Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “LEECHES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,045 records · Page 58Linked to original sources
PubMed1974

Different properties of synapses between a single sensory neurone and two different motor cells in the leech C.N.S.

In leech ganglia, an individual sensory cell that responds specifically to noxious mechanical stimulation of the skin (N cell) excites two different motoneurones. One raises the annuli of the skin into ridges (the AE cell), while the other innervates logitudinal muscles and thereby shortens the body segment (L cell). A comparison has been made of the way in which these two synapses behave when their common presynaptic cell is stimulated in various conditions.1. Using previously described criteria, N sensory cells have been shown to make monosynaptic chemical connexions with both the AE and L motoneurones (Nicholls & Purves, 1972). Following a single stimulus, the excitatory synaptic potential recorded in the AE motoneurone was only about one tenth the size of that in the L cell (approximately 0.5 mV compared to 5 mV). Trains of impulses in the same N sensory cell gave rise to synaptic potentials in the AE and the L motoneurones that underwent phases of facilitation and depression; the facilitation, however, was characteristically greater and longer lasting at synapses upon the AE motoneurone.2. The differences between the two synapses were accentuated in Ringer fluid containing increased concentrations of Ca and also in the cold. Under both of these conditions repetitive firing by the N sensory cell could give rise to synaptic potentials in the AE motoneurone which progressively increased in amplitude, while those in the L motoneurone became smaller.3. The results suggest that the differences in synaptic transmission can be accounted for by variations in the amount of transmitter released at the presynaptic N cell terminals, rather than by differences in the post-synaptic cells. The animal's behaviour corresponds to expectations from the physiology of the synapses.

Action Potentials↗
PubMed1975

Calcium dependent action potentials produced in leech Retzius cells by tetraethylammonium chloride.

1. Retzius cells of leech segmental ganglia were exposed to tetraethylammonium chloride (TEA) presented both extracellularly, dissolved in the perfusing fluid, and intracellulary, by iontophoresis from a microelectrode. 2. Extracellular TEA, 10 and 25 mM, greatly prolonged the cells' action potentials, and the higher concentration increased their amplitude as well. At 10 mM the characteristic changes developed gradually over a period of about half an hour, while at 25 mM they appeared much more rapidly. However, at both concentrations the changes were reversible within minutes, even after long soaks in drug-containing solution. It is therefore probable that the drug acted at the outer surface of the membrane. 3. Intracellular TEA also prolonged the action potentials but there were several differences from the response produced by extracellular application. The changes developed gradually, and for a time, each firing of the cell was a complex event consisting of several early, brief depolarizations followed by a single much larger and more prolonged one. The large, late depolarization eventually obliterated the early ones; its gradual development suggested that it was produced only after TEA diffused to some extrasomatic portion of the cell. Intracellular TEA always caused progressive depolarization; this and the changes in the action potential were both irreversible, suggesting that the site of action was on the inner surface of the membrane. 4. Manipulations of external Na and Ca provided evidence that (a) in the absence of TEA, Retzius cell action potentials were exclusively Na-dependent, (b) that the early depolarizations in the complex action potentials produced by intracellular TEA were Na-dependent, while the later, large depolarization was Ca-dependent and (c) that the prolonged action potentials produced by extracellular TEA contained a large Ca-dependent component. 5. We conclude that TEA, acting from either side of the membrane, caused a voltage-sensitive, slowly activated Ca current to become a major contributor to the inward current of the action potential, probably by blocking the outward K current which ordinarily counteracts it. However, we cannot rule out the possibility that TEA enabled a Ca current by some means independent of its presumed action on K conductance. 6. Data resembling ours in some respects have been obtained from studies of the action of TEA on frog dorsal root ganglion cells, frog neuromuscular junction, and squid stellate ganglion. No clear counterpart of our findings has been reported form experiments on squid and amphibian axons, molluscan neurones, or frog skeletal muscle fibres.

Action Potentials↗
PubMed1976

Physiological properties and receptive fields of mechanosensory neurones in the head ganglion of the leech: comparison with homologous cells in segmental ganglia.

A study of the head ganglion of the leech was made to compare the properties of specific sensory cells in this ganglion with those of homologous neurones in the segmental ganglia. 1. In the head ganglion, cells were identified that had electrical properties, sensory modalities and adaptation properties similar to those of touch (T), pressure (P) and nociceptive (N) cells in the segmental ganglia. The cell bodies of these neurones were situated in characteristics positions that could be correlated with those in the segmental ganglia. Several lines of evidence suggested that they were primary sensory neurones. Fewer T, P and N neurones were identified in the head ganglion than would be expected from its six constituent segmental ganglia. 2. The receptive fields of identified T, P and N cells were situated on the external surface of the head and the interior of the mouth with considerable overlap. They were generally smaller in size than those situated on the main part of the body. The receptive fields were also displaced anteriorly so that some of them were situated in segments anterior to those of the innervating cells. 3. The morphology of the sensory cells in the head ganglion was studied by intracellular injection of horseradish perioxidase. The general branching characteristics of the cells and the structural appearance of their processes resembled those of homologous cells in the segmental ganglia. However, the routes taken to the periphery by some of the cells were not constant from head ganglion to head ganglion. This variability was confirmed by electrophysiological evidence, and differed from the constancy seen in segmental sensory cells.

Action Potentials↗
PubMed1976

Receptive fields, geometry and conduction block of sensory neurones in the central nervous system of the leech.

1. In segmental ganglia of the leech, the cutaneous mechanosensory neurones responding to to touch innervated the skin of their own segment and of part of the anterior and posterior adjacent segments. Each touch receptive field could be divided into three non-overlapping areas: a central part innervated by the branches of the cell which ran in the nerve roots of the ganglion containing the cell body, and anterior and posterior parts innervated by its branches which ran in the nerve roots of the anterior and posterior adjacent ganglia. 2. Impulses originating from the anterior and posterior parts of the receptive fields were susceptible to conduction block within the central nervous system when the touch cells fired repetitively at frequencies that could readily be elicited with weak mechanical stimulation. In contrast, impulses originating from the central part of the receptive fields were less susceptible to block. 3. The morphology of touch cells revealed by intracellular injection of horseradish peroxidase suggested that conduction block occurred at specific bifurcation points where small cell processes joined the main process. Different physiological experiments supported this conclusion. 4. In some touch cells, bifurcation points with particularly low safety margins of conduction operated as low-pass filters, limiting the frequency of impulses capable of invading certain branches. 5. The results suggest that mechanical stimuli which would likely be encountered by the animal can lead to conduction block within its central nervous system and as a result modify its integrative activities.

Action Potentials↗
PubMed1977

Close relation between TEA responses and Ca-dependent membrane phenomena of four identified leech neurones.

1. Tetraethylammonium chloride (TEA) was applied to four kinds of identified neurones in leech segmental ganglia, namely, the sensory cells responding to touch (T), pressure (P) and noxious (N) stimuli and the Retzius cell (R).2. TEA prolonged the action potentials of these cells to characteristically different degrees, in the order R > N > P > T, regardless of exposure time. This result was the same whether TEA was presented to the whole ganglion via the bathing fluid or injected iontophoretically into the soma of the cell under study.3. TEA in Na-free solution caused the behaviour of the N cell membrane to be dominated by a Ca-dependent, Mn-blockable event identical in every respect except smaller size to the previously described behaviour of the R cell under the same conditions. The P cell displayed a still smaller event of the same kind, but none was detectable in the T cell.4. In the absence of both TEA and Na, when Ca was the only extra-cellular cation available to carry current, active membrane responses to depolarization were present in the R cell (previous study) and the N cell; such responses were minimal in the P cell and absent from the T cell.5. Differences among the four cells in density of a divalent cation conductance mechanism are the simplest explanation for these observations, though a more complex explanation based on multiple, pharmacologically distinct K conductances is not excluded by our data.

Action Potentials↗
PubMed1978

Destruction of a single cell in the central nervous system of the leech as a means of analysing its connexions and functional role.

A method has been devised for killing an individual neurone in the C.N.S. of the leech by injecting it with Pronase. The technique has been used to examine the role of individual sensory and motor cells involved in producing reflex movements.1. After a neurone was injected with Pronase, either in an intact animal or an isolated ganglion, its cell body lost its resting and action potentials. Some hours later the injected cell's axons in the periphery failed to conduct impulses. In the intact animal the cell body could no longer be discerned after a few weeks.2. To test for destruction of processes within the neuropile, cells were injected first with the enzyme horseradish peroxidase (HRP) and then several hours later with Pronase. Absence of the characteristic HRP reaction product indicated that Pronase had spread throughout the arborization of the cell.3. Injection of Pronase into one cell did not produce overt electrophysiological or anatomical changes in other cells in the ganglion including neurones that were originally electrically coupled to the killed cell.4. Evidence that an individual cell was the only motoneurone supplying particular muscles was provided by destruction of that cell in otherwise intact animals, which resulted in a characteristic motor deficit in the area supplied by the killed cell. Over a period of months, functional recovery of the affected muscles occurred by way of homologous cells in adjacent ganglia.5. A further application of the technique was to trace the connexion that a particular sensory neurone makes onto two motoneurones that are electrically coupled. Normally, the sensory neurone gives rise to excitatory potentials in both post-synaptic cells. Synaptic potentials could still be recorded in one motor cell after the other had been destroyed by Pronase, indicating that synapses were made directly onto both of the motoneurones.

Animals↗
PubMed1980

Segregation of leech neurones by the effect of sparteine on action potential duration.

1. Sparteine (SPT) and 3- or 4-aminopyridine, were applied to leech segmental ganglia and the electrophysiological responses of the Retzius (R) and sensory neurones responding to pressure (P), touch (T), and noxious (N) stimuli analysed. 2. SPT 0.05-0.5 mM when presented via the bath to the whole ganglion prolonged the action potentials of these neurones to characteristically different degrees; the cells were clearly segregated in the order R greater than N greater than P greater than T at 0.5 mM, regardless of exposure time. 3. The plateau of the prolonged action potentials in the R and N cells was sustained by either Ca or Sr and was blocked by Mn, in normal or Na-free Ringer. These responses were similar to those seen in the same cell types with TEA under the same condition. 4. The SPT prolongation of action potentials was favoured by alkalinization of the Ringer solution. This implies that the drug acted in its uncharged form. SPT was ineffective when applied by pressure into the somata of these four neurones. This may be because SPT was charged at the intracellular pH or because it acted at some external membrane site. 5. The aminopyridines when applied in the bath had no effect on the repolarization of these four neurones. 6. These results suggest that TEA and SPT probably act on repolarization by similar mechanisms. The parameter of membrane function principally affected is probably a K current which contributes to repolarization to different degrees in the four cells and which may be activated by Ca.

Action Potentials↗
PubMed1981

Transmission at a 'direct' electrical connexion mediated by an interneurone in the leech.

1. Touch sensory neurones in the leech excite a rapidly conducting interneurone called the S-cell. Although the electrical synaptic connexion between the two cells is monosynaptic by physiological criteria, intracellular staining reveals that the touch cells and the S-cell do not make contact, but instead are linked by a pair of small interneurones. 2. The electrical coupling between touch cells and S-cells rectifies, in that depolarizing current but not hyperpolarizing current passes from the touch cell into the S-cell. The rectifying junction is between the touch cells and coupling interneurones, while the connexion between coupling interneurones and the S-cell passes current in both directions. 3. Selective destruction of the coupling interneurones by intracellular injection of a protease interrupts the disynaptic electrical connexion between touch and S-cells. 4. The touch cell's geometry and membrane properties account for the failure of impulses that are generated in certain portions of the receptive field in the skin to propagate beyond the first branch-points of the touch cell axon within the ganglion. Conduction block at branch-points is used to examine physiologically the spatial distribution of contacts between the touch cell and the coupling interneurones. In addition, it is shown that under natural conditions branch-point failure presynaptically reduces the effectiveness of the electrical synaptic connexions.

Horseradish Peroxidase↗
PubMed1981

Morphology and distribution of touch cell terminals in the skin of the leech.

1. The receptor terminals of individual mechanosensory neurones responding to light touch (T cells) have been visualized directly in the skin of the leech by injecting horseradish peroxidase (HRP) into their cell bodies in the central nervous system. The axons of injected cells could be followed from their origin in the neuropile of the ganglion to their terminals in the skin. 2. The axons of T cells run through ipsilateral nerve roots in the body wall to the base of the layer of epithelial cells in the skin. Here axons branch extensively and turn between the epithelial cells to end a few microns from the skin surface. These terminals are situated in intercellular spaces immediately below the junctional complex joining the outer ends of the epithelial cells. 3. The T cell terminals are free nerve endings with a beaded appearance; they contain large mitochondria and clusters of vesicles. 4. An individual T cell makes about 100 endings within a square millimetre of skin in the centre of its territory, and is estimated to make a total of several hundred endings. 5. The distribution of T cell endings observed directly agrees with physiological studies of receptive field organization and emphasizes the high degree of specificity of connexions of these neurones with their peripheral targets.

Animals↗
PubMed1982

Chemical transmission between individual Retzius and sensory neurones of the leech in culture.

1. Chemical synaptic transmission develops between individual identified neurones dissected from leech ganglia and maintained in culture. Impulses in Retzius cells give rise to hyperpolarizing synaptic potentials in pressure (P) sensory cells. In suitable medium the potentials develop by 3 days and can be observed for more than 3 weeks. 2. The synaptic potentials occur after a synaptic delay, exhibit facilitation and depression and are reversed by hyperpolarization. The blocking effects of reduced calcium and raised magnesium concentrations in the bathing fluid provide additional evidence for the chemical nature of transmission. 3. An increase in chloride conductance is involved in the generation of the synaptic potential in the P cell. With high intracellular Cl in the post-synaptic cell, the synaptic potentials become reversed and amplified. The amplitudes of these reversed responses range from 1 to 20 mV with a falling phase lasting for seconds. 4. Changes in the membrane potential of the presynaptic cell that modify the amplitude and duration of the action potential influence the efficacy of transmission. In addition, impulses in Retzius cells initiated from hyperpolarized values of membrane potential evoke smaller synaptic potentials in the P cells than impulses arising from a depolarized level. 5. With neurones placed directly next to one another in the dish, maintained depolarization of the presynaptic Retzius cell in the absence of conducted action potentials gives rise to slow synaptic potentials in the P cells. In some pairs, the response in the P cell consists of a marked increase in 'noise'. 6. Injection of horseradish peroxidase into the Retzius cell reveals neurites with distinctive varicosities growing over the P cell.

Animals↗
PubMed1982

Expanded receptive fields of cutaneous mechanoreceptor cells after single neurone deletion in leech central nervous system.

1. Individual sensory neurones responding to touch (T) and to noxious (N) stimuli applied to the skin of the leech were killed by injecting pronase into their cell bodies, situated within the C.N.S. This procedure destroys one neurone in its entirety without damaging the cells. 2. When three out of four N cells within a ganglion have been killed, the receptive field of the remaining N sensory cell expands to cover the denervated area of skin. Similarly the field of the touch cell that innervates dorsal skin spreads across the mid line to innervate contralateral skin after the three touch cells on that side have been deleted. 3. The spread is graded and develops with time. The earliest effects appear within 4 weeks and the full spread develops by 3 months. 4. No detectable spread of receptive fields occurs if only two N cells, one on each side, are killed. 5. Following deletion of N cells, the receptive fields of T and pressure sensory cells are unaffected. Similarly, if T cells have been killed, the fields of N cells or pressure cells do not become enlarged. 6. These results represent a modality-specific mechanism by which one sensory cell can be influenced to extend the territory it supplies in the periphery in response to a minimal lesion without its own terminals having been damaged.

Action Potentials↗
PubMed1983

The role of 5-hydroxytryptamine as a transmitter between identified leech neurones in culture.

The synthesis, storage, release and synaptic actions of 5-hydroxytryptamine (5-HT or serotonin) were studied in order to characterize the synaptic connexion that develops between pairs of identified neurones dissected from the central nervous system of the leech and maintained in culture. Experiments were made with Retzius cells (which are known to contain 5-HT in vivo) and pressure sensory neurones on which they form chemical synapses in culture. Individual, isolated Retzius cells in culture synthesized [3H]5-HT from either [3H]tryptophan or [3H]5-hydroxytryptophan [( 3H]5-HTP). These cells did not synthesize other putative neurotransmitters, such as acetylcholine, dopamine, octopamine, noradrenaline or gamma-aminobutyric acid from their respective precursors. The monoaminergic character of Retzius cells was also demonstrated by staining with Neutral Red and by histofluorescence. Individual, isolated Retzius cells that had synthesized and accumulated [3H]5-HT released this compound when depolarized. Transmitter release was calcium-dependent and was blocked by magnesium. When incubated with [3H]5-HT and washed, Retzius cells in culture accumulated approximately 100 times more labelled 5-HT than did non-serotonergic cells, and 10 times more than Retzius cell somata acutely isolated from the animal and incubated in vitro. Chlorimipramine, a blocker of 5-HT uptake, decreased the amount of [3H]5-HT accumulated by Retzius cells and also caused a reversible increase in the amplitude of the synaptic response in the pressure sensory cell elicited by stimulation of the Retzius cell. Pressure sensory neurones in culture and in vivo responded to 5-HT focally applied by pressure ejection from a micropipette. Small pulses elicited a small, slow hyperpolarization. This response was due, at least in part, to an increase in chloride conductance and desensitized rapidly. With larger pulses, a larger, faster non-desensitizing depolarization was elicited. Together, these results provide evidence that 5-HT released from Retzius cells could be responsible for the chemical synaptic potentials seen in pressure sensory neurones in culture.

5-Hydroxytryptophan↗
PubMed1983

Structural and functional analysis of synaptic transmission between identified leech neurones in culture.

The fine structure and physiological properties of chemical synapses that develop between identified leech neurones in culture have been studied by electron microscopy and by quantal analysis. Earlier work has shown that the transmitter liberated by isolated Retzius cells, serotonin, evokes chloride-dependent inhibitory post-synaptic potentials (i.p.s.p.s) in P sensory cells, and also in Retzius cells. When pairs of Retzius cells or Retzius and P sensory cells were placed in close apposition in culture for a few days, their somata extended numerous fine processes which came into contact and interdigitated. In the region of interdigitation, only narrow spaces, approximately 20-25 nm wide separated the membranes. The appearance of the cytoplasm of the two neurones was distinctive: in particular, Retzius cells contained agranular vesicles, as well as abundant dense core vesicles which were not as prevalent in P cells. Structures resembling synapses developed by 4 days, with characteristic vesicles clustered in terminals of the Retzius cell apposed to the post-synaptic membrane. In the presence of raised Mg or lowered Ca in the culture medium, the i.p.s.p. in the P cell evoked by an impulse in the Retzius cell became diminished in amplitude. The time-to-peak and half-time of decay were unchanged. Under these conditions, with repeated stimulation, quantal fluctuations of these post-synaptic potentials and failures were observed. In addition, there occurred spontaneous events which resembled miniature synaptic potentials and had amplitudes and time courses similar to those of the unitary events evoked by presynaptic impulses. The amplitudes of evoked synaptic potentials in raised Mg were distributed in accord with the Poisson equation. The agreement was good when either the spontaneous miniature potentials or the failures of evoked release were used to calculate m, the mean number of quanta per trial. With larger values of m the results were distributed as predicted by the binomial equation. These morphological and electrophysiological experiments together indicate that the inhibitory potentials observed in P cells result from quantal units of transmitter released by presynaptic terminals of the Retzius cell which are in close apposition to the post-synaptic membrane.

Action Potentials↗
PubMed1983

Accurate regeneration of an electrical synapse between two leech neurones after destruction of the ensheathing glial cell.

An interneurone, the S cell in the central nervous system of the leech, regenerates its severed axon and forms an electrical synapse with its target, another S cell, entirely within the ensheathment of two glial cells. After the two glial cells were killed selectively by intracellular injection of protease, axonal regeneration and synapse formation occurred in a normal fashion during the month following nerve injury. Soon after reconnexion of S cells, the conduction of impulses across the non-rectifying electrical junction between the cells was more reliable from the target than into it from the thinner regenerating axon. The distal segments of severed S-cell axons survived for weeks or months after destruction of their glial cells, indicating that the ensheathing glia is not required for long-term survival of axon segments. The distal axon segment of the S cell remained connected to the target axon at the normal region of synapse midway between ganglia within the nerve cord. In about half the cases in which reconnexion between injured S cell and target S cell occurred between 10 and 25 days following nerve crush, the regenerating neurone had formed an electrical synapse with its severed distal axon and had thereby become reconnected, indirectly, with its target. In the other cases, reconnexion was by direct contact. By 4 weeks, the proportion of injured S cells that were coupled and making direct contact with their targets rose to more than 80% of the total population, indicating that regeneration continued until the two S cells contacted one another directly. This is similar to the course of S-cell regeneration in the presence of the ensheathing glia. Microscopy of the regenerating neurone and both its distal axon segment and its target showed that the site of synapse formation in the absence of the usual glial sheath was normal. Fluorescence microscopy following intracellular injection of Lucifer Yellow dye, which crosses between S cells at the electrical synapse, showed that the regenerated synapse formed specifically between S cells. Moreover, the target did not form alternative synapses when regeneration failed.

Animals↗
PubMed1984

Distribution of receptors for acetylcholine and 5-hydroxytryptamine on identified leech neurones growing in culture.

The spatial distribution of receptors on identified leech neurones removed from the C.N.S. and grown in culture has been studied by applying acetylcholine (ACh) and 5-hydroxytryptamine (5-HT) ionophoretically and by pressure. Two cells were selected: a neurone called anterior Pagoda (Ap), that shows responses to ACh, and the pressure sensory neurone (P cell), upon which 5-HT synapses form in culture. ACh receptors of Ap neurones in culture had properties similar to those of their counterparts in situ. Thus, ACh responses of Ap cells were mediated by Cl- and were blocked by curare and alpha-bungarotoxin. The cell bodies of these neurones in culture had low (10 mV/nC) and uniform sensitivity to ACh over the surface of the soma. When a sprout grew out from the Ap cell, a region of increased sensitivity appeared at its base, with a gradient of sensitivity decreasing toward the tip of the neurite. Characteristically, the base was 3-5 times more sensitive to ACh than the soma or the growth cone. Cells with multipolar processes developed a similar pattern of sensitivity for each sprout. P sensory neurones in culture showed similar distributions of sensitivity to 5-HT and ACh. Experiments made with voltage clamp suggested that the non-uniform responses to transmitter represent true differences in sensitivity. Together these findings suggest that the receptors for ACh and 5-HT have a greater density at the base of each neurite compared to that of the soma and the tip.

Acetylcholine↗
PubMed1986

Voltage dependence of 5-hydroxytryptamine release at a synapse between identified leech neurones in culture.

The release of 5-hydroxytryptamine (5-HT) from presynaptic terminals has been studied by the voltage-clamp technique at synapses made by isolated Retzius and pressure (P) sensory neurones dissected from the leech C.N.S. and maintained in tissue culture. At these synapses facilitation, depression and modulation of release occur with action potentials and with voltage-clamp pulses. Depolarization of Retzius cells from a constant holding potential by steps of varying amplitude (5 ms in duration) caused graded release of 5-HT. The steep transfer function for release using these short test pulses resembled that seen at the giant synapse of the squid: synaptic potentials increased markedly with presynaptic depolarizations beyond -25 mV and decreased with large depolarizing pulses beyond +40 mV. When the steady holding potential of voltage-clamped Retzius cells was suddenly displaced to a new value within the range of -40 mV to -85 mV, there followed a slow but smaller change of the post-synaptic P-cell membrane potential in the same direction. After an initial delay of about 40 ms, the post-synaptic potential reached its new level with an exponential time course and a time constant of 0.7 s. Since Retzius and P cells are not electrically coupled, these effects can be accounted for by alterations in tonic release of transmitter. Changes of presynaptic holding potential to a more depolarized level resulted in an increase in voltage noise recorded in the P cell. Conversely, hyperpolarization from a depolarized level reduced noise. Noise analysis showed that these changes could be accounted for by quantal events with a mean amplitude of about 0.15 mV. This value is similar to that for spontaneous miniature potentials and quantal fluctuations observed at synapses between Retzius and P cells. Changes in steady holding potential also had marked effects upon the transfer function observed with brief depolarizing pulses of the Retzius cell. The post-synaptic responses evoked by depolarizations to 0 mV with pulses of 5 ms duration were reduced in amplitude as the holding potential of the Retzius cell was increased from the resting value of -45 to -75 mV. For example, depolarization to 0 mV starting from -45 mV evoked synaptic potentials as much as ten times larger than those evoked by depolarizations to 0 mV starting from -75 mV.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1987

Conduction block silences parts of a chemical synapse in the leech central nervous system.

1. The pressure (P) sensory neurones innervating the ventral skin of the medicinal leech have receptive fields comprising a central region of skin innervated by two thicker axons and two neighbouring regions innervated by two thinner axons. Impulses originating in the thinner axons may fail to propagate through the central ganglion, apparently blocked at the branch point of large and small axons. 2. The P neurone excites the longitudinal (L) motoneurone, and blocked impulses originating in the anterior fine axon produce e.p.s.p.s that are less than one-half normal amplitude. Blocked impulses in the posterior fine axon are typically ineffective. 3. The branches of P and L neurones, marked with intracellularly injected horseradish peroxidase or with Lucifer Yellow, make synaptic contact at up to sixty-six sites within the neuropile. Of P neurone branches emerging from two fine axons, those from the posterior axon make fewer contacts, usually one or two at most, while branches from the anterior axon represent no more than half the total contacts. From cell to cell there is some variation in the total number of contacts, the distribution of branches, and the strength of transmission. 4. The locations of contacts measured morphologically correlate well with their distributions as predicted from reductions in e.p.s.p. amplitude during conduction block.

Animals↗
PubMed1989

An inwardly directed electrogenic sodium-bicarbonate co-transport in leech glial cells.

1. We have used double-barrelled ion-sensitive microelectrodes to measure the intracellular pH, pHi, the intracellular Na+ activity, aiNa, and the membrane potential in identified glial cells of the central nervous system of the leech Hirudo medicinalis to study the effect of CO2-HCO3-. 2. When a HEPES-buffered saline was exchanged for a saline buffered with 2% CO2 + 11 mM-HCO3-, keeping the pH constant at 7.4, the mean steady-state pHi of the glial cells increased from 6.85 +/- 0.06 to 7.18 +/- 0.13 (mean +/- S.D., n = 25). 3. This CO2-HCO3- -dependent alkalinization was inhibited in the absence of external Na+ (exchanged by N-methyl-D-glucamine), but was unaffected by the inhibitor of Na+-H+ exchange, amiloride (2 mM). 4. The aiNa of the glial cells increased by 2-4 mM from a mean steady state of 7.2 +/- 2 mM (mean +/- S.D., n = 6) upon introduction of CO2-HCO3- -buffered saline. This CO2-HCO3- -dependent rise in aiNa increased to about double when the pHi had been decreased by acid loading the cells (addition and subsequent removal of NH4+). 5. The CO2-HCO3- -dependent increases of pHi and aiNa were inhibited by the stilbene 4,4-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS, 0.5-1.0 mM). 6. Removal of external Cl- and depletion of intracellular Cl- did not inhibit the CO2-HCO3- -dependent alkalinization. 7. The CO2-HCO3- -dependent alkalinization was unaffected by inhibitors of the carbonic anhydrase, acetazolamide (0.2 mM) or ethoxzolamide (2 microM). 8. The membrane potential became more negative by 3-20 mV upon addition of CO2-HCO3-. This hyperpolarization was even further enlarged in the presence of Ba2+ (which reduces the K+ permeability) or at increased external K+ concentration (which depolarizes the membrane and brings the membrane potential to the K+ equilibrium potential). The CO2-HCO3- -induced membrane hyperpolarization was inhibited in Na+-free saline and in the presence of DIDS. Ouabain (0.5 mM) sometimes reduced, but never abolished, the hyperpolarization. 9. The stoichiometry of the co-transport is suggested to be 2 HCO3-:1 Na+ with an equilibrium potential of -90 mV calculated for this coupling ratio in the steady state. 10. It is concluded that in the presence of CO2-HCO3- an inwardly directed electrogenic Na+-HCO3- co-transport is stimulated across the glial membrane, which greatly determines the pHi and thereby affects the intracellular buffering power of the glial cells.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗