Biomedical subjects

Gert Stange

Publications and source records attributed to Gert Stange.

4 recordsLinked to original sources

PubMed2006

The mapping of visual space by identified large second-order neurons in the dragonfly median ocellus.

In adult dragonflies, the compound eyes are augmented by three simple eyes known as the dorsal ocelli. The outputs of ocellar photoreceptors converge on relatively few second-order neurons with large axonal diameters (L-neurons). We determine L-neuron morphology by iontophoretic dye injection combined with three-dimensional reconstructions. Using intracellular recording and white noise analysis, we also determine the physiological receptive fields of the L-neurons, in order to identify the extent to which they preserve spatial information. We find a total of 11 median ocellar L-neurons, consisting of five symmetrical pairs and one unpaired neuron. L-neurons are distinguishable by the extent and location of their terminations within the ocellar plexus and brain. In the horizontal dimension, L-neurons project to different regions of the ocellar plexus, in close correlation with their receptive fields. In the vertical dimension, dendritic arborizations overlap widely, paralleled by receptive fields that are narrow and do not differ between different neurons. These results provide the first evidence for the preservation of spatial information by the second-order neurons of any dorsal ocellus. The system essentially forms a one-dimensional image of the equator over a wide azimuthal area, possibly forming an internal representation of the horizon. Potential behavioural roles for the system are discussed.

Animals↗

PubMed2005

A spatiotemporal white noise analysis of photoreceptor responses to UV and green light in the dragonfly median ocellus.

Adult dragonflies augment their compound eyes with three simple eyes known as the dorsal ocelli. While the ocellar system is known to mediate stabilizing head reflexes during flight, the ability of the ocellar retina to dynamically resolve the environment is unknown. For the first time, we directly measured the angular sensitivities of the photoreceptors of the dragonfly median (middle) ocellus. We performed a second-order Wiener Kernel analysis of intracellular recordings of light-adapted photoreceptors. These were stimulated with one-dimensional horizontal or vertical patterns of concurrent UV and green light with different contrast levels and at different ambient temperatures. The photoreceptors were found to have anisotropic receptive fields with vertical and horizontal acceptance angles of 15 degrees and 28 degrees, respectively. The first-order (linear) temporal kernels contained significant undershoots whose amplitudes are invariant under changes in the contrast of the stimulus but significantly reduced at higher temperatures. The second-order kernels showed evidence of two distinct nonlinear components: a fast acting self-facilitation, which is dominant in the UV, followed by delayed self- and cross-inhibition of UV and green light responses. No facilitatory interactions between the UV and green light were found, indicating that facilitation of the green and UV responses occurs in isolated compartments. Inhibition between UV and green stimuli was present, indicating that inhibition occurs at a common point in the UV and green response pathways. We present a nonlinear cascade model (NLN) with initial stages consisting of separate UV and green pathways. Each pathway contains a fast facilitating nonlinearity coupled to a linear response. The linear response is described by an extended log-normal model, accounting for the phasic component. The final nonlinearity is composed of self-inhibition in the UV and green pathways and inhibition between these pathways. The model can largely predict the response of the photoreceptors to UV and green light.

Animals↗

PubMed2005

Volatile organic compounds as signals in a plant-herbivore system: electrophysiological responses in olfactory sensilla of the moth Cactoblastis cactorum.

The morphological sensillum types on the antennae of male and female Cactoblastis cactorum were visualized by scanning electron microscopy. Electrophysiological recordings were performed for the first time on single olfactory sensilla of C. cactorum. The male sensilla trichodea house a receptor cell responding to the putative pheromone component (9Z,12E)-tetradecadienyl acetate. The sensilla trichodea of the females were much shorter than those of the males and contained specialized receptor cells responding to certain terpenoids, the most frequent being the nerolidol-sensitive cell. The sensilla auricillica and sensilla basiconica of both sexes contained cells responding less specifically to terpenoid compounds as well as to green leaf volatiles. Cells of the sensilla coeloconica responded to aliphatic aldehydes and acids. Eight volatile organic compounds emitted by Opuntia stricta, a host plant of C. cactorum, were identified using gas chromatography-mass spectrometry, beta-caryophyllene being the major compound. Five compounds identified by gas chromatography in the headspace of O. stricta elicited responses in olfactory receptor cells of C. cactorum, nonanal being the most active compound and therefore a candidate attractant of C. cactorum.

Age Factors↗

PubMed2002

The renal type IIa Na/Pi cotransporter: structure-function relationships.

The type IIa Na/Pi cotransporter mediates proximal tubular brush-border membrane secondary active phosphate (Pi) flux. It is rate limiting in tubular Pi reabsorption and, thus, a final target in many physiological and pathophysiological situations of altered renal Pi handling. In the present short review, we will briefly summarize our current knowledge about the transport mechanism (cycle) as well as particular regions of the transporter protein ("molecular domains") that potentially determine transport characteristics.

Amino Acid Sequence↗