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 487 records · Page 27Linked to original sources
PubMed1984

Cell lineage, cell-cell interaction, and segment formation in the ectoderm of a glossiphoniid leech embryo.

Cell division patterns and cell-cell interactions in the germinal bands of the glossiphoniid leech Helobdella triserialis were studied with the aid of a cell lineage tracer dye. Each germinal band of the Helobdella embryo consists of five columns, or bandlets, of primary blast cells, designated as the mesodermal m bandlet and ectodermal n, o, p, and q bandlets. Primary blast cells of each ectodermal bandlet appear to undergo stereotyped, lineage-specific cell divisions. The metameric segmentation pattern of the leech thus appears to arise through a series of segmentally iterated, stereotyped cell divisions of serially homologous primary blast cell clones. Cell-cell interactions were studied by means of cell ablations. With one exception, blast cells underwent their stereotyped divisions without regard to the presence or absence of their normal neighbors. In the one exceptional case, o blast cells underwent divisions normally characteristic of p blast cells when their normal neighboring p bandlet was deleted. However, both o and p blast cells underwent their normal stereotyped divisions when their neighboring m, n, and q bandlets were deleted. It is proposed that the differential choice of pathway by the o and p blast cells depends upon their relative position with respect to each other and to a polarity cue external to the germinal band.

Animals↗
PubMed1984

Developmental interdeterminacy in embryos of the leech Helobdella triserialis.

In embryonic development of the leech Helobdella triserialis, each of the four paired positionally identifiable, ectodermal teloblasts (N, O, P, and Q) generates a bandlet of blast cell progeny that merges with ipsilateral bandlets into a germinal band. Left and right germinal bands coalesce into the germinal plate which gives rise to the segmental tissues of the leech and wherein the progeny of each teloblast generate a characteristic pattern of epidermal and neuronal cells. Experiments reported here show that the positionally identified O teloblast sometimes generates the P pattern and vice versa. The reversal of these teloblasts' generative identities was shown to correspond to the formation of chiasmata by their blast cell bandlets, so that the positions of their bandlets in the germinal band are reversed as well. Thus it is the position of the bandlet in the germinal band, rather than the position of the parent teloblast, which correlates with the fate of o and p blast cells. Moreover, two types of ablation experiments have shown that, in the absence of generative P teloblast progeny, those cells which would normally generate the O pattern take on a new fate and give rise to the P pattern in the nervous system, both at the gross pattern level in the segmental ganglia, and at the level of identified neurons in the peripheral nervous system. If related, these phenomena suggest that the O and P teloblasts, which derive from the symmetric cleavage of the OP proteloblasts, have a common developmental pluripotency. And in that case, the fates of their progeny are determined hierarchically on the basis of relative position in the nascent germinal band, with P-type fate being preferred.

Animals↗
PubMed1987

Centrifugation redistributes factors determining cleavage patterns in leech embryos.

In the normal development of glossiphoniid leech embryos, cytoplasmic reorganization prior to the first cleavage generates visibly distinct domains of yolk-deficient cytoplasm, called teloplasm. During an ensuing series of stereotyped and unequal cell divisions, teloplasm is segregated primarily into cell CD of the two-cell stage and then into cell D of the four-cell and eight-cell stages. The subsequent fate of cell D is also unique in that it alone undergoes further cleavages which generate five bilateral pairs of embryonic stem cells, the mesodermal (M) and ectodermal (N, O/P, O/P, and Q) teloblasts. Here we report studies on the effects of centrifugation on cleavage pattern and protein composition of individual blastomeres of the leech Helobdella triserialis. Centrifugation partially stratifies the cytoplasm of each cell, generating a layer of clear cytoplasm in cell CD derived largely from teloplasm. After centrifuging embryos at the two-cell stage, clear cytoplasm present in cell CD and normally inherited by cell D is redistributed and can be inherited by both cells C and D at the second cleavage. The developmental fates of cells C and D in centrifuged embryos correlate with the amount of clear cytoplasm they receive. In particular, when clear cytoplasm has been distributed roughly equally between the two cells, both cell C and cell D undergo further cleavages resembling the pattern of divisions normally associated with cell D. Likewise, non-yolk-associated proteins, normally found in higher quantities in cell D than in cell C, appear evenly disbursed between the two cells under conditions which induce this fate change. These results are consistent with the idea that the fates of cells C and D are influenced by the distribution or cellular localization of cytoplasmic components.

Animals↗
PubMed1988

Developmental origin of segmental differences in the leech ectoderm: survival and differentiation of the distal tubule cell is determined by the host segment.

The body plan of the adult leech is metameric, with each hemisegmental complement of ectodermal and mesodermal tissues being produced from a set of seven serially repeated embryonic blast cells. Previous studies have shown that homologous o blast cells give rise to an almost identical complement of descendant cells in each of the 21 abdominal segments, but that one o blast cell derivative--the distalmost cell of the nephridial tubule--is only present in 15 abdominal segments in the mature leech. Here we show that all o blast cells generate a presumptive distal tubule cell and that this cell migrates to its normal position in all abdominal segments. However, in segments which normally do not contain the mesodermal portion of the nephridium, the distal tubule cell dies before undergoing its terminal morphological differentiation. To ascertain whether the fate of the distal tubule cell is determined by its lineage history or by the segmental environment into which it is born, we utilized a previously described procedure for altering the segmental register between different embryonic cell lines. This procedure allowed us to effectively transplant o blast cells into more posterior segments prior to the cell divisions which generate their descendant clones. The results indicate that the survival or death of the distal tubule cell is determined by the identity of the host segment and that a given distal tubule cell could be effectively murdered or rescued by slipping its blast cell precursor into an appropriate segment. These findings suggest that the segment-specific pattern of distal tubule cell survival is not inherent to the O cell line, but arises from interactions with surrounding tissues.

Abdomen↗
PubMed1989

Segmental specificity and lateral asymmetry in the differentiation of developmentally homologous neurons during leech embryogenesis.

This paper describes the embryonic development of three leech neurons which undergo spatially regulated patterns of differentiation. In leeches, the nervous system arises from an iterated array of embryonic cell lineages, and each neuron is represented by a set of bilaterally symmetric and segmentally repeated homologs. Two of the cells discussed here, the neurons nz4 and mz3, stain with antibodies to the neuropeptides SCP and FMRFamide during the course of their embryonic differentiation, but only a subset of the initially immunoreactive homologs continue to express this immunoreactivity into postembryonic life. Those nz4 cells which retain immunoreactivity are referred to as RAS neurons, and the persistently immunoreactive mz3 cells referred to as CAS neurons. The subset of homologs which show persistent expression is segment specific, such that the mature RAS and CAS neurons occupy different segmental domains. In addition, both neurons display a final pattern of expression which is laterally asymmetric, with only one of the two homologs in each segment maintaining the RAS or CAS phenotype. Asymmetric differentiation can occur in either orientation for any given segment, although there is a very strong tendency for the persistently immunoreactive cells to lie on opposite sides of successive segments. The fate of the transiently immunoreactive homologs is unclear, but labeling with intracellular lineage tracers suggests that there are some mz3 neurons which survive late into postemobryonic life and never express detectable levels of immunoreactivity. Intracellular lineage tracers also allowed us to follow the development of a third neuron, mz4, which does not stain for either peptide. The mz4 neuron is initially paired, but undergoes an asymmetric pattern of cell death which also shows a strong tendency to alternate sides in successive segments. These spatially coordinated patterns of neuronal survival and/or differentiation suggest that cell interactions play a role in determining the developmental choices made by individual neurons, and a subsequent paper will characterize those interactions through experimental manipulation.

Animals↗
PubMed1989

Axon outgrowth along segmental nerves in the leech. I. Identification of candidate guidance cells.

We studied the development of the major extraganglionic components of the germinal plate in embryos of the glossiphoniid leech Helobdella triserialis to improve our understanding of the mechanism of segmental nerve formation. We examined the outgrowth of groups of axons from ganglionic neurons into the segmental nerves, the migration of peripheral neurons and epidermal specializations to their definitive sites, and the development of circular and longitudinal muscle fibers. We visualized axons, as well as neurons and epidermal specializations, by means of fluorescent cell lineage tracers injected earlier into blastomeres and muscle fibers by means of immunofluorescence. The development of cells in all groups was found to follow a stereotyped pattern. Axons of ganglionic neurons approach some identified peripheral neurons located along the segmental nerve paths but not, in general, epidermal specializations and muscle fibers. Near the somata of a subset of peripheral neurons they approach, axons cease or interrupt their growth. These findings identify a set of candidate guidance cells for axonal outgrowth in the leech, similar to those previously described in the developing nervous system of insects.

Animals↗
PubMed1980

Actions of glutamate, kainate, dihydrokainate and analogues on leech neurone acidic amino acid receptors.

Intracellular recordings have been made from leech Retzius cells. L-Glutamate and kainate both excite these cells, kainate being about 100 times more potent than glutamate. Cross desensitization was observed between glutamate and kainate. Dihydrokainate was found to be equipotent with kainate on these neurones. Esterification of either kainate or dihydrokainate rendered the compounds inactive as did the addition of a benzyloxycarbonyl group on the nitrogen of both compounds. These results suggest that the double bond in the side chain of kainate is not necessary for its potent activity on leech Retzius neurones. But, that free carboxyl groups and an unsubstituted nitrogen are essential for glutamate-like activity.

Amino Acids↗
PubMed1991

Cloning and sequencing of a leech homolog to the Drosophila engrailed gene.

We have cloned and sequenced a homolog (ht-en) to the Drosophila engrailed (en) gene from the glossiphoniid leech, Helobdella triserialis. Amino acid comparisons of the ht-en homeodomain and C-terminal residues with the corresponding residues encoded by en-class genes of other species reveal 75-79% sequence identity. In addition, the ht-en sequence appears to have a serine-rich region 16 residues C-terminal from the homeodomain, which by analogy to Drosophila may be a target site for phosphorylation. The leech gene encodes some amino acid substitutions for residues that are highly conserved in other species. These are found within the second and third of the three putative helices of the homeodomain, and in both of the intervening turn regions.

Amino Acid Sequence↗
PubMed1981

The contemporary use of the medicinal leech.

Over 100 000 patients with head injuries are admitted to General Hospitals every year in Britain (Jennet, 1978). A fair proportion of these have periorbital haematoma. Evacuation of the haematoma using a leech is a painless procedure which can be carried out by a nurse. It allows the patient to open his eye and see immediately, relieving him of discomfort and disfigurement. It allows the doctor or nurse to open the eye easily and painlessly for observation of pupil size and reaction. Leeches are cheap and very easily kept.

Eyelid Diseases↗
PubMed1982

gamma-D-glutamylglycine as an antagonist of kainic acid on leech Retzius neurones.

Intracellular recordings were made from Retzius cells from the segmental ganglia of the leech, Hirudo medicinalis, gamma-D-Glutamylglycine, (50 microM), reversibly and preferentially antagonised the excitatory action of kainate, having no effect on actions of quisqualate or carbachol but at this concentration the antagonism was of short duration, reversing prior to washing off the gamma-D-glutamylglycine. However, higher concentrations of gamma-D-glutamylglycine (250-500 microM) reversibly antagonised both quisqualate and carbachol-induced excitatory responses, indicating a lack of specificity. The value of gamma-D-glutamylglycine in determining the possible site of action of kainate on leech Retzius cells is discussed.

Animals↗
PubMed1984

The application of irritant chemicals selectively to the skin of the leech ganglion/body wall preparation.

A technique is described for applying chemical irritants selectively to the skin of a superfused ganglion/body wall preparation of the horse leech, Haemopis sanguisuga. Details are given of the intracellular recording from sensory neurones of the effects of the irritant dibenzoxazepine and of mechanical stimulation. Dibenzoxazepine produced changes in the spontaneous firing pattern in the nociceptive cells of the leech but did not affect the response to mechanical stimulation of the skin in any type of sensory cell. It is possible that the system described could be used as a model of cutaneous excitation evoked by drugs or mechanical stimulation in higher animals.

Action Potentials↗
PubMed1992

Target influences on the development of leech neurons.

A pair of Retzius neurons is found in each segmental midbody ganglion of the CNS of the leech Hirudo medicinalis. Although all Retzius neurons appear to have the same cell lineage and are indistinguishable from one another through the initial phases of axonogenesis, later in development two pairs of Retzius neurons--those in the segments containing the male and female reproductive ducts--acquire distinctive morphological and physiological characteristics. Experimental manipulations of the reproductive ducts in early embryos have indicated that the outgrowing Retzius axons receive a signal from these peripheral targets that triggers major changes in their developmental program. Such 'end-organ specification' has been shown to contribute to the differentiation of neurons in other nervous systems as well, and the mechanisms underlying such control can be investigated in great detail in the relatively simple, segmented nervous system of the leech.

Animals↗
PubMed1993

Oxygen-binding properties of extracellular hemoglobin from the leech, Hirudo medicinalis. Effects of pH, cations and temperature.

Electron microscopy of the extracellular hemoglobin from the medicinal leech, Hirudo medicinalis, revealed a typical annelid two-tiered hexagonal structure. The dimensions of the molecule were 30.2 +/- 1.6 nm corner to corner across the hexagon and 18.9 +/- 1.1 nm in height. The oxygenation properties of this high-molecular-weight hemoglobin have been thoroughly studied. The effects of hemoglobin concentration, pH, temperature and concentration of specific cations on the oxygen affinity and the degree of cooperativity have been investigated with special consideration given to physiological conditions. At near-physiological cation concentrations (6 mM Ca2+, 0.125 M Na+), the oxygen affinity and cooperativity tend to increase with increasing alkalinity. At physiological conditions ((pH 7.5) temperature 20 degrees C), they reach P50 values of 5.0 mmHg and n50 = 3.1. An alkaline Bohr effect with considerable magnitude (phi = -0.50) is observed at pH 7.0-8.0. The oxygen-binding properties are also affected by cations. Both oxygen affinity and cooperativity rise with increasing cation concentrations. Divalent cations, such as Ca2+ and Mg2+, bring about larger effects than monovalent ones. They begin to be effective at concentrations as low as 0.1 mM. The magnitude and position of the Bohr effect of H. medicinalis hemoglobin are controlled by cations to such an extent that this Bohr effect can be predominantly ascribable to the oxygen-linked binding of the physiologically available allosteric effectors Ca2+ and Na+. The results obtained indicate that protons and cations are effective allosteric regulators of achaete (leech) extracellular hemoglobins.

Animals↗
PubMedDate not supplied

Identification of RFamide neuropeptides in the medicinal leech.

Using a four-step reverse phase HPLC separation and RIA, five RFamide peptides were purified from CNS extracts of the leech Hirudo medicinalis. YMRFamide, FMRFamide, YLRFamide, FLRFamide, and GGKYMRFamide were identified by a combination of antiserum specificity in RIA, Edman degradation, and mass spectrometry. At least three of these five endogenous peptides can modulate neuromuscular interactions in the leech (38). FMRFamide-like immunoreactivity was selectively released from neural processes on isolated heart tubes in the presence of calcium and depolarizing levels of potassium.

Amino Acid Sequence↗
PubMed1996

Biochemical properties of the angiotensin-converting-like enzyme from the leech Theromyzon tessulatum.

This article reports the evidence and the biochemical properties of an angiotensin-converting (ACE)-like enzyme from head parts of the leech Theromyzon tessulatum. After solubilization from membranes with Triton X-114, the ACE-like enzyme was purified from the detergent-poor fraction. Four steps of purification including gel permeation and anion exchange chromatographies followed by a reversed-phase HPLC were needed. This poor glycosylated peptidyl dipeptidase (of ca. 120 kDa) hydrolyzes, at pH 8.4 and at 37 degrees C, the Phe8-His9 bond of angiotensin I with a high catalytic activity (i.e., K(m): 830 microM and Kcat/K(m): 153 s-1 mM-1). The hydrolysis of angiotensin I is inhibitable at 80% by captopril (IC50 = 175 nM) and lisinopril (IC50 = 35 nM). This activity is strictly dependent on the presence of NaCl and is increased by Zn2+. This zinc metallopeptidase also attacks peptides that have in their sequence either Gly-His, Gly-Phe, or Phe-His bond [e.g., enkephalins (Kcat/K(m): 12 s-1 mM-1) or bradykinin (Kcat/K(m): 2200 s-1 mM-1]. Taken together, these arguments are consistent with an ACE-like activity implicated in metabolism of angiotensins and bradykinin in leeches.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1986

A preliminary report on the effects of parasitism by the leeches Theromyzon cooperi and Placobdella garoui on the physiology of the redbilled teal Anas erythrorhyncha.

The effects of parasitism by leeches Theromyzon cooperi and Placobdella garoui on the redbilled teal Anas erythrorhyncha were investigated. Leeches with initial body mass ranging from 5.2 to 28.4 mg were allowed to parasitize redbilled teal clamped in Perspex containers. Theromyzon cooperi increased its body mass after parasitism with a mean of 10.5-fold compared to 6.9-fold for P. garoui. Changes were also observed in values of various haematological and biochemical variables of the redbilled teal monitored during this investigation.

Animals↗
PubMed1993

A comparison of the performance of two sensory systems in host detection and location in the medicinal leech Hirudo medicinalis.

1. Mechanical and visual stimuli associated with surface waves were separated into their two components. 2. Unfed leeches responded to the mechanical component of artificially generated surface waves by swimming towards their source. 3. Leeches also responded to and orientated towards the source of the waves using visual cues derived from the same surface waves. 4. Visual stimuli elicited fewer and less accurate responses.

Animals↗
PubMed1994

Cellular and molecular approaches to neural repair in the medicinal leech.

Investigation of repair processes and the effects of damage in the leech has the advantage that it is possible to work with single neurons, and that leech neurons can regenerate. The effects of surface topology on neuronal outgrowth in culture were investigated using patterned substrates produced by photolithography. On grooved substrates with a depth, width and separation of 2 microns, the processes of cultured neurons showed significant alignment. In studies on regeneration, different mechanosensory neurons were shown to respond differently to lesions of their axons. High threshold units (N cells) respond by sprouting of additional processes from the axon hillock region within the CNS, whereas low threshold cells respond with a sprouting only at the lesion site in the nerve root and not within the CNS. Sprouted processes are retained for over a year. When a neuron of a particular modality is killed, cells of the same modality (but not the other) expand their receptive fields to cover the denervated skin. Single channel patch clamp recording experiments have been initiated on damaged neurons. Experiments are in progress to clone genes whose expression is regulated after peripheral nerve injury.

Animals↗