828 research outputs found
Origin of pulsed emission from the young supernova remnant SN 1987A
To overcome difficulties in understanding the origin of the submillisecond optical pulses from SN 1987A a model similar to that of Kundt and Krotscheck for pulsed synchrotron emission from the Crab was applied. The interaction of the expected ultrarelativistic e(sup + or -) pulsar wind with the pulsar dipole electromagnetic wave reflected from the walls of a pulsar cavity within the SN 1987A nubula can generate pulsed optical emission with efficiency at most eta(sub max) is approximately equal to 10(exp -3). The maximum luminosity of the source is reproduced and other observational constraints can be satisfied for an average wind energy flow is approximately equal to 10(exp 38) erg/(s steradian) and for electron Lorentz factor gamma is approximately equal to 10(exp 5). This model applied to the Crab yields pulsations of much lower luminosity and frequency
Quasiperiodic oscillations in bright galactic-bulge X-ray sources
Quasiperiodic oscillations with frequencies in the range 5-50 Hz have recently been discovered in X-rays from two bright galactic-bulge sources and Sco X-1. These sources are weakly magnetic neutron stars accreting from disks which the plasma is clumped. The interaction of the magnetosphere with clumps in the inner disk causes oscillations in the X-ray flux with many of the properties observed
Does SN 1987A contain a rapidly vibrating neutron star
If the recently reported 0.5 ms-period pulsed optical signal from the direction of Supernova 1987A originated in a young neutron star, its interpretation as a rotational period has difficulties. The surface magnetic field would have to be much lower than expected, and the high rotation rate may rule out preferred nuclear equations of state. It is pointed out here that a remnant radial vibration of a neutron star, excited in the supernova event, may survive for several years with about the observed (gravitationally redshifted) period. Heavy ions at the low-density stellar surface, periodically shocked by the vibration, may efficiently produce narrow pulses of optical cyclotron radiation in a surface field of about a trillion gauss
Liveness-Based Garbage Collection for Lazy Languages
We consider the problem of reducing the memory required to run lazy
first-order functional programs. Our approach is to analyze programs for
liveness of heap-allocated data. The result of the analysis is used to preserve
only live data---a subset of reachable data---during garbage collection. The
result is an increase in the garbage reclaimed and a reduction in the peak
memory requirement of programs. While this technique has already been shown to
yield benefits for eager first-order languages, the lack of a statically
determinable execution order and the presence of closures pose new challenges
for lazy languages. These require changes both in the liveness analysis itself
and in the design of the garbage collector.
To show the effectiveness of our method, we implemented a copying collector
that uses the results of the liveness analysis to preserve live objects, both
evaluated (i.e., in WHNF) and closures. Our experiments confirm that for
programs running with a liveness-based garbage collector, there is a
significant decrease in peak memory requirements. In addition, a sizable
reduction in the number of collections ensures that in spite of using a more
complex garbage collector, the execution times of programs running with
liveness and reachability-based collectors remain comparable
Role of dorsomedial striatum neuronal ensembles in incubation of methamphetamine craving after voluntary abstinence
Abstract
We recently developed a rat model of incubation of methamphetamine craving after choice-based voluntary abstinence. Here, we studied the role of dorsolateral striatum (DLS) and dorsomedial striatum (DMS) in this incubation. We trained rats to self-administer palatable food pellets (6 d, 6 h/d) and methamphetamine (12 d, 6 h/d). We then assessed relapse to methamphetamine seeking under extinction conditions after 1 and 21 abstinence days. Between tests, the rats underwent voluntary abstinence (using a discrete choice procedure between methamphetamine and food; 20 trials/d) for 19 d. We used in situ hybridization to measure the colabeling of the activity marker Fos with Drd1 and Drd2 in DMS and DLS after the tests. Based on the in situ hybridization colabeling results, we tested the causal role of DMS D1 and D2 family receptors, and DMS neuronal ensembles in "incubated" methamphetamine seeking, using selective dopamine receptor antagonists (SCH39166 or raclopride) and the Daun02 chemogenetic inactivation procedure, respectively. Methamphetamine seeking was higher after 21 d of voluntary abstinence than after 1 d (incubation of methamphetamine craving). The incubated response was associated with increased Fos expression in DMS but not in DLS; Fos was colabeled with both Drd1 and Drd2 DMS injections of SCH39166 or raclopride selectively decreased methamphetamine seeking after 21 abstinence days. In Fos-lacZ transgenic rats, selective inactivation of relapse test-activated Fos neurons in DMS on abstinence day 18 decreased incubated methamphetamine seeking on day 21. Results demonstrate a role of DMS dopamine D1 and D2 receptors in the incubation of methamphetamine craving after voluntary abstinence and that DMS neuronal ensembles mediate this incubation.
SIGNIFICANCE STATEMENT:
In human addicts, abstinence is often self-imposed and relapse can be triggered by exposure to drug-associated cues that induce drug craving. We recently developed a rat model of incubation of methamphetamine craving after choice-based voluntary abstinence. Here, we used classical pharmacology, in situ hybridization, immunohistochemistry, and the Daun02 inactivation procedure to demonstrate a critical role of dorsomedial striatum neuronal ensembles in this new form of incubation of drug craving
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Intraflagellar transport delivers tubulin isotypes to sensory cilium middle and distal segments.
Sensory cilia are assembled and maintained by kinesin-2-dependent intraflagellar transport (IFT). We investigated whether two Caenorhabditis elegans α- and β-tubulin isotypes, identified through mutants that lack their cilium distal segments, are delivered to their assembly sites by IFT. Mutations in conserved residues in both tubulins destabilize distal singlet microtubules. One isotype, TBB-4, assembles into microtubules at the tips of the axoneme core and distal segments, where the microtubule tip tracker EB1 is found, and localizes all along the cilium, whereas the other, TBA-5, concentrates in distal singlets. IFT assays, fluorescence recovery after photobleaching analysis and modelling indicate that the continual transport of sub-stoichiometric numbers of these tubulin subunits by the IFT machinery can maintain sensory cilia at their steady-state length
Crab Pulsar Photometry and the Signature of Free Precession
Optical photometry for the pulsar PSR0531+21 has been extended with new
observations that strengthen evidence for a previously observed 60 seconds
periodicity. This period is found to be increasing with time at approximately
the same rate as the rotational period of the pulsar. The observed period and
its time dependence fit a simple free precession model.Comment: 6 pages, 7 figures. Published in A&
Distinct fos-expressing neuronal ensembles in the ventromedial prefrontal cortex mediate food reward and extinction memories
In operant learning, initial reward-associated memories are thought to be distinct from subsequent extinction-associated memories.
Memories formed during operant learning are thought to be stored in “neuronal ensembles.” Thus, we hypothesize that different
neuronal ensembles encode reward- and extinction-associated memories. Here, we examined prefrontal cortex neuronal ensembles
involved in the recall of reward and extinction memories of food self-administration.Wefirst trained rats to lever press for palatable food
pellets for 7 d (1 h/d) and then exposed them to 0, 2, or 7 daily extinction sessions in which lever presses were not reinforced. Twenty-four
hours after the last training or extinction session, we exposed the rats to either a short 15 min extinction test session or left them in their
homecage (a control condition). We found maximal Fos (a neuronal activity marker) immunoreactivity in the ventral medial prefrontal
cortex of rats that previously received 2 extinction sessions, suggesting that neuronal ensembles in this area encode extinction memories.
We then used the Daun02 inactivation procedure to selectively disrupt ventral medial prefrontal cortex neuronal ensembles that were
activated during the 15 min extinction session following 0 (no extinction) or 2 prior extinction sessions to determine the effects of
inactivating the putative food reward and extinction ensembles, respectively, on subsequent nonreinforced food seeking 2 d later.
Inactivation of the food reward ensembles decreased food seeking, whereas inactivation of the extinction ensembles increased food
seeking. Our results indicate that distinct neuronal ensembles encoding operant reward and extinction memories intermingle within the
same cortical area
Long-Term Stability of an Area-Reversible Atom-Interferometer Sagnac Gyroscope
We report on a study of the long-term stability and absolute accuracy of an
atom interferometer gyroscope. This study included the implementation of an
electro-optical technique to reverse the vector area of the interferometer for
reduced systematics and a careful study of systematic phase shifts. Our data
strongly suggests that drifts less than 96 deg/hr are possible after
empirically removing shifts due to measured changes in temperature, laser
intensity, and several other experimental parameters.Comment: 4 pages, 4 figures, submitted to PR
Role of dopamine in dorsal medial prefrontal cortex in yohimbine-induced reinstatement of food seeking in rats
In humans, relapse to maladaptive eating habits during dieting is
often provoked by stress.Weadapted a drug relapse-reinstatement
model to study the role of stress in relapse to food seeking
(Nair et al., Prog. Neurobiol., 2009). In our model, the anxiogenic
drug yohimbine, an alpha-2 adrenoceptor antagonist, that causes
stress-like responses in humans and laboratory animals, reliably
reinstates food seeking.Werecently found that yohimbine-induced
reinstatement of food seeking is attenuated by systemic injections
of SCH23390 (a D1-family receptor antagonist) but not clonidine
(an alpha-2 adrenoceptor agonist). Here, we studied the role of
the medial prefrontal cortex (mPFC) in yohimbine-induced reinstatement.
We trained food-restricted rats to lever-press for 35%
high-fat pellets every other day (9–15 3 h sessions). We then extinguished
the food-reinforced operant responding for 10–14 days by
removing the pellets. Subsequently, we tested the effect of systemic
injections of yohimbine (0, 2 mg/kg) on reinstatement of food
seeking. In Exp. 1we found that yohimbine-induced reinstatement
was associated with strong induction of Fos (a marker of neuronal
activity) in the dorsal mPFC and weaker Fos induction in the ventral
mPFC. In Exp. 2 we found that dorsal but not ventral mPFC
injections of the D1-family receptor antagonist SCH23390 (0.5,
1.0g/side) decreased yohimbine-induced reinstatement of food
seeking. Our data indicate a critical role of dorsal mPFC dopamine in
reinstatement food seeking induced by the pharmacological stressor
yohimbine
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