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D H Paul

Publications and source records attributed to D H Paul.

At least 19 recordsLinked to original sources
PubMed2006

Neuronal network models of phase separation between limb CPGs of digging sand crabs.

Ordinary differential equations are used to model a peculiar motor behaviour in the anomuran decapod crustacean Emerita analoga. Little is known about the neural circuitry that permits E. analoga to control the phase relationships between movements of the fourth legs and pair of uropods as it digs into sand, so mathematical models might aid in identifying features of the neural structures involved. The geometric arrangement of segmental ganglia controlling the movements of each limb provides an intuitive framework for modelling. Specifically, due to the rhythmic nature of movement, the network controlling the fourth legs and uropods is viewed as three coupled identical oscillators, one dedicated to the control of each fourth leg and one for the pair of uropods, which always move in bilateral synchrony. Systems of Morris-Lecar equations describe the voltage and ion channel dynamics of neurons. Each central pattern generator for a limb is first modelled as a single neuron and then, more realistically as a multi-neuron oscillator. This process results in high-dimensional systems of equations that are difficult to analyse. In either case, reduction to phase equations by averaging yields a two-dimensional system of equations where variables describe only each oscillator's phase along its limit cycle. The behaviour observed in the reduced equations approximates that of the original system. Results suggest that the phase response function in the two dimensional system, together with minimal input from asymmetric bilateral coupling parameters, is sufficient to account for the observed behaviour.

Action Potentials↗
PubMed2002

Cerebellar regulation of sensorimotor activity in brown trout.

Evoked field potentials were recorded from the mesencephalic ('optic') tectum, cerebellar corpus, midline rhombencephalon, and spinal cord of decerebrated brown trout in response to single electrical shocks given to an optic nerve. Evoked responses were also recorded from the rhombencephalon and spinal cord following stimulation (singly and with trains) to the optic tectum and to the cerebellar corpus. The potentials recorded from the tectum in response to optic nerve stimulation were similar in form to those reported by other workers from other species of teleost. The rhombencephalic responses to optic nerve and tectal stimulation were complex and comprised presumed pre- and post-synaptic events. Cerebellar stimulation evoked no detectable responses in these brain regions, but when given prior to tectal stimulation (by up to 10 ms), tectally-evoked spinal cord responses were reduced in amplitude by as much as 85%. After cerebellar ablation, there was no difference from controls in the latency, form or amplitude of any response, even when tested with paired pulse stimulation. However, when the cerebellum was ablated, rhombencephalic and spinal responses to optic nerve and tectal stimulation were markedly enhanced (by 200-300%). These clear-cut complimentary consequences of cerebellar ablation or stimulation emphasize the gain-setting role of the cerebellum and indicate, at least in relation to optically evoked motor activity, that cerebellar regulation acts at the level of the supraspinal drive to spinal motor circuits and not within the sensory centers.

Animals↗
PubMed2001

Serotonergic and octopaminergic systems in the squat lobster Munida quadrispina (Anomura, Galatheidae).

Immunocytochemical mapping of serotonergic and octopaminergic neurons in the central nervous system of the squat lobster Munida quadrispina reveal approximately 120 serotonin-immunoreactive cell bodies (distributed throughout the neuromeres except in abdominal ganglion 5) and 48 octopamine-immunoreactive cell bodies (in brain and thoracic neuromeres but none in the circumesophageal or abdominal ganglia). Immunopositive neuropils for both amines are distributed in multiple areas in each neuromere and overlap extensively. Serotonergic and octopaminergic neurons have extensive bilateral projections in abdominal ganglia, whereas the majority of projections in thoracic and subesophageal ganglia are unilateral (contralateral to soma). This difference correlates with typical differences between abdominal and thoracic motor system coordination. Processes of immunoreactive cells for both amines form extensive, peripheral, neurosecretory-like structures. Serotonin seems to be released peripherally in more segments, and from more nerves per segment, than octopamine. M. quadrispina has fewer serotonergic and octopaminergic immunoreactive cells, in particular, fewer segmentally repeated cells, than other species studied to date. Nevertheless, the general organization of the aminergic systems is similar, and several aminergic cells have locations and morphologies that strongly suggest homology with identified aminergic cells in other crustaceans. Among these are segmentally repeated neurons that, in M. quadrispina, form serotonin-immunopositive tubular structures in the thoracic hemiganglia innervating pereiopods 1-3 that are unlike anything reported previously for any species. Comparisons of immunocytochemical maps within one species and between species exhibiting different behaviors provide insights into possible sites of action, functional differences between, and evolution of biogenic aminergic systems.

Animals↗
PubMed1999

Receptor potentials and electrical properties of nonspiking stretch-receptive neurons in the sand crab Emerita analoga (Anomura, Hippidae).

Receptor potentials and electrical properties of nonspiking stretch-receptive neurons in the sand crab Emerita analoga (Anomura, Hippidae). Four nonspiking, monopolar neurons with central somata and large peripheral dendrites constitute the sole innervation of the telson-uropod elastic strand stretch receptor in Emerita analoga. We characterized their responses to stretch and current injection, using two-electrode current clamp, in intact cells and in two types of isolated peripheral dendritic segments, one that included and one that excluded the dendritic termini (mechanosensory membrane). The membrane potentials of intact cells at rest (mean +/- SD: -57 +/- 4. 4 mV, n = 30), recorded in peripheral or neuropil processes, are similar to the membrane potentials of isolated dendritic segments and always less negative than membrane potentials of motoneurons and interneurons recorded in the same preparations. Ion substitution experiments indicate that the membrane potential is influenced strongly by Na+ conductance, probably localized in the mechanotransducing terminals within the elastic strand. The form of the receptor potential in response to ramp-hold-release stretch remains the same as stretch amplitude is varied and is not dependent on initial membrane potential (-70 to -30 mV) or recording site: initial depolarization (slope follows ramp of applied stretch), terminated by rapid, partial repolarization to a plateau (delayed depolarization) that is intermediate between the peak depolarization and the initial potential and sustained for the duration of the stretch. Responses to depolarizing current pulses are similar to stretch-evoked receptor potentials, except for small amplitude stimuli: an initial peak occurs only in response to stretch and probably reflects elastic recoil of the extracellular matrix surrounding the dendritic terminals. The rapid, partial repolarization depends on holding potential and is abolished by 4-aminopyridine (4-AP; 10 mM), implicating a fast-activating, fast-inactivating K+ conductance; TEA (60 mM) abolishes the remaining slow repolarization to the plateau. In intact cells, but not dendritic segments, regenerative depolarizations can arise in response to stretch or depolarizing current pulses; they are reduced by CdCl2 (10 microM) in the saline containing TEA and 4-AP and probably reflect current spread from Ca2+ influx at presynaptic terminals in the ganglion. We found no evidence for other voltage-activated conductances. Unlike morphologically similar "nonspiking" thoracic receptors of other species, E. analoga's nonspiking neurons are electrically compact and do not boost the analogue afferent signal by voltage-activated inward currents. The most prominent (only?) voltage-activated extra-ganglionic conductances are for potassium; by reducing the slope of the stretch-plateau depolarization curve, they extend each neuron's functional range to the full range of sensitivity of the receptor.

4-Aminopyridine↗
PubMed1998

Digging in sand crabs: coordination of joints in individual legs.

Sand crabs use their multi-jointed legs to dig into sand. Combined movement and electromyogram (EMG) analyses showed that the pattern of intra-leg coordination in the legs of two sand crabs of different families (Blepharipoda occidentalis and Emerita analoga) is similar in legs 2 and 3, but very different in leg 4. For example, the sequence of proximal joint movements in legs 2 and 3 is elevation, retraction, depression and protraction (similar to backward walking in most decapods), but the sequence of proximal joint movements in leg 4 is elevation, protraction, retraction and depression (similar to forward walking). The synergies are the same during leg movements in sea water and in sand, suggesting that the same motor programme is used in both situations. At the transition from sea water into sand, however, both the frequency and amplitude of the EMG potentials increase, and the phasing of the motor output to leg 2 (and presumably leg 3) changes from proportional (both power and return strokes co-vary with period) to return stroke constant (power strokes co-vary much more with period than do return strokes). The motor output to leg 4 remains intermediate between proportional and return stroke constant in sea water and in sand. On the basis of the segmental specialisation of the motor patterns for the legs, we hypothesize that sand crab digging may be an evolutionary mosaic of disparate ancestral locomotor behaviours.

Animals↗
PubMed1997

A map of distal leg motor neurons in the thoracic ganglia of four decapod crustacean species.

We describe the numbers, central positions, and axonal exit routes of the distal leg motor neurons of four decapod species: squat lobsters (Munida quadrispina), spiny sand crabs (Blepharipoda occidentalis), mole sand crabs (Emerita analoga), and signal crayfish (Pacifastacus leniusculus). As predicted by previous physiological and anatomical identification of axons at the periphery in crayfish and lobsters, cobalt backfills reveal about seventeen cell bodies, which are found in four areas in the ganglion. By comparing their positions and neurite morphologies with the previously identified neurons, functional identifications could be assigned to most of them. The common inhibitor and stretcher inhibitor are located posterior-medial. An anterior-lateral cluster of about twelve somata includes the opener identical to stretcher excitor, one of two bender excitors (bender excitor alpha), four flexor excitors, and two excitors each to the extensor, reductor, and closer muscles. Three cell bodies are posterior-lateral. Of these, the opener inhibitor and the second bender excitor (bender excitor beta) are on about the same dorsoventral plane. The third posterior-lateral cell, the accessory flexor excitor, is noticeably more dorsal than the other two posterior-lateral cell bodies. The reductor muscle is innervated by at least three neurons: the putative common inhibitor and fast and slow excitors. None of the leg motor neurons project into the contralateral hemiganglion. The most variable feature across species is the nerve through which motor axons exit the ganglion: axons leave the ganglia via different routes in each of the four species examined. These differences in the axons' pathway, however, are insufficient to explain the differences in motor output and behaviour of these four species.

Animals↗
PubMed1994

Replacement of an inherited stretch receptor by a newly evolved stretch receptor in hippid sand crabs.

Primary sensory neurons that are motoneuron-like in morphology and often nonspiking (transmit afferent signals as graded depolarizations) characterize an unusual type of stretch receptor in decapod crustaceans. Nonspiking and spiking receptors occur in similar positions at homologous joints in different species and have been presumed to be homologous, the spiking one considered "primitive". To better understand the evolutionary origin of these stretch receptors and why some are nonspiking, we examined the spiking telson-uropod stretch receptors in the spiny sand crab Blepharipoda occidentalis (Albuneidae) and the squat lobster Munida quadrispina (Galatheidae) and compared them with the nonspking telson-uropod stretch receptor of the mole sand crab Emerita analoga (Hippidae). The position, morphology and responses to stretch of the sensory neurons, and the ultrastructure of the elastic strand portion of the receptor are similar in M. quadrispina and B. occidentalis, except that in B. occidentalis the receptor muscles are substantially smaller and the extracellular matrix of the elastic receptor strand is both more extensive and more organized, reminiscent of the ultrastructure of E. analoga's nonspiking receptor. We conclude that the spiking telson-uropod stretch receptors of albuneids and galatheids are homologous. The differences in the ultrastructure of their receptor strands imply that the efficiency of coupling receptor length change to deformation of the dendritic termini increases in the order M. quadrispina < B. occidentalis < E. analoga. The spiking and nonspiking telson-uropod stretch receptors differ anatomically in three major respects that appear to preclude their homology. (1) The receptor strands are on opposite sides of a conserved muscle. (2) The sensory somata are in different regions of the sixth abdominal ganglion: a lateral cluster of somata for the spiking sensory neurons and two medial clusters, one anterior, one posterior, for the nonspiking sensory neurons. (3) The neuropil projections of the sensory neurons are different. We conclude that the hippid's nonspiking telson-uropod stretch receptor evolved de novo and not by modification of the ancestral anomuran telson-uropod stretch receptor (which Hippidae have lost).

Action Potentials↗
PubMed1993

Differential responses of single reticulospinal cells to spatially localized stimulation of the optic tectum in a teleost fish, Salmo trutta.

To determine whether the topographically organized retinal input to the optic tectum is subsequently mapped onto the reticular formation, the responses of antidromically identified reticulospinal cells to tectal surface stimulation were investigated in 45 decerebrated, paralysed trout. The tectum was stimulated through a silver ball surface electrode at 24 different locations, and extracellular recordings were made from the rhombencephalic brainstem with glass microelectrodes filled with a 10% solution of horseradish peroxidase (HRP) in Tris buffer (pH 7.4). After recording, the HRP was, in some cases, iontophoretically expelled from the pipette to identify its location and visualized in histological sections by a modified Hanker-Yates method. Individual reticulospinal neurons discharged 1-4 spikes at short latency in response to stimulation of each of the 24 tectal locations. From one tectal location per cell, this initial response was followed by a late, sustained burst. With a short stimulus train (6 pulses, 55 Hz) the burst could last for over a second with discharge rates of up to 500 Hz. Sometimes this burst could be evoked from neighbouring tectal locations, but only by greatly increasing the stimulus strength. We conclude that the reticular formation receives a highly divergent monosynaptic connection from all locations of the tectum and that the longer latency, sustained burst response is due to a mapped connection between the tectum and the reticular formation. Since the late burst could be preceded by a silent period lasting for approximately 32 ms, we cannot rule out a dependence on interneurons situated between the tectum and the reticulospinal cells.

Animals↗
PubMed1992

Brainstem neurons projecting to different levels of the spinal cord of the dogfish Scyliorhinus canicula.

Neurons in the brain that project to different levels of the spinal cord in the dogfish Scyliorhinus canicula have been identified by retrograde labelling with horseradish peroxidase. Injections have been made at four different levels, namely, cervical (segments 3-6), pectoral (segments 16-18), pelvic (segments 34-36) and caudal (segments 60-80). Labelled neurons were located in the diencephalon, mesencephalon and rhombencephalon. Twenty nuclei contained labelled cells following cervical injections. Fourteen of these contained labelled cells following pectoral injections as did nine following pelvic injections and only seven after caudal injections. Of the three diencephalic nuclei projecting to the cord only nucleus thalamus ventralis pars medialis projected further than cervical regions. From the mesencephalon, the tectospinal projection, which arises from tectal and tectotegmental regions, reaches only as far as the cervical cord. The reticulospinal system, arising from cell groups in both the mesencephalon and rhombencephalon, provides the major descending pathway and reaches the most caudal levels. From the octaval region a vestibulospinal pathway arises from nucleus octavus magnocellularis, to reach all levels of the cord, and from nucleus octavus descendens, to project only as far as the pectoral cord. Other rhombencephalic cell groups--the trigeminal nuclei and nuclei B, F and G--project at least as far as the pectoral cord. We conclude that few brainstem nuclei can directly affect the whole spinal cord, whereas many nuclei may have an impact on its most rostral regions; here we have found labelled spinal interneurons with long descending axons that reach the most caudal cord levels.

Animals↗
PubMed1991

Pedigrees of neurobehavioral circuits: tracing the evolution of novel behaviors by comparing motor patterns, muscles, and neurons in members of related taxa.

Comparisons of homologous elements in neurobehavioral circuits that have diverged during speciation to mediate different behaviors should reveal the nature of evolutionary changes in nervous systems. When the pedigree of a particular behavior can be traced-by comparing motor patterns and their neural substrates in related taxa whose phylogeny is known from other (non-neurobehavioral) criteria-divergent and convergent evolutionary changes can be distinguished and the order of their occurrence reconstructed. An example of reconstructing a behavioral pedigree (for the novel mode of swimming in the crab Emerita [Hippidae]) is presented, and implications about the evolution and organization of neurobehavioral circuits engendered by this and some other studies of functionally defined neuronal networks are reviewed. Specific neural differences in related animals can only be attributed to natural selection when they can be related to species differences in function or behavior. Differences that cannot be so related, as well as apparently non-adaptive characters in individual nervous systems, are attributed to ontogenetic processes, which apparently, in some cases, introduced and, in other cases, resisted change through evolutionary time. More expressly-comparative investigations of discrete neurobehavioral circuits are needed for an understanding of the interdependence of evolutionary processes and ontogenetic and functional constraints on the organization of neuronal systems.

Animals↗
PubMed1990

Functional morphology of the telson-uropod stretch receptor in the sand crab Emerita analoga.

The telson-uropod stretch receptor in Emerita analoga belongs to a segmental array of axial-coxal receptors having sensory neurons with central somata. It consists of an elastic strand innervated by four giant, nonspiking, mechanoreceptive neurons. We examined the elastic (sensory) strand by light and electron microscopy to discover whether 1) functional differences between the four sensory neurons could be surmised from their peripheral terminations and 2) the process of mechano-electric transduction in this type of receptor might be revealed by the ultrastructure of the dendritic terminals. The elastic strand is divided into nonoverlapping domains by the mechanoreceptive neurons. We discerned no differences other than their serial order along the strand. Each neuron has three morphological zones in the periphery. In the zone of dendrite entry, the dendrite bifurcates into 40-60 microns primary branches that enter the strand at acute to right angles and turn rostrally and caudally along the strand's axis. The zone of branching consists of 4-35 microns diameter dendritic branches within the strand. Approximately 21,000 dendritic tips (diameters, 0.1-0.7 micron; lengths, 3-20 microns) per sensory neuron arise via short stubs from all levels of the zone of branching and constitute the zone of dendrite termination. The repeated bifurcations of dendrites within the zone of branching take place by radial intrusion of longitudinally oriented, partitions of extracellular matrix each of which extends the length of the pair of dendritic branches it divides. Tips project into these partitions. Since they change shape when the elastic strand is stretched, which compresses the extracellular matrix of the partitions, they are probably the site of mechanosensory transduction. Cross-sectional profiles of dendritic tips are significantly larger but less numerous in stretched than in relaxed receptors. We propose a model in which stretch compresses distal portions of tips until they are too small to be recognized. The large profiles are the proximal portions of tips that have been expanded by hydrostatic pressure. The very large number of dendritic tips/nonspiking mechanoreceptor may be what endows each neuron with 1) high sensitivity to stretch of the elastic strand and 2) ability to respond to a broader range of tensions than is usual for single sensory cells (the entire range experienced by the stretch receptor).

Animals↗
PubMed1990

Dynamic characteristics of vestibular-driven compensatory fin movements of the dogfish.

Compensatory pectoral fin reflexes were studied in decerebrate dogfish subjected to sinusoidal oscillation (0.01-1.0 Hz). At 0.01 Hz the peak response of the depressor muscle was in phase with head position. At higher frequencies the phase advanced and at 1 Hz approached that of maximum angular velocity. Peak response amplitude was steady from 0.01 to 0.07 Hz but thereafter increased markedly. We suggest that the high frequency response depends upon vertical semicircular canal input.

Animals↗
PubMed1985

Nonspiking local interneuron in the motor pattern generator for the crayfish swimmeret.

We describe a type of nonspiking premotor local interneuron (interneuron IA) in the abdominal nervous system of Pacifasticus leniusculus. All of its branches are restricted to one side of the midline. These interneurons are identifiable and occur as bilateral pairs, one neuron on each side of abdominal ganglia 3, 4, and 5. The membrane potential of interneuron IA oscillated in phase with the swimmeret rhythm, a motor pattern generated in each of these ganglia, because the neuron received postsynaptic potentials in phase with the rhythm. Sustained hyperpolarization of an individual interneuron IA initiated generation of the swimmeret rhythm in all the ganglia of a quiescent nervous system. Sustained depolarization stopped the swimmeret rhythm in all the active ganglia of a nervous system that was generating the rhythm. Currents injected into one interneuron reset the rhythm. Comparisons of the shapes of the IA interneurons in different ganglia showed that they are similar to each other and distinct from other local interneurons in these ganglia. Interneuron IA has a large integrative segment and relatively few branches that are largely restricted to the lateral neuropil, to which all other kinds of swimmeret neurons also project. We conclude that this interneuron occurs only once in each hemiganglion in abdominal segments 3, 4, and 5, and that it is identifiable. Furthermore, this interneuron is an essential component of the circuit in each hemiganglion that generates the swimmeret rhythm. The interneuron was dye coupled to a particular identifiable motor neuron and not to any other neurons. The motor neuron was not dye-coupled to any other local interneurons. The ability of this motor neuron to reset the rhythm is attributed to its being electrically coupled to interneuron IA in its ganglion.

Animals↗
PubMed1984

Projections of cerebellar Purkinje cells in the dogfish, Scyliorhinus.

In the dogfish Scyliorhinus degenerating axons and terminals arising from Purkinje cells and resulting from small superficial lesions made in the cerebellar corpus were found to be predominantly restricted to the ipsilateral cerebellar nucleus; none was observed in the tegmentum. Horseradish peroxidase placed within the cerebellar nucleus was transported retrogradely to the Purkinje cells. It appears that in these fishes, as in mammals, cerebellar output is relayed through cerebellar nuclei.

Animals↗
PubMed1984

The activity of cerebellar neurones of the decerebrate dogfish Scyliorhinus during spontaneous swimming movements.

Patterns of activity of cerebellar neurones in response to cutaneous stimulation and during spontaneous, swimming-like movements were examined, using microelectrodes, in decerebrate dogfish (Scyliorhinus canicula). Continuous swimming movements, lasting for several hours, were obtained in fish in which the medial longitudinal fasciculus (m.l.f.) was lesioned in the rhombencephalon. Purkinje cells (P cells) and some stellate cells (S cells) were observed to discharge rhythmically, in phase with swimming movements. These units were distributed throughout the cerebellum, but with no apparent somatotopic distribution. After curarization, rhythmic motor discharges could still be recorded from ventral roots and phase locked P cell discharges were recorded from the cerebellum. P cells that discharged rhythmically during active swimming movements, did not do so when the body was oscillated passively during quiescent periods. Cutaneous stimulation evoked burst discharges in many P cells at long latency (ca. 100 ms) both before and after curarization and whether or not a rhythmic motor output was being generated. In rhythmically discharging units, a similar response was obtained when cutaneous stimulation was applied during that part of a cycle when the unit was most or least active. It was concluded that cerebellar neurones discharged in phase with the output of the spinal locomotory rhythm generators and independently of peripheral sensory feed-back.

Action Potentials↗
PubMed1983

The activity of cerebellar nuclear neurones in relation to stimuli which evoke a pectoral fin reflex in dogfish.

Extracellular single-unit recordings from the cerebellar nucleus were classified into type I and type II units on the basis of their spontaneous discharges. Type I units discharged at a very regular frequency, giving interspike interval histograms with narrow distributions. Type II units had irregular discharges. Type I units were identified as cerebellar nuclear units by their antidromic responses to stimulation of the contralateral brachium conjunctivum (b.c.) in the mid-brain and by their inhibitory responses to stimulation of the cerebellar cortex. Type II units were not driven antidromically by b.c. stimulation but were inhibited by stimulating the cerebellar cortex. Activity of the nuclear neurones was monitored following subcutaneous electrical stimulation of a fin that elicits a reflex elevation. 67% of units responded, the majority with an increased discharge frequency (excitation, 59%) but some with a decreased discharge frequency ('inhibition', 8%). Latencies of both excitatory and inhibitory responses were greater than 50-400 msec. Most excitatory responses lasted for at least 500 msec; several lasted for more than 10 sec. Inhibitory responses lasted for about 500 msec. With units tested by bilateral fin stimulation, the same qualitative response was obtained whichever fin was stimulated. These results are discussed in relation to the known responses of cerebellar Purkinje cells recorded under similar experimental conditions.

Action Potentials↗
PubMed1982

Comparison of cerebellar Purkinje cell simple spike discharges in adult rats after undernutrition during the suckling period and nutritionally normal rats.

The spontaneous activity of cerebellar Purkinje cells was compared in 100- to 130-day-old rats undernourished during the suckling period (i.e. 0-21 days) and subsequently nutritionally rehabilitated (PU rats), with that in rats of the same strain and of similar age fed normally (age controls), and in normally fed rats of the same strain but approximately one month younger (weight controls). Simple spike activity of single cells was recorded with extracellular microelectrodes in pentothal-anaesthetized animals. The discharge patterns were assessed by on-line computer analysis of the interspike interval distributions with subsequent transformation of the data to enable the results to be evaluated by an analysis of variance. In addition, the distribution of the mean interval, the percentage of intervals less than 30 ms, the percentage of intervals greater than or equal to 150 ms, and the time spent in intervals greater than 150 ms, were compared for the PU rats and pooled controls by a nonparametric statistical test on the untransformed data. None of the results indicated that there were any significant differences between the simple spike activity of Purkinje cells from age- and weight- control rats nor between that in PU rats and the control groups. These results are discussed in relation to the previously reported deficits of granule cells in the cerebella of PU rats.

Action Potentials↗