A far-ultraviolet-driven photoevaporation flow observed in a protoplanetary disk

Most low-mass stars form in stellar clusters that also contain massive stars, which are sources of far-ultraviolet (FUV) radiation. Theoretical models predict that this FUV radiation produces photodissociation regions (PDRs) on the surfaces of protoplanetary disks around low-mass stars, which affects planet formation within the disks. We report James Webb Space Telescope and Atacama Large Millimeter Array observations of a FUV-irradiated protoplanetary disk in the Orion Nebula. Emission lines are detected from the PDR; modeling their kinematics and excitation allowed us to constrain the physical conditions within the gas. We quantified the mass-loss rate induced by the FUV irradiation and found that it is sufficient to remove gas from the disk in less than a million years. This is rapid enough to affect giant planet formation in the disk.

A Search for Heterocycles in GOTHAM Observations of TMC-1

We have conducted an extensive search for nitrogen-, oxygen-, and sulfur-bearing heterocycles toward Taurus Molecular Cloud 1 (TMC-1) using the deep, broadband centimeter-wavelength spectral line survey of the region from the GOTHAM large project on the Green Bank Telescope. Despite their ubiquity in terrestrial chemistry, and the confirmed presence of a number of cyclic and polycyclic hydrocarbon species in the source, we find no evidence for the presence of any heterocyclic species. Here, we report the derived upper limits on the column densities of these molecules obtained by Markov Chain Monte Carlo (MCMC) analysis and compare this approach to traditional single-line upper limit measurements. We further hypothesize why these molecules are absent in our data, how they might form in interstellar space, and the nature of observations that would be needed to secure their detection.

Detection of two interstellar polycyclic aromatic hydrocarbons via spectral matched filtering

Unidentified infrared emission bands are ubiquitous in many astronomical sources. These bands are widely, if not unanimously, attributed to collective emissions from polycyclic aromatic hydrocarbon (PAH) molecules, yet no single species of this class has been identified in space. Using spectral matched filtering of radio data from the Green Bank Telescope, we detected two nitrile-group-functionalized PAHs, 1- and 2-cyanonaphthalene, in the interstellar medium. Both bicyclic ring molecules were observed in the TMC-1 molecular cloud. In this paper, we discuss potential in situ gas-phase PAH formation pathways from smaller organic precursor molecules.

Kinetic Monte Carlo simulations of water ice porosity: extrapolations of deposition parameters from the laboratory to interstellar space

Using an off-lattice kinetic Monte Carlo model we reproduce experimental laboratory trends in the density of amorphous solid water (ASW) for varied deposition angle, rate and surface temperature. Extrapolation of the model to conditions appropriate to protoplanetary disks and interstellar dark clouds indicate that these ices may be less porous than laboratory ices.

Analysis of menisci formed on cones for single field of view parasite egg microscopy

Parasite ova caused to accumulate in a single microscopic field simplifies monitoring soil-transmitted helminthiasis by optical microscopy. Here we demonstrate new egg-accumulating geometries based on annular menisci formed on the surface of a wetted cone. Fluidic features extracted from profile images of the system provided mathematical representations of the meniscus gradient that were compared quantitatively to numerical solutions of an axisymmetric Young-Laplace equation. Our results show that the governing dynamics of these systems is dominated by the surface tension of the fluid. These image analysis and mathematical tools provide simple quantitative methods for system analysis and optimization.

In vivo recordings of spontaneous and odor-modulated dynamics in the Limax olfactory lobe

The major central site of olfactory information processing in the terrestrial slug Limax maximus is the procerebral lobe of the cerebral ganglion, which exhibits oscillatory dynamics of its local field potential and propagates activity waves from its apex to its base, as determined by multisite optical and electrical measurements in vitro. The learning-dependent uptake of Lucifer yellow into procerebral neurons suggests that the procerebral lobe may form learned representations of odors. To determine the role of the procerebral lobe in odor processing and odor learning, we developed procedures to implant fine wire electrodes in the lobe, which allowed recordings of local field potential in freely behaving slugs. The procerebral lobe displays oscillatory dynamics of its local field potential in vivo; however the amplitude and frequency of the local field potential are much more variable in vivo than in vitro. Odor presentation leads to increased frequency and amplitude of the local field potential signal. Several lines of evidence indicate that the variations in the local field potential signal recorded in vivo are not due to movement artifacts or activity in adjacent muscles. Multiple amine, gaseous, and peptide neuromodulators known to be present in the procerebral lobe provide pathways by which activity or coupling of bursting neurons in the procerebral lobe could be altered, resulting in the observed amplitude and frequency modulation of the local field potential.

Nitric oxide and carbon monoxide modulate oscillations of olfactory interneurons in a terrestrial mollusk

Spontaneous or odor-induced oscillations in local field potential are a general feature of olfactory processing centers in a large number of vertebrate and invertebrate species. The ubiquity of such oscillations in the olfactory bulb of vertebrates and analogous structures in arthropods and mollusks suggests that oscillations are fundamental to the computations performed during processing of odor stimuli. Diffusible intercellular messengers such as nitric oxide (NO) and carbon monoxide (CO) also are associated with central olfactory structures in a wide array of species. We use the procerebral (PC) lobe of the terrestrial mollusk Limax maximus to demonstrate a role for NO and CO in the oscillatory dynamics of the PC lobe: synthesizing enzymes for NO and CO are associated with the PC lobes of Limax, application of NO to the Limax PC lobe increases the local field potential oscillation frequency, whereas block of NO synthesis slows or stops the oscillation, the bursting cells of the PC lobe that drive the field potential oscillation are driven to higher burst frequency by application of NO, the nonbursting cells of the PC lobe receive trains of inhibitory postsynaptic potentials, presumably from bursting cells, due to application of NO, and application of CO to the PC lobe by photolysis of caged CO results in an increase in oscillation frequency proportional to CO dosage.

The ontogeny of GABA- and glutamate-like immunoreactivity in the embryonic Australian freshwater crayfish, Cherax destructor

The distribution and ontogeny of GABA- and glutamate-like immunoreactivity in embryos of the Australian freshwater crayfish Cherax destructor were investigated over the period from 30% development until hatching. GABA-like immunoreactive cells and fibres appeared first in the brain at 40-45% development. By 70% development, GABA-like immunoreactive cells were present in almost all ganglia, and GABA-like immunoreactive fibres were distributed extensively throughout the neuropil, commissures and connectives of the central nervous system, and were also found in peripheral nerve roots supplying the appendages and the abdominal musculature. In contrast, glutamate-like immunoreactivity did not appear in the central nervous system until 60-65% development. By the time of hatching, the distribution of glutamate-like immunoreactivity was restricted to discrete regions of neuropil and fibre staining in the thoracic and abdominal nerve cord, the abdominal musculature and the appendages. The precocious establishment of the extensive distribution of GABA-like immunoreactive neurons in the developing crayfish embryo is consistent with the possibility that these neurons play a trophic role in controlling or modulating the development of the nervous system.

Supraspinal influence on the development of motor behavior in the fetal lamb

To examine the involvement of supraspinal inputs in the maturation of motor activity patterns in the developing fetal lamb, we recorded spontaneous electromyographic activity from spinally innervated muscles at approximately 45, 65, and 95 days gestation (G45, G65, and G95; term = 147 days). At G45, fetal activity occurred in synchronized activity-inactivity cycles of approximately 2 min duration, with the activity phase lasting 22.2 +/- 4.8 s and the inactivity phase lasting 95.4 +/- 13.3 s (mean +/- standard error of the mean, n = 5). At G65 and G95, the organization of activity was clearly different from that at G45 in that it was no longer cyclic, nor was the discharge of different muscles synchronized. By contrast, after spinal cord transection at G62, synchronised cyclic activity occurred in muscles innervated by segmental levels below the transection, both at G65 and G95. At G65 the duration of the activity phase of the cycle was 53.5 +/- 6.0 s, while the inactivity phase lasted 171.6 +/- 22.1 s; these durations did not alter between G65 and G95. Since spinal cord transection leads to the motor behavior of the G65 fetus reverting to the cyclic pattern characteristic of the G45 fetus, we conclude that supraspinal inputs begin to modulate the output of the spinal pattern generators at some stage between G45 and G65. The observation that spinally transected fetuses generate identical behavior at G65 and G95, both in terms of its cyclic character and the duration of cycles, suggests that spinal circuits undergo little autonomous development over this period; that is, the altered behavior observed in the developing intact fetus reflects the influence of supraspinal inputs on the motor circuits of the spinal cord.

Development of patterns of activity in diaphragm of fetal lamb early in gestation

To examine the development of respiratory motor activity early in mammalian development and its relationship to nonrespiratory activity, we recorded spontaneous electromyogram activity from chronically instrumented fetal lambs over the period from 45 to 65 days' gestation (G45 to G65, term = G147). Two distinct forms of motor behavior were observed at G45 in recordings made from the costal diaphragm and longissimus dorsi muscles. The predominant behavior consisted of cycles of sustained, coincident activity in the two muscles alternating with periods of inactivity. The incidence of this type of activity declined between G45 and G65 and the cyclic nature of the discharges disappeared in most animals. The second form of motor behavior at G45 consisted of episodes of repetitive bursting activity lasting up to 20 min that were confined to the diaphragm. These bursts had a duration of 97.5 +/- 8.3 ms (mean +/- S.E.M.) and frequently occurred as doublets in which two bursts were separated by an intervening period of 100-200 ms. The mean duration of these bursts declined to 69.7 +/- 7.7 ms at G65, doublets became rare, and bursts evolved a stereotyped form by G65 that was characterized by an abrupt onset and rapid decline in discharge intensity. Repetitive bursts of this form evolve into the mature respiratory motor pattern over the second half of gestation. At G45, episodes of repetitive bursting were almost always linked with episodes of sustained discharge, while at G65 these two forms of behavior were always segregated. We conclude that the neurons responsible for generating the respiratory rhythm in the lamb are assembled into a functional rhythm generator and make appropriate connections to motor output pathways as early as G45. The generation of the respiratory rhythm at G45 appears to be triggered by episodes of widespread motor activity that occur in both respiratory and nonrespiratory muscles.

Oscillations and gaseous oxides in invertebrate olfaction

Olfactory systems combine an extraordinary molecular sensitivity with robust synaptic plasticity. Central neuronal circuits that perform pattern recognition in olfaction typically discriminate between hundreds of molecular species and form associations between odor onsets and behavioral contingencies that can last a lifetime. Two design features in the olfactory system of the terrestrial mollusk Limax maximus may be common elements of olfactory systems that display the twin features of broad molecular sensitivity and rapid odor learning: spatially coherent oscillations in the second-order circuitry that receives sensory input; and involvement of the interneuronal messengers nitric oxide (NO) and carbon monoxide (CO) in sensory responses and circuit dynamics of the oscillating olfactory network. The principal odor processing center in Limax, the procerebrum (PC) of the cerebral ganglion, contains on the order of 10(5) local interneurons and receives both direct and processed input from olfactory receptors. Field potential recordings in the PC show an oscillation at approximately 0.7 Hz that is altered by odor input. Optical recordings of voltage changes in local regions of the PC show waves of depolarization that originate at the distal pole and propagate to the base of the PC. Weak odor stimulation transiently switches PC activity from a propagating mode to a spatially uniform mode. The field potential oscillation in the PC lobe depends on intercellular communication via NO, based on opposing effects of reagents that decrease or increase NO levels in the PC. Inhibition of NO synthase slows the field potential oscillation, while application of exogenous NO increases the oscillation frequency. A role for CO in PC dynamics is suggested by experiments in which CO liberation increases the PC oscillation frequency. These design features of the Limax PC lobe odor processing circuitry may relate to synaptic plasticity that subserves both connection of new receptors throughout the life of the slug and its highly developed odor learning ability.

Origin of tonic electrical activity patterns in the diaphragm of the fetal lamb

The respiratory pattern generator in fetal and postnatal life activates the phrenic nucleus and diaphragm muscle with phasic bursts of activity. In the fetus, diaphragmatic activity is also characterized by tonic activity patterns of unknown origin. We have examined whether such activity is diaphragmatic, or radiated from nearby ribcage muscles, by placing two sets of electrodes side-by-side in the costal portion of the diaphragm in five fetuses. The rationale for this approach is that if tonic activity, radiates to the diaphragm it should be recorded by both sets of electrodes and there should be no delay between the action potentials from each set of electrodes. Of 24 single tonic units identified, 15 were recorded from only one of the two sets of electrodes in the diaphragm. In the 9 tonic units recorded from both sets of electrodes, there was a time delay between the appearance of the action potentials in the two recordings (mean +/- S.E.M. 1.6 +/- 0.2 ms). This is the expected conduction delay along the muscle fibres separating the two electrodes. Since tonic diaphragmatic activity persisted in fetuses with the spinal cord transected rostral or caudal to the phrenic nucleus, we conclude that the spinal cord alone is sufficient to produce the tonic activity recorded from the fetal diaphragm but that the brain may also generate such activity.

Differential recruitment of inspiratory muscles in response to chemical drive

Changes in the intensity of EMG activity in the costal diaphragm, crural diaphragm and external intercostal muscle during inspiration were assessed in intact, awake lambs following abrupt transitions in the composition of the inspired gases from air to either a hypoxic/hypoxic mixture (10% O2, 90% N2), a hyperoxic/hypercapnic mixture (40% O2, 6% CO2, 54% N2) or a hypoxic/hypercapnic mixture (10% O2, 6% CO2, 84% N2). A regression method was used to compare the dynamic responses of the three muscles over the 10-min period following each transition. The relationship between the dynamic response functions of the costal and crural diaphragm was the same in each of the three experimental conditions, indicating that these separate components of the diaphragm comprise a single functional unit during breathing. The relationship between the dynamic response functions of the external intercostal muscle and the costal diaphragm varied according to the composition of the inspired gas mixture. This result suggests that the central and peripheral chemoreceptors exert differential effects on the activation of the diaphragm and the external intercostal muscles during breathing, consistent with the hypothesis that sensory information from these receptors is processed, at least in part, in parallel pathways which project separately to the phrenic and external intercostal motoneurons.

Precursor of respiratory pattern in the early gestation mammalian fetus

Recordings of respiratory muscle activity in fetal lambs from early in gestation provide insight into the organization of the central pattern generator for respiration in mammals. Evidence presented here is consistent with the recent hypothesis that production of the respiratory pattern involves two separate neural modules: one, the 'rhythm' module, which specifies the respiratory cycle and another, the 'form' module, which creates the characteristic shape of each burst of activity within this cycle. The rhythm module is already functional when gestation is 35% complete while the form module appears to be constructed gradually over the second half of gestation.

Easily-implantable electrodes for chronic recording of electromyogram activity in small fetuses

A method is described for the construction of simple, robust electrodes suitable for obtaining long-term chronic recordings of electromyogram activity from delicate muscles of small experimental animals. The electrodes are equipped with small, gold-plated barbed tips which have the form of harpoons that may be pushed directly into a muscle, where they remain without being sutured into place. These features greatly facilitate the instrumentation of muscles which are very thin or of limited accessibility. The electrodes have been used successfully to obtain chronic recordings of respiratory muscle activity from early gestation fetal lambs in utero.

Distribution of GABA-like immunoreactive neurons in the slug Limax maximus

Immunohistochemical techniques were used to study the distribution of gamma-amino butyric acid (GABA)-like immunoreactive neurons in the nervous system of the slug Limax maximus. Approximately 170 GABA-like immunoreactive cell bodies were found in the central nervous system. These were located in the cerebral, buccal and pedal ganglia. Most GABA-like immunoreactive neurons had small cell bodies, which were aggregated into discrete clusters within the cerebral and pedal ganglia. Three pairs of longer, uniquely identifiable, GABA-like immunoreactive cells were found in the cerebral ganglion. GABA-like immunoreactive nerve fibres were also found in all of the central ganglia but were absent from peripheral nerves. These results suggest that GABA acts as a central neurotransmitter in the slug. The possible roles of GABA-ergic neurotransmission in the slug are discussed.

Distribution of FMRFamide-like immunoreactivity in the nervous system of the slug Limax maximus

The distribution of FMRFamide-like immunoreactive neurons in the nervous system of the slug Limax maximus was studied using immunohistochemical methods. Approximately one thousand FMRFamide-like immunoreactive cell bodies were found in the central nervous system. Ranging between 15 micron and 200 micron in diameter, they were found in all 11 ganglia of the central nervous system. FMRFamide-like immunoreactive cell bodies were also found at peripheral locations on buccal nerve roots. FMRFamide-like immunoreactive nerve fibres were present in peripheral nerve roots and were distributed extensively throughout the neuropil and cell body regions of the central ganglia. They were also present in the connective tissue of the perineurium, forming an extensive network of varicose fibres. The large number, extensive distribution and great range in size of FMRFamide-like immunoreactive cell bodies and the wide distribution of immunoreactive fibres suggest that FMRFamide-like peptides might serve several different functions in the nervous system of the slug.

Sustained branchial apnea in the Australian short-finned eel, Anguilla australis

Branchial and cutaneous O2 uptake as well as branchial ventilatory stroke volume and frequency were measured by twin-chamber respirometry in conscious unoperated eels (Anguilla australis) at 20 degrees C. The branchial ventilatory pattern comprised alternating periods of apnea and eupnea, together constituting a "Standard Breathing Cycle" (SBC = 1 apneic period plus the ensuing period of eupnea). SBC time in 17 eels averaged 15.5 min of which only 23% was devoted to eupnea. Reduction of the PO2 of inspired water from 155 to 80 torr significantly increased the proportion of time devoted to eupnea to 49% of SBC time without significantly changing SBC time. Absolute cutaneous O2 uptake (5.8 ml O2 X h-1 X kg-1) was largely independent of the frequency or occurrence of eupnea, with the relative contribution of the skin to total O2 uptake averaging 47%. The histological appearance of the skin in A. australis is very similar to that described in A. anguilla: eel skin is only poorly vascularized. It was concluded that the skin may contribute to O2 requirements other than its own, and that this adaptation is a consequence of the unusual intermittent pattern of gill ventilation.