Contralateral Partner Research Articles

Enabled/VASP is required to mediate proper sealing of opposing cardioblasts during Drosophila dorsal vessel formation.

The Drosophila dorsal vessel (DV) is comprised of two opposing rows of cardioblasts (CBs) that migrate toward the dorsal midline during development. While approaching the midline, CBs change shape, enabling dorsal and ventral attachments with their contralateral partners to create a linear tube with a central lumen. We previously demonstrated DV closure occurs via a "buttoning" mechanism where specific CBs advance ahead of their lateral neighbors, and attach creating transient holes, which eventually seal. Here, we investigate the role of the actin-regulatory protein enabled (Ena) in DV closure. Loss of Ena results in DV cell shape and alignment defects. Live analysis of DV formation in ena mutants shows a reduction in CB leading edge protrusion length and gaps in the DV between contralateral CB pairs. These gaps occur primarily between a specific genetic subtype of CBs, which express the transcription factor seven-up (Svp) and form the ostia inflow tracts of the heart. In WT embryos these gaps between Svp+ CBs are observed transiently during the final stages of DV closure. Our data suggest that Ena modulates the actin cytoskeleton in order to facilitate the complete sealing of the DV during the final stages of cardiac tube formation.

Substance P receptor antagonists fosaprepitant and spantide in an UVR‐B‐induced cataract mouse model

AbstractPurposeTo investigate the neurokinin receptor‐1 (NKR‐1) antagonists fosaprepitant and spantide in an UVR‐B‐induced cataract mouse model. To examine their effect on the expression of pro‐inflammatory cytokines and chemokines in ocular tissues of both eyes after unilateral UVR‐B exposure.MethodsMice were injected intraperitoneally with NKR‐1 antagonists before and after unilateral UVR‐B exposure to a 5‐fold cataract threshold dose. The contralateral partner eye was completely shielded during the experiment. Control mice were similarly injected with saline only. Mice were categorized into latency period groups of 3 and 7 days following exposure. Subsequently, eyes were enucleated and ocular tissues were microsurgically dissected for NKR‐1 protein concentration by enzyme‐linked immunosorbent assay (ELISA). Cytokines and chemokines in ocular tissue samples were measured using a Multiplex Immunoassay.ResultsPretreatment with fosaprepitant decreases NKR‐1 protein levels in mouse eyes after UVR‐B exposure to only one eye. NKR‐1 protein level was reduced in the exposed cornea, lens epithelium, iris/ciliary body, aqueous humor, retina and choroid as well as in the unexposed lens epithelium when compared with the saline treated mice. Spantide I treatment showed nearly the same NKR‐1 level in comparison to the saline group. Initiated fosaprepitant injection resulted in a significant reduction of Gro‐alpha/CXCL1 in the exposed cornea. No differences were measured between the treatment groups of other tested cytokines/chemokines in the mouse eye.ConclusionThe UVR‐B induced expression of NKR‐1 in ocular tissues is decreased by fosaprepitant in the exposed as well as in the unexposed partner eye. A previously reported sympathizing NKR‐1 upregulation in the unexposed partner eye can be counteracted by fosaprepitant. Therefore, substance P and its receptor seem to be the signaling molecules involved in the contralateral reaction following unilateral UVR‐B exposure.

INTRAPAPILLARY PROLIFERATION IN OPTIC DISK PITS: Clinical Findings and Time-Related Changes.

To investigate the structural changes of intrapapillary proliferations associated with optic disk pits (ODPs) and optic disk pit maculopathy (ODP-M) using enhanced depth-spectral domain-optical coherence tomography (SD-EDI-OCT) and megahertz optical coherence tomography (MHz-OCT). Sixteen eyes of patients with ODPs were studied. Papillary and peripapillary areas were repeatedly examined with SD-EDI-OCT over time. To evaluate swept-source OCT, some of the patients additionally received MHz-OCT-imaging. MHz-OCT or SD-EDI images showed the entire form of the pits from opening to bottom in 13 of the 16 cases. The shape of ODPs varied considerably. In patients with unilateral ODP, deep intrapapillary depressions in the optic disk of the contralateral partner eye were a prevalent finding. Intrapapillary proliferations were observed in all ODP-cases during follow-up. The aspect of intrapapillary and prepapillary tissue, septae, and cavities changed over time. This effect was especially pronounced inside the ODP while the eye experienced simultaneous ODP-M. All examined eyes with ODP showed signs of intrapapillary and prepapillary tissue, which developed over time. SD-EDI-OCT and MHz-OCT are able to detect characteristic ODP-related findings and are a useful means to monitor time-related changes within intrapapillary and prepapillary tissue related to ODP and ODP-M.

Integrins are required for cardioblast polarisation in Drosophila

BackgroundThe formation of a tubular organ, such as the heart, requires the communication of positional and polarity signals between migratory cells. Key to this process is the establishment of a new luminal domain on the cell surface, generally from the apical domain of a migratory cell. This domain will also acquire basal properties, as it will produce a luminal extracellular matrix. Integrin receptors are the primary means of cell adhesion and adhesion signaling with the extracellular matrix. Here we characterise the requirement of Integrins in a genetic model of vasculogenesis, the formation of the heart in Drosophila.ResultsAs with vertebrates, the Drosophila heart arises from lateral mesoderm that migrates medially to meet their contralateral partners, to then assemble a midline vessel. During migration, Integrins are among the first proteins restricted to the presumptive luminal domain of cardioblasts. Integrins are required for normal levels of leading edge membrane motility. Apical accumulation of Integrins is enhanced by Robo, and reciprocally, apicalisation of luminal factors like Slit and Robo requires Integrin function. Integrins may provide a template for the formation of a lumen by stabilising lumen factors like Robo. Subsequent to migration, Integrin is required for normal cardioblast alignment and lumen formation. This phenotype is most readily modified by other mutations that affect adhesion, such as Talin and extracellular matrix ligands.ConclusionOur findings reveal an instructive role for Integrins in communicating polarising information to cells during migration, and during transition to an epithelial tube structure.

Avoiding a Sticky Situation

The Drosophila heart is formed by two rows of cardioblasts that make dorsal and ventral junctions with their contralateral partners to create the cardiac lumen. Two groups, Santiago-Martínez et al . and Medioni et al ., found that the extracellular guidance factor Slit and its receptor Robo played a critical role in this process. Santiago-Martínez et al . performed electron microscopy on Drosophila embryos at stages late in heart development and observed that opposing cardioblasts initiated contact at dorsal regions and underwent a shape change to contact each other ventrally. Immunohistochemical analysis revealed that, like Slit, Robo localized to cardioblast lumenal surfaces. Slit overexpression, which led to its mislocalization as well as that of Robo, caused formation of ectopic lumens between cardioblasts and neighboring cells. Robo overexpression was associated with loss of adhesion between contralateral cardioblasts, whereas cells expressing Robo loss-of-function mutants adhered inappropriately (obliterating the lumen). Conversely, mutation of the gene that encodes E-cadherin eliminated adhesion between contralateral cardioblasts, whereas E-cadherin overexpression led to inappropriate adhesion. Consistent with this, Robo loss-of-function mutants showed increased accumulation of E-cadherin (concentrated at sites of junctional contact in wild-type cardioblasts) in the region of cell apposition. The authors concluded that Slit and Robo promote lumen formation by preventing E-cadherin-mediated adhesion. Medioni et al ., who used in vivo three-dimensional and time-lapse imaging to investigate Drosophila cardiac lumen formation, found that cardioblasts carrying slit or robo / robo2 mutants failed to undergo shape changes that would limit the area of dorsal contact and enable them to make contact ventrally. Instead, they formed an extended contact region with no lumen (or a small ventrally displaced one). Moreover, slit mutants showed an increase in the region in which Armadillo (a marker for the "junctional domain") was found and a decrease in the region in which Dystroglycan (a marker for the "lumenal domain") was found. Thus, the authors conclude that Slit plays a central role in creating the cardiac lumen both by promoting formation of a nonadherent membrane region and by regulating cardioblast shape. Helenius and Beitel provide thoughtful analysis, noting that localization of Slit and Robo on the same cells may indicate an autocrine function and commenting on differences in membrane polarization between cardioblasts and epithelial cells and in the processes involved in epithelial and cardiac lumen formation. E. Santiago-Martínez, N. H. Soplop, R. Patel, S. G. Kramer, Repulsion by Slit and Roundabout prevents Shotgun/E-cadherin–mediated cell adhesion during Drosophila heart tube lumen formation. J. Cell Biol. 182 , 241-248 (2008). [Abstract] [Full Text] C. Medioni, M. Astier, M. Zmojdzian, K. Jagla, M. Sémériva, Genetic control of cell morphogenesis during Drosophila melanogaster cardiac tube formation. J. Cell Biol. 182 , 249-261 (2008). [Abstract] [Full Text] I. T. Helenius, G. J. Beitel, The first "Slit" is the deepest: the secret to a hollow heart. J. Cell Biol. 182 , 221-223 (2008). [Abstract] [Full Text]

Bilateral impact of unilateral visual cortex lesions on the superior colliculus.

We examined the functional impact of a long-standing, unilateral primary visual cortex lesion on the superior colliculus (SC) using radiolabeled 2-deoxyglucose (2DG) as a marker of neural activity. In accord with known corticotectal connectivity and functional influence, 2DG uptake in the superficial layers of the ipsilesional SC was decreased. We also found a decrease in the superficial layers of the contralesional SC. These data suggest that modifications in activity in one SC can have a substantial influence on activity in its contralateral partner, and that processing in one visual hemifield does not occur independently of processing of signals in the opposite hemifield. The effects are not mediated by the contralateral hemisphere but are probably mediated by intercollicular circuitry.

Asynchronous swimmeret beating during defense turns in the crayfish, Procambarus clarkii.

Swimmeret beating was monitored in freely moving specimens of the crayfish Procambarus clarkii as they exhibited defense turn responses to tactile stimuli. Analysis of videotape records revealed alterations in swimmeret beating during turning responses compared to straight, forward walking. During turns, swimmerets beat with shorter periods and smaller amplitude power strokes than during straight walking. Coordination between swimmerets also changed. Swimmerets on the side toward which the animal turned tended to lag behind their contralateral partners, rather than beat in synchrony as in straight walking, and ipsilateral coordination was loosened relative to straight walking. Asynchronous swimmeret beating accompanied asymmetric motions of the uropods in a manner similar to that observed during statocyst-dependent equilibrium reactions in P. clarkii, but removal of the statoliths did not eliminate turn-associated responses of the swimmerets. The coordinated action of the swimmerets and uropods may contribute to the torque that rotates the animal in the yaw plane. Implications of the observed changes in swimmeret coordination for understanding the underlying neuronal control system are discussed.

Intracellular Ca2+Dynamics During Spontaneous and Evoked Activity of Leech Heart Interneurons: Low-Threshold Ca Currents and Graded Synaptic Transmission

In oscillatory neuronal networks that pace rhythmic behavior, Ca(2+) entry through voltage-gated Ca channels often supports bursting activity and mediates graded transmitter release. We monitored simultaneously membrane potential and/or ionic currents and changes of Ca fluorescence (using the fluorescence indicator Ca Orange) in spontaneously active and experimentally manipulated oscillator heart interneurons in the leech. We show that changes in Ca fluorescence in these interneurons during spontaneous bursting and evoked activity reflect the slow wave of that activity and that these changes in Ca fluorescence are mediated by Ca(2+) entry primarily through low-threshold Ca channels. Spatial and temporal maps of changes in Ca fluorescence indicate that these channels are widely distributed over the neuritic tree of these neurons. We establish a correlation between the amount of transmitter released, as estimated by the integral of the postsynaptic current, and the change in Ca fluorescence. In experiments in which we were able to record presynaptic low-threshold Ca currents, associated IPSCs, and presynaptic changes in Ca fluorescence from fine neuritic branches of heart interneurons near their region of synaptic contact with their contralateral partner, there was a close association between the rise in Ca fluorescence and the rise of the postsynaptic conductance. The changes in Ca fluorescence that we record at the end of fine neuritic branches appear to reflect changes in [Ca(2+)](i) that mediate graded synaptic release in leech heart interneurons. These results indicate that widely distributed low-threshold Ca currents play an important role in generating rhythmic activity and in mediating graded transmitter release.

Morphometry of human lumbar apophyseal joints. A novel technique.

The anatomy of cadaveric lumbar apophyseal joints was examined as part of a study of possible correlations between lumbar apophyseal morphology, arthrosis, and cartilage thickness and stiffness. To establish the morphometry of human upper lumbar apophyseal joints using an objective technique. The apophyseal joints of 30 unfixed lumbar motion segments, all from different cadavers (24 male, five female, and one unknown, mean age 35 years, range 16-78 years) were exposed by dissection and disarticulation. Twenty-five motion segments were L1-L2, three were L2-L3, and two were L3-L4. The extent of fibrillation and linear dimensions of 29 of these specimens were examined, whereas the vertebrae and joints of 22 of them (18 being L1-L2) were cast in araldite resin. The casts of the vertebrae were sectioned cephalocaudally at 1-mm intervals. Image processing of photographic slides of the sections established the orientations and dimensions of the lumbar apophyseal joints and their shapes using Fourier analysis. Apophyseal joint surface area was 158 +/- 43 mm2, cephalocaudal length 15.2 +/- 2.7 mm, and straight line length between anterior and posterior borders was 13.2 +/- 1.9 mm. The joints were orientated at 62.5 +/- 11.8 degrees to the coronal plane. Average maximum depth of concavity was 1.8 +/- 0.7 mm. The posterior edges of two joint pairs twisted inward toward the midsagittal plane in a cephalocaudal direction; thus, some apophyseal joints bear part of the axial spinal load. The right inferior surfaces were more elongated cephalocaudally (but not longer) than their contralateral partners. Inferior apophyses were significantly more elongated cephalocaudally (but not longer) than their ipsilateral articulating superior surfaces. In theory, Fourier analysis of joint surfaces was objective, but it dictated the criterion by which joints were grouped; care must be exercised so that measurement methods do not categorize joints artificially. "Symmetry" is too subjective to be applied to contralateral apophyseal joints; correlation coefficients should be quoted for areas and orientations. The morphology of contralateral lumbar apophyseal joint pairs was significantly correlated in all respects, as was the morphology of articulating lumbar apophyseal surfaces.

Spinal cord coordination of hindlimb movements in the turtle: interlimb temporal relationships during bilateral scratching and swimming.

Hindlimb interlimb coordination was examined in turtles during symmetrical "same-form" behaviors in which both hindlimbs utilized the same movement strategy ("form") and during asymmetric "mixed-form" behaviors in which the form exhibited by one hindlimb differed from that of its contralateral partner. In spinal turtles, three forms of scratching were examined: rostral, pocket, and caudal. Bilateral symmetrical same-form scratching was studied for each of the forms. Asymmetric mixed-form scratching (rostral scratching of a hindlimb and pocket scratching of the other hindlimb) was also examined. In intact turtles, two forms of swimming were examined: forward swimming and back-paddling. The symmetrical behavior of bilateral forward same-form swimming and the asymmetric behavior of turning mixed-form swimming (forward swimming of 1 hindlimb and back-paddling of the other hindlimb) were studied. For all behaviors examined, most episodes displayed absolute or 1:1 coordination; in this type of coordination, during each movement cycle that began and ended with the onset of ipsilateral hip flexion, there was a single onset of contralateral hip flexion. For most of these episodes there was out-of-phase coordination between hip movements; the onset of contralateral hip flexion occurred near the onset of ipsilateral hip extension midway through the ipsilateral movement cycle. Bilateral caudal/caudal same-form scratching displayed out-of-phase 1:1 coordination during some episodes and in-phase 1:1 coordination during other episodes. During in-phase coordination, the onset of contralateral hip flexion occurred near the onset of ipsilateral hip flexion close to the start of the ipsilateral movement cycle. In a few cases of bilateral same-form scratching there were episodes of relative or 2:1 coordination; in this type of coordination, during each movement cycle of the slowly moving limb that began and ended with ipsilateral hip flexion, there were two distinct occurrences of the onset of contralateral hip flexion. The observation that out-of-phase movements of the hip occurred during symmetrical as well as asymmetric behaviors is consistent with the hypothesis that timing signals related to hip movement play a major role in interlimb phase control. The neural mechanisms responsible for interlimb phase control are not well understood in vertebrates. The present demonstration of bilateral scratching in spinal turtles suggests that this preparation may be suitable for additional experiments to examine mechanisms of vertebrate interlimb phase control.

Sensory-induced plasticity of motor pattern selection in the lobster stomatogastric nervous system.

In a previous study, a bilateral sensory input pathway to the crustacean stomatogastric nervous system was reported to induce the functional switching of an identified motor neuron (VD) from one rhythm generating neural network (the pyloric circuit) to another (the cardiac sac network). In the present in vitro study on the spiny lobster, Palinurus vulgaris, we have shown that under certain conditions, repetitive trains of phasic stimulation (1 s, 40 Hz) of one of these sensory nerves elicits either an increase or a decrease in efficacy of the VD switching response. In preparations showing no previous sign either of increase or decrease in VD switching, either response can be induced by prior conditioning stimulation. The increasing effect can be induced by unpaired conditioning stimulation of the contralateral sensory nerve. Conversely, the decrease in switching efficacy is obtained by pairing stimulation of the sensory-motor pathway with that applied to its contralateral partner. Both the experimentally induced increase and decrease in VD switching are long-lasting, remaining observable for at least 20 min and in some cases up to 3 h after the original conditioning procedure. Our results suggest that this system provides a suitable 'simple' model for the analysis of experience-related plasticity of the switching of a neuron from one network to another.

The Active Control of Wing Rotation by Drosophila

This paper investigates the temporal control of a fast wing rotation in flies, the ventral flip, which occurs during the transition from downstroke to upstroke. Tethered flying Drosophila actively modulate the timing of these rapid supinations during yaw responses evoked by an oscillating visual stimulus. The time difference between the two wings is controlled such that the wing on the outside of a fictive turn rotates in advance of its contralateral partner. This modulation of ventral-flip timing between the two wings is strongly coupled with changes in wing-stroke amplitude. Typically, an increase in the stroke amplitude of one wing is correlated with an advance in the timing of the ventral flip of the same wing. However, flies do display a limited ability to control these two behaviors independently, as shown by flight records in which the correlation between ventral-flip timing and stroke amplitude transiently reverses. The control of ventral-flip timing may be part of an unsteady aerodynamic mechanism that enables the fly to alter the magnitude and direction of flight forces during turning maneuvers.

Modeling a Neural Oscillator that Paces Heartbeat in the Medicinal Leech

Heartbeat in the medicinal leech is paced by a neural oscillator comprising two elemental oscillators whose activity is coordinated by intersegmental coordinating fibers. The elemental oscillators each consist of a bilateral pair of heart interneurons linked by reciprocal inhibitory synapses. The activity cycle of each elemental oscillator consists of alternating bursts of action potentials (plateau/burst phase) and periods of inhibition (inactive phase). Oscillation ensues in the reciprocally inhibitory pairs because each neuron is able to escape from the inhibition of its contralateral partner and thus move on to the plateau/burst phase

A local circuit interaction in the flight system of the locust

Most of the interneurons that have been identified in the locust flight system to date are spiking, intersegmental interneurons and the described interactions between them are spike-mediated postsynaptic potentials. We wished to discover whether the same interneurons also communicate via subthreshold interactions to form local circuits independent of their spike-mediated connections. Using a deafferented flight preparation of the locust and glass microelectrodes, we recorded simultaneously from the neuropil segments of different interneurons within a single thoracic ganglion. Interneuron 301 had an indirect connection with the contralateral 301 and an indirect connection feeding back to itself. The feedback circuit could be activated with subthreshold stimuli. Spikes in a 301 affected self and contralateral partner, whereas subthreshold stimuli affected only self. Thus, this paper demonstrates the existence of 2 pathways from a single interneuron that can be functionally separate depending on whether activity in the interneuron is subthreshold or suprathreshold for spiking. The results show that dendritic regions of spiking intersegmental interneurons in the locust can participate in local circuits whose operation could have a considerable role to play in neural integration.

Preflight development of bilateral wing coordination in the chick (Gallus domesticus): effects of induced bilateral wing asymmetry.

The performance of bilaterally synchronous wing-flapping by chick hatchlings suggests but does not prove the existence of a bilateral coordinating mechanism. The present research tests for bilateral coordination by using the technique of induced asymmetry. The onset of bilateral wing coordination was defined as the age when induced bilateral asymmetry produced by right wing amputation, immobilization, or weighting influenced the drop-evoked flapping rate of the left wing. Unilateral right wing immobilization or weighting immediately before testing reduced the flapping rate of the contralateral left wing of 3-5 day chicks, the youngest examined. Weighted and unweighted wings flapped synchronously. Therefore, a mechanism which acts across the body midline to synchronize wing-flapping by slowing the rate of the more rapidly flapping wing to match that of its slower contralateral partner was present by 3-5 days. This is several days before the onset of flight. The flapping rate of the left wing of chicks that had their right wing amputated on Day 1 was similar in rate to that of intact chicks when tested at 7 and 13 days. "Wing-flapping" on the amputated side of some unilateral amputees was made visible by a prosthesis attached to the stump of the amputated wing. Bilaterally coordinated flapping in the unilateral amputees indicated that the sensory and trophic periphery of a given wing and flight-related adaptive significance are not necessary for the postnatal production of bilaterally synchronized wing-flapping. However, the slowed flapping produced by unilateral wing weighting or immobilization indicates that wing-flapping rate is modulated by sensory feedback, even at preflight stages.

Synaptic Actions of Oesophageal Proprioceptors in the Mollusc, Philine

ABSTRACT The buccal ganglia of Philine each contain a group of mechanoreceptors, consisting of 1 large and 3 small cells, with receptive fields in the oesophagus. Synaptic contacts occur between the receptors; the large cell providing an EIPSP input to its contralateral partner and to the two groups of smaller receptors. The small receptors make weak excitatory contacts with both the large receptors. The sensory cells synapse with other buccal motoneurones and interneurones, some of which show periodic activity associated with the feeding movements. Protraction phase neurones are divisible into two groups, one of which receives EPSPs from the receptors, while the other group receives IPSPs. Retraction phase neurones receive a biphasic EIPSP. The receptors provide excitatory synaptic input to a pair of interneurons which ‘gate’ the feeding cycle. A third class of neurones which are not rhythmically active during feeding receive a predominantly inhibitory EIPSP.

Neural Control of Radular Retractor Muscles of the Pulmonate Snail, Planorbarius Corneus (L.): Functional Anatomy and Properties of Neuromuscular Units

ABSTRACT The paired supralateral radular retractor muscles of Planorbarius are innervated by eight (four pairs) of buccal motoneurones. Each motoneurone supplies both muscles, the ipsi- and contralateral motor responses being similar, and identical to those produced by its contralateral partner. This arrangement apparently secures equivalence of motor output to the two muscles, irrespective of discrepancies in spiking between homologous motoneurones across the midline, and relates to the strong mechanical linkage between the muscles exerted by the radula. The neuromuscular units are essentially non-overlapping, have properties which range from tonic to phasic, and may act independently providing the flexibility in control required of bifunctional muscles participating in both tensing and retraction of the radula during each feeding cycle.

Control of paralysed axial muscles by electrical stimulation.

The function of a paralysed axial (laryngeal, facial, extraocular) muscle could conceivably be restored if it were made to contract again like its contralateral partner. A muscle stimulation device was designed and constructed so that the stimulus delivered to a given paralysed muscle was modulated by a signal reflecting the contractile state of its contralateral partner. Studies in dog larygneal muscles indicate that paralysed muscles stimulated by such an open-loop device could mimic their partners. However, their tracking accuracies were limited by the nature of their stimulus-reponse characteristics. On the other hand, significantly greater tracking accuracies were observed if a closed-loop device was employed, that is, if feedback information from the stimulated muscles was also used to control the device stimulus level. Considerations in implanting such a (closed-loop or open-loop) device in paralysed axial muscles for chronic stimulation are discussed.

TESTOSTERONE AND OESTRADIOL IN DOGS WITH TESTICULAR TUMOURS

ABSTRACT The mean peripheral plasma concentration of oestradiol was found to be increased in 3 dogs with Sertoli cell tumours and in 3 dogs with seminomas, whereas the plasma testosterone showed no difference as compared to a group of dogs without testicular neoplasia. In two thirds of the cases the concentration of oestradiol in the spermatic venous blood draining the neoplastic testes was clearly higher than in the normal dogs. The testosterone concentration in the spermatic venous blood from the tumour bearing testes was lower than in the spermatic venous blood of the contralateral partner testes in the same dogs, though not different from the spermatic venous concentration in the control dogs. There was no correlation between the presence or absence of signs of feminization and the peripheral or spermatic venous concentration of sex steroids. It is concluded that not only Sertoli cell tumours, but also seminomas can secrete increased amounts of oestrogens. This is possibly due to the presence of a larger than normal mass of tissue capable of converting testosterone, or its precursors, to oestradiol.

Retzius' cells from segmental ganglia of four species of leeches: Comparative neuronal geometry

1. 1. Iontophoretic injection of procion yellow into Retzius' cells of four leeches ( Haemopis, Hirudo, Macrobdella and Placobdella) demonstrates that their neuronal geometries are similar. 2. 2. Each neuron invariably sends axons out the anterior and posterior lateral roots, has processes extending into the neuropile and is electrically coupled to its contralateral partner.