Ca2+-independent regulation of neurosecretion by intracellular Na+

While secretion from nerve endings is strictly controlled by an increase in cytoplasmic free calcium several reports suggest intracellular sodium may serve a regulatory role. Whether sodium acts directly to modulate secretion or indirectly by influencing cytoplasmic calcium dynamics is unknown. This study shows, based on parallel experiments studying [Na+]i, [Ca2+]i and vasopressin secretion, that sodium acts directly to regulate secretion in isolated nerve endings from the rat neurohypophysis. The elevation in secretion that develops is dose-dependently related to the [Na+]i and can occur in the absence of changes in [Ca2+]i.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29036/1/0000069.pd

Ca 2+ and frequency dependence of exocytosis in isolated somata of magnocellular supraoptic neurones of the rat hypothalamus

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66206/1/jphysiol.2003.051136.pd

Secretagogue effects on intracellular calcium in pancreatic duct cells

Regulation of intracellular free calcium ([Ca 2+ ] i ) in single epithelial duct cells of isolated rat and guinea pig pancreatic interlobular ducts by secretin, carbachol and cholecystokinin was studied by microspectrofluorometry using the Ca 2+ -sensitive, fluorescent probe Fura-2. Rat and guinea pig duct cells exhibited mean resting [Ca 2+ ] i of 84 nM and 61 nM, respectively, which increased by 50%–100% in response to carbachol stimulation, thus demonstrating the presence of physiologically responsive cholinergic receptors in pancreatic ducts of both species. The carbachol-induced increase in [Ca 2+ ] i involved both mobilization of Ca 2+ from intracellular stores and stimulation of influx of extracellular Ca 2+ . In contrast, neither cholecystokinin nor secretin showed reproducible or sizeable increses in [Ca 2+ ] i . Both rat and guinea pig duct cells showed considerable resting Ca 2+ permeability. Lowering or raising the extracellular [Ca 2+ ] i led, respectively, to a decrease or increase in the resting [Ca 2+ ] i . Application of Mn 2+ resulted in a quenching of the fluorescence signal indicating its entry into the cell. The resting Ca 2+ and Mn 2+ permeability could be blocked by La 3+ suggesting that it is mediated by a Ca 2+ channel.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47456/1/424_2004_Article_BF00370610.pd

Autoradiographic evidence that transport of newly synthesized neuropeptides is directed to release sites in the X-organsinus gland of Cardisoma carnifex

Sections of isolated X-organ — sinus gland neurosecretory systems of the crab, Cardisoma carnifex , were studied by light-and electron microscopy with conventional and autoradiographic procedures. The somata only were exposed to a pulse of 3 H-leucine (5 min-5 h) and the entire system perfused with chase medium for various times (1–72 h) before fixation. Within 1 h, radiolabel is concentrated in Golgi complexes and nascent granules of both large and small somata. Label is undetectable in the terminal region following a 10 h chase. It is found in the nerve tract near terminals at 14 h, while after a 19 h chase, label is concentrated in terminal profiles abutting blood sinuses of the neurohemal organ (sinus gland). Following a 72 h chase, label is distributed throughout the terminal region. Each of the six morphologically distinguishable terminal types shows labelling. These observations show that the vast majority of newly formed granules are initially transported to release sites of the perisinus terminals. They thus provide an explanation for previous analyses indicating that newly synthesized peptides are preferentially secreted.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47688/1/441_2004_Article_BF00313962.pd

Regulation of syntaxin1A–munc18 complex for SNARE pairing in HEK293 cells

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65811/1/jphysiol.2004.067249.pd

Intracellular calcium and hormone release from nerve endings of the neurohypophysis in the presence of opioid agonists and antagonists

Rat neural lobes and isolated nerve terminals from the neurohypophysis were stimulated in the presence of different opioid agonists and antagonists. The secretion of arginine vasopressin and oxytocin and rise in cytoplasmic calcium induced by depolarization were analyzed by radioimmunoassay and the fluorescent probe fura-2, respectively. The kappa-agonists dynorphin A 1 -13 and dynorphin A 1 -8 did not affect electrically evoked release of vasopressin, although oxytocin release was slightly reduced. U-50 488, a relatively specific kappa-receptor agonist, had no effect on the amount of vasopressin or oxytocin secreted, although it significantly reduced K + -evoked changes in [Ca 2+ ] i in isolated nerve endings. Two kappa-receptor antagonists, MR 2266 and diprenorphin, alone had no effect on vasopressin and oxytocin secretion from isolated nerve endings depolarized with potassium. Opioid agonists less selective for the kappa receptors, etorphin and ethylketocyclazocin, were found to inhibit the release of both vasopressin and oxytocin significantly. Naloxone, a nonselective opiate receptor antagonist, alone had no effect on vasopressin release but potentiated the electrically evoked release of oxytocin. Naloxone also could overcome the inhibitory effect of etorphin on oxytocin and vasopressin release observed after electrical stimulation of the neural lobe. A number of inconsistencies therefore exist between the effects of opioid agonists and antagonists on neuropeptide release and on the evoked changes in [Ca 2+ ] i . In view of these inconsistencies and the high concentrations of opioid agonists and antagonists necessary to modify release, we conclude that it is doubtful that opioid molecules have a physiological role in controlling neurohypophysial secretion.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46563/1/221_2004_Article_BF00230936.pd

Thermal tolerances and preferences of fishes of the Virgin River system (Utah, Arizona, Nevada)

Critical thermal maxima (CTM) and thermal preferenda of the common fishes of the Virgin River were examined. Differences in final temperature preferenda and CTM for species with low thermal lability (speckled dace, spinedace, roundtail chub) correspond well with differences in their distribution and abundance in the river. These species shifted their acute thermal preferences relatively little as acclimation temperature increased. For thermally labile species (woundfin, red shiner, desert sucker, and fiannehnouth sucker), the final preferendum is a less precise indicator of probable distribution. The woundfin, an endangered fish, has a high CTM (39.5 C at 25 C acclimation) and a labile acute preferendum (slope nearest 1) compared to other species in the system. The introduced red shiner likewise has a high CTM and a labile acute preferendum. In cooler temperatures, its acute preferendum shifts more rapidly than does that of the woundfin. At higher temperatures (above 15 C), the red shiner does not shift its acute preferendum as rapidly as does the woundfin. The red shiner, however, has a higher final preferendum. For thermally labile species, influence of acclimation temperature on mean preferendum, together with CTM, provides a better insight into distributional relationships within the system

Effects of Toxins on Ca 2+ Currents and Peptide Release from Nerve Terminals a

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72911/1/j.1749-6632.1994.tb26610.x.pd

Tomosyn Expression Pattern in the Mouse Hippocampus Suggests Both Presynaptic and Postsynaptic Functions

The protein tomosyn decreases synaptic transmission and release probability of vesicles, and is essential for modulating synaptic transmission in neurons. In this study, we provide a detailed description of the expression and localization patterns of tomosyn1 and tomosyn2 in the subareas of the mouse hippocampus. Using confocal and two-photon high-resolution microscopy we demonstrate that tomosyn colocalizes with several pre- and postsynaptic markers and is found mainly in glutamatergic synapses. Specifically, we show that tomosyn1 is differentially distributed in the mouse hippocampus and concentrated mainly in the hilus and mossy fibers. Surprisingly, we found that tomosyn2 is expressed in the subiculum, CA1 and CA2 pyramidal cell bodies, dendrites and spines, and colocalizes with PSD95, suggesting a postsynaptic role. These results suggest that in addition to the well-characterized presynaptic function of tomosyn in neurotransmitter release, tomosyn2 might have a postsynaptic function, and place tomosyn as a more general regulator of synaptic transmission and plasticity