Resonant quantum transitions in trapped antihydrogen atoms.

The hydrogen atom is one of the most important and influential model systems in modern physics. Attempts to understand its spectrum are inextricably linked to the early history and development of quantum mechanics. The hydrogen atom's stature lies in its simplicity and in the accuracy with which its spectrum can be measured and compared to theory. Today its spectrum remains a valuable tool for determining the values of fundamental constants and for challenging the limits of modern physics, including the validity of quantum electrodynamics and--by comparison with measurements on its antimatter counterpart, antihydrogen--the validity of CPT (charge conjugation, parity and time reversal) symmetry. Here we report spectroscopy of a pure antimatter atom, demonstrating resonant quantum transitions in antihydrogen. We have manipulated the internal spin state of antihydrogen atoms so as to induce magnetic resonance transitions between hyperfine levels of the positronic ground state. We used resonant microwave radiation to flip the spin of the positron in antihydrogen atoms that were magnetically trapped in the ALPHA apparatus. The spin flip causes trapped anti-atoms to be ejected from the trap. We look for evidence of resonant interaction by comparing the survival rate of trapped atoms irradiated with microwaves on-resonance to that of atoms subjected to microwaves that are off-resonance. In one variant of the experiment, we detect 23 atoms that survive in 110 trapping attempts with microwaves off-resonance (0.21 per attempt), and only two atoms that survive in 103 attempts with microwaves on-resonance (0.02 per attempt). We also describe the direct detection of the annihilation of antihydrogen atoms ejected by the microwaves.

Distinct ionotropic GABA receptors mediate presynaptic and postsynaptic inhibition in retinal bipolar cells.

Ionotropic GABA receptors can mediate presynaptic and postsynaptic inhibition. We assessed the contributions of GABA(A) and GABA(C) receptors to inhibition at the dendrites and axon terminals of ferret retinal bipolar cells by recording currents evoked by focal application of GABA in the retinal slice. Currents elicited at the dendrites were mediated predominantly by GABA(A) receptors, whereas responses evoked at the terminals had GABA(A) and GABA(C) components. The ratio of GABA(C) to GABA(A) (GABA(C):GABA(A)) was highest in rod bipolar cell terminals and variable among cone bipolars, but generally was lower in OFF than in ON classes. Our results also suggest that the GABA(C):GABA(A) could influence the time course of responses. Currents evoked at the terminals decayed slowly in cell types for which the GABA(C):GABA(A) was high, but decayed relatively rapidly in cells for which this ratio was low. Immunohistochemical studies corroborated our physiological results. GABA(A) beta2/3 subunit immunoreactivity was intense in the outer and inner plexiform layers (OPL and IPL, respectively). GABA(C) rho subunit labeling was weak in the OPL but strong in the IPL in which puncta colocalized with terminals of rod bipolars immunoreactive for protein kinase C and of cone bipolars immunoreactive for calbindin or recoverin. These data demonstrate that GABA(A) receptors mediate GABAergic inhibition on bipolar cell dendrites in the OPL, that GABA(A) and GABA(C) receptors mediate inhibition on axon terminals in the IPL, and that the GABA(C):GABA(A) on the terminals may tune the response characteristics of the bipolar cell.

A diversity of GABA receptors in the retina.

GABA, a major inhibitory transmitter in the vertebrate retina, plays important roles in processing visual information. There are three functional families of retinal GABA receptors, the ionotropic GABAA and GABAC receptors and the metabotropic GABAB receptor. GABAC receptors are enriched in the retina, compared to other parts of the CNS. GABAC and GABAB receptors are found on subsets of neurons, whereas GABAA receptors are ubiquitous. The distinct functional properties of GABAA, GABAB and GABAC receptors suggests that individual neurons with different receptor complements have unique responses to GABA.

A cytokinesis checkpoint requiring the yeast homologue of an APC-binding protein.

Checkpoint controls ensure that events of the cell-division cycle are completed with fidelity and in the correct order. In budding yeast with a mutation in the motor protein dynein, the mitotic spindle is often misaligned and therefore slow to enter the neck between mother cell and budding daughter cell. When this occurs, cytokinesis (division of the cytoplasm into two) is delayed until the spindle is properly positioned. Here we describe mutations that abolish this delay, indicating the existence of a new checkpoint mechanism. One mutation lies in the gene encoding the yeast homologue of EB1, a human protein that binds the adenomatous polyposis coli (APC) protein, a tumour suppressor. EB1 is located on microtubules of the mitotic spindle and is important in spindle assembly. EB1 may therefore, by associating with microtubules, contribute to the sensor mechanism that activates the checkpoint. Another mutation affects Stt4, a phosphatidylinositol-4-OH kinase. Cold temperature is an environmental stimulus that causes misalignment of the mitotic spindle in yeast and appears to activate this checkpoint mechanism.

Different combinations of GABAA and GABAC receptors confer distinct temporal properties to retinal synaptic responses.

This study addresses how gamma-aminobutyric acid-A(GABAA) and GABAC receptors confer distinct temporal properties to neuronal synaptic responses. The retina is a model system for the study of postsynaptic contributions to synaptic responses because GABAergic amacrine cells synapse onto neurons, which have different combinations of GABAA and GABAC receptors. It is not known, however, how GABAA versus GABAC receptors influence the time course of retinal synaptic responses or what proportion of inhibitory input is mediated by each receptor type. We examined the time courses of synaptic responses mediated by GABA receptors in ganglion and bipolar cells by recording currents evoked by activating amacrine cells with a stimulating electrode in the salamander retinal slice. The pharmacologically isolated, GABAergic synaptic currents were long-lasting in bipolar cells and relatively brief in ganglion cells. The receptors that mediated these temporally distinct synaptic responses exhibited different pharmacological properties. In ganglion cells, GABAergic synaptic currents were abolished by the GABAA receptor antagonists bicuculline or SR95531. In bipolar cells, the GABAC receptor antagonist 3-aminopropyl[methyl]phosphonic acid (3-APMPA) largely blocked GABAergic synaptic responses; the remaining response was blocked by bicuculline or SR95531. The GABAA receptor component of the bipolar cell response was relatively brief compared with the GABAC receptor component. Puffing GABA onto ganglion cell dendrites or bipolar cell terminals yielded similar pharmacological and kinetic results, indicating that transmitter release differences did not determine the response time courses. Moreover, the GABAC receptors on bipolar cells may be different from those reported in rat or fish retina because imidazole-4-acetic acid (I4AA), which acts as an antagonist in these preparations, acts as an agonist in salamander. Our data show that the prolonged synaptic responses in bipolar cells were mediated predominantly by GABAC receptors, whereas transient synaptic responses in ganglion cells were mediated by GABAA receptors.

Grief in chronic illness: assessment and management.

Grief is a normal reaction to the loss of physical function. Its symptoms, however, are often mistaken for major depressive episode and treatment may be inappropriate. Symptoms of grief include a preoccupation with the lost object (a limb, a function, a loved one), somatic distress, inappropriate behavior, hostility, and denial. Depression may be a manifestation of illness or drug therapy. Grief should be treated like a major depressive episode but without antidepressive medications. The first step in management of grief is the development of a proper therapeutic milieu which will encourage the reappearance of self worth. Once the milieu is established, specific rehabilitation problems can be addressed. In formulating a prognosis, it is important to consider the severity of the patient's disability, the premorbid psychologic make-up, and the type of family and community support available to the patient.

Chloroplast DNA evolution and the origin of amphidiploid Brassica species.

The origin and evolution of a hybrid species complex in the genus Brassica (cabbage, turnip, mustard, rapeseed oil) has been explored through mutational analysis of the maternally inherited chloroplast genome. A detailed chloroplast DNA phylogeny enables identification of the maternal parent for most of the amphidiploids examined and permits quantitative resolution of the relative time of hybridization as well as the relative divergence of the diploid parents. Contradictory chloroplast and nuclear phylogenies obtained for two accessions of the amphidiploid B. napus (rapeseed oil) lead to the hypothesis that introgressive hybridization has also figured in their recent evolution.