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At least 163 records · Page 9Linked to original sources
PubMed2003

Dopamine in crayfish and other crustaceans: distribution in the central nervous system and physiological functions.

Dopamine is widely distributed in the crustacean nervous system and has a diverse array of physiological effects. Immunocytochemical studies of several species have shown that dopamine- and/or tyrosine hydroxylase-containing cells occur in all ganglia of the central nervous system and that processes from some of these cells link ganglia of the ventral nerve cord. This study describes the distribution of tyrosine hydroxylase-containing cells in the central nervous system of a crayfish (Orconectes rusticus) and compares this information to available data from other species. The distribution of tyrosine hydroxylase (an enzyme in the synthetic pathway between tyrosine and dopamine) in O. rusticus is similar to that reported for marine species. However, differences were observed in the number of neurons in some ganglia and in the axonal projections of the L cell, which were more extensive in O. rusticus than in other species studied thus far. We also review the physiological effects of dopamine in crayfish and other crustaceans, focusing on the amine's actions in the endocrine, cardiovascular, and nervous systems, and on behavior when injected into freely-moving animals.

Animals↗
PubMed2003

The effects of serotonin and ecdysone on primary sensory neurons in crayfish.

The overall behaviors and motivational states observed during social interactions and throughout the molting cycle of crayfish have been linked to the effects of humoral neuromodulators. Both serotonin (5-HT) and a molt-related hormone, 20-hydroxyecdysone (20-HE), are known to be present in the hemolymph of crustaceans. To determine if they alter the activity of a primary sensory neuron that monitors proprioceptive information, we examined their effects on the activity of the slow-adapting muscle receptor organ (MRO) of the crayfish abdomen, a model sensory system that has been extensively studied. 5-HT within the range of 100 nM to 1 microM, increases the firing frequency of the neuron during sustained stimulation. In experiments in which 20-HE was added alone, an increase in the firing frequency also occurred, although to a lesser degree than that for 5-HT at the same concentrations. When the MRO is first exposed to 20-HE, followed sequentially by 5-HT, the activity increases to about the same degree as in the reverse order of exposure. This outcome indicates that mixtures of these endogenous neuromodulators, at various levels, are more important in alternating behavior than the absolute level of any one of them introduced alone.

Animals↗
PubMed2003

Neural basis of a simple behavior: abdominal positioning in crayfish.

Crustaceans have been used extensively as models for studying the nervous system. Members of the Order Decapoda, particularly the larger species such as lobsters and crayfish, have large segmented abdomens that are positioned by tonic flexor and extensor muscles. Importantly, the innervation of these tonic muscles is known in some detail. Each abdominal segment in crayfish is innervated bilaterally by three sets of nerves. The anterior pair of nerves in each ganglion controls the swimmeret appendages and sensory supply. The middle pair of nerves innervates the tonic extensor muscles and the regional sensory supply. The superficial branch of the most posterior pair of nerves in each ganglion is exclusively motor and supplies the tonic flexor muscles of that segment. The extension and flexion motor nerves contain six motor neurons, each of which is different in axonal diameter and thus produces impulses of different amplitude. Motor programs controlling each muscle can be characterized by the identifiable motor neurons that are activated. Early work in this field discovered that specific central interneurons control the abdominal positioning motor neurons. These interneurons were first referred to as "command neurons" and later as "command elements." Stimulation of an appropriate command element causes a complex, widespread output involving dozens of motor neurons. The output can be patterned even though the stimulus to the command element is of constant interval. The command elements are identifiable cells. When a stimulus is repeated in a command element, from either the same individual or from different individuals, the output is substantially the same. This outcome depends upon several factors. First, the command elements are not only identifiable, but they make many synapses with other neurons, and the synapses are substantially invariant. There are separate flexion-producing and extension-producing command elements. Abdominal flexion-producing command elements excite other flexion elements and inhibit extensor command elements. The extension producing elements do the opposite. These interactions insure that interneurons of a particular class (flexion- or extension-producing) synaptically recruit perhaps twenty others of similar output, and that command elements promoting the opposing movements are inhibited. This strong reciprocity and the recruitment of similar command elements give a powerful motor program that appears to mimic behavior.

Abdomen↗
PubMed2003

Amine neurochemistry and aggression in crayfish.

A primary goal of our research is to explore proximate mechanisms important in recruiting adaptive social behaviors. For instance, if one of three different behaviors may be expressed in a particular set of circumstances, how do neurochemical mechanisms bias behavior towards the expression of one act in lieu of the other possibilities? In this article, we review recent results suggesting that serotonin may play such a role in the control of aggression in crayfish. First, we summarize techniques that have been optimized for sensitive characterization of neurochemical profiles in crayfish. Then, borrowing concepts from behavioral ecology, we review a framework for quantitative investigation, which regards behavior as a set of individual decisions, each with a particular probability for occurrence, a motivational context, and controlled by its own distinct neurochemical mechanisms.

Aggression↗
PubMed2003

The neural basis of dominance hierarchy formation in crayfish.

Fifty years of study of the nervous system and behavior of crayfish have revealed neural circuits for movements that are similar to those seen during formation of a dominance hierarchy. Given this background, it is of interest to ask what is understood about the neural substrates of dominance hierarchy formation. Here we will consider the social behavior that crayfish display in the wild and in the laboratory, and its relationship to movements released by activation of specific neural circuits. We will consider how these movements might be knit together to produce the behavior patterns that are characteristic of dominant and subordinate animals.

Agonistic Behavior↗
PubMed1993

Cellular organization and growth-related plasticity of the crayfish olfactory midbrain.

Little knowledge is available concerning the detailed anatomy of the crusctacean central olfactory pathway. We are using radiolabeling, Golgi and biocytin/neurobiotin tracer methodologies, at the correlated light and electron microscopical levels, to study the olfactory midbrain of the freshwater crayfish. We have found that primary afferent fibers from the antennular olfactory receptor cells branch extensively throughout the length of the glomerular columns within the olfactory lobes in the midbrain. Globuli cells of the lateral cell clusters ramify as dendritic arborizations within both the olfactory and accessory lobes; their axons project out the olfactory-globular tracts to the lateral protocerebrum, often branching to both sides. Developmental plasticity involving the connections made by afferent fibers within the olfactory lobes may permit detailed examination of organizational changes within the midbrain as the animal grows and adds new afferent input from the periphery.

Afferent Pathways↗
PubMed1995

Gap junctions revealed by freeze-fracture electron microscopy.

Gap junctions provide the basis for the formation of elaborate networks of communication between cells in animal tissues. Electron microscopic examination of thin sections of plastic embedded gap junctions has provided valuable information on the anatomy and function of these remarkable structures. Freeze-fracture electron microscopy, however, has made available unique vistas of gap junction-bearing intramembrane surface--surface previously inaccessible to the researcher's eyes. Data on population density, distribution, size, geometry of intramembrane particle packing, and structural responses of gap junction components to experimental manipulation are simply and easily obtained with freeze fracture. Recent developments of sophisticated protocols of immunocytochemistry as applied to freeze-fracture replicas further serve to reinforce the notion that freeze-fracture is a powerful tool for study of gap junctions. Molecular techniques of gap junction gene transfection promise to add a truly unique dimension to investigations of the broad spectrum of functional roles of gap junctions.

Animals↗
PubMed2002

Phenotype plasticity in postural muscles of the crayfish Orconectes limosus Raf.: correlation of myofibrillar ATPase-based fiber typing with electrophysiological fiber properties and the effect of chronic nerve stimulation.

The characteristics of the medial and lateral superficial extensor muscles (sem and sel) in the crayfish Orconectes limosus abdomen and their developmental and activity-dependent plasticity were studied. It was shown that both muscles are innervated by at least five excitatory and one inhibitory motor neuron in a nonuniform pattern. The muscles are composed of at least three different mATPase histochemistry-based fiber types that are all different from a fourth type in the uniform deep extensor muscles. sem and sel are composed of different ratios of these fiber types but do not show a constant fiber type pattern between segments and even between hemisegments. The three histochemically defined superficial extensor-fiber types have characteristic electrophysiological properties. The fiber types were shown to develop successively during the first postembryonic stages of development without a change in the number of muscle fibers. Based on histochemical ATPase staining after 21 days of chronic stimulation by means of an implantable, double-hook electrode, we show preliminary evidence that the fiber composition in the sem can switch from the presumably fast fiber type III to an intermediate type II. Repeated axotomy up to 53 days had no effect on the fiber type composition of the muscles.

Adenosine Triphosphatases↗
PubMed2001

Crayfish freshwater adaptation starts in eggs: ontogeny of osmoregulation in embryos of Astacus leptodactylus.

Osmoregulation was studied throughout the embryonic development of Astacus leptodactylus. Egg-carrying females were held in freshwater (FW) and in three dilute seawater media (200, 400, 600 mosm kg(-1), 6.8, 13.6, 20.4 per thousand salinity). In FW, changes in peri-embryonic fluid (PEF) and (when available) embryonic hemolymph osmolality were followed from newly-laid eggs to hatching (for an embryonic eye index, EI, of 430-450 microm) and in first-stage juveniles. The PEF and/or hemolymph osmolality remained stable at about 360-380 mosm kg(-1) from early to late (EI 410 microm) embryos; it decreased prior to hatching (EI 420 microm) and in newly-hatched juveniles, down to 290 mosm kg(-1). Artificial opening and removal of the egg membranes, followed by direct exposure to FW, demonstrated that the ability to hyper-osmoregulate, and consequently to survive, in FW appears in embryos with EI > or = 410 microm, i.e., only a few hours or days before hatching. Following a transfer to the dilute seawater media, the PEF/hemolymph osmolality increased slowly over 18-20 days and became isosmotic with the external media at 13.6 and 20.4 per thousand. The embryos died at EI 380-395 microm in these media, and only at 6.8 per thousand was the development completed until successful hatch. These results demonstrate that (1) the embryos become able to osmoregulate in FW shortly before hatching, (2) the embryos are osmo-protected in the eggs during their development, (3) embryonic development and hatching are possible up to a salinity of 7 per thousand. These results are discussed in relation to freshwater adaptation of crayfish.

Adaptation, Physiological↗
PubMed2001

Alterations in habituation of the tail flip response in epigean and troglobitic crayfish.

We demonstrate that the probability of the crayfish, P. clarkii, to tail flip in response to a touch on the dorsal tail fan is dependent on both the size and the behavioral state of the animal. Alterations in the animal's internal physical state, such as when the animal autotomizes its chelipeds, will cause larger-sized animals to tail flip; if they were not autotomized, then no tail flip response would occur. Altering the external environment by removal of water causes small crayfish, which normally habituate slowly, to rapidly habituate. Observation of large adult crayfish in a species, O. australis packardi, one that evolved to live in total cave darkness, revealed that they are more likely to tail flip than are the sighted, adult P. clarkii. Results indicate that the behavioral state of the crayfish can result in rapid and long-term alterations in the tail flip response and in habituation rates to repetitive stimuli. This ability to show plasticity in gain setting may be regulated by neuromodulators and can occur in large adults of the sighted crayfish. Differences between the two species indicate that size may not be the sole contributing factor to account for tail flip behaviors. J. Exp. Zool. 290:163-176, 2001.

Animals↗
PubMed2001

Is the unique negatively charged polypeptide of crayfish yolk HDL a component of crustacean vitellin?

The yolk protein of Cherax quadricarinatus contains six major high-density lipoprotein (HDL) subunits with the approximate molecular masses of 177, 155, 106, 95, 86, and 75 kDa, of which only the 106-kDa polypeptide is negatively charged. On the basis of their molecular weights, time of appearance and disappearance, their floating density and susceptibility to enzyme degradation (by a serine proteinase), these six HDL polypeptides were classified into two subgroups. One group comprises the higher-molecular-weight compounds above 106 kDa, and the other includes the lower-molecular-weight compounds up to 95 kDa. Other than being different from the lower-molecular-weight polypeptides, the negatively charged 106-kDa polypeptide was significantly different from members of its higher-molecular-weight group belonging to a different, less abundant, yolk protein as shown by HPLC separation. Immunological studies and peptide mapping in which the 106-kDa polypeptide did not show similarity to any of the other HDL components confirmed these differences. Moreover, the amino acid composition of the 106-kDa polypeptide was different from that of known vitellin from other crustacean species. This unique negatively charged polypeptide presents an enigma as it is known to be a secondary vitellogenic-related HDL polypeptide, immunolocalized in yolk globules; however, it is different to all the other HDL polypeptides, thus presenting the question whether it is indeed a component of "classical" crustacean vitellin.

Animals↗
PubMed2002

Effects of some steroids and other compounds on ovarian growth of the red swamp crayfish, Procambarus clarkii, during early vitellogenesis.

The effects of spiperone, a dopaminergic receptor blocker, the terpenoid JHIII, and the steroids 17alpha-hydroxyprogesterone and 17beta-estradiol (10(-7) mol/crayfish) were assayed in vivo on females of the red swamp crayfish, Procambarus clarkii, during early vitellogenesis. All these compounds were injected twice a week for 3 weeks. The rate of molting in response to these compounds was also determined. At the end of the experiment the ovaries were dissected out, in order to determine the gonadosomatic indexes and oocyte diameters. Spiperone, 17alpha-hydroxyprogesterone, and 17beta-estradiol produced a significant increase in the gonadosomatic index, while only the first two compounds were able to significantly increase the oocyte diameter; therefore, the effect of 17beta-estradiol the on gonadosomatic index could be merely due to increased water uptake by the ovary. Spiperone could be causing a decrease in secretion of the gonad and/or mandibular inhibiting hormones from the eyestalks, and 17alpha-hydroxyprogesterone could be having a direct stimulatory effect on vitellogenin production. Concerning molting, of the compound tested, only JHIII had a significant (P < 0.05) stimulatory effect, producing a 100% molting rate versus 66.7% among the controls.

17-alpha-Hydroxyprogesterone↗