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Biomedical subjects

B McNeill

Publications and source records attributed to B McNeill.

9 recordsLinked to original sources
PubMed2006

Type IV carbonic anhydrase is present in the gills of spiny dogfish (Squalus acanthias).

Physiological and biochemical studies have provided indirect evidence for a membrane-associated carbonic anhydrase (CA) isoform, similar to mammalian type IV CA, in the gills of dogfish (Squalus acanthias). This CA isoform is linked to the plasma membrane of gill epithelial cells by a glycosylphosphatidylinositol anchor and oriented toward the plasma, such that it can catalyze the dehydration of plasma HCO(3)(-) ions. The present study directly tested the hypothesis that CA IV is present in dogfish gills in a location amenable to catalyzing plasma HCO(3)(-) dehydration. Homology cloning techniques were used to assemble a 1,127 base pair cDNA that coded for a deduced protein of 306 amino acids. Phylogenetic analysis suggested that this protein was a type IV CA. For purposes of comparison, a second cDNA (1,107 base pairs) was cloned from dogfish blood; it encoded a deduced protein of 260 amino acids that was identified as a cytosolic CA through phylogenetic analysis. Using real-time PCR and in situ hybridization, mRNA expression for the dogfish type IV CA was detected in gill tissue and specifically localized to pillar cells and branchial epithelial cells that flanked the pillar cells. Immunohistochemistry using a polyclonal antibody raised against rainbow trout type IV CA revealed a similar pattern of CA IV immunoreactivity and demonstrated a limited degree of colocalization with Na(+)-K(+)-ATPase immunoreactivity. The presence and localization of a type IV CA isoform in the gills of dogfish is consistent with the hypothesis that branchial membrane-bound CA with an extracellular orientation contributes to CO(2) excretion in dogfish by catalyzing the dehydration of plasma HCO(3)(-) ions.

Amino Acid Sequence↗
PubMed2006

Chemoreceptor plasticity and respiratory acclimation in the zebrafish Danio rerio.

The goals of this study were to assess the respiratory consequences of exposing adult zebrafish Danio rerio to chronic changes in water gas composition (hypoxia, hyperoxia or hypercapnia) and to determine if any ensuing effects could be related to morphological changes in branchial chemoreceptors. To accomplish these goals, we first modified and validated an established non-invasive technique for continuous monitoring of breathing frequency and relative breathing amplitude in adult fish. Under normal conditions 20% of zebrafish exhibited an episodic breathing pattern that was composed of breathing and non-breathing (pausing/apneic) periods. The pausing frequency was reduced by acute hypoxia (Pw(O)2<130 mmHg) and increased by acute hyperoxia (Pw(O)2>300 mmHg), but was unaltered by acute hypercapnia. Fish were exposed for 28 days to hyperoxia (Pw(O)2>350 mmHg), or hypoxia (Pw(O)2=30 mmHg) or hypercapnia (Pw(CO)2=9 mmHg). Their responses to acute hypoxia or hypercapnia were then compared to the response of control fish kept for 28 days in normoxic and normocapnic water. In control fish, the ventilatory response to acute hypoxia consisted of an increase in breathing frequency while the response to acute hypercapnia was an increase in relative breathing amplitude. The stimulus promoting the hyperventilation during hypercapnia was increased Pw(CO)2 rather than decreased pH. Exposure to prolonged hyperoxia decreased the capacity of fish to increase breathing frequency during hypoxia and prevented the usual increase in breathing amplitude during acute hypercapnia. In fish previously exposed to hyperoxia, episodic breathing continued during acute hypoxia until Pw(O)2 had fallen below 70 mmHg. In fish chronically exposed to hypoxia, resting breathing frequency was significantly reduced (from 191+/-12 to 165+/-16 min(-1)); however, the ventilatory responses to hypoxia and hypercapnia were unaffected. Long-term exposure of fish to hypercapnic water did not markedly modify the breathing response to acute hypoxia and modestly blunted the response to hypercapnia. To determine whether branchial chemoreceptors were being influenced by long-term acclimation, all four groups of fish were acutely exposed to increasing doses of the O(2) chemoreceptor stimulant, sodium cyanide, dissolved in inspired water. Consistent with the blunting of the ventilatory response to hypoxia, the fish pre-exposed to hyperoxia also exhibited a blunted response to NaCN. Pre-exposure to hypoxia was without effect whereas prior exposure to hypercapnia increased the ventilatory responses to cyanide. To assess the impact of acclimation to varying gas levels on branchial O(2) chemoreceptors, the numbers of neuroepithelial cells (NECs) of the gill filament were quantified using confocal immunofluorescence microscopy. Consistent with the blunting of reflex ventilatory responses, fish exposed to chronic hyperoxia exhibited a significant decrease in the density of NECs from 36.8+/-2.8 to 22.7+/-2.3 filament(-1).

Adaptation, Physiological↗
PubMed2006

Characterization of a branchial epithelial calcium channel (ECaC) in freshwater rainbow trout (Oncorhynchus mykiss).

The entry of calcium (Ca2+) through an apical membrane epithelial calcium channel (ECaC) is thought to a key step in piscine branchial Ca2+ uptake. In mammals, ECaC is a member of the transient receptor potential (TRP) gene family of which two sub-families have been identified, TRPV5 and TPRV6. In the present study we have identified a single rainbow trout (Oncorhynchus mykiss) ECaC (rtECaC) that is similar to the mammalian TRPV5 and TRPV6. Phylogenetic analysis of the protein sequence suggests that an ancestral form of the mammalian genes diverged from those in the lower vertebrates prior to the gene duplication event that gave rise to TRPV5 and TRPV6. The putative model for Ca2+ uptake in fish proposes that the mitochondria-rich cell (also termed ionocyte or chloride cell) is the predominant or exclusive site of transcellular Ca2+ movements owing to preferential localisation of ECaC to the apical membrane of these cells. However, the results of real-time PCR performed on enriched gill cell populations as well as immunocytochemistry and in situ hybridisation analysis of enriched cells, cell cultures and whole gill sections strongly suggest that ECaC is not exclusive to mitochondria-rich cells but that it is also found in pavement cells. Not only was ECaC protein localized to areas of the gill normally having few mitochondria-rich cells, but there was also no consistent co-localization of ECaC- and Na+/K+-ATPase-positive (a marker of mitochondria rich cells) cells. Taken together, the results of the present study suggest that although ECaC (mRNA and protein) does exist in trout gill, its cellular distribution is more extensive than previously thought, thus suggesting that Ca2+ uptake may not be restricted to mitochondria-rich cells as was proposed in previous models.

Amino Acid Sequence↗
PubMed2005

Circulating catecholamines and cardiorespiratory responses in hypoxic lungfish (Protopterus dolloi): a comparison of aquatic and aerial hypoxia.

Circulating catecholamine levels and a variety of cardiorespiratory variables were monitored in cannulated bimodally breathing African lungfish (Protopterus dolloi) exposed to aquatic or aerial hypoxia. Owing to the purported absence of external branchial chemoreceptors in lungfish and the minor role played by the gill in O2 uptake, it was hypothesized that plasma catecholamine levels would increase only during exposure of fish to aerial hypoxia. The rapid induction of aquatic hypoxia (final PWo2 = 25.9+/-1.6 mmHg) did not affect the levels of adrenaline (A) or noradrenaline (NA) within the plasma. Similarly, none of the measured cardiorespiratory variables--including heart rate (fH), blood pressure, air-breathing frequency (fV), O2 consumption (Mo2), CO2 excretion (Mco2), or blood gases--were influenced by acute aquatic hypoxia. In contrast, however, the rapid induction of aerial hypoxia (inspired Po2=46.6+/-3.3 mmHg) caused a marked increase in the circulating levels of A (from 7.9+/-2.0 to 18.8+/-6.1 nmol L(-1)) and NA (from 7.7+/-2.2 to 19.7+/-6.3 nmol L(-1)) that was accompanied by significant decreases in Mo2, arterial Po2 (Pao2), and arterial O2 concentration (Cao2). Air-breathing frequency was increased (by approximately five breaths per hour) during aerial hypoxia and presumably contributed to the observed doubling of pulmonary Mco2 (from 0.25+/-0.04 to 0.49+/-0.07 mmol kg(-1) h(-1)); fH and blood pressure were unaffected by aerial hypoxia. An in situ perfused heart preparation was used to test the possibility that catecholamine secretion from cardiac chromaffin cells was being activated by a direct localized effect of hypoxia. Catecholamine secretion from the chromaffin cells of the heart, while clearly responsive to a depolarizing concentration of KCl (60 mmol L(-1)), was unaffected by the O2 status of the perfusion fluid. The results of this study demonstrate that P. dolloi is able to mobilize stored catecholamines and increase f(V) during exposure to aerial hypoxia while remaining unresponsive to aquatic hypoxia. Thus, unlike in exclusively water-breathing teleosts, P. dolloi would appear to rely solely on internal/airway O2 chemoreceptors for initiating catecholamine secretion and cardiorespiratory responses.

Analysis of Variance↗
PubMed2005

Nitric oxide and the control of catecholamine secretion in rainbow trout Oncorhynchus mykiss.

An in situ saline-perfused posterior cardinal vein preparation was used to assess the role of nitric oxide (NO) in the regulation of basal and stimulus-evoked catecholamine secretion from rainbow trout Oncorhynchus mykiss chromaffin cells. Addition of the NO donor, sodium nitroprusside (SNP) to the inflowing perfusate abolished catecholamine secretion during electrical field stimulation, thereby establishing the potential for NO to act as a potent inhibitor of catecholamine release. A possible role for endogenously produced NO was established by demonstrating that stimulus-evoked (depolarizing levels of KCl or electrical field stimulation) catecholamine secretion was markedly stimulated in the presence of the nitric oxide synthase (NOS) inhibitors l-NAME and 7-NI. Although in vitro experiments demonstrated that catecholamine degradation was enhanced by NO in a dose-dependent manner, the dominant factor contributing to the reduction in catecholamine appearance in the perfusate was specific inhibition of catecholamine secretion. Subsequent experiments were performed to identify the NOS isoform(s) contributing to the inhibition of stimulus-evoked catecholamine secretion. Inducible NOS (iNOS; an enzyme that can be activated in the absence of Ca2+), although present in the vicinity of the chromaffin cells (based on mRNA measurements), does not appear to play a role because stimulus-evoked NO production was eliminated during perfusion with Ca2+-free saline. The potential involvement of endothelial NOS (eNOS) was revealed by showing that hypoxic perfusate evoked NO production and corresponded with an inhibition of stimulus-evoked catecholamine secretion; chemical removal of the endothelium (using saponin) prevented the production of NO during hypoxia. However, because removal of the endothelium did not affect NO production during electrical field stimulation, it would appear that the neuronal form of NOS (nNOS) is the key isoform modulating catecholamine secretion from trout chromaffin cells.

Analysis of Variance↗
PubMed1980

Effect of practice on visual backward masking.

Five experiments studied practice effects for 4, 7, 11 subjects on visual backward masking using a signal-detection procedure under various conditions. Exp. I determined the minimum perceptible critical stimulus duration (CSD) for criterion identification of a target stimulus, the letter T or A. In Exp. II, the stimulus was presented at the critical stimulus duration (CSD) followed by a pattern mask at intervals of 20 to 120 msec. for 15 separate sessions. In Exp. III (N = 4) the mask followed the CSD in intervals of 2-msec. increments until subjects reached criterion accuracy. Exps. IV and V (Ns = 4, 7) provided partial replications of Exps. II and III. Naive subjects were used, and the stimulus duration was constant for all subjects. When masking functions were obtained at a threshold, considerable variability was found and subjects improve slowly or not at all over sessions. With a fixed supra-threshold stimulus, all subjects improve with practice. The inportance of these findings is discussed as they relate to common (and largely untested) assumptions made in the backward masking and perception literature.

Adult↗
PubMed1975

A biofeedback treatment for stuttering.

Auditory feedback of laryngeal muscle tension was found to reduce stuttering dramatically in an exploratory study of a single patient. Amplitude of EMG signals was similarly reduced. Apparently, the therapeutic effect of biofeedback cannot be attributed to masking, distraction, or suggestion.

Adult↗