Dopamine Transporter-Dependent and -Independent Endogenous Dopamine Release from Weaver Mouse Striatum In Vitro

Abstract: The weaver mutant mouse (wv/wv) has an ～70% loss of nigrostriatal dopamine (DA) neurons, but the fractional DA release evoked by amphetamine (but not a high potassium level) has been shown to be greater from striatal slices of the weaver compared with +/+ mice. In the present work we tested the hypothesis that fractional DA release from weaver striatum would be greater when release was mediated by the DA transporter. Serotonin (5-HT)-stimulated fractional DA release was greater from weaver than from +/+ striatum. The release evoked by 5-HT in the presence of 10 µM nomifensine (an antagonist of the DA transporter) was less than in its absence, but the difference between weaver and +/+ striatum remained. In the presence of nomifensine, 1-(m-chlorophenyl)biguanide, classified as a 5-HT₃ agonist, also induced a greater fractional release from weaver compared with +/+ striatum. When veratridine was used at a low concentration (1 µM), the fractional evoked release of DA was higher from the weaver in the presence and absence of nomifensine. These findings suggest that the reason for the difference in the responsiveness of the two genotypes to these release-inducing agents is not related to DA transporter function.     

Stress-Related Changes in Cerebral Catecholamine and Indoleamine Metabolism: Lack of Effect of Adrenalectomy and Corticosterone

The concentrations of catecholamine and indoleamine metabolites were measured in intact and adrenalectomized mice to determine whether adrenal hormones mediate or modulate the stress-induced responses. Thirty minutes of footshock resulted in significant increases of the ratios of the dopamine (DA) catabolite, dihydroxyphenylacetic acid (DOPAC), to DA in prefrontal cortex, nucleus accumbens, striatum, hypothalamus, and brainstem, and of homovanillic (HVA)/DA ratios in nucleus accumbens, striatum, amygdala, and hypothalamus. Ratios of 3-methoxy-4-hydroxyphenylethyleneglycol to norepinephrine (NE) were also increased in prefrontal cortex, nucleus accumbens, septum, amygdala, hypothalamus, hippocampus, and brainstem. The concentration of NE was decreased in amygdala. 5-Hydroxyindoleacetic acid (5-HIAA)/5-hydroxytryptamine (5-HT, serotonin) ratios and free tryptophan were also increased in every brain region. Very similar data were obtained from mice restrained for 30 min. Adrenalectomy resulted in increased HVA/DA ratios in prefrontal cortex and striatum, and 5-HIAA/5-HT in septum. The stress-related changes were largely similar in adrenalectomized mice. Significant interactions between adrenalectomy and footshock treatment occurred in prefrontal cortical DOPAC/DA and hypothalamic NE which was depleted only in adrenalectomized mice, suggesting tendencies for these measures to be more responsive in adrenalectomized mice. Corticosterone administration (0.5-2.0 mg/kg s.c.) which resulted in plasma concentrations in the physiological range did not alter the concentrations of the cerebral metabolites measured in any region. We conclude that adrenal hormones do not mediate cerebral catecholamine or indoleamine metabolism in stress, although adrenalectomy may affect HVA and 5-HIAA metabolism, and there was a tendency for catecholamines to be more sensitive to stress in adrenalectomized animals.     

Coloboma Hyperactive Mutant Mice Exhibit Regional and Transmitter-Specific Deficits in Neurotransmission

Abstract: The mouse mutant coloboma ( Cm /+), which exhibits profound spontaneous hyperactivity and bears a deletion mutation on chromosome 2, including the gene encoding synaptosomal protein SNAP-25, has been proposed to model aspects of attention-deficit hyperactivity disorder. Increasing evidence suggests a crucial role for SNAP-25 in the release of both classical neurotransmitters and neuropeptides. In the present study, we compared the release of specific neurotransmitters in vitro from synaptosomes and slices of selected brain regions from Cm /+ mice with that of +/+ mice. The release of dopamine (DA) and serotonin (5-HT) from striatum, and of arginine vasopressin and corticotropin-releasing factor from hypothalamus and amygdala is calcium-dependent. Glutamate release from and content in cortical synaptosomes of Cm /+ mice are greatly reduced, which might contribute to the learning deficits in these mutants. In dorsal striatum of Cm /+ mutants, but not ventral striatum, KCI-induced release of DA is completely blocked and that of 5-HT is significantly attenuated, suggesting that striatal DA and 5-HT deficiencies may be involved in hyperactivity. Further, although acetylcholine failed to induce hypothalamic corticotropin-releasing factor release from Cm /+ slices, restraint stress increased plasma corticosterone levels in Cm /+ mice to a significantly higher level than in +/+ mice, suggesting an important role for arginine vasopressin in hypothalamic-pituitary-adrenal axis activation. These results suggest that reduced SNAP-25 expression may contribute to a region-specific and neurotransmitter-specific deficiency in neurotransmitter release.     

Serotonin transporter function, but not expression, is dependent on brain-derived neurotrophic factor (BDNF): in vivo studies in BDNF-deficient mice

In the present study, we used high-speed chronoamperometry to examine serotonin (5-HT) transporter (5-HTT) function in vivo in 2-, 5-, and 10-month-old brain-derived neurotrophic factor (BDNF)+/- mice. The rate of clearance of exogenously applied 5-HT was measured in CA3 region of hippocampus. In 2-month-old mice, the rate of 5-HT clearance did not differ between BDNF+/+ and BDNF+/- mice. In BDNF+/+ mice, 5-HT clearance rate (Tc) increased markedly with age. In contrast, Tc remained relatively static in BDNF+/- mice across 2-, 5-, and 10-month age groups. At 5 months of age, female BDNF+/+ mice had a lower maximal velocity (Vmax) for 5-HT clearance than male BDNF+/+ mice. There was a similar trend in 5-month-old BDNF+/- mice, but this did not reach statistical significance. There was an age-dependent increase in KT value for 5-HT clearance (i.e., decreased in vivo affinity of 5-HTT), but no significant effect of genotype or gender. 5-HTT density, as measured by [3H]cyanoimipramine binding, was not different between BDNF+/+ and BDNF+/- mice, although there was a significant increase in 5-HTT binding with age. The selective 5-HT reuptake inhibitor fluvoxamine (50 and 100 pmol) significantly decreased 5-HT clearance in BDNF+/+ mice, but not in BDNF+/- mice. Our data suggest that the profoundly reduced ability of 5- and 10-month-old BDNF+/- mice to clear 5-HT is not because of a decrease in the total number of 5-HTTs, but may be due to functional deficits in the 5-HTT, e.g., in the machinery/signaling required for insertion of 5-HTTs into the plasma membrane and/or activation of the 5-HTT once it is positioned to take up 5-HT from extracellular fluid.     

Alternating extremely low frequency magnetic field increases turnover of dopamine and serotonin in rat frontal cortex

The aim of this study was to evaluate the influence of an extremely low frequency sinusoidal magnetic field (ELF MF) with frequency of 10 Hz and intensity of 1.8-3.8 mT on the levels of the biogenic amines dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 3-methoxytyramine (3-MT), 5-hydroxytryptamine (5-HT), 5-hydroxyindolacetic acid (5-HIAA), and noradrenaline (NA), as well as on DA and 5-HT turnover in corpus striatum and frontal cortex of adult male Wistar rats. We found that ELF MF exposure for 14 days, 1 h daily, did not influence the level of the examined biogenic amines and metabolites, but increased the rate of synthesis (turnover) of DA and 5-HT in rat frontal cortex as compared to control, sham exposed rats. On the basis of the present results and our previous findings, extremely low frequency magnetic field (ELF MF) exposure has been found to alter both turnover and receptor reactivity of monoaminergic systems, as well as some behaviors induced by these systems or their agonists and antagonists.     

Altered serotonin and dopamine metabolism in the CNS of serotonin 5-HT(1A) or 5-HT(1B) receptor knockout mice

Measurements of serotonin (5-HT), dopamine (DA), and noradrenaline, and of 5-HT and DA metabolites, were obtained by HPLC from 16 brain regions and the spinal cord of 5-HT(1A) or 5-HT(1B) knockout and wild-type mice of the 129/Sv strain. In 5-HT(1A) knockouts, 5-HT concentrations were unchanged throughout, but levels of 5-HT metabolites were higher than those of the wild type in dorsal/medial raphe nuclei, olfactory bulb, substantia nigra, and locus coeruleus. This was taken as an indication of increased 5-HT turnover, reflecting an augmented basal activity of midbrain raphe neurons and consequent increase in their somatodendritic and axon terminal release of 5-HT. It provided a likely explanation for the increased anxious-like behavior observed in 5-HT(1A) knockout mice. Concomitant increases in DA content and/or DA turnover were interpreted as the result of a disinhibition of DA, whereas increases in noradrenaline concentration in some territories of projection of the locus coeruleus could reflect a diminished activity of its neurons. In 5-HT(1B) knockouts, 5-HT concentrations were lower than those of the wild type in nucleus accumbens, locus coeruleus, spinal cord, and probably also several other territories of 5-HT innervation. A decrease in DA, associated with increased DA turnover, was measured in nucleus accumbens. These changes in 5-HT and DA metabolism were consistent with the increased aggressiveness and the supersensitivity to cocaine reported in 5-HT(1B) knockout mice. Thus, markedly different alterations in CNS monoamine metabolism may contribute to the opposite behavioral phenotypes of these two knockouts.     

Methamphetamine-elicited alterations of dopamine- and serotonin-metabolite levels within μ-opioid receptor knockout mice: a microdialysis study

μ-Opioid receptors (μ-ORs) modulate methamphetamine (MA)-induced behavioral responses, increased locomotor activity and stereotyped behavior in the mouse model. We investigated the changes in dopamine (DA) and serotonin (5-HT) metabolism in the striatum following either acute or repeated MA treatment using in vivo microdialysis. We also studied the role of μ-ORs in the modulation of MA-induced DA and 5-HT metabolism within μ-OR knockout mice. Subsequent to either acute or repeated intraperitoneal administration of MA, wild-type mice revealed decreases in extracellular concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) in a dose-dependent manner. Moreover, wild-type mice had reductions in basal concentrations of DOPAC and HVA following repeated MA treatment with a higher dose. The effects of acute, repeated or challenge MA administration upon extracellular levels of DOPAC and HVA within μ-OR knockout mice significantly differed from the wild-type controls. The duration of recovery to the basal levels of extracellular DA and 5-HT metabolites induced by MA were much longer in wild-type mice than for μ-OR knockout mice. These findings suggest that μ-ORs play a modulatory role in MA-induced DA and 5-HT metabolism in the mouse striatum. This possible mechanism of MA-induced behavioral change as modulated by μ-OR merits further study.     

In vivo efflux of serotonin in the dorsal raphe nucleus of 5-HT1A receptor knockout mice

In the dorsal raphe nucleus (DR), extracellular serotonin (5-HT) regulates serotonergic transmission through 5-HT1A autoreceptors. In this work we used in vivo microdialysis to examine the effects of stressful and pharmacological challenges on DR 5-HT efflux in 5-HT1A receptor knockout (5-HT1A-/-) mice and their wild-type counterparts (5-HT1A+/+). Baseline 5-HT concentrations did not differ between both lines of mice, which is consistent with a lack of tonic control of 5-HT1A autoreceptors on DR 5-HT release. (R)-(+)-8-Hydroxy-2-(di-n-propylamino)tetralin hydrobromide (8-OH-DPAT, 0.5 mg/kg) reduced 5-HT levels to 30% of basal values in 5-HT1A+/+ mice, but not in 5-HT1A-/- mice. The selective 5-HT1B receptor agonist 1,4-dihydro-3-(1,2,3,6-tetrahydro-4-pyridinyl)-5H-pyrrolo[3,2-b]pyridin-5-one dihydrochloride (CP 93129, 300 micro m) reduced dialysate 5-HT to the same extent (30-40% of baseline) in the two genotypes, which suggests a lack of compensatory changes in 5-HT1B receptors in the DR of such mutant mice. Both a saline injection and handling for 3 min increased DR dialysate 5-HT in mutants, but not in 5-HT1A+/+ mice. Fluoxetine (5 and 20 mg/kg) elevated 5-HT in a dose-dependent manner in both genotypes. However, this effect was markedly more pronounced in the 5-HT1A-/- mice. The increased responsiveness of the extracellular 5-HT in the DR of 5-HT1A receptor knockout mice reflects a lack of the autoinhibitory control exerted by 5-HT1A autoreceptors.     

5-HT(2A) receptors: location and functional analysis in intestines of wild-type and 5-HT(2A) knockout mice

The distribution and function of the 5-hydroxytryptamine (5-HT(2A)) receptor were investigated in the intestines of wild-type (5-HT(2A) +/+) and knockout (5-HT(2A) -/-) mice. In 5-HT(2A) +/+ mice, rats, and guinea pigs, 5-HT(2A) receptor immunoreactivity was found on circular and longitudinal smooth muscle cells, neurons, enterocytes, and Paneth cells. Muscular 5-HT(2A) receptors were concentrated in caveolae; neuronal 5-HT(2A) receptors were found intracellularly and on the plasma membranes of nerve cell bodies and axons. Neuronal 5-HT(2A) immunoreactivity was detected as early as E14 in ganglia, intravillus nerves, and the deep muscle plexus. The 5-HT(2A) -/- colon did not express 5-HT(2A) receptors and did not contract in response to exogenous 5-HT. 5-HT(2A) -/- enterocytes were smaller, Paneth cells fewer, and muscle layers thinner (and showed degeneration) compared with those of 5-HT(2A) +/+ littermates. The 5-HT(2A) receptor may thus be required for the maintenance and/or development of enteric neuroeffectors and other enteric functions, although gastrointestinal and colonic transit times in 5-HT(2A) -/- and +/+ mice did not differ significantly.     

Essential role of NMDA receptor channel ε4 subunit (GluN2D) in the effects of phencyclidine, but not methamphetamine

Phencyclidine (PCP), a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, increases locomotor activity in rodents and causes schizophrenia-like symptoms in humans. Although activation of the dopamine (DA) pathway is hypothesized to mediate these effects of PCP, the precise mechanisms by which PCP induces its effects remain to be elucidated. The present study investigated the effect of PCP on extracellular levels of DA (DA(ex)) in the striatum and prefrontal cortex (PFC) using in vivo microdialysis in mice lacking the NMDA receptor channel ε1 or ε4 subunit (GluRε1 [GluN2A] or GluRε4 [GluN2D]) and locomotor activity. PCP significantly increased DA(ex) in wildtype and GluRε1 knockout mice, but not in GluRε4 knockout mice, in the striatum and PFC. Acute and repeated administration of PCP did not increase locomotor activity in GluRε4 knockout mice. The present results suggest that PCP enhances dopaminergic transmission and increases locomotor activity by acting at GluRε4.     

THE EFFECT OF BROMOCRIPTINE ON RAT STRIATAL ADENYLATE CYCLASE AND RAT BRAIN MONOAMINE METABOLISM

In slices and homogenate from rat brain striatum bromocriptine in marked contrast to DA. NA and apomorphine. had no stimulatory effect on adenylate cyclase activity, but antagonised the stimulatory effects of both NA and DA. Bromocriptine (10 mg/kg s.c.) decreased the turnover of DA in striatum and limbic structures 3h after drug administration. However, an increase in the turnover of NA in the brain stem and that of 5-HT in the cortex was observed 4h following treatment with bromocriptine. Possible modes of action of bromocriptine are discussed.     

Alterations in Extracellular and Tissue Levels of Biogenic Amines in Rat Brain Induced by the Serotonin2 Receptor Antagonist, Ritanserin

Systemic administration of ritanserin elicited rapid changes in dopamine (DA) and serotonin (5-HT) levels in both dialysate and neuronal tissue extracts. These effects occurred in both a site-selective and a dose-related manner. Increases in extracellular levels of DA and 5-HT in the nucleus accumbens were maximal at 120-140 min after treatment. A dose of 0.63 mg/kg of ritanserin elicited larger and more prolonged increases in extracellular DA and 5-HT levels than did the 0.3 mg/kg dose. By contrast, 0.63 mg/kg of ritanserin elicited no changes in either DA or 5-HT levels with dialysate collected from the striatum. Ritanserin also induced dose-related decreases in tissue levels of DA and 5-HT from the nucleus accumbens. The site specificity of action was again noted in that there were no dose-dependent decreases in tissue levels of DA or 5-HT measured from the striatum. Ritanserin exerted little effect on metabolite levels from either dialysate or tissue extracts. Taken together, these findings show that selective 5-HT2 receptor antagonism modulates DA and 5-HT neurotransmission in a specific manner. These actions appear to involve increased release of DA and 5-HT rather than significant changes in metabolism. These findings add further weight to the importance of 5-HT2 receptor interactions as an important component of antipsychotic activity.     

Novel multifunctional neuroprotective iron chelator-monoamine oxidase inhibitor drugs for neurodegenerative diseases. In vivo selective brain monoamine oxidase inhibition and prevention of MPTP-induced striatal dopamine depletion

Several multifunctional iron chelators have been synthesized from hydroxyquinoline pharmacophore of the iron chelator, VK-28, possessing the monoamine oxidase (MAO) and neuroprotective N-propargylamine moiety. They have iron chelating potency similar to desferal. M30 is a potent irreversible rat brain mitochondrial MAO-A and -B inhibitor in vitro (IC50, MAO-A, 0.037 +/- 0.02; MAO-B, 0.057 +/- 0.01). Acute (1-5 mg/kg) and chronic [5-10 mg/kg intraperitoneally (i.p.) or orally (p.o.) once daily for 14 days]in vivo studies have shown M30 to be a potent brain selective (striatum, hippocampus and cerebellum) MAO-A and -B inhibitor. It has little effects on the enzyme activities of the liver and small intestine. Its N-desmethylated derivative, M30A is significantly less active. Acute and chronic treatment with M30 results in increased levels of dopamine (DA), serotonin(5-HT), noradrenaline (NA) and decreases in DOPAC (dihydroxyphenylacetic acid), HVA (homovanillic acid) and 5-HIAA (5-hydroxyindole acetic acid) as determined in striatum and hypothalamus. In the mouse MPTP (N-methy-4-phenyl-1,2,3,6-tetrahydropyridine) model of Parkinson's disease (PD) it attenuates the DA depleting action of the neurotoxin and increases striatal levels of DA, 5-HT and NA, while decreasing their metabolites. As DA is equally well metabolized by MAO-A and -B, it is expected that M30 would have a greater DA neurotransmission potentiation in PD than selective MAO-B inhibitors, for which it is being developed, as MAO-B inhibitors do not alter brain dopamine.     

Selective reduction by isolation rearing of 5-HT1A receptor-mediated dopamine release in vivo in the frontal cortex of mice

Serotonin (5-HT)1A receptors modulate in vivo release of brain monoaminergic neurotransmitters which may be involved in isolation-induced aggressive behavior. The present study examined the effect of isolation rearing on the 5-HT1A receptor-mediated modulation of dopamine (DA), 5-HT and noradrenaline (NA) release in the frontal cortex of mice. The selective 5-HT1A receptor agonist (S)-5-[-[(1,4-benzodioxan-2-ylmethyl)amino]propoxy]-1,3-benzodioxole HCl (MKC-242) increased the release of DA and NA and decreased the release of 5-HT in the frontal cortex of mice. The effect of MKC-242 on DA release was significantly less in isolation-reared mice than in group-reared mice, while effects of the drug on NA and 5-HT release did not differ between both groups. The effect of the other 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin on cortical DA release was also less in isolation-reared mice than in group-reared mice, and that of the drug on cortical 5-HT release did not differ between both groups. In contrast to MKC-242-induced DA release, amphetamine-induced increase in cortical DA release in vivo was greater in isolation-reared mice. The present findings suggest that isolation rearing enhances the activity of cortical dopaminergic neurons and reduces selectively the 5-HT1A receptor-mediated release of DA in the cortex.     

Brain region-specific alterations of 5-HT2A and 5-HT2C receptors in serotonin transporter knockout mice

The aim of the present studies was to determine the effects of reduced or absent serotonin (5-HT) transporters (5-HTTs) on 5-HT2A and 5-HT2C receptors. The density of 5-HT2C receptors was significantly increased in the amygdala and choroid plexus of 5-HTT knockout mice. On the other hand, the density of 5-HT2A receptors was significantly increased in the hypothalamus and septum, but reduced in the striatum, of 5-HTT knockout mice. However, 5-HT2A mRNA was not changed in any brain region measured. 5-HT2C mRNA was significantly reduced in the choroid plexus and lateral habenula nucleus of these mice. The function of 5-HT2A receptors was evaluated by hormonal responses to (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI). Oxytocin, but not adrenocorticotrophic hormone or corticosterone, responses to DOI were significantly greater in 5-HTT knockout mice. In addition, Gq and G11 proteins were not significantly changed in any brain region measured. The present results suggest that the constitutive alteration in the function of 5-HTTs changes the density of 5-HT2A and 5-HT2C receptors in a brain region-specific manner. These changes may not be mediated by alterations in their gene expression or in the level of Gq/11 proteins. The alterations in these receptors may be related to the altered behaviors of 5-HTT knockout mice.     

Role of high-affinity dopamine uptake and impulse activity in the appearance of extracellular dopamine in striatum after administration of exogenous L-DOPA: studies in intact and 6-hydroxydopamine-treated rats

The differential behavioral and neurochemical effects of exogenous L-DOPA in animals with intact versus dopamine (DA)-denervated striata raise questions regarding the role of DA terminals in the regulation of dopaminergic neurotransmission after administration of exogenous L-DOPA. In vivo microdialysis was used to monitor the effect of exogenous L-DOPA on extracellular DA in intact and DA-denervated striata of awake rats. In intact striatum, a small increase in extracellular DA was observed after administration of L-DOPA (50 mg/kg i.p.) but in DA-denervated striatum a much larger increase in extracellular DA was elicited. Additional experiments assessed the role of high-affinity DA uptake and impulse-dependent neurotransmitter release in the effect of exogenous L-DOPA on extracellular DA in striatum. Pretreatment with GBR-12909 (20 mg/kg i.p.), a selective DA uptake inhibitor, enhanced the ability of L-DOPA to increase extracellular DA in intact striatum. However, in DA-denervated striatum, inhibition of DA uptake did not alter the extracellular DA response to L-DOPA. Impulse-dependent neurotransmitter release was blocked by the infusion of tetrodotoxin (TTX; 1 microM), an inhibitor of fast sodium channels, through the dialysis probe. Application of TTX significantly attenuated the L-DOPA-induced increase in extracellular DA observed in striatum of intact rats pretreated with GBR-12909. In a similar manner, TTX infusion significantly attenuated the increase in extracellular DA typically observed in striatum of 6-OHDA-lesioned rats after the administration of L-DOPA. The present results indicate that DA terminals, via high-affinity uptake, play a crucial role in the clearance of extracellular DA formed from exogenous L-DOPA in intact striatum. This regulatory mechanism is absent in the DA-denervated striatum. In addition, this study has shown that DA synthesized from exogenous L-DOPA primarily is released by an impulse-dependent mechanism in both intact and DA-denervated striatum. The latter result suggests an important role for a nondopaminergic neuronal element in striatum that serves as the primary source of extracellular DA formed from exogenous L-DOPA.     

Role of aquaporin water channels in airway fluid transport, humidification, and surface liquid hydration

Several aquaporin-type water channels are expressed in mammalian airways and lung: AQP1 in microvascular endothelia, AQP3 in upper airway epithelia, AQP4 in upper and lower airway epithelia, and AQP5 in alveolar epithelia. Novel quantitative methods were developed to compare airway fluid transport-related functions in wild-type mice and knockout mice deficient in these aquaporins. Lower airway humidification, measured from the moisture content of expired air during mechanical ventilation with dry air through a tracheotomy, was 54-56% efficient in wild-type mice, and reduced by only 3-4% in AQP1/AQP5 or AQP3/AQP4 double knockout mice. Upper airway humidification, measured from the moisture gained by dry air passed through the upper airways in mice breathing through a tracheotomy, decreased from 91 to 50% with increasing ventilation from 20 to 220 ml/min, and reduced by 3-5% in AQP3/AQP4 knockout mice. The depth and salt concentration of the airway surface liquid in trachea was measured in vivo using fluorescent probes and confocal and ratio imaging microscopy. Airway surface liquid depth was 45 +/- 5 microm and [Na(+)] was 115 +/- 4 mM in wild-type mice, and not significantly different in AQP3/AQP4 knockout mice. Osmotic water permeability in upper airways, measured by an in vivo instillation/sample method, was reduced by approximately 40% by AQP3/AQP4 deletion. In doing these measurements, we discovered a novel amiloride-sensitive isosmolar fluid absorption process in upper airways (13% in 5 min) that was not affected by aquaporin deletion. These results establish the fluid transporting properties of mouse airways, and indicate that aquaporins play at most a minor role in airway humidification, ASL hydration, and isosmolar fluid absorption.     

Effects of ethanol on brain monoamine content of spontaneously hypertensive rats (SHR)

Spontaneously hypertensive rats (SHR) were administered either 2.4 g/kg ethanol or an isocaloric glucose daily for 4 weeks and the levels of norepinephrine (NE), epinephrine (EP), dopamine (DA), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in different brain regions were determined. Results indicated a 3-fold increase in NE level in brain stem and hypothalamus and more than 2-fold increase in DA in corpus striatum in alcohol-treated rats as compared to controls. There was a significant increase in the level of DA in the corpus striatum but the levels in cerebral cortex, brain stem and hippocampus were decreased instead. Decreases in 5-HT levels were found in hypothalamus, brain stem, cortex and cerebellum of alcohol-treated brain as compared to untreated controls. These results indicate alterations of the biogenic amine contents in different regions of the SHR brain after chronic ethanol ingestion. Since stimulated release of biogenic amines in the SHR brain has been implicated in the regulation of blood pressure, changes due to ethanol ingestion may be a risk factor in hypertensive patients.     

Monoamine Neurotransmitter Metabolism and Locomotor Activity During Chemical Hypoxia

The effects of hypoxia on metabolism of 5-hydroxytryptamine (5-HT or serotonin) and 3,4-dihydroxyphenylethylamine (DA or dopamine) were compared with those on open-field activity in male CD-1 mice. Chemical hypoxia was induced with NaNO2. Hypoxia did not alter striatal concentrations of DA, 5HT, Trp, Tyr, 5-hydroxyindoleacetic acid, or homovanillic acid. However, NaNO2 (75 mg/kg) reduced the rates of conversion of [3H]Tyr to [3H]DA (-41%) and [3H]Trp to [3H]5-HT (-39%). Hypoxia also reduced dihydroxyphenylacetic acid (DOPAC) levels (-27%) and DOPAC/DA ratios (-20%). Open-field behavior, as measured in an automated activity monitor, decreased in a dose-dependent fashion with 75-150 mg/kg of NaNO2 (-35 to -90%). Comparison with previous studies suggests that the syntheses of dopamine, serotonin, and the amino acids are equally vulnerable to hypoxic insults but may be less sensitive than the synthesis of acetylcholine.