The effects of the 5-hydroxytryptamine(1A) agonist 8-hydroxy-2-(di-n-propylamino)tetralin on spontaneous activity, cocaine-induced hyperactivity and behavioral sensitization: a microanalysis of locomotor activity.
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The influence of the 5-hydroxytryptamine(1A) agonist 8-hydroxy-2-(di-n-propylamino)tetralin (DPAT) on locomotor hyperactivity induced by the acute and chronic administration of cocaine was assessed. Horizontal activity was measured in the periphery and center of an open field test enclosure equipped with photobeams; vertical activity was also recorded. Peripheral hyperactivity induced by an acute administration of cocaine (10 or 20 mg/kg) was significantly enhanced by 0.2 mg/kg DPAT. In contrast, central and vertical activities were reduced in a dose-related manner by DPAT (0.1 and 0.2 mg/kg); DPAT also suppressed central (0.2 mg/kg) and vertical (0.1 and 0.2 mg/kg) activities when administered alone. Similar observations were made on day 1 of chronic treatment with DPAT (0, 0.1, or 0.2 mg/kg) injected 15 min before an injection of cocaine (0, 10, or 15 mg/kg) administered twice daily for 7 days. By day 7 of repeated DPAT treatment, sensitization of DPAT-evoked peripheral activity developed, which contrasted with tolerance to the central and vertical hypoactivity evoked by DPAT. Sensitization developed to the repeated treatment with 15 mg/kg cocaine but not 10 mg/kg cocaine. Interestingly, enhancements of all activity measures were observed between days 1 and 7 in rats cotreated with DPAT plus either dose of cocaine. This sensitization to DPAT plus cocaine was expressed on challenge with DPAT and cocaine but not with cocaine alone. The present study implies that the stimulation of 5-hydroxytryptamine(1A) receptors is capable of modulating the hyperactivity evoked by cocaine, possibly via modulation of the mesoaccumbens dopamine circuit thought to mediate the behavioral effects of cocaine. (+info)
Targeted disruption of Hoxd9 and Hoxd10 alters locomotor behavior, vertebral identity, and peripheral nervous system development.
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The five most 5' HoxD genes, which are related to the Drosophila Abd-B gene, play an important role in patterning axial and appendicular skeletal elements and the nervous system of developing vertebrate embryos. Three of these genes, Hoxd11, Hoxd12, and Hoxd13, act synergistically to pattern the hindlimb autopod. In this study, we examine the combined effects of two additional 5' HoxD genes, Hoxd9 and Hoxd10. Both of these genes are expressed posteriorly in overlapping domains in the developing neural tube and axial mesoderm as well as in developing limbs. Locomotor behavior in animals carrying a double mutation in these two genes was altered; these alterations included changes in gait, mobility, and adduction. Morphological analysis showed alterations in axial and appendicular skeletal structure, hindlimb peripheral nerve organization and projection, and distal hindlimb musculature. These morphological alterations are likely to provide the substrate for the observed alterations in locomotor behavior. The alterations observed in double-mutant mice are distinct from the phenotypes observed in mice carrying single mutations in either gene, but exhibit most of the features of both individual phenotypes. This suggests that the combined activity of two adjacent Hox genes provides more patterning information than activity of each gene alone. These observations support the idea that adjacent Hox genes with overlapping expression patterns may interact functionally to provide patterning information to the same regions of developing mouse embryos. (+info)
Relationships of the extinct moa-nalos, flightless Hawaiian waterfowl, based on ancient DNA.
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The extinct moa-nalos were very large, flightless waterfowl from the Hawaiian islands. We extracted, amplified and sequenced mitochondrial DNA from fossil moa-nalo bones to determine their systematic relationships and lend insight into their biogeographical history. The closest living relatives of these massive, goose-like birds are the familiar dabbling ducks (tribe Anatini). Moa-nalos, however, are not closely related to any one extant species, but represent an ancient lineage that colonized the Hawaiian islands and evolved flightlessness long before the emergence of the youngest island, Hawaii, from which they are absent. Ancient DNA yields a novel hypothesis for the relationships of these bizarre birds, whereas the evidence of phylogeny in morphological characters was obscured by the evolutionary transformation of a small, volant duck into a giant, terrestrial herbivore. (+info)
Reconstitution of Listeria motility: implications for the mechanism of force transduction.
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Listeria monocytogenes and some other infectious bacteria polymerize their host cell's actin into tails that propel the bacteria through the cytoplasm. Here we show that reconstitution of this behavior in simpler media resolves two aspects of the mechanism of force transduction. First, since dilute reconstitution media have no cytoskeleton, we consider what keeps the tail from being pushed backward rather than the bacterium being propelled forward. The dependence of the partitioning of motion on the friction coefficient of the tail is derived. Consistent with experiments, we find that the resistance of the tail to motion is sensitive to its length. That even small tails are stationary in intact cells is attributed to anchoring to the cytoskeleton. Second, the comparatively low viscosity of some reconstitution media magnifies the effects of diffusion, such that a large gap will develop between the bacterium and its tail if they are unattached. At the viscosities of diluted platelet extracts, steady-state gaps of several bacterium lengths are predicted. Since such gaps are not observed, we conclude that Listeria must be attached to their tails. We consider what purposes such attachments might serve under physiological conditions. The implications for related pathogens and amoeboid locomotion are also discussed. (+info)
Chemo-anemotaxis: a behavioral response to sex pheromone in nonflying insects.
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The cockroach, Periplaneta americana, running on a Y-ring globe, moves downwind if an air current is directed toward the head. However, if the air current carries sex pheromone, then upwind movement is elicited. This orientation behavior is apparently a mechanism to facilitate the orientation of males searching for pheromone-secreting females. (+info)
Paradoxical actions of the serotonin precursor 5-hydroxytryptophan on the activity of identified serotonergic neurons in a simple motor circuit.
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Neurotransmitter synthesis is regulated by a variety of factors, yet the effect of altering transmitter content on the operation of neuronal circuits has been relatively unexplored. We used electrophysiological, electrochemical, and immunohistochemical techniques to investigate the effects of augmenting the serotonin (5-HT) content of identified serotonergic neurons embedded in a simple motor circuit. The dorsal swim interneurons (DSIs) are serotonergic neurons intrinsic to the central pattern generator (CPG) for swimming in the mollusc Tritonia diomedea. As expected, treatment with the serotonin precursor 5-hydroxytryptophan (5-HTP) increased the intensity of serotonin immunolabeling and enhanced the potency of synaptic and modulatory actions elicited by the DSIs. It also greatly enhanced the ability of the DSIs to evoke rhythmic CPG activity. After 5-HTP treatment, microvoltammetric measurements indicated an increase in a putative 5-HT electrochemical signal during swim CPG activation. Paradoxically, the spiking activity of the serotonergic neurons decreased to a single burst at the onset of the rhythmic motor program, whereas the overall duration of the episode remained about the same. 5-HTP treatment gradually reduced the rhythmicity of the CPG output. Thus, more serotonin did not result in a more robust swim motor program, suggesting that serotonin synthesis must be kept within certain limits for the circuit to function correctly and indicating that altering neurotransmitter synthesis can have serious consequences for the output of neural networks. (+info)
Kinematics and modeling of leech crawling: evidence for an oscillatory behavior produced by propagating waves of excitation.
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Many well characterized central pattern generators (CPGs) underlie behaviors (e.g., swimming, flight, heartbeat) that require regular rhythmicity and strict phase relationships. Here, we examine the organization of a CPG for leech crawling, a behavior whose success depends more on its flexibility than on its precise coordination. We examined the organization of this CPG by first characterizing the kinematics of crawling steps in normal and surgically manipulated animals, then by exploring its features in a simple neuronal model. The behavioral observations revealed the following. (1) Intersegmental coordination varied considerably with step duration, whereas the rates of elongation and contraction within individual segments were relatively constant. (2) Steps were generated in the absence of both head and tail brains, implying that midbody ganglia contain a CPG for step production. (3) Removal of sensory feedback did not affect step coordination or timing. (4) Imposed stretch greatly lengthened transitions between elongation and contraction, indicating that sensory pathways feed back onto the CPG. A simple model reproduced essential features of the observed kinematics. This model consisted of an oscillator that initiates propagating segmental waves of activity in excitatory neuronal chains, along with a parallel descending projection; together, these pathways could produce the observed intersegmental lags, coordination between phases, and step duration. We suggest that the proposed model is well suited to be modified on a step-by-step basis and that crawling may differ substantially from other described CPGs, such as that for swimming in segmented animals, where individual segments produce oscillations that are strongly phase-locked to one another. (+info)
Circadian modulation of dopamine receptor responsiveness in Drosophila melanogaster.
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We investigated the circadian function of Drosophila dopamine receptors by using a behaviorally active decapitated preparation that allows for direct application of drugs to the nerve cord. Quinpirole, a D2-like dopamine receptor agonist, induces reflexive locomotion in decapitated flies. We show that the amount of locomotion induced changes as a function of the time of day, with the highest responsiveness to quinpirole during the subjective night. Furthermore, dopamine receptor responsiveness is under circadian control and depends on the normal function of the period gene. The head pacemaker is at least partly dispensable for the circadian modulation of quinpirole-induced locomotion, because changes in agonist responsiveness persist in decapitated flies that are aged for 12 h. This finding suggests a role for the period-dependent molecular oscillators in the body in the modulation of amine receptor responsiveness. (+info)