Abdominal Ganglion Of Crayfish Research Articles

A Lateral Excitatory Network in the Escape Circuit of Crayfish

A phasic stimulus directed to the rear of a crayfish (Procambarus clarkii) creates mechanosensory input to the lateral giant (LG) interneuron, a command neuron for escape. A single LG spike is necessary and sufficient to produce a highly stereotyped tail flip that thrusts the animal away from the source of stimulation. Here we describe a lateral excitatory network among primary afferent axons in the last abdominal ganglion of crayfish that produces nonlinear amplification of the sensory input to the command circuitry for escape. The lateral excitation is mediated by electrical synapses between central terminals of primary mechanosensory afferents. The network enables stimulated afferents to recruit unstimulated afferents that contribute additional input to LG and to mechanosensory interneurons that also converge on LG. When depolarized, the LG neuron increases its own inputs from primary afferents and primary interneurons by facilitating the recruitment of both. Conversely, hyperpolarization of LG reduces the excitability of primary afferents and primary interneurons. The crayfish's decision to escape, previously thought to lie exclusively in the synaptic integrative properties of LG, is now seen to depend on the interactions between LG dendritic postsynaptic potentials and the responses of primary afferent terminals in the lateral excitatory network.

Electrophysiological and theoretical analysis of depolarization-dependent outward currents in the dendritic membrane of an identified nonspiking interneuron in crayfish.

Depolarization-dependent outward currents were analyzed using the single-electrode voltage clamp technique in the dendritic membrane of an identified nonspiking interneuron (LDS interneuron) in situ in the terminal abdominal ganglion of crayfish. When the membrane was depolarized by more than 20 mV from the resting potential (65.0 +/- 5.7 mV), a transient outward current was observed to be followed by a sustained outward current. Pharmacological experiments revealed that these outward currents were composed of 3 distinct components. A sustained component (I(s)) was activated slowly (half rise time > 5 msec) and blocked by 20 mM TEA. A transient component (I(t1)) that was activated and inactivated very rapidly (peak time < 2.5 msec, half decay time < 1.2 msec) was also blocked by 20 mM TEA. Another transient component (I(t2)) was blocked by 100 microM 4AP, activated rapidly (peak time < 10.0 msec) and inactivated slowly (half decay time > 131.8 msec). Two-step pulse experiments have revealed that both sustained and transient components are not inactivated at the resting potential: the half-maximal inactivation was attained at -21.0 mV in I(t1), and -38.0 mV in I(t2). I(s) showed no noticeable inactivation. When the membrane was initially held at the resting potential level and clamped to varying potential levels, the half-maximal activation was attained at -36.0 mV in I(s), -31.0 mV in I(t1) and -40.0 mV in I(t2). The activation and inactivation time constants were both voltage dependent. A mathematical model of the LDS interneuron was constructed based on the present electrophysiological records to simulate the dynamic interaction of outward currents during membrane depolarization. The results suggest that those membrane conductances found in this study underlie the outward rectification of the interneuron membrane as well as depolarization-dependent shaping of the excitatory synaptic potential observed in current-clamp experiments.

The result of evolutionary limb loss on the complement of motor neurons in a crayfish limb nerve revealed by serial homology

Many macruran decapod crustaceans show sexual dimorphism of abdominal appendages adapted for use as secondary reproductive organs. Not only does the Australian crayfish, Cherax destructor, show no external, abdominal dimorphism, but both males and females have lost the pleopods of the first abdominal segment entirely. The first nerves of the abdominal ganglia of crayfish and lobsters carry the axons of the pleopod motor neurons. We used intracellular cobalt infusion into the first nerves of the first and second abdominal ganglia to reveal the motor neuron complement of these ganglia in males and females. The first nerves of the second abdominal ganglia of both males and females have approximately 37 motor neurons associated with them. The homologous nerves in the first abdominal segment, where there are no pleopods, have only 8 or 9 motor neurons associated with them. The evolutionary implications of this difference are discussed.

Neurons in the third abdominal ganglion of the early postnatal crayfish: a quantitative and ultrastructural study

Ultrastructural data on the third abdominal ganglion of the crayfish was heretofore only available for adult individuals. The fine structure of neurons in the adult that are involved in the escape response has been described in detail, but no similar data existed for the postnatal individual. An increase in the number of neurons in the third abdominal ganglion during postnatal stages had been reported, which suggested that several changes in the features of neurons may occur. Here we describe the general anatomy and ultrastructure of the early postnatal third abdominal ganglion, with emphasis on neurons, and we compare their characteristics to those of the adult. Abdominal ganglia of 56 crayfish of 0, 8, 10, 18, 25, 50, 110, and 150 postnatal days were processed under cacodylate buffered aldehyde fixatives, osmicated, embedded in plastic, sectioned, and examined by light and electron microscopy. The anatomy of postnatal ganglia is homologous to the anatomy of the adult ganglia except that the perineurium is not developed in postnatals. The area of neurons within the postnatal ganglion shows no stratification, but neurons are grouped in nuclei according to their size. Neurons constitute a homogeneous population in different stages of maturity, as revealed particularly by the ultrastructure of the nucleolus. Postnatal development is evident in the perineurium, which may provide structural support to the ganglion.

Regional characteristics of the membrane response of an identified crayfish nonspiking interneuron to intracellularly injected current.

1. We investigated the membrane response of the local directionally selective (LDS) interneuron, a nonspiking cell identified in the terminal abdominal ganglion of crayfish, to intracellularly injected current in different regions within the cell by single-electrode, discrete current-clamp experiments. The site of electrode impalement into the cell was visualized in situ together with the cell structure under a dissecting microscope. 2. The LDS interneuron has dendritic branches on both hemiganglia connected by a thick segment crossing the midline. Irrespective of the site of electrode impalement, the interneuron showed outward rectification upon depolarization from the resting potential level. When hyperpolarizing current was injected, a linear relationship was observed between the voltage response of the interneuron and the amount of injected current. Upon large hyperpolarization, however, the interneuron showed inward rectification. 3. The input resistance of the interneuron measured within the linear range of the membrane response was significantly lower in the transverse segment than in lateral dendrites (0.001 < P < 0.01). The time constant of the transient voltage response to step current injection was also significantly shorter in the transverse segment than in the lateral dendrites (0.001 < P < 0.01). 4. Although the regional difference in the input resistance could be accounted for, at least partly, by different geometric conditions of each dendritic branch into which current was injected, the regional difference in the time constant of the membrane response cannot be accounted for by structural differences because the time constant is independent of the membrane area. It is thus suggested that the passive properties of the interneuron membrane that are related to its response time constant show regional variability within the cell.

Specific second messengers activate the caudal photoreceptor of crayfish

The caudal photoreceptor (CPR) found in the last abdominal ganglion of crayfish is a well-known example of a non-retinal photosensitive element. In addition to light sensitivity, this cell has been assigned a command role for a walking behavior. The molecular mechanism of transduction in this cell has not been previously studied. The involvement of an intermediate messenger substance is suggested by its long latency to response, its prolonged afterdischarge, and by the requirement for an amplification process for the efficient transduction of light. We tested the effect of some putative second messengers by pressure injecting them into the CPR and noting the physiological response. Here we report that intracellular injection of inositol 1,4,5-triphosphate (IP 3), calcium, and the guanosine nucleotide GTP mimics the light response, while cAMP, IP 1 and IP 2 have no effect on the firing rate. The key intermediate in transduction in vertebrate photoreceptors, cGMP, was ineffective in this system. This work adds to the growing body of evidence that IP 3 plays a role in invertebrate phototransduction.

Relationships between cell size and nuclear morphology in crayfish neurons

The morphology and ultrastructure of cell nuclei in neurons of the third abdominal ganglion of crayfish were studied from alternating series of ultrathin and semithin sections. The ganglion contains approximately 850 neurons with sizes between 10 and 200 μm. Cell nuclei show a great variability. Their size, the chromatin distribution, the number of nuclear pores, the degree of nucleolar segregation and the size of nucleolus vary in close relationships with the cell size.

Light modulation of postural flexor motoneurones in the tail-fan of the squat lobsterGalathea strigosa (Crustacea, Anomura)

Photosensitivity in the terminal abdominal ganglion (G5) of an anomuran, the squat lobsterGalathea strigosa (Crustacea, Decapoda, Anomura), is described. In contrast to the caudal photoreceptors (CPRs) of long-tailed natantid and macruran decapod crustaceans, the caudal photosensitive elements in G5 inG. strigosa apparently lack the conventional spiking rostral conduction pathways to the thoracic ganglia, and instead make their output connections to a bilateral pair of tonic flexor motoneurones originating within the caudal ganglion itself. These flexor motoneurones modulate the activity of two bilaterally paired uropod coxopodite tonic flexor muscles. This photomodulated motoneurone (PMMN) activity is not abolished by sectioning the abdominal nerve cord anterior to G5. The pattern of photosensitivity, while differing from that shown by other CPRs, resembles instead the pattern attributed to photosensitive interneurones (PSIs) of rostral abdominal ganglia of crayfish and other long-tailed decapod crustaceans.

Functional organization of crayfish abdominal ganglia: II. Sensory afferents and extensor motor neurons

Abdominal ganglia of crayfish contain identifiable neuropils, commissures, longitudinal tracts, and vertical tracts. To determine the functional significance of this ganglionic framework, we backfilled the following types of neurons with cobalt chloride: sensory hair afferents, slow and fast extensor motor neurons, the segmental stretch receptor neurons, and their inhibitory accessory cells. After the cobalt ions were precipitated and intensified, we studied the central projections of the filled neurons within the ganglionic structures. All of the axons of these neurons exit or enter each of the first five abdominal ganglia through the second pair of nerves. Our description of the central projections of the hair afferents is the first in the literature. These afferents innervate the large ventral horseshoe neuropil (HN) in the core of each ganglion. This neuropil is homologous to the insect ventral association centers, which also process sensory information. Furthermore, we discovered that some of the crayfish afferents innervate glomeruli within the HN. The slow and fast extensor motor neurons, the stretch receptor neurons, and the accessory cells branch mostly in the dorsal part of the ganglion. We reinterpret previous identifications of the extensor neurons that were based largely on soma position. Together with our previous descriptions of the flexor motor neurons, these results allow us to relate both rapid tail-flips and slower postural movements to the structure of the segmental ganglia.

Opposing parallel connections through crayfish local nonspiking interneurons.

Unilateral local nonspiking interneurons in the terminal (sixth) abdominal ganglion of crayfish (Procambarus clarkii Girard) can be classified into two major groups of PL and AL types by their gross morphology and somatic position. These premotor interneurons are the neural components of uropod motor pattern formation. They receive sensory input from the exopodite of the contralateral side as well as that of the ipsilateral side. Small fluctuations in their membrane potentials cause sustained change in activity of the motoneurons innervating the uropod muscles. PL interneurons, which make noninverting connections to an identified closer, the reductor motoneuron No. 1, mainly receive excitatory input from the afferents of the contralateral exopodite, whereas inverting PL interneurons receive inhibitory input. AL interneurons receive distinctly different input from the afferents. Noninverting AL interneurons mainly receive inhibitory input, whereas inverting AL interneurons receive excitatory input. The rate of discharge of the reductor motoneurons is increased by sensory stimulation. The PL interneurons form either excitatory or disinhibitory pathways, which are relevant in function to the observed increase of the motoneuron. Conversely, the AL interneurons form either inhibitory or disfacilitatory pathways. Thus, the PL and the AL interneurons are fractionated in function and distinguishable in terms of their physiology by their input and output correlations. Functional meaning of the presence of these two types of unilateral local nonspiking interneurons of opposing connections in the uropod motor control system is discussed.

Elements Other Than Neurons or Glia of Nervous Abdominal Ganglia of Crayfish (Decapoda, Astacidea)

[Les elements cellulaires des ganglions abdominaux de l'ecrevisse, autres que les neurones et la glie, sont etudies en microscopie electronique. Le tissu nerveux est recouvert par deux couches cellulaires: le neurilemme, ou des fibroblastes sont observes parmi le reseau de collagene, et le perineurium, un tissu spongieux qui forme les sinus perineuriaux. Dans la zone nerveuse interne du ganglion, on observe des cellules a cytoplasme dense, inserees dans le reseau de materiel dense extracellulaire. Ces elements derivent probablement d'hemocytes migrateurs et sont consideres comme des macrophages nerveux., Les elements cellulaires des ganglions abdominaux de l'ecrevisse, autres que les neurones et la glie, sont etudies en microscopie electronique. Le tissu nerveux est recouvert par deux couches cellulaires: le neurilemme, ou des fibroblastes sont observes parmi le reseau de collagene, et le perineurium, un tissu spongieux qui forme les sinus perineuriaux. Dans la zone nerveuse interne du ganglion, on observe des cellules a cytoplasme dense, inserees dans le reseau de materiel dense extracellulaire. Ces elements derivent probablement d'hemocytes migrateurs et sont consideres comme des macrophages nerveux.]

Characterization of the Na +, K +-ATPase in a microsomal preparation from the abdominal ganglia of crayfish. Effect of neurodepressing hormone (NDH)

1. 1. The Na +, K +-ATPase activity of crayfish abdominal ganglia was characterized and the effect of neurodepressing hormone (NDH) on it was studied. 2. 2. At 20°C, 50% of the ATPase activity in the microsomal fraction was ouabain-sensitive. The enzyme activity decreased by pre-incubation at higher temperatures. 3. 3. The optimum monovalent cation concentrations were 40 mM NaCl and 12 mM KCl. The hydrolysis of ATP showed a strict dependence on Mg 2+. 4. 4. NDH increased the Na +, K +-ATPase activity and the enhancement was concentration- and time-dependent. 5. 5. Treatment of the membranes with sodium-dodecylsulphate (SDS) resulted in a 4-fold increase of ATPase specific activity. 75% of activity is ouabain sensitive. The SDS-treated enzyme was not responsive to NDH. 6. 6. NDH effect on the spontaneous firing rate of motoneurons in isolated abdominal ganglia shows a temperature-dependence similar to that of the effect on ATPase.

Glial Cells in Abdominal Ganglia of Crayfish

AbstractGlial cells of abdominal ganglia of crayfish have been studied by transmission electron microscopy. Four cell types can be defined: (1) perivascular glial cells, close to the vascular spaces; (2) perineuronal glial cells, the processes of which ensheathe neuron perikarya; (3) adaxonal glial cells ensheathing axons; (4) neuropilar glial cells, associated with synapsing terminals in the neuropile.Neuropilar glia, adaxonal glia and the system formed by perineuronal and perivascular glia separate different functional zones of the neurons from the hemolymph or the electron dense extracellular matrix. These glial arrangements could play a similar role in hemato‐neuronal transport. Gap‐like junctions between glia and neuron cell bodies are frequent and could be involved in direct triggering of glial activities related to neurons.

An analysis of the action of salts upon abdominal ganglia of crayfish

An analysis of the action of salts upon abdominal ganglia of crayfish