Biomedical subjects

Rhanor Gillette

Publications and source records attributed to Rhanor Gillette.

6 recordsLinked to original sources

PubMed2006

Nitric oxide potentiates cAMP-gated cation current in feeding neurons of Pleurobranchaea californica independent of cAMP and cGMP signaling pathways.

Critical roles for nitric oxide (NO) in regulating cell and tissue physiology are broadly appreciated, but aspects remain to be explored. In the mollusk Pleurobranchaea, NO synthase activity is high in CNS ganglia containing motor networks for feeding and locomotion, where a cAMP-gated cation current (I(Na,cAMP)) is also prominent in many neurons. We examined effects of NO on I(Na,cAMP) using voltage-clamp methods developed to analyze cAMP signaling in the live neuron, focusing on the identified metacerebral giant neuron of the feeding network. NO donors enhanced the I(Na,cAMP) response to injected cAMP by an averaged 85%. In dose-response measures, NO increased the current stimulated by cAMP injection without altering either apparent cAMP binding affinity or cooperativity of current activation. NO did not detectably alter levels of native cAMP or synthesis or degradation rates as observable in both current saturation and decay rate of I(Na,cAMP) responses to cAMP injection. NO actions were not exerted by cGMP signaling, as they were not mimicked by cGMP analogue nor blocked by inhibitors of guanylate cyclase and protein kinase G. NO potentiation of I(Na,cAMP) was broadly distributed among many other neurons of the feeding motor network in the buccal ganglion. However, NO did not affect a second type of I(Na,cAMP) found in locomotor neurons of the pedal ganglia. These results suggest that NO acts through a novel mechanism to regulate the gain of cAMP-dependent neuromodulatory pathways that activate I(Na,cAMP) and may thereby affect the set points of feeding network excitability and reactivity to exogenous input.

Animals↗

PubMed2004

Spurious serotonin dimer formation using electrokinetic injection in capillary electrophoresis from small volume biological samples.

One normally assumes that the analytical measurement process does not introduce spurious compounds. Capillary electrophoresis is a separation method frequently used for small-volume biological measurements. We demonstrate the potential for creating new peaks in a capillary electropherogram when using electrokinetic injections and illustrate the potential deleterious effects with biological samples involving serotonin and nitric oxide measurements. Specifically, when measuring the serotonin content from individual neurons using electrokinetic injections from 360 nL stainless steel vials, we detect a new peak that we identify as a serotonin dimer. We do not observe this peak when using hydrodynamic injections.

Animals↗

PubMed2004

Systemic serotonin sulfate in opisthobranch mollusks.

Serotonin (5-hydroxytryptamine, 5-HT) is a ubiquitous modulatory neurotransmitter with roles as a neurohormone and neurotransmitter. However, few studies have been performed characterizing this molecule and its related metabolites in circulating fluids. Here, we demonstrate native 5-HT sulfate, but much lower levels of 5-HT, in hemolymph of the marine mollusk Pleurobranchaea californica. The metabolite 5-HT sulfate forms from 5-HT uptake and metabolism in central ganglia of Aplysia californica and in the visceral nerve and eye of Pleurobranchaea, but not in hemolymph itself. In addition, 5-hydroxyindole acetic acid (5-HIAA), while not detected in hemolymph, forms in higher quantities than does 5-HT sulfate in the eye and visceral nerve, and gamma-glu-5-HT is also observed in this area but never in hemolymph. As systemic 5-HT sulfate appears not to originate from the optic region or from systemic 5-HT, 5-HT sulfate likely derives from the nervous system. Circulating 5-HT sulfate is at least 10-fold higher during the light portion of a 12 : 12-h light/dark cycle than during the dark portion (p < 0.0007), but there is no obvious trend for free systemic tryptophan (Trp) (p > 0.3) in Pleurobranchaea. 5-HT in mollusks is associated with general arousal state; thus, diurnal systemic changes in a 5-HT catabolite may reflect a regulatory role for indole catabolism in behavioral rhythms.

5-Hydroxytryptophan↗

PubMed2003

Functional optical coherence tomography for detecting neural activity through scattering changes.

We have demonstrated functional optical coherence tomography (fOCT) for neural imaging by detecting scattering changes during the propagation of action potentials through neural tissue. OCT images of nerve fibers from the abdominal ganglion of the sea slug Aplysia californica were taken before, during, and after electrical stimulation. Images acquired during stimulation showed localized reversible increases in scattering compared with those acquired before stimulation. Motion-mode OCT images of nerve fibers showed transient scattering changes from spontaneous action potentials. These results demonstrate that OCT is sensitive to the optical changes in electrically active nerve fibers.

Abdomen↗

PubMed2003

Directional avoidance turns encoded by single interneurons and sustained by multifunctional serotonergic cells.

Avoidance turns in the sea slug Pleurobranchaea are responses to noxious stimuli and replace orienting turns to food stimuli after avoidance conditioning or satiation. Avoidance turns proved to be centrally patterned behaviors, the fictive expression of which could be elicited in reduced preparations and the isolated CNS. Activity in one of a bilateral interneuron pair, the A4 cells, was necessary and sufficient to drive the avoidance turn toward the contralateral side. Single A4 cells appeared to encode both turn direction and angle, in contrast to directional behaviors of other animals in which displacement angle is usually encoded by multiple units. The As1-4 cells, bilateral serotonergic cell clusters, excited the prolonged A4 burst during the turn through electrical and chemical coupling. However, during the escape swim, As1-4 became integral elements of the swim motor network, and A4 activity was entrained to the swim rhythm by alternating excitatory-inhibitory inputs, with only weak spiking. This provides a likely mechanism for the previously observed suppression of the avoidance turn by escape swimming. These observations add significant new aspects to the multiplying known functions of As1-4 and their homologs in other molluscs and point to a pivotal role of these neurons in the organization of gastropod behavior. Simple functional models predict (1) the essential actions of inhibitor neurons in the directionality of the turning network motor output and (2) an integrating role for As1-4 in the behavioral switch between turning avoidance and swimming escape, on the basis of their response to increasing stimulus intensity.

Animals↗

PubMed2002

Interfering with nitric oxide measurements. 4,5-diaminofluorescein reacts with dehydroascorbic acid and ascorbic acid.

4,5-Diaminofluorescein (DAF-2) is widely used for detection and imaging of NO based on its sensitivity, noncytotoxicity, and specificity. In the presence of oxygen, NO and NO-related reactive nitrogen species nitrosate 4,5-diaminofluorescein to yield the highly fluorescent DAF-2 triazole (DAF-2T). However, as reported here, the DAF-2 reaction to form a fluorescent product is not specific to NO because it reacts with dehydroascorbic acid (DHA) and ascorbic acid (AA) to generate new compounds that have fluorescence emission profiles similar to that of DAF-2T. When DHA is present, the formation of DAF-2T is attenuated because the DHA competes for DAF-2, whereas AA decreases the nitrosation of DAF-2 to a larger extent, possibly because of additional reducing activity that affects the amount of available N(2)O(3) from the NO. The reaction products of DAF-2 with DHA and AA have been characterized using capillary electrophoresis with laser-induced fluorescence detection and electrospray mass spectrometry. The reactions of DAF-2 with DHA and AA are particularly significant because DHA and AA often colocalize with nitric-oxide synthase in the central nervous, cardiovascular, and immune systems, indicating the importance of understanding this chemistry.

Animals↗