition leading to synapse formation.

Animals↗