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A Carleton

Publications and source records attributed to A Carleton.

14 recordsLinked to original sources
PubMed2003

Compact, continuous-wave, singly resonant optical parametric oscillator based on periodically poled RbTiOAsO4 in a Nd:YVO4 laser.

We describe a compact all-solid-state continuous-wave, singly resonant optical parametric oscillator (SRO) based on periodically poled RbTiOAsO4. The SRO is pumped at 1.064 microm by a Nd:YVO4 laser, which is itself pumped by a 3-W diode laser. Using the intracavity technique produced an oscillation threshold for the SRO of only 1.6 W (diode-laser power). For 3 W of diode pump power some 65 mW was obtained in the (nonresonant) idler (wavelength 3.52 microm). Temperature tuning over the range 10-100 degrees C resulted in tuning ranges of 1.52-1.54 and 3.41-3.54 microm for the signal and the idler waves, respectively. Importantly, relaxation oscillations were absent.

Journal Article↗
PubMed2001

A dendrodendritic reciprocal synapse provides a recurrent excitatory connection in the olfactory bulb.

Neuronal synchronization in the olfactory bulb has been proposed to arise from a diffuse action of glutamate released from mitral cells (MC, olfactory bulb relay neurons). According to this hypothesis, glutamate spills over from dendrodendritic synapses formed between MC and granule cells (GC, olfactory bulb interneurons) to activate neighboring MC. The excitation of MC is balanced by a strong inhibition from GC. Here we show that MC excitation is caused by glutamate released from bulbar interneurons located in the GC layer. These reciprocal synapses depend on an unusual, 2-amino-5-phosphonovaleric acid-resistant, N-methyl-d-aspartate receptor. This type of feedback excitation onto relay neurons may strengthen the original sensory input signal and further extend the function of the dendritic microcircuit within the main olfactory bulb.

2-Amino-5-phosphonovalerate↗
PubMed2001

Dose-dependent, prion protein (PrP)-mediated facilitation of excitatory synaptic transmission in the mouse hippocampus.

Disruption of both alleles of the prion protein gene, Prnp, has been shown repeatedly to abolish the susceptibility of mice to developing prion diseases. However, conflicting results have been obtained from phenotypic analyses of prion protein (PrP)-deficient (Prnp0/0) mice lines. To explore the possible neurophysiological properties associated with expression or absence of the normal isoform of the cellular prion protein (PrPC), we used conventional in vitro extracellular field potential recordings in the hippocampal CA1 area of mice from two independently-derived Prnp0/0 strains. Basal synaptic transmission and a short-term form of synaptic plasticity were analysed in this study. Results were compared with animals carrying a wild-type mouse PrP transgene to investigate whether PrP expression levels influence glutamatergic synaptic transmission in the hippocampus. There was a clear correlation between excitatory synaptic transmission and PrP expression; i.e. the range of synaptic responses increased with the level of PrPC expression. On the other hand, the probability of transmitter release, as assessed by paired-pulse facilitation, appeared unchanged. Interestingly, whereas the overall range for synaptic responses was still greater in older mice over-expressing PrPC, this effect in these animals appeared to be due to better recruitment of fibres rather than facilitation of synaptic transmission per se. Taken together, these data are strong evidence for a functional role for PrPC in modulating synaptic transmission.

Animals↗
PubMed2000

Bicoid-independent formation of thoracic segments in Drosophila.

The maternal determinant Bicoid (Bcd) represents the paradigm of a morphogen that provides positional information for pattern formation. However, as bicoid seems to be a recently acquired gene in flies, the question was raised as to how embryonic patterning is achieved in organisms with more ancestral modes of development. Because the phylogenetically conserved Hunchback (Hb) protein had previously been shown to act as a morphogen in abdominal patterning, we asked which functions of Bcd could be performed by Hb. By reestablishing a proposed ancient regulatory circuitry in which maternal Hb controls zygotic hunchback expression, we show that Hb is able to form thoracic segments in the absence of Bcd.

Animals↗
PubMed1999

Multiple and opposing roles of cholinergic transmission in the main olfactory bulb.

The main olfactory bulb is a critical relay step between the olfactory epithelium and the olfactory cortex. A marked feature of the bulb is its massive innervation by cholinergic inputs from the basal forebrain. In this study, we addressed the functional interaction between cholinergic inputs and intrinsic bulbar circuitry. Determining the roles of acetylcholine (ACh) requires the characterization of cholinergic effects on both neural excitability and synaptic transmission. For this purpose, we used electrophysiological techniques to localize and characterize the diverse roles of ACh in mouse olfactory bulb slices. We found that cholinergic inputs have a surprising number of target receptor populations that are expressed on three different neuronal types in the bulb. Specifically, nicotinic acetylcholine receptors excite both the output neurons of the bulb, i.e., the mitral cells, as well as interneurons located in the periglomerular regions. These nicotine-induced responses in interneurons are short lasting, whereas responses in mitral cells are long lasting. In contrast, muscarinic receptors have an inhibitory effect on the firing rate of interneurons from a deeper layer, granule cells, while at the same time they increase the degree of activity-independent transmitter release from these cells onto mitral cells. Cholinergic signaling thus was found to have multiple and opposing roles in the olfactory bulb. These dual cholinergic effects on mitral cells and interneurons may be important in modulating olfactory bulb output to central structures required for driven behaviors and may be relevant to understanding mechanisms underlying the perturbations of cholinergic inputs to cortex that occur in Alzheimer's disease.

2-Amino-5-phosphonovalerate↗
PubMed1998

Long-term but not short-term plasticity at mossy fiber synapses is impaired in neural cell adhesion molecule-deficient mice.

Cell adhesion molecules (CAMs) are known to be involved in a variety of developmental processes that play key roles in the establishment of synaptic connectivity during embryonic development, but recent evidence implicates the same molecules in synaptic plasticity of the adult. In the present study, we have used neural CAM (NCAM)-deficient mice, which have learning and behavioral deficits, to evaluate NCAM function in the hippocampal mossy fiber system. Morphological studies demonstrated that fasciculation and laminar growth of mossy fibers were strongly affected, leading to innervation of CA3 pyramidal cells at ectopic sites, whereas individual mossy fiber boutons appeared normal. Electrophysiological recordings performed in hippocampal slice preparations revealed that both basal synaptic transmission and two forms of short-term plasticity, i.e., paired-pulse facilitation and frequency facilitation, were normal in mice lacking all forms of NCAM. However, long-term potentiation of glutamatergic excitatory synapses after brief trains of repetitive stimulation was abolished. Taken together, these results strongly suggest that in the hippocampal mossy fiber system, NCAM is essential both for correct axonal growth and synaptogenesis and for long-term changes in synaptic strength.

Animals↗